阅读说明：本技术 激光诱导熔石英损伤样品缺陷的太赫兹近场检测系统及方法 (Terahertz near field detection system and method for sample damage defect induced by laser melting of quartz ) 是由 张振 刘艺 马勇 潘武 肖惠云 冉佳 黄文� 郝宏刚 李国军 于 2021-07-30 设计创作，主要内容包括：本发明公开了激光诱导熔石英损伤样品缺陷的太赫兹近场检测系统及方法,包括激光诱导损伤单元和太赫兹近场检测单元；激光诱导损伤单元：激光I发射的激光诱导样品产生损伤；激光II发射的激光照射样品以便通过CCD探测器监视样品表面损伤情况。太赫兹近场检测单元：激光源III发射的激光经分束镜II分为泵浦光和探测光；泵浦光经电导天线辐射出太赫兹波、再经斩波器后照射到损伤后的样品的下表面；探测光到达光电导微探针的针尖,用于产生自由载流子,在太赫兹电场的作用下产生光电流；光电导微探针用于检测穿过样品的太赫兹波。本发明可在线直接检测熔石英损伤后缺陷,同时高分辨率表征表层与亚表层的缺陷,能够较准确的标定损伤缺陷位置。(The invention discloses a terahertz near field detection system and method for detecting defects of a damaged sample of laser-induced fused quartz, wherein the terahertz near field detection system comprises a laser-induced damage unit and a terahertz near field detection unit; laser-induced damage unit: the laser I emits laser to induce the sample to generate damage; the laser emitted by the laser II irradiates the sample so as to monitor the damage condition of the surface of the sample through a CCD detector. Terahertz near field detection unit: laser emitted by the laser source III is divided into pump light and probe light by the beam splitter II; the pumping light radiates terahertz waves through the conductive antenna, and then irradiates the lower surface of the damaged sample through the chopper; the detection light reaches the needle tip of the photoconductive microprobe and is used for generating free carriers and generating photocurrent under the action of a terahertz electric field; the photoconductive microprobe is used to detect terahertz waves passing through a sample. The method can directly detect the defects of the damaged fused quartz on line, simultaneously characterize the defects of the surface layer and the subsurface layer with high resolution, and can accurately calibrate the positions of the damaged defects.)

1. The terahertz near field detection system for detecting the defects of the damaged sample of the laser-induced fused quartz is characterized by comprising a laser-induced damage unit and a terahertz near field detection unit; the laser induced damage unit comprises a laser source I (1), a laser source II (8) and a CCD detector (29), and the terahertz near field detection unit comprises a laser source III (11), a beam splitter II (12), a conductive antenna (18), a chopper (19) and a photoconductive microprobe (22);

the laser I (1) is used for emitting laser to induce the sample (9) to generate damage;

the laser II (8) is used for emitting laser, and irradiating the sample so as to monitor the damage condition of the surface of the sample through a CCD detector (29);

the laser source III (11) is used for emitting laser;

the beam splitter II (12) is used for splitting laser emitted by the laser source III (11) into pump light and probe light; the pump light radiates terahertz waves through the conductive antenna (18), and then is converted by the chopper (19) and irradiates the lower surface of the sample (9) which is damaged by the laser-induced damage unit; the detection light reaches the needle tip of the photoconductive microprobe (22) and is used for generating free carriers, so that photocurrent is generated under the action of a terahertz electric field;

the photoconductive microprobe (22) is used for detecting terahertz waves passing through the sample (9).

2. The system for detecting the terahertz near field of the sample defect of the laser-induced damage to the fused quartz as claimed in claim 1, wherein the laser-induced damage unit further comprises an attenuation sheet (2), a beam splitter I (4) and an energy calorimeter (5); the laser emitted by the laser I (1) is attenuated by the attenuation sheet (2); the laser attenuated by the attenuation sheet (2) is divided into two beams of laser by the beam splitter I (4), one beam of laser is used for monitoring the energy output by the laser source I (1) in real time by the energy calorimeter (5), and the other beam of laser is used for inducing the sample (9) to generate damage.

3. The system for detecting the terahertz near field defects of the laser-induced fused quartz damaged sample according to claim 1, wherein the laser-induced damage unit further comprises a reflecting mirror and a lens; the reflector is used for changing the laser propagation path, and the lens is used for focusing the laser on the surface of the sample (9) to induce damage.

4. The system for detecting the terahertz near field defects of the laser-induced fused quartz damaged sample according to claim 1, wherein a pumping light path of the terahertz near field detection unit further comprises a time-delay light path, and the time-delay light path comprises a plurality of reflectors which are sequentially arranged; the pumping light enters the conductive antenna (18) after being reflected by a plurality of reflectors and delayed.

5. The system for detecting the terahertz near field defect of the laser-induced fused quartz damaged sample according to claim 1, wherein the pumping light path of the terahertz near field detection unit further comprises a lens, and the lens is used for focusing the pumping light laser passing through the chopper (19) on the lower surface of the sample (9).

6. The system for detecting the terahertz near field defect of the laser-induced fused quartz damaged sample according to claim 1, wherein a lens is further included on a detection optical path of the terahertz near field detection unit for focusing the detection light at a tip of the photoconductive microprobe (22).

7. The system for detecting the terahertz near field defect of the laser-induced fused quartz damaged sample according to claim 1, wherein the terahertz near field detection unit further comprises a current amplifier (23) and a phase-locked amplifier (24); the detection light reaches the needle point of the photoconductive microprobe (22) and is used for generating free carriers, so that photocurrent is generated under the action of a terahertz electric field and then input into the phase-locked amplifier (24) through the current amplifier (23), and the phase-locked amplifier (24) combines with an output reference signal to obtain a complete terahertz pulse waveform along with the change of a delay line.

8. The system for detecting the terahertz near field defect of the laser-induced fused quartz damaged sample according to any one of claims 1 to 7, further comprising a displacement table (10), wherein the displacement table (10) is used for moving the sample (9) from the detection area of the laser-induced damage unit to the detection area of the terahertz near field detection unit.

9. A terahertz near field detection method for laser-induced fused quartz damage sample defects is characterized by comprising the following steps:

s1, preparing a laser-induced damage fused quartz sample, and observing the surface of the fused quartz sample in real time through a CCD detector;

s2, moving the fused quartz sample subjected to laser induced damage to a terahertz near field unit detection area;

and S3, detecting a terahertz signal by using a photoconductive microprobe, and performing terahertz scanning near-field imaging on the fused quartz damage sample.

Technical Field

The invention relates to the technical field of optical element damage detection, in particular to a terahertz near field detection system and method for detecting defects of a laser-induced fused quartz damaged sample.

Background

Fused silica components have good optical properties and are the preferred materials for high power laser devices. Currently, 80% of the optical elements in inertial confinement fusion devices are composed of fused quartz. The damage of the fused quartz element in an ultraviolet region (355nm) is the most serious, the problem of optical element damage is a technical bottleneck restricting the development of a high-power laser system, and the development of a plurality of application fields is restricted seriously by the damage of a laser-induced optical element. In order to deeply analyze the damage phenomenon of the fused quartz laser, people set up a damage detection test platform to carry out experimental research on the laser-induced damage of the fused quartz. One of the key links in the fused quartz laser induced damage research experiment is the detection of the fused quartz damage point. The conventional fused quartz damage point detection method comprises weak absorption instrument detection and CCD surface image detection. The weak absorption instrument detects whether the sample is damaged or not through the change of the absorption rate of the sample, and the defect of sample damage cannot be represented. Surface image detection by using the CCD cannot provide defect information of damaged sample subsurface layers, and the CCD lens is easily damaged by too strong real-time laser.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: based on the defects of the existing commonly used weak absorption instrument detection and CCD detection, the invention provides the terahertz near field detection system and method for solving the defect that the laser-induced fused quartz damages the sample.

The invention is realized by the following technical scheme:

the terahertz near field detection system for detecting the defects of the damaged sample of the laser-induced fused quartz comprises a laser-induced damage unit and a terahertz near field detection unit; the laser induced damage unit comprises a laser source I, a laser source II and a CCD detector, and the terahertz near field detection unit comprises a laser source III, a beam splitter II, a conductive antenna, a chopper and a photoconductive microprobe; the laser I is used for emitting laser to induce the sample to generate damage; the laser II is used for emitting laser, and irradiating the sample so as to monitor the damage condition of the surface of the sample through a CCD detector; the laser source III is used for emitting laser; the beam splitter II is used for dividing laser emitted by the laser source III into pump light and probe light; the pump light radiates terahertz waves through the conductive antenna, and then irradiates the lower surface of the sample which is damaged by the laser induced damage unit after being converted by the chopper; the detection light reaches the needle tip of the photoconductive microprobe and is used for generating free carriers, and further generating photocurrent under the action of a terahertz electric field; the photoconductive microprobe is used for detecting terahertz waves passing through a sample.

At present, the conventional fused quartz damage point detection method comprises weak absorption instrument detection and CCD surface image detection. The weak absorption instrument detects whether the sample is damaged or not through the change of the absorption rate of the sample, and the defect of sample damage cannot be represented. Surface image detection by using the CCD cannot provide defect information of damaged sample subsurface layers, and the CCD lens is easily damaged by too strong real-time laser. The invention combines the laser-induced fused quartz damage device with the terahertz near-field imaging system, can directly detect the defects of the fused quartz after being damaged on line, can represent the defects of the surface layer and the subsurface layer at high resolution, can accurately calibrate the positions of the damaged defects, and can also provide phase spectrum information of the fused quartz damaged sample.

Further preferably, the laser induced damage unit further comprises an attenuation sheet, a beam splitter I and an energy calorimeter; the laser emitted by the laser I is attenuated by the attenuation sheet; the laser attenuated by the attenuator is divided into two beams of laser by the beam splitter I, one beam of laser is used for monitoring the energy output by the laser source I in real time by the energy calorimeter, and the other beam of laser is used for inducing the sample to generate damage.

Further preferably, the laser induced damage unit further comprises a reflector and a lens; the reflector is used for changing the laser propagation path, and the lens is used for focusing the laser on the surface of the sample to induce damage.

Preferably, the pumping light path of the terahertz near field detection unit further comprises a delay light path, and the delay light path comprises a plurality of reflectors which are sequentially arranged; the pumping light enters the conductive antenna after being reflected by a plurality of reflectors for time delay.

Further preferably, the terahertz near-field detection unit further includes a lens on the pump light path, and the lens is used for focusing the pump light laser passing through the chopper on the lower surface of the sample.

Further preferably, the terahertz near-field detection unit further includes a lens on a detection optical path for focusing the detection light at a tip of the photoconductive microprobe.

Preferably, the terahertz near-field detection unit further comprises a current amplifier and a lock-in amplifier, the detection light reaches the needle tip of the photoconductive microprobe and is used for generating free carriers, so that photocurrent is generated under the action of the terahertz electric field and then input to the lock-in amplifier through the current amplifier, and the lock-in amplifier combines the output reference signal to obtain a complete terahertz pulse waveform along with the change of the delay line.

Further preferably, the terahertz near-field detection device further comprises a displacement table, wherein the displacement table is used for moving the detection region of the sample damage unit induced by the laser to the detection region of the terahertz near-field detection unit.

A terahertz near field detection method for laser-induced fused quartz damage sample defects comprises the following steps:

s1, preparing a laser-induced damage fused quartz sample, and observing the surface of the fused quartz sample in real time through a CCD detector;

s2, moving the fused quartz sample subjected to laser induced damage to a terahertz near field unit detection area;

and S3, detecting a terahertz signal by using a photoconductive microprobe, and performing terahertz scanning near-field imaging on the fused quartz damage sample.

The invention has the following advantages and beneficial effects:

the invention combines the laser-induced fused quartz damage device with the terahertz near-field imaging system, can directly detect the defects of the fused quartz after being damaged on line, can represent the defects of the surface layer and the subsurface layer at high resolution, can accurately calibrate the positions of the damaged defects, and can also provide phase spectrum information of the fused quartz damaged sample.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:

FIG. 1 is a schematic diagram of an apparatus for detecting defects of a laser-induced fused quartz damage sample by using a terahertz near field.

Reference numbers and corresponding part names in the drawings:

1-laser source I, 2-attenuator, 3-mirror I, 4-beam splitter I, 5-energy calorimeter, 6-lens I, 7-lens II, 8-laser source II, 9-sample, 10-displacement stage, 11-laser source III, 12-beam splitter II, 13-mirror II, 14-mirror III, 15-mirror IV, 16-mirror V, 17-mirror VI, 18-photoconductive antenna, 19-chopper, 20-off-axis parabolic mirror, 21-lens III, 22-photoconductive microprobe, 23-current amplifier, 24-lock-in amplifier, 25-controller, 26-mirror VII, 27-lens IV, 28-mirror VIII, 29-CCD detector.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.

Example 1

The embodiment provides a terahertz near field detection system for detecting defects of a fused quartz damaged sample, which mainly comprises a laser induced damage unit, a terahertz near field detection unit and a displacement table 10, wherein the three units are described in detail as follows:

1. laser-induced damage unit

The laser induced damage unit comprises a laser source I1, an attenuation sheet 2, a reflector I3, a beam splitter I4, an energy calorimeter 5, a lens I6, a lens II7, a laser source II8 and a CCD detector 29;

laser source I1 used was Nd: YAG nanosecond pulse laser source, the laser that laser source I sent out adjusts intensity through attenuator 2, is reflected by speculum I3 again, is divided into two bundles of laser through beam splitter I4: a laser beam is used for the energy meter 5 to monitor the laser energy output by the laser source I1 in real time; another laser beam is collimated by the lens I6 and focused by the lens II7 to finally reach the fused silica sample 9, and the damage to the sample 9 is induced by the laser beam.

Laser source II8 employs a He — Ne laser source for irradiating sample 9. The controller 25 is loaded with the software of the CCD detector 29, and the surface damage condition of the sample 9 can be observed through the CCD detector 29.

2. Displacement table

The displacement table 10 is used for moving the sample 9 from the detection region of the laser-induced damage unit to the detection region of the terahertz near-field detection unit. In the embodiment, the displacement table 10 adopts an electric control three-dimensional displacement table, and after the damage of the laser-induced fused quartz sample 9 is formed, the electric control displacement table controls the sample to move into the terahertz near-field imaging system for continuous monitoring.

3. Terahertz near field detection unit

The terahertz near-field detection unit comprises a laser source III11, a beam splitter II12, a mirror II13, a mirror III14, a mirror IV15, a mirror V16, a mirror VI17, a conductive antenna 18, a chopper 19, an off-axis parabolic mirror 20, a lens III21, a photoconductive microprobe 22, a mirror VII26, a lens IV27, a mirror VIII28, a current amplifier 23, a phase-locked amplifier 24 and a controller 25.

In a transmission-type terahertz scanning near-field imaging system, according to a coherent detection principle, a laser source III11 adopts a femtosecond laser to generate femtosecond pulse laser with the central wavelength of 780nm, and the femtosecond laser is divided into pump light and detection light by a beam splitter II 12:

in the pump laser light path, the pump laser light changes the optical path difference between the pump laser light and the detection laser light through a delay light path formed by a reflecting mirror II13, a reflecting mirror III14, a reflecting mirror IV15 and a reflecting mirror V16, and the pump laser light is focused on the photoconductive antenna 18 through the reflecting mirror VI17 so as to radiate terahertz waves. The radiated terahertz waves are modulated by an optical chopper 19, collimated by an off-axis parabolic mirror 20, focused by a lens III21 (being a terahertz lens) and irradiated to the lower surface of a sample 9, and the terahertz waves passing through the sample 9 are detected by a photoconductive microprobe 22 positioned near the surface of the sample 9.

In a detection light path, the detection laser is reflected by a reflector VII26, focused by a lens IV27, reflected by a reflector VIII28 and then reaches the needle tip of the photoconductive microprobe 22 to generate free carriers, further generates photocurrent under the action of a terahertz electric field, and then is input to a phase-locked amplifier 24 through a current amplifier 23, a reference signal of a chopper 19 is transmitted to the phase-locked amplifier 24, the phase-locked amplifier 24 combines the reference signal to obtain a complete terahertz pulse waveform along with the change of a delay line, a terahertz time-domain signal acquired and processed by the phase-locked amplifier 24 transmits output to a controller 25, and data can be further processed on the controller 25.

Example 2

The embodiment provides a terahertz near field detection method for detecting defects of a laser-induced fused quartz damaged sample, which is implemented by adopting the terahertz near field detection system for detecting defects of the laser-induced fused quartz damaged sample provided in the embodiment 1, and comprises the following specific steps:

s1, preparing a laser-induced damage fused quartz sample, and observing the surface of the fused quartz sample in real time through a CCD detector.

In the light-induced fused quartz sample damage research, the laser energy irradiated on the surface of the fused quartz sample 9 needs to be changed, and the damage condition of the fused quartz sample 9 under different energies is observed. The induced damage fused silica sample 9 was achieved by:

(1) the laser source II8 and the CCD detector 29 were turned on to observe the lower surface of the fused silica sample 9 in real time.

(2) The attenuation sheet 2 and the laser source I1 are adjusted to change the laser energy, the laser energy in the light path is measured through the energy calorimeter 5, the laser is collimated through the lens I6 and focused on the surface of the fused quartz sample 9 through the lens II7, and the fused quartz sample 9 is induced to be damaged.

And S2, moving the fused quartz sample subjected to laser induced damage to a terahertz near field unit detection area.

And controlling an electrically-controlled three-dimensional displacement platform for loading the sample 9 to move the sample 9 to a terahertz near-field detection region (shown as a sample schematic position filled with a dotted line in fig. 1).

And S3, detecting a terahertz signal by using a photoconductive microprobe, and performing terahertz scanning near-field imaging on the fused quartz damage sample.

The electric control three-dimensional displacement platform controls the sample 9 to move in two dimensions in the near field detection area, the photoconductive microprobe 22 is used for detecting terahertz signals, and terahertz scanning near field imaging is carried out on the fused quartz damage sample 9. High-resolution images of the defects of the surface layer and the subsurface layer of the fused quartz damaged sample 9 are obtained through terahertz near-field imaging, the position of the damaged defect can be calibrated accurately, and meanwhile phase spectrum information of the fused quartz damaged sample 9 can be obtained.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.