CN220399276U - Single-shot terahertz time-domain spectrometer - Google Patents

Abstract

The utility model provides a single-shot terahertz time-domain spectrometer which comprises a femtosecond laser module, a terahertz generation module, an excitation light module, a sample module and a single-shot terahertz detection module. Through the combination of the femtosecond laser module, the terahertz generating module, the excitation light module, the sample module and the single terahertz detecting module, a complete terahertz time-domain waveform and spectrum information thereof can be obtained by only scanning single terahertz pulses. The scheme provided by the utility model is a compact laboratory-level single-shot terahertz time-domain spectrometer, can obtain time-domain spectrum, frequency-domain spectrum, dielectric constant, refractive index spectrum, phase spectrum, absorption spectrum and conductivity parameters of a sample, has stable performance of an experimental system and high repeatability, and is suitable for dynamics research in an irreversible process.

Description

Single-shot terahertz time-domain spectrometer

Technical Field

The utility model relates to the technical field of terahertz spectrum, in particular to a single-shot terahertz time-domain spectrometer.

Background

Terahertz time-domain spectroscopy (THz-TDS) technology is widely applied to various fields such as materials, biomedicine, chemistry, pharmacy, security inspection, nondestructive inspection and the like. However, the conventional scanning THz-TDS technology is only suitable for spectrum detection under a terahertz radiation source with a higher repetition frequency and stability, and it usually takes several minutes or even several tens of minutes to acquire a complete terahertz time-domain waveform by changing the delay of the detection light to scan point by point and reconstruct the terahertz time-domain waveform. For terahertz radiation sources with low repetition frequencies or large fluctuations and detection of samples in irreversible processes, the scanning THz-TDS technique will no longer be applicable.

The existing terahertz time-domain spectrometer in the laboratory is suitable for the research of reversible ultrafast dynamic processes, but cannot realize single irreversible ultrafast dynamic process observation. The main reason is that the traditional terahertz time-domain spectroscopy technology needs to change the point-by-point scanning of the delay of the detection light for acquiring the terahertz time-domain waveform, and on the other hand, the irreversible detection process is always a transient process (the duration is in the picosecond or nanosecond order). Therefore, there is a technical problem that the conventional terahertz time-domain spectroscopy technology cannot realize single-shot detection of an irreversible process.

The Chinese patent No. 212843972U discloses a single-shot terahertz transient spectrum detection module, which comprises a fourth off-axis parabolic mirror, a second gas nozzle, a short-pass filter, a second converging lens and a visible spectrometer, wherein terahertz light passes through the fourth off-axis parabolic mirror, the second gas nozzle, the short-pass filter, the second converging lens and the visible spectrometer in sequence, and nitrogen or inert gas is sprayed out of the second gas nozzle to serve as a nonlinear medium. The scheme has the advantages that: and the terahertz light sequence of the sample and external laser are subjected to collinear superposition to generate a four-wave mixing signal, and finally the four-wave mixing signal enters a spectrum detection module for imaging display. The generation of four-wave mixing is carried out in the environment with nitrogen or inert gas as a nonlinear medium, so that the wide spectrum measurement of terahertz light is effectively improved.

However, the above scheme also has disadvantages: nitrogen or inert gas is sprayed out of the gas nozzle as a nonlinear medium, when the whole detection module needs to be moved, the detection module is limited by the gas nozzle, and the detection module cannot meet the requirements of users; in addition, for single-shot terahertz detection, the visible spectrometer is used in the scheme, parameters such as time resolution, time window, signal to noise ratio and the like of terahertz detection are greatly limited, detection requirements of a weak terahertz electric field cannot be met, phase information of a sample in a terahertz wave band cannot be obtained, and physical information such as refractive index of the sample in the terahertz wave band cannot be obtained.

Disclosure of Invention

The purpose of the utility model is that: aiming at the defects in the background technology, the single-shot terahertz time-domain spectrometer is provided, and the scheme comprises the following steps:

the device comprises a femtosecond laser module, a terahertz generation module, an excitation light module, a sample module and a single-shot terahertz detection module; the femtosecond laser module is used for generating femtosecond laser; the terahertz generation module comprises a nonlinear crystal, a ITO (IndiumTinOxide) film and a reflection focusing assembly, wherein the nonlinear crystal is used for rectifying femtosecond laser to generate terahertz light, the ITO film is used for separating the terahertz light from the femtosecond laser, and the reflection focusing assembly is used for focusing the separated terahertz light to the sample module and transmitting the terahertz light emitted by the sample module to the single-shot terahertz detection module; the excitation light module is used for splitting femtosecond laser emitted by the ITO film into excitation light and detection light, the excitation light is used for being incident to the sample module, and the detection light is used for being incident to the single-shot terahertz detection module; the sample module is used for positioning a sample to be detected; the single-shot terahertz detection module is used for detecting transmission waveforms and transmission spectrums of the sample in terahertz wave bands.

Further, the reflection focusing assembly comprises a first polyethylene disc, a first reflecting mirror, a first off-axis parabolic objective and a second off-axis parabolic objective, wherein the first polyethylene disc is used for filtering residual fundamental frequency light and frequency multiplication light in terahertz light, the first reflecting mirror is provided with a plurality of reflection light paths, the first off-axis parabolic objective is used for focusing the terahertz light to the sample module, and the second off-axis parabolic objective is used for collimating the terahertz light emitted by the sample module into parallel light.

Further, the sample module is also provided with a three-dimensional electric translation stage, and the three-dimensional electric translation stage is used for adjusting the micro movement of the sample in a three-dimensional space.

Preferably, the excitation light module comprises a frequency doubling crystal and a first delay component comprising a dichroic mirror. The frequency doubling crystal is used for generating excitation light by frequency doubling femtosecond laser. The dichroic mirror is used for transmitting the femtosecond laser and reflecting the excitation light. The first delay component is used for adjusting the optical path of the excitation light so that the flight time of the excitation light and the terahertz light in the sample module are overlapped.

Further, the excitation light module further comprises a third off-axis parabolic objective that propagates and focuses excitation light to the sample module.

Further, the beam diameter of the excitation light at the sample module position is larger than the beam diameter of the terahertz light.

Further, the single-shot terahertz detection module comprises a terahertz unit, a detection light unit, a beam combining lens, an electro-optic crystal, a beam splitting lens, a first imaging unit and a second imaging unit; the terahertz unit is used for focusing the incident single-shot terahertz light on the electro-optical crystal, the detection light unit is used for converting the incident detection light into a detection light sequence with uniform interval time, and the detection light sequence is overlapped with the flight time of the single-shot terahertz light and is focused on the electro-optical crystal; the beam splitter is used for equally dividing the detection light sequence emitted by the electro-optical crystal into a first light sequence and a second light sequence according to the light intensity ratio, and respectively entering the first imaging unit and the second imaging unit; the first imaging unit is used for imaging the first light sequence to obtain a first image, the second imaging unit is used for imaging the second light sequence to obtain a second image, and the first image and the second image are used for obtaining a time domain waveform of single terahertz light.

From the above, the technical scheme provided by the utility model has the beneficial effects that: through the combination of femto second laser module, terahertz produce module, excitation light module, sample module and single terahertz detection module, not only with terahertz produce, with the interaction of sample and terahertz detection integration become an overall system, can also separate terahertz detection module alone, promote the compatibility and the practicality of equipment. The scheme provided by the utility model is a compact laboratory-level single-shot terahertz time-domain spectrometer, the parameters such as time-domain spectrum, frequency-domain spectrum, dielectric constant, refractive index spectrum, phase spectrum, absorption spectrum, conductivity and the like of a sample can be obtained, and the experimental system has stable performance and high repeatability and is suitable for dynamics research in an irreversible process. Other advantageous effects of the present utility model will be described in detail in the detailed description section which follows.

Drawings

FIG. 1 is a schematic block diagram of the overall structure of the present utility model;

fig. 2 is a schematic diagram of a terahertz generating module and an excitation light module according to the present utility model;

fig. 3 is a schematic diagram of a single-shot terahertz detection module of the present utility model.

The reference numerals in the drawings denote:

a 100-femtosecond laser module; a 200-terahertz generation module; 201-a nonlinear crystal; 202-ITO film; 203-a first polyethylene disc; 204-a first mirror; 205-a first off-axis parabolic objective; 206-a second off-axis parabolic objective; 300-an excitation light module; 301-frequency doubling crystals; 302-a dichroic mirror; 303-a first delay component; 304-a third off-axis parabolic objective; 305-a second polyethylene disc; 400-sample module; 500-a single terahertz detection module; a 510-terahertz unit; 511-a fourth off-axis parabolic mirror; 512-a second mirror; 513-a first terahertz wire grid; 520-a probe light unit; 521-a second delay component; 522-a stepped mirror; 523-lens; 524-master bias sheet; 530-beam combining mirror; 540-an electro-optic crystal; 550-beam splitters; 560-a first imaging unit; 561-first camera; 562-a first polarizer; 570-a second imaging unit; 571-a second camera; 572-second polarizer; 601-femtosecond laser; 602-terahertz light; 603-excitation light; 604-probe light.

Detailed Description

Other advantages and effects of the present disclosure will become readily apparent to those skilled in the art from the following disclosure, which describes embodiments of the present disclosure by way of specific examples. It will be apparent that the described embodiments are merely some, but not all embodiments of the present disclosure. The disclosure may be embodied or practiced in other different specific embodiments, and details within the subject specification may be modified or changed from various points of view and applications without departing from the spirit of the disclosure. It should be noted that the following embodiments and features in the embodiments may be combined with each other without conflict. All other embodiments, which can be made by one of ordinary skill in the art without inventive effort, based on the embodiments in this disclosure are intended to be within the scope of this disclosure.

It is noted that various aspects of the embodiments are described below within the scope of the following claims. It should be apparent that the aspects described herein may be embodied in a wide variety of forms and that any specific structure and/or function described herein is merely illustrative. Based on the present disclosure, one skilled in the art will appreciate that one aspect described herein may be implemented independently of any other aspect, and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented and/or a method practiced using any number of the aspects set forth herein. In addition, such apparatus may be implemented and/or such methods practiced using other structure and/or functionality in addition to one or more of the aspects set forth herein.

It should also be noted that the illustrations provided in the following embodiments merely illustrate the basic concepts of the disclosure by way of illustration, and only the components related to the disclosure are shown in the drawings and are not drawn according to the number, shape and size of the components in actual implementation, and the form, number and proportion of the components in actual implementation may be arbitrarily changed, and the layout of the components may be more complicated. In addition, in the following description, specific details are provided in order to provide a thorough understanding of the examples. However, it will be understood by those skilled in the art that the aspects may be practiced without these specific details.

The embodiment of the utility model provides a single-shot terahertz time-domain spectrometer, which comprises a femtosecond laser module 100, a terahertz generation module 200, an excitation optical module 300, a sample module 400 and a single-shot terahertz detection module 500. In this embodiment, the femtosecond laser module 100 preferably employs a commercial titanium sapphire laser with a repetition rate of 1kHz, a center wavelength of 800nm, a pulse width of about 100fs, and a maximum output energy of 4mJ. The femtosecond laser 601 emitted from the femtosecond laser module 100 first propagates to the terahertz generation module 200 for generating terahertz light 602. In this embodiment, the terahertz generation module 200 adopts a more mature terahertz generation mode, i.e. nonlinear crystal light rectification, to generate terahertz light 602. The specific scheme is as follows: as shown in fig. 2, the terahertz generating module includes a nonlinear crystal 201, an ITO film 202, a first polyethylene disk 203, a first mirror 204, a first off-axis parabolic mirror 205 (OAP 1) and a second off-axis parabolic mirror 206 (OAP 2), where the femtosecond laser first generates terahertz light 7 through light rectification of the nonlinear crystal 201, and then the femtosecond laser 602 and the terahertz light 602 together propagate to the ITO film 202, the ITO film 202 separates the terahertz light 602 from the terahertz laser 601, the reflected terahertz light 602 passes through the first polyethylene disk 203 and the first mirror 204, and the first polyethylene disk 203 is used to filter out residual fundamental frequency light and frequency doubling light in the terahertz light 602, and then focuses to the sample module 400 through the first off-axis parabolic mirror 205. The terahertz light 602 emitted from the sample module 400 is collimated into parallel light by the second off-axis parabolic objective 206, and finally propagates to the single-shot terahertz detection module 500 for detecting the transmission waveform and transmission spectrum of the sample in the terahertz wave band.

In this embodiment, the sample to be measured is placed at the sample module 400, and the terahertz light 602 reaching the sample is focused, which is more beneficial to the spectrum detection of smaller samples (millimeter-order samples, even hundred-micrometer-order samples) in the terahertz wave band. It should be noted that, the sample module 400 may further be provided with a three-dimensional electric translation stage to adjust the micro movement of the sample to be measured in the three-dimensional space, so as to facilitate accurately placing the sample at the terahertz focal point, so as to adapt to the requirements of different sample sizes, and meanwhile, avoid errors caused by manually adjusting the sample position.

Correspondingly, the femtosecond laser transmitted through the ITO film 202 is pumped through the frequency doubling crystal 301 as laser light with a center wavelength of 400nm, and a first delay element 303 including a dichroic mirror 302 is disposed behind the frequency doubling crystal 301. The dichroic mirror 302 transmits 800nm femtosecond laser light 601 and reflects 400nm excitation light 603. The excitation light 603 propagates to the sample location, and the 800nm femtosecond laser light transmitted through the dichroic mirror 302 propagates to the single-shot terahertz detection module 500 for detecting the terahertz light 602.

In this embodiment, the first delay component 303 delays the time by increasing the optical path of the excitation light 603, and is used to adjust the excitation light 603 to coincide with the time of flight of the terahertz light 602 at the sample. In this embodiment, excitation light 603 is directed to sample module 400 using a third off-axis parabolic objective 304 (OAP 3) of the same focal length. The third off-axis parabolic objective 304 is placed at a distance from the sample less than the focal length to produce a beam diameter large enough that the beam diameter of the excitation light 603 is greater than the spot diameter of the terahertz light 602 at the focal point. The remaining excitation light 603 is blocked by the second puck 305.

In this embodiment, the optical path schematic diagram of the single-shot terahertz detection module 500 is shown in fig. 3, and includes a terahertz unit 510, a detection light unit 520, a beam combiner 530, an electro-optical crystal 540, a beam splitter 550, a first imaging unit 560, and a second imaging unit 570. Wherein the terahertz unit 510 includes a fourth off-axis parabolic mirror 511 and a second reflecting mirror 512, which focus the incident single-shot terahertz light 602 at the electro-optic crystal 540. The detection light unit 520 comprises a second delay element 521, a stepped mirror 522, and a lens 523, each step of the stepped mirror 522 being capable of converting an incident single detection light 604 into a sequence of detection lights 604 of uniform time interval by specular reflection, the sequence of detection lights 604 coinciding with the time of flight of the single terahertz light 602 and being focused at the electro-optic crystal 540 by means of the lens 523.

The beam combiner 530 is configured to co-linearly propagate the single terahertz light 602 emitted from the terahertz unit 510 and the probe light 604 emitted from the probe light unit 520 to the electro-optical crystal 540. The electro-optical crystal 540 is disposed between the beam combiner 530 and the beam splitter 550, and is used for modulating the sequence of the probe light 604. The beam splitter 550 divides the detection light 604 emitted from the electro-optical crystal 540 into two beams of a first light sequence and a second light sequence according to the light intensity ratio, and the two beams are respectively incident to the first imaging unit 560 and the second imaging unit 570.

The first imaging unit 560 and the second imaging unit 570 include a first camera 561 and a second camera 571, respectively, which are both infrared cameras. The first camera 561 images the first light sequence to obtain a first image, the second camera 571 images the second light sequence to obtain a second image, and the first image and the second image obtain the time domain waveform of the single terahertz light 602 through a differential technology, that is, the terahertz time domain waveform can be obtained through analyzing the imaging of the infrared camera.

In addition, the terahertz unit 510 further includes a first terahertz wire grid 513 that polarizes the single-shot terahertz light 602. In this embodiment, two first terahertz wire grids 513 are employed, and in other embodiments, more terahertz wire grids may be used in order to enhance polarization. The detection light unit 520 further includes a main polarizer 524 that polarizes the detection light 604, so that the single-emission terahertz light 602 and the detection light 604 are polarized in the same direction.

In the present embodiment, the electro-optical crystal 540 is a zinc telluride crystal, and the beam combiner 530 is an ITO film. A first polarizer 562 is disposed between the first camera 561 and the beam splitter 550, and a second polarizer 572 is disposed between the second camera 571 and the beam splitter 550, and the polarization directions of the first polarizer 562 and the second polarizer 572 are perpendicular to the polarization direction of the main polarizer 524.

It should be noted that, the single-shot terahertz detection module 500 is not limited to the optional femtosecond laser module 100, the terahertz generation module 200, the excitation optical module 300, the sample module 400, and the like, and a person skilled in the art can apply the single-shot terahertz detection module 500 to most of low-frequency terahertz time-domain waveform detection (0.1 THz-3 THz) according to the above manner, and can be used as a single terahertz time-domain spectrometer, and can complete the detection of the terahertz time-domain waveform only by inputting two terahertz light 602 and the femtosecond laser 601 which are propagated in parallel to the single-shot terahertz detection module 500.

In a word, the scheme provided by the embodiment satisfies that each laser pulse can acquire a complete terahertz waveform, and after Fourier transformation, terahertz frequency spectrum information is obtained. In addition, the scheme provided by the embodiment is a compact laboratory-level single-shot terahertz time-domain spectrometer, the parameters such as time-domain spectrum, frequency-domain spectrum, dielectric constant, refractive index spectrum, phase spectrum, absorption spectrum, conductivity and the like of a sample can be obtained, the experimental system is stable in performance, high in repeatability and suitable for dynamic research in an irreversible process.

While the foregoing is directed to the preferred embodiments of the present utility model, it will be appreciated by those skilled in the art that various modifications and adaptations can be made without departing from the principles of the present utility model, and such modifications and adaptations are intended to be comprehended within the scope of the present utility model.

Claims (7)

1. The single-shot terahertz time-domain spectrometer is characterized by comprising a femtosecond laser module (100), a terahertz generation module (200), an excitation optical module (300), a sample module (400) and a single-shot terahertz detection module (500);

the femtosecond laser module (100) is used for generating femtosecond laser;

the terahertz generation module (200) comprises a nonlinear crystal (201), an ITO film (202) and a reflection focusing assembly, wherein the nonlinear crystal (201) is used for rectifying femtosecond laser to generate terahertz light, the ITO film (202) is used for separating the terahertz light from the femtosecond laser, the reflection focusing assembly is used for focusing the separated terahertz light to the sample module (400) and transmitting the terahertz light emitted by the sample module (400) to the single terahertz detection module (500);

the excitation light module (300) is used for splitting femtosecond laser emitted by the ITO film (202) into excitation light and detection light, the excitation light is used for being incident to the sample module (400), and the detection light is used for being incident to the single-shot terahertz detection module (500); the sample module (400) is used for positioning a sample to be detected;

the single-shot terahertz detection module (500) is used for detecting a transmission waveform and a transmission spectrum of a sample in a terahertz wave band.

2. The single-shot terahertz time-domain spectrometer according to claim 1, characterized in that the reflection focusing assembly comprises a first polyethylene disc (203), a first reflecting mirror (204), a first off-axis parabolic objective lens (205) and a second off-axis parabolic objective lens (206), the first polyethylene disc (203) is used for filtering out residual fundamental frequency light and frequency multiplication light in terahertz light, the first reflecting mirror (204) is provided with a plurality of reflection light paths, the first off-axis parabolic objective lens (205) is used for focusing terahertz light to the sample module (400), and the second off-axis parabolic objective lens (206) is used for collimating terahertz light emitted by the sample module (400) into parallel light.

3. The single-shot terahertz time-domain spectrometer according to claim 1, characterized in that the sample module (400) is further provided with a three-dimensional motorized translation stage for adjusting the micro-movement of the sample in three-dimensional space.

4. The single-shot terahertz time-domain spectrometer of claim 1, characterized in that the excitation light module (300) comprises a frequency doubling crystal (301) and a first delay component (303), the first delay component comprises a dichroic mirror (302), the frequency doubling crystal (301) is used for generating excitation light by frequency doubling femtosecond laser, the dichroic mirror (302) is used for transmitting the femtosecond laser and reflecting the excitation light, and the first delay component (303) is used for adjusting the optical path of the excitation light so that the flight time of the excitation light and the terahertz light in the sample module (400) coincide.

5. The single-shot terahertz time-domain spectrometer of claim 4, in which the excitation light module (300) further comprises a third off-axis parabolic objective (304), the third off-axis parabolic objective (304) propagating excitation light to the sample module (400) and focusing.

6. The single-shot terahertz time-domain spectrometer of claim 5, wherein a beam diameter of the excitation light at the sample module (400) location is greater than a beam diameter of the terahertz light.

7. The single-shot terahertz time-domain spectrometer of claim 1, wherein the single-shot terahertz detection module (500) includes a terahertz unit (510), a detection light unit (520), a beam combiner (530), an electro-optic crystal (540), a beam splitter (550), a first imaging unit (560), and a second imaging unit (570); the terahertz unit (510) is used for focusing incident single-shot terahertz light on the electro-optical crystal (540), the detection light unit (520) is used for converting the incident detection light into a detection light sequence with uniform interval time, and the detection light sequence is overlapped with the flight time of the single-shot terahertz light and is focused on the electro-optical crystal (540); the beam combining lens (530) is used for collinearly transmitting single terahertz light and detection light sequences to the electro-optical crystal (540), the electro-optical crystal (540) is arranged between the beam combining lens (530) and the beam splitting lens (550) and used for modulating the detection light sequences, and the beam splitting lens (550) is used for equally dividing the detection light sequences emitted by the electro-optical crystal (540) into a first light sequence and a second light sequence according to the light intensity ratio and respectively incident to the first imaging unit (560) and the second imaging unit (570); the first imaging unit (560) is used for imaging a first light sequence to obtain a first image, the second imaging unit (570) is used for imaging a second light sequence to obtain a second image, and the first image and the second image are used for obtaining a time domain waveform of single terahertz light.