阅读说明：本技术 太赫兹偏振信息及时域波形的单次测量装置及方法 (Single measurement device and method for terahertz polarization information and time domain waveform ) 是由 林庆钢 徐世祥 宋其迎 王弘耿 王宏宇 陆小微 蔡懿 于 2019-11-20 设计创作，主要内容包括：本发明公开一种太赫兹偏振信息及时域波形的单次测量装置及方法,包括：脉冲展宽单元对光源发出的探测超短脉冲进行展宽,生成啁啾探测脉冲,啁啾探测脉冲射入偏振调节单元；偏振调节单元调节啁啾脉冲的偏振方向,获得圆偏振啁啾探测脉冲。合束单元将所要探测的太赫兹脉冲及圆偏振啁啾探测脉冲合束,太赫兹调制单元调制圆偏振啁啾探测脉冲,使太赫兹脉冲波形加载到圆偏振啁啾探测脉冲,获得椭偏啁啾探测脉冲。相位延迟单元将椭偏啁啾探测脉冲相位延迟,接收单元获得入射的椭偏啁啾探测脉冲在某一线偏振方向的干涉光谱,通过对干涉光谱进行傅里叶变换和滤波处理,在单次测量中得到太赫兹脉冲的偏振及时域波形信息,结构简单,不受激光抖动的影响。(The invention discloses a single measurement device and a single measurement method for terahertz polarization information and time domain waveforms, wherein the single measurement device comprises the following steps: the pulse stretching unit stretches the detected ultrashort pulse emitted by the light source to generate a chirp detection pulse, and the chirp detection pulse is transmitted into the polarization adjusting unit; the polarization adjusting unit adjusts the polarization direction of the chirp pulse to obtain a circularly polarized chirp detection pulse. The beam combination unit combines the terahertz pulse to be detected and the circular polarization chirp detection pulse, and the terahertz modulation unit modulates the circular polarization chirp detection pulse to load the terahertz pulse waveform to the circular polarization chirp detection pulse to obtain the elliptic chirp detection pulse. The phase delay unit delays the phase of the ellipsometric chirp detection pulse, the receiving unit obtains an interference spectrum of the incident ellipsometric chirp detection pulse in a certain linear polarization direction, the interference spectrum is subjected to Fourier transform and filtering processing, polarization and time domain waveform information of the terahertz pulse are obtained in single measurement, the structure is simple, and the ellipsometric chirp detection pulse is not influenced by laser jitter.)

1. The device for measuring the terahertz polarization information and the time domain waveform at a single time is characterized by comprising the following components: the terahertz polarization modulation device comprises a pulse widening unit, a polarization adjusting unit, a beam combining unit, a terahertz modulation unit, a phase delay unit and a receiving unit;

the pulse stretching unit is used for stretching incident detection ultrashort pulses from a light source into chirp detection pulses, and the chirp detection pulses are incident to the polarization adjusting unit;

the polarization adjusting unit is used for adjusting the polarization direction of the incident chirp detection pulse into circular polarization to obtain a circular polarization chirp detection pulse, and the circular polarization chirp detection pulse is incident to the beam combining unit;

the beam combining unit is used for combining the terahertz pulse to be detected and the circularly polarized chirped detection pulse and transmitting the combined terahertz pulse to the terahertz modulation unit;

the terahertz modulation unit is used for loading the incident information of the terahertz pulse to the circular polarization chirp detection pulse to obtain a modulated elliptic polarization chirp detection pulse and transmitting the modulated elliptic polarization chirp detection pulse to the phase delay unit;

the phase delay unit is configured to introduce a birefringence phase delay to the modulated ellipsometric chirp detection pulse, decompose the modulated ellipsometric chirp detection pulse into three or four beams of polarization chirp detection pulses, and transmit the linear polarization chirp detection pulse to the receiving unit;

the receiving unit is used for obtaining an interference spectrum of the incident linear polarization chirp detection pulse, so that Fourier transform and filtering processing are carried out on the interference spectrum, and meanwhile, polarization information and time domain waveforms of the terahertz pulse are obtained.

2. The apparatus for single measurement of terahertz polarization information and time-domain waveforms of claim 1, wherein:

the pulse stretching unit comprises two prisms which are arranged oppositely and used for stretching the detection ultrashort pulse emitted by the light source into the chirp detection pulse and then the chirp detection pulse is incident to the polarization adjusting unit.

3. The apparatus for single measurement of terahertz polarization information and time-domain waveforms of claim 1, wherein:

the polarization adjusting unit comprises a first polarizer and a quarter-wave plate;

the first polarizer is used for adjusting the polarization direction of the incident chirp detection pulse into linear polarization to obtain a linear polarization detection pulse, and the linear polarization detection pulse is incident to the quarter-wave plate;

the quarter wave plate is used for adjusting the polarization direction of the linear polarization pulse to be circular polarization to obtain the circular polarization chirp detection pulse, and the circular polarization chirp detection pulse is incident to the terahertz modulation unit.

4. The apparatus for single measurement of terahertz polarization information and time-domain waveforms of claim 1, wherein:

the terahertz modulation unit comprises an electro-optic crystal, and the crystal direction of the electro-optic crystal is in the vertical direction.

5. The apparatus for single measurement of terahertz polarization information and time-domain waveforms of claim 1, wherein:

the phase delay unit comprises a first birefringent crystal and a second birefringent crystal;

the optical axis direction of the first birefringent crystal forms an included angle of 0 degree or 90 degrees with the horizontal direction, and the first birefringent crystal is used for providing birefringent phase delay for the modulated ellipsometric chirp detection pulse in the horizontal and vertical directions, modulating the modulated ellipsometric chirp detection pulse into two horizontal and vertical polarization linear polarization chirp detection pulses with phase delay between the two pulses, and irradiating the two pulses to the second birefringent crystal;

the optical axis direction of the second birefringent crystal forms an included angle of 45 degrees or-45 degrees with the horizontal direction, and the second birefringent crystal is used for providing birefringent phase delay for the two beams of linear polarization chirp detection pulses in the direction of 45 degrees or-45 degrees, and decomposing the two beams of linear polarization chirp detection pulses into three beams or four beams of linear polarization chirp detection pulses with 45-degree polarization or-45-degree polarization and phase delay between the three beams or four beams.

6. The apparatus for single measurement of terahertz polarization information and time-domain waveforms of claim 1, wherein:

the phase delay unit further comprises a second polarizer, and the polarization direction of the second polarizer is a horizontal direction or a vertical direction and is used for limiting the polarization direction of the linear polarization detection pulse.

7. The single-time measurement device for terahertz polarization information and time-domain waveforms according to any one of claims 1 to 6, wherein: the receiving unit comprises a spectrometer and is used for obtaining an interference spectrum of the incident linear polarization chirp detection pulse, so that the interference spectrum is subjected to Fourier transform and filtering processing, and meanwhile, polarization information and time domain waveforms of the terahertz pulse are obtained.

8. A single measurement method for terahertz polarization information and time domain waveforms is characterized by comprising the following steps:

controlling a pulse extension unit to widen a detected ultrashort pulse from a light source into a chirp detection pulse, wherein the chirp detection pulse is incident to the polarization adjustment unit;

controlling a polarization adjusting unit to adjust the polarization direction of the incident chirp detection pulse into circular polarization to obtain a circular polarization chirp detection pulse, and enabling the obtained circular polarization chirp detection pulse to be incident to the beam combining unit;

controlling a beam combining unit to combine the terahertz pulse to be detected and the circularly polarized chirped detection pulse and enable the combined terahertz pulse and the circularly polarized chirped detection pulse to be incident to the terahertz modulation unit;

controlling a terahertz modulation unit to load the incident information of the terahertz pulse to the circularly polarized chirped detection pulse to obtain a modulated elliptically polarized chirped detection pulse and incident the modulated elliptically polarized chirped detection pulse to the phase delay unit;

controlling a phase delay unit to introduce birefringence phase delay to the modulated ellipsometric chirp detection pulse, decomposing the modulated ellipsometric chirp detection pulse into three beams or four beams of polarization chirp detection pulses, and enabling the linear polarization chirp detection pulse to be incident to a receiving unit;

and controlling a receiving unit to obtain an interference spectrum of the incident linear polarization chirp detection pulse, so as to obtain polarization information and a time domain waveform of the terahertz pulse by performing Fourier transform and filtering processing on the interference spectrum.

9. The method for single measurement of terahertz polarization information and time-domain waveforms according to claim 8, wherein: the phase delay unit comprises a first birefringent crystal with an included angle of 0 degree or 90 degrees between the optical axis direction and the horizontal direction, a second birefringent crystal with an included angle of 45 degrees or minus 45 degrees between the optical axis direction and the horizontal direction and a second polarizer;

the controlling the phase delay unit introduces a birefringence phase delay to the modulated ellipsometric chirp detection pulse, and decomposes the modulated ellipsometric chirp detection pulse into three beams or four beams of polarization chirp detection pulses, where the linear polarization chirp detection pulse is incident to the receiving unit, including:

controlling the first refraction double crystal to provide birefringent phase delay for the modulated ellipsometric chirp detection pulse in the horizontal and vertical directions, modulating the modulated ellipsometric chirp detection pulse into two beams of horizontal and vertical polarization linear polarization chirp detection pulses with phase delay between the two beams, and enabling the two beams to be incident to the second birefringence crystal of which the optical axis direction and the horizontal direction form an included angle of 45 degrees or-45 degrees;

controlling the second birefringent crystal to provide birefringent phase delay for the two beams of the linear polarization chirp detection pulses in the direction of 45 degrees or-45 degrees, and decomposing the two beams of the linear polarization chirp detection pulses into three beams or four beams of linear polarization chirp detection pulses with 45-degree polarization or-45-degree polarization and phase delay between the three beams of the linear polarization chirp detection pulses;

controlling the second polarizer to limit the polarization direction of the linearly polarized probe pulse.

Technical Field

The invention relates to the technical field of terahertz optics, in particular to a single-time measuring device and method for terahertz polarization information and time domain waveforms.

Background

The terahertz wave is an electromagnetic wave with a frequency band of 0.1-10 THz and is positioned between microwave and infrared light. Due to its special band range, the light source and detection technology of terahertz waves was seriously lacking before 1980, and thus this band was called "terahertz blank" at that time. However, with the development of the ultra-short pulse technology, the related generation and detection means of the terahertz wave are rapidly developed, and the excellent characteristics of the terahertz wave are more and more emphasized by people, and the advantages thereof include: the material has the advantages of low photon energy (single photon energy is only in the magnitude of meV), high penetrability (for some non-polar materials), strong absorptivity (for most polar materials), and the like, and can be widely applied to the fields of medical imaging, security inspection, optical communication, and the like.

Currently, methods for detecting terahertz pulses include a photoconductive method based on a photoconductive antenna, an electro-optic sampling method based on a linear electro-optic effect of an electro-optic crystal, and an ABCD method based on air plasma. However, most of these methods are limited to detecting single polarization information of the terahertz pulse, which not only loses part of the terahertz information, but also cannot detect the polarization-related characteristic of the object. For example, chiral discrimination of chiral molecules, non-contact measurement of electronic characteristics, etc., and thus some terahertz polarization detection methods have appeared, for example, ABCD polarization detection method based on additional orthogonal arrangement voltage, electro-optical sampling polarization detection method based on rotating electro-optical crystal or half-wave plate, etc. Although the methods can realize the measurement of the terahertz pulse polarization information, the terahertz pulse polarization information still needs to be scanned and measured by a translation table or a rotating device for multiple times of detection, and the terahertz pulse polarization information cannot be detected once, so that the polarization-related characteristics of a rapidly-changing sample cannot be analyzed.

Disclosure of Invention

The invention mainly aims to provide a device and a method for measuring terahertz polarization information and time domain waveforms at a single time, and aims to solve the technical problem of measuring terahertz polarization information and time domain waveforms at a single time in the prior art.

In order to achieve the above object, a first aspect of the present invention provides a single-shot measurement apparatus for terahertz polarization information and time domain waveforms, including: the terahertz polarization modulation device comprises a pulse widening unit, a polarization adjusting unit, a beam combining unit, a terahertz modulation unit, a phase delay unit and a receiving unit;

the pulse stretching unit is used for stretching incident detection ultrashort pulses from a light source into chirp detection pulses, and the chirp detection pulses are incident to the polarization adjusting unit;

the polarization adjusting unit is used for adjusting the polarization direction of the incident chirp detection pulse into circular polarization to obtain a circular polarization chirp detection pulse, and the circular polarization chirp detection pulse is incident to the beam combining unit;

the beam combining unit is used for combining the terahertz pulse to be detected and the circularly polarized chirped detection pulse and transmitting the combined terahertz pulse to the terahertz modulation unit;

the terahertz modulation unit is used for loading the incident information of the terahertz pulse to the circular polarization chirp detection pulse to obtain a modulated elliptic polarization chirp detection pulse and transmitting the modulated elliptic polarization chirp detection pulse to the phase delay unit;

the phase delay unit is configured to introduce a birefringence phase delay to the modulated ellipsometric chirp detection pulse, decompose the modulated ellipsometric chirp detection pulse into three or four beams of polarization chirp detection pulses, and transmit the linear polarization chirp detection pulse to the receiving unit;

the receiving unit is used for obtaining an interference spectrum of the incident linear polarization chirp detection pulse, so that Fourier transform and filtering processing are carried out on the interference spectrum, and meanwhile, polarization information and time domain waveforms of the terahertz pulse are obtained.

The second aspect of the present invention provides a method for single measurement of terahertz polarization information and time domain waveform, including:

controlling a pulse extension unit to widen a detected ultrashort pulse from a light source into a chirp detection pulse, wherein the chirp detection pulse is incident to the polarization adjustment unit;

controlling a polarization adjusting unit to adjust the polarization direction of the incident chirp detection pulse into circular polarization to obtain a circular polarization chirp detection pulse, and enabling the obtained circular polarization chirp detection pulse to be incident to the beam combining unit;

controlling a beam combining unit to combine the terahertz pulse to be detected and the circularly polarized chirped detection pulse and enable the combined terahertz pulse and the circularly polarized chirped detection pulse to be incident to the terahertz modulation unit;

controlling a terahertz modulation unit to load the incident information of the terahertz pulse to the circularly polarized chirped detection pulse to obtain a modulated elliptically polarized chirped detection pulse and incident the modulated elliptically polarized chirped detection pulse to the phase delay unit;

controlling a phase delay unit to introduce birefringence phase delay to the modulated ellipsometric chirp detection pulse, decomposing the modulated ellipsometric chirp detection pulse into three beams or four beams of polarization chirp detection pulses, and enabling the linear polarization chirp detection pulse to be incident to a receiving unit;

and controlling a receiving unit to obtain an interference spectrum of the incident linear polarization chirp detection pulse, so as to obtain polarization information and a time domain waveform of the terahertz pulse by performing Fourier transform and filtering processing on the interference spectrum.

As can be seen from the above description, the terahertz polarization information and time domain waveform single measurement device is used in combination with the terahertz polarization information and time domain waveform single measurement method, so that the system structure can be simplified and the measurement can be performed at the same time, the measurement process is not affected by laser jitter, and the polarization and time domain waveform information of the terahertz pulse can be obtained at the same time by only one detection.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic structural diagram of a single measurement apparatus for terahertz polarization information and time domain waveforms according to a first embodiment of the present invention;

FIG. 2 is a schematic connection diagram of a single-pass measurement apparatus for terahertz polarization information and time-domain waveforms according to a first embodiment of the present invention;

fig. 3 is a schematic flow chart illustrating an implementation of the terahertz polarization information and time domain waveform single measurement apparatus according to the first embodiment of the present invention;

FIG. 4 is a flow chart of a single measurement method according to a first embodiment of the present invention;

100-a light source; 110-a pulse stretching unit; 111-a prism; 120-a polarization adjustment unit; 121-a first polarizer; 122-quarter wave plate; 130-a beam combining unit; 131-a parabolic mirror; 140-a terahertz modulation unit; 141-an electro-optic crystal; 150-phase delay unit; 151-first birefringent crystal; 152-a second birefringent crystal; 153-a second polarizer; 160-a receiving unit; 161-spectrometer.

Detailed Description

In order to make the objects, features and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Fig. 1 is a schematic structural diagram of a single measurement apparatus for terahertz polarization information and time-domain waveforms according to a first embodiment of the present invention. In this embodiment, a single measurement device for terahertz polarization information and time domain waveform is provided, including: the terahertz wave detector comprises a pulse stretching unit 110, a polarization adjusting unit 120, a beam combining unit 130, a terahertz modulating unit 140, a phase delay unit 150 and a receiving unit 160;

the light source 100 can be a titanium-doped sapphire femtosecond laser, and the output ultrashort pulse is a femtosecond laser with the central wavelength of 800nm and the pulse width of 35 fs.

The pulse stretching unit 110 stretches the detected ultrashort pulse emitted by the light source 100 to generate a chirp detection pulse, and the chirp detection pulse is incident into the polarization adjusting unit 120; the polarization adjustment unit 120 adjusts the polarization direction of the chirped pulse, obtaining a circularly polarized chirped probe pulse. The beam combining unit 130 combines the terahertz pulse to be detected and the circularly polarized chirped detection pulse, and the terahertz modulation unit 140 modulates the circularly polarized chirped detection pulse, so that the whole terahertz pulse waveform is loaded to the circularly polarized chirped detection pulse, and the elliptically polarized chirped detection pulse is obtained. The phase delay unit 150 performs phase delay processing on the elliptically polarized chirped detection pulse, then the receiving unit 160 obtains an interference spectrum of the incident linearly polarized chirped detection pulse, and the polarization and time domain waveform information of the terahertz pulse can be obtained simultaneously in a single measurement by performing fourier transform and filtering processing on the interference spectrum.

Referring to fig. 2 and 3, fig. 2 is a schematic connection diagram of a single measurement device for terahertz polarization information and time-domain waveforms according to a first embodiment of the present invention; fig. 3 is a schematic flow chart illustrating an implementation of the terahertz polarization information and time domain waveform single measurement method according to the first embodiment of the present invention.

Specifically, the pulse stretching unit 110 includes two prisms 111 disposed opposite to each other, and is configured to stretch the detection ultrashort pulse emitted from the light source 100 into a chirped detection pulse, and to be incident on the polarization adjustment unit 120.

The pulse widening unit 110 is arranged opposite to the polarization adjusting unit 120, and can be an isosceles right-angle prism 111 made of two pieces of quartz glass, the right-angle side length of the isosceles right-angle prism 111 is 60mm, and the material is ZF 52. The isosceles right prism 111 is used to introduce material dispersion, thereby broadening the detected ultrashort pulse output from the light source 100 into a chirped pulse with a pulse width of 12ps, and transmitting the chirped pulse to the polarization adjustment unit 120. The chirp pulse is a pulse with frequency changing with time, and different frequencies of the incident detection pulse carry different phase delays by using material dispersion of a prism pair, so that each frequency component of the detection pulse is staggered in time to become the detection chirp pulse. The purpose of widening the probe pulse into a chirped pulse is to achieve a single measurement of a terahertz pulse using a time-frequency mapping relationship.

Specifically, the polarization adjustment unit 120 includes a first polarizer 121 and a quarter-wave plate 122;

a first polarizer 121 for adjusting the polarization direction of the incident chirped detection pulse to be linear polarization to obtain a linear polarization detection pulse, and the linear polarization detection pulse is incident to the quarter-wave plate 122;

the quarter wave plate 122 is configured to adjust the polarization direction of the linearly polarized pulse to be circularly polarized, so as to obtain a circularly polarized chirp detection pulse, where the circularly polarized chirp detection pulse is incident to the terahertz modulation unit 140.

A first polarizer 121 disposed opposite to the quarter-wave plate 122, and optionally using a graham laser prism 111, having an optical axis in a horizontal direction, for adjusting a polarization direction of the incident chirp detection pulse to a horizontal linear polarization, and transmitting the horizontal linear polarization to the quarter-wave plate 122; the polarization direction of the ultra-short pulse output by the titanium sapphire femtosecond laser is horizontal polarization, and the first polarizer 121 can avoid polarization change caused by a prism pair.

The quarter-wave plate 122 is disposed opposite to the beam combining unit 130, and may be an 800nm broadband zero-order quarter-wave plate 122, and the fast axis or slow axis direction of the quarter-wave plate forms an included angle of 45 degrees with the horizontal direction, so as to adjust the polarization direction of the linearly polarized chirp detection pulse to be circularly polarized and transmit the linearly polarized chirp detection pulse to the beam combining unit 130.

Specifically, the beam combining unit 130 may select an off-axis parabolic mirror 131 with a small hole, the detection pulse is transmitted to the terahertz adjusting unit after passing through the small hole, the terahertz pulse to be detected is reflected and focused by the off-axis parabolic mirror 131 and then transmitted to the terahertz adjusting unit, and the detection pulse and the ultrafast terahertz pulse to be detected are combined by adjusting the off-axis parabolic mirror 131.

Optionally, the terahertz modulation unit 140 applies a zinc telluride crystal (ZnTe) 1mm thick with the light emitting crystal 141 being a (111) crystal face, the crystal orientation (0-11) of which is set in the vertical direction, and modulates the measured ultrafast terahertz pulse onto the detection pulse by using the linear electro-optic effect, because the detection pulse is a chirp pulse, the pulse range of the detection pulse is larger than that of the terahertz pulse by reasonably setting the chirp amount of the chirp pulse, so that the entire terahertz pulse waveform is loaded onto the detection pulse, thereby implementing the single measurement of the terahertz pulse.

The linear electro-optic effect is a second-order nonlinear effect, under the action of an electro-optic field and a low-frequency electric field or a direct-current electric field, a crystal without an inversion center can cause the birefringence phase difference of the crystal, the birefringence phase difference is in direct proportion to the low-frequency electric field or the direct-current electric field, and the terahertz pulse serves as the low-frequency electric field or the direct-current electric field. Since the detection pulse is a chirped pulse, according to the time-frequency mapping relationship, terahertz pulses at different time instants are loaded onto different frequency components of the detection pulse.

Specifically, the phase delay unit 150 includes a first birefringent crystal 151 and a second birefringent crystal 152;

the first birefringent crystal 151 has an included angle of 0 degree or 90 degrees between the optical axis direction and the horizontal direction, and is configured to provide birefringent phase delays to the modulated circularly polarized chirp detection pulses in the horizontal and vertical directions, modulate the modulated circularly polarized chirp detection pulses into two horizontally and vertically polarized linearly polarized chirp detection pulses with phase delays therebetween, and inject the two linearly polarized chirp detection pulses into the second birefringent crystal 152;

a first birefringent crystal 151, which is optionally a 6mm thick α -BBO crystal, having an optical axis in a horizontal direction, for introducing a birefringent phase difference between horizontal and vertical components of an incident circularly polarized chirp detection pulse, and transmitting the birefringent phase difference to a second birefringent crystal 152;

the second birefringent crystal 152 has an included angle of 45 degrees or-45 degrees between the optical axis direction and the horizontal direction, and is used for providing birefringent phase delay for the two linearly polarized chirp detection pulses in the 45 degrees or-45 degrees direction, and decomposing the two linearly polarized chirp detection pulses into three or four linearly polarized chirp detection pulses with phase delay between each other and with 45o polarization or-45 o polarization.

A second birefringent crystal 152, which may be a 6mm thick α -BBO crystal having an optical axis oriented at 45 ° to the horizontal, for introducing a birefringent phase difference between 45 ° and-45 ° components of the incident chirp detection pulse, and transmitting the resultant to a second polarizer 153;

further, the phase delay unit 150 further includes a second polarizer 153, and the polarization direction of the second polarizer 153 is a horizontal direction or a vertical direction, and is used for limiting the polarization direction of the linearly polarized probe pulse.

The second polarizer 153 is disposed opposite to the receiving unit 160, and may be a grazing laser prism 111 having an optical axis in a horizontal direction, so as to allow only the detection pulse in the horizontal direction to pass through and be transmitted to the receiving unit 160.

Specifically, the receiving unit 160 includes a spectrometer 161, and the spectrometer 161 is configured to obtain an interference spectrum of the incident linearly polarized chirped detection pulse, so as to simultaneously obtain polarization information and a time domain waveform of the terahertz pulse by performing fourier transform and filtering processing on the interference spectrum. The spectrometer 161 may be a fiber optic spectrometer 161, of the type HR 4000.

Referring to fig. 4, fig. 4 is a schematic flow chart of a single measurement method according to a first embodiment of the present invention; in this embodiment, a method for measuring terahertz polarization information and a time domain waveform in a single time is provided, which specifically includes:

step S110, controlling the pulse expanding unit 110 to widen the detected ultrashort pulse from the light source 100 into a chirp detection pulse, where the chirp detection pulse is incident to the polarization adjusting unit 120;

step S120, controlling the polarization adjustment unit 120 to adjust the polarization direction of the incident chirp detection pulse to be circular polarization, obtaining a circular polarization chirp detection pulse, and allowing the obtained circular polarization chirp detection pulse to be incident to the beam combining unit 130;

step S130, controlling the beam combining unit 130 to combine the terahertz pulse to be detected and the circularly polarized chirped detection pulse and to inject the combined terahertz pulse and the circularly polarized chirped detection pulse into the terahertz modulating unit 140;

step S140, controlling the terahertz modulation unit 140 to load the incident terahertz pulse information to the circularly polarized chirped detection pulse, obtaining a modulated ellipsometric chirped detection pulse, and emitting the modulated ellipsometric chirped detection pulse to the phase delay unit 150;

step S150, controlling the phase delay unit 150 to introduce a birefringence phase delay to the modulated ellipsometric chirp detection pulse, decomposing the modulated ellipsometric chirp detection pulse into three or four beams of polarization chirp detection pulses, and transmitting the linear polarization chirp detection pulses to the receiving unit 160;

step S160, controlling the receiving unit 160 to obtain the interference spectrum of the incident linear polarization chirp detection pulse, so as to obtain the polarization information and the time domain waveform of the terahertz pulse at the same time by performing fourier transform and filtering processing on the interference spectrum.

In the above-mentioned single measurement method of terahertz polarization information and time domain waveform, the phase delay unit 150 includes a first birefringent crystal 151 whose optical axis direction forms an included angle of 0 degree or 90 degrees with the horizontal direction, a second birefringent crystal 152 whose optical axis direction forms an included angle of 45 degrees or-45 degrees with the horizontal direction, and a second polarizer 153;

the controlling phase delay unit 150 introduces a birefringent phase delay to the modulated ellipsometric chirp detection pulse, decomposes the modulated ellipsometric chirp detection pulse into three or four beams of polarization chirp detection pulse, and the linear polarization chirp detection pulse is incident to the receiving unit 160, including:

controlling the first refraction double crystal to provide birefringent phase delay for the modulated ellipsometric chirp detection pulse in the horizontal and vertical directions, modulating the modulated ellipsometric chirp detection pulse into two horizontal and vertical polarization linear polarization chirp detection pulses with phase delay between them, and irradiating to the second birefringence crystal 152 with an included angle of 45 degrees or-45 degrees between the optical axis direction and the horizontal direction;

controlling the second birefringent crystal 152 to provide birefringent phase delays in the 45-degree or-45-degree directions for the two linearly polarized chirp detection pulses, and decomposing the two linearly polarized chirp detection pulses into three or four linearly polarized chirp detection pulses with phase delays between each other, wherein the three or four linearly polarized chirp detection pulses are 45-degree polarized or-45-degree polarized;

the second polarizer 153 is controlled to limit the polarization direction of the linearly polarized probe pulse.

In order to more clearly illustrate the working principle of the terahertz polarization information and time domain waveform single measurement device, the following further introduces from the theoretical direction.

Let the probe pulse be (Ex, Ey), and the stokes parameter of the probe pulse after passing through the pulse stretching unit 110, the polarization adjusting unit 120, the beam combining unit 130, and the terahertz modulating unit 140 can be expressed as:

in the formula, alpha is an included angle between the polarization direction of the terahertz pulse to be detected and the (0-11) crystal direction of the (111) crystal face zinc telluride crystal,

a birefringence phase difference caused by the terahertz pulse to be detected. From this equation, the horizontal component of the detected terahertz pulse is proportional to S2, and the vertical component is proportional to S1. The terahertz polarization information and time domain waveform single measurement device is used for simultaneously detecting Eout Stokes parameters S1 and S2.

The spectrum of the probe pulse obtained in the spectrometer 161 can be expressed as:

in the formula, S₂₃(λ)＝S₂(λ)-iS₃(λ)，arg[S₂₃(λ)]Is S₂₃The argument of (lambda), -2 pi L lambda + phi (lambda) is the birefringence phase difference introduced by the alpha-BBO crystal,

Φ(λ)＝(φ₀(lambda) +2 pi L) + o (lambda), where d is the crystal thickness, lambda₀In order to detect the center wavelength of the pulse,i.e., 800nm, o (λ) is the higher order term of the taylor expansion.

Performing inverse fourier transform on equation (2) to obtain:

wherein the content of the first and second substances,

s1(λ) and S2(λ) can be obtained from equation (3) using fourier transform and filtering processing:

in the formula, phi (lambda) and S0 (lambda) can be calibrated in advance without terahertz pulses. By obtaining S1 (lambda) and S2 (lambda), the time domain waveforms of the horizontal and vertical components of the terahertz pulse can be obtained, and therefore single measurement of the polarization and time domain information of the terahertz pulse is achieved.

Furthermore, the terahertz polarization information and the crystal thickness of the time domain waveform single measurement device are reasonably selected according to the required detection terahertz pulse. The selection of the crystal thickness affects the central frequency and the bandwidth range of the terahertz pulses that can be detected, and also has certain requirements on the resolution of the spectrometer 161 used, and the corresponding relationships are respectively (the spectral width within-80 dB of the spectrum is taken as the spectral range in the formula calculation):

in the formula, b is a chirp coefficient introduced by the prism 111, c is a speed of light, ω 0 is a center frequency of the terahertz pulse to be detected, and τ p is a pulse width of the terahertz pulse to be detected.

For an alpha-BBO crystal of 6mm, under the condition of detecting pulse, the requirements of the center wavelength and the spectrum width of the terahertz pulse which can be detected and the resolution of the used spectrometer 161 are as follows:

Δλ≤0.1nm

according to the embodiment, the system structure can be simplified by utilizing the terahertz polarization information and the time domain waveform single measurement device, the measurement process is not influenced by laser jitter, and the polarization and the time domain waveform information of the terahertz pulse can be obtained simultaneously only by single detection.

For details that are not described in the present embodiment, please refer to the description of the embodiment shown in fig. 1 to fig. 4, which will not be described herein again.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

It should be noted that the above-mentioned embodiments of the apparatus and method are described as a series of acts or combinations for simplicity of description, but it should be understood by those skilled in the art that the present invention is not limited by the order of acts or steps described, as some steps may occur in other orders or concurrently according to the present invention. Further, those skilled in the art will appreciate that the embodiments described in the specification are presently preferred and that no acts or modules are necessarily required of the invention.

In the above embodiments, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments.

In the above description, for those skilled in the art, there are variations on the specific implementation and application range according to the concepts of the embodiments of the present invention, and in summary, the content of the present specification should not be construed as a limitation to the present invention.