Photoacoustic detection system and laser spot calibration method

Abstract

The invention relates to the technical field of photoacoustic measurement, and particularly provides a photoacoustic detection system and a laser spot calibration method. Optical devices such as a microscope are additionally arranged in an existing film thickness photoacoustic measurement device to carry out data acquisition on spot characteristic parameters at different positions of a light path; light spot jitter amplitudes and jitter frequencies of the pump light and the probe light are obtained according to the light spot images, and the light spot jitter amplitudes and the jitter frequencies of the pump light and the probe light are reduced by actively adjusting a light beam adjuster; and according to the light spot image of the sample to be detected and / or the standard sample, the light spot centroid distance of the pump light and the probe light and the fluctuation amplitude and fluctuation frequency of the centroid distance are obtained, and accordingly, a light beam regulator of the pump light and the probe light is adjusted, and the light spot coincidence ratio of the pump light spot and the probe light spot is improved. By actively controlling the movement of the light beam regulator, the light spot jitter is tracked, the light spot overlap ratio of the pump light and the probe light is improved, and the signal-to-noise ratio of a photoacoustic measurement signal is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of photoacoustic measurement, and particularly relates to a photoacoustic detection system and a laser spot calibration method. Background Art

[0002] In the semiconductor field, the photoacoustic effect principle is widely used to measure a series of film layer parameters such as the film thickness, sound velocity, and Young's modulus of metal and dielectric films.

[0003] The photoacoustic measurement principle is as follows: The pump light irradiates on the surface of the sample to be measured, ultrasonic waves are excited inside the sample to be measured, the ultrasonic waves propagate into the sample and are reflected at the interface of different material film layers, forming an echo signal that returns to the surface, causing changes in the surface topography and reflectivity of the sample. By measuring these changes on the sample surface with the probe light, the transmission time of the ultrasonic wave in the material can be obtained, and the film thickness value of the sample can be calculated based on this time.

[0004] According to the photoacoustic measurement principle, the ultrasonic signal is generated by the pump light at the spot area. Theoretically, to obtain the photoacoustic signal with the best signal-to-noise ratio, the probe light spot needs to coincide with the pump light spot as much as possible, and the size and position of the coincident spot should be as stable as possible. In the existing technical solutions, corresponding optical instruments are usually used to perform static calibration on the spot position, size, and spot coincidence before the measurement starts. However, during the actual measurement process, due to the operation of various optical, mechanical, and electronic components, the spot size, spot position, and spot coincidence usually have dynamic changes, and at this time, noise will be introduced into the measurement result, and the signal-to-noise ratio of the photoacoustic signal will decrease.

[0005] Therefore, there is an urgent need to design a measurement method that can compensate for external noise and improve the signal-to-noise ratio of the photoacoustic signal. Summary of the Invention

[0006] In view of this, the present invention aims to provide a photoacoustic detection system and a laser spot calibration method. By introducing an imaging module into the existing film thickness ultrasonic measurement device, data collection is performed on the spot characteristic parameters at a specific position in the optical path, and by adjusting the optical path components, the spot coincidence is improved to achieve the calibration of the pump light spot and the probe light spot.

[0007] To achieve the above object, the technical solution of the present invention is realized as follows: On the one hand, the present invention provides a photoacoustic detection system, including: A light source for emitting a probe light and a pump light, the pump light being used to induce changes in the optical properties of the sample to be measured; An imaging module for collecting spot images of the pump light and the probe light at at least one position in the optical path; A signal processing module, which obtains the spot jitter amplitude, jitter frequency and centroid distance of the pump light and the probe light at the at least one position based on the spot image at the at least one position; A beam regulator, which is arranged on the optical path of the pump light and / or the probe light, and is used to suppress the spot jitter of the pump light and / or the probe light and make the pump light spot and the probe light spot coincide according to the spot jitter amplitude, jitter frequency and centroid distance at the at least one position; A detector, which is used to receive the probe light reflected by the sample to be measured.

[0008] Preferably, the beam regulator includes a mirror.

[0009] Preferably, the beam regulator includes a beam diameter adjusting lens group.

[0010] Preferably, the photoacoustic detection system further includes: a standard sample piece, which is arranged on the fixing device of the sample to be measured; The obtaining of the spot jitter amplitude, jitter frequency and centroid distance of the pump light and the probe light at the at least one position based on the spot image at the at least one position includes: Obtaining the spot jitter amplitude and jitter frequency of the pump light and the probe light based on the spot image on the surface of the mirror, the surface of the sample to be measured or the surface of the standard sample piece; Obtaining the centroid distance of the pump light and the probe light based on the spot image on the surface of the sample to be measured or the surface of the standard sample piece.

[0011] On the other hand, the present invention provides a laser spot calibration method, which uses a photoacoustic detection system, and beam regulators are arranged on the optical paths of the pump light and the probe light, and a beam regulator is arranged on the optical path of the pump light and / or the probe light. The laser spot calibration method includes: Collecting the spot images of the pump light and the probe light at at least one position on the optical path, obtaining the spot jitter amplitude, jitter frequency and centroid distance of the pump light and the probe light at the at least one position based on the spot images at the at least one position; adjusting the beam regulator located on the optical path of the pump light and / or the probe light according to the spot jitter amplitude, jitter frequency and centroid distance of the pump light and the probe light, suppressing the spot jitter of the pump light and / or the probe light and making the pump light spot and the probe light spot coincide.

[0012] Preferably, beam regulators are arranged on the optical paths of the pump light and the probe light, and the beam regulator includes a mirror; Determining the first motion curve of the mirror on the optical path of the pump light according to the spot jitter amplitude and jitter frequency of the pump light at the at least one position, determining the second motion curve of the mirror on the optical path of the probe light according to the spot jitter amplitude and jitter frequency of the probe light at the at least one position, and suppressing the spot position jitter amplitude and jitter frequency of the pump light and the probe light through the movement of the mirror.

[0013] Preferably, according to the centroid distance between the pump light spot and the probe light spot on the surface of the sample to be measured and / or the standard sample, the third motion curve of the mirror on the pump light path and the fourth motion curve of the mirror on the probe light path are designed to make the fluctuation amplitude of the centroid distance less than the preset coincidence threshold.

[0014] Preferably, the first motion curve and the third motion curve are superimposed and fitted to obtain the motion control curve of the mirror on the pump light path; the second motion curve and the fourth motion curve are fitted to obtain the motion control curve of the mirror on the probe light path.

[0015] Preferably, a beam regulator is provided on the light path of the pump light or the probe light, and the beam regulator includes a mirror; According to the spot jitter amplitude and jitter frequency of the pump light and the probe light at the at least one position, the fifth motion curve of the mirror on the pump light path or the probe light path is determined, and the spot positions of the pump light and the probe light are jittered with the same amplitude and the same frequency by the mirror motion.

[0016] Preferably, according to the centroid distance between the pump light spot and the probe light spot on the surface of the sample to be measured and / or the standard sample, the sixth motion curve of the mirror on the pump light path or the probe light path is designed to make the fluctuation amplitude of the centroid distance less than the preset coincidence threshold.

[0017] Preferably, the fifth motion curve and the sixth motion curve are superimposed and fitted to obtain the motion control curve of the mirror on the pump light path or the probe light path.

[0018] Preferably, it further includes: after the mirrors on the pump light path and the probe light path move according to the corresponding motion control curves, calculating the fluctuation amplitude and fluctuation frequency of the centroid distance between the pump light and the probe light on the sample to be measured, and using the fluctuation amplitude and fluctuation frequency of the centroid distance to correct the ultrasonic measurement signal obtained by the film thickness ultrasonic measurement, so as to reduce the influence of the centroid distance between the pump light spot and the probe light spot on the ultrasonic measurement signal.

[0019] Preferably, the beam regulator includes a beam diameter adjustment mirror group; The method further includes: collecting the spot images of the pump light and the probe light at any position on the light path, obtaining the spot diameter change curves of the pump light and the probe light at the any position based on the spot images at the any position; adjusting the beam diameter adjustment mirror group of the pump light and the probe light according to the spot diameter change curves of the pump light and the probe light to reduce the spot diameter change of the pump light and the probe light.

[0020] Compared with the prior art, the present invention can achieve the following beneficial effects: In the present invention, innovatively, during the photoacoustic detection process, the interference of the pump light and probe light spot jitter on the detection result is considered. The imaging module is used to collect data on the spot characteristic parameters at specific positions in the optical path. Based on the obtained spot size, spot position jitter, and spot overlap degree, etc., the beam adjustment component is controlled. By adjusting the optical path components, the overlap degree of the pump light and probe light spots is improved, and the influence of spot jitter on the ultrasonic measurement signal is effectively reduced, thereby significantly improving the signal-to-noise ratio of photoacoustic measurement. The present invention can effectively reduce the noise caused by spot jitter caused by factors such as mechanical vibration. By dynamically controlling the movement of the optical path components and suppressing spot jitter through active compensation, the stability and reliability of photoacoustic measurement are improved. The invention can improve the accuracy of ultrasonic measurement and more accurately measure parameters such as the film thickness of the sample.

[0021] The present invention not only reduces the spot jitter problem caused by factors such as mechanical vibration through dynamic control of the beam regulator, but also further corrects the noise that cannot be eliminated by the active control of the beam regulator through a compensation algorithm. Compared with the traditional method of only calibrating the pump light and probe light before detection without considering the spot jitter caused by external factors during the detection process, the solution of the present invention can suppress the influence of the jitter caused by external factors on the detection result and effectively improve the signal-to-noise ratio of the photoacoustic signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings: Figure 1 is a structural diagram of a photoacoustic detection system provided according to an embodiment of the present invention; Figure 2 is a structural diagram of a photoacoustic detection system provided with a beam combining and condensing module according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation to the present invention. Similar elements in different embodiments are labeled with related similar element numbers. In the following embodiments, many details are described to enable a better understanding of the present invention. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other elements, materials, and methods. In some cases, some operations related to the present invention are not shown or described in the specification, in order to avoid the core part of the present invention being overwhelmed by excessive description. For those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations based on the description in the specification and the general technical knowledge in the art.

[0024] It should be noted that, without conflict, the embodiments and features in the embodiments of the present invention can be combined with each other to form various embodiments. At the same time, the steps or actions in the method description can also be reordered or adjusted in an obvious manner by those skilled in the art. Therefore, the various sequences in the specification and drawings are only for clearly describing a certain embodiment and do not mean that they are the necessary sequences, unless it is stated that a certain sequence must be followed.

[0025] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention. In addition, terms such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more.

[0026] In the description of the present invention, it should be noted that, unless otherwise clearly defined and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0027] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0028] Please refer to Figure 1 , in an embodiment of the present invention, an optoacoustic detection system applicable to film thickness optoacoustic measurement is provided. The imaging module collects data on the spot characteristic parameters at different positions of the optical path, calculates and obtains parameter information such as spot size, spot jitter, and centroid coincidence degree based on the collected spot images, and actively controls the beam regulator to suppress spot jitter, reduce the centroid distance of the spot, and improve the coincidence degree of the pump light and the probe light, so as to solve the problem that factors such as external mechanical disturbances affect the signal-to-noise ratio of the ultrasonic measurement signal.

[0029] Specifically, the optoacoustic detection system includes the following components arranged in sequence along the optical path: A light source. During the optoacoustic measurement process, a laser module is usually used as the light source to provide laser light to irradiate the sample to be measured for ultrasonic pumping and ultrasonic detection.

[0030] A beam splitting module: It is arranged on the rear optical path of the laser emitted by the laser module, and splits the light emitted by the laser module into two paths. One path is the pump light for exciting the sample to be measured; the other path is the probe light for ultrasonic detection.

[0031] Beam adjuster: It includes a mirror on the pump light path and a mirror on the probe light path, as well as controllers for the above two mirrors. The pump light mirror and the probe light mirror are respectively used to adjust the reflection directions of the pump light and the probe light. The movement parameters of the pump light mirror and the probe light mirror can be adjusted in real time through the pump light mirror controller and the probe light mirror controller, including the coordinates of the deflection center of the mirror reflection surface of the mirror, the periodic motion equilibrium position, the rotation amplitude of the mirror, the frequency, etc. The above parameters can be specifically presented as the mirror movement control curve. The pump light and probe light spot images are obtained through the imaging module, and then the movement control curves of the pump light mirror and the probe light mirror are designed. The pump light mirror controller and the probe light mirror controller respectively control the movement of the mirror according to the movement control curves of the pump light mirror and the probe light mirror. The probe light mirror and the pump light mirror can reflect the probe light and the pump light onto the sample to be measured. The surface of the sample to be measured is ultrasonically excited by the pump light, inducing changes in the optical properties of the surface of the sample to be measured. Then, by detecting the probe light reflected by the sample to be measured, the film thickness information on the surface of the sample to be measured is obtained based on the information of the sample to be measured carried by the reflected probe light.

[0032] Photoelectric conversion module: It is used to receive the probe light reflected by the sample to be measured, convert the fluctuation of the received probe light intensity into the fluctuation of an electrical signal, obtain a photoacoustic signal capable of characterizing the information of the sample to be measured, and finally transmit it to the signal processing module.

[0033] Signal processing module: It is used to process and compensate the photoacoustic signal, calculate the measured value of the film thickness of the sample to be measured, and solve the measurement result of the film thickness of the sample to be measured.

[0034] Imaging module: It is used to obtain the spot images on the pump light path and the probe light path.

[0035] Calculate parameters such as the spot size, the jitter of the spot position, and the spot overlap degree based on the spot images obtained by the imaging module, and design the movement of the beam regulator according to these parameters to suppress the spot jitter and solve the influence of external disturbances on the signal-to-noise ratio of the ultrasonic film thickness measurement signal. Usually, optical devices such as CCD can be used for the imaging module. The imaging module can obtain spot images at multiple arbitrary positions, or only obtain spot images at a small number of positions. In the embodiments of the present invention, the imaging module obtains one or more of the spot images on the reflecting surfaces of the pump light mirror and the probe light mirror in the beam regulator, the spot images of the pump light and the probe light on the standard sample, and the spot images on the sample to be measured. Usually, during the spot calibration process, the spot images of the pump light and the probe light at any one of the above three positions are collected by the imaging module, and the spot calibration can be performed according to the selected position. In scenarios where higher precision requirements for spot calibration are required, the spot images of the pump light and the probe light at multiple positions can also be collected, and the spot images of the pump light and the probe light at one of the positions are selected for spot calibration, and the spot calibration results are verified and compensated using the spot images of the pump light and the probe light at other positions, which can further improve the accuracy of spot calibration.

[0036] Among them, the standard sample is used to calibrate the system to ensure the accuracy of the measurement. The sample to be measured is the sample for which the film thickness actually needs to be measured.

[0037] As a feasible embodiment, as Figure 2 shown, a beam combining module and a focusing module can also be sequentially arranged on the rear optical path of the beam regulator to achieve coaxial measurement of the pump light and the probe light. This design requires filtering out the interference of the pump light when collecting the reflected light of the probe light. In addition, the beam combining module can be omitted, and the focusing module can be designed to include two sub-modules to focus the pump light and the probe light respectively.

[0038] As a feasible embodiment, the beam regulator includes a beam diameter adjustment mirror group for adjusting the beam diameters of the pump light and the probe light to suppress the jitter problem of the spot size. Here, the jitter refers to the change in the size of the spot diameter, rather than the change in the centroid position. The beam diameter adjustment mirror group can be arranged on the optical path between the laser module and the beam splitting module. According to the spot images collected by the imaging module, analyze the change in the spot diameter, or the difference between the spot diameter and the preset diameter, and then feedback to the beam regulator. The beam regulator drives the beam diameter adjustment mirror group through the corresponding controller to change the spot diameter and suppress the jitter problem of the spot diameter. At this time, the spot diameters of the pump light and the probe light are simultaneously adjusted by a single beam diameter adjustment mirror group. In addition, two beam diameter adjustment mirror groups can also be designed on the rear optical path of the beam splitting module, that is, one beam diameter adjustment mirror group is arranged on the optical paths of the pump light and the probe light respectively, and the spot diameters of the pump light and the probe light are adjusted by the two beam diameter adjustment mirror groups respectively.

[0039] To achieve the spot calibration of the pump light and the probe light in the above photoacoustic detection system, an embodiment of the present invention provides a laser spot calibration method. It should be noted that the laser spot calibration method of the present invention is not limited to the above-mentioned device and system, but is applicable to any film thickness photoacoustic measurement device and system. When the film thickness ultrasonic measurement device has no spot imaging function, only an imaging module needs to be optimized and added on its basis, and then a closed-loop feedback control can be formed. Specifically, the laser spot calibration method includes the following steps: Collect the pump light spot image and the probe light spot image at any position in the optical path through the imaging module. In the embodiment of the present invention, the pump light spot and the probe light spot on the reflecting surfaces of the pump light mirror and the probe light mirror are respectively collected in real time through the imaging module. Selecting the mirror position for imaging can effectively provide a clear object surface compared with other lens planes in the optical path, which is convenient for the imaging module to capture the spot. To achieve a better imaging effect, a temporary imaging plate can also be added to the optical path to capture the pump light spot image and the probe light spot image at any position in the optical path.

[0040] During the process of the imaging module collecting the spot image, record the jitter position of the pump light spot at each moment, perform time series analysis on the centroid position of the spot, form a pump light spot jitter curve, and determine the spot jitter amplitude of the pump light through the jitter curve and the jitter frequency . Similarly, record the jitter position of the probe light spot at each moment, perform time series analysis on the centroid position of the spot, form a probe light spot jitter curve, and determine the spot jitter amplitude of the probe light through the jitter curve and the jitter frequency . According to the calculated spot jitter amplitude and the jitter frequency of the pump light, design the first motion curve of the mirror on the pump light optical path, that is, control the pump light mirror to swing periodically according to the calculated spot jitter amplitude and the jitter frequency to adjust the position of the pump light in real time and reduce the spot jitter. Similarly, according to the calculated spot jitter amplitude and the jitter frequency of the probe light, design the second motion curve of the mirror on the probe light optical path, that is, control the probe light mirror to swing periodically according to the calculated spot jitter amplitude and the jitter frequency Perform periodic swinging to adjust the position of the detection light in real time and reduce the spot jitter. It can be understood that the acquisition of the spot image and the movement adjustment of the mirror are carried out in real time. Therefore, the spot jitter amplitude generally refers to the difference between the real-time position and the reference position of the spot in the spot image. The reference position can be obtained by calculation in advance or can be the balanced position of the spot jitter within a period of time before the current moment. This process is essentially a tracking process of the mirror for the pump light and the detection light. In this way, the spot jitter amplitude and jitter frequency of the detection light and the detection light are detected as much as possible during the optical path transmission process. For the spot jitter of the detection light and the detection light during the optical path transmission process, the reasons for its generation include the factors of the optical path itself during the measurement process and also the regular vibrations and irregular noises from the outside. By obtaining the continuous spot images of the two optical path mirrors of the excitation light and the detection light for a period of time t respectively, the continuously changing spot centroid coordinates within a period of time can be obtained through the existing spot centroid coordinate algorithm, and then the periodic change functions of the spot centroid coordinates in the two optical paths with respect to time can be obtained: ; ; Among them, is the periodic change of the pump light spot centroid coordinates with respect to time, is the periodic change of the detection light spot centroid coordinates with respect to time, represents the initial phase of the pump light spot centroid coordinates, represents the initial phase of the detection light spot centroid coordinates, represents time. The periodic change functions of the spot centroid coordinates in the above two optical paths with respect to time are respectively input into the mirror controllers of the pump light and the detection light, and the mirror in the excitation light optical path is dynamically controlled to suppress the spot jitter of the excitation light.

[0041] As an optional embodiment, after recording and obtaining the pump light spot jitter curve and the detection light spot jitter curve, the jitter amplitude and jitter frequency of the pump light and the detection light can also be analyzed, and the change of the jitter amplitude difference and the change of the jitter frequency difference of the pump light and the detection light can be calculated. Taking one of the pump light and the detection light as the reference light, the other light is used to track the reference light to achieve the same frequency and the same amount of jitter of the pump light and the detection light, and realize the relative jitter suppression. During the relative jitter suppression process, the pump light mirror or the detection light mirror can be selected for control adjustment according to the change of the jitter amplitude difference and the change of the jitter frequency difference of the pump light and the detection light. Compared with suppressing the pump light jitter and the detection light jitter separately, the method of using one light to track the jitter of the other light only needs to control the mirror on the optical path of one light during the control process, and the control process is simpler.

[0042] According to the principle of measuring film thickness by photoacoustic method, when there is a misalignment between the pump light and the probe light, the photoacoustic signal characterizing the film thickness will fluctuate with the degree of spot misalignment. Therefore, after suppressing the jitter of the pump light and probe light spots, it is necessary to further adjust the pump light and the probe light so that the centroids of the pump light spot and the probe light spot coincide as much as possible. To achieve this goal, it is also necessary to collect the spot images on the surface of the sample to be measured and / or the standard sample through the imaging module. Generally, when there is no sample to be measured, only when calibrating the photoacoustic detection system before measurement, it is necessary to collect the pump light and probe light spots on the surface of the standard sample. When actually measuring the sample to be measured, directly collect the pump light and probe light spots on the surface of the sample to be measured and perform spot calibration. In special cases, it is also possible to collect spots for both the standard sample and the sample to be measured.

[0043] After collecting the pump light and probe light spot images on the surface of the standard sample, based on these spots, the centroid distance D between the pump light spot and the probe light spot can be calculated, presenting an overall centroid distance fluctuation curve of the pump light and probe light spots. According to the centroid distance between the pump light and probe light spots on the surface of the sample to be measured, design the third motion curve of the mirror on the pump light path and the fourth motion curve of the mirror on the probe light path. According to the fluctuation curve, the pump light mirror and the probe light mirror in the beam adjuster can be adjusted to change the equilibrium position of the periodic motion of the mirror. Make the distance D between the centroid coordinates of the pump light spot and the centroid coordinates of the probe light spot on the surface of the sample to be measured less than the preset coincidence threshold , and improve the coincidence degree of the pump light spot and the probe light spot.

[0044] During the adjustment process, it is possible to choose to adjust the pump light mirror and the probe light mirror simultaneously, or only adjust the pump light mirror or the probe light mirror individually. When a certain mirror is not adjusted, there is no corresponding motion curve. The specific adjustment method can be realized through control algorithms such as PID, which is not within the scope of discussion of the present invention.

[0045] As an alternative embodiment, the beam adjuster further includes a motion control component, and the pump light mirror controller and the probe light mirror controller control the motion control component to adjust the motion parameters of the pump light mirror and the probe light mirror. The motion control component can be a galvanometer or an electric displacement stage.

[0046] Regarding the situation of collecting pump light and probe light spot images on the surface of the sample to be measured, or the situation of collecting spot images on both the sample to be measured and the standard sample at the same time, the specific design process is the same as the above design method of collecting spot images on the surface of the standard sample, and will not be elaborated here.

[0047] After obtaining the first, second, third, and fourth motion curves, the first and third motion curves corresponding to the pump light are superimposed and fitted to form the motion control curve for the reflector in the pump light path. The second and fourth motion curves corresponding to the probe light are superimposed and fitted to form the motion control curve for the reflector in the probe light path. The first motion curve reflects the rotation curve of the reflector around its axis, while the third motion curve reflects the change in the center position of the reflector. These two curves are fitted to form a multidimensional control curve, and the superimposed fitting is a superposition of the motion dimensions. The superimposed fitting principle for the second and fourth motion curves is similar to the above.

[0048] The two motion control curves are fed back to the pump light reflector controller and the probe light reflector controller, which drive the corresponding reflectors according to the corresponding curves. The above design basically eliminates regular vibrations introduced by the optical path and external factors, and can partially eliminate irregular noise.

[0049] As an optional embodiment, when selecting one light beam to track the jitter of another light beam, a beam adjuster including a reflector can be provided only in the optical path of the pump light or the probe light. When no beam adjuster is provided in the optical path of the other light beam, the present invention uses the pump light as the reference light for illustration. When the pump light serves as the reference light, a reflector is provided only in the optical path of the probe light. Based on the spot images captured by the imaging module at any position of the pump light and the probe light, the pump light spot jitter curve and the probe light spot jitter curve are obtained. Using the pump light spot jitter curve as a reference, the probe light is driven to track the pump light, achieving relative stillness of the pump light and the probe light. Using the pump light spot jitter curve as a reference, a fifth motion curve of the reflector in the probe light path is obtained to achieve the aforementioned tracking purpose. This ensures that after the reflector in the probe light path moves according to the fifth motion curve, the pump light and probe light spot position jitter amplitudes and jitter frequencies are the same.

[0050] Furthermore, based on the light spot images collected by the imaging module on the surface of the sample to be tested and / or the standard sample of the pump light and the detection light, and with the position of the centroid of the pump light spot as a reference, the change in the distance between the centroid of the detection light spot and the centroid of the pump light spot is obtained, and the sixth motion curve of the reflector in the beam adjuster on the detection light path is designed to ensure that after the reflector on the detection light path moves according to the sixth motion curve, the fluctuation amplitude of the distance between the centroids of the pump light and the detection light spots is less than a preset overlap threshold.

[0051] The motion control curve of the reflector in the detection light path can be obtained by superimposing and fitting the fifth motion curve and the sixth motion curve. When the detection light is used as the reference light and the pump light is used to track the detection light, the specific calculation and control method is the same as above.

[0052] Similarly, a beam diameter adjustment lens group can also be provided only on the optical path of the pump light or the probe light. By the same method as above, taking one beam of light as a reference, a beam diameter adjustment lens group is provided on the optical path of the other beam of light. By controlling this beam diameter adjustment lens group, the tracking of the jitter of the spot size of the reference light is realized, so that the difference in the spot diameters of the pump light and the probe light meets the preset requirements.

[0053] As an optional embodiment, in order to eliminate as much as possible the noise that cannot be eliminated by the mirror control, after the mirrors on the optical paths of the pump light and the probe light move according to the corresponding motion control curve, the fluctuation amplitude Amp of the centroid distance and the fluctuation frequency Freq of the centroid distance between the pump light and the probe light on the sample to be measured are calculated based on the spot image. Then, the fluctuation amplitude Amp of the centroid distance and the fluctuation frequency Freq of the centroid distance are input into the signal processing module of the ultrasonic measurement signal, and they are corrected during the analysis of the ultrasonic signal on both sides, reducing the influence of the centroid distance between the pump light spot and the probe light spot on the ultrasonic measurement signal and improving the signal-to-noise ratio of the ultrasonic measurement signal.

[0054] As an optional embodiment, in addition to correcting the spot jitter and the spot coincidence degree, a beam diameter adjustment lens group, such as a 4f lens group, can also be added to the optical path. The spot images of the pump light and the probe light at any position in the optical path are collected through the imaging module. In the embodiment of the present invention, the pump light spot and the probe light spot on the surfaces of the pump light mirror and the probe light mirror are collected. According to the spot image, the change in the spot diameter can be obtained, specifically manifested as the spot diameter change curve of the spot size jitter. The beam diameter adjustment lens group of the pump light is adjusted according to the spot diameter change curve of the pump light to reduce the change in the spot diameter of the pump light; the beam diameter adjustment lens group of the probe light is adjusted according to the spot diameter change curve of the probe light to reduce the change in the spot diameter of the probe light. The suppression of the spot diameter jitter is realized, and the signal-to-noise ratio of the ultrasonic measurement signal can also be further improved.

[0055] In summary, the above description is only the preferred embodiments of this specification and is not used to limit the protection scope of this specification. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this specification shall be included within the protection scope of this specification.

[0056] The system, device, module or unit illustrated by the above one or more embodiments can be specifically implemented by a computer chip or entity, or by a product with certain functions. A typical implementation device is a computer. Specifically, the computer can be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or any combination of these devices.

[0057] It should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, commodity or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, commodity or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, commodity or device comprising said element.

[0058] Each embodiment in this specification is described in a progressive manner. For the parts that are the same or similar among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and reference can be made to the corresponding parts of the method embodiment for the relevant content.

[0059] The specific embodiments of this specification have been described above. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than in the embodiments and still achieve the desired result. Additionally, the processes depicted in the figures do not necessarily require the specific order or sequential order shown to achieve the desired result. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A photoacoustic detection system, characterized in that, Comprising: A light source for emitting detection light and pump light, wherein the pump light is used to induce changes in the optical properties of a sample to be measured; An imaging module for collecting spot images of the pump light and the detection light at at least one position in the optical path; A signal processing module for obtaining the spot jitter amplitude, jitter frequency, and centroid distance of the pump light and the detection light at the at least one position based on the spot images at the at least one position; A beam regulator disposed on the optical path of the pump light and / or the detection light, for suppressing the spot jitter of the pump light and / or the detection light and making the pump light spot and the detection light spot coincide according to the spot jitter amplitude, jitter frequency, and centroid distance at the at least one position; A detector for receiving the detection light reflected by the sample to be measured.

2. The photoacoustic detection system according to claim 1, wherein The beam regulator includes a mirror.

3. The photoacoustic detection system according to claim 1 or 2, characterized in that The beam regulator includes a beam diameter adjustment lens group.

4. The photoacoustic detection system according to claim 2, characterized in that, The photoacoustic detection system further includes: a standard sample piece, a fixing device for the sample to be measured; The obtaining the spot jitter amplitude, jitter frequency, and centroid distance of the pump light and the detection light at the at least one position based on the spot images at the at least one position includes: Obtaining the spot jitter amplitude and jitter frequency of the pump light and the detection light based on the spot images on the surface of the mirror, the surface of the sample to be measured, or the surface of the standard sample piece; Obtaining the centroid distance of the pump light and the detection light based on the spot images on the surface of the sample to be measured or the surface of the standard sample piece.

5. A laser spot calibration method using a photoacoustic detection system, characterized in that, A beam regulator is disposed on the optical path of the pump light and / or the detection light, and the laser spot calibration method includes: Collecting spot images of the pump light and the detection light at at least one position in the optical path, obtaining the spot jitter amplitude, jitter frequency, and centroid distance of the pump light and the detection light at the at least one position based on the spot images at the at least one position; adjusting the beam regulator located on the optical path of the pump light and / or the detection light according to the spot jitter amplitude, jitter frequency, and centroid distance of the pump light and the detection light, suppressing the spot jitter of the pump light and / or the detection light and making the pump light spot and the detection light spot coincide.

6. The laser spot calibration method according to claim 5, characterized in that A beam regulator is disposed on the optical path of the pump light and the detection light, and the beam regulator includes a mirror; Determining a first motion curve of the mirror on the pump light optical path according to the spot jitter amplitude and jitter frequency of the pump light at the at least one position, determining a second motion curve of the mirror on the detection light optical path according to the spot jitter amplitude and jitter frequency of the detection light at the at least one position, and suppressing the spot position jitter amplitude and jitter frequency of the pump light and the detection light through the mirror motion.

7. The laser spot calibration method according to claim 6, characterized in that, Designing a third motion curve of the mirror on the pump light optical path and a fourth motion curve of the mirror on the detection light optical path according to the centroid distance of the pump light and the detection light on the surface of the sample to be measured and / or the standard sample piece, so that the fluctuation amplitude of the centroid distance is less than a preset coincidence threshold.

8. The laser spot calibration method according to claim 7, wherein Superposing and fitting the first motion curve and the third motion curve to obtain a motion control curve of the mirror on the pump light optical path; fitting the second motion curve and the fourth motion curve to obtain a motion control curve of the mirror on the detection light optical path.

9. The laser spot calibration method according to claim 5, wherein A beam regulator is disposed on the optical path of the pump light or the detection light, and the beam regulator includes a mirror; Determine the fifth motion curve of the mirror on the pump light or probe light path according to the spot jitter amplitude and jitter frequency of the pump light and the probe light at the at least one position, and make the spot position jitter amplitudes of the pump light and the probe light the same and the jitter frequencies the same by moving the mirror.

10. The laser spot calibration method according to claim 9, characterized in that, Design the sixth motion curve of the mirror on the pump light or probe light path according to the centroid distance between the spots of the pump light and the probe light on the surface of the sample to be measured and / or the standard sample piece, so that the fluctuation amplitude of the centroid distance is less than a preset coincidence threshold.

11. The laser spot calibration method according to claim 10, wherein Superpose and fit the fifth motion curve and the sixth motion curve to obtain the motion control curve of the mirror on the pump light or probe light path.

12. The laser spot calibration method according to claim 8 or 11, wherein Further comprising: After the mirror on the pump light and probe light paths moves according to the corresponding motion control curve, calculate the fluctuation amplitude and fluctuation frequency of the centroid distance between the pump light and the probe light on the sample to be measured, and use the fluctuation amplitude and fluctuation frequency of the centroid distance to correct the ultrasonic measurement signal obtained by the ultrasonic measurement of the film thickness, so as to reduce the influence of the centroid distance between the pump light spot and the probe light spot on the ultrasonic measurement signal.

13. The laser spot calibration method according to claim 5, characterized in that The beam adjuster includes a beam diameter adjustment mirror group; The method further comprises: collecting the spot images of the pump light and the probe light at any position on the optical path, obtaining the spot diameter change curves of the pump light and the probe light at the any position based on the spot images at the any position; adjusting the beam diameter adjustment mirror group of the pump light and the probe light according to the spot diameter change curves of the pump light and the probe light, so as to reduce the change of the spot diameters of the pump light and the probe light.

Images