A single-shot terahertz transient spectroscopy system

Abstract

The present invention relates to the field of laser systems, and to a single-shot terahertz transient spectroscopy system, comprising a chirped picosecond light generating module, which generates laser light and sequentially transmits it to a pulse compression module, a terahertz generating module, a sample module, and a spectrum detection module. The chirped picosecond light generating module also transmits the laser light to the spectrum detection module for generating a four-wave mixing signal; the pulse compression module separates a laser beam and transmits it to an excitation light module, which is then used to excite the sample after laser pumping the excitation light module; the terahertz generating module and the spectrum detection module both include a nitrogen propagation medium or an inert gas propagation medium. The present invention processes the sample by generating a spatially separated pulse sequence, and then overlaps it with the excitation light; it also overlaps it with the chirped laser in a colinear manner to generate a four-wave mixing signal, and finally performs imaging display. By using nitrogen or an inert gas as an environment of a nonlinear medium, the wide-spectrum measurement of terahertz light is effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of laser systems, in particular to a transient spectrum observation technology, and in particular to a single-shot terahertz transient spectrum system. Background Art

[0002] Traditional terahertz transient spectroscopy is suitable for the study of reversible ultrafast dynamic processes, but it cannot achieve single-shot observation of irreversible ultrafast dynamic processes. The reason is that traditional terahertz transient spectroscopy is based on point-by-point measurement of terahertz pulse time domain signals on the one hand, and on the other hand, in order to obtain complete ultrafast dynamic information, additional point-by-point measurement of time is required in the detection of dynamic processes. Therefore, there is a technical problem here: traditional terahertz transient spectroscopy cannot achieve single-shot detection of transient spectra of irreversible processes.

[0003] In the past decade or so, single-shot terahertz spectroscopy measurement technology has made some progress, and it can achieve single-shot measurement of the spectrum of a single or two or three terahertz pulses. However, on the one hand, this technology can only measure a single or two or three terahertz pulses, and cannot measure the entire terahertz pulse sequence containing dozens or hundreds of pulses, so it is still impossible to achieve terahertz transient spectral detection of irreversible ultrafast dynamic processes. On the other hand, this technology is based on the sum frequency effect of the detection light and terahertz in nonlinear crystals, but the nonlinear crystal itself will absorb terahertz light, which makes this technology unable to achieve wide-spectrum detection. So there is another technical problem here: the nonlinear crystal medium relied on by the traditional single-shot terahertz spectrum detection method leads to a limited range of detection light.

[0004] Therefore, the existing single-shot terahertz transient measurement technology has areas that need to be improved urgently, and it needs to be studied and optimized to obtain a more reasonable technical solution to solve the shortcomings of the existing technology. Summary of the invention

[0005] In order to overcome the defects of the prior art mentioned above, the present invention provides a single-shot terahertz transient spectroscopy system, which aims to improve the composition structure of the system, use a practical spatially separated pulse technology to achieve single-shot detection of transient spectra, and use inert gas as a nonlinear medium to achieve wide-spectrum terahertz detection.

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

[0007] A single-shot terahertz transient spectroscopy system comprises a chirped picosecond light generating module, which generates laser light and sequentially transmits the laser light to a pulse compression module, a terahertz generating module, a sample module and a spectrum detection module through an electromagnetic wave propagation path. The chirped picosecond light generating module also transmits the laser light to the spectrum detection module through another electromagnetic wave propagation path for generating a four-wave mixing signal. The pulse compression module separates a separate laser light and transmits it to an excitation light module. After the laser pumps the excitation light module, an excitation light pulse is generated and transmitted to the sample module for exciting the sample. The terahertz generating module and the spectrum detection module both comprise a nitrogen propagation medium or an inert gas propagation medium.

[0008] The single-shot terahertz transient spectroscopy system disclosed above processes terahertz light by means of four-wave mixing, and uses nitrogen or inert gas as a nonlinear medium, which not only greatly improves the broadband detection of terahertz light, but also realizes the transient observation of single-shot terahertz light; in the spectral detection module, the terahertz light is imaged to detect the spectrum at different points respectively.

[0009] Furthermore, the above technical solution discloses a chirped picosecond light generating module, which includes a laser, which can generally be a titanium sapphire laser, and a laser amplifier can be used to match the laser output.

[0010] Furthermore, the pulse compression module includes a pulse compression box. The pulse compression box receives 50% of the laser light from the chirped picosecond light generation module, processes it, and outputs a 100-femtosecond laser pulse, a portion of which is transmitted to the terahertz generation module for generating terahertz light, and the other portion is transmitted to the excitation light module for generating an excitation light pulse.

[0011] Furthermore, the terahertz generation module is used to generate terahertz light. The present invention adopts an updated terahertz generation module structure. Here is a specific feasible solution: the terahertz generation module includes a frequency doubling crystal, a phase delay plate, a dichroic wave plate, a first plane reflector and a first concave reflector, which are used for laser passage or reflection in sequence. The first plane reflector is set at a certain angle to the propagation path of the laser and deflects the laser to the first concave reflector. The first concave reflector reflects and focuses the laser. The terahertz generation module also includes a first gas nozzle, which provides a nitrogen propagation medium or an inert gas propagation medium to the laser that is focused after reflection. The terahertz light propagates to the sample module after passing through the propagation medium. When configured in this way, the laser is processed by a frequency doubling crystal to obtain a frequency doubling light pulse, and then the time delay of the fundamental frequency light and the frequency doubling light pulse is adjusted through a phase delay plate, and then the polarization of the fundamental frequency light is changed through a two-color wave plate to make it parallel to the polarization of the frequency doubling light. After passing through the first plane reflector and the first concave reflector, the laser passes through the first gas nozzle, and the first gas nozzle sprays nitrogen or inert gas outward as the medium through which the laser passes, generating a terahertz light supercontinuum in the medium, which is then propagated to the sample module.

[0012] Furthermore, a sample to be tested is placed at the sample module, and the terahertz light reaching the sample module generates a spatially separated pulse sequence. Specifically, the sample module includes a blazed grating for generating a spatially separated pulse sequence. After passing through the blazed grating, the terahertz light coincides with the excitation light pulse generated by the excitation light module at the sample, and the excitation light pulse is used to excite the sample.

[0013] Furthermore, the sample module also includes a high-resistance silicon wafer. The terahertz light passes through the high-resistance silicon wafer before reaching the blazed grating. A first off-axis parabolic mirror and a second off-axis parabolic mirror are respectively arranged between the high-resistance silicon wafer and the blazed grating and between the blazed grating and the sample. The high-resistance silicon wafer is used to filter out residual fundamental frequency light and frequency-doubled light in the terahertz light. After being collimated into parallel light by the first off-axis parabolic mirror, the terahertz light reaches the blazed grating. The blazed grating performs spatial separation of the terahertz light and generates a spatially separated pulse sequence. The spatially separated pulse sequence propagates to the sample after passing through the second off-axis parabolic mirror and overlaps with the excitation light pulse at the sample.

[0014] Furthermore, the sample module also includes a third off-axis parabolic mirror, and the terahertz light after passing through the sample is collimated by the third off-axis parabolic mirror and then propagated to the spectrum detection module.

[0015] Furthermore, the terahertz light reaching the spectrum detector module is processed and displayed as an image, which is convenient for observation at various points. Specifically, the following specific feasible scheme is given: the spectrum detection module includes a visible spectrometer, the terahertz light from the sample module and the chirped laser from the chirped picosecond light generation module converge and collinear at the fourth off-axis parabolic mirror, and generate a four-wave mixing signal after passing through the nitrogen propagation medium or the inert gas propagation medium at the second gas nozzle. The four-wave mixing signal passes through the short-pass filter and the second converging lens in turn and enters the visible spectrometer. At the short-pass filter, the chirped laser is filtered out, and the remaining four-wave mixing signal finally enters the visible spectrometer for imaging to obtain a visible spectrum, and the visible spectrum can be inverted to obtain a terahertz spectrum.

[0016] Furthermore, the spectrum detection module is optimized, and the following specific feasible solutions are given: the spectrum detection module also includes a first delay component, the first delay component includes a plurality of reflectors and a first converging lens, and the chirped laser passes through the first delay component and the first converging lens and propagates to the fourth off-axis parabolic mirror. The fourth off-axis parabolic mirror is provided with a small hole, and the chirped laser passes through the small hole and converges with the terahertz light on a collinear basis.

[0017] Furthermore, the excitation light module disclosed in the above technical solution is described. The excitation light module includes an optical parametric amplifier and a third converging lens. A second delay component is arranged between the optical parametric amplifier and the third converging lens. The second delay component includes a plurality of reflectors. The chirped laser passing through the optical parametric amplifier enters the second delay component after being adjusted by the deflection reflector, and then is adjusted by the deflection reflector and then propagated to the sample module after passing through the converging lens.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention sets a blazed grating at the sample module and generates a spatially separated pulse sequence, which is overlapped with the excitation light to process the sample; the terahertz light sequence passing through the sample is also collinearly overlapped with the chirped laser to generate a four-wave mixing signal, which finally enters the spectrum detection module for imaging display. Both the generation of terahertz light and the generation of four-wave mixing are carried out in an environment with nitrogen or inert gas as a nonlinear medium, which effectively improves the wide-spectrum measurement of terahertz light. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only represent some embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 It is a schematic diagram of the components of the spectral system;

[0022] Figure 2 is a schematic diagram of the components of the terahertz generation module;

[0023] Figure 3 It is a schematic diagram of the component modules of the sample module;

[0024] Figure 4 It is a schematic diagram of the components of the spectrum detection module;

[0025] Figure 5 It is a schematic diagram of the components of the excitation light module;

[0026] Figure 6 This is a top view of the principle of generating a spatially separated pulse train;

[0027] Figure 7 It is a side view of the principle of generating spatially separated pulse trains;

[0028] Figure 8 This is the principle diagram of chirped laser four-wave mixing;

[0029] Fig. 9 This is the schematic diagram of the single-shot detection transient spectroscopy.

[0030] The meanings of the numbers in the accompanying drawings are as follows: 110, chirped picosecond light generation module; 120, pulse compression module; 130, terahertz generation module; 132, frequency doubling crystal; 133, phase delay plate; 134, two-color wave plate; 135, first plane reflector; 136, first concave reflector; 137, first gas nozzle; 140, sample module; 142, high-resistance silicon wafer; 143, first off-axis parabolic mirror; 144, blazed grating; 145, second off-axis parabolic mirror; 146, Sample; 147, third off-axis parabolic mirror; 150, spectral detection module; 152, first delay component; 153, first converging lens; 154, fourth off-axis parabolic mirror; 155, second gas nozzle; 156, short-pass filter; 157, second converging lens; 158, visible spectrometer; 160, excitation light module; 162, optical parametric amplifier; 163, first deflection mirror; 164, second delay component; 165, second deflection mirror; 166, third converging lens. DETAILED DESCRIPTION

[0031] The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments.

[0032] It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. The specific structures and functional details disclosed herein are only used to describe the exemplary embodiments of the present invention. However, the present invention can be embodied in many alternative forms, and it should not be understood that the present invention is limited to the embodiments set forth herein.

[0033] Example

[0034] This embodiment describes the generation of terahertz light and its use for spectral imaging observation of sample 146, and discloses an improved spectral system that can realize single-shot terahertz transient spectral observation.

[0035] Specifically, Figure 1 As shown, a single-shot terahertz transient spectroscopy system disclosed in this embodiment includes a chirped picosecond light generating module 110, which generates laser and propagates it to a pulse compression module 120, a terahertz generating module 130, a sample module 140 and a spectrum detection module 150 in sequence through an electromagnetic wave propagation path. The chirped picosecond light generating module 110 also propagates the laser to the spectrum detection module 150 through another electromagnetic wave propagation path for generating a four-wave mixing signal; the pulse compression module 120 separates a separate laser and propagates it to an excitation light module 160, and the laser pumping excitation light module 160 then generates an excitation light pulse and propagates it to the sample module 140 for exciting the sample 146; the terahertz generating module 130 and the spectrum detection module 150 both include a nitrogen propagation medium or an inert gas propagation medium.

[0036] like Fig. 9 As shown, the single-shot terahertz transient spectroscopy system disclosed above processes terahertz light by means of four-wave mixing, and uses nitrogen or inert gas as a nonlinear medium, which not only greatly improves the broadband detection of terahertz light, but also realizes the transient observation of single-shot terahertz light; in the spectral detection module 150, the terahertz light is imaged and processed to detect the spectrum at different points respectively.

[0037] The above technical solution discloses a chirped picosecond light generating module 110 , and the chirped picosecond light generating module 110 includes a laser.

[0038] Preferably, in this embodiment, a titanium sapphire laser may be used, and a laser amplifier may be used in combination with the laser output.

[0039] The pulse compression module 120 includes a pulse compression box. The pulse compression box receives 50% of the laser light from the chirped picosecond light generation module 110, processes it, and outputs a 100-femtosecond laser pulse. A portion of the laser pulse is transmitted to the terahertz generation module 130 for generating terahertz light, and the other portion is transmitted to the excitation light module 160 for generating an excitation light pulse.

[0040] The terahertz generation module 130 is used to generate terahertz light. The present invention adopts a newer structure of the terahertz generation module 130. Here are some specific feasible solutions: Figure 2 As shown, the terahertz generation module 130 includes a frequency doubling crystal 132, a phase delay plate 133, a dichroic wave plate 134, a first plane reflector 135 and a first concave reflector 136, which are used for the laser to pass through or reflect in sequence. The first plane reflector 135 is set at a certain angle with the propagation path of the laser and deflects the laser to the first concave reflector 136. The first concave reflector 136 reflects and focuses the laser. The terahertz generation module 130 also includes a first gas nozzle 137. The first gas nozzle 137 provides a nitrogen propagation medium or an inert gas propagation medium for the laser that is focused after reflection. The terahertz light propagates to the sample module 140 after passing through the propagation medium. When configured in this way, the laser is processed by the frequency doubling crystal 132 to obtain a frequency doubling light pulse, and then the time delay of the fundamental frequency light and the frequency doubling light pulse is adjusted by the phase delay plate 133, and then the polarization of the fundamental frequency light is changed by the dichroic wave plate 134 to make it parallel to the polarization of the frequency doubling light. After passing through the first plane reflector 135 and the first concave reflector 136, the laser passes through the first gas nozzle 137, and the first gas nozzle 137 sprays nitrogen or inert gas outward as the medium through which the laser passes, generating a terahertz light supercontinuum in the medium, which then propagates to the sample module 140.

[0041] A sample 146 to be tested is placed at the sample module 140, and the terahertz light reaching the sample module 140 generates a spatially separated pulse sequence, specifically, Figure 5 As shown, the sample module 140 includes a blazed grating 144 for generating a spatially separated pulse sequence. After the terahertz light passes through the blazed grating 144 , it overlaps with the excitation light pulse generated by the excitation light module 160 at the sample 146 , and the excitation light pulse is used to excite the sample 146 .

[0042] The sample module 140 further includes a high-resistance silicon wafer 142. The terahertz light first passes through the high-resistance silicon wafer 142 before reaching the blazed grating 144. A first off-axis parabolic mirror 143 and a second off-axis parabolic mirror 145 are respectively arranged between the high-resistance silicon wafer 142 and the blazed grating 144 and between the blazed grating 144 and the sample 146. The high-resistance silicon wafer 142 is used to filter out the residual fundamental frequency light and frequency-doubled light in the terahertz light. After being collimated into parallel light by the first off-axis parabolic mirror 143, the terahertz light reaches the blazed grating 144. The blazed grating 144 performs spatial separation of the terahertz light and generates a spatially separated pulse sequence. The spatially separated pulse sequence propagates to the sample 146 after passing through the second off-axis parabolic mirror 145 and overlaps with the excitation light pulse at the sample 146.

[0043] Preferably, in this embodiment, Figure 6 , Figure 7 and Figure 8 As shown, the lines of the blazed grating 144 are placed horizontally, and the terahertz light is introduced into a step-like time delay in the vertical direction after being reflected by the blazed grating 144 .

[0044] The sample module 140 further includes a third off-axis parabolic mirror 147 . The terahertz light after passing through the sample 146 is collimated by the third off-axis parabolic mirror 147 and then propagates to the spectrum detection module 150 .

[0045] The terahertz light reaching the spectrum detector module is processed and displayed as an image, which is convenient for observation at various points. Specifically, the following specific feasible solutions are given: Figure 6 , Figure 8 and Fig. 9 As shown, the spectrum detection module 150 includes a visible spectrometer 158. The terahertz light from the sample module 140 and the chirped laser from the chirped picosecond light generation module 110 converge and collinear at the fourth off-axis parabolic mirror 154, and generate a four-wave mixing signal after passing through the nitrogen propagation medium or the inert gas propagation medium at the second gas nozzle 155. The four-wave mixing signal passes through the short-pass filter 156 and the second converging lens 157 in sequence and enters the visible spectrometer 158. At the short-pass filter, the chirped laser is filtered out, and the remaining four-wave mixing signal finally enters the visible spectrometer 158 for imaging to obtain a visible spectrum, and the visible spectrum can be inverted to obtain a terahertz spectrum.

[0046] The spectrum detection module 150 is optimized, and the following specific feasible solutions are given: the spectrum detection module 150 also includes a first delay component 152, and the first delay component 152 includes a plurality of reflectors and a first converging lens 153. The chirped laser passes through the first delay component 152 and the first converging lens 153 and propagates to the fourth off-axis parabolic mirror 154. The fourth off-axis parabolic mirror 154 is provided with a small hole, and the chirped laser passes through the small hole and converges with the terahertz light to be collinear.

[0047] Preferably, the first delay component 152 in this embodiment includes three reflectors, and performs three 90° steering adjustments on the terahertz light.

[0048] The excitation light module 160 disclosed in the above technical solution is explained. The excitation light module 160 includes an optical parametric amplifier 162 and a third converging lens 166. A second delay component 164 is arranged between the optical parametric amplifier 162 and the third converging lens 166. The second delay component 164 includes a plurality of reflectors. The chirped laser passing through the optical parametric amplifier 162 enters the second delay component 164 after being adjusted by the deflection reflector, and then is adjusted by the deflection reflector and propagates to the sample module 140 after passing through the converging lens.

[0049] Preferably, the second delay component 164 in this embodiment includes two reflectors and performs two 90° steering adjustments on the laser.

[0050] Preferably, a first deflecting reflector 163 and a second deflecting reflector 165 are provided in this embodiment. The first deflecting reflector 163 transmits the laser regulated by the optical parametric amplifier 162 to the second delay component 164. The laser emitted from the second delay component 164 passes through the second deflecting reflector 165 and then transmits to the sample module 140.

[0051] The above are the embodiments of the present invention, but the present invention is not limited to the above optional embodiments. Those skilled in the art can arbitrarily combine the above methods to obtain other various embodiments. Anyone can obtain other various forms of embodiments under the enlightenment of the present invention. The above specific embodiments should not be understood as limiting the scope of protection of the present invention. The scope of protection of the present invention shall be based on the definition in the claims, and the description can be used to interpret the claims.

Claims

1. A single-shot terahertz transient spectroscopy system, characterized in that: The invention comprises a chirped picosecond light generating module (110), wherein the chirped picosecond light generating module (110) generates laser light and sequentially transmits the laser light to a pulse compression module (120), a terahertz generating module (130), a sample module (140) and a spectrum detection module (150) through an electromagnetic wave propagation path; the chirped picosecond light generating module (110) further transmits the laser light to the spectrum detection module (150) through another electromagnetic wave propagation path for generating a four-wave mixing signal; the pulse compression module (120) separates a single laser light and transmits it to an excitation light module (160); the laser pumping excitation light module (160) then generates an excitation pulse and transmits the laser light to the sample module (140) for exciting a sample (146); the terahertz generating module (130) and the spectrum detection module (150) both comprise a nitrogen propagation medium or an inert gas propagation medium; The terahertz generation module (130) comprises a frequency doubling crystal (132), a phase delay plate (133), a dichroic wave plate (134), a first plane reflector (135), and a first concave reflector (136) which are used in sequence for laser light to pass through or reflect. The first plane reflector (135) is arranged at a certain angle with a propagation path of the laser light and deflects the laser light to the first concave reflector (136). The first concave reflector (136) reflects and focuses the laser light. The terahertz generation module (130) further comprises a first gas nozzle (137). The first gas nozzle (137) provides a nitrogen propagation medium or an inert gas propagation medium for the laser light that is focused after reflection. The terahertz light propagates to the sample module (140) after passing through the propagation medium. The spectrum detection module (150) includes a visible spectrometer (158). The terahertz light from the sample module (140) and the chirped laser light from the chirped picosecond light generation module (110) converge and collinear at the fourth off-axis parabolic mirror (154), and generate a four-wave mixing signal after passing through the nitrogen propagation medium or the inert gas propagation medium at the second gas nozzle (155). The four-wave mixing signal passes through the short-pass filter (156) and the second converging lens (157) in sequence and then enters the visible spectrometer (158).

2. The single-shot terahertz transient spectroscopy system according to claim 1, characterized in that: The chirped picosecond light generating module (110) comprises a laser.

3. The single-shot terahertz transient spectroscopy system according to claim 1, characterized in that: The pulse compression module (120) comprises a pulse compression box.

4. The single-shot terahertz transient spectroscopy system according to claim 1, characterized in that: The sample module (140) includes a blazed grating (144) for generating a spatially separated pulse sequence, and the terahertz light passes through the blazed grating (144) and overlaps with the excitation light pulse generated by the excitation light module (160) at the sample (146).

5. The single-shot terahertz transient spectroscopy system according to claim 4, characterized in that: The sample module (140) further comprises a high-resistance silicon wafer (142), and the terahertz light first passes through the high-resistance silicon wafer (142) before reaching the blazed grating (144). A first off-axis parabolic mirror (143) and a second off-axis parabolic mirror (145) are respectively arranged between the high-resistance silicon wafer (142) and the blazed grating (144), and between the blazed grating (144) and the sample (146).

6. The single-shot terahertz transient spectroscopy system according to claim 4 or 5, characterized in that: The sample module (140) further comprises a third off-axis parabolic mirror (147), and the terahertz light that has passed through the sample (146) is collimated by the third off-axis parabolic mirror (147) and then propagates to the spectrum detection module (150).

7. The single-shot terahertz transient spectroscopy system according to claim 1, characterized in that: The spectral detection module (150) further comprises a first delay component (152), wherein the first delay component (152) comprises a plurality of reflectors and a first converging lens (153), and the chirped laser light propagates to a fourth off-axis parabolic mirror (154) after passing through the first delay component (152) and the first converging lens (153).

8. The single-shot terahertz transient spectroscopy system according to claim 1, characterized in that: The excitation light module (160) comprises an optical parametric amplifier (162) and a third converging lens (166); a second delay component (164) is provided between the optical parametric amplifier (162) and the third converging lens (166); the second delay component (164) comprises a plurality of reflectors; the chirped laser light passing through the optical parametric amplifier (162) enters the second delay component (164) after being adjusted by the deflecting reflector, and then is adjusted by the deflecting reflector and propagates through the converging lens to the sample module (140).

Images