CN220730041U - A system for measuring terahertz pulse group velocity in a sample - Google Patents

A system for measuring terahertz pulse group velocity in a sample Download PDF

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CN220730041U
CN220730041U CN202222840249.6U CN202222840249U CN220730041U CN 220730041 U CN220730041 U CN 220730041U CN 202222840249 U CN202222840249 U CN 202222840249U CN 220730041 U CN220730041 U CN 220730041U
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terahertz
sample
group velocity
parabolic reflector
pulse
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赵航
赵跃进
谭永
董立泉
刘明
孔令琴
褚旭红
许靖
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Yangtze River Delta Research Institute Of Beijing University Of Technology Jiaxing
Beijing Institute of Technology BIT
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Yangtze River Delta Research Institute Of Beijing University Of Technology Jiaxing
Beijing Institute of Technology BIT
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Abstract

The utility model discloses a system for measuring terahertz pulse group velocity in a sample, and relates to the technical field of terahertz wave band optical measurement. The optical system comprises a laser, a spectroscope, an optical parametric amplifier, a chopper, a terahertz generation crystal, a terahertz filter, a first off-axis parabolic reflector, a second off-axis parabolic reflector, a third off-axis perforated parabolic reflector, an optical delay device, a first convex lens, a measured sample, a second convex lens, a quarter wave plate, a Wollaston prism and a photoelectric balance detector, wherein the laser, the spectroscope, the optical parametric amplifier, the chopper and the terahertz generation crystal are arranged on an optical path. The system has the advantages of simple structure, low construction cost, high stability, strong repairability and easy maintenance.

Description

一种样品中太赫兹脉冲群速度的测量系统A system for measuring terahertz pulse group velocity in a sample

技术领域Technical Field

本实用新型涉及太赫兹波段光学测量技术领域,具体而言,涉及一种样品中太赫兹脉冲群速度的测量系统。The utility model relates to the technical field of terahertz band optical measurement, in particular to a measurement system for terahertz pulse group velocity in a sample.

背景技术Background technique

色散,即材料的折射率随入射光频率的变化而变化的特性,该色散特性会造成脉冲展宽、群相位失匹配等现象,制约了自由空间光学系统、光纤通讯系统向高质量方向的发展。而含有丰富频率成分的光脉冲在样品内的传播速度就是由色散和折射率共同决定。色散和折射率测量实质就是测量不同频率的光脉冲在色散介质中传输相同距离所用的时间延迟,或测量具有丰富频率分量的光脉冲在色散介质中的群速度。Dispersion is the property that the refractive index of a material changes with the frequency of the incident light. This dispersion property can cause pulse broadening and group phase mismatch, which restricts the development of free-space optical systems and fiber-optic communication systems towards high quality. The propagation speed of light pulses with rich frequency components in the sample is determined by both dispersion and refractive index. The essence of dispersion and refractive index measurement is to measure the time delay for light pulses of different frequencies to transmit the same distance in a dispersive medium, or to measure the group velocity of light pulses with rich frequency components in a dispersive medium.

目前,针对紫外、可见光、红外等频段样品色散或群速度测量方法有很多,包括时延法、相移法、干涉法等。例如,时延法是测量不同频率光脉冲通过样品的时延量,进而通过多项式拟合得到群速度值;相移法通过比较参考值和测量值之间的相位差,从而得到群速度值;干涉法利用迈克尔逊干涉仪,通过调节迈克尔逊干涉仪的参考臂和测量臂的相对距离,得出参考值和测量值之间的相位差。但上述方法,难以用于测量太赫兹频段内脉冲的群速度参数,阻碍太赫兹频率内群速度参数测量的因素可能有以下三点:At present, there are many methods for measuring the dispersion or group velocity of samples in the ultraviolet, visible light, infrared and other frequency bands, including the time delay method, phase shift method, interference method, etc. For example, the time delay method measures the time delay of light pulses of different frequencies passing through the sample, and then obtains the group velocity value through polynomial fitting; the phase shift method obtains the group velocity value by comparing the phase difference between the reference value and the measured value; the interference method uses a Michelson interferometer to adjust the relative distance between the reference arm and the measurement arm of the Michelson interferometer to obtain the phase difference between the reference value and the measured value. However, the above methods are difficult to use to measure the group velocity parameters of pulses in the terahertz frequency band. The factors that hinder the measurement of group velocity parameters in the terahertz frequency may be the following three points:

(1)太赫兹脉冲通常包含非常丰富的频率成分,其频率覆盖范围通常超过5倍频程,通过测量所有单一频率的时延或相位以最终获得太赫兹脉冲群速度的方式,具有非常巨大的工作量且对系统的稳定性需求极高。(1) Terahertz pulses usually contain a very rich frequency component, and their frequency coverage range usually exceeds 5 octaves. The method of measuring the time delay or phase of all single frequencies to ultimately obtain the terahertz pulse group velocity is extremely labor-intensive and places extremely high demands on the stability of the system.

(2)太赫兹脉冲的频谱分布通常是不规则的,不服从严格的高斯型,通过每一频点的时延或相位参数只能近似计算整个太赫兹脉冲的群速度。(2) The spectral distribution of terahertz pulses is usually irregular and does not obey a strict Gaussian shape. The group velocity of the entire terahertz pulse can only be approximately calculated by the time delay or phase parameters of each frequency point.

(3)受太赫兹源和探测器技术水平的限制,搭建太赫兹频段内时延法、相移法或干涉法测量太赫兹脉冲群速度参数的系统难度较高。(3) Due to the limitations of the technology level of terahertz sources and detectors, it is difficult to build a system that measures the velocity parameters of terahertz pulse groups by using the time delay method, phase shift method or interference method within the terahertz frequency band.

因此,亟需一种新的测量装置,实现对样品内太赫兹脉冲群速度参数的直接测量。Therefore, a new measurement device is urgently needed to realize the direct measurement of the terahertz pulse group velocity parameters in the sample.

实用新型内容Utility Model Content

本实用新型提供的一种样品中太赫兹脉冲群速度的测量系统就是利用物质内普遍存在的克尔效应对样品内太赫兹脉冲群速度参数进行测量,本实用新型中测量太赫兹脉冲群速度的灵敏度可以达到0.001mm/ps,可以应用于对频率组成成分复杂的太赫兹脉冲在样品内的群速度值进行测量。The utility model provides a system for measuring the group velocity of terahertz pulses in a sample, which uses the Kerr effect that is ubiquitous in materials to measure the group velocity parameters of terahertz pulses in the sample. The sensitivity of measuring the group velocity of terahertz pulses in the utility model can reach 0.001mm/ps, and can be applied to measuring the group velocity values of terahertz pulses with complex frequency components in samples.

为达上述目的,本实用新型提供了一种样品中太赫兹脉冲群速度的测量系统,其包括设置在光路上的激光器、分光镜、光参量放大器、斩波器、太赫兹产生晶体,太赫兹滤波片、第一离轴抛物面反射镜、第二离轴抛物面反射镜、第三离轴打孔抛物面反射镜、光学延迟装置、第一凸透镜、被测样品、第二凸透镜、四分之一波片、沃拉斯顿棱镜、光电平衡探测器;其中:To achieve the above-mentioned purpose, the utility model provides a system for measuring the group velocity of terahertz pulses in a sample, which comprises a laser, a spectroscope, an optical parametric amplifier, a chopper, a terahertz generating crystal, a terahertz filter, a first off-axis parabolic reflector, a second off-axis parabolic reflector, a third off-axis perforated parabolic reflector, an optical delay device, a first convex lens, a sample to be measured, a second convex lens, a quarter-wave plate, a Wollaston prism, and a photoelectric balance detector arranged on an optical path; wherein:

所述激光器优选钛蓝宝石飞秒激光放大器,用于发射波长为800nm、脉冲宽度为35fs的激光,800nm的飞秒激光经过所述分光镜分出一束作为泵浦光和一束作为探测光。泵浦光通过所述光参量放大器,转化为波长为800~2600nm中任意波长、脉冲宽度为50fs的激光,并通过所述斩波器、所述太赫兹产生晶体产生太赫兹脉冲;太赫兹脉冲经过所述太赫兹滤波片滤除杂散光,再依次经过所述第一离轴抛物面反射镜、第二离轴抛物面反射镜进行波前调制,之后再经由第三离轴打孔抛物面反射镜反射后聚焦至所述被测样品。探测光依次经过所述光学延迟装置、所述第一凸透镜、所述第三离轴打孔抛物面反射镜后与太赫兹脉冲共同聚焦于所述被测样品上,所述被测样品由强太赫兹脉冲激发三阶非线性克尔效应,导致同时聚焦于所述被测样品上的探测光发生偏振旋转;受太赫兹脉冲调制的探测光脉冲经由所述第二凸透镜汇聚成平行光后通过所述四分之一波片、所述沃拉斯顿棱镜进行偏振态分束后,通过所述光电平衡探测器进行信号采集;调节所述光学延迟装置,可以得到用以计算样品太赫兹脉冲群速度的时间延迟信息。The laser is preferably a titanium sapphire femtosecond laser amplifier, which is used to emit a laser with a wavelength of 800nm and a pulse width of 35fs. The 800nm femtosecond laser is separated into a beam as a pump light and a beam as a detection light through the beam splitter. The pump light is converted into a laser with a wavelength of any wavelength between 800 and 2600nm and a pulse width of 50fs through the optical parametric amplifier, and a terahertz pulse is generated through the chopper and the terahertz generating crystal; the terahertz pulse passes through the terahertz filter to filter out stray light, and then passes through the first off-axis parabolic reflector and the second off-axis parabolic reflector in turn for wavefront modulation, and then is reflected by the third off-axis perforated parabolic reflector and focused to the sample under test. The detection light passes through the optical delay device, the first convex lens, and the third off-axis perforated parabolic reflector in sequence, and is focused on the sample under test together with the terahertz pulse. The sample under test is excited by the third-order nonlinear Kerr effect of the strong terahertz pulse, causing the detection light focused on the sample under test to undergo polarization rotation; the detection light pulse modulated by the terahertz pulse is converged into parallel light by the second convex lens, and then passes through the quarter-wave plate and the Wollaston prism for polarization state splitting, and then the signal is collected by the photoelectric balanced detector; the optical delay device is adjusted to obtain time delay information for calculating the sample terahertz pulse group velocity.

在本实用新型的一实施例中,所述被测样品厚度在300μm~3mm之间。In an embodiment of the present invention, the thickness of the sample to be measured is between 300 μm and 3 mm.

在本实用新型的一实施例中,所述激光器为钛蓝宝石飞秒激光放大器,所述斩波器的斩波频率为30~400Hz。In one embodiment of the present invention, the laser is a titanium sapphire femtosecond laser amplifier, and the chopping frequency of the chopper is 30-400 Hz.

在本实用新型的一实施例中,所述光参量放大器输出波长在800~2600nm之间。In one embodiment of the present invention, the output wavelength of the optical parametric amplifier is between 800 and 2600 nm.

在本实用新型的一实施例中,所述太赫兹产生晶体为DAST晶体。其还可被DSTMS、BNA、OH1等晶体替换。In one embodiment of the present invention, the terahertz generating crystal is a DAST crystal, which can also be replaced by DSTMS, BNA, OH1 and other crystals.

在本实用新型的一实施例中,所述太赫兹产生晶体产生的太赫兹电场强度为0.1~80MV/cm。In one embodiment of the present invention, the terahertz electric field strength generated by the terahertz generating crystal is 0.1-80 MV/cm.

在本实用新型的一实施例中,所述由第三离轴打孔抛物面反射镜反射的太赫兹波与所述被测样品所在平面的夹角介于80°~100°之间。In one embodiment of the present invention, the angle between the terahertz wave reflected by the third off-axis perforated parabolic reflector and the plane where the measured sample is located is between 80° and 100°.

在本实用新型的一实施例中,所述第一离轴抛物面反射镜和第二离轴抛物面反射镜焦距比例应为1:4,其优选值应该小于1:2。In one embodiment of the present invention, the focal length ratio of the first off-axis parabolic reflector and the second off-axis parabolic reflector should be 1:4, and the preferred value should be less than 1:2.

在本实用新型的一实施例中,所述被测量的样品以石英和蓝宝石为例。本系统所述可被测量的样品包括但不限于各种用于太赫兹波段的窗口材料、基底材料、生物样品、半导体材料、晶体等,如石英、金刚石、硅、砷化镓、氮化硅、蓝宝石、聚乙烯、有机溶剂、蛋白质溶液等。In one embodiment of the utility model, the samples to be measured are quartz and sapphire. The samples that can be measured in the system include but are not limited to various window materials, substrate materials, biological samples, semiconductor materials, crystals, etc. for terahertz bands, such as quartz, diamond, silicon, gallium arsenide, silicon nitride, sapphire, polyethylene, organic solvents, protein solutions, etc.

在本实用新型的一实施例中,所述被测量的太赫兹脉冲频段覆盖0.1~10THz。In an embodiment of the present invention, the measured terahertz pulse frequency band covers 0.1~10THz.

本实用新型的有益效果是:本实用新型提供的一种样品中太赫兹脉冲群速度的测量系统创新的应用了样品中普遍存在的三阶非线性克尔效应现象,实现了对样品中太赫兹脉冲群速度的直接测量。太赫兹脉冲聚焦到被测样品上,并在被测样品中传播,传播过程激发了样品的各向异性。探测光在同一时刻聚焦到样品中的同一位置,并同时在样品内传播。太赫兹脉冲和探测光脉冲在样品内相遇时,由于样品的三阶非线性克尔效应,太赫兹脉冲会改变探测光脉冲的偏振状态。通过调整探测光路线上的时间延迟装置,使探测光脉冲和太赫兹脉冲以一定的时间间隔先后到达样品。由于太赫兹脉冲和探测光脉冲在样品内具有不同的群速度,因此当时间间隔较小时,太赫兹脉冲和探测光脉冲依然可以在样品内追击相遇并产生对探测光脉冲偏振态的调制。调整时间延迟装置,测量探测光脉冲被调制的时间范围,即可基于参考的探测光脉冲速度、时间范围和样品厚度等参数,获得太赫兹脉冲群速度参数。本实用新型中测量太赫兹脉冲群速度的灵敏度可以达到0.001mm/ps,是首次实现对样品内太赫兹脉冲传播群速度的直接测量。本实用新型的系统构成简单、建置成本低、稳定性高、并且容易维护。本实用新型首次实现对样品内太赫兹脉冲群速度的直接测量,并具有较高的灵敏度,在太赫兹领域内元器件制造、样品检测、基底窗口材料分析、自由空间内太赫兹系统搭建与仪器制造等方面均具有极大的科研和应用价值。The beneficial effects of the utility model are as follows: the utility model provides a system for measuring the group velocity of terahertz pulses in a sample, which innovatively applies the third-order nonlinear Kerr effect phenomenon that is commonly present in the sample, and realizes direct measurement of the group velocity of terahertz pulses in the sample. The terahertz pulse is focused on the sample to be measured and propagates in the sample to be measured, and the propagation process excites the anisotropy of the sample. The detection light is focused on the same position in the sample at the same time and propagates in the sample at the same time. When the terahertz pulse and the detection light pulse meet in the sample, the terahertz pulse will change the polarization state of the detection light pulse due to the third-order nonlinear Kerr effect of the sample. By adjusting the time delay device on the detection light route, the detection light pulse and the terahertz pulse arrive at the sample successively at a certain time interval. Since the terahertz pulse and the detection light pulse have different group velocities in the sample, when the time interval is small, the terahertz pulse and the detection light pulse can still chase and meet in the sample and produce modulation of the polarization state of the detection light pulse. By adjusting the time delay device and measuring the time range in which the detection light pulse is modulated, the terahertz pulse group velocity parameters can be obtained based on the reference detection light pulse velocity, time range, sample thickness and other parameters. The sensitivity of measuring the terahertz pulse group velocity in the utility model can reach 0.001mm/ps, which is the first time to directly measure the group velocity of terahertz pulse propagation in a sample. The system structure of the utility model is simple, the construction cost is low, the stability is high, and it is easy to maintain. The utility model realizes the direct measurement of the terahertz pulse group velocity in the sample for the first time, and has a high sensitivity. It has great scientific research and application value in the field of terahertz components manufacturing, sample detection, substrate window material analysis, terahertz system construction in free space and instrument manufacturing.

附图说明BRIEF DESCRIPTION OF THE DRAWINGS

为了更清楚地说明本实用新型实施例或现有技术中的技术方案,下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍。显而易见地,下面描述中的附图仅仅是本实用新型的一些实施例,对于本领域普通技术人员来讲,在不付出创造性劳动的前提下,还可以根据这些附图获得其他的附图。In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

图1为本实用新型提供的样品中太赫兹脉冲群速度的测量系统示意图(俯视图);FIG1 is a schematic diagram (top view) of a system for measuring the terahertz pulse group velocity in a sample provided by the present invention;

图2为本实用新型中使用的太赫兹脉冲频谱;FIG2 is a spectrum of terahertz pulses used in the present invention;

图3为本实用新型中系统对石英样品的测量结果;FIG3 is a measurement result of a quartz sample by the system of the present invention;

图4为本实用新型中系统对蓝宝石样品的测量结果。FIG. 4 is a measurement result of a sapphire sample by the system of the present invention.

附图标记说明:1-激光器;2-分光镜;3-光参量放大器;4-斩波器;5-太赫兹产生晶体;6-太赫兹滤波片;7-第一离轴抛物面反射镜;8-第二离轴抛物面反射镜;9-第三离轴打孔抛物面反射镜;10-光学延迟装置;11-第一凸透镜;12-被测样品;13-第二凸透镜;14-四分之一波片;15-沃拉斯顿棱镜;16-光电平衡探测器。Explanation of the accompanying drawings: 1-laser; 2-beamsplitter; 3-optical parametric amplifier; 4-chopper; 5-terahertz generating crystal; 6-terahertz filter; 7-first off-axis parabolic reflector; 8-second off-axis parabolic reflector; 9-third off-axis perforated parabolic reflector; 10-optical delay device; 11-first convex lens; 12-sample to be measured; 13-second convex lens; 14-quarter wave plate; 15-Wollaston prism; 16-photoelectric balance detector.

具体实施方式Detailed ways

下面将结合本实用新型实施例中的附图,对本实用新型实施例中的技术方案进行清楚、完整地描述。显然,所描述的实施例仅仅是本实用新型一部分实施例,而不是全部的实施例。基于本实用新型中的实施例,本领域普通技术人员在没有付出创造性劳动前提下所获得的所有其他实施例,都属于本实用新型保护的范围。The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

图1为本实用新型提供的样品中太赫兹脉冲群速度的测量系统示意图(俯视图),其包括设置在光路上的激光器1、分光镜2、光参量放大器3、斩波器4、太赫兹产生晶体5,太赫兹滤波片6、第一离轴抛物面反射镜7、第二离轴抛物面反射镜8、第三离轴打孔抛物面反射镜9、光学延迟装置10、第一凸透镜11、被测样品12、第二凸透镜13、四分之一波片14、沃拉斯顿棱镜15、光电平衡探测器16,其中:FIG1 is a schematic diagram (top view) of a system for measuring the group velocity of terahertz pulses in a sample provided by the present invention, which includes a laser 1, a beam splitter 2, an optical parametric amplifier 3, a chopper 4, a terahertz generating crystal 5, a terahertz filter 6, a first off-axis parabolic reflector 7, a second off-axis parabolic reflector 8, a third off-axis perforated parabolic reflector 9, an optical delay device 10, a first convex lens 11, a sample to be measured 12, a second convex lens 13, a quarter wave plate 14, a Wollaston prism 15, and a photoelectric balance detector 16, wherein:

激光器1用于发射波长为800nm、脉冲宽度为35fs的激光,800nm的飞秒激光经过分光镜2分出一束作为泵浦光和一束作为探测光。泵浦光通过光参量放大器3,转化为波长为800~2600nm中任意波长、脉冲宽度为50fs的激光,并通过斩波器4、太赫兹产生晶体5产生太赫兹脉冲。太赫兹脉冲经过太赫兹滤波片6滤除杂散光,再依次经过第一离轴抛物面反射镜7、第二离轴抛物面反射镜8进行波前调制,之后再经由第三离轴打孔抛物面反射镜9反射后聚焦至被测样品12。探测光依次经过光学延迟装置10、第一凸透镜11、第三离轴打孔抛物面反射镜9后与太赫兹脉冲共同聚焦于被测样品12上,所述被测样品12由强太赫兹脉冲激发三阶非线性克尔效应,导致同时聚焦于所述被测样品12上的探测光发生偏振旋转。受太赫兹脉冲调制的探测光脉冲经由第二凸透镜13汇聚成平行光后通过四分之一波片14、沃拉斯顿棱镜15进行偏振态分束后,通过光电平衡探测器16进行信号采集。调节所述光学延迟装置,可以得到用以计算样品太赫兹脉冲群速度的时间延迟信息。The laser 1 is used to emit a laser with a wavelength of 800nm and a pulse width of 35fs. The 800nm femtosecond laser is separated into a beam as a pump light and a beam as a detection light through a beam splitter 2. The pump light is converted into a laser with a wavelength of any wavelength between 800 and 2600nm and a pulse width of 50fs through an optical parametric amplifier 3, and a terahertz pulse is generated through a chopper 4 and a terahertz generating crystal 5. The terahertz pulse passes through a terahertz filter 6 to filter out stray light, and then passes through a first off-axis parabolic reflector 7 and a second off-axis parabolic reflector 8 in sequence for wavefront modulation, and then is reflected by a third off-axis perforated parabolic reflector 9 and focused on a sample 12 to be measured. The detection light passes through the optical delay device 10, the first convex lens 11, and the third off-axis perforated parabolic reflector 9 in sequence, and is focused on the sample 12 under test together with the terahertz pulse. The sample 12 under test is excited by the third-order nonlinear Kerr effect by the strong terahertz pulse, causing the detection light focused on the sample 12 under test to rotate in polarization. The detection light pulse modulated by the terahertz pulse is converged into parallel light by the second convex lens 13, and then polarization-state beam splitting is performed by the quarter-wave plate 14 and the Wollaston prism 15, and then the signal is collected by the photoelectric balanced detector 16. By adjusting the optical delay device, the time delay information used to calculate the sample terahertz pulse group velocity can be obtained.

图1中,第一离轴抛物面反射镜7的等效焦距可以为1英寸,第二离轴打孔抛物面反射镜8的等效焦距可以为4英寸。In FIG. 1 , the equivalent focal length of the first off-axis parabolic reflector 7 may be 1 inch, and the equivalent focal length of the second off-axis perforated parabolic reflector 8 may be 4 inches.

本实施例中,被测样品12厚度在300μm~3mm之间。In this embodiment, the thickness of the sample 12 to be tested is between 300 μm and 3 mm.

本实施例中,激光器1为钛蓝宝石飞秒激光放大器,斩波器4的斩波频率为30~400Hz。In this embodiment, the laser 1 is a titanium sapphire femtosecond laser amplifier, and the chopper frequency of the chopper 4 is 30-400 Hz.

本实施例中,光参量放大器3输出波长在800~2600nm之间。In this embodiment, the output wavelength of the optical parametric amplifier 3 is between 800 and 2600 nm.

本实施例中,太赫兹产生晶体5为DAST晶体,其还可被DSTMS、BNA、OH1等晶体替换。In this embodiment, the terahertz generating crystal 5 is a DAST crystal, which can also be replaced by DSTMS, BNA, OH1 and other crystals.

本实施例中,太赫兹产生晶体5产生的太赫兹电场强度为0.1~ 80MV/cm。In this embodiment, the terahertz electric field strength generated by the terahertz generating crystal 5 is 0.1~80MV/cm.

本实施例中,由第三离轴打孔抛物面反射镜9反射的太赫兹波与被测样品12所在平面的夹角介于80°~100°之间。In this embodiment, the angle between the terahertz wave reflected by the third off-axis perforated parabolic reflector 9 and the plane where the sample 12 to be measured is located is between 80° and 100°.

本实施例中,第一离轴抛物面反射镜7和第二离轴抛物面反射镜8焦距比例应为1:4,其优选值应该小于1:2。In this embodiment, the focal length ratio of the first off-axis parabolic reflector 7 and the second off-axis parabolic reflector 8 should be 1:4, and the preferred value should be less than 1:2.

本实施例中,被测量的样品12以石英和蓝宝石为例。本系统可被测量的样品包括但不限于各种用于太赫兹波段的窗口材料、基底材料、生物样品、半导体材料、晶体等,如石英、金刚石、硅、砷化镓、氮化硅、蓝宝石、聚乙烯、有机溶剂、蛋白质溶液等。In this embodiment, quartz and sapphire are used as examples of the sample 12 to be measured. The samples that can be measured by this system include, but are not limited to, various window materials, substrate materials, biological samples, semiconductor materials, crystals, etc. for terahertz bands, such as quartz, diamond, silicon, gallium arsenide, silicon nitride, sapphire, polyethylene, organic solvents, protein solutions, etc.

如图2所示,本实施例中被测量的太赫兹脉冲频段覆盖0.1~10THz。As shown in FIG. 2 , the terahertz pulse frequency band measured in this embodiment covers 0.1 to 10 THz.

本实用新型采用以下方法进行测量,该方法可以应用于例如图1所示的系统中,其包括以下步骤:The utility model adopts the following method for measurement, which can be applied to the system shown in Figure 1, for example, and includes the following steps:

S1:所述激光器发射波长为800nm的激光。S1: The laser emits laser light with a wavelength of 800 nm.

S2:800nm的激光经过所述分光镜分出一束泵浦光和一束探测光。S2: The 800nm laser is separated into a pump light and a detection light through the beam splitter.

S3:泵浦光通过所述光参量放大器,转化为波长为800~2600nm中任意波长、脉冲宽度为50fs的激光,并通过所述斩波器、所述太赫兹产生晶体产生太赫兹脉冲。太赫兹脉冲经过所述太赫兹滤波片滤除杂散光,再依次经过所述第一离轴抛物面反射镜、第二离轴抛物面反射镜进行波前调制,之后再经由第三离轴打孔抛物面反射镜反射后聚焦至所述被测样品。S3: The pump light is converted into a laser with a wavelength of any wavelength between 800 and 2600 nm and a pulse width of 50 fs through the optical parametric amplifier, and a terahertz pulse is generated through the chopper and the terahertz generating crystal. The terahertz pulse passes through the terahertz filter to filter out stray light, and then passes through the first off-axis parabolic reflector and the second off-axis parabolic reflector in turn for wavefront modulation, and then is reflected by the third off-axis perforated parabolic reflector and focused to the sample under test.

S4:探测光依次经过所述光学延迟装置、所述第一凸透镜、所述第三离轴打孔抛物面反射镜后与太赫兹脉冲共同聚焦于所述被测样品上,所述被测样品由强太赫兹脉冲激发三阶非线性克尔效应,导致同时聚焦于所述被测样品上的探测光发生偏振旋转。受太赫兹脉冲调制的探测光脉冲经由所述第二凸透镜汇聚成平行光后通过所述四分之一波片、所述沃拉斯顿棱镜进行按偏振态分束后,通过所述光电平衡探测器进行信号采集。调节所述光学延迟装置,可以得到用以计算样品太赫兹脉冲群速度的时间延迟信息。S4: The detection light passes through the optical delay device, the first convex lens, and the third off-axis perforated parabolic reflector in sequence and is focused on the sample under test together with the terahertz pulse. The sample under test is excited by the third-order nonlinear Kerr effect by the strong terahertz pulse, causing the detection light focused on the sample under test to rotate in polarization. The detection light pulse modulated by the terahertz pulse is converged into parallel light by the second convex lens, and then passes through the quarter-wave plate and the Wollaston prism to split according to the polarization state, and then the signal is collected by the photoelectric balanced detector. By adjusting the optical delay device, the time delay information used to calculate the sample terahertz pulse group velocity can be obtained.

S5:基于测量到的时间延迟信息获取时间范围t,并由折射率表获得探测光脉冲在样品中的参考速度,则对于厚度为l的被测样品,太赫兹脉冲在样品中群速度参数可由公式获取。S5: Based on the measured time delay information, the time range t is obtained, and the reference velocity of the detection light pulse in the sample is obtained from the refractive index table. Then, for the sample with a thickness of l , the group velocity parameter of the terahertz pulse in the sample can be obtained by the formula.

图3为应用图1所述系统对厚度l为0.6mm石英样品的测量结果,可以观察到时间范围t约为1ps;由折射率表获得探测光脉冲在石英样品中的折射率n为1.4533,对应的参考速度为0.2064mm/ps;经公式计算,本实施例中太赫兹脉冲在石英样品中的传播群速度参数为0.154mm/ps。FIG3 shows the measurement result of a quartz sample with a thickness of 0.6 mm using the system described in FIG1 . It can be observed that the time range t is approximately 1 ps. The refractive index n of the detection light pulse in the quartz sample obtained from the refractive index table is 1.4533, and the corresponding reference velocity is 0.2064 mm/ps. According to the formula calculation, the propagation group velocity parameter of the terahertz pulse in the quartz sample in this embodiment is 0.154 mm/ps.

图4为应用图1所述系统对厚度l为0.6mm蓝宝石样品的测量结果,可以观察到时间范围t约为2.6ps;由折射率表获得探测光脉冲在蓝宝石样品中的折射率n为1.7601,对应的参考速度为0.1704mm/ps;经公式计算,本实施例中太赫兹脉冲在蓝宝石样品中的传播群速度参数为0.098mm/ps。FIG4 shows the measurement results of a sapphire sample with a thickness of 0.6 mm using the system described in FIG1 . It can be observed that the time range t is approximately 2.6 ps. The refractive index n of the detection light pulse in the sapphire sample obtained from the refractive index table is 1.7601, and the corresponding reference velocity is 0.1704 mm/ps. According to the formula calculation, the propagation group velocity parameter of the terahertz pulse in the sapphire sample in this embodiment is 0.098 mm/ps.

本实用新型创新的应用了样品中普遍存在的三阶非线性克尔效应现象,首次实现了对样品中太赫兹脉冲群速度高灵敏度的直接测量,测量灵敏度可达0.001mm/ps。和传统时延法以及相位法逐一测量各频率点折射率进而间接近似计算色散和群速度的方法相比,本实用新型可以直接获得任意频率成分构成的太赫兹脉冲在样品中的群速度。本实用新型的系统构成简单、建置成本低、稳定性高、并且容易维护。本实用新型首次实现对样品内太赫兹脉冲群速度的直接测量,并具有较高的灵敏度,在太赫兹领域内元器件制造、样品检测、基底窗口材料分析、自由空间内太赫兹系统搭建与仪器制造等方面均具有极大的科研和应用价值。The utility model innovatively applies the third-order nonlinear Kerr effect phenomenon that is commonly present in samples, and for the first time realizes the high-sensitivity direct measurement of the terahertz pulse group velocity in the sample, with a measurement sensitivity of up to 0.001mm/ps. Compared with the traditional time delay method and phase method that measure the refractive index of each frequency point one by one and then indirectly approximate the calculation of dispersion and group velocity, the utility model can directly obtain the group velocity of terahertz pulses composed of any frequency components in the sample. The system structure of the utility model is simple, the construction cost is low, the stability is high, and it is easy to maintain. The utility model realizes the direct measurement of the terahertz pulse group velocity in the sample for the first time, and has a high sensitivity. It has great scientific research and application value in the field of terahertz components manufacturing, sample detection, substrate window material analysis, free space terahertz system construction and instrument manufacturing.

本领域普通技术人员可以理解:附图只是一个实施例的示意图,附图中的模块或流程并不一定是实施本实用新型所必须的。Those skilled in the art can understand that the accompanying drawings are only schematic diagrams of an embodiment, and the modules or processes in the accompanying drawings are not necessarily required for implementing the present utility model.

本领域普通技术人员可以理解:实施例中的模块可以按照实施例描述分布于实施例的装置中,也可以进行相应变化位于不同于本实施例的一个或多个装置中。上述实施例的模块可以合并为一个模块,也可以进一步拆分成多个子模块。Those skilled in the art can understand that the modules in the embodiments can be distributed in the devices of the embodiments according to the description of the embodiments, or can be located in one or more devices different from the embodiments with corresponding changes. The modules in the above embodiments can be combined into one module, or can be further divided into multiple sub-modules.

最后应说明的是:以上实施例仅用以说明本实用新型的技术方案,而非对其限制;尽管参照前述实施例对本实用新型进行了详细的说明,本领域的普通技术人员应当理解:其依然可以对前述实施例所记载的技术方案进行修改,或者对其中部分技术特征进行等同替换;而这些修改或者替换,并不使相应技术方案的本质脱离本实用新型实施例技术方案的精神和范围。Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the utility model, rather than to limit it. Although the utility model has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the utility model.

Claims (8)

1. The system for measuring the terahertz pulse group velocity in the sample is characterized by comprising a laser, a spectroscope, an optical parametric amplifier, a chopper and a terahertz generation crystal which are arranged on an optical path, a terahertz filter, a first off-axis parabolic reflector, a second off-axis parabolic reflector, a third off-axis perforated parabolic reflector, an optical delay device, a first convex lens, a measured sample, a second convex lens, a quarter-wave plate, a Wollaston prism and a photoelectric balance detector, wherein:
the laser is a titanium sapphire femtosecond laser amplifier and is used for emitting laser with the wavelength of 800nm and the pulse width of 35fs, and the femtosecond laser with the wavelength of 800nm is split into a beam serving as pump light and a beam serving as probe light through the spectroscope; the pump light is converted into laser with the pulse width of 50fs at any wavelength of 800-2600 nm through the optical parametric amplifier, and terahertz pulse is generated through the chopper and the terahertz generating crystal; the terahertz pulse filters stray light through the terahertz filter, sequentially passes through the first off-axis parabolic reflector and the second off-axis parabolic reflector to carry out wave front modulation, and then is focused to the sample to be measured after being reflected by the third off-axis perforated parabolic reflector; the detection light sequentially passes through the optical delay device, the first convex lens and the third off-axis perforated parabolic reflector and then is focused on the sample to be detected together with terahertz pulses; the three-order nonlinear kerr effect is excited by the strong terahertz pulse of the tested sample, so that the detection light focused on the tested sample simultaneously rotates in polarization; the detection light pulse modulated by the terahertz pulse is converged into parallel light through the second convex lens, polarized beam splitting is carried out through the quarter wave plate and the Wollaston prism, and then signal acquisition is carried out through the photoelectric balance detector; and adjusting the optical delay device to obtain time delay information for calculating the terahertz pulse group velocity of the sample.
2. The system for measuring terahertz pulse group velocity in a sample according to claim 1, wherein the thickness of the measured sample is 300 μm to 3mm.
3. The system for measuring the terahertz pulse group velocity in a sample according to claim 1, wherein the laser is a titanium sapphire femtosecond laser amplifier, and the chopper has a chopping frequency of 30-400 hz.
4. The system for measuring the terahertz pulse group velocity in a sample according to claim 1, wherein the terahertz electric field strength generated by the terahertz generating crystal is 0.1-80 mv/cm.
5. The system for measuring the group velocity of terahertz pulses in a sample according to claim 1, wherein an included angle between the terahertz wave reflected by the third off-axis perforated parabolic mirror and a plane in which the sample to be measured is located is between 80 ° and 100 °.
6. The system of claim 1, wherein the first off-axis parabolic mirror and the second off-axis parabolic mirror have a focal length ratio of less than 1:2.
7. the system of claim 1, wherein the sample comprises a window material for terahertz wave band, a base material, a biological sample, a semiconductor material, a crystal.
8. The system for measuring the terahertz pulse group velocity in a sample according to claim 1, wherein the terahertz pulse frequency band can cover 0.1-10 thz.
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