WO2025191101A1 - Spectroscopic imaging method and device - Google Patents

Abstract

The method comprises illuminating with an illumination light beam the object at one or more imaging locations. The illuminating results in an interaction of the illumination light with the object. The method comprises collecting the detection light from the one or more imaging locations, the detection light resulting from the illumination light interacting with the object. The method comprises generating interferogram data from the detection light. The generating of the interferogram data includes splitting the collected detection light into at least a first detection light portion and a second detection light portion. The generating of the interferogram data further includes directing the first detection light portion along a first optical path having a first optical path length, and directing the second detection light portion along a second optical path, wherein a difference of the first optical path length and the second optical path length is alterable. The generating of the interferogram data further includes recombining the first detection light portion and the second detection light portion to generate an interference electromagnetic field. The generating of the interferogram data further includes detecting by means of a detector the interference electromagnetic field to generate the interferogram data. The method comprises constructing, based on the power spectral density associated with the interaction of the illumination light beam with the object, an interferogram from the interferogram data.

Description

Description Title: Spectroscopic imaging method and device Cross-reference to related application _{[0001] This application claims the benefit of the priority European patent application no.} 24163369.2, filed on 13 March 2024. The disclosure of European patent application no. 24163369.2 is hereby incorporated herein in its entirety. Background of the disclosure _{[0002] Mechanical properties of cells and tissues at various scales have a role to play in} determining biological function. In recent years, the transduction of mechanical cues, ex- trinsically induced by the cellular microenvironment or intracellularly generated, into bio- chemical signals that regulate cell proliferation, migration and tissue dynamics has been understood more profoundly. _{[0003] On cellular scales, elastic and viscous properties regulate cell differentiation and} migration as well as determine response to physical forces and the cellular environment` Changes in cell stiffness, for example, have been associated with immune and epithelial tumor aggressiveness and the level of stemness in limbal stem cells. The elasticity of the extracellular environment, on the other hand, directs lineage specification in stem cells, drives tumor progression and regulates cadherin-dependent collective migration. _{[0004] At a tissue level, mechanical properties of tissues are drivers of morphogenesis and} multicellular organization. Tissue-level mechanical properties further have an effect on onset and progression of many diseases, such as eye disease, cancer or atherosclerosis. _{[0005] Molecular components, such as proteins, can routinely be visualized in situ with} tools such as fluorescence microscopy. The measuring of cellular mechanical properties in vivo or the assessing of the mechanical properties of living cells and tissues at high spatio- temporal resolution in a non-invasive fashion has been a challenge. A further limitation of some approaches is, moreover, that merely the quasi-static Young’s modulus can be meas- ured. The quasi-static Young’s modulus has by convention been conceptually linked to stiffness. Moreover, some techniques of measuring the mechanical properties of objects, e.g., biological objects such as the cells or the tissues, require direct contact with the ob- jects. _{[0006] Brillouin spectroscopy has been known in the field of material science for assess- ment of material elasticity and viscosity by means of measurement of the components of the elastic tensor, such as the longitudinal modulus or shear modulus, in the GHz frequen-} cy range. Application of Brillouin spectroscopy in biology and a combination with scan- ning confocal microscopy (termed Brillouin microscopy) has enabled imaging of viscoe- lastic properties of living matter in 3D in a noncontact, label-free and high-resolution fash- ion. _{[0007] International patent application WO 2016/187675 discloses a spectroscopic imag- ing device for optical coherence tomography for generating an optical image of an object.} The spectroscopic imaging device comprises a microlens array. The microlens array may be arranged at an image plane or at a Fourier plane. Summary of the disclosure _{[0008] The object of the present disclosure is achieved by the features of the independent claims. Aspects of the disclosure are further defined by the features of the dependent} claims. _{[0009] A spectroscopic imaging device and an imaging method for Brillouin spectroscopy} imaging of an object (or probe) are disclosed. The device includes an illumination light source, an interferometer, and a detector. _{[0010] The illumination light source provides an illumination light beam for illuminating the object. The illumination light passes along an illumination light path to the object for} illuminating the object. _{[0011] The method comprises illuminating with an illumination light beam the object at one or more imaging locations. The illuminating results in an interaction of the illumina-} tion light with the object. _{[0012] The illumination light beam has an illumination wavelength. The illumination} wavelength may, for example, lie in the visible spectrum (approximately 400-750 nm), the infrared spectrum (larger than approximately 750 nm), or the ultraviolet spectrum (smaller than approximately 400 nm). For example, the illumination wavelength may be 780nm. However, the present disclosure is not limited to the illumination wavelength lying in visi- ble spectrum. The illumination wavelength may have any value and/or lie in a spectral range suitable for spectroscopic imaging. _{[0013] The illumination light beam may further have an illumination polarization. Exam-} ples of the illumination polarization are an s-polarization, a p-polarization, or combinations _{thereof. The spectroscopic imaging device may comprise an illumination polarizer and/or an illumination waveplate to adjust the illumination polarization. The illumination polariz-} er and/or the illumination waveplate are arranged along the illumination light path. The _{illumination polarization of the illumination light beam may be adjusted by the illumina- tion polarizer and/or the illumination waveplate, by directing the illumination light beam onto the illumination polarizer and/or the illumination waveplate. The adjusting of the il- lumination polarization enables measuring one or more components of the elastic tensor of the object (examples of at least one physical property of the object). Examples of the com- ponents of the elastic tensor are, amongst others, a shear modulus (also termed elastic shear stiffness) or a longitudinal modulus. For example, the illumination polarization being an s- polarization and a detection polarization (see below) being a p-polarization, allows for measuring the shear modulus. [0014] The illumination light source illuminates one or more imaging locations at the ob-} ject, e.g., on a surface of the object or within the object. _{[0015] In one aspect, the one or more imaging locations form a two-dimensional plane.} The spectroscopic imaging device may include an illumination device for two-dimensional _{illumination of the object. In this aspect, the spectral imaging device (also referred to as “spectroscopic imaging device”) enables 'full-field' imaging of the two-dimensional plane.} The two-dimensional imaging of the two-dimensionally illuminated object may be imple- mented by means of the detector. The detector may include a two-dimensional array detec- tor. An example of the two-dimensional array detector is a camera. In this aspect, the spec- tral imaging device may be a light-sheet and wide-field spectral imaging device. _{[0016] The detector may comprise a detection objective lens. The detection objective lens} is configured to collect detection light from the object and direct the detection light to- wards the interferometer. The detection light travels along a detection light path to the de- tector. The detector may be a point detector or an array detector. _{[0017] The detection light has a detection polarization. Examples of the detection polariza-} tion are an s-polarization, a p-polarization, or combinations thereof. The spectroscopic im- aging device may comprise a detection polarizer and/or a detection waveplate to adjust the detection polarization. The detection polarizer and/or the detection waveplate are arranged along the detection light path. The detection polarization of the detection light may be ad- justed by the detection polarizer and/or the detection waveplate, by directing the detection light beam onto the detection polarizer and/or the detection waveplate. The adjusting of the detection polarization enables measuring one or more components of the elastic tensor of _{the object (examples of the at least one physical property of the object). Generally, adjust-} ing the detection polarization dependently on the illumination polarization enables selec- tively measuring different ones of the at least one physical property. _{[0018] The method comprises collecting the detection light from the one or more imaging locations, the detection light resulting from the illumination light interacting with the ob-} ject. _{[0019] In one aspect of the disclosure, the spectral imaging device comprises a filter for} spectral filtering of the detection light. The filtering of the detection light enables filtering out one or more wavelength portions from the detection light. One example of the filter is a _{first vapor cell or an atomic gas cell. In one aspect, the one or more wavelength portions correspond to at least one narrowband for narrowband spectral filtering. The at least one} narrowband may be wavelength range at a wavelength of approximately 780nm, but is not _{limited thereto. The narrowband spectral filtering, e.g., via the atomic gas cell, allows to suppress background, for example due to elastic scattering. An example of the elastic scat- tering is Rayleigh scattering. The suppression of the Rayleigh scattering enables Brillouin} imaging applications in biology and other fields. _{[0020] The method comprises generating interferogram data from the detection light. The} generating of the interferogram data includes splitting the collected detection light into at least a first detection light portion and a second detection light portion. _{[0021] The generating of the interferogram data further includes directing the first detec-} tion light portion along a first optical path having a first optical path length, and directing the second detection light portion along a second optical path, wherein a difference of the first optical path length and the second optical path length is alterable. _{[0022] The generating of the interferogram data further includes recombining the first de-} tection light portion and the second detection light portion to generate an interference elec- tromagnetic field. _{[0023] The generating of the interferogram data further includes detecting by means of the} detector the interference electromagnetic field to generate the interferogram data. _{[0024] The interferometer is configured to split the detection light into at least the first detection light portion of the detection light and the second detection light portion of the} detection light. The splitting of the detection light is not limited to the detection light being split into the first detection light portion and the second portion. The detection light may be split into more portions than the first detection light portion and the second portion, for example into three, four, or more portions. For example, the detection light may be split into the first detection light portion of the detection light, the second detection light portion _{of the detection light and at least a third portion of the detection light. The splitting of the detection light into more than the first detection light portion and the second portion ena-} bles enhancing a sensitivity of measuring the at least one physical property of the object (see below). _{[0025] The interferometer is further configured to direct at least the first detection light portion of the detection light along the first optical path of the first optical path length and the second detection light portion of the detection light along the second optical path of the} second optical path length, wherein the first optical path length and the second optical path length are different. The at least third portion of the detection light, if present, is directed along at least a third optical path of at least a third optical path length. _{[0026] The first optical path is associated with a first geometrical path length ^^^ and a} first refractive index ^_^. The first optical path length depends on the first geometrical path length ^_^^ and the first refractive index ^_^. The second optical path is associated with a _{second geometrical path length ^^^ and a second refractive index ^^. The second optical} path length depends on the second geometrical path length ^_^^ and the second refractive index ^_^. The at least third optical path, if present, is associated with at least a third geo- _{metrical path length ^^^ and at least a third refractive index ^^. The at least third optical} path length depends on the at least third geometrical path length ^_^^ and the at least third refractive index ^_^. _{[0027] The interferometer is further configured to recombine at least the first detection} light portion of the detection light and the second detection light portion of the detection light and subsequently direct the recombined detection light to the detector. The at least third portion, if present, is recombined with the first detection light portion and the second detection light portion by the interferometer. _{[0028] The splitting and the recombining of the detection light results in an interference of} at least a first electric field associated with the first detection light portion of the detection light and a second electric field associated with the second detection light portion of the detection light, and further, if present, a third electric field associated with the third portion of the detection light. In case the splitting of the detection light results in the at least third portion of the detection light, the at least third portion interferes with the first detection light portion and the second portion. The interference results in the interference electro- _{magnetic field associated with the detection light, which travels and/or is directed to the detector, where the interferogram data are generated by sampling the interference electro- magnetic field by means of the detector. The sampling according to the present disclosure includes detecting by means of the detector the interference electromagnetic field. The sampling further includes the detecting of the interference electromagnetic field at one or} more detection times. The one or more detection times may depend on an altering of at _{least one of the first optical path length and/or the second optical path length (see below). For example, the one or more detection times as well as a total data acquisition time may depend on a speed of this altering, i.e., on how fast the at least one of the first optical path length and/or the second optical path length are altered. For example, when the optical path} length is altered in a stepwise manner (see below), the speed of achieving these stepwise changes of the optical path length determines the one or more detection times. The one or _{more detection times in turn determine the data acquisition time (see below) associated with the sampling. The one or more detection times may depend on one or more pre-} selected optical path length differences being achieved by the altering (see below). _{[0029] The interference electromagnetic field and the interferogram data depend on a rela-} tive optical path length (or optical path length difference) of the first optical path, the sec- ond optical path, and, if present, the at least third optical path. _{[0030] The optical path length difference results in a time delay τ between the first detec-} tion light portion of the detection light, the second detection light portion of the detection light, and, if present, the third portion of the detection light. When the first portion, the second portion, and, if present, the at least third portion are recombined by the interferome- ter, the first portion, the second portion, and, if present, the at least third portion will have _{undergone the time delay ^ or time delays ^^. The interference electromagnetic field and the interferogram data depend on the time delay τ or time delays ^^. [0031] The interferometer is further configured to alter at least one of the first optical path} length of the first optical path and/or the second optical path length of the second optical path. The at least third optical path length of the third optical path, if present, may be al- tered by the interferometer in addition to, or alternatively to, the altering of at least one of the first optical path length and/or the second optical path length. _{[0032] The altering of the at least one of the first optical path length of the first optical} path and/or the second optical path length of the second optical path enables generating the interferogram data for different combinations of the first optical path length, the second optical path length, and, if present, the at least third optical path length. In other words, the _{altering enables spatially sampling the interference electromagnetic field in the spatial do-} main (or optical path length domain). For example, one of the first optical path length, the second optical path length, and, if present, the at least third optical path length may be al- tered in a stepwise manner. In one example of the stepwise altering, the one of the first optical path length, the second optical path length, and, if present, the at least third optical path length may be altered by a constant incremental optical path length step, but the dis- closure is not limited thereto. _{[0033] Due to the detection light travelling at the speed of light, the spatial sampling may} be interpreted as temporal sampling in the delay time domain (or time domain) via the rela- _{tion ^ = ^^^^^⁄ ^ , where ^ is the time delay of due to the optical path length difference, ^^ is the optical path length difference, and ^ is the vacuum speed of light. [0034] The optical path length difference ^^^^^ is due to a change in at least one refractive index n and/or in at least one geometrical path ^^^. The altering of the at least one of the} first optical path length of the first optical path and/or the second optical path length of the _{second optical path results from the change in the at least one refractive index n and/or in the at least one geometrical path ^^^^^^. According to one aspect of the disclosure, the spectroscopic imaging device may include one or more electro-optic modulators and/or one or more liquid crystal variable retarders, arranged in at least one of the first optical path, the second optical path, and/or, if present, the at least third optical path. The one or more electro-optic modulators and/or the one or more liquid crystal variable retarders ena- ble changing the at least one refractive index n, by applying an electrical field to the one or more electro-optic modulators and/or the one or more liquid crystal variable retarders. [0035] The sampling (spatial sampling or temporal sampling) of the interference electro- magnetic field enables determining the interferogram. The determining of the interfero-} gram may be associated with a reduced data acquisition time (and reduced overall imaging _{time) based on exploiting knowledge about an interaction of the illumination light beam} with the object. _{[0036] The knowledge about the interaction may include spectroscopic knowledge. The} spectroscopic knowledge may take the form of mathematically describing the interfero- gram by means of a function of time (or delay time). The function of time (or delay time) may be a Fourier transform of a power spectral density associated with the interaction of _{the illumination light beam with the object (see below). One example of the function of} time (or delay time) is a parametric function. The present disclosure thus provides a speedup of Brillouin spectral imaging. The speedup enables imaging dynamic biological processes occurring in the biological objects. _{[0037] In combination with a conventional one of the camera, which is capable of record-} ing millions of pixels at the same time, two-dimensional Brillouin spectral imaging, in which a two-dimensional object illumination plane is illuminated by means of the light- sheet, is enabled and sped up. The speedup results in a substantial reduction of the imaging time. The speedup further decreases light exposure, thus reducing photodamage of biologi- _{cal objects. The speedup is beneficial in case the interaction of the illumination light beam with the object is relatively weak, which results in a weak signal. This speedup enables} measuring a longitudinal modulus. Moreover, this speedup enables measuring a shear _{modulus based on the interaction of the illumination light beam with acoustic shear waves} of the object, which is known to be weaker than the interaction of the illumination light _{beam with longitudinal acoustic waves. [0038] The detection light comprises Brillouin scattered light, resulting from Brillouin scattering of the illumination light beam by the object. Alternatively or additionally, the} detection light may further comprise Raman scattered light resulting from Raman scatter- _{ing of the illumination light beam by the object. Moreover, the detection light may com- prise fluoresced light which is fluoresced by one or more types of fluorophore. [0039] In one aspect, the spectral imaging device may be an infinity-corrected spectral} imaging device having an objective lens and a tube lens, wherein the interferometer is ar- _{ranged between the objective lens and the tube lens in a first infinity-corrected space or} infinity space. _{[0040] The method comprises constructing, based on the power spectral density associated with the interaction of the illumination light beam with the object, an interferogram from} the interferogram data. _{[0041] The spectral imaging device further comprises a memory and a processor. The} memory is configured to store the interferogram data. The processor is configured to pro- cess the interferogram data. _{[0042] The processing of the interferogram data comprises the constructing the interfero- gram as a function the time (or delay time) τ from the interferogram data. The constructing of the interferogram may comprise fitting a function of the delay time τ (or a function of} time) to the interferogram data. _{[0043] The fitting of the function may comprise fitting at least one parametric function to} the interferogram data, wherein the at least one parametric function is a function of the _{delay time τ (or a function of time) and of at least one parameter. [0044] The parametric function may be a Fourier transform of a line shape (also termed} peak). The at least one parameter may represent at least one property of the line shape. The line shape may be a spectral line shape that describes a power spectral density, or a portion of the power spectral density. The power spectral density may be associated with the inter- _{action of the illumination light beam with the object. The at least one parameter may repre-} sent, for example, one or more of a position of a spectral peak of the line shape, a width of the spectral peak, and/or an amplitude of the spectral peak. Examples of the line shape are _{a Lorentzian line shape, a Gaussian line shape, a Voigt line shape, or a damped harmonic oscillator line shape, but are not limited thereto. The at least one parameter may be related} to at least one physical property of the object 50. _{[0045] The fitting of the function may further comprise estimating at least one parameter} associated with the function. When the parametric function is used for fitting the interfero- gram, e.g., the Fourier transform for two Lorentzian line shapes symmetrically arranged about a central peak at the illumination wavelength (or the illumination frequency), the estimated at least one parameter represents properties of the Lorentzian line shapes. _{[0046] The estimation of the at least one parameter enables measuring at least one physical} property of the object. The measuring of at least one physical property of the object ena- bles imaging the object with respect to the at least one physical property of the object. _{[0047] The method may comprise the measuring from the constructed interferogram of the} at least one physical parameter associated with the one or more imaging locations. _{[0048] Specifically, the estimation of the at least one parameter enables measuring the at} least one physical property of the object at a corresponding one of the one or more imaging _{locations of the object, at which the object is illuminated by the illumination light beam,} and from which the scattered light is detected. The measuring of the at least one physical property of the object associated with the one or more imaging locations enables imaging the object with respect to the at least one physical property. _{[0049] For example, in the case of the Brillouin scattering, a position or shift of the spec-} tral peaks with respect to the illumination wavelength (or illumination frequency) as well as a line width (e.g., a FWHM linewidth) of the measured power spectral density enables measuring (imaging) viscoelastic properties of the object. _{[0050] The parametric function describing the interferogram enables reducing a sampling} number of the interference electromagnetic field for generating the interferogram data. The _{reduction of the number of data samples reduces the data acquisition time. [0051] For example, using two symmetrically shifted Lorentzian peaks as the parametric} function to describe the power spectral density of the Brillouin scattered light enables re- _{ducing the sampling number for the constructing of the interferogram by approximately a} factor of 10.000. _{[0052] The spectroscopic imaging device may further comprise a microlens array ar- ranged along the detection light path at an image plane or in an infinity space. The micro-} lens array enables recording directional information for associated with the one or more imaging locations. _{[0053] The method may comprise recording directional information for associated with the one or more imaging locations. The recording of the direction information enables measuring the elastic tensor associated with the one or more imaging locations of the ob-} ject. _{[0054] The processor may be further configured to measure from the directional infor-} mation at least one second physical parameter associated with the one or more imaging locations. Brief description of the drawings _{[0055] FIG. 1 shows a spectroscopic imaging device according to an aspect of the disclo- sure for Brillouin spectroscopy imaging of an object (or probe). [0056] FIG. 2 shows a portion of FIG. 1 in detail as well as details regarding an illumina-} tion of the object. _{[0057] FIG. 3 illustrates Brillouin scattering due to an illumination light beam interacting} with a biological object and properties of a Brillouin spectrum that depend on physical properties of the object, wherein a central peak is due to Rayleigh scattering of the illumi- _{nation light beam, wherein the frequency axis indicates frequencies relative to an illumina-} tion frequency. _{[0058] FIG. 4 shows a Brillouin spectrum with an Anti-Stokes peak and a Stokes peak} relative to a central Rayleigh peak, wherein the frequency axis indicates frequencies rela- tive to an illumination frequency. _{[0059] FIG. 5 shows an interferometer and a detector of the spectral imaging device ac-} cording to one aspect of the disclosure. _{[0060] FIG. 6 shows a general power spectral density about a central peak due to Rayleigh} scattering, wherein the frequency axis indicates frequencies relative to an illumination fre- quency. _{[0061] FIG. 7 illustrates a method according to the disclosure. [0062] FIG. 8 shows a further aspect of the spectroscopic imaging device according to the} disclosure. _{[0063] FIG. 9 shows details regarding a detection light path of the spectroscopic imaging device according to an aspect of the spectroscopic imaging device, shown in FIG. 8. [0064] FIG. 10 shows details regarding a detection light path of the spectroscopic imaging device according to another aspect of the spectroscopic imaging device shown in FIG. 8. [0065] FIG. 11 illustrates a method according to the disclosure, using a spectroscopic im- aging device as shown in FIG. 9 or 10.} Detailed description of the disclosure _{[0066] The disclosure relates to a spectral imaging device 10 for imaging an object, the} spectral imaging device 10 being configured to measure a power spectral density of detec- tion light 66 collected from the object 50. _{[0067] The disclosure further relates to a method 100 for imaging an object 50, the method} 100 comprising measuring the power spectral density of the detection light 66 collected from the object 50. _{[0068] An example of the power spectral density of the detection light 66 collected from} the object 50 is a Brillouin spectrum. Another example of the power spectral density of the detection light 66 collected from the object 50 is a Raman spectrum. _{[0069] As shown in FIG. 1, the spectral imaging device 10 comprises an illumination light} source 11 for producing illumination light. The illumination light has an illumination wavelength and an illumination frequency. The illumination light source 11 comprises a laser light source. The illumination light source 11 may be configured to alter the illumina- tion wavelength of the illumination light. _{[0070] The illumination light is directed to the object 50 as an illumination light beam 15} to illuminate the object 50. The illumination light beam 15 illuminates the object 50 at one or more imaging locations 54 (see FIG. 2). For example, the illumination light beam 15 is focused at the object 50 by means of an illumination objective lens 17 to illuminate the object 50 at the one or more imaging locations 54. _{[0071] The method 100 comprises illuminating 110 with the illumination light beam 15 the} object 50 at one or more imaging locations 54, the illuminating resulting in an interaction of the illumination light beam 15 with the object 50. _{[0072] The illumination objective lens 17 has an illumination focus. The illumination ob-} jective 17 is arranged with respect to the object 50 such that the illumination focus is posi- tioned at the object 50. When the illumination light beam 15 passes through the illumina- tion objective lens 17, the illumination light beam 15 is focused by the illumination objec- tive lens 17 at the illumination focus to illuminate the object 50 at the one or more imaging locations 54. _{[0073] In one aspect, the illumination objective lens 17 may be a spherical lens that focus-} es the illumination light beam 15 at a single point (point-like illumination) for illuminating the object 50 at substantially a single one of the one or more imaging locations 54 at the object 50. In this aspect, the illumination objective lens 17 may have a high numerical ap- erture (NA). For example, in the case of a confocal setup the object 50 may be illuminated using the point-like illumination. _{[0074] In another aspect, the illumination objective lens 17 may be a spherical lens that} focuses the illumination light beam 15 along an elongate focus (line-like illumination), for illuminating the object 50 at ones of the one or more imaging locations 54 which are ar- ranged substantially along a line. In this aspect, the illumination objective lens 17 may have a low numerical aperture (NA). _{[0075] In a further aspect shown in FIG. 1, the illumination objective lens 17 may focus} the illumination light beam 15 at an object illumination plane 53 by means of sheet-like illumination for illuminating the object 50 at ones of the one or more imaging locations 54 which are arranged substantially at a plane or sheet. In this aspect, the illumination objec- tive lens 17 may be a cylindrical lens. In another aspect, the illumination light beam 15 may be scanned for achieving the sheet-like illumination. For example, in the case of a SPIM (selective plane illumination microscopy) setup, the object 50 is illuminated using the sheet-like illumination. _{[0076] The illumination light beam 15, travelling from the illumination light source 11 to} the object 50, interacts with the object 50. Due to the interaction, the illumination light beam 15 may be partly scattered elastically by the object 50 (e.g., by Rayleigh scattering). Due to the interaction, the illumination light beam 15 may be partly Brillouin scattered by object 50. _{[0077] The Brillouin scattering is an inelastic process arising from the interaction of the} illumination light beam 15 from the illumination light source 17, such as a laser, with pho- nons or acoustic waves in the object 50. The phonons or acoustic waves result in quasi- _{particles due to spontaneous thermally induced density fluctuations in the object 50. A fraction of the illumination light beam 15, on the order of approximately 10-11 to 10-10, in-} teracts inelastically with the object, e.g., the phonons, which results in a change of an ener- gy and a momentum of photons of the Brillouin scattered light. _{[0078] In the inelastic process of the Brillouin scattering, the scattered light may gain en-} ergy or lose energy. When energy is gained by the scattered light, a phonon may be annihi- lated in the object 50. When energy is lost by the scattered light, a phonon may be created in the object 50. The afore-mentioned gain and loss of energy by the photons of the scat- tered light result in two peaks in the power spectral density of the scattered-light (termed Brillouin-Anti-Stokes peak for the gain and Brillouin-Stokes peak for the loss) symmetri- cally shifted with respect to a central peak at ^_^ , which is due to the Rayleigh scattering at the illumination frequency ^_^ of the illumination light, e.g., produced by a laser (see FIG. _{4). The frequencies of the Brillouin scattered light are ^^ − ^^ and ^^ + ^^ . The frequen-} cy-shifted peaks have a linewidth One example of the linewidth is a FWHM (full width at half maximum) linewidth (see FIGS.3 and 4). _{[0079] The method 100 comprises collecting 120 the detection light 66 from the one or} more imaging locations 54, the detection light 66 resulting from the illumination light 15 _{interacting with the object 50. A portion of the scattered light is collected as the detection} light 66 from the one or more imaging locations 54 illuminated by the illumination light _{beam 15. The detection light 66 may be collected from the object 50 at a detection direc-} tion 68 which is substantially perpendicular to an illumination direction 19 of the illumina- tion light beam 15 at the object 50. In one aspect, the detection direction 68 may be per- _{pendicular to the object illumination plane 53 (see FIG. 1). However, the present disclosure} is not limited to such perpendicular arrangements of the detection direction 68 and the il- lumination direction 19. _{[0080] In FIG. 1, the collection of the detection light 66 for two of the one or more imag-} ing locations 54 is illustrated. In one aspect of the disclosure, the detection light 66 may comprise some of the elastically scattered light (Rayleigh scattered light) and some of the Brillouin scattered light. In another aspect of the disclosure, the elastically scattered light is largely filtered out of the detection light (see below). In yet a further aspect, the detection _{light 66 may include Raman scattered light and/or fluoresced light. In the case of the detec-} tion light 66 including fluoresced light, the imaging method according to the present dis- closure enables demixing of fluoresced light originating from different fluorophores. _{[0081] For example, the spectral imaging device 10 may comprise a detection objective} lens 62 which collects the portion of the scattered light. The detection objective lens 62 has a detection focal plane (object plane 57) and is arranged with respect to the object 50 such that the detection focal plane (object plane 57) is positioned at the object 50. When the illumination light beam 15 passes through the detection objective lens 62, the light scat- tered by the object 50 is collected at the object plane 57 (detection focal plane) by the de- tection objective lens 62. _{[0082] The spectral imaging device 10 further comprises an interferometer 80. The detec- tion light 66 travels and/or is directed along a detection light path 64 to the interferometer} 80. From the interferometer 80, the detection light travels along the detection light path 64 to a detector 90. The detection light may travel and/or be directed along the detection light path 64 as a detection light beam. _{[0083] The detection light path 64 and/or the detection light 66 comprises for the one or more imaging locations 54, from which detection light is collected, associated detection} beamlets (indicated in FIGS.1 and 2 by the continuous lines and dash-dotted lines). _{[0084] In another aspect, the spectral imaging device 10 may comprise a filter 70 (see FIG.} 2) for removing the Rayleigh scattered component of the detection light. An example of _{the filter 70 is a first vapor cell or an atomic gas cell. An example of the first vapor cell/atomic cell is a first Rubidium cell. The filter 70 enables suppressing a dominating} Rayleigh background to conduct practical Brillouin imaging applications in biology and beyond. The filter 70 may be arranged along the detection light path 64 between the detec- tion objective lens 62 and the interferometer 80. _{[0085] The method 100 comprises generating interferogram data from the detection light} 66. The generating of the interferogram data includes splitting 130 the collected detection light 66 into at least a first detection light portion 86-1 and a second detection light portion 86-2. _{[0086] The generating of the interferogram data further includes directing 140 the first detection light portion 86-1 along a first optical path 87-1 having a first optical path length, and directing 150 the second detection light portion 86-2 along a second optical path 87-2} having a second optical path length, wherein a difference of the first optical path length and the second optical path length is alterable. _{[0087] The generating of the interferogram data further includes recombining 160 the first} detection light portion 86-1 and the second detection light portion 86-2 to generate an in- terference electromagnetic field. _{[0088] The generating of the interferogram data further includes detecting 170 by means of} the detector 90 the interference electromagnetic field to generate the interferogram data. _{[0089] In one aspect, the interferometer 80 may be a Michelson interferometer (shown in} FIG.1). The Michelson interferometer 80 comprises a beamsplitter 82. At the beamsplitter 82, the detection light 66 is split into a first detection light portion 86-1 and a second detec- tion light portion 86-2. _{[0090] As shown in FIG. 1 and 4, the first detection light portion 86-1 passes through (is} transmitted by) the beamsplitter 82 in a substantially non-deflecting manner. The first de- tection light portion 86-1 subsequently impinges on a first retroreflector 88-1 and is subse- quently reflected back to the beamsplitter 82. The first detection light portion86-1 subse- quently impinges on the beamsplitter 82 and is deflected by the beamsplitter 82 towards the detector 90. The detector 90 may be a point detector or an array detector. The array _{detector may be part of a camera. In one aspect, a camera lens of the camera may function as a tube lens 40 for focusing the interference electromagnetic field onto to the array detec- tor. In another aspect, a combination of multiple lenses may act in conjunction to focus the} interference electromagnetic field onto to the array detector. _{[0091] In one aspect of the disclosure, the spectroscopic imaging device 10 may be an in- finity-corrected spectroscopic imaging device, wherein the objective lens 62 forms a first infinity space 42 (or first infinity-corrected space) between the objective lens 62 and the tube lens 40, in which the interferometer 80 is arranged. In the first infinity space 42 (see FIG. 1), the detection beamlets of the detection light 66 (indicated by the continuous lines and dash-dotted lines), which are associated with the one or more imaging locations 54 in the object 50, are composed of parallel rays (see FIGS. 1, 2, and 10). [0092] As the first detection light portion 86-1 travels from the beamsplitter 82 to the first} retroreflector 88-1 and subsequently from the first retroreflector via the beamsplitter 82 to the detector 90, the first detection light portion 86-1 acquires a first phase according to a first optical path travelled by the first detection light portion 86-1. The first optical path is associated with a first optical path length. The first optical path length depends on a first geometrical distance along the first optical path and on a first refractive index at the first optical path. _{[0093] In the aspect shown in FIG. 1, the first geometrical distance depends on a first arm} length ^_^ of a first arm 84-1 of the interferometer 80 (see FIG. 5). The first optical path _{leads along the first arm 84-1. The first arm 84-1 extends between the beamsplitter 82 and} the first retroreflector 88-1. The first phase depends on the first arm length ^_^ and the first refractive index ^_^. _{[0094] As further shown in FIG. 2, the second detection light portion 86-2 is deflected by} the beamsplitter 82 towards a second retroreflector 88-2. The second detection light por- tion 86-2 impinges on the second retroreflector 88-2 and is subsequently reflected back to the beamsplitter 82. The second detection light portion 86-2 subsequently impinges on the beamsplitter 82 and passes through (is transmitted by) the beamsplitter 82 towards the de- tector 90. _{[0095] As the second detection light portion 86-2 travels from the beamsplitter 82 to the} second retroreflector 88-2 and subsequently from the second retroreflector 88-2 via the beamsplitter 82 to the detector 90, the second detection light portion 86-2 acquires a sec- ond phase according to a second optical path travelled by the second detection light portion 86-2. The second optical path is associated with a second optical path length. The second optical path length depends on a second geometrical distance along the second optical path and on a second refractive index at the second optical path. _{[0096] In the aspect shown in FIG. 1, the second geometrical distance depends on a second} arm length ^_^ of a second arm 84-2 of the interferometer 80 (see FIG. 5). The second opti- _{cal path leads along the second arm 84-2. The second arm 84-2 extends between the} beamsplitter 82 and the second retroreflector 88-2. The second phase therefore depends on the second length ^_^ and the second refractive index ^_^. _{[0097] The second retroreflector 88-2 is movably arranged. The moveable arrangement of} the second retroreflector 88-2 results enables altering the second optical path length. The moveable arrangement of the second retroreflector 88-2 results in the second arm length ^_^ being changeable. Moving the second retroreflector 88-2 changes the second arm length ^_^, which in turn alters the second optical path length. _{[0098] For example, to provide the movability of the second retroreflector 88-2, the second} retroreflector 88-2 may be arranged on a scanning arm (not shown) to scan the second dis- tance ^_^ through a scanning range. In an example, the scanning of the scanning arm (not _{shown) may comprise a piezo motor (not shown) to move the second retroreflector 88-2} with respect to the beamsplitter 82. The moving of the second retroreflector 88-2 may be conducted in a stepwise manner by stepper motor. The scanning range may be associated _{with a scanning step size and a scanning step number. The piezo motor enables a scanning step size of approximately 1-100 nm. In one aspect, the piezo motor may alter scan the second distance ^^ through a scanning range of approximately 300 nm or more. In another} aspect, a combination of the piezo motor with a stepper motor may be used, in which the piezo motor enables more precise scanning step sizes, and the stepper motor enables more coarse scanning step size, to achieve a large scanning range, for example between 0.3 m and 1 m. _{[0099] The scanning range associated with the scanning arm enables sampling an interfer-} ence electromagnetic field resulting from the interference of the first detection light portion 86-1 and the second detection light portion 86-2. For example, the sampling range may be sampled in the stepwise manner. Correspondingly, the sampling range may be associated with a sampling step size ^^_^^^ and a sampling step number N. _{[00100] At the beamsplitter 82, the first detection light portion 86-1 and the second} detection light portion 86-2 are recombined. Based on the superposition principle, the first detection light portion 86-1 and the second detection light portion 86-2 interfere and gen- erate an interference light beam. The interference light beam is associated with an interfer- ence electromagnetic field. The interference electromagnetic field depends on a difference between the first optical path length and the second optical path length (optical path length difference ^^_^^^). _{[00101] The interference electromagnetic field impinges on the detector 90. The} detector 90 samples the interference electromagnetic field and generates interferogram data. The interferogram data are transmitted to a processing unit 93, which comprises a processor 97 and a memory 96. The interferogram data are stored in the memory 96. The processor 97 is configured to process the interferogram data. _{[00102] The interferogram may be sampled by the altering of the optical path length} difference. As explained above, this altering may be, for example, achieved by changing the second arm length ^_^. The interferogram may be sampled through a sampling range by scanning the optical path length difference through the scanning range. _{[00103] The scanning range of the optical path length difference corresponds to a} time delay range, which is due to the optical path length and a corresponding difference in _{travel time (time delay) of the detection light being linked by the speed of light: ^ = ^^^^^⁄ ^ , where τ is difference in travel time or time delay of the detection light, ^^^^^ is the optical path length difference, c is the vacuum speed of light. Correspondingly, the sampling step size ^^^^^ may be a time delay step size ^^, and the sampling step number may be a number N of the time delay. For example, the time delay may be incrementally increased, leading after N sampling steps to a maximum time delay ^^ = ^^ + ^ × ^^ (which turns into ^^ = ^ × ^^ for an initial time delay ^^ of zero). Based on the sampling, the interferogram ^(^) may thus be constructed as a function of time. [00104] The method 100 comprises constructing 180, based on the power spectral} density associated with the interaction of the illumination light beam 15 with the object, an interferogram from the interferogram data. _{[00105] In the case of the Michelson interferometer 80, the intensity of the interfer- ence electromagnetic field sampled by the detector is given by + where ^(^) is the interference electromagnetic field, 〈∙〉^ indicates the average over time t (corresponding to an integration time of the de- tector 90), ^ = ^^^^^⁄ ^ = 2∆^^⁄ ^ is the time delay between the two arms of the Michelson interferometer 80 and ^^ = 〈|^(^)|^〉^. The term 〈^(^)^(^ − ^)〉^ is the autocorrelation} function for the interference electromagnetic field over time t. _{[00106] According to the Wiener–Khinchin theorem, the autocorrelation function of the interference electromagnetic field 〈^(^)^(^ − ^)〉^ corresponds to the Fourier trans- form of the power spectral density of the interference electromagnetic field: 〈^(^)^(^ − ^)〉^ = Re^ℱ{^^(^)}^, where ^^(^) is the power spectral density of the interference elec- tromagnetic field, ℱ{∙} denotes the Fourier transform operation, and Re{∙} denotes the real} part of the argument. _{[00107] Based on the Nyquist–Shannon sampling theorem as well as mathematical} properties of the discrete Fourier transform, the following requirements for constructing _{the interferogram ^(^) from the interferogram data have to be met: The time delay step size} (or sampling rate) is required to be at least twice the maximum optical frequency found in _{the power spectral density, which means that ^^ < 1⁄ 2^^^^ = ^^^^⁄ 2^ (or correspond- ingly for the change in the second arm length: ^^^ < ^^^^⁄ 4 ). The maximum time delay ^^ is required to be sufficiently large to achieve a spectral resolution ∆^. The required} sampling number thus becomes: _{[00108] For Brillouin scattering, which requires sub-GHz spectral resolution, for example a resolution of ∆^ ≈ 0.5 GHz, and the illumination wavelength chosen to be, e.g., ^ = 780n ^ ^^^ m, the required sampling number would become ^ > 10 . In the case of the integration time of the detector 90 lying in a range of 10-100ms for acquiring the Brillouin} spectrum from a biological object, this required sampling number results in a data acquisi- tion time of ~3-30 hours. Compressive sensing approaches have been attempted but could not significantly improve the data acquisition time. _{[00109] According to the presently disclosed example, properties of the Brillouin} spectrum may be exploited to improve an efficiency of acquiring the Brillouin spectrum. For example, the symmetric shape (see FIG. 4 for a symmetric spectrum relative to a cen- _{tral peak at ^^ = 2^^^ associated with the illumination frequency ^^) of the Brillouin} spectrum enables reducing the required sampling number potentially by a factor of > 10^{^^}. Furthermore, according to the present disclosure, the exploiting of the properties of the Brillouin spectrum, such as the symmetric shape, is enabled by exploiting knowledge _{about the interaction of the illumination light beam 15 with the object 50. The exploiting of} the knowledge may include using a mathematical description of the Brillouin spectrum, which is described in the following paragraphs. The mathematical description may be a _{parametric mathematical description, e.g., a function of the delay time τ (or a function of} time). _{[00110] A generic mathematical description of a power spectral density ^^(^) hav- ing two peaks symmetrically shifted by Ω = 2^^^ about the central peak at ^^ , due to the} elastically scattered light and described by means of a Dirac delta function, is given by _{^^(^) = ^^^(^ − ^^) + ^(^ − ^^), with ^(^) = ^(^ − Ω) + ^(−^ − Ω) describing the two off-center peaks (sidebands), and ^(^) describing a one-sided power spectral den-} sity that is non-zero in a limited range to one side of the central peak at ^_^ (see FIG. 6). Based on the Wiener-Khinchin theorem (see above), the autocorrelation function _{〈^(^)^(^ − ^)〉^ of the interference electromagnetic field is linked to the one-sided power spectral density ^(^) in the following way: 〈^(^)^(^ − ^)〉^ = cos(^^^) ^^^ + 2Re^^^^^^^^(^)^^, where ^^(^) is the Fourier transform of ^(^). Moreover, ^^^^^^^(^) is the Fourier transform of ^(^ − Ω), the real part of which is Re^^^^^^^^(^)^ =} cos⁽Ω^⁾Re^^^{^}(^)^. _{[00111] It can be seen from the foregoing formula that the autocorrelation function 〈^(^)^(^ − ^)〉^ is a product of the two real functions (i) cos(^^^) and ^^ + the former oscillating at the frequency ^^ = ^^⁄ 2^ and the latter slowly varying function, when f(^) is bandwidth limited at + Ω ≪ ^^ (as shown in FIG. 5).} The two factors of the product thus change on different times scales. The different time _{scales enable measuring, i.e., construct from the data samples (or interferogram data) de- tected by the detector 90, the first factor cos(^^^) and the second factor ^(^) by under- sampling the interferogram (see also below). From the measured second factor ^(^), the power spectral density ^^(^) can be reconstructed by taking the inverse Fourier transform of ^(^) or of cos(^^^) ∙ ^(^) (the options resulting merely in a relative shift of the argu-} ment of the corresponding results by ^_^ but each containing the full information of the power spectral density ^^(^)). _{[00112] The mathematical description ^(^) of the one-sided power spectral density may be a parametric mathematical description ^(^, ^) of the one-sided power spectral density, where p is a set of at least one parameter. One example of the parametric mathe- matical description ^(^, ^) for the case of the Brillouin spectrum (see in FIGS. 3 and 4) may be the Lorentzian line shape (or Lorentzian peak) ^(^, ^) = using} as the at least one parameter the intensity of the Brillouin peak ^_^, the frequency shift ^_^, _{and the linewidth , i.e., the set of the at least one parameter being ^ = {^^ , ^, ^^ [00113] Other examples of the parametric mathematical description ^(^, ^) of the one-sided power spectral density are the Gaussian line shape (or Gaussian peak) based on the Gaussian function, the Voigt line shape (Voigt peak) based on a convolution of the} Lorentzian line shape and the Gaussian line shape, or the damped harmonic oscillator line _{shape (or damped harmonic oscillator peak). Further examples of the parametric mathe- matical description ^(^, ^) of the one-sided power spectral density are multiples or linear} combinations of the afore-mentioned examples. _{[00114] The Fourier transform of the one-sided power spectral density, parametrical- ly described by the Lorentzian line shape, is given} . It fol- lows that the interferogram for the Lorentzian line shape can be written in a parametric _{from [00115] It can be seen from the foregoing formula for the parametric form of the} interferogram, based on the Lorentzian line shape, that the interferogram can be regarded _{as the product of the two oscillating functions (i) cos(^^^) and (ii) ^(^) = ^^ + 2 ^^ ^^^|^|∆^ cos(Ω^), the former oscillating at the frequency ^^ = ^^⁄ 2^ and the latter oscillating at the frequency ^^ = Ω⁄ 2^ , with ^^ ≫ ^^. Similar to the case of acoustic} beats, the interferogram, based on the Lorentzian line shape, may be regarded as oscillating _{at the higher frequency ^^ and having an amplitude ^(^) oscillating at a slower frequency} ^_^ . When the interferogram is plotted in a graph against time, the slower oscillating ampli- _{tude ^(^) will appear to envelop the faster oscillation, whence the term envelope stems. [00116] The method may comprise the measuring 190 from the constructed interfer- ogram of the at least one first physical parameter associated with the one or more imaging locations 54. In order to measure the interferogram, the difference of the frequencies ^^ and ^^ may be exploited. Due to ^^ ≫ ^^ and ^^ ≫ the amplitude (envelope) will change insignificantly over a single period ^^^ = 2^ of the oscillating function cos(^^^). This means that the oscillating function cos(^^^) is measurable by means of a low sam- pling number ^^, e.g., three or four data samples, within the single period. In principle, ^^ = 3 data samples are sufficient for determining the amplitude, phase and offset. [00117] In one aspect of the disclosure, a sign of the amplitude (negative or positive) within the single period may be measured. For example, a reference laser beam (not shown) may be made to travel through interferometer 80 to the detector 90 to enable de-} tecting the sign of the amplitude. The reference laser beam may be shaped such that the reference laser beam is detected substantially at one or more edges of the detector 90 such _{that the reference laser beam does not interfere with the interference electromagnetic field.} A comparison of a phase of the interference electromagnetic field of the amplitude with a reference phase of the reference laser beam, the sign of the amplitude can be inferred. For _{example, a phase difference of the phase and the reference phase of a value of ^ indicates the sign of the amplitude being negative. Usage of the reference laser beam thus enables} measuring the sign of the amplitude concurrently with the imaging method according to _{the disclosure. The usage of the reference laser beam thus avoids repeating the detecting of the interference electromagnetic field for comparing a measured phase with an expected phase based on the optical path length difference. The repeating is prone to reducing a phase stability of the interferometer 80. The usage of the reference beam thus enables em- ploying a scanning arm which fulfills less demanding requirements as to positional repeat- ability and/or precision. [00118] After measuring the oscillating function cos(^^^), the amplitude (envelope) ^(^) remains to be measured. The sampling conditions (see above) will be applied to the function ^(^) instead of to the full autocorrelation function 〈^(^)^(^ − ^)〉^. Therefore, depending on the spectral components in ^(^), the autocorrelation function 〈^(^)^(^ −} ^^)〉 _^ can be measured with the sampling number being smaller than required by the Nyquist-Shannon theorem. _{[00119] In particular, if ^(^) = 0 for ^ greater than some ^^^^ , then ^(^) can be constructed by means of with sampling with a time delay step size ^^ <} ^ where _{^^^^ represents a bandwidth of the one-sided power spectral density ^(^). resulting for the autocorrelation function 〈^(^)^(^ − ^)〉^ in the following sampling number: ^ = [00120] If for Brillouin spectra measured from a biological object at 780nm, the bandwidth may be approximated by ^^^^ + Ω ≲ 2^ ∙ 7^^^, the sampling number would approximately be ^ > ^} ^^^^ ^ ∆^ _{≈ 30, which is a reduction in the sampling number N of approximately 10^ to 10^ in comparison with the sampling number ^ > 10^ calculated} based on the Nyquist-Shannon theorem alone (see above). _{[00121] The reduction in the sampling number N is not limited to Brillouin spectros- copy and is applicable to any symmetric power spectral density ^^(^) = ^^^(^ − ^^) + ^(^ − ^^), with ^(^) = − Ω) associated with the interaction of the} illumination light 15 with the object 50. _{[00122] When the autocorrelation function 〈^(^)^(^ − ^)〉^ has been measured, i.e., constructed from the data samples detected by the detector 90, the at least one parameter of} the parametric mathematical description of the one-sided power spectral density may be estimated. From the estimated the at least one parameter, at least one physical property of the object may be measured. _{[00123] The frequency of the scattered light ^^ ± ^^ associated with both peaks and} the linewidth of the two peaks depend on material properties (an example of the at least one physical property) of the object at a corresponding one of the one or more imaging locations 54 of the object, at which the object is illuminated by the illumination light, and from which the scattered light is detected. This dependence enables detection of these ma- terial properties. As a result, the material properties of the object may be measured by de- tecting the scattered light. Thereby, the material properties of the object may be imaged. _{[00124] Specifically, for a selected one of the one or more imaging locations 54, the frequency of the scattered light ^^ ± ^^ and the linewidth of the two peaks depend on a} rigidity and a viscosity of the object at the selected one of the one or more imaging loca- _{tions 54. The frequency of the scattered light ^^ ± ^^ and the linewidth at the selected one of the one or more imaging locations 54 differ, for example, for a solid structural com-} ponent (e.g., collagen fibers) or a liquid structural component (e.g., cytosol) in the case of a biological one of the object, as illustrated in FIG.3. _{[00125] More specifically, the frequency of the scattered light ^^ ± ^^ is related to a sound velocity ^ and a refractive index ^ of the object. The frequency shift of the scattered light ^^ is further related to the illumination wavelength ^^ = ^⁄ ^^ . The overall relation- ship is given by the formula ^^ = (2^⁄ ^^ ) ^ sin (^/2) , where ^ is the angle between the illumination light and the scattered light. The sound velocity ^ is related to a longitudinal modulus (an elastic modulus) of the object according to ^′  =  ^/^^, where ^ is the mass} density of the object. The linewidth on the other hand, is related to an acoustic attenua- tion and a viscosity, i.e., dissipative mechanical properties, of the object according to = _{^^^, where ^ is an attenuation coefficient of the object. [00126] The aforementioned viscoelastic properties of the material, i.e., the longitu- dinal modulus ^′ and the attenuation coefficient ^, may be conceptually regarded as com- ponents of a complex longitudinal modulus ^ = ^′ + ^^″, where the real part ^′ of the} complex longitudinal modulus provides information about the elastic properties of a mate- _{rial, and the imaginary part ^″ is related to the longitudinal viscosity ^ = 2 ^^ of the medium via the relation ^^ = 2^^^. [00127] The longitudinal modulus differs from the Young’s modulus ^, which is reflected in that the longitudinal modulus ^′ is on the order of GPa, and the Young’s mod- ulus ^ on the order of kPa. [00128] Interpreting the Brillouin spectrum scattered by the object and recorded by a} detected generally requires considering relevant spatial and temporal scales involved of the Brillouin scattering with respect to the biological process of interest. _{[00129] Biological objects are heterogeneous media, in which various time scales and spatial scales determine the behaviors of the objects. These time scales and spatial} scales affect a propagation and a dissipation of the phonons or acoustic waves in the object, which results in the Brillouin spectrum associated with the object. _{[00130] FIGS. 8, 9, and 10 show further aspects of the disclosure of the spectroscop- ic imaging device 10. Fig.11 shows a further aspect of the method according to the disclo- sure, using the spectroscopic imaging device shown in FIG. 9 or 10. [00131] As shown in FIG. 8, the spectroscopic imaging device 10 may further com- prise a microlens array 30. The microlens array 30 enables measuring the elastic tensor of} the object 50 in a multiplexed fashion without moving or rotating the object 50 _{[00132] The microlens array 30 enables recording a direction of the detection light 66. In particular, the microlens array 30 enables detection the direction, at which the rays of the detection beamlets, associated with the one or more imaging locations 54, are cap- tured by the detection objective lens 62. The spectrometer is simultaneously capable, for each one of the one or more imaging locations 54, of reconstructing the power spectral density ^^(^) and of recording the directional information. Accordingly, the method may} further comprise recording 200 the directional information associated with the one or more imaging locations 54. _{[00133] The spectroscopic imaging device shown in FIG. 8 comprises a spectromet- ric device 77. In one aspect of the disclosure, the spectrometric device 77 includes the in- terferometer 80 described above and shown in FIGS. 1, 5, 9, and 10. [00134] In another aspect of the disclosure, the spectrometric device 77 includes a second vapor cell. An example of the second vapor cell is, e.g., a second Rubidium vapor cell. The second vapor cell may use laser-induced circular dichroism for spectral detection.} See, for example, Hutchins et al., "Full-field optical spectroscopy at a high spectral resolu- tion using atomic vapors," Opt. Express 31, 4334-4346 (2023), the disclosure of which is incorporated herein by reference. _{[00135] In a further aspect of the disclosure, the spectrometric device 77 includes a line-scanning Brillouin microscope. See, for example, Bevilacqua et al., “High-resolution} line-scan Brillouin microscopy for live imaging of mechanical properties during embryo _{development.”, Nat Methods 20, 755–760 (2023), DOI:10.1038/s41592-023-01822-1, the} disclosure of which is incorporated herein by reference. _{[00136] As shown in FIG. 9, according to an aspect of the disclosure, the microlens array 30 may be arranged at an image plane 44. The detection light 66, collected by the detection objective lens 62, is focused at the image plane 44. The detection light 66 is transmitted by the microlens array 44 and collected by a collimating lens 59. The detection} light 62 is transmitted by the collimating lens 59 and travels along detection light path 64 _{to the interferometer 80. After passing through the interferometer 80, the detection light 62 travels and/or is directed to the detector 90. The detector 90 thereby detects a pattern gen- erated by the microlens array 30. [00137] The microlens array 30 arranged at the image plane 44 enables generating superpixels recording directional information relating to the object 50. The superpixels} include multiple pixels of the detector 90, each one of the multiple pixels recording associ- ated directional information. Individual ones of the plurality of views may be imaged onto different portions of the detection 90. _{[00138] The method may comprise the measuring 210 from the directional infor- mation of the at least one second physical parameter associated with the one or more imag- ing locations 54. [00139] As shown in FIG. 9, the detection beamlets of the detection light 62 (indi-} cated by the continuous lines and dash-dotted lines), which are associated with the one or _{more imaging locations 54 in the object 50, are focused at the image plane 44. As shown in} FIG. 9, the detection beamlets are transmitted by the microlens array 44 and collected by _{collimating lens 59. The detection beamlets are transmitted by the collimating lens 59 and travel along the detection light path 64 to the interferometer 80. The detection beamlets} travel and/or are directed to the detector 90 after passing through the interferometer 80. _{[00140] As shown in FIG. 10, according to another aspect of the disclosure, the mi-} crolens array 30 may be arranged in a second infinity space (or infinity-corrected space) 43. The detection light 66, collected by the detection objective lens 62, is composed of parallel rays in the second infinity space 43. The detection light 62 is transmitted by the collimating lens 59 and travels along detection light path 64 to the interferometer 80. After passing through the interferometer 80, the detection light 62 travels and/or is directed to _{the detector 90. The detector 90 thereby detects a pattern generated by the microlens array} 30. _{[00141] The microlens array 30 arranged in the second infinity space 43 enables} generating a plurality of views of the object 50. Individual ones of the plurality of views may be imaged onto different portions of the detection 90. _{[00142] As shown in FIG. 10, the detection beamlets of the detection light 62 (indi-} cated by the continuous lines and dash-dotted lines), which are associated with the one or more imaging locations 54 in the object 50, are composed of parallel rays in the second infinity space 43. The detection beamlets are transmitted by the microlens array 44 and collected by collimating lens 59. The detection beamlets are transmitted by the collimating lens 59 and travel along the detection light path 64 to the interferometer 80. The detection beamlets travel and/or are directed to the detector 90 after passing through the interferome- ter 80. _{[00143] As shown in FIG. 8, the spectroscopic imaging device 10 may further com- prise an illumination polarizer 37 to adjust an illumination polarization of the illumination light beam 15. The illumination polarizer 37 includes an illumination waveplate. The illu- mination polarizer 37 is arranged along the illumination light path 19. [00144] As shown in FIGS. 9 and 10, the spectroscopic imaging device 10 may fur- ther comprise a detection polarizer 35 to adjust a detection polarization of the detection} light 66. The detection polarizer 35 includes a detection waveplate. The detection polarizer _{35 is arranged along the detection light path 64. [00145] By adjusting the illumination polarization of the illumination light beam 15 and the detection polarization of the detection light 66, both the longitudinal modulus as well as a transverse modulus can be measured. The longitudinal modulus and the trans- verse modulus are required to determine the elastic tensor. From the measured power spec- tral density ^^(^), the Brillouin shift and the sound velocity are derivable. Solving the Christoffel equations enables deriving the elastic tensor (see, e.g., the section “Calculation of stiffness tensor”, arXiv: 2411.11712 [physics.optics], the disclosure of which is incorpo-} rated herein by reference). _{[00146] Reference numerals 10 Spectral imaging device 11 Illumination light source 15 Illumination light beam 17 Illumination objective lens 19 Illumination direction/illumination light path 30 Microlens array 33 Image plane 35 Polarizer 37 Waveplate 40 Tube lens 42 First infinity space 43 Second infinity space 44 Image plane 50 Object 53 Object illumination plane 54 Imaging location 57 Object plane 59 Collimating lens 62 Detection objective lens 64 Detection light path 66 Detection light 68 Detection direction 70 Filter 75 Device for collecting, filtering and collimating/focusing detection light 77 Spectrometric device 80 Interferometer 82 Beamsplitter 84-1 First arm 84-2 Second arm 86-1 First detection light portion 86-2 Second detection light portion 88-1 First retroreflector 88-2 Second retroreflector L1 First distance L2 Second distance 90 Detector 93 Processing unit 96 Memory 97 Processor}

Claims

Claims _{1. Imaging method (100) for imaging at least one physical property of an object (50) at} one or more imaging locations (54), the method including: ^ _{illuminating (110) with an illumination light beam (15) the object (50) at one or} more imaging locations (54), the illuminating resulting in an interaction of the il- lumination light (15) with the object (50); ^ _{collecting (120) detection light (66) from the one or more imaging locations (54),} the detection light (66) resulting from the illumination light (15) interacting with the object (50); ^ _{generating interferogram data from the detection light (66), including: (i) splitting (130) the collected detection light (66) into at least a first detection} light portion (86-1) and a second detection light portion (86-2); (_{ii) directing (140) the first detection light portion (86-1) along a first optical path (87-1) having a first optical path length, and (150) directing the second detection light portion (86-2) along a second optical path (87-2) having a second optical path length, wherein a difference of the first optical path} length and the second optical path length is alterable; (_{iii)recombining (160) the first detection light portion (86-1) and the second de-} tection light portion (86-2) to generate an interference electromagnetic field; (_{iv)detecting (170) by means of a detector (90) the interference electromagnetic field to generate the interferogram data; ^ constructing (180), based on a power spectral density associated with the interac-} tion of the illumination light (15) with the object (50), an interferogram from the in- terferogram data. _{2. The method of claim 1, further comprising measuring (190) from the constructed inter- ferogram at least one first physical parameter associated with the one or more imaging} locations (54). _{3. The imaging method of claim 1 or 2, wherein the one or more imaging locations (54)} form a two-dimensional plane.

_{4. The imaging method of any one of claims 1 to 3, wherein the detecting (170) comprises} sampling the interference electromagnetic field by means of a two-dimensional array detector (90). _{5. The imaging method of any one of claims 1 to 4, wherein the generating of the inter- ferogram data further comprises altering (155) the difference of the first optical path} length and the second optical path length. _{6. The imaging method of claim 5, wherein the altering (155) comprises changing at least} one geometrical path length or at least one refractive index associated with one or more of the first optical path (87-1) and the second optical path (87-2) _{7. The imaging method of claim 5 or 6, wherein the altering (155) is repeated a sampling} number N of times. _{8. The imaging method of any one of claims 1 to 7, wherein the constructing (180) of the} interferogram further comprises fitting the interferogram data to a Fourier transform of the power spectral density associated with the interaction of the illumination light (15) with the object (50). _{9. The imaging method of claim 8, wherein the power spectral density is described by a} parametric mathematical function having at least one parameter, the at least one pa- rameter being related to at least one physical property of the object (50). _{10. The imaging method of claim 9, wherein the parametric mathematical function describ- ing the power spectral density comprises at least one spectroscopic line shape. 11. The imaging method of claim 9 or 10, wherein the parametric mathematical function} describing the power spectral density is symmetric with respect to a frequency of the il- lumination light (15). _{12. The imaging method of any one of claims 9 to 11, wherein the parametric mathemati-} cal function describing the power spectral density has a limited bandwidth. _{13. The imaging method of any one of claims 9 to 12, wherein the parametric mathemati-} cal function describing the power spectral density comprises a Lorentzian peak, a Gaussian peak, a Voigt peak, and a damped harmonic oscillator peak.

_{14. The imaging method of any one of claims 1 to 13, further comprising recording (200)} directional information associated with the one or more imaging locations (54). _{15. The imaging method of any one of claims 1 to 14, measuring (210) form the directional information a second physical parameter associated with the one or more imaging loca-} tions (54). _{16. Spectroscopic imaging device (10) for imaging at least one physical property of an object (50) at one or more imaging locations (54), the spectroscopic imaging device} (10) comprising ^ _{an illumination light source (11) for illuminating with an illumination light beam} (15) the object (50) at one or more imaging locations (54) ^ _{an interferometer (80) configured to (i) split collected detection light (66) collected from the object (50) into at least} a first detection light portion (86-1) and a second detection light portion (86- 2); (_{ii) direct the first detection light portion (86-1) along a first optical path (87-1)} having a first optical path length, and directing the second detection light portion (86-2) along a second optical path (87-2), wherein a difference of the first optical path length and the second optical path length is alterable; (_{iii) to recombine the first detection light portion (86-1) and the second} detection light portion (86-2) to generate an interference electromagnetic field ^ _{a detector (90) configured to detect by means of a detector (90) the interference electromagnetic field to generate the interferogram data; and ^ a memory (96) configured to store the interferogram data, and ^ a processor (97) configured to construct, based on a power spectral density associ-} ated with an interaction of the illumination light (15) with the object (50), an inter- ferogram from the interferogram data. _{17. The spectroscopic imaging device (10) according to claim 16, wherein the processor} (97) is further configured to measure from the constructed interferogram at least one f_{irst physical parameter associated with the one or more imaging locations (54).}

_{18. The spectroscopic imaging device (10) according to claim 17, further comprising a} detection objective lens (62) configured to collect detection light (66) from the one or more imaging locations (54). _{19. The spectroscopic imaging device (10) according to claim 16 or 18, wherein the illu-} mination light source (11) is configured to two-dimensionally illuminate the object (50). _{20. The spectroscopic imaging device (10) according to any one of claims 16 to 19, where-} in the processor (97) is further configured to fit the interferogram data to a Fourier transform of the power spectral density associated with the interaction of the illumina- tion light (15) with the object (50) _{21. The spectroscopic imaging device (10) according to any one of claims 16 to 20, where-} in to memory (96) is further configured to store a description by a parametric mathe- matical function of the power spectral density, the parametric mathematical function having at least one parameter, the at least one parameter being related to at least one physical property of the object (50). _{22. The spectroscopic imaging device (10) according to any one of claims 16 to 21, further comprising a microlens array arranged along the detection light path (64) at an image plane (44) or in an infinity space (43). 23. The spectroscopic imaging device (10) according to claim 22, wherein the processor (97) is further configured to measure from the directional information at least one sec-} ond physical parameter associated with the one or more imaging locations (54).