CN201017131Y - An ultrashort pulse laser scanning device - Google Patents

Abstract

The utility model discloses an ultrashort pulse laser scanning device. It includes an acousto-optic modulator and a two-dimensional acousto-optic deflector on the same optical path. The two-dimensional acousto-optic deflector is composed of two acousto-optic deflectors placed orthogonally. 45±5 degrees. The modulation frequency of the acousto-optic modulator is f _AOM =f±10%f to the distance D=L±10%L of the two-dimensional acousto-optic deflector. When the acousto-optic deflector is used to scan the laser two-dimensionally, the device can better compensate for the spatial dispersion and time dispersion introduced when the acousto-optic deflector is used to scan the ultrashort pulse laser beam. The device has a simple structure and is easy to adjust the optical path, and is suitable for the fields of femtosecond laser storage, imaging and laser microprocessing, and is especially suitable for random scanning of laser beams.

Description

An ultrashort pulse laser scanning device

technical field

The utility model belongs to the technical field of laser scanning, in particular to an ultrashort pulse laser scanning device with dispersion compensation function based on a two-dimensional Acoustic-Optical Deflector (AOD), which is suitable for femtosecond laser storage, imaging and Laser micromachining and other fields.

Background technique

Using acousto-optic deflectors to scan laser light is a very promising laser scanning technology. It is especially suitable for the fields of femtosecond laser storage, imaging and laser microprocessing. However, when using an acousto-optic deflector to scan an ultrashort pulse laser, the laser beam will produce spatial dispersion and temporal dispersion, which will affect the excitation efficiency of multiphotons. Therefore, spatial and temporal dispersion must be compensated for when ultrashort pulses are scanned using an AOD.

At present, there have been many articles and patents on the compensation method. R.Salomé in "Ultra-fastrandom-access scanning in two-photon microscopy using acousto-optic deflectors" (J Neurosci Methods.2006 Jun 30; 154(1-2): 161-174) (two-photon based on acousto-optic deflectors Microscopy Ultrafast Random Scanning, "Journal of Neuroscience Methods", 2006, Vol. 154, pp. 161-174) uses an AOM placed obliquely at 45 degrees while compensating the spatial dispersion of the two-dimensional AOD. For temporal dispersion, another pair of prisms are used to compensate. Designing the optical path in this way appears to be more complicated. Chinese patent "a laser scanning device based on two-dimensional acousto-optic deflector" (patent application number: 200510019130.0). The patent mentioned that placing a prism obliquely at 45 degrees in the optical path at an appropriate distance in front of the two-dimensional acousto-optic deflector can simultaneously realize spatial dispersion compensation and temporal dispersion compensation for the two-dimensional acousto-optic deflector. The utility model device uses an acousto-optic modulator to replace the prism in the above-mentioned Chinese patent, and places it at an appropriate position in front of the two-dimensional acousto-optic deflector. It can also achieve better results. Compared with the former two, it has a simple optical path structure. Advantages such as avoiding precise adjustment of prism incidence angle.

Contents of the invention

The purpose of the utility model is to provide an ultrashort pulse laser scanning device, which can simultaneously and accurately compensate the spatial dispersion and time of the laser beam.

The utility model provides an ultrashort pulse laser scanning device, which is characterized in that the device includes an acousto-optic modulator and a two-dimensional acousto-optic deflector located on the same optical path, and the two-dimensional acousto-optic deflector is placed orthogonally It is composed of two acousto-optic deflectors, and the angle between one acousto-optic deflector and the acousto-optic modulator is 45±5 or 135±5 degrees.

The device of the utility model can simultaneously compensate the spatial dispersion and time dispersion introduced by the two-dimensional acousto-optic deflector, improve the focusing quality of the laser beam and the multi-photon excitation efficiency, the optical path is simple and easy to adjust, and the transmittance of the laser beam in the system is high. It is suitable for the fields of femtosecond laser storage, imaging and laser microprocessing, and is especially suitable for random scanning of laser beams, which is convenient for large-scale industrial application.

Description of drawings

FIG. 1 is a schematic diagram of a structure of a two-dimensional scanning device of the present invention.

Figure 2(a) is the left view of Figure 1, and Figures 2(b), 2(c), and 2(d) are different structures that can achieve the same function.

Figure 3 is the experimental optical path of the laser beam emitted by the laser, which is compensated for dispersion by the acousto-optic modulator, and then directly hits the light screen on the light screen through the two-dimensional acousto-optic deflector.

Fig. 4 is the experimental optical path of measuring the shape of the spot when the laser emitted by the laser passes through the two-dimensional acousto-optic deflector and directly hits the light screen.

Fig. 5(a) is the light spot after AOM compensation, (b) is the light spot without AOM compensation, and (c) the comparison diagram of the edge of the light spot under the former two structures. It can be seen from the comparison figure that the effect of spatial dispersion compensation is obvious.

Fig. 6 is a time half-width diagram of ultrashort pulse laser in different states. The pulsed laser with an initial pulse width of 120 femtoseconds is stretched to 572 femtoseconds after passing through two acousto-optic deflectors (as shown in Figure 4), and the pulse width is compressed back after being compensated by the acousto-optic modulator (as shown in Figure 3). to 128 femtoseconds.

Fig. 7 shows the transmission efficiency of the whole system at different frequency points of the two-dimensional acousto-optic deflector, and the transmission rate of the whole system is 50% to 70%.

FIG. 8 is a schematic structural diagram of an imaging system built with a compensated optical path.

FIG. 9 is a full-field scanning image of 170 nm fluorescent beads obtained by using the optical path shown in FIG. 8 to build a microscope for scanning.

Fig. 10 shows the measurement results of X, Y, and Z axis resolutions of the built microscope with 170 nanometer spheres as samples.

FIG. 11 is a schematic diagram of an equivalent structure of a pair of confocal lenses arranged behind the AOM 1 .

FIG. 12 is a schematic diagram of one structure in which the AOM 1 is placed laterally.

Detailed ways

Below in conjunction with accompanying drawing and example the utility model is described in further detail.

As shown in Figures 1 and 2(a), the device of the present invention includes an Acoustic-Optical Modulator (Acoustic-Optical Modulator, AOM) 1 and a two-dimensional AOM on the same optical path. It consists of two acousto-optic deflectors 2 and 3 placed alternately. The included angle between the acousto-optic deflectors 2 and 3 and the acousto-optic modulator 1 is 45±5 degrees or 135±5 degrees. The effect of dispersion compensation is better when the included angles between the AOM 1 and the AODs 2 and 3 are both 45 degrees or 135 degrees. When the acousto-optic debugger 1 uses positive first-order light diffraction, both acousto-optic deflectors 2 and 3 use negative first-order diffracted light; when acousto-optic modulator 1 uses negative first-order diffracted light, acousto-optic deflectors 2 and 3 Both use positive first-order diffracted light.

In addition to the above structure, the following three structures can achieve the same purpose, as shown in Figure 2(b), 2(c), and 2(d). When using the structure shown in Figure 2 (b), when the AOM 1 uses the positive first-order diffracted light, the AOD 2 uses the negative first-order diffracted light, and the AOD 3 uses the positive first-order diffracted light; when Acousto-optic modulator 1 uses negative first-order diffracted light, acousto-optic deflector 2 uses positive first-order diffracted light, and acousto-optic deflector 3 uses negative first-order diffracted light. When using the structure shown in Figure 2 (c), when the AOM 1 uses the positive first-order diffracted light, the AOD 2 uses the positive first-order diffracted light, and the AOD 3 uses the negative first-order diffracted light; when Acousto-optic modulator 1 uses negative first-order diffracted light, acousto-optic deflector 2 uses negative first-order diffracted light, and acousto-optic deflector 3 uses positive first-order diffracted light. When using the structure shown in Figure 2(d), when AOM 1 uses positive first-order diffracted light, AOD 2 and 3 both use positive first-order diffracted light; when AOM 1 uses negative first-order diffracted light For diffracted light, AOD 2 and 3 both use negative first-order diffracted light. When building the optical path, you can choose a suitable solution according to the actual situation.

The modulation frequency of the acousto-optic modulator 1 is f _AOM , f _AOM =f±10%f, which can compensate the spatial dispersion of the two-dimensional acousto-optic deflector. The larger f _AOM is, the larger the spatial compensation amount is, and the spatial compensation effect is optimal when the modulation frequency f _AOM =f. f satisfies the requirements of formula I:

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; AOD</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; )</span>$

Among them, f _AOD is the center frequency when a single acousto-optic deflector works.

Assuming that the distance between the AOM 1 and the two-dimensional AOD is D, D=L±10%L. Adjusting the distance D between the acousto-optic modulator 1 and the two-dimensional acousto-optic deflector can adjust the compensation amount of time dispersion, and the two are proportional. When the distance between the AOM 1 and the two-dimensional AOD is larger than L, negative time dispersion will be introduced, and when the distance D is L, the time dispersion will be fully compensated. L satisfies the requirements of formula II,

$\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="GDD\; m"\; filenames="Y20062016334900091.png,Y20062016334900101.png"\; state="\{\{state\}\}">GDD</figure-callout></span><figure-callout\; id="2"\; label="GDD\; m"\; filenames="Y20062016334900091.png,Y20062016334900101.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}\frac{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;<figure-callout\; id="2"\; label="c"\; filenames="Y20062016334900091.png,Y20062016334900101.png"\; state="\{\{state\}\}">c</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; v</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; AOD</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; II</span>}<span\; class="notranslate">\; )</span>$

Among them, GDD _M is the group delay dispersion introduced by all materials in the optical path, f _AOD is the center frequency of the AOD, λ is the wavelength of the incident laser light wave, c is the speed of light, and v is the acousto-optic wave of the ultrasonic wave in the AOM The velocity of propagation in a crystal.

When the two-dimensional acousto-optic deflector is used to scan the ultrashort pulse laser, the device can accurately compensate the spatial dispersion and time dispersion introduced when the acousto-optic deflector is used to scan the ultrashort pulse laser. The maximum transmission efficiency is 10% higher than the method using prism compensation.

Example 1

Build the test light path as shown in Figure 3. Laser 4 incident laser light (center wavelength 800 nanometers, bandwidth 10 nanometers, initial pulse width 120 femtoseconds) passes through the acousto-optic modulator 1 placed obliquely at 45 degrees, and exits with negative first-order diffracted light. The modulation frequency of the acousto-optic modulator 1 135.7MHz. Since the AOD used in this experiment is sensitive to the polarization state of the incident light, a 1/2 wave plate 5 is arranged between the AOM 1 and the two-dimensional AOD. The laser beam passes through the 1/2 wave plate 5 and then goes to the two-dimensional acousto-optic deflector with a central operating frequency of 96MHz. The two-dimensional acousto-optic deflectors all use positive first-order diffracted light, and the outgoing light hits the light screen 6, and the light spot on the light screen is captured by the CCD7 to obtain the result shown in Figure 5(a). The laser beam is not compensated and directly hits the light screen 6 through the two-dimensional acousto-optic deflector (as shown in Figure 4). The light spot obtained by shooting is shown in Figure 5(b). c) can be seen.

The distance D between the acousto-optic modulator 1 and the two-dimensional acousto-optic deflectors 2 and 3 is 58 cm. Fine-tuning D makes the time width of the laser pulse return to 128 femtoseconds after passing through the compensation system. However, the pulse width of the original laser is measured to be 572 femtoseconds after the pulse of the original laser passes directly through the two powered acousto-optic deflectors. The comparison of the time compensation effect can be seen from Figure 6.

The transmission efficiency of the laser beam is measured when the acousto-optic deflector works at different frequency points for the device of the present invention, and the experimental results shown in FIG. 7 are obtained. The transmittance of the whole system is between 50% and 70%.

Example 2

The laser beam after space and time compensation is guided into the microscope objective lens 8 (a 60 times oil lens is used in the experiment, NA=1.24), and the optical path is shown in FIG. 8 . The dichroic mirror 9 is used to reflect the excitation light and transmit the signal light, and the PMT 10 is used for signal detection. Scan the 170nm fluorescent bead sample 11 to get the experimental picture as shown in Fig. 9, and analyze the X and Y axis resolutions, which are measured to be 374 and 385 nanometers respectively, as shown in Fig. 10(a) and 10(b). Using PZT for Z-axis resolution measurement, the minimum Z-axis resolution is 1.1 microns, as shown in Figure 10(c).

For the AOM 1, its modulation frequency is often higher (for example, to compensate the dispersion of a two-dimensional AOD with a center operating frequency of 96 MHz, the modulation frequency of the AOM 1 needs to be loaded to 135.74 MHz). For near-infrared or infrared lasers, there are some technical difficulties in making an acousto-optic modulator with a higher modulation frequency. We can choose an acousto-optic modulator 1 with a lower modulation frequency and a set of confocal lenses (12, 13) to achieve the same compensation effect. The specific implementation method is shown in FIG. 11 , along the direction of the optical path, confocal first and second lenses 12 and 13 are sequentially arranged between the AOM 1 and the two-dimensional AOD. The focal length of the first lens 12 is f1, the focal length of the second lens 13 is f2, the AOM 1 is located at the front focal point F1 of the first lens 12, the frequency of the AOM 1 is f _AOM ', and f _AOM ' satisfies formula III Require.

f _AOM '=f2/f1 f _AOM (III)

The two-dimensional AOD is located at a distance D from the back focus F ₂ ′ of the second lens 13 . The diffracted light order used by the acousto-optic modulator is opposite to the diffracted light order when the bus lens group is not used. This equivalent optical path structure can realize the use of an acousto-optic modulator with a lower modulation frequency to compensate the dispersion of the two-dimensional acousto-optic deflector, and achieve the same compensation effect. This makes the specific implementation of the device easier.

The acousto-optic modulator 1 is usually placed at an angle of 45 degrees to the horizontal plane (as shown in Figures 1 and 2(a)). Since the incident light and the diffracted light of the AOM may not be coaxial, the height of the light beam in the above structure may change after exiting the AOM 1 , which is inconvenient for system design and integrated packaging. If the acousto-optic modulator 1 is placed horizontally (as shown in Figure 12), the two-dimensional acousto-optic deflector at the back forms an angle of 45 ± 5 degrees with the horizontal plane. At this time, the height of the beam in the optical path remains unchanged, which will facilitate the adjustment of the optical path. build.

Claims (7)

1. An ultrashort pulse laser scanning device, its characterized in that: the device comprises an acousto-optic modulator (1) and a two-dimensional acousto-optic deflector which are positioned on the same optical path, wherein the two-dimensional acousto-optic deflector is composed of two acousto-optic deflectors (2 and 3) which are orthogonally arranged, and the included angle between one acousto-optic deflector and the acousto-optic modulator (1) is 45 +/-5 degrees or 135 +/-5 degrees.

2. An ultrashort pulse laser scanning device according to claim 1, wherein: the included angle between one acousto-optic deflector and the acousto-optic modulator (1) is 45 degrees or 135 degrees.

3. Ultrashort pulsed laser scanning device according to claim 1 or 2, characterized in that: the acousto-optic modulator (1) is arranged in the horizontal direction, and the two-dimensional acousto-optic deflector forms an included angle of 45 +/-5 degrees with the horizontal plane.

4. An ultrashort pulse laser scanning device according to claim 1 or 2, wherein: when the two acousto-optic deflectors (2, 3) are the same,

frequency f of the acousto-optic modulator (1) _AOM = f ± 10%:

in the formula (I) f _AOD The center frequency of the single acousto-optic deflector during operation;

an interval D, D = L + -10% L of the acousto-optic modulator (1) to the two-dimensional acousto-optic deflector, wherein L satisfies the requirement of formula (II),

GDD in formula (II) _M Group delay dispersion introduced by all materials in the optical path, wherein lambda is the wavelength of an incident laser light wave, c is the light speed, and v is the propagation speed of the ultrasonic wave in the crystal of the acousto-optic modulator (1).

5. An ultrashort pulse laser scanning device according to claim 3, wherein: when the two acousto-optic deflectors (2, 3) are the same,

frequency f of the acousto-optic modulator (1) _AOM = f ± 10%:

in the formula (I) f _AOD The center frequency of the single acousto-optic deflector during operation;

an interval D, D = L + -10% L of the acousto-optic modulator (1) to the two-dimensional acousto-optic deflector, wherein L satisfies the requirement of formula (II),

GDD in formula (II) _M Group delay dispersion introduced by all materials in the optical path, wherein lambda is the wavelength of an incident laser light wave, c is the light speed, and v is the propagation speed of the ultrasonic wave in the crystal of the acousto-optic modulator (1).

6. Ultrashort pulsed laser scanning device according to claim 4, wherein: confocal first and second lenses (12, 13) are sequentially arranged between the acousto-optic modulator (1) and the two-dimensional acousto-optic deflector along the optical path direction; the focal length of the first lens (12) is F1, the focal length of the second lens (13) is F2, and the acousto-optic modulator (1) is positioned at the front focal point F of the first lens (12) ₁ Where the frequency of the acousto-optic modulator (1) is f _AOM ’，f _AOM ' satisfies the requirement of formula III:

f _AOM ′＝f2/f1f _AOM (III)

the two-dimensional acousto-optic deflector is located at a distance D from the back focal point F2' of the second lens (13).

7. An ultrashort pulse laser scanning device according to claim 5, wherein: confocal first and second lenses (12, 13) are sequentially arranged between the acousto-optic modulator (1) and the two-dimensional acousto-optic deflector along the optical path direction; the focal length of the first lens (12) is F1, the focal length of the second lens (13) is F2, and the acousto-optic modulator (1) is positioned at the front focal point F of the first lens (12) ₁ Where the frequency of the acousto-optic modulator (1) is f _AOM ’，f _AOM ' satisfies the requirement of formula III:

f _AOM ′＝f2/f1f _AOM (III)

the two-dimensional acousto-optic deflector is located at a distance D from the back focus F2' of the second lens (13).

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