A femtosecond laser sum-frequency spectrum detection device based on dispersion and bandwidth compression

Abstract

The present invention discloses a femtosecond laser sum-frequency spectrum detection device based on dispersion and bandwidth compression. The femtosecond infrared laser beam generated by a laser is split into a first and a second split beam. The first split beam is converted into femtosecond mid-infrared light; the second split beam is converted into picosecond green light. The picosecond green light passes through a first aperture, then is simultaneously focused by a stroke-adjustable reflective unit and the wavelength-tunable femtosecond mid-infrared light generated by the aforementioned frequency doubling / difference frequency module onto a point on a Y-cut quartz crystal. The Y-cut quartz crystal generates an intrinsic sum-frequency signal. After passing through a quartz glass sheet, the intrinsic sum-frequency signal is focused together with the picosecond green light and femtosecond mid-infrared light emitted from the Y-cut quartz crystal onto a point on the surface of a sample to be measured, generating a sample sum-frequency signal. The intrinsic sum-frequency signal and the sample sum-frequency signal are transmitted collinearly into a spectrometer. The present invention employs a simple and direct spectral bandwidth compression method, significantly reducing complexity, compressing the spectral bandwidth of green light, and enabling sum-frequency spectrum detection.

Description

Technical Field

[0001] The present 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] Sum frequency vibrational spectroscopy, an advanced second-order nonlinear spectroscopy technique, has rapidly emerged in recent decades. This characterization technique boasts selectivity and sensitivity for interfaces and molecular group orientations, while also being unrestricted by harsh environmental conditions. The principle of sum frequency vibrational spectroscopy is to simultaneously focus infrared and visible light on an interface. Due to the symmetry of the material at the interface being broken, a sum frequency signal is generated, the frequency of which is the sum of the frequencies of the infrared and visible light. First, upon absorbing infrared light, the molecule transitions to an excited state, then absorbs visible light, transitioning to a virtual state. Finally, the photon emitted upon returning to the ground state is the sum frequency signal. A significant advantage of sum frequency vibrational spectroscopy is its interface selectivity. This method relies primarily on the second-order nonlinear polarizability, a tensor with 27 components. In experiments, different polarization combinations can be used to measure different components. By performing coordinate transformations and solving equations, and applying a Gaussian distribution function, the second-order nonlinear polarizability can be converted into Euler orientation angles, thereby providing information on the structure and orientation of the molecular groups at the interface.

[0003] Sum frequency generation refers to the co-propagation of two photons with frequencies ω1 and ω2 together with wave vectors k1 and k2 in a nonlinear medium, generating a photon whose combined frequency sum is ω3 = ω1 + ω2; 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 method of generating spatially chirped pulses is to use a simple mirror image after the pulse dispersion to naturally generate 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, achieving high spectral resolution requires bandwidth compression of broadband femtosecond laser pulses, converting them into intense, narrowband picosecond laser pulses. Existing spectral compression methods typically employ time-domain nonlinear bandwidth compression techniques. While these techniques successfully address conversion efficiency issues, they often require complex system design, precise tuning, optimization, and characterization, and expensive optical components. Summary of the Invention

[0005] The purpose of the present invention is to address the above-mentioned problems existing in the prior art and provide a femtosecond laser sum-frequency spectrum detection method based on dispersion and bandwidth compression, which reduces the complexity of the system, significantly compresses the spectral bandwidth of green laser pulses and realizes interference sum-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 includes a laser. The femtosecond infrared laser generated by the laser is divided into a first split beam and a second split beam by a first beam splitter. The first split beam passes through an optical parametric amplifier and a frequency doubling / difference frequency module in sequence to generate wavelength-tunable femtosecond mid-infrared light. The second split beam passes through a dispersion unit and a second beam splitter and is 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 them through a second plano-convex lens in parallel. The BBO crystal set at the focus generates picosecond green light with compressed spectral bandwidth. After passing through the first aperture, the picosecond green light is simultaneously focused on a point of the Y-cut quartz crystal by the stroke-adjustable 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 on a point on the surface of the sample to be measured, generating a sample sum frequency signal. The intrinsic sum frequency signal and the sample sum frequency signal are transmitted collinearly into the spectrometer.

[0008] As described above, the fifth plane reflector is arranged on a manual precision translation stage. 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 and seventh plane reflectors. The reflected light of the seventh plane reflector passes through the third plano-convex lens, and is then reflected by the eighth and ninth plane reflectors in sequence to be incident on 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 at the same incident point.

[0012] As described above, the sample to be tested and the gold mirror are placed on the movable portion of the stepper motor height translation stage, and the fixed portion of the stepper motor height translation stage is set on the movable portion 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 non-sum frequency signal light and excess stray light. 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 uses a small number of optical elements and is based on the principle of dispersion and frequency spectroscopy to achieve bandwidth compression of green femtosecond laser pulses, reducing the complexity of the system and the difficulty of tuning optimization. In addition, the interference sum-frequency spectrum detection is successfully achieved by using 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 the picosecond green light spectra before and after bandwidth compression; the horizontal axis represents the wavelength range; the vertical axis represents the normalized spectral intensity;

[0018] Figure 3It is the interference sum frequency spectrum recorded 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 after detection using the bandwidth compression method; 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] Wherein: 1-laser; 2-first beam splitter; 3-optical parametric amplifier; 4-frequency doubling / difference frequency module; 5-first plane mirror; 6-second plane mirror; 7-first plano-convex lens; 8-equilateral dispersion prism; 9-third plane mirror; 10-second beam splitter; 11-fourth plane mirror; 12-fifth plane mirror; 13-manual precision translation stage; 14-second plano-convex lens; 15-BBO crystal; 16-first aperture; 17-sixth plane mirror; 18-stepping motor translation unit; 19-seventh plane Reflecting mirror; 20-third plano-convex lens; 21-eighth plane reflecting mirror; 22-ninth plane reflecting mirror; 23-tenth plane reflecting mirror; 24-Y-cut quartz crystal; 25-eleventh plane reflecting mirror; 26-quartz glass plate; 27-first concave reflecting mirror; 28-sample to be tested; 29-gold mirror; 30-stepping motor height translation stage; 31-stepping motor horizontal translation stage; 32-second concave reflecting mirror; 33-twelfth plane reflecting mirror; 34-second aperture; 35-fourth plano-convex lens; 36-filter; 37-spectrometer. DETAILED DESCRIPTION

[0020] In order to facilitate ordinary technicians in this field 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 of which are as follows: the femtosecond infrared laser generated by the laser 1 is split into two beams by a first beam splitter 2, the first beam split 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 beam split after the first beam splitter 2 is split into two beams after passing through a dispersion unit and a second beam splitter 10, and the fourth plane reflector 11 and the fifth plane reflector 12 respectively reflect the two beams after the second beam splitter 10 and then pass them in parallel through a focusing second plano-convex lens 1. 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 cause the two beams of light to produce a sum frequency effect at the BBO crystal, thereby generating picosecond green light with 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. A first aperture 16 is used to filter non-sum frequency signal light and excess stray light. The resulting bandwidth-compressed picosecond green light is then simultaneously focused onto a point on a Y-cut quartz crystal 24 via a stroke-adjustable reflector unit and the wavelength-tunable femtosecond mid-infrared light generated by the aforementioned frequency doubling / difference module 4. The Y-cut quartz crystal 24 generates an intrinsic sum frequency signal. This intrinsic sum frequency signal, after passing through a quartz glass plate 26 (to generate a phase difference), is then focused together with the picosecond green light and femtosecond mid-infrared light emitted from the Y-cut quartz crystal 24 onto a point on the surface of a sample to be measured 28, generating a sample sum frequency signal. Finally, the intrinsic sum frequency signal and the sample sum frequency signal are collinearly transmitted into a spectrometer CCD for recording by a high-speed CCD camera. This invention overcomes the shortcomings of conventional time-domain bandwidth compression technology, such as expensive optical components and complex systems, by adopting a simpler and more direct spectral bandwidth compression method, significantly reducing system complexity, compressing the spectral bandwidth of the green laser pulse, and enabling detection of phase interference sum frequency spectra.

[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 beam of light after being split by the first beam splitter 2 is reflected by the second plane mirror 6, and then 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 split into two beams of light by the second beam splitter 10.

[0023] In some embodiments, the stroke adjustment reflection unit includes a sixth plane mirror 17, a stepper motor translation unit 18, a seventh plane mirror 19, a third plano-convex lens 20, an eighth plane mirror 21, a ninth plane mirror 22, and a tenth plane mirror 23. The first adjustment mirror and the second adjustment mirror are arranged on the stepper motor translation unit 18. The picosecond green light after bandwidth compression is reflected to the first adjustment mirror by the sixth plane mirror 17. The reflected light of the first adjustment mirror is incident on the second adjustment mirror, and the reflected light of the second adjustment mirror is incident on the seventh plane mirror 19. The stepper motor translation unit 18 is used to adjust the distance between the first adjustment mirror and the second adjustment mirror and the sixth plane mirror 17 and the seventh plane mirror 19, thereby adjusting the stroke length of the picosecond green light after bandwidth compression. The reflected light of the seventh plane mirror 19 passes through the third plano-convex lens 20, and is then reflected by the eighth plane mirror 21 and the ninth plane mirror 22 in sequence to be incident on 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 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. 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 measured 28 or the gold mirror 29.

[0026] In some embodiments, the sample to be tested 28 and the gold mirror 29 are placed on the movable portion of a stepper motor height translation stage 30, and the fixed portion of the stepper motor height translation stage 30 is disposed on the movable portion of a 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 so that the focal point of the reflected light from the concave reflector 27 is on the sample to be tested 28 or the gold mirror 29. The stepper motor height translation stage 30 is used to adjust the height of the sample to be tested 28 and the gold mirror 29 so that the sample to be tested 28 or the gold mirror 29 is located at the focal point of the reflected light from 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. 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, and 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. Among them, the optical parametric amplifier 3 is a two-stage optical parametric amplifier based on the generation of white light supercontinuum. Its wavelength tuning can be achieved by controlling the rotation or translation of key optical components. It can convert part of the infrared femtosecond laser pulses separated by the beam splitter 2 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 components, which can extend the wavelength 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, 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 μm, and the minimum deviation angle is 65.5°.

[0035] The third plane mirror 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 mirror 11 and the fifth plane mirror 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 mirror 11, and the plane mirror 12 to ensure that the two beams of light reflected by the fourth plane mirror 11 and the fifth plane mirror 12 are parallel to each other and the distance between them is less than 50 mm. In addition, it is necessary to ensure that the distance from the second beam splitter 10 to the fourth plane mirror 11 and the fifth plane mirror 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 generate 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 position of the manual precision translation stage 13 installed below the plane reflector 12, the optical path difference between the two beams after being reflected by the fourth plane reflector 11 and the fifth plane reflector 12 is adjusted. The two 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 mirror 11, and the fifth plane mirror 12, as well as the front and rear positions of the manual precision translation stage 13, the two parts of light focused on the BBO crystal 15 are optimally superimposed in both 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 change 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 to focus the light beam; the eighth plane reflector 21, the ninth plane reflector 22, and the tenth plane reflector 23 are used to transform 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 plate 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 sample's sum frequency signal; the gold mirror 29 serves 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 switch the horizontal positions of the sample 28 and the gold mirror 29. The above motors also use 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 optical path and guide the signal into the spectrometer CCD37 for detection. The spectrometer has a focal length of 750 mm, a resolution of 0.02 nm, and a CCD with a pixel array of 1600×400.

[0048] The second aperture 34 is used to filter non-sum frequency signal light and excess 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 excess 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. The HIT type expandable stepper motor controller is used.

[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 CCD 37 to receive, process, and display the detected spectrum. It is used to communicate with stepper motor control unit 38 to achieve program-automated control of the entire detection system.

[0053] In this embodiment, the bandwidth-compressed picosecond green light 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 whose frequency 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 using a plane mirror and a concave mirror to generate a sum frequency signal of the sample to be tested whose frequency 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 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 time delayed and interference fringes are generated at the detection point. Note that the quartz glass plate 26 cannot affect the picosecond green light and femtosecond mid-infrared light; finally, the intrinsic sum frequency signal light and the sample sum frequency signal light of the sample to be measured are transmitted collinearly into the spectrometer CCD for recording using the twelfth plane reflector 33, the second concave reflector 32 (focusing lens), the second aperture 34, etc.

[0055] Figure 2 The following diagram shows the picosecond green light spectrum using the bandwidth compression method in this embodiment and the picosecond green light spectrum using only BBO crystal for frequency doubling without bandwidth compression. By comparison, the picosecond green light bandwidth before compression is about 2.1nm, while 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 2700-3100 cm -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 sum-frequency spectra.

[0058] It should be noted that the embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A femtosecond laser sum 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 beam and a second split beam by a first beam splitter (2). The first split beam 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 beam passes through a dispersion unit and a second beam splitter (10) and is divided into two beams. The fourth plane reflector (11) and the fifth plane reflector (12) respectively reflect the two beams split by the second beam splitter (10) and pass through a second plano-convex lens (14) in parallel. The BBO crystal (11) provided at the lens focus of the second plano-convex lens (14) is provided. 5) Generate picosecond green light with compressed spectral bandwidth. The picosecond green light passes through the first aperture (16) and is simultaneously focused on 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 plate (26) and is focused together with the picosecond green light and femtosecond mid-infrared light emitted from the Y-cut quartz crystal (24) on a point on the surface of the sample to be measured (28), generating a sample sum frequency signal. The intrinsic sum frequency signal and the sample sum frequency signal are collinearly transmitted into the spectrometer. 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).

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

3. The femtosecond laser sum frequency 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 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 picosecond green light output by the first aperture (16) 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); the reflected light of the seventh plane reflector (19) passes through the third plano-convex lens (20) and then sequentially reflected by the eighth plane reflector (21) and the ninth plane reflector (22) to enter the Y-cut quartz crystal (24).

4. The femtosecond laser sum frequency 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.

5. The femtosecond laser sum frequency 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 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 to be tested (28) and the gold mirror (29).

6. The femtosecond laser sum frequency 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. Then, the intrinsic sum frequency signal light and sample sum frequency signal light are incident on the spectrometer (37).

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