Photoacoustic detection system and laser spot calibration method

Abstract

The present application relates to photoacoustic measurement technical field, specifically provide a kind of photoacoustic detection system and laser spot calibration method, optical device such as microscope is additionally arranged in existing film thickness photoacoustic measurement device, and the spot characteristic parameter at different positions of light path is carried out data acquisition, according to spot image, the spot jitter amplitude and jitter frequency of pump light and probe light are obtained, the spot jitter amplitude and jitter frequency of pump light and probe light are reduced by active adjustment beam adjuster;And according to the spot image of sample and / or standard sample piece to be measured, the spot centroid spacing, the fluctuation amplitude and fluctuation frequency of centroid spacing of pump light and probe light are obtained, and the beam adjuster of pump light and probe light is adjusted accordingly, and the coincidence degree of pump light spot and probe light spot is improved.The present application is actively controlled by the movement of beam adjuster, and the coincidence degree of pump light and probe light spot is improved by tracking spot jitter, and the signal-to-noise ratio of photoacoustic measurement signal is effectively improved.

Description

TECHNICAL FIELD

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

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

[0003] The photoacoustic measurement principle is as follows: the pump light is irradiated on the surface of a sample to be measured, ultrasonic waves are excited inside the sample to be measured, the ultrasonic waves propagate to the inside of the sample and are reflected at the interface of the film layers of different materials to form echo signals returning to the surface, so that the surface topography and reflectivity of the sample change. These changes in the surface of the sample are measured by a probe light, so that the transmission time of the ultrasonic waves in the material can be obtained, and the film thickness value of the sample can be calculated according to the time.

[0004] According to the principle of photoacoustic measurement, the ultrasonic signal is generated by the pump light at the light spot area. In theory, 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 coincided light spot need to be kept stable as much as possible. In the prior art, the position, size and coincidence degree of the light spot are usually calibrated statically by using corresponding optical instruments before the measurement starts. However, in the actual measurement process, due to the operation of various optical, mechanical and electronic components, the size, position and coincidence degree of the light spot usually change dynamically during the measurement process. At this time, the measurement result will introduce noise, and the signal-to-noise ratio of the photoacoustic signal is reduced.

[0005] Therefore, it is urgent to design a measurement method which can compensate for external noise and improve the signal-to-noise ratio of the photoacoustic signal. SUMMARY

[0006] Therefore, the application aims to provide a photoacoustic detection system and a laser spot calibration method. An imaging module is introduced into an existing film thickness ultrasonic measurement device to collect data of the light spot characteristic parameters at specific positions of the light path. By adjusting the light path components, the coincidence degree of the light spot is improved, and the calibration of the pump light spot and the probe light spot is realized.

[0007] To achieve the above-mentioned purpose, the technical scheme of the application is as follows:

[0008] The application provides a photoacoustic detection system, which comprises:

[0009] a light source for emitting probe light and pump light, the pump light being used to induce changes in the optical properties of a sample to be measured;

[0010] an imaging module for collecting light spot images of the pump light and the probe light at at least one position of the light path.

[0011] a signal processing module configured to obtain a spot jitter amplitude, a spot jitter frequency and a spot centroid distance of the pump light and the probe light at the at least one position based on the at least one position spot image;

[0012] a beam adjuster disposed in the light path of the pump light and / or the probe light, and configured to suppress the spot jitter of the pump light and / or the probe light and to overlap the pump light spot and the probe light spot according to the spot jitter amplitude, the spot jitter frequency and the spot centroid distance of the pump light and the probe light at the at least one position;

[0013] a detector configured to receive the probe light reflected by the sample under test.

[0014] Preferably, the beam adjuster comprises a mirror.

[0015] Preferably, the beam adjuster comprises a beam diameter adjuster.

[0016] Preferably, the photoacoustic detection system further comprises a standard sample disposed in the fixing device of the sample under test.

[0017] The signal processing module is configured to obtain a spot jitter amplitude, a spot jitter frequency and a spot centroid distance of the pump light and the probe light at the at least one position based on the at least one position spot image, which comprises:

[0018] The signal processing module is configured to obtain a spot jitter amplitude, a spot jitter frequency and a spot centroid distance of the pump light and the probe light at the at least one position based on the at least one position spot image, which comprises:

[0019] The signal processing module is configured to obtain a spot jitter amplitude, a spot jitter frequency and a spot centroid distance of the pump light and the probe light at the at least one position based on the at least one position spot image, which comprises:

[0020] The present application provides another aspect of a laser spot calibration method, which employs a photoacoustic detection system, and a beam adjuster is disposed in the light path of the pump light and the probe light, and the laser spot calibration method comprises:

[0021] collecting a spot image of the pump light and the probe light at at least one position in the light path, obtaining a spot jitter amplitude, a spot jitter frequency and a spot centroid distance of the pump light and the probe light at the at least one position based on the at least one position spot image, and adjusting the beam adjuster in the light path of the pump light and / or the probe light according to the spot jitter amplitude, the spot jitter frequency and the spot centroid distance of the pump light and the probe light to suppress the spot jitter of the pump light and / or the probe light and to overlap the pump light spot and the probe light spot.

[0022] Preferably, the beam adjuster comprises a mirror.

[0023] The first movement curve of the mirror on the light path of the pump light is determined according to the spot jitter amplitude and the jitter frequency of the pump light at the at least one position, the second movement curve of the mirror on the light path of the probe light is determined according to the spot jitter amplitude and the jitter frequency of the probe light at the at least one position, and the mirror movement is used to suppress the spot position jitter amplitude and the jitter frequency of the pump light and the probe light.

[0024] Preferably, the third movement curve of the mirror on the light path of the pump light and the fourth movement curve of the mirror on the light path of the probe light are designed according to the centroid distance of the pump light and the probe light on the surface of the sample and / or the standard sample, so that the fluctuation amplitude of the centroid distance is less than a preset coincidence threshold.

[0025] Preferably, the first movement curve and the third movement curve are superimposed and fitted to obtain the movement control curve of the mirror on the light path of the pump light, and the second movement curve and the fourth movement curve are fitted to obtain the movement control curve of the mirror on the light path of the probe light.

[0026] Preferably, a beam adjuster is arranged on the light path of the pump light or the probe light, and the beam adjuster comprises a mirror.

[0027] The fifth movement curve of the mirror on the light path of the pump light or the probe light is determined according to the spot jitter amplitude and the jitter frequency of the pump light and the probe light at the at least one position, and the mirror movement is used to make the spot position jitter amplitudes of the pump light and the probe light the same and the jitter frequencies the same.

[0028] Preferably, the sixth movement curve of the mirror on the light path of the pump light or the probe light is designed according to the centroid distance of the pump light and the probe light on the surface of the sample and / or the standard sample, so that the fluctuation amplitude of the centroid distance is less than a preset coincidence threshold.

[0029] Preferably, the fifth movement curve and the sixth movement curve are superimposed and fitted to obtain the movement control curve of the mirror on the light path of the pump light or the probe light.

[0030] Preferably, the method further comprises: calculating the fluctuation amplitude and the fluctuation frequency of the centroid distance of the pump light and the probe light on the sample after the mirror on the light path of the pump light and the probe light moves according to the corresponding movement control curves, and using the fluctuation amplitude and the 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 of the pump light spot and the probe light spot on the ultrasonic measurement signal.

[0031] Preferably, the beam adjuster comprises a beam diameter adjusting mirror group.

[0032] The method further comprises: collecting a light spot image of the pump light and the probe light at any position of an optical path, obtaining a light spot diameter variation curve of the pump light and the probe light at the any position based on the light spot image at the any position, and adjusting a light beam diameter adjusting lens group of the pump light and the probe light according to the light spot diameter variation curve of the pump light and the probe light, so as to reduce the light spot diameter variation of the pump light and the probe light.

[0033] Compared with the prior art, the application can achieve the following beneficial effects:

[0034] In the photoacoustic detection process, the application innovatively considers the interference of pump light and probe light spot jitter on the detection result, uses an imaging module to collect data of light spot characteristic parameters at a specific position of an optical path, controls a light beam adjusting component according to the obtained light spot size, light spot position jitter and light spot coincidence degree, adjusts optical path components, improves the light spot coincidence degree of the pump light and the probe light, effectively reduces the influence of light spot jitter on the ultrasonic measurement signal, and significantly improves the signal-to-noise ratio of photoacoustic measurement. The application can effectively reduce the noise caused by light spot jitter caused by mechanical vibration and other factors, suppresses the light spot jitter through active compensation by dynamically controlling the movement of the optical path components, thereby improving the stability and reliability of photoacoustic measurement, and improving the accuracy of ultrasonic measurement and more accurately measuring the film thickness and other parameters of the sample.

[0035] The application not only reduces the light spot jitter problem caused by mechanical vibration and other factors through dynamic control of the light beam adjusting component, but also further corrects the noise that cannot be eliminated by active control of the light beam adjusting component through a compensation algorithm. Compared with the conventional calibration of the pump light and the probe light before detection without considering the light spot jitter caused by external factors during detection, the application can suppress the influence of jitter caused by external factors on the detection result, and effectively improve the signal-to-noise ratio of the photoacoustic signal. BRIEF DESCRIPTION OF DRAWINGS

[0036] The accompanying drawings, which form a part of the present application, are included to provide a further understanding of the application and are incorporated herein for purposes of illustration. The embodiments of the present application, together with its advantages, can best be understood by referring to the following description taken in connection with the accompanying drawings, in which:

[0037] Figure 1 is a structural diagram of a photoacoustic detection system provided according to an embodiment of the application;

[0038] Figure 2 is a structural diagram of a photoacoustic detection system provided according to an embodiment of the application. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and do not constitute a limitation on the present application. In different embodiments, similar elements are associated with similar element labels. In the following embodiments, many details are described in order to make the present application better understood. However, those skilled in the art can easily recognize that some features can be omitted in different cases, or can be replaced by other elements, materials or methods. In some cases, some operations related to the present application are not shown or described in the specification in order to avoid the core part of the present application being overwhelmed by too much description, and it is not necessary for those skilled in the art to describe these related operations in detail according to the description in the specification and general technical knowledge in the art.

[0040] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other to form various embodiments without conflict. Meanwhile, each step or action in the method description can be sequentially adjusted or adjusted in a manner that can be easily seen by those skilled in the art. Therefore, the various sequences in the specification and drawings are only for the purpose of clearly describing a certain embodiment, and do not mean a necessary sequence, unless otherwise stated that a certain sequence must be followed.

[0041] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features limited by "first", "second" and the like can explicitly or implicitly include one or more features. In the description of the present application, unless otherwise stated, the meaning of "a plurality of" is two or more.

[0042] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "linking" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be direct connection, or indirect connection through intermediate medium, or internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0043] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0044] Please refer to Figure 1 In an embodiment of the present application, a photoacoustic detection system suitable for film thickness photoacoustic measurement is provided. The imaging module is used to collect data of spot feature parameters at different positions of the light path. The spot size, spot jitter and centroid coincidence degree and other parameter information are calculated and obtained according to the collected spot image. The spot jitter is suppressed, the spot centroid distance is reduced, the coincidence degree of the pump light and the probe light is improved, and the problem of the influence of external mechanical disturbance and other factors on the signal-to-noise ratio of the ultrasonic measurement signal is solved by actively controlling the light beam adjuster.

[0045] Specifically, the photoacoustic detection system comprises, in sequence along the light path:

[0046] The light source is usually a laser module in the photoacoustic measurement process. The laser module is used to provide laser irradiation to the sample to be measured for ultrasonic pumping and ultrasonic detection.

[0047] The light splitting module is arranged at the rear end of the laser module. The light emitted by the laser module is split 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.

[0048] The light beam adjuster comprises a mirror on the light path of the pump light and a mirror on the light path of the probe light, and a controller of the two mirrors, and the pump light mirror and the probe light mirror are respectively used for adjusting the reflection direction of the pump light and the probe light. The motion 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 mirror reflection center of the mirror, the balance position of periodic motion, the rotation amplitude of the mirror, the frequency and the like, which can be specifically presented as a mirror motion control curve. The pump light and the probe light spot images are obtained through the imaging module, and then the motion control curve of the pump light mirror and the probe light mirror is designed, and the pump light mirror controller and the probe light mirror controller control the mirror motion according to the motion control curve of the pump light mirror and the probe light mirror respectively. The probe light mirror and the pump light mirror can reflect the probe light and the pump light to the sample to be measured, the surface of the sample to be measured is excited by the pump light, the optical property change of the surface of the sample to be measured is induced, and then the probe light reflected by the sample to be measured is detected, and the film thickness information of the surface of the sample to be measured is obtained according to the information of the sample to be measured carried by the reflected probe light.

[0049] The photoelectric conversion module is used for receiving the probe light reflected by the sample to be measured, converting the fluctuation of the received probe light intensity into the fluctuation of the electric signal, obtaining the photoacoustic signal capable of representing the information of the sample to be measured, and finally transmitting the signal into the signal processing module.

[0050] The signal processing module is used for processing and compensating the photoacoustic signal, calculating the film thickness measurement value of the sample to be measured, and calculating the measurement result of the film thickness of the sample to be measured.

[0051] The imaging module is used for obtaining the spot images on the light paths of the pump light and the probe light.

[0052] According to the parameters such as the spot size, spot position jitter and spot overlap degree calculated based on the spot image acquired by the imaging module, the motion of the beam adjuster is designed to control, so as to suppress the spot jitter and solve the influence of external disturbance on the signal-to-noise ratio of the film thickness ultrasonic measurement signal. Generally, the imaging module can adopt optical devices such as CCD. The imaging module can acquire spot images at multiple arbitrary positions or only a small number of positions. In the embodiment of the present application, the imaging module acquires one or more of the spot images on the reflecting surface of the pump light mirror and the probe light mirror in the beam adjuster, 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. Generally, in the spot calibration process, the imaging module is used to collect the spot images of the pump light and the probe light at any one of the above three positions, and the spot calibration is performed according to the selected position. In the scene with high requirement for spot calibration accuracy, the spot images of the pump light and the probe light at multiple positions can also be collected, the spot images of the pump light and the probe light at one position are selected for spot calibration, and the spot images of the pump light and the probe light at other positions are used to verify and compensate the spot calibration result, so as to further improve the accuracy of spot calibration.

[0053] The standard sample is used to calibrate the system to ensure the accuracy of measurement. The sample to be measured is the sample whose film thickness needs to be measured.

[0054] As a feasible embodiment, as shown in Figure 2 As shown in the figure, a beam combining module and a focusing module can also be sequentially arranged on the rear optical path of the beam adjuster to realize the same beam measurement of the pump light and the probe light. This design needs to filter out the interference of the pump light when collecting the reflected light of the probe light. In addition, the beam combining module can also be omitted, and the focusing module can be designed to include two sub-modules to focus the pump light and the probe light respectively.

[0055] As a feasible embodiment, the beam adjuster includes a beam diameter adjusting mirror group for adjusting the beam diameter of the pump light and the probe light to suppress the jitter problem of the spot size. The jitter here refers to the change of the spot diameter, not the change of the centroid position. The beam diameter adjusting mirror group can be arranged on the optical path between the laser module and the light splitting module. According to the spot image collected by the imaging module, the change of the spot diameter or the difference between the spot diameter and the preset diameter is analyzed, and then the beam adjuster is fed back. The beam adjuster drives the beam diameter adjusting mirror group to change the spot diameter through the corresponding controller to suppress the jitter problem of the spot diameter. At this time, the spot diameters of the pump light and the probe light are adjusted by the single beam diameter adjusting mirror group. In addition, two beam diameter adjusting mirror groups can also be designed on the rear optical path of the light splitting module, i.e. one beam diameter adjusting mirror group is arranged on the optical path of the pump light and the probe light respectively, and the two beam diameter adjusting mirror groups are used to adjust the spot diameters of the pump light and the probe light respectively.

[0056] To realize the above-mentioned pump light and probe light spot calibration of the photoacoustic detection system, the embodiment of the present application provides a laser spot calibration method. It should be noted that the laser spot calibration method of the present application 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 does not have a spot image function, only an imaging module needs to be added and optimized on the basis thereof, and then a closed-loop feedback control is formed. Specifically, the laser spot calibration method comprises the following steps:

[0057] The imaging module acquires the pump light spot image and the probe light spot image at any position in the optical path. In the embodiment of the present application, the imaging module acquires the pump light spot and the probe light spot on the reflecting surface of the pump light mirror and the probe light mirror, respectively. The mirror position is selected for imaging. Compared with other lens planes in the optical path, the mirror can effectively provide a clear object plane, which facilitates the spot capture of the imaging module. In order to achieve better imaging effect, a temporary imaging plate can also be added in the optical path to capture the pump light spot image and the probe light spot image at any position in the optical path.

[0058] During the acquisition of the spot image by the imaging module, the jitter position of the pump light spot at each moment is recorded, and the time series analysis of the spot centroid position is performed to form a pump light spot jitter curve. The spot jitter amplitude and the jitter frequency of the pump light are determined through the jitter curve. Similarly, the jitter position of the probe light spot at each moment is recorded, and the time series analysis of the spot centroid position is performed to form a probe light spot jitter curve. The spot jitter amplitude and the jitter frequency of the probe light are determined through the jitter curve. According to the calculated spot jitter amplitude and the jitter frequency of the pump light, a first motion curve of the mirror on the pump light path is designed, that is, the pump light mirror is controlled to periodically swing according to the calculated spot jitter amplitude and the jitter frequency , so as 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, a second motion curve of the mirror on the probe light path is designed, that is, the probe light mirror is controlled to periodically swing according to the calculated spot jitter amplitude and the jitter frequency The periodic swing is performed to adjust the position of the probe light in real time, and to reduce the spot jitter. It can be understood that the spot image acquisition and the movement adjustment of the mirror are performed in real time, so the spot jitter amplitude generally refers to the difference between the real-time position of the spot in the spot image and the reference position. The reference position can be obtained by calculation or can be the balanced position of the spot jitter in a period of time before the current time. The process is essentially a tracking process of the mirror for the pump light and the probe light. In this way, the spot jitter amplitude and the jitter frequency of the probe light and the probe light during the optical path transmission are as far as possible. For the spot jitter of the probe light and the probe light during the optical path transmission, the causes include factors of the optical path itself during the measurement process and regular vibration and irregular noise from the outside. By obtaining continuous spot images of a period of time t through the mirrors in the excitation light and the probe light, the continuously changing spot centroid coordinates in a period of time can be obtained through the existing spot centroid coordinate algorithm, and then the periodic variation functions of the spot centroid coordinates with time in the two optical paths are obtained:

[0059] ;

[0060] ;

[0061] wherein, is the periodic variation of the pump light spot centroid coordinates with time, is the periodic variation of the probe light spot centroid coordinates with time, represents the initial phase of the pump light spot centroid coordinates, represents the initial phase of the probe light spot centroid coordinates, represents time. The periodic variation functions of the spot centroid coordinates with time in the above two optical paths are input into the mirror controllers of the pump light and the probe light, respectively, and the mirror in the excitation light path is controlled dynamically to achieve the suppression of the excitation light spot jitter.

[0062] As an optional embodiment, after obtaining the pump light spot jitter curve and the probe light spot jitter curve, the jitter amplitude and the jitter frequency of the pump light and the probe light can also be analyzed, and the jitter amplitude difference change and the jitter frequency difference change of the pump light and the probe light are calculated. One of the pump light and the probe light is taken as the reference light, and 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 probe light, and to achieve the relative jitter suppression. In the relative jitter suppression process, the pump light mirror or the probe light mirror can be selected and controlled according to the jitter amplitude difference change and the jitter frequency difference change of the pump light and the probe light. Compared with the suppression of the pump light jitter and the probe light jitter respectively, the method of selecting one light to track the jitter of the other light only needs to control the mirror in the optical path of one light in the control process, and the control process is simpler.

[0063] From the principle of measuring film thickness by photoacoustic, when there is a misalignment between the pump light and the probe light, the photoacoustic signal representing the thickness of the film will fluctuate with the degree of misalignment of the light spots. Therefore, after the pump light and the probe light spot jitter is suppressed, the pump light and the probe light still need to be further adjusted so that the pump light spot and the probe light spot can be as much as possible to coincide with the center of mass. In order to achieve this purpose, the imaging module is also needed to collect the light spot image on the surface of the sample to be measured and / or the standard sample. Generally, when there is no sample to be measured, only when the photoacoustic detection system is calibrated before measurement, the pump light and the probe light spots on the surface of the standard sample need to be collected. When the sample to be measured is measured, the pump light and the probe light spots on the surface of the sample to be measured are directly collected for light spot calibration. In special cases, the light spots of the standard sample and the sample to be measured can also be collected.

[0064] After collecting the pump light and the probe light spot image on the surface of the standard sample, the pump light and the probe light spot center of mass distance D can be calculated based on the light spot, and the whole presents as a pump light and a probe light spot center of mass distance fluctuation curve. According to the pump light and the probe light spot center of mass distance on the surface of the sample to be measured, the third movement curve of the mirror in the pump light path and the fourth movement curve of the mirror in the probe light path are designed. According to the fluctuation curve, the pump light mirror and the probe light mirror in the beam adjuster can be adjusted to change the balance position of the periodic motion of the mirror. The distance D between the pump light spot center of mass coordinate and the probe light spot center of mass coordinate on the surface of the sample to be measured is less than the preset coincidence threshold , and the coincidence of the pump light spot and the probe light spot is improved.

[0065] During the adjustment process, the pump light mirror and the probe light mirror can be adjusted simultaneously, or only the pump light mirror or the probe light mirror can be adjusted. When a mirror is not adjusted, there is no corresponding movement curve. The specific adjustment method can be realized by PID control algorithm, which is not within the scope of discussion of the present application.

[0066] As an optional embodiment, the beam adjuster further comprises 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 table.

[0067] As for the case of collecting the pump light and the probe light spot image on the surface of the sample to be measured, or the case of collecting the light spot image on the surface of the sample to be measured and the standard sample at the same time, the specific design process is the same as the design method of collecting the light spot image on the surface of the standard sample, which will not be repeated here.

[0068] After obtaining the first motion curve, the second motion curve, the third motion curve and the fourth motion curve, the first motion curve and the third motion curve corresponding to the pump light are superimposed and fitted to form a motion control curve of the mirror on the pump light path; the second motion curve and the fourth motion curve corresponding to the probe light are superimposed and fitted to form a motion control curve of the mirror on the probe light path. The first motion curve reflects a rotation curve of the mirror rotating around the axis, and the third motion curve reflects a curve of the center position of the mirror changing. The two curves are fitted into a multi-dimensional control curve, and the superimposition and fitting are superimposition in the motion dimension. The superimposition and fitting principles of the second motion curve and the fourth motion curve are the same as above.

[0069] The above two motion control curves are fed back to the pump light mirror controller and the probe light mirror controller, and the corresponding mirrors are driven according to the corresponding curves respectively. Through the above design, regular vibration of the light path and external introduction is basically eliminated, and part of irregular noise can be eliminated.

[0070] As an optional embodiment, when the method of selecting one light to track the jitter of another light is adopted, only one light beam adjuster including a mirror can be arranged on the light path of the pump light or the probe light, and no light beam adjuster is arranged on the light path of the other light. In the implementation of the present application, only the pump light is taken as an example for illustration. When the pump light is taken as the reference light, only the mirror is arranged on the light path of the probe light. According to the light spot images collected 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. The pump light spot jitter curve is taken as a reference to drive the probe light to track the pump light, so that the relative static state of the pump light and the probe light is realized. The fifth motion curve of the mirror on the probe light path is obtained by taking the pump light spot jitter curve as a reference, so that the pump light and the probe light have the same jitter amplitude and the same jitter frequency after the mirror on the probe light path moves according to the fifth motion curve.

[0071] Further, according to the light spot images collected by the imaging module on the surface of the sample to be measured and / or the standard sample of the pump light and the probe light, and taking the light spot centroid position of the pump light as a reference, the distance change of the light spot centroid of the probe light relative to the light spot centroid of the pump light is obtained. The sixth motion curve of the mirror in the light beam adjuster on the probe light path is designed, so that the fluctuation amplitude of the distance between the light spot centroids of the pump light and the probe light is less than a preset coincidence threshold after the mirror on the probe light path moves according to the sixth motion curve.

[0072] The fifth motion curve and the sixth motion curve are superimposed and fitted to obtain the motion control curve of the mirror on the probe light path. When the probe light is taken as the reference light and the probe light is tracked by the pump light, the specific calculation and control method is the same as above.

[0073] Similarly, only one beam diameter adjustment mirror group can be arranged on the light path of the pump light or the probe light. By the same method as described above, one of the two beams of light is taken as a reference, and the other beam of light is arranged with a beam diameter adjustment mirror group. By controlling the beam diameter adjustment mirror group, the tracking of the spot size jitter of the reference light is realized, so that the spot diameter difference between the pump light and the probe light meets the preset requirements.

[0074] As an optional embodiment, in order to eliminate the noise that cannot be eliminated by the mirror control as much as possible, after the mirrors on the light paths of the pump light and the probe light move according to the corresponding motion control curves, the fluctuation amplitude Amp 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 according to the spot images, and then the fluctuation amplitude Amp and the fluctuation frequency Freq of the centroid distance are input into the signal processing module of the ultrasonic measurement signal, and are corrected in the ultrasonic signal analysis process, 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, and improve the signal-to-noise ratio of the ultrasonic measurement signal.

[0075] As an optional embodiment, in addition to correcting the spot jitter and the spot coincidence degree, a beam diameter adjustment mirror group, such as a 4f mirror group, can be additionally arranged in the light path, and the spot images of the pump light and the probe light at any position in the light path are collected by the imaging module. In the embodiment of the present application, the pump light spot and the probe light spot on the surfaces of the pump light mirror and the probe light mirror are collected, and the diameter change of the spot can be obtained according to the spot image, which is specifically represented as a spot diameter change curve of the spot size jitter. The beam diameter adjustment mirror group of the pump light is adjusted according to the spot diameter change curve of the pump light, so as to reduce the spot diameter change of the pump light. The beam diameter adjustment mirror group of the probe light is adjusted according to the spot diameter change curve of the probe light, so as to reduce the spot diameter change of the probe light. The spot diameter jitter suppression is realized, and the signal-to-noise ratio of the ultrasonic measurement signal can be further improved.

[0076] In summary, the above description is only a preferred embodiment of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0077] The system, device, module or unit illustrated in one or more embodiments above 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 electronic mail device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0078] It is also important to note that the terms "comprises", "comprising", or other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0079] Various embodiments in the specification are described with progressive manner. Identical or similar parts in various embodiments can refer to each other, and each embodiment focuses on the difference from other embodiments. In particular, for system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and the relevant parts can refer to the description of method embodiments.

[0080] The above describes specific embodiments of the specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims can be performed in an order different than the order in which they are recited in the embodiments and still achieve desirable results. In addition, the processes depicted in the figures do not necessarily require the particular order shown, or sequential order, to achieve the desired results. In certain implementations, multitasking and parallel processing can be advantageous.

Claims

1. A photoacoustic detection system, characterized by The method comprises the following steps: a light source is used to emit probe light and pump light, and the pump light is used to induce a change in optical characteristics of a sample to be measured; an imaging module is used to collect a light spot image of the pump light and the probe light at at least one position in an optical path; a signal processing module is used to obtain a light spot jitter amplitude, a jitter frequency and a centroid distance of the pump light and the probe light at the at least one position based on the light spot image at the at least one position; a light beam adjuster is arranged in the optical path of the pump light and / or the probe light, and is used to suppress the light 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 light spot jitter amplitude, the jitter frequency and the centroid distance at the at least one position; a detector is used to receive the probe light reflected by the sample to be measured; the light beam adjuster comprises a mirror; when the light beam adjusters are arranged in the optical paths of the pump light and the probe light, a first motion curve of the mirror in the optical path of the pump light is determined according to the light spot jitter amplitude and the jitter frequency of the pump light at the at least one position, a second motion curve of the mirror in the optical path of the probe light is determined according to the light spot jitter amplitude and the jitter frequency of the probe light at the at least one position, and the motion of the mirror is used to suppress the light spot position jitter amplitude and the jitter frequency of the pump light and the probe light; when the light beam adjuster is arranged in the optical path of the pump light or the probe light, a fifth motion curve of the mirror in the optical path of the pump light or the probe light is determined according to the light spot jitter amplitude and the jitter frequency of the pump light and the probe light at the at least one position, and the motion of the mirror is used to make the light spot position jitter amplitudes of the pump light and the probe light the same and the jitter frequencies the same.

2. The photoacoustic detection system of claim 1, wherein, The light beam adjuster comprises a mirror.

3. The photoacoustic detection system of claim 1 or 2, wherein The light beam adjuster comprises a light beam diameter adjusting mirror group.

4. The photoacoustic detection system of claim 2, wherein, The photoacoustic detection system further comprises a standard sample arranged in a fixing device of the sample to be measured. The method for obtaining the light spot jitter amplitude, the jitter frequency and the centroid distance of the pump light and the probe light at the at least one position based on the light spot image at the at least one position comprises the following steps: the light spot jitter amplitude and the jitter frequency of the pump light and the probe light are obtained based on the light spot image of the mirror surface, the sample surface or the standard sample surface; the centroid distance of the pump light and the probe light is obtained based on the light spot image of the sample surface or the standard sample surface.

5. A method of laser spot calibration using a photoacoustic detection system, the method comprising: directing a laser beam at a sample; detecting a photoacoustic signal from the sample; and determining a laser spot size based on the detected photoacoustic signal. The method for calibrating the laser light spot comprises the following steps: light spot images of the pump light and the probe light at at least one position in an optical path are collected, light spot jitter amplitudes, jitter frequencies and centroid distances of the pump light and the probe light at the at least one position are obtained based on the light spot images at the at least one position, and a light beam adjuster arranged in the optical path of the pump light and / or the probe light is adjusted according to the light spot jitter amplitudes, the jitter frequencies and the centroid distances of the pump light and the probe light, so as to suppress the light spot jitter of the pump light and / or the probe light and make the pump light spot and the probe light spot coincide; the light beam adjuster comprises a mirror; When the light paths of the pump light and the probe light are both provided with the beam adjuster, the first motion curve of the mirror on the light path of the pump light is determined according to the spot jitter amplitude and the jitter frequency of the pump light at the at least one position, the second motion curve of the mirror on the light path of the probe light is determined according to the spot jitter amplitude and the jitter frequency of the probe light at the at least one position, and the mirror motion is used to suppress the spot position jitter amplitude and the jitter frequency of the pump light and the probe light; When the light path of the pump light or the probe light is provided with the beam adjuster, the fifth motion curve of the mirror on the light path of the pump light or the probe light is determined according to the spot jitter amplitude and the jitter frequency of the pump light and the probe light at the at least one position, and the mirror motion is used to make the spot position jitter amplitudes of the pump light and the probe light the same and the jitter frequencies the same.

6. The method of laser spot calibration of claim 5, wherein, When the light paths of the pump light and the probe light are both provided with the beam adjuster, the third motion curve of the mirror on the light path of the pump light and the fourth motion curve of the mirror on the light path of the probe light are designed according to the spot centroid distance on the surface of the sample to be measured and / or the standard sample, so that the fluctuation amplitude of the centroid distance is less than a preset coincidence threshold.

7. The method of laser spot calibration of claim 6, wherein, The first motion curve and the third motion curve are superimposed and fitted to obtain the motion control curve of the mirror on the light path of the pump light, and the second motion curve and the fourth motion curve are fitted to obtain the motion control curve of the mirror on the light path of the probe light.

8. The method of laser spot calibration of claim 5, wherein, When the light paths of the pump light and the probe light are both provided with the beam adjuster, the sixth motion curve of the mirror on the light path of the pump light or the probe light is designed according to the spot centroid distance on the surface of the sample to be measured and / or the standard sample, so that the fluctuation amplitude of the centroid distance is less than a preset coincidence threshold.

9. The method of laser spot calibration of claim 8, wherein, The fifth motion curve and the sixth motion curve are superimposed and fitted to obtain the motion control curve of the mirror on the light path of the pump light or the probe light.

10. The laser spot calibration method of claim 7 or 9, wherein, Further comprising: After the mirrors on the light paths of the pump light and the probe light move according to the corresponding motion control curves, the fluctuation amplitude and the fluctuation frequency of the centroid distance of the pump light and the probe light on the sample to be measured are calculated, and the ultrasonic measurement signal obtained by the film thickness ultrasonic measurement is corrected by using the fluctuation amplitude and the fluctuation frequency of the centroid distance, so as to reduce the influence of the centroid distance of the pump light spot and the probe light spot on the ultrasonic measurement signal.

11. The method of laser spot calibration of claim 5, wherein, The beam adjuster comprises a beam diameter adjusting mirror group; The method further comprises: collecting spot images of the pump light and the probe light at any position on the light path, obtaining a spot diameter change curve of the pump light and the probe light at the any position based on the spot images at the any position, and adjusting the beam diameter adjusting mirror group of the pump light and the probe light according to the spot diameter change curve of the pump light and the probe light, so as to reduce the spot diameter change of the pump light and the probe light.

Images