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WO2012167907A1 - Dispositif et procédé pour la détermination de propriétés de matériau d'une sonde-substrat dans le spectre de fréquence térahertzienne - Google Patents

Dispositif et procédé pour la détermination de propriétés de matériau d'une sonde-substrat dans le spectre de fréquence térahertzienne Download PDF

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Publication number
WO2012167907A1
WO2012167907A1 PCT/EP2012/002376 EP2012002376W WO2012167907A1 WO 2012167907 A1 WO2012167907 A1 WO 2012167907A1 EP 2012002376 W EP2012002376 W EP 2012002376W WO 2012167907 A1 WO2012167907 A1 WO 2012167907A1
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WIPO (PCT)
Prior art keywords
tera
hertz
light pulses
substrate sample
polarization
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
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PCT/EP2012/002376
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German (de)
English (en)
Inventor
Milan Berta
Volker Feige
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Automation Dr Nix GmbH and Co KG
Original Assignee
Automation Dr Nix GmbH and Co KG
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Priority to EP12730793.2A priority Critical patent/EP2718692A1/fr
Publication of WO2012167907A1 publication Critical patent/WO2012167907A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/21—Polarisation-affecting properties
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3563—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing solids; Preparation of samples therefor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation
    • G01N21/3586—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation by Terahertz time domain spectroscopy [THz-TDS]

Definitions

  • the invention relates to a method for determining material properties of a coated or uncoated substrate sample, in particular in
  • electromagnetic Tera-Hertz frequency spectrum in particular of a coated with at least one layer, preferably fiber-reinforced substrate sample.
  • the invention further relates to a device for determining the material properties of a coated or uncoated substrate sample in
  • Tera-Hertz electromagnetic frequency range in particular of one
  • the object of the invention is therefore to provide a method and a device with which investigations can be made in a simple, cost-effective manner with respect to the material properties of a substrate coated with at least one layer or also of an uncoated substrate.
  • the object is achieved by illuminating a substrate sample with at least two terahertz light pulses of different polarization, at least two collinear propagating terahertz emitters of different polarization, in particular with the same beam cross-section, and reflecting off the substrate sample / or transmitted by the substrate sample tera-heart light pulses in terms of intensity and / or electric field strength in at least two, preferably three different polarization directions are measured time-resolved.
  • a device which comprises at least one pulsed laser, in particular a femtosecond laser for generating pump light pulses and sampling light pulses, in particular wherein from the pump light pulses by beam splitting sampling light pulses are divisible and the at least two of the pump light pulses has optically pumped tera-heart emitter, with which tera-Hertz light pulses of at least two different polarization directions can be generated and having a first optical path with optical components, by means of which the tera-Hertz light pulses are collinear superimposed on a substrate sample and which has a second beam path, with the Tera Hertz light pulses reflected by a substrate sample and / or transmitted through the substrate sample at least one of the optically sampled by the sampling light pulses, the Tera Hertz light pulses in at least two three different polar Tera Hertz detector detecting the directions of detection can be supplied.
  • a pulsed laser in particular a femtosecond laser for generating pump light pulses and sampling light pulses
  • Tera-Hertz light pulses are pulsed electromagnetic waves whose frequency lies in the Tera-Hertz frequency spectrum defined above.
  • a substrate sample is a piece of substrate to be examined or the entire substrate to be examined itself, which is uncoated or has at least one layer, wherein material properties of the substrate itself and / or the at least one layer are to be investigated.
  • Such a substrate may eg
  • fiber reinforced material e.g. with fibers of for example carbon, glass, aramid, basalt, natural fiber etc,
  • the fibers may be formed as a scrim, in particular multiaxial scrims, knitted fabrics, knitted fabrics, woven fabrics or other textile inserts in a matrix material.
  • a pumping light pulse is a pulsed electromagnetic wave, e.g. for providing energy to other sources of radiation powered by this energy, e.g. the Tera-Hertz emitter.
  • the wavelength of a pumping light pulse may be e.g. in the visible range and in the shorter-wave ultraviolet and the longer-wave infrared. Preferably, the wavelength may be in the range of 800 to 1600 nanometers.
  • the pulse duration may be in the femtosecond range, e.g. in the range of 10 to 200 fs, preferably 50 to 150 femtoseconds.
  • a Tera-Hertz emitter is a device for generating electromagnetic, in particular pulsed electromagnetic radiation, the frequency of which lies in the aforementioned Tera-Hertz frequency spectrum.
  • a Tera-Hertz emitter is preferably optically pumped by the aforementioned pump light pulses and converts the energy thus provided into Tera-Hertz light pulses. The pulse duration of this
  • Radiation of a Tera-Hertz emitter is preferably in the picosecond range, e.g. 0.1 to 10 picoseconds, more preferably in the range of 1 to 5 picoseconds.
  • a Tera-Hertz detector is a device with which Tera-Hertz light pulses can be detected, in particular with regard to the field strength and / or intensity and / or polarization. Such a detector may preferably be sampled optically,
  • Tera-Hertz Whenever the term "Tera-Hertz" is used before a term, this is to indicate that the device indicated by the term has the properties mentioned by the term in the Tera-Hertz frequency range mentioned above, ie, for example, a detector in this range is sensitive to detection
  • the invention advantageously offers the possibility of collecting the radiation from a single illuminated measuring surface and evaluating it with respect to a plurality of polarizations using either a Tera-Hertz detector or several Tera-Hertz detectors, to which the Tera Hertz light pulses originating from the illuminated measuring surface are blurred at least partially distributed in each case.
  • the invention relates to a non-contact and / or contacting device for
  • the device comprises a measuring unit with at least two generating sections for generating Tera-Hertz light pulses of at least two different ones
  • an optical system for receiving the Tera-Hertz Echo light pulse for the deflection into a detection unit Focusing the incident Tera-Hertz pulsed light on the sample surface or for the radiation through the sample, an optical system for receiving the Tera-Hertz Echo light pulse for the deflection into a detection unit.
  • Detection unit consists of an optical system for the distribution of the Tera-Hertz echo on at least one polarization-sensitive detection section for Recognition of an electric field amplitude-time resolved waveform of Terahertz echo pulses.
  • the use of more than one polarization-sensitive detection section for the detection of time-resolved electric fields of the waveform of the Tera-Hertz echo pulse (waveform) is possible.
  • the contacting version of the invention includes an alignment edge.
  • Sections, figures, components of the invention and bibliographic references are assigned by numbers in the text.
  • the pictures are labeled " Figure" and a picture number, e.g. Figure 1, marked.
  • the illustrations contain only part numbers or symbols.
  • the components of the invention are indicated by numbers in parentheses, e.g. (1).
  • the section indications have unique numbers, e.g. 1.
  • the invention relates to a device for measuring the properties (the thickness (s) and / or the dielectric properties and / or
  • the device is suitable for:
  • Substrates e.g. Refractive indices, extinction coefficients, complex
  • the coatings must be for the given electromagnetic radiation
  • Samples / materials for Tera-Hertz radiation silicon, sapphire, plastic, wood, composites.
  • a sufficiently transparent pattern may be one
  • anisotropic systems are various composite materials such as carbon fiber reinforced polymers (carbon fiber reinforced plastic, CFRP) or in general the fiber reinforced polymers (fiber reinforced plastic, FRP), wood, etc.
  • isotropic systems are various non-metallic substrates, metallic substrates, concrete, plastic, etc Composite materials are used in aircraft, in shipbuilding, in rotor blades for
  • the use of the device may include:
  • the meter consists of three main units ( Figure 1): the ultrafast femtosecond light pulse delivery unit (7), the Tera-Hertz light pulse delivery unit (6) and the Tera-Hertz light pulse detection unit ( Figure 1). 2).
  • the unit for generating laser light pulses a laser is used to generate ultra-short femtosecond light pulses.
  • the beam of the laser is split into two sub-beams: a pump beam and a scanning beam.
  • the scanning beam is directed to a time delay unit (5) in which the pulses are spatially shifted and delayed in time just at the time the optical scanning is to occur.
  • the pump beam is directed into the Tera-Hertz light pulse emitting part (6) where the multiple emitters excite pulses of different polarization.
  • the Tera-Hertz impulse is provided by appropriate optical
  • Components (3a) guided on the sample surface (4) The return of this pulse via suitable optical components (3b) in the Tera-Hertz (2) recognition serving part.
  • the delayed scanning beam is also used.
  • the entire system is controlled by a processing and control unit (1). Here the signals are controlled, processed and evaluated.
  • the delay line is placed in the branch of the pumping beam with almost the same function.
  • this configuration reduces the delay line
  • the Terahertz light pulse delivery unit consists of at least two Tera-Hertz emitters (34a) (34b), all emitting Tera-Hertz radiation with different polarization directions.
  • two emitters (34a) (34b) having vertical polarization directions Tera-Hertz emit light pulses, which are collimated by the lenses (39a) (39b).
  • Both Tera-Hertz beams are summarized by the use of a polarizing beam splitter (40a) in this construction.
  • non-polarizing beamsplitters can also be used to combine the radiation from more than two emitters.
  • the example in Figure 3 the example in Figure 3, the
  • condensed radiation from both emitters is directed onto the sample surface via the non-polarizing beam splitter 41b (for example made of silicon) and then focused onto the surface by means of a lens 39d.
  • the changed pulse is reflected back into the system.
  • the radiation is then deflected by the non-polarizing beam splitter (41b) into the detection system.
  • the reflected radiation is then detected by a detection system.
  • the Tera-Hertz beam gets through
  • the polarization-sensitive Tera-Hertz detection unit generates at least three polarization signals (d s i, d S 2, d S 3).
  • the scanning beam is also distributed in all individual detectors to a
  • the structure can be supplemented by an optical beam, which serves to measure the thickness of a thin and optically transparent topcoat on the pattern.
  • the optical beam serving for this purpose is split at the front beam splitter (32b), guided by means of beam splitter (42b) into the beam path intended for an optical beam which is transparent to a terahertz beam (e.g.
  • the optical beam is reflected at the top and bottom surfaces of the topcoat applied to the sample and then guided by means of beam splitters (42a) and / or mirrors into the cross-correlation unit (37) where the time delay the echo is measured.
  • the goal here is to measure the thickness of an optically transparent or transmissive coating based on the shorter wavelength of the radiation more precisely in the optical or near or mid-infrared region (depending on the laser type).
  • the design offers the following advantages: it is possible to perform a simultaneous measurement with more than one Tera-Hertz emitter, ie it is not necessary to disassemble the configuration or manipulate the sample. So you can, for example Position multiple highly polarized beams and perform a measurement with different polarizations without having to rotate components. The different emitters are separated from each other, so that no mutual interference can occur, as would be the case with an on-chip multipolarization emitter. Also possible is simultaneous detection with more than one Tera-Hertz detector, i. without the need for dismantling the bodywork or
  • the structure is modular and has interchangeable emitter and detector units. Only one laser unit is used, which currently accounts for the majority of the cost of a time domain Tera Hertz
  • TDTS Spectroscopy
  • the advantage of the invention lies in the way in which the input data are analyzed: Here, a calculation and a comparison of the system and the
  • a coated and painted rotor blade of a wind turbine consists of a GRP substrate (64) with a putty filling compound (63) (optional).
  • a putty coating (62) is sprayed on to improve the adhesion.
  • Inner coating (61) (a base coat) is applied to form an elastic
  • the last applied topcoat (60) (surface finish) has a protective function.
  • Their thickness usually ranges between 0 to a few hundred microns.
  • the thickness of the filler coating usually ranges between 0 to a few micrometers.
  • the usual thickness of the inner coating is about 300 - 450 pm. The thickness of the
  • top coat is approx. 30 - 100 pm.
  • the thickness of the basecoat and the surface finish is influenced by many factors such as viscosity, density and temperature of the paint applied to the substrate as well as the humidity, ambient temperature, etc.
  • the thickness of the basecoat can be 50% in the lower area or 200% in the upper area required thickness. This depends on the factors mentioned above.
  • Thickness deviation must be repaired costly. Accordingly, the thickness of the paint application of each layer must be measured and checked accordingly.
  • CFRP, GRP and / or other FRPs are increasingly being used in vehicle, aircraft, ship structures, etc., because of their relatively stiff and strong material properties relative to their non-isotropic structure, which are additionally distinguished by their low weight.
  • the typical fiber orientations in these composites are unidirectional, bi-directional and tridirectional.
  • the complex structure reinforces the
  • CFRP it is a multi-layered structure in which the carbon fiber layers alternate in direction (see Figure 5a).
  • the individual layers are anisotropic or even double refractive in the relevant frequency range.
  • Such a fiber layer may reflect or transmit the radiation or reflect only part of the radiation.
  • the level and mode of interaction of the sample with the radiation depends on the polarization angle of the light pulse on the fibers in the FRP layer.
  • the process for producing most FRPs depends on the part to be created. Many FRP semi-finished products are made from a single layer of carbon fiber embedded in a plastic matrix (epoxy, polymer, etc.). In contrast, the production of
  • Resistant graphite polymer parts from the layered and alternating laying of structured carbon fiber fabric in a shape modeled on the final shape of the product.
  • Tissue fiber is in the sense of optimizing the strength
  • the mold is then filled with a corresponding filler (multi-composite epoxy, thermosetting polymer) and is then heat or air cured (until the completion of the corresponding filler (multi-composite epoxy, thermosetting polymer) and is then heat or air cured (until the completion of the corresponding filler (multi-composite epoxy, thermosetting polymer) and is then heat or air cured (until the completion of the corresponding filler (multi-composite epoxy, thermosetting polymer) and is then heat or air cured (until the completion of the
  • the result is a cured (epoxy, polymer) matrix during polymerization (or curing).
  • the resulting composite is extremely resistant to corrosion with stiff material properties with high strength.
  • the originality of such a substrate is important for the factors of safety and health. Manufacturers are endeavoring to produce substrates which have a longer life and / or material stiffness, etc., but which may look like a normal FRP. Fingerprint analysis may help to identify illegal or unauthorized replicas or copies of the substrate and / or the
  • Reveal coating The possibility of creating the fingerprint (a compilation of typical material properties) of such a structure is discussed in 9..
  • a large group of anisotropic materials consists of natural materials and biomaterials with a fibrous structure (eg wood). Biomaterials of such composition are found in muscles, bones and arteries.
  • Time domain Tera-Hertz spectroscopy possible.
  • CFRP composites consist of carbon fibers (401) embedded in a plastic matrix (400), as shown in FIG.
  • the high quality fibers used to augment load bearing in aircraft are generally made from a polyacrylonitrile (PAN) fiber.
  • PAN polyacrylonitrile
  • These PAN fibers are temperature-stabilized in different process steps, carbonized and in a final process step, the so-called graphitization, the
  • the measuring system can be used on the one hand in the incoming goods inspection as well as in the production control. Since the material properties of the CFRP substrate can also be determined under a coating or a coating system which is transparent or translucent for THz radiation, these quality or originality controls can also be performed during or after the Coating process done.
  • the carbon fibers have a diameter of about 5 to 10 pm. Carbon fibers, like graphite, have a non-negligible electrical conductivity, so that a strong reflection of the THz pulse exists when the THz polarization is directed in the direction of the fiber orientation.
  • various plastics are used, such as epoxy, bismaleimide resin or polyimides. Depending on the
  • the risk potential of a lightning strike is differentiated between CFRP materials with and without coated copper lightning protection and different types of fiber fabric.
  • the structure or arrangement of the fibers in the composite determines the physical properties from a macroscopic point of view.
  • the various arrangements of the fibers can in principle be distinguished into uni- (402) and bidirectional (403) fiber structures, with different ones in particular for the bidirectional structures
  • the various carbon fibers, plastic matrix polymers and fiber-fabric structures have an influence on the reflection and propagation of the electromagnetic THz wave, so that these different substance combinations for the coating thickness measurement are to be analyzed.
  • CFCs Due to its directional structure (uni-, bi-, tri-), CFCs (but also general FRPs) react angularly depending on the polarization of the incident radiation.
  • An example of the reflection sensitivity of a CFRP pattern on polarized Tera-Hertz radiation is illustrated by the following facts. The reflection of a polarized Tera-Hertz pulse was measured in two configurations in a zero angle reflection geometry, ie, the sample was irradiated vertically and the radiation was also detected in the vertical direction.
  • a sample of CFRP consisted of unidirectional layers of carbon fibers in vertical (0 and 90 °) configurations, see Figure 5a. In such a sample, two or more different fiber layers can be distinguished.
  • FIG 5 a only the top two layers are shown: the top layer (layer 1) (70) and the next inside layer (layer 2) (71).
  • the sample is examined in two configurations of the incident, polarized Tera-Hertz light pulses.
  • configuration A 252)
  • Figure 5b the fibers of the cover layer (layer 1) ran parallel to the polarization of the incident radiation and the fibers of the underlying layer (layer 2) perpendicular to the incident radiation.
  • the fibers in Layer 1 behave like a good conductor along the carbon fibers due to the high electrical conductivity, and the layers reflect most of the incident radiation. This reflection is expressed by a strong pulse at 0 ps in Figure 8a at three different measurement points on the sample (102a) (102b) (102c).
  • Configuration B was prepared to have a contraposition.
  • configuration B 253 ( Figure 5b)
  • the fibers in the upper layer of the sample (layer 1) are perpendicular to the polarization of the incident Tera-Hertz radiation.
  • the fibers in layer 1 transmit most of the incident radiation (and reflect it due to the nonuniform directionality of the fibers as well). This is expressed by the decrease in the amplitude of the 1st light pulse (at 0 ps) in Figure 8 b.
  • the fibers in the underlying layer (layer 2) were positioned parallel to the polarization of the incident radiation and these fibers have a reflection; this is indicated by a pulse at about 3 ps in Figure 8b, which looks like a reverberation of the first pulse (at 0 ps).
  • waveforms for three different measurement points are shown on sample (03a) (103b) (103c).
  • the structure of the CFK layers can also be designed differently, e.g. Layer 1: 0 °, Layer 2: 60 °, Layer 3: 120 °, but the partial transparency and reflectance of the different
  • Layers is also present and can be analyzed in the same way.
  • the position and location of the two pulses (in Figure 8b) allow the determination of the thickness and material properties of the layers (see 30).
  • the reflection and / or transmission of the electromagnetic pulses in the construction of a uni-, bi- or tri-directional FVK sample can be collected in one area.
  • an area of 25 x 25 mm was examined on a bi-directional CFK sample in 2/2 twill construction using TDTS in reflection geometry.
  • the effective dimension of the spot area of the Tera-Hertz radiation was less than about 2 mm.
  • Illustration in Figure 9c shows the structure of the threads in the visible structure in Figure 9a. All representations of the area are almost on the same scale
  • FIG. 9b A typical waveform for maximum (154) (white area), minimum (155) (black area), and intermediate (156) (gray area) values in Figure 9b is shown next to Figure 9d (with the relative time delay in picoseconds on the x -Axis (157) and on the y-axis (158) you can see the electric field in arbitrary units).
  • positions ⁇ , P2 and P3 are also assigned.
  • the white color refers to areas with cover layer fibers running parallel to the polarization (eg. Position P ⁇ denotes the gray color areas where cover layer fibers perpendicular (to the polarization.
  • Transient or mixed ranges (example: position P3).
  • the most complex response (example: position P 3 ) is obtained in the areas on the surface where the threads have different orientations (in x and y direction and possibly also in z direction).
  • the waveforms of these areas can contribute greatly to fingerprint analysis of the FRPs.
  • the imaging data also allow the determination of the slope of the threads (159) within the structure needed for authentication (see below).
  • characteristics typical for a substrate for authenticating the substrate can be defined, identified and measured:
  • Threads consist of fibers and a structure is created by weaving the threads into a structure
  • Polarization direction of the incident radiation stimulates ei and ⁇ 2 and optionally also e3.
  • ei and ⁇ 2 stimulates ei and ⁇ 2 and optionally also e3.
  • the anisotropic sample rotates the polarization (reflection) and influences the ellipticity (transmission) of the incident polarization.
  • the sample is illuminated with at least two polarizations of each separate emitters in the proposed device.
  • the orientation of the refractive index ellipsoid on the surface of the sample can be determined by at least three polarization signals (d s i, d S 2, d S 3). These three signals can be due to the polarization sensitive
  • Detection unit (50) can be determined, e.g. by a triplet on photoconductive switches (35a) (35b) (35c) or by opto-electronic scanning ( Figure 13 or 16).
  • the thicknesses of the fiber system layers (if any) together with the properties of the plastic matrix material provide a fingerprint of the sample. This fingerprint can be matched to previous reference measurements to identify the sample and / or provide proof of originality. A comparison of the fingerprint with a standard pattern is also possible.
  • each color layer is measured by wet comb technique.
  • a calibrated, comb-like structure is inserted into the paint until it stops to check the color depth.
  • Thin film changes depending on the layer thickness of a transparent conductive film or a transparent optical film.
  • a nondestructive paint thickness gauge has been developed based on the principle of continuous wave interference to reduce the damage done to the product.
  • a thin film to be measured is irradiated with light, and the interference of the reflected light and the light reflected at the back of the thin film is decomposed into each wavelength.
  • a spectral intensity distribution is generated and the layer thickness is measured based on this distribution.
  • a polarization-sensitive detector is used in some of these experiments, the sample or emitter (emitting the radiation with linear polarization) must be rotated to examine an anisotropic sample.
  • Reflected interface each having a discontinuous refractive index and gives a reflected Tera Hertz light pulse (a Tera-Hertz echo pulse).
  • the separate pulses are resolved and their time delay analyzed.
  • Coating thickness measuring devices are limited to the resolution of the individual reflection pulses in the time domain or they are not sensitive to anisotropic substrates, since the sensitivity of the measurement is determined by the orientation of the polarization of the radiation, the anisotropic sample and the polarization-selective detector.
  • the pulsed electromagnetic Tera-Hertz radiation can be detected by means of the so-called optical scanning technique. This is the most commonly used technique for mapping the Tera-Hertz signal into TDTS.
  • the technique of optical scanning is understood to be the imaging of the electric field of the Tera-Hertz light pulse within a photoconductive switch (GaAs crystal, low-temperature growth GaAs, SnGa, etc.) and / or within an electro-optic crystal (Pockels cell, ZnTe crystal, LiNbOa).
  • a photoconductive switch GaAs crystal, low-temperature growth GaAs, SnGa, etc.
  • electro-optic crystal Pockels cell, ZnTe crystal, LiNbOa
  • Other techniques which do not use scanning by an optical beam e.g.
  • the technique based on the Schottky diode can also be used.
  • the optical scanning method uses a split optical beam, the scanning beam (170). This interacts with the detector media (173) (electro-optic crystal or photoconductive switch) in the electric field of the Tera-Hertz light pulse (171).
  • the scheme of electro-optic scanning by means of electro-optic crystal is shown in Figure 14 and explained below.
  • the linear polarization (172) of the scanning optical pulse (170) is modified due to the changed induced birefringence (174) of the electro-optic crystal (173), which is due to the presence of the electric (Tera-Hertz) field amplitude E (171).
  • the Induced birefringence depends on the value of the electric field E.
  • the polarization of the scanning beam is optionally elliptical (176) and divided into two vertically polarized beams (178), which are spatially separated by a prism polarizer (177) (eg Wollaston prism).
  • a prism polarizer (177) eg Wollaston prism
  • Difference in optical intensity (imaging of ellipticity) using a pair of balanced photodiodes (179) (also called differential photodiodes) in terms of relative delay time yields a signal proportional to the Tera-Hertz field.
  • An analyzer (1 75) ( ⁇ / 4 plate or ⁇ / 2 plate or polarizer) in the beam allows easy balancing of the photodiodes before the measurement. Without the analyzer (e.g., K / 4 or ⁇ / 2 plates), the differential photodiodes must be balanced by rotating them along the beam axis along with the prism polarizer.
  • the electro-optic and dielectric properties (e.g., refractive index) of the electro-optic crystal are affected by the electric field of the Tera-Hertz light pulse.
  • both of the above techniques are sensitive to polarization of the incident Tera-Hertz beam.
  • the complete polarization of the incident radiation is detected, e.g. through the introduction of several photoconductive, juxtaposed
  • the Tera-Hertz light is an electromagnetic wave whose wavelength is approximately 30 to 3000 pm in a vacuum and whose frequency is approximately 0.1 to 10 Tera-Hertz.
  • the Tera-Hertz pulse passes through layers of electrically non-conductive material on a metallic or non-metallic substrate, eg
  • a Tera-Hertz light pulse is emitted onto an object made up of different layers of color, the Tera-Hertz light pulse is reflected at each layer transition with a different refractive index (Fresnel reflection) and a reflected Tera-Hertz light pulse (Tera-Hertz echo pulse light) is obtained.
  • the different impulses and / or system functions are resolved, the waveforms analyzed and compared with a physical model. Measurements at different orientations of the polarization of the incident radiation are analyzed together.
  • the device is an improvement of a polarization-selective TDTS measurement system in a zero-degree reflection geometry, see Figure 11.
  • the zero-angle setup is preferred (due to better alignment of the sample), but the design can also be used with non-zero reflection geometry. Angle or in transmission geometry as well as at other angles.
  • This simple construction for the time domain Tera-Hertz spectroscopy (TDTS) works with free-space or guided Tera-Hertz light pulses using a (fiber-coupled)
  • the polarization of the emitted radiation is
  • the Radiation can additionally be polarized with a polarizer (263).
  • the Tera-Hertz pulses are focused by a pair of lenses (266a) and (266b) (lenses of plastic or other transparent material) onto a beam splitter (264) on the sample (30).
  • the focused impulse interacts with the sample (30) and becomes a significant portion of the radiation
  • the emitter and detector in this construction are polarization-selective, ie the radiation emitted by the emitter is polarized and the detector responds only to a specific polarization of the radiation.
  • the pumping as well as the optical scanning beam can be uncovered beams in the free space or else fiber-coupled beams (268a), (268b). It is also possible to use parabolic mirrors instead of plastic lenses or other transmission lenses for directing the radiation onto the sample surface. Compared with this
  • a polarizer is an optical component for linear polarization of the
  • a polarizing beam splitter is an optical component for splitting the incident radiation into two perpendicularly polarized beams at reflection and / or transmission (preferably at 90 ° angle), e.g. freestanding wire mesh polarizers or Wollaston prisms
  • a non-polarizing beam splitter is an optical one
  • Polarization e.g. a beam splitter made of silicon.
  • Sample surface are stimulations in at least two different ones Polarization directions ei and ⁇ 2 required, the response in at least three different polarization directions d s i, d S2 . d S 3 must be recognized.
  • the parameters of the Tera-Hertz pulses (spectral response in the frequency domain,
  • Phase shift as well as rotation and ellipticity are at Rejection or
  • the simple design emits and detects in only one polarization (see Figure 15 and Figure 11) and is able to measure the anisotropic properties of the sample. This requires turning the meter or sample. Some samples are too large to be rotated (car or plane) and it is also time-consuming to turn the meter. In addition, it would have to be ensured that the measuring positions would be the same. Generally, at least three such polarization-selective TDTS (Geder responds to a different polarization) must be arranged in a structure to successfully evaluate a point on the sample.
  • the polarization-selective TDTS structure for a further two (or more) terahertz emitter adds the different polarizations of radiation (ei and e 2) radiate.
  • the polarization-selective TDTS structure for a further two (or more) terahertz emitter adds the different polarizations of radiation (ei and e 2) radiate.
  • Detection unit by two and / or more Tera-Hertz emitter which can detect polarizations in different angles and directions (relative to each other), are complemented.
  • the main advantages of such a device are as follows (further see 5):
  • the pump beam is directed by a beam splitter or switch to separate emitters.
  • the polarization resolution is ensured by using at least two emitters (34a) (34b), each of which has Tera-Hertz radiation
  • these polarizations are perpendicular to each other and are e.g. + 45 ° and -45 ° to the vertical plane of the structure (other orientation such as 0 and 90 ° is also good).
  • the radiation coming from the emitters becomes by the structure the
  • Sample surface (38) out.
  • the guidance and collimation takes place via lenses (39a) (39b) and / or parabolic mirrors, polarizers and / or polarizing or non-polarizing beam splitters (40a) and / or non-polarizing beam splitters (41b), and lastly the radiation on the Sample surface focused by means of a lens.
  • the radiation After reflection and / or transmission from and / or through the surfaces of a multilayered sample (38) or one and / or anisotropic sample, the radiation is directed into the polarization sensitive detection unit.
  • the detection unit which consists of three individual polarization-selective detectors (e.g., photoconductive switches).
  • polarizing beam splitters 40c and analyzers (40b) and lenses (39e) (39f) (39g) to the individual detectors (35a) (35b) (35c) divided.
  • the beam non-polarizing beam splitters are used, but the
  • Each of the detectors respond to a different polarization and their orientation is 0 °, 45 ° and 90 ° to the vertical plane of the structure (-45 °, 0 ° and + 45 ° is also good), (or 0 °, 60 ° and 120 ° is also sufficient if the inefficiency of using non-polarizing beam splitters with respect to reflection losses is acceptable).
  • All detectors can be carried out either as a fiber-coupled as well as space-coupled photoconductive switch, the electro-optical detectors of non-linear crystals (ZnTe, LiNbO ß etc.) are manufactured, or other, suitable for time-domain terahertz pulses detectors are used (see 13).
  • two normalizing detectors (36a) (36b) with additional, focusing lenses (39h) (39c) for detecting and monitoring the delivered Tera-Hertz pulses can also be integrated into the setup (see Figure 3) to normalize the detected pulses .
  • These normalization detectors can also use the technique of optical scanning just like the other existing in the device detectors. In this case one can use a non-polarizing beam splitter instead of a polarizing beam splitter (40a) or the
  • the optical beam emitted by the laser (31) can be free-space-guided or
  • a beam splitter 32a
  • the pumping beam is delayed by a delay line (33) to enable detection by optical scanning. It is further divided by a beam splitter (32b) into beams for all involved transmitters and / or thickness measurement from an optical beam path.
  • the scanning beam is split further by the beam splitter (32c) into beams for all the detectors involved and / or for the cross-correlation unit (37).
  • At least two polarization-selective emitters are sufficient (alignment 0 and 90 °). Multiple emitters may be coupled in the structure directly adjacent thereto, e.g. in 45 ° orientation or with different spectral response. This is similar to a basic design (with an emitter and a detector) with an emitter-detector pair in three or more
  • Angular orientations The purpose is as follows: The measurement analysis and evaluation method used in the basic setup in various angular orientations of the sample can be used within our setup for each of the pairings.
  • a delay line unit In the construction, a delay line unit (33) is used. It may consist of one delay line or a plurality of separate and coupled (207) (208) delay lines. The coupling of several
  • Delay lines which each have different speeds of movement or vibration mechanisms, offers the advantage that a larger
  • Range is increased by a delay line with higher
  • the time delay distance is compensated by a suitable length of the beam path, e.g. through the fiber length.
  • the build ensures that the time delay window is enlarged or into different ones
  • Time delay window is split (with one detector for each window).
  • the entire time delay window is calculated from the
  • Time delay window for a time delay line multiplied by the number of detectors This may be useful in examining isotropic materials (there is no dependency on the input polarization) with three different detectors or from deep samples with three consecutive detectors for each time slot or for the virtual extension of the delay path using fast and short delay lines.
  • the delay line may be placed in the pumping or scanning arm of the optical beam, depending on what provides better stability of the optical beam with respect to the measurement or emitter processes. It can be shown that the photoconductive switch delay line in the pump beam is capable of generating terahertz beams with lower spatial fluctuation.
  • the delay line has its own, relative position coordinate system (in a longitudinal dimension), which z. B. can be implemented by means of linear optical encoder. 20 Definition of a topcoat / surface finish with optical pulse
  • An additional optical pulse can be connected to the optical system to measure a potentially transparent (translucent) topcoat (finish) on the product (if applicable). Measurement with a separate optical laser beam allows the determination of the characteristics of such a coating with much higher precision due to the shorter duration / length of the pulse (about 100 fs (femtoseconds) lasting optical pulses compared to 2 ps (picoseconds) lasting Tera-Hertz pulses ).
  • the separate pulse also allows the measurement of the distance of the structure from the sample surface. This may be important to maintain a certain distance from the sample surface.
  • This optical pulse is coupled into the system by means of non-polarizing polyethylene beam splitter (42b) (pellicle beam splitter, polyethylene terephthalate (PET) film).
  • Time delay (s) of the 2 or more incoming reflected pulses measured. Then the thickness of the surface finish or the distance of the sample is determined with a similar algorithm which is also used to determine the thickness by means of terahertz radiation (see Figure 30).
  • the reflection of a polyester film in the system is called
  • Reference pulse used The spacing of the two pulses is determined using a technique very similar to the cross-correlation described above.
  • the design can be changed to extend its physical delay line.
  • the electro-optic scanning method is used to determine the Tera-Hertz pulses.
  • a part of the beam of a femtosecond laser (31) is delayed by means of a delay line (33).
  • An asynchronous optical scanning system (ASOPS) can also be used for the detection.
  • the system requires two femtosecond lasers, each having a slightly different repetition rate: one is for emission and one for sampling.
  • the scanning beam from one of the lasers is directed to the detection unit or forwarded in the usual way to the different polarization-selective detectors.
  • an active polarizer For switching the polarization of the emitted Tera-Hertz radiation, an active polarizer can be used that monitors the polarization of the radiation by means of external stimulation on a crystal structure (e.g.
  • the detection unit can also consist of successive electro-optical scanning units.
  • the three electro-optic sample crystals are placed consecutively (see Figure 13).
  • the Tera-Hertz radiation optionally elliptically polarized, is directed by means of lenses (80) (81b) (81c) to each of the electro-optic crystals (82a) (82b) (83c).
  • the scanning beam (88) is distributed to all the individual detectors, so that a time-resolved detection by the beam splitter (83a) (83b) (84a) (84b) (84d) and / or mirror (85a) (85b) can take place.
  • Polarization of the optical beam can be adjusted.
  • Polarisers, lambda / 4-plates or lambda / 2-plates and / or Pockels cells can be used for these active (87) or passive (86a) (86b) polarizers.
  • the beam is then used by the Tera-Hertz gear for detection by means of metallized mirror, which for Tera-Hertz (84c) (84e) is permeable and / or distracted by normal mirror (85b).
  • the optical scanning assembly (89a) (89b) (89c) consists of an analyzer (eg, quarter and half wave plate or polarizer) and a prism polarizer, eg, a Wollaston prism, which spatially scans the scanning beam into two beams of perpendicular polarization (see 13) splits. The polarized beams are then detected by different diodes. Another arrangement is to run the Tera-Hertz beam parallel to each of the electro-optic crystals (as shown in Figure 3).
  • an analyzer eg, quarter and half wave plate or polarizer
  • a prism polarizer eg, a Wollaston prism
  • the emitted Tera-Hertz radiation is by a mechanical or
  • opto-electric chopper (206) e.g., by rotating blades in the optical beam (using electro-optic radiation)) or clocked by a periodic signal at the emitter (using a photoconductive switch).
  • the clock frequency is then used to separate the useful signals by means of a lock-in amplifier (217) to which the signals are passed from the detector.
  • the emitter can be modulated at different frequencies to provide crosstalk signals in the
  • Femtosecond lasers with ultrashort pulses usually belong to laser class II, III or IV.
  • the optical beam path for protection of the human eye or the skin (laser class IV) with opaque material shield is also susceptible to contamination, ie against dust particles present in the air. Therefore, the laser beam may need to be in a fiber or in a chamber under protective atmosphere (see 17).
  • the Tera-Hertz beam is not harmful to humans and causes no damage to human tissue in the radiation intensities used.
  • Tera-Hertz radiation is extremely sensitive to humidity. Therefore, the Tera-Hertz beam may need to be protected in a closed enclosure or in a flushing chamber (see 17).
  • the device may additionally be provided with an alignment collar (21) after the last lens located in front of the sample (22), which makes positioning the device to the sample surface easier. This is especially necessary for the hand-held device (not guided by positioning system (209)).
  • the registration edge (21) causes a flat surface sample (24) to be positioned in the beam impact site of the generated and concentrated Tera Hertz beam (23).
  • the alignment edge allows the curved surface sample (38) to be placed in a position where the curvature of the sample surface coincides with that of the aligned beam.
  • the shape of the inner surface of the alignment edge is pre-calculated according to the beam shape (e.g., for a zero order Gaussian beam, see Fig. 27) to correspond to the various circular areas and / or cylindrical surfaces.
  • the alignment edge can be circular or cylindrically symmetric for ball or
  • Cylinder surfaces be. Another function of the Alignment Edge is to center a circular or cylindrical object on the incident axis of the emitted beam (see Figure 12).
  • a focused beam can be approximated in different ways.
  • the complex electric field E (r, z) (the amplitude E (r, z)) may be described by the following equation (pages 90 and 91)
  • r is the radial distance from the beam center axis
  • k 2 ⁇ / ⁇ is the number of waves (as radians per meter) and
  • R (z) is the radius of curvature of the wavefront of the beam
  • ⁇ ( ⁇ ) is the phase shift, an additional feature in the phase that you get at
  • Gaussian rays can be observed.
  • Equation 3 expresses that a concentrated beam
  • the radius of the waveforms depends on the distance of the beam impingement. Other beam shapes are also possible.
  • the Tera-Hertz radiation is strongly absorbed by water, and the fingerprint of water can be observed in experiments in a free-space environment with air that is not completely dry. Therefore, in order to increase the resolution, sensitivity and stability, one can also rinse the entire assembly with a non-invasive gas that is transparent to terahertz radiation, e.g. Nitrogen or air with known / predetermined degree of humidity (dry air or air with defined humidity (228) (229)). However, the humidity can also be reduced by retracting
  • a non-invasive gas that is transparent to terahertz radiation
  • the entire measuring head is purged with gas which exits the device at the last lens (22).
  • the cylindrical (233) alignment edge directs the gas flow to the
  • This gas flow ensures that the lens remains clean and / or a predetermined distance to the sample surface is maintained.
  • a laminar gas flow is preferred so that the Tera-Hertz radiation and the optical beam are not affected by turbulence.
  • the gas enters the tunnel through an opening for the purge gas (25) in the alignment edge (21) (233).
  • the entire Tera-Hertz beam path is filled with the defined purge gas.
  • the gas flows from a pressure tank (235), which is part of the structure.
  • the gas pressure and flow into the chamber of the optical path and into the measuring head are regulated by two independent valves (234) (236).
  • the measuring head can also be placed under vacuum (228) to increase the measuring stability.
  • the device consists of an electro-optical control unit (215) and a measuring head (222).
  • the two units are connected by the required network connections (232) for power supply and data connection (ports X1_01 to X2_04 in Figure 2).
  • Power cable e.g., 230V / 400V at 50Hz / 60Hz
  • 203 (204) and / or batteries or uninterruptible power supply (201) and / or fuel cell.
  • the beam path includes a grating stretcher (205) for additional pulse shaping to compensate for the scattering caused by the fiber-coupled beam path, or a chopper (206) of a mechanical nature or a system for clocking electro-optic pulses in the beam path.
  • the electrical signals at the emitters can also be clocked.
  • An optional positioning system (209) for lateral imaging and fingerprint analysis of samples is also possible.
  • a real-time control system (1) is for data acquisition and control of others
  • the measuring head (222) consists of the actual measuring optics (226) (see Figure 3 for details), control electronics (227) and sensors (e.g.
  • the measuring head has its own switch (225) or via switches and control diodes (223) and / or a display unit for communication with the user.
  • the algorithm (212) for the evaluation of the measured waveforms is part of the real time control system (1). With the collected data, the algorithm (by (214)) distributes all significant signals (components (302) to (309)) further. It includes an analysis of the system and its response (components (310) to (320)) as well as an evaluation of the properties of the sample (components (321) to (330)).
  • all the input data (302) - (306) are read and collected (by (214)), ie the signals from the Tera-Hertz detector unit (or detector units) for a reference value (normally this is a metal plate) d r i, ⁇ , d r 3 (302) and for the sample d s i, d S 2, d S 3 (303), the signals from the normalization Tera-Hertz detector (d n i, d n 2) (305), the optical signals of the sample and reflections (Ii) (304) resulting therefrom, as well as the reference signals from the laser beam (l r1 ) (306).
  • the signals are checked for completeness, compared and normalized (307).
  • a set of normalized measurement (308) and reference data (309) is created and passed to the
  • Light pulse interact the multilayer structure and / or the substrate together with the different gas states in the chamber.
  • An idealized momentum g, (t) (312) is set (is also converted into the frequency domain, g, (t) -> Gi (f) (314)) and the idealized response function of the system Hj (f) (316) and hj (t) (317) is constructed as follows: hi (t) is a function of G (t) and gi (t), H, (f) -> h, (t) (315).
  • the idealized measured response function of the system (316) (317) and the idealized pulse (318) (319) both in the time and frequency domain
  • the unknown parameters are initialized (320).
  • Unknown parameters here are the features of the system: the layer thickness (321), material properties of the layers and the substrate (322).
  • the material properties (refractive indices and extinction coefficient, etc., see point 3, page 4) are parameterized by means of a suitable function (constant and / or linear and / or quadratic). These original parameters are then in the Adjustment process entered.
  • the fitting process generates a model system response (324) using the parameters and a model
  • the fitting process calculates the response function of the model in the frequency and / or time domain.
  • the model system response is then idealized with
  • the fitting procedure is ended when the quantified deviation is below a predetermined threshold (positive answer (329)) (i.e., the correlation between model and measured response exceeds a predetermined threshold).
  • the parameters of the multilayer structure and the substrate (330) are then transferred to the data memory or displayed to the user (210) in the graphical display field.
  • Section 13 (Polarization Selective and Sensitive Detection of Tera-Hertz Radiation) mentions the possibility of detecting the total polarization of Terahertz radiation by using an electro-optic crystal in a given arrangement (eg a ZnTe crystal with [111 ] Alignment in its crystallographic axis, see Figure 16).
  • a lambda / 2 plate is placed in front of the prism polarizer (e.g., Wollaston prism) to balance the
  • phase retarder e.g.
  • phase retarder (175) Purpose of the phase retarder (175) is a regulated and continuous phase switching and / or reversal of the polarization orientation for balancing the differential diodes (179) (see Fig.
  • the differential diodes are balanced prior to measurement if there is still no Tera-Hertz field (electric field) present in the detector crystal (173) (120) (82a) (82b) (82c). In our case, the possibility of using a Tera-Hertz field (electric field) present in the detector crystal (173) (120) (82a) (82b) (82c). In our case, the possibility of using a Tera-Hertz field (electric field) present in the detector crystal (173) (120) (82a) (82b) (82c). In our case, the possibility of using a
  • Section 26 (Alignment edge) on page 16 of the original document describes how to determine the properties of coatings on cylindrical samples or on cylindrical and / or curved specimens. For such an analysis, calibration and / or correction of the reflected electromagnetic pulses (and / or in particular their amplitude) should take place at the radius of the curved
  • A amplitude of the reflected electromagnetic pulse
  • a 0 the normalized value (424) of the reflection on a plane metal surface
  • Figure 1 Schematic diagram of the structure: Laser (7) delivers ultrashort electromagnetic femtosecond pulses in the optical or near-infrared frequency range; Emission unit (6) emits picosecond electromagnetic pulses in the terahertz and / or far-infrared frequency range; Radiation guide optics for the
  • the signals are controlled, processed and evaluated in the processing and control unit (1). It will be one
  • the delay line (5) is preferably in the branch of the pumping beam (between laser (7) and emitter unit (6)), see sub-figure a) with text, but can also be positioned in the branch of the scanning beam (between laser (7 ) and detector unit (2)) (see sub-picture b). An overview of the transmission setup is shown in sub-figure c).
  • FIG. 2 Infrastructure of the proposed device with internal connections.
  • Alignment edge where airflow towards the sample surface ensures that the probe maintains a certain distance from the sample surface.
  • Figure 3 the proposed polarization-sensitive TDTS measurement setup in zero-degree reflection geometry.
  • the beam of a femtosecond oscillator / laser (31) is split twice: into the pump beam and the scanning beam. This is done by means of beam splitters (32a).
  • Figure 4 Cross-section of the coating structure of the rotor blade of a
  • Top coat (finish) (60), inner coat (primer) (61), putty coat (thin) (62), putty fill (optional) (63), carbon fiber in epoxy matrix (with ground surface) (64).
  • Figure 5 Schema overview of fibers in two layers in a unidirectional FRP matrix in an absolute and relative coordinate system. Upper layer (layer 1) of the FRP (70), inner layer (layer 2) of the FRP (71). Configuration A (252): The polarization of the incident radiation is parallel to the fibers in the cover layer. Configuration B (253): The polarization of the incident radiation is perpendicular to the fibers in the cover layer.
  • Figure 6 Fiber embedding (401) in a plastic matrix (400)
  • Fabric structures (403) - bi-directional fabric structures, (404) - quasi-isotropic structure, (405) - partially warp reinforced, (406) - canvas fabric (taffeta)
  • Figure 8 Measurement of a CFK sample in two polarization configurations of the radiation and fiber directions.
  • Configuration A overview in Figure 5b (252) and results of the measurement in Figure 8a
  • Cover layer (layer 1 (70), Fig. 5a) parallel to the incident polarization and the surface reflected most of the radiation (momentum at 0 ps).
  • the radiation reflected by the underlying layer (layer 2 (71), fig. 5b) was not recognizable.
  • the fibers in the cap layer were perpendicular to the incident polarization and the surface reflected less (smaller impulse at 0 ps).
  • the reflected radiation from the underlying layer can now be detected as a pulse at about 3 ps.
  • Figure 9 A photo of the visible area (a), an xy raster image in Tera-Hertz light (b) and a schematic image (c) of a bidirectional CFK sample in K2 / 2 twill weave.
  • reflected waveforms become three
  • Figure 10 The ellipses of refractive indices on the surface of an anisotropic sample.
  • the ellipse can be described by its principal axes ⁇ ⁇ ⁇ , ⁇ 2, the angle of rotation ⁇ or by three points (d s i, d S 2 > d S 3) lying on its contour line (303).
  • the three points on the outline are detected by means of three detectors.
  • the light is radiated from two emitters (e- ⁇ , e 2), or optionally by another emitter (e 3) to enhance the sensitivity even more.
  • the arrows indicate the polarization of the radiation emitted by the emitters or point to the radiation to which the emitter is sensitive.
  • Figure 11 A simple polarization-selective TDTS measurement setup in a perpendicular (zero degrees) reflection geometry.
  • the emitter and the detector are both
  • Refractive index ellipsoids if you put the sample in two or more
  • Figure 2 Alignment edge to align the sample surface in the focused beam a) Align the alignment edge (21) with a flat or cylindrical sample (plate or rod) (24). b) Aligning edge with curved surface sample (26), Reflection in focus: Planar wavefront reflected at a wide spatial angle, c) Aligned edge with curved sample
  • the alignment edge may be on spherical samples
  • the alignment edge can in cylindrical samples (sub-image a) and sub-image f)) be symmetrical in two planes.
  • FIG. 13 Electro-optical scanning with several, successively connected electro-optical crystals (Pockels cells). The Tera-Hertz beam is refocused to enhance detection in the next crystal. Any set of electro-optical crystals and optical detectors (lambda / 4 or lambda / 2-plate,
  • the optical pulse is split and actively or passively polarized so that the position of the optical axis in the electro-optic crystal also coincides.
  • a Pockels cell serves as an active polarizer, and a lambda / 2 plate and / or wireframe polarizer are used as passive polarizers.
  • Figure 14 Schematic image of the electro-optical scanning: The polarization of an optical pulse (170) is due to the birefringence (174), which in the
  • Amplitude E is generated, modified in proportion to the value of the field. Imaging the resulting differences in intensity (representing ellipticity (76) (178)) using a pair of balanced photodiodes (179) in terms of relative delay time yields a signal that is proportional to the Tera-Hertz field.
  • Figure 15 Algorithm of the evaluation of the insertion or insertion
  • Figure 16 Schematic representation of a multidirectional, electro-optical
  • the polarization of the linearly polarized scanning rays (88) is set on an active or passive polarizer (to produce elliptical or special linear polarization).
  • the beam is then passed through a mirror transparent to Tera-Hertz radiation (84a) into an electro-optic crystal of particular crystallographic orientation (eg, [111]).
  • the elliptic Terahertz beam interacts with the crystal, changing its material properties and affecting the elliptical optical beam.
  • the beam through a non-polarizing beam splitters (122) are divided into two separate optical sensor units (123) (124).
  • Figure 17 Comparison of the reflections of cylindrical surfaces by means of measurement and simulation.
  • the amplitude of the spectral distribution (422) in given units over the frequency (423) in THz is shown in sub-figure a).
  • Measurements (420) and simulations (421) compared.
  • the amplitude (429) of the reflected electromagnetic pulse in given units over the radius (428) of the cylindrical sample in mm is shown in sub-figure b).
  • Amplitudes of the electromagnetic pulse are here reflected from a curved surface and shown for the measurements (425), simulations (426) and a best-fit function (427) over the radius (428) of the cylindrical sample.
  • the results are normalized to the value (424) of the reference measurement on a flat metal surface.
  • a flat metallic surface was simulated and measured as a reference.
  • processing and control unit e.g., real-time 2
  • processing and control unit e.g., real-time 1

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Abstract

L'invention concerne un dispositif et un procédé pour la détermination de propriétés de matériau d'une sonde-substrat revêtue ou non revêtue dans le spectre de fréquence térahertzienne électromagnétique, en particulier d'une sonde-substrat revêtue d'au moins une couche, de préférence à renforcement de fibres. Ledit dispositif et ledit procédé sont caractérisés en ce que la sonde-substrat est éclairée avec au moins deux impulsions lumineuses térahertziennes de polarisation différente, ayant en particulier la même section transversale de rayon, produites par au moins deux émetteurs térahertziens, se propageant de façon colinéaire, et les impulsions lumineuses térahertziennes réfléchies par la sonde-substrat et/ou transmises par la sonde-substrat sont mesurées avec résolution temporelle en ce qui concerne l'intensité et/ou la force du champ électrique dans au moins deux, de préférence trois directions de polarisation différentes.
PCT/EP2012/002376 2011-06-06 2012-06-05 Dispositif et procédé pour la détermination de propriétés de matériau d'une sonde-substrat dans le spectre de fréquence térahertzienne Ceased WO2012167907A1 (fr)

Priority Applications (1)

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EP12730793.2A EP2718692A1 (fr) 2011-06-06 2012-06-05 Dispositif et procédé pour la détermination de propriétés de matériau d'une sonde-substrat dans le spectre de fréquence térahertzienne

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DE102011104708.9 2011-06-06
DE201110104708 DE102011104708A1 (de) 2011-06-06 2011-06-06 Verfahren und Vorrichtung zur Bestimmung von Material-Eigenschaften einer Substrat-Probe im Tera-Hertz-Frequenzspektrum

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CN110071419A (zh) * 2018-01-22 2019-07-30 中国科学院上海光学精密机械研究所 一种飞秒激光脉冲净化的系统和方法
EP3521809A4 (fr) * 2016-09-27 2020-06-03 Shenzhen Institute of Terahertz Technology and Innovation Spectrographe de détection d'état de polarisation totale térahertz
CN113030127A (zh) * 2019-12-09 2021-06-25 通用电气公司 评估涂层微结构的系统和方法
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CN115541529A (zh) * 2022-08-30 2022-12-30 青岛青源峰达太赫兹科技有限公司 基于六自由度机械臂的任意曲面太赫兹成像方法
ES2942982R1 (es) * 2020-08-14 2023-06-08 Helmut Fischer Gmbh Inst Fuer Elektronik Und Messtechnik Metodo y dispositivo para procesar datos asociados con un modelo

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CN113424070A (zh) * 2019-07-19 2021-09-21 赫尔穆特费舍尔股份有限公司电子及测量技术研究所 包括至少一个THz设备的装置和操作这种装置的方法
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CN113030127A (zh) * 2019-12-09 2021-06-25 通用电气公司 评估涂层微结构的系统和方法
ES2942982R1 (es) * 2020-08-14 2023-06-08 Helmut Fischer Gmbh Inst Fuer Elektronik Und Messtechnik Metodo y dispositivo para procesar datos asociados con un modelo
CN113340843A (zh) * 2021-05-31 2021-09-03 苏州锐心观远太赫兹科技有限公司 基于太赫兹时域谱的无损检测方法及检测系统
CN115541529A (zh) * 2022-08-30 2022-12-30 青岛青源峰达太赫兹科技有限公司 基于六自由度机械臂的任意曲面太赫兹成像方法

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