阅读说明：本技术 一种键合板条键合面相对损耗值的获取方法 (Method for obtaining relative loss value of bonding surface of bonding strip ) 是由 张建中 马占宇 柴全 苑勇贵 王钢 王超 于 2020-06-02 设计创作，主要内容包括：本发明提供一种键合板条键合面相对损耗值的获取方法,属于激光键合晶体板条的质量检测领域,首先运用已知反射率的标准反射面获取白光干涉装置回损校对值；然后通过干涉仪的延迟线结构,对待测板条中垂直键合面的深度方向扫描测试,获取各个反射面的分布式干涉强度信号,以及键合面的深度定位；进一步利用探头中已知反射率薄膜为标准,将干涉信号转化为反射率的分布式结果,并结合标准反射面的损耗校对值对测量结果校准；再利用菲涅尔反射公式将表面反射率测量结果转化为晶体的折射率,进而计算出键合面处理想的菲涅尔反射率理论值；最后通过键合面的反射率测量值与菲涅尔反射率理论值对比,得到键合面相对损耗值,以此评价键合面质量。(The invention provides a method for obtaining a relative loss value of a bonding surface of a bonding plate strip, which belongs to the field of quality detection of laser bonding crystal plate strips, and comprises the steps of firstly obtaining a return loss calibration value of a white light interference device by using a standard reflecting surface with known reflectivity; then, through a delay line structure of an interferometer, scanning and testing the depth direction of a vertical bonding surface in the strip to be tested to obtain distributed interference intensity signals of all reflecting surfaces and depth positioning of the bonding surface; further converting the interference signal into a distributed result of the reflectivity by using a known reflectivity film in the probe as a standard, and calibrating the measurement result by combining a loss calibration value of a standard reflecting surface; converting the surface reflectivity measurement result into the refractive index of the crystal by utilizing a Fresnel reflection formula, and further calculating an ideal Fresnel reflectivity theoretical value at the bonding surface; and finally, comparing the reflectivity measurement value of the bonding surface with the Fresnel reflectivity theoretical value to obtain a relative loss value of the bonding surface so as to evaluate the quality of the bonding surface.)

1. A method for obtaining a relative loss value of a bonding surface of a bonding strip is characterized by comprising the following steps: the method comprises the following steps:

the method comprises the following steps: debugging a white light interference measurement system according to the size, the type and the absorption spectrum of the bonding lath to be measured;

step two: the white light interference measurement system tests a standard reflecting surface with known reflectivity to obtain an interference signal value, and evaluates measurement signal fluctuation caused by probe distance change to obtain a calibration reference value of return loss;

step three: a delay line structure in the white light interference measurement system performs scanning test on the bonding lath to be tested to obtain a distributed interference intensity signal of each reflecting surface;

step four: the known reflectivity film in a probe of a white light interference measurement system is used as a standard, the relative intensity value of the distributed interference intensity signal is converted into a distributed result of the reflectivity, and the measurement result is calibrated by combining a calibration reference value of return loss;

step five: converting the true surface reflectivity measurement result of the distributed result into the refractive index of the crystal by utilizing a Fresnel formula, and calculating an ideal Fresnel reflectivity theoretical value at the bonding surface;

step six: and obtaining a relative loss value of the bonding surface by comparing the reflectivity measured value of the bonding surface in the distributed result with the Fresnel reflectivity theoretical value.

2. The method for obtaining the relative loss value of the bonding surface of the bonding strip as claimed in claim 1, wherein: the white light interference system in the first step adopts an optical fiber Michelson interferometer structure and is matched with an optical fiber probe, the light source is a wide-spectrum white light source, the end face of the optical fiber probe is provided with a self-focusing lens, and a layer of film with known reflectivity and transmissivity is used for calibrating the reflectivity of the reflecting surface to be measured; the high-precision scanning of the delay line can accurately position the optical path of the reflecting surface to be measured.

3. A method of obtaining a relative loss value of a bonding face of a bonding strip as claimed in claim 1 or 2, wherein: and the scanning test in the third step is to perform the scanning test along the direction vertical to the bonding surface of the bonding strip to be tested.

4. A method of obtaining a relative loss value of a bonding face of a bonding strip as claimed in claim 1 or 2, wherein: the fifth step is specifically as follows: and by utilizing a Fresnel reflection formula, taking the refractive index of air as 1 on the two outer surfaces of the strip, obtaining the refractive indexes of YAG crystals of the two parts of the strip according to the reflectivity measurement results of the two outer surfaces in the distributed result, and calculating the ideal Fresnel reflectivity at the bonding surface according to the two refractive indexes to be used as the theoretical value of the reflectivity of the bonding surface.

5. A method of obtaining a relative loss value of a bonding face of a bonding strip as claimed in claim 3, wherein: the fifth step is specifically as follows: and by utilizing a Fresnel reflection formula, taking the refractive index of air as 1 on the two outer surfaces of the strip, obtaining the refractive indexes of YAG crystals of the two parts of the strip according to the reflectivity measurement results of the two outer surfaces in the distributed result, and calculating the ideal Fresnel reflectivity at the bonding surface according to the two refractive indexes to be used as the theoretical value of the reflectivity of the bonding surface.

6. The method for obtaining the relative loss value of the bonding surface of the bonding strip as claimed in claim 4, wherein: bonding surface relative loss value in step sixR_{Measured value}For reflectance measurements of the bonding surface in the distributed result, R_{Theoretical value}As a theory of Fresnel reflectivityThe value is obtained.

7. The method for obtaining the relative loss value of the bonding surface of the bonding strip as claimed in claim 5, wherein: bonding surface relative loss value in step six

Technical Field

The invention relates to a method for acquiring a relative loss value of a bonding surface of a bonding plate strip, belonging to the field of quality detection of laser bonding crystal plate strips.

Background

The laser bonding lath prepared by thermal diffusion bonding can improve the laser thermal performance and the beam quality in the aspect of laser technology, and is beneficial to the integration of a laser system and the acquisition of large-size crystal laths. The diffusion bonding manufacturing method is originated from the processing technology of semiconductors, and Lee et al (Proc. SPIE.1992,1624: 2-10.) have been applied to the preparation application of composite laser crystal slabs firstly. With the rapid development of high-power lasers, the quality requirements on the bonding crystal, especially the bonding quality of the bonding surface, are higher and higher. The current detection technology mainly centers on the following points: tsunekane et al [ IEEEjournal of Selected topocs in Quantum Electronics,1997,3(1):0-18 ] obtained the distribution of residual stress at the bonding surface by an optical measurement method of birefringence; sugiyama et al Applied Optics,1998,37(12): 2407-. But the method is a detection method which cannot trace the source, and only can represent the influence of the whole crystal on the light beam. Besides, the method also comprises various microscopic amplification material detection methods, including lateral surface microscopic chromatography, Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), atomic force microscope (ARM), electron microprobe detection (EPMA) and the like. The detection of the microscopic magnification can qualitatively observe the local defect distribution of the crystal bonding surface, but all the detection methods need to carry out destructive treatment of ion grinding and thinning on a sample to be detected, and have low detection efficiency and high cost.

The optical fiber white light interference technology (or called low coherence light interference technology) originates from a partial coherent light theory, and as a measurement technology, has the advantages of being capable of aligning with static parameters to realize absolute measurement, free from the periodic influence of an optical transfer function, capable of realizing measurement in a large dynamic range, and widely applied due to extremely strong anti-interference capability. The main applications of white light interference technology currently include: polarization state measurements [ Journal of Lightwave Technology 2014.32(22): 3641-. However, application research and development aiming at laser slab testing are lacked at present, particularly, bonding quality detection is aimed at, a distributed testing method of a bonding slab is developed based on an optical fiber white light interferometry technology, particularly the traceable advantage of light spot distributed detection, a novel bonding surface quality characterization parameter is provided, the technical difficulty and cost of detection are reduced, and quantitative data support is provided for research and development of a high-power laser.

Disclosure of Invention

The invention aims to provide a method for acquiring a relative loss value of a bonding surface of a bonding strip, which creatively introduces an optical fiber white light interferometry into the field of quality detection of the bonding strip aiming at the limitation of the existing quality detection method of the bonding strip, provides the relative loss of the bonding surface as a novel quality evaluation parameter of the bonding surface, realizes lossless, efficient, low-cost, quantitative and traceable distributed measurement, and provides quality guarantee for the research and development of a high-power laser.

The purpose of the invention is realized as follows: the method comprises the following steps: debugging a white light interference measurement system according to the size, the type and the absorption spectrum of the bonding lath to be measured;

step two: the white light interference measurement system tests a standard reflecting surface with known reflectivity to obtain an interference signal value, and evaluates measurement signal fluctuation caused by probe distance change to obtain a calibration reference value of return loss;

step three: a delay line structure in the white light interference measurement system performs scanning test on the bonding lath to be tested to obtain a distributed interference intensity signal of each reflecting surface;

step four: the known reflectivity film in a probe of a white light interference measurement system is used as a standard, the relative intensity value of the distributed interference intensity signal is converted into a distributed result of the reflectivity, and the measurement result is calibrated by combining a calibration reference value of return loss;

step five: converting the true surface reflectivity measurement result of the distributed result into the refractive index of the crystal by utilizing a Fresnel formula, and calculating an ideal Fresnel reflectivity theoretical value at the bonding surface;

step six: and obtaining a relative loss value of the bonding surface by comparing the reflectivity measured value of the bonding surface in the distributed result with the Fresnel reflectivity theoretical value.

The invention also includes such structural features:

1. the white light interference system in the first step adopts an optical fiber Michelson interferometer structure and is matched with an optical fiber probe, the light source is a wide-spectrum white light source, the end face of the optical fiber probe is provided with a self-focusing lens, and a layer of film with known reflectivity and transmissivity is used for calibrating the reflectivity of the reflecting surface to be measured; the high-precision scanning of the delay line can accurately position the optical path of the reflecting surface to be measured.

2. And the scanning test in the third step is to perform the scanning test along the direction vertical to the bonding surface of the bonding strip to be tested.

3. The fifth step is specifically as follows: and by utilizing a Fresnel reflection formula, taking the refractive index of air as 1 on the two outer surfaces of the strip, obtaining the refractive indexes of YAG crystals of the two parts of the strip according to the reflectivity measurement results of the two outer surfaces in the distributed result, and calculating the ideal Fresnel reflectivity at the bonding surface according to the two refractive indexes to be used as the theoretical value of the reflectivity of the bonding surface.

4. Bonding surface relative loss value in step sixR_{Measured value}For reflectance measurements of the bonding surface in the distributed result, R_{Theoretical value}Is the fresnel reflectivity theoretical value.

Compared with the prior art, the invention has the beneficial effects that: the invention relates to a method for acquiring a relative loss value of a bonding surface of a bonding strip, which realizes the acquisition of the relative loss value of the bonding surface through various steps, and the loss value can provide innovative help and new evaluation indexes for subsequent research, measurement and evaluation, so that the corresponding measurement is more accurate, namely: 1. the invention innovatively provides the relative loss value of the bonding surface of the laser lath as a quantitative index for the quality evaluation of the bonding surface, so that the detection difficulty and the detection cost are reduced while the quality of the bonding surface is effectively analyzed; 2. the optical fiber white light interference system is applied to the field of quality detection of laser bonding battens, high-precision and large-dynamic-range testing of the quality of a bonding surface is realized, and the method is a basis for realizing a set of nondestructive, high-efficiency, quantitative and traceable systematic testing method; 3. the measurement result of the standard reflecting surface with known reflectivity is used as the return loss correction value of the measuring device, the test result of the lath is effectively calibrated, and the measurement precision and stability are further improved.

Drawings

FIG. 1 is a schematic diagram of a measurement system of the present invention;

FIG. 2 is a schematic representation of the interference principle of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

The invention comprises the following steps:

1. preliminarily evaluating the size, the type and the absorption spectrum of the batten to be measured, and debugging an interference measurement system;

defining the measurement depth of the crystal, and providing a debugging standard for scanning a delay line; the absorption spectrum of the doped part of the crystal is determined, and a reference is provided when the wavelength of a light source is selected, so that an absorption peak is effectively avoided; the method is characterized in that a bonding structure is definite, and comprises the bonding layer number and the bonding surface depth coarse positioning, the common double-layer bonding structure is taken as a research object, and packaging, film coating or integration are not carried out.

2. Testing a standard reflecting surface with known reflectivity by using a white light interference system to obtain an interference signal value, evaluating measurement signal fluctuation caused by probe distance change, and giving a calibration reference value of return loss;

the white light interference system adopts an optical fiber Michelson interferometer structure and is matched with an optical fiber probe, wherein the light source is a wide-spectrum white light source which is stable and continuous; the end face of the optical fiber probe is provided with a self-focusing lens which collimates and receives return light, wherein the optical fiber probe comprises a layer of film with known reflectivity and transmissivity and is used for calibrating the reflectivity of a reflecting surface to be measured; the high-precision scanning of the delay line can accurately position the optical path of the reflecting surface to be measured.

The standard reflecting surface with known reflectivity is tested, so that the deviation caused by the light path conversion of the probe part, especially the measurement signal fluctuation caused by the distance change between the object to be measured and the probe can be accurately acquired, and the calibration reference value of the return light loss is given.

3. Carrying out scanning test on the bonded strip, and carrying out scanning test along the direction vertical to the bonding surface through a delay line structure to obtain distributed interference intensity signals of each reflecting surface and depth positioning of the bonding surface;

the high-precision real-time scanning of the delay line structure is matched with the real-time signal acquisition of the detection module, and the corresponding interference intensity value in the process of gradually increasing the optical path difference is accurately obtained.

4. Converting the relative intensity value of the interference signal into a distributed result of the reflectivity by using a known reflectivity film in the probe as a standard, and calibrating the measurement result by combining a return loss calibration value;

the detection module detects the interference intensity alternating term, and the interference intensity alternating term can be accurately converted into the reflectivity corresponding to each reflecting surface to be detected through taking the relative value of logarithmic subtraction.

5. Converting the surface reflectivity measurement result into the refractive index of the crystal by utilizing a Fresnel formula, and calculating an ideal Fresnel reflectivity theoretical value at the bonding surface;

and by utilizing a Fresnel reflection formula, taking the refractive index of air as 1 on the two outer surfaces of the strip, calculating the refractive indexes of YAG crystals at the two parts of the strip according to the reflectivity measurement results of the two outer surfaces, and calculating the ideal Fresnel reflectivity at the bonding surface according to the two refractive indexes to be used as the theoretical value of the reflectivity of the bonding surface.

6. And comparing the reflectivity measured value of the bonding surface with the Fresnel reflectivity theoretical value to obtain a relative loss value of the bonding surface so as to evaluate the quality of the bonding surface.

And dividing the measured value of the reflectivity of the bonding surface by the theoretical value of the reflectivity of the bonding surface, taking the logarithm, and defining the logarithm as the relative loss value of the bonding surface so as to evaluate the quality defect condition of the bonding surface.

The optical fiber white light interference system adopts a Michelson interferometer structure light path, the light path connection is realized by a single mode fiber, and a stable continuous wide-spectrum light source avoiding the absorption wavelength of the lath needs to be selected for the white light source, so that the measurement result is not influenced by the light absorption of the lath.

The optical fiber probe is used for a bridging device of an optical fiber light path and a light passing light path in the crystal, comprises a self-focusing lens and a film for fixing known reflectivity and transmissivity, and provides a measurement comparison reference value of the strip reflectivity while effectively connecting the optical fiber light path and a space light path. The self-focusing lens structure can better receive reflected light of the lath and couple the reflected light back to the optical fiber light path, and can converge light spots to be smaller, thereby being convenient for tracing the quality defect of the bonding surface.

The detector collects the interference intensity values of the optical delay line of the scanning arm at each position, the high-precision positioning of the matched delay line can accurately measure the reflected light intensity values of the lath at each position in the detection depth direction, particularly the reflected light intensity of the bonding surface and the front and rear surfaces, and the distributed test of the bonding lath is realized.

By comparing with the strength of the film with known reflectivity in the probe, the reflectivity distribution in the depth direction of the crystal, especially the reflectivity at the bonding surface, even the reflectivity of a plurality of bonding surfaces can be accurately obtained. If the detection of the bidirectional probe is matched, the reflectivity of the multiple bonding surfaces of the laser crystal of the bonding structure can be further detected with high precision.

The reflectivity distribution result can be further calibrated by matching with the test result of the standard known reflecting surface before the test of the strip, in particular to calibrate the return loss error of the optical path distance between the probe and the strip.

The lath is a crystal which is subjected to surface polishing treatment and is not packaged and integrated, the surface reflection of the lath can be calculated by reasonably applying Fresnel reflection consensus to obtain two refractive indexes of different parts of the bonded lath, and then the theoretical value of the reflectivity of the bonding surface formed by bonding the two parts together is calculated by applying a Fresnel reflection formula.

The measured value of the reflectivity of the bonding surface obtained in the distributed scanning test is compared with a theoretical value, namely, the logarithm is obtained by dividing, so that the relative loss of the bonding surface is obtained.

Examples of binding parameters:

with reference to fig. 1, the optical fiber white light interference system of the present invention includes a wide spectrum white light source 1, optical fiber couplers 2 and 4, a self-focusing optical fiber probe 3, a faraday rotator 5, an optical delay line system 6, and a detection collection system 7, wherein the optical devices are connected via a single mode optical fiber as shown in fig. 1, the detection light in the optical fiber is incident into the bonding strip via the self-focusing lens probe, the incident direction is perpendicular to the crystal bonding surface, and the diameter of the light spot is 100 μm, so as to realize spot-type detection of the light spot on the bonding surface.

The coupler 2 in the light path can be replaced by a circulator, the optical delay line system controls the reflector to move through the high-precision electric scanning device, and the detection and acquisition system carries out real-time monitoring and acquisition on the interference light intensity value.

Step 1, in the debugging process of the optical path, especially, information such as the size parameter of the crystal to be tested and the doping type of the slab is determined, the scanning range of the delay line is adjusted in a targeted manner, and the accuracy of the depth direction distributed scanning test is improved.

In this embodiment, a common composite crystal slab formed by bonding Yb-doped YAG crystal and pure YAG is taken as an example, and the quality of the bonding surface directly affects the working performance of the solid-state laser as the bonding surface is used as an interface for constraining thermal expansion of the doped region. Two outer surfaces of the crystal parallel to the bonding surface are both subjected to superfine grinding and polishing, and are not subjected to other processes such as film coating, and the detection light is perpendicularly emitted into the crystal from the outer surfaces to the bonding interface.

And 2, before detecting the bonded strip, performing contrast test on a standard single crystal with known refractive index, particularly relating to the test of the outer surface reflectivity of the crystal, gradually moving to change the distance between the crystal and the probe to obtain the return loss value of the probe at different distances, and taking the return loss value as a calibration reference value of the subsequent test.

Step 3, a specific light interference principle process of optical detection of the bonding surface: the wide-spectrum light source continuously emits light, enters the optical fiber probe through the coupler 1, then is converged and emitted into the bonded crystal lath, then each reflecting surface including the reflecting surface with known reflectivity in the probe can generate continuous reflected light, the reflected light is reflected back to an optical fiber light path for the second time through the optical fiber probe, then is divided into two identical continuous light signals through the coupler 4 with the splitting ratio of 50:50, the two light signals are respectively reflected by two arms of the interferometer, one arm directly returns through the Faraday rotator, the other arm returns through the optical delay line, the two reflected light paths interfere after passing through the coupler 4 for the second time, and the interference intensity is acquired by the detection acquisition system in real time.

The interference intensity value detected by the detector is matched with the scanning distance of the delay line in real time, the detection intensity value is ensured to be consistent with the actual optical path position of the strip, the optical delay line is continuously scanned, and the distributed test in the depth direction of the strip is realized by matching with the continuous detection of the detection and acquisition system.

The specific interference principle is shown in fig. 2, where the first row and the second row respectively represent two-arm continuous optical signals equally divided by the coupler, and the four reflected signals respectively represent: the probe comprises a probe internal reflection film, an outer surface of the side of the strip close to the probe, a strip bonding surface and the other outer surface of the strip.

In the moving process of the scanning delay line, the optical path difference of the reflected signals of the same surfaces of the two arms gradually increases, as shown in fig. 2, the first column corresponds to the optical path difference of 0, and the second column and the third column are sequentially the process of gradually increasing the optical path difference. While the detector detects the corresponding interference signal as shown in the third row of the figure.

And by combining technologies such as balanced detection and the like, the interference alternating-current intensity value is taken as the interference intensity value detected by the detector, and the peak intensity of the interference white spectrum is extracted by matching with a signal processing means, so that weak signal observation is facilitated, and a logarithmic value is taken and recorded. The formula specifically expressed is:

of reflectivity in step 4Calculating, if the reflectivity needs to be taken into the above equation, then: i is₁＝I_{Fixed arm}×R₁，I₂＝I_{Scanning arm}×R₂The size of the reflectivity can be reflected through the detection of the interference intensity value of the corresponding position.

The reflectivity of other reflecting surfaces except the reflecting surface of the probe can be effectively measured by the film with known reflectivity in the optical fiber probe and the interference relative intensity detection of the optical fiber white light interference measuring system.

And particularly, calibrating the obtained reflectivity, and calibrating a reference value corresponding to the return loss according to the change of the distance between the strip and the probe, which is obtained in the step 2.

And 5, substituting the refractive index of air as 1 into a Fresnel reflection formula, and calculating the refractive indexes n and n' of the two parts corresponding to the front and rear reflection surfaces. The theoretical reflectivity of the bonding surface is then calculated, i.e.:

and 6, dividing the measured reflectivity value of the bonding surface by the theoretical key value, taking a logarithmic value, and defining the logarithmic value as the relative loss of the bonding surface, namely:and testing the bonding surface based on the white light interference system, and evaluating and measuring the quality of the bonding surface at the position of the light spot according to the relative loss.

In summary, the invention belongs to the field of quality detection of laser bonded crystal slabs, and particularly relates to a distributed test method of a bonded crystal slab based on optical fiber white light interference, which comprises the steps of firstly, obtaining a return loss calibration value of a white light interference device by using a standard reflecting surface with known reflectivity; then, through a delay line structure of an interferometer, scanning and testing the depth direction of a vertical bonding surface in the strip to be tested to obtain distributed interference intensity signals of all reflecting surfaces and depth positioning of the bonding surface; further converting the interference signal into a distributed result of the reflectivity by using a known reflectivity film in the probe as a standard, and calibrating the measurement result by combining a loss calibration value of a standard reflecting surface; converting the surface reflectivity measurement result into the refractive index of the crystal by utilizing a Fresnel reflection formula, and further calculating an ideal Fresnel reflectivity theoretical value at the bonding surface; and finally, comparing the reflectivity measurement value of the bonding surface with the Fresnel reflectivity theoretical value to obtain a relative loss value of the bonding surface so as to evaluate the quality of the bonding surface.