Femtosecond laser sum frequency spectrum detection device based on dispersion and bandwidth compression

Abstract

The invention discloses a femtosecond laser sum frequency spectrum detection device based on dispersion and bandwidth compression, which is characterized in that femtosecond infrared laser generated by a laser is split into first split light and second split light, and the first split light is converted into femtosecond mid-infrared light; the second beam splitting light is converted into picosecond green light, the picosecond green light passes through a first diaphragm and then is focused to one point of a y-cut quartz crystal together with wavelength-tunable femtosecond mid-infrared light generated by the frequency doubling / difference frequency module through a stroke adjusting reflection unit, and the y-cut quartz crystal generates an intrinsic sum frequency signal; after passing through the quartz glass sheet, the intrinsic sum frequency signal, picosecond green light and femtosecond mid-infrared light emitted by the y-cut quartz crystal are jointly focused on one point on the surface of a sample to be detected, a sample sum frequency signal is generated, and the intrinsic sum frequency signal and the sample sum frequency signal are collinearly transmitted into a spectrograph. According to the method, a simple and direct spectral bandwidth compression method is adopted, the complexity is remarkably reduced, the spectral bandwidth of green light is compressed, and the sum frequency spectrum is detected.

Description

Technical Field

[0001] The invention relates to the technical field of sum frequency spectrum detection, and in particular to a femtosecond laser sum frequency spectrum detection device based on dispersion and bandwidth compression. Background Art

[0002] As an advanced second-order nonlinear spectroscopy technique, sum frequency vibration spectroscopy has rapidly emerged in recent decades. The outstanding features of this characterization technique are its selectivity and sensitivity to the surface interface and the direction of molecular groups, and it is not restricted by harsh environmental conditions during operation. The main principle of sum frequency vibration spectroscopy is to focus infrared light and visible light on the surface interface at the same time. Since the symmetry of the material at the interface is destroyed, a sum frequency signal is generated, and the frequency of the signal is the sum of the frequencies of infrared light and visible light. First, after the molecule absorbs infrared light, the vibration energy level transitions to the excited state, and then absorbs visible light to transition to the virtual state. Finally, the photon emitted when it returns to the ground state is the sum frequency signal. A significant advantage of sum frequency vibration spectroscopy is that it has surface selectivity, which mainly depends on the second-order nonlinear polarizability, which is a tensor with 27 components. In the experiment, different components can be measured using different polarized light combinations. By transforming the coordinates of the components and solving equations, the second-order nonlinear polarizability can be converted into the Euler orientation angle by using the Gaussian distribution function, thereby obtaining information such as the structure and orientation of the molecular groups on the interface.

[0003] Sum frequency generation refers to the frequency ω 1 and ω 2 The two photons and the wave vector k 1 and k 2 propagate together in a nonlinear medium, generating a photon whose combined frequency sums to ω 3 =ω 1 +ω 2 ; In a special case, photons of different energies are symmetrical about a central frequency ω with a magnitude of ±Δω FF , at a constant second harmonic frequency ω SH The signal photon is generated by combining the spectral components ω+Δω and ω-Δω of the pulse in the frequency domain. Our method takes advantage of this phenomenon. The spectral components ω+Δω and ω-Δω of the pulse are mixed together in the frequency domain, producing a compressed spectral bandwidth at the second harmonic. The method of generating spatially chirped pulses is to use a simple mirror image after the pulse is dispersed, which naturally produces two pulses with completely opposite chirp symmetry. The signal bandwidth Δλ SH It is proportional to the spectral bandwidth of each frequency component in the Fourier plane and can be easily derived from the geometric configuration of the system.

[0004] In laser sum-frequency spectroscopy, in order to obtain higher spectral resolution, it is usually necessary to compress the bandwidth of broadband femtosecond laser pulses and convert them into strong narrowband picosecond laser pulses. Existing spectral compression methods usually use time-domain nonlinear bandwidth compression technology. Although it successfully solves the conversion efficiency problem, it usually requires more complex system design, precise tuning, optimization and characterization, and expensive optical components in experiments. Summary of the invention

[0005] The purpose of the present invention is to address the above-mentioned problems existing in the prior art and to provide a femtosecond laser and frequency spectrum detection method based on dispersion and bandwidth compression, which reduces the complexity of the system, significantly compresses the spectral bandwidth of the green laser pulse and realizes interference and frequency spectrum detection.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A femtosecond laser and spectrum detection device based on dispersion and bandwidth compression comprises a laser, wherein the femtosecond infrared laser generated by the laser is divided into a first split light and a second split light by a first beam splitter, the first split light sequentially passes through an optical parametric amplifier and a frequency doubling / difference frequency module to generate a wavelength-tunable femtosecond mid-infrared light; the second split light passes through a dispersion unit and a second beam splitter to be divided into two beams, a fourth plane reflector and a fifth plane reflector respectively reflect the two beams split by the second beam splitter and then pass through a second plano-convex lens in parallel, and the lens of the second plano-convex lens is The BBO crystal arranged at the focus generates picosecond green light with compressed spectral bandwidth. After passing through the first aperture, the picosecond green light is focused to a point of the y-cut quartz crystal simultaneously through the stroke adjustment reflection unit and the wavelength tunable femtosecond mid-infrared light generated by the aforementioned frequency doubling / difference frequency module. The y-cut quartz crystal generates an intrinsic sum frequency signal. After passing through the quartz glass sheet, the intrinsic sum frequency signal is focused together with the picosecond green light and femtosecond mid-infrared light emitted by the y-cut quartz crystal at a point on the surface of the sample to be measured to generate a sample sum frequency signal. The intrinsic sum frequency signal and the sample sum frequency signal are colinearly transmitted into the spectrometer.

[0008] As described above, the fifth plane reflector is arranged on the manual precision translation stage, and the manual precision translation stage adjusts the spatial overlap and time delay of the light reflected by the fourth plane reflector and the light reflected by the fifth plane reflector at the BBO crystal by adjusting the distance between the fifth plane reflector and the second plano-convex lens.

[0009] As described above, the dispersion unit includes a second plane reflector, a first plano-convex lens, an equilateral dispersion prism, and a third plane reflector. The second split light beam is reflected by the second plane reflector, focused by the first plano-convex lens, and then incident on the equilateral dispersion prism. The outgoing light of the equilateral dispersion prism is reflected by the third plane reflector, and then split into two beams by the second beam splitter.

[0010] As described above, the stroke adjustment reflection unit includes a sixth plane reflector, a stepper motor translation unit, a seventh plane reflector, a third plano-convex lens, an eighth plane reflector, a ninth plane reflector, and a tenth plane reflector. The picosecond green light output by the first aperture is reflected by the sixth plane reflector to the first adjustment reflector. The reflected light of the first adjustment reflector is incident on the second adjustment reflector. The reflected light of the second adjustment reflector is incident on the seventh plane reflector. The stepper motor translation unit is used to adjust the distance between the first adjustment reflector and the second adjustment reflector and the sixth plane reflector and the seventh plane reflector. The reflected light of the seventh plane reflector passes through the third plano-convex lens, and then is reflected by the eighth plane reflector and the ninth plane reflector in sequence to enter the Y-cut quartz crystal.

[0011] As described above, the femtosecond mid-infrared light emitted by the frequency doubling / difference frequency module is reflected by the first plane reflector and the tenth plane reflector in sequence, and then enters the Y-cut quartz crystal non-collinearly with the picosecond green light and at the same incident point.

[0012] As mentioned above, the sample to be tested and the gold mirror are placed on the moving part of the stepper motor height translation stage, and the fixed part of the stepper motor height translation stage is arranged on the moving part of the stepper motor horizontal translation stage. The stepper motor horizontal translation stage is used to adjust the horizontal position of the sample to be tested and the gold mirror.

[0013] As mentioned above, the picosecond green light, femtosecond mid-infrared light, intrinsic sum frequency signal and sample sum frequency signal are reflected by the second concave reflector, then reflected by the twelfth plane reflector, and finally filtered by the second aperture for filtering the non-sum frequency signal light and excess stray light, and then the intrinsic sum frequency signal light and sample sum frequency signal light are incident on the spectrometer.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The present invention utilizes a small number of optical elements and realizes bandwidth compression of green femtosecond laser pulses based on the principle of dispersion and frequency, thereby reducing the complexity of the system and the difficulty of tuning optimization. In addition, interference and frequency spectrum detection is successfully realized by utilizing the bandwidth-compressed green laser pulses and another infrared laser pulse. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the optical path structure diagram of the present invention;

[0017] Figure 2 This is a comparison of picosecond green light spectra before and after bandwidth compression; the horizontal axis represents the wavelength range; the vertical axis represents the normalized spectrum intensity;

[0018] Figure 3It is the interference sum frequency spectrum obtained by superimposing the intrinsic sum frequency signal light in the infrared frequency range of 2700-3100cm-1 and the sample sum frequency signal light generated by the standard sample gold film in the spectrometer CCD. The horizontal axis represents the frequency range of the infrared laser pulse; the vertical axis represents the intensity of the detected interference sum frequency signal.

[0019] Among them: 1-laser; 2-first beam splitter; 3-optical parametric amplifier; 4-frequency doubling / difference frequency module; 5-first plane reflector; 6-second plane reflector; 7-first plano-convex lens; 8-equilateral dispersion prism; 9-third plane reflector; 10-second beam splitter; 11-fourth plane reflector; 12-fifth plane reflector; 13-manual precision translation stage; 14-second plano-convex lens; 15-BBO crystal; 16-first aperture; 17-sixth plane reflector; 18-stepping motor translation unit; 19-seventh plane Reflector; 20-third plano-convex lens; 21-eighth plane reflector; 22-ninth plane reflector; 23-tenth plane reflector; 24-Y-cut quartz crystal; 25-eleventh plane reflector; 26-quartz glass plate; 27-first concave reflector; 28-sample to be tested; 29-gold mirror; 30-stepping motor height translation stage; 31-stepping motor horizontal translation stage; 32-second concave reflector; 33-twelfth plane reflector; 34-second aperture; 35-fourth plano-convex lens; 36-filter; 37-spectrometer. DETAILED DESCRIPTION

[0020] In order to facilitate those skilled in the art to understand and implement the present invention, the present invention is further described in detail below in conjunction with implementation examples. It should be understood that the implementation examples described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0021] A femtosecond laser and spectrum detection device based on dispersion and bandwidth compression, the main detection steps are as follows: the femtosecond infrared laser generated by the laser 1 is divided into two beams by a first beam splitter 2, the first split light after the first beam splitter 2 is sequentially passed through an optical parametric amplifier 3 and a frequency doubling / difference frequency module 4 to generate wavelength-tunable femtosecond mid-infrared light with a wavelength range of 2500-4000nm; the second split light after the first beam splitter 2 is split through a dispersion unit and a second beam splitter 10 and then split into two beams, a fourth plane reflector 11 and a fifth plane reflector 12 respectively reflect the two beams after the second beam splitter 10 and then pass through a focusing second plano-convex lens 1 in parallel. 4. A BBO crystal 15 is placed at the lens focus of the second plano-convex lens 14. The frequency domain nonlinear optical phenomenon is used to make the two beams of light produce a sum frequency effect at the BBO crystal, thereby generating picosecond green light with a compressed spectral bandwidth. The spatial overlap and time delay of the light reflected by the fourth plane reflector 11 and the light reflected by the fifth plane reflector 12 are adjusted by the manual precision translation stage 13 under the fifth plane reflector 12. The manual precision translation stage 13 adjusts the spatial overlap and time delay of the light reflected by the fourth plane reflector 11 and the light reflected by the fifth plane reflector 12 at the BBO crystal 15 by adjusting the distance between the fifth plane reflector 12 and the second plano-convex lens 14. The first aperture 16 is used to filter non-sum frequency signal light and redundant stray light; the obtained bandwidth-compressed picosecond green light is focused to a point of the y-cut quartz crystal 24 through the stroke adjustment reflection unit and the wavelength-tunable femtosecond mid-infrared light generated by the aforementioned frequency doubling / difference frequency module 4, and the y-cut quartz crystal 24 generates an intrinsic sum frequency signal, and the intrinsic sum frequency signal passes through the quartz glass sheet 26 (generating a phase difference) and is focused together with the picosecond green light and femtosecond mid-infrared light emitted by the y-cut quartz crystal 24 on a point on the surface of the sample to be tested 28, generating a sample sum frequency signal, and finally the intrinsic sum frequency signal and the sample sum frequency signal are co-linearly transmitted to the spectrometer CCD and recorded by a high-speed CCD camera. The present invention overcomes the disadvantages of expensive optical components and complex systems in traditional time-domain bandwidth compression technology, adopts a simpler and more direct spectral bandwidth compression method, significantly reduces the complexity of the system, compresses the spectral bandwidth of the green laser pulse, and realizes the detection of phase interference sum frequency spectrum.

[0022] In some embodiments, the dispersion unit includes a second plane mirror 6, a first plano-convex lens 7, an equilateral dispersion prism 8, and a third plane mirror 9. The second split light after being split by the first beam splitter 2 is reflected by the second plane mirror 6, and then is focused by the first plano-convex lens 7 and incident on the equilateral dispersion prism 8. The outgoing light of the equilateral dispersion prism 8 is reflected by the third plane mirror 9, and then is split into two beams by the second beam splitter 10.

[0023] In some embodiments, the stroke adjustment reflection unit includes a sixth plane reflector 17, a stepper motor translation unit 18, a seventh plane reflector 19, a third plano-convex lens 20, an eighth plane reflector 21, a ninth plane reflector 22, and a tenth plane reflector 23. The first adjustment reflector and the second adjustment reflector are arranged on the stepper motor translation unit 18. The picosecond green light after bandwidth compression is reflected to the first adjustment reflector by the sixth plane reflector 17. The reflected light of the first adjustment reflector is incident on the second adjustment reflector. The reflected light of the second adjustment reflector is incident on the seventh plane reflector 19. The stepper motor translation unit 18 is used to adjust the distance between the first adjustment reflector and the second adjustment reflector and the sixth plane reflector 17 and the seventh plane reflector 19, thereby adjusting the stroke length of the picosecond green light after bandwidth compression. The reflected light of the seventh plane reflector 19 passes through the third plano-convex lens 20, and then is reflected by the eighth plane reflector 21 and the ninth plane reflector 22 in sequence to enter the Y-cut quartz crystal 24.

[0024] In some embodiments, the femtosecond mid-infrared light emitted by the frequency doubling / difference frequency module 4 is reflected by the first plane reflector 5 and the tenth plane reflector 23 in sequence, and then enters the Y-cut quartz crystal 24 non-collinearly with the picosecond green light and at the same incident point.

[0025] In some embodiments, the intrinsic sum frequency signal light, picosecond green light, and femtosecond mid-infrared light emitted by the Y-cut quartz crystal 24 are reflected by the eleventh plane reflector 25, and the intrinsic sum frequency signal light is reflected by the eleventh plane reflector 25 and then passes through the quartz glass plate 26. The intrinsic sum frequency signal light passing through the quartz glass plate 26, and the picosecond green light and femtosecond mid-infrared light reflected by the eleventh plane reflector 25 are all focused and reflected by the concave reflector 27 onto the sample to be tested 28 or the gold mirror 29.

[0026] In some embodiments, the sample 28 to be tested and the gold mirror 29 are placed on the moving part of the stepper motor height translation stage 30, and the fixed part of the stepper motor height translation stage 30 is set on the moving part of the stepper motor horizontal translation stage 31. The stepper motor horizontal translation stage 31 is used to adjust the horizontal position of the sample 28 to be tested and the gold mirror 29, so that the focal point of the reflected light of the concave reflector 27 is on the sample 28 to be tested or the gold mirror 29, and the stepper motor height translation stage 30 is used to adjust the height of the sample 28 to be tested and the gold mirror 29, so that the sample 28 to be tested or the gold mirror 29 is located at the focal point of the reflected light of the concave reflector 27.

[0027] In some embodiments, the picosecond green light, femtosecond mid-infrared light, intrinsic sum frequency signal and sample sum frequency signal reflected by the sample to be tested 28 and the gold mirror 29 are reflected by the second concave reflector 32, then reflected by the twelfth plane reflector 33, and finally filtered by the second aperture 34 for filtering non-sum frequency signal light and excess stray light, and then the intrinsic sum frequency signal light and the sample sum frequency signal light are incident on the spectrometer CCD37.

[0028] In this embodiment:

[0029] Laser 1 is used to generate stable infrared femtosecond laser pulses. It adopts an infrared femtosecond laser with a laser output power of 40W, an emission wavelength of 1030nm, and a pulse width of 200-10000fs.

[0030] The beam splitter 2 is used to split the laser pulse output by the laser 1 into two parts.

[0031] The optical parametric amplifier 3 and the frequency doubling / difference frequency module 4 are both commercial modules, wherein the optical parametric amplifier 3 is a two-stage optical parametric amplifier based on white light supercontinuum generation, and its wavelength tuning can be achieved by controlling the rotation or translation of key optical elements, and a part of the infrared femtosecond laser pulses separated by the beam splitter 2 can be converted into wavelength-tunable femtosecond mid-infrared light; and the wavelength tuning of the frequency doubling / difference frequency module 4 is also achieved by controlling the rotation or translation of key optical elements, and the wavelength can be extended to 4.0um.

[0032] A first plane reflector 5 and a second plane reflector 6 are used to transform the light path;

[0033] A first plano-convex lens 7, used for focusing the light beam;

[0034] The equilateral dispersion prism 8 is used to disperse the laser pulse. The prism size is 20 mm, the material is H-ZF13 (CDGM), the application band is 420 nm to 2.3 um, and the minimum deviation angle is 65.5°.

[0035] The third plane reflector 9 is used to change the optical path; the second beam splitter 10 is used to split the dispersed laser output by the dispersion prism 8 into two parts; the fourth plane reflector 11 and the fifth plane reflector 12 are used to direct the two parts of laser light split by the second beam splitter 10 into the second plano-convex lens 14 in parallel; during the specific operation, it is necessary to carefully adjust the relative positions of the rotating dispersion prism 8, the second beam splitter 10, the plane reflector 11, and the plane reflector 12 to ensure that the two beams of light reflected by the fourth plane reflector 11 and the fifth plane reflector 12 are parallel to each other and the distance between them is less than 50 mm, and in addition, it is necessary to ensure that the distance from the second beam splitter 10 to the fourth plane reflector 11 and the fifth plane reflector 12 is as equal as possible.

[0036] The second plano-convex lens 14, with a size of 50 mm, is used to focus the two parts of light into the BBO crystal 15 to produce a sum frequency effect, thereby generating a new sum frequency green laser pulse (picosecond green light). The BBO crystal 15 used in this embodiment has a size of 5×5×2 mm (length×width×thickness), a cutting angle of θ=22.8°, and a light aperture of>90%. By fine-tuning the front and rear positions of the manual precision translation stage 13 installed under the plane reflector 12, the optical path difference between the two beams of light after being reflected by the fourth plane reflector 11 and the fifth plane reflector 12 is adjusted. The two parts of chirped pulses formed at the BBO crystal 15 are equal in time and symmetrically opposite in space. In specific operation, a laser power meter needs to be placed directly behind the BBO crystal 15. By carefully adjusting the relative positions of the rotating dispersion prism 8, the second beam splitter 10, the fourth plane reflector 11, and the fifth plane reflector 12 and the front and rear positions of the manual precision translation stage 13, the two parts of light focused on the BBO crystal 15 can be optimally superimposed in space and time, thereby maximizing the power of the new green laser pulse generated by the sum frequency effect.

[0037] The first aperture 16 and the second aperture 34 are used to filter out the transmitted non-sum frequency signal light and redundant stray light.

[0038] The sixth plane reflector 17 and the seventh plane reflector 19 are used to transform the light path.

[0039] The stepper motor translation unit 18 is used to transform the optical path and change the optical path of the picosecond green light by translation, so that the femtosecond mid-infrared light reaching the detection sample is consistent with the optical path of the picosecond green light. The total stroke of the stepper motor translation unit is 300 mm.

[0040] The third plano-convex lens 20 is used for focusing the light beam; the eighth plane reflector 21, the ninth plane reflector 22 and the tenth plane reflector 23 are used for changing the light path.

[0041] Y-cut quartz crystal 24, used to generate intrinsic sum frequency signal;

[0042] The eleventh plane reflector 25 is used to reflect the intrinsic sum frequency signal, femtosecond mid-infrared light and picosecond green light transmitted from the Y-cut quartz crystal 24 .

[0043] The quartz glass sheet 26 is used to delay the intrinsic sum frequency signal generated by the Y-cut quartz crystal 24 in time, and has a size of 10×5×2 mm (length×width×thickness).

[0044] The concave reflector 27 has a focal length of F=300 mm and is used to refocus the intrinsic sum frequency signal, femtosecond mid-infrared light and picosecond green light reflected by the eleventh plane reflector 25 onto the surface of the sample to be tested 28 to generate the sum frequency signal of the sample; the gold mirror 29 is used as a standard sample for comparison and reference.

[0045] The stepper motor height translation stage 30 is used to adjust the sample height and optimize the signal; the stepper motor horizontal translation stage 31 is used to translate and switch the horizontal positions of the sample 28 to be tested and the gold mirror 29. The above motors also adopt OSMS standard stepper motors;

[0046] The concave reflector 32 has a focal length of F=150 mm and is used to transform the signal light path and perform collimation.

[0047] The twelfth plane reflector 33 is used to change the light path and guide the signal into the spectrometer CCD37 for detection. The focal length of the spectrometer is 750 mm, the resolution of the spectrometer is 0.02 nm, and the CCD adopts a 1600×400 pixel array.

[0048] The second aperture 34 is used to filter non-sum frequency signal light and redundant stray light.

[0049] The fourth plano-convex lens 35 is used to focus the light beam.

[0050] The filter 36 is used to filter out non-sum frequency signal light and redundant stray light.

[0051] The stepper motor control unit 38 is used for motor control of the stepper motor translation unit 18, the stepper motor height translation stage 30, and the stepper motor horizontal translation stage 31 and for communicating with the computer 39, and adopts a HIT type expandable stepper motor controller.

[0052] Computer 39 is used to communicate with laser 1 to change laser parameters. It is used to communicate with optical parametric amplifier 3 to change the wavelength of infrared light. It is used to communicate with spectrometer CCD37 to receive, process and display the detected spectrum. It is used to communicate with stepper motor control unit 38 to realize program automatic control of the entire detection system.

[0053] In this embodiment, the picosecond green light with compressed bandwidth and another path of femtosecond mid-infrared light are non-collinearly focused and transmitted through the Y-cut quartz crystal 24 to generate an intrinsic sum frequency signal, the frequency of which is the sum of the frequencies of the femtosecond mid-infrared light and the picosecond green light; the transmitted femtosecond mid-infrared light, the intrinsic sum frequency signal light, and the picosecond green light are refocused onto the surface of the sample to be tested by using a plane reflector and a concave reflector to generate a sum frequency signal of the sample to be tested, the frequency of which is the sum of the frequencies of the femtosecond mid-infrared light and the picosecond green light; the optical path difference between the picosecond green light and the femtosecond mid-infrared light is adjusted by adjusting the stepper motor translation unit 18, so that the picosecond green light and the femtosecond mid-infrared light overlap in space and in time when they reach the surface of the Y-cut quartz crystal 24 and the surface of the sample to be tested 28.

[0054] A quartz glass plate 26 is placed in the optical path before the intrinsic sum frequency signal light reaches the surface of the sample to be measured, so that the intrinsic sum frequency signal and the signal of the sample to be measured are delayed in time and interference fringes are generated at the detection point. Note that the quartz glass plate 26 cannot affect the picosecond green light and the femtosecond mid-infrared light. Finally, the twelfth plane reflector 33, the second concave reflector 32 (focusing lens), the second aperture 34, etc. are used to transmit the intrinsic sum frequency signal light and the sample sum frequency signal light of the sample to be measured into the spectrometer CCD in a colinear manner for recording.

[0055] Figure 2 The picosecond green light spectrum using the bandwidth compression method in this embodiment and the picosecond green light spectrum without bandwidth compression but only using BBO crystal for frequency doubling are given. After comparison, the picosecond green light bandwidth before compression is about 2.1nm, and the picosecond green light bandwidth after compression is about 0.8nm. It can be seen that the picosecond green light spectrum bandwidth has been significantly compressed.

[0056] Figure 3 The 2700-3100cm -1 The interference sum frequency spectrum of the intrinsic sum frequency signal light in the infrared frequency range and the sample sum frequency signal light generated by the standard sample gold film is superimposed and recorded in the CCD of the spectrometer. It can be seen that obvious sum frequency signal interference fringes appear on the spectrum.

[0057] In summary, the present invention overcomes the shortcomings of traditional time-domain bandwidth compression technology, such as expensive optical components and complex systems, and adopts a simpler and more direct spectral bandwidth compression method, which significantly reduces the complexity of the system and realizes the detection of interference and frequency spectra.

[0058] It should be noted that the embodiments described in the present invention are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the described embodiments or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the attached claims.

Claims

1. A femtosecond laser and spectrum detection device based on dispersion and bandwidth compression, comprising a laser (1), characterized in that: The femtosecond infrared laser generated by the laser (1) is divided into a first split light and a second split light by a first beam splitter (2); the first split light passes through an optical parametric amplifier (3) and a frequency doubling / difference frequency module (4) in sequence to generate wavelength-tunable femtosecond mid-infrared light; the second split light passes through a dispersion unit and a second beam splitter (10) to be divided into two beams; a fourth plane reflector (11) and a fifth plane reflector (12) respectively reflect the two beams split by the second beam splitter (10) and pass them through a second plano-convex lens (14) in parallel; a BBO crystal (11) arranged at the lens focus of the second plano-convex lens (14) 5) generating picosecond green light with compressed spectral bandwidth, the picosecond green light passes through the first aperture (16), and then is focused to a point of the y-cut quartz crystal (24) by the stroke adjustment reflection unit and the wavelength tunable femtosecond mid-infrared light generated by the aforementioned frequency doubling / difference frequency module (4), the y-cut quartz crystal (24) generates an intrinsic sum frequency signal, the intrinsic sum frequency signal passes through the quartz glass sheet (26), and is focused together with the picosecond green light and femtosecond mid-infrared light emitted by the y-cut quartz crystal (24) at a point on the surface of the sample to be measured (28), generating a sample sum frequency signal, and the intrinsic sum frequency signal and the sample sum frequency signal are co-linearly transmitted to the spectrometer.

2. A femtosecond laser and spectrum detection device based on dispersion and bandwidth compression according to claim 1, characterized in that: The fifth plane reflector (12) is arranged on a manual precision translation stage (13), and the manual precision translation stage (13) adjusts the spatial overlap and time delay of the light reflected by the fourth plane reflector (11) and the light reflected by the fifth plane reflector (12) at the BBO crystal (15) by adjusting the distance between the fifth plane reflector (12) and the second plano-convex lens (14).

3. A femtosecond laser and spectrum detection device based on dispersion and bandwidth compression according to claim 1, characterized in that: The dispersion unit comprises a second plane reflecting mirror (6), a first plano-convex lens (7), an equilateral dispersion prism (8), and a third plane reflecting mirror (9); the second split light beam is reflected by the second plane reflecting mirror (6), focused by the first plano-convex lens (7), and then incident on the equilateral dispersion prism (8); the outgoing light of the equilateral dispersion prism (8) is reflected by the third plane reflecting mirror (9), and then split into two light beams by the second beam splitter (10).

4. The femtosecond laser and spectrum detection device based on dispersion and bandwidth compression according to claim 1, characterized in that: The stroke adjustment reflection unit comprises a sixth plane reflection mirror (17), a stepping motor translation unit (18), a seventh plane reflection mirror (19), a third plano-convex lens (20), an eighth plane reflection mirror (21), a ninth plane reflection mirror (22), and a tenth plane reflection mirror (23); the picosecond green light output by the first aperture (16) is reflected to the first adjustment reflection mirror via the sixth plane reflection mirror (17); the reflected light of the first adjustment reflection mirror is incident on the second adjustment reflection mirror; the reflected light of the second adjustment reflection mirror is incident on the seventh plane reflection mirror (19); the stepping motor translation unit (18) is used to adjust the distance between the first adjustment reflection mirror and the second adjustment reflection mirror and the sixth plane reflection mirror (17) and the seventh plane reflection mirror (19); the reflected light of the seventh plane reflection mirror (19) passes through the third plano-convex lens (20) and then sequentially reflected by the eighth plane reflection mirror (21) and the ninth plane reflection mirror (22) to enter the Y-cut quartz crystal (24).

5. The femtosecond laser and spectrum detection device based on dispersion and bandwidth compression according to claim 1, characterized in that: The femtosecond mid-infrared light emitted by the frequency doubling / difference frequency module (4) is reflected by the first plane reflector (5) and the tenth plane reflector (23) in sequence, and then enters the Y-cut quartz crystal (24) non-collinearly with the picosecond green light and at the same incident point.

6. The femtosecond laser and spectrum detection device based on dispersion and bandwidth compression according to claim 1, characterized in that: The sample to be tested (28) and the gold mirror (29) are placed on the moving part of the stepper motor height translation stage (30), and the fixed part of the stepper motor height translation stage (30) is arranged on the moving part of the stepper motor horizontal translation stage (31). The stepper motor horizontal translation stage (31) is used to adjust the horizontal position of the sample to be tested (28) and the gold mirror (29).

7. The femtosecond laser and spectrum detection device based on dispersion and bandwidth compression according to claim 1, characterized in that: The picosecond green light, femtosecond mid-infrared light, intrinsic sum frequency signal and sample sum frequency signal are reflected by the second concave reflector (32), then reflected by the twelfth plane reflector (33), and finally filtered by the second aperture (34) to filter non-sum frequency signal light and excess stray light, and then the intrinsic sum frequency signal light and sample sum frequency signal light are incident on a spectrometer (37).

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