Light spot identification method in photoacoustic measurement process and photoacoustic measurement system

Abstract

The invention relates to the technical field of photoacoustic measurement, and particularly provides a light spot identification method in a photoacoustic measurement process and a photoacoustic measurement system, and the method comprises the steps: carrying out the noise reduction of a light spot image through a noise reduction method, carrying out the calculation through two-dimensional Gaussian fitting, and obtaining an initial light spot mass center coordinate and a light spot Gaussian peak gray scale; segmenting the light spot image according to a set gray threshold; and then the edge of the light spot is corrected through a distance threshold value, the elliptical light spot is simplified into a circular light spot, and a final light spot centroid coordinate is calculated and obtained through a weighted average algorithm. According to the light spot identification method, precise positioning of the mass center of the light spot is realized, and subsequent light spot calibration is facilitated. The photoacoustic measurement system using the method can realize high-precision alignment of the pump light and the probe light, and the signal-to-noise ratio of the photoacoustic measurement photoacoustic signal is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of photoacoustic measurement, and in particular relates to a light spot recognition method and a photoacoustic measurement system during a photoacoustic measurement process. Background Art

[0002] In the semiconductor field, photoacoustics are widely used to measure a range of film parameters, including thickness, acoustic velocity, and Young's modulus, in metal and dielectric films. As a nondestructive testing technique, photoacoustics generates photoacoustic signals through the interaction of laser light with materials. Analyzing these signals can yield detailed information about the material.

[0003] The specific principle of photoacoustic measurement is as follows: a pump light source is used to illuminate the surface of the sample to be measured, exciting ultrasonic waves. The ultrasonic waves propagate inside the sample and are reflected at the interface between the film layers of different materials, forming an echo signal. The echo signal returns to the sample surface, causing changes in the surface morphology and reflectivity. The deformation or reflectivity change caused by the ultrasonic wave is then measured by detection light. By analyzing the detected signal, the transmission time of the ultrasonic wave in the material can be obtained, and then the film thickness value and other physical parameters of the sample can be calculated.

[0004] To improve the signal-to-noise ratio of the photoacoustic signal, the probe light spot should ideally overlap with the pump light spot as closely as possible, and the spot size and position should remain as stable as possible after the overlap. Existing solutions typically use optical instruments to statically calibrate the spot position, size, and overlap before measurement begins.

[0005] However, in actual measurement, due to the operation of various optical, mechanical, and electronic components, the spot size, spot position, and spot overlap often change dynamically during the measurement process. This introduces noise into the measurement results, reducing the photoacoustic signal-to-noise ratio. This dynamic change poses a challenge to the accuracy and repeatability of the measurement results.

[0006] During the spot calibration process, there are also problems with identifying the center of mass of the spot. Due to the interference of external noise, it is often difficult to accurately identify the center of mass and the radius of the spot, resulting in an inability to accurately determine whether the center of mass and the radius of the spot coincide during the calibration process. This also affects the signal-to-noise ratio of the final photoacoustic measurement signal, resulting in errors in the film thickness measurement results. In addition, since the pump light and the probe light are usually incident on the sample surface at different angles, affected by the irradiation angle, the pump light spot and the probe light spot appear as elliptical spots of different shapes on the sample surface. Elliptical spots of different shapes and angles are difficult to completely align and overlap, which further increases the difficulty of center of mass positioning and spot calibration. Summary of the Invention

[0007] In view of this, the present invention aims to provide a light spot recognition method and a photoacoustic measurement system during the photoacoustic measurement process, perform two threshold segmentations of grayscale and distance on the light spot image after noise filtering, simplify the blurred elliptical light spot into a circular light spot, and then calculate more accurate light spot centroid coordinates, solving the problem that traditional methods cannot accurately locate the light spot centroid coordinates.

[0008] To achieve the above object, the technical solution created by the present invention is implemented as follows: The present invention provides a method for spot recognition during photoacoustic measurement, comprising: Collect the spot image on the photoacoustic measurement optical path, calculate the initial spot centroid coordinates and the spot Gaussian peak grayscale, determine the grayscale threshold according to the spot Gaussian peak grayscale, and set the grayscale amplitude of the pixel points in the spot image with a grayscale less than the grayscale threshold to 0; Obtain the spot edge coordinate point set of the spot image after grayscale threshold assignment, obtain the minimum value of the distance between the initial spot centroid coordinate and the pixel points in the spot edge coordinate point set, use this minimum value as the distance threshold, and assign the grayscale value of the pixel points in the spot image whose distance from the initial spot centroid coordinate is greater than the distance threshold to 0; According to the spot image after the distance threshold is assigned, the final spot centroid coordinates are calculated.

[0009] Preferably, an imaging module is added during the photoacoustic measurement process, and the imaging module is used to collect the light spot image on the photoacoustic measurement light path.

[0010] Preferably, calculating and obtaining the initial coordinates of the centroid of the light spot and the Gaussian peak grayscale of the light spot includes: The initial center of mass coordinates of the light spot and the Gaussian peak grayscale of the light spot are obtained through two-dimensional Gaussian fitting calculation.

[0011] Preferably, before calculating the initial coordinates of the centroid of the light spot and the Gaussian peak grayscale of the light spot, the method further includes: Noise detection is performed on the spot image. By calculating the grayscale difference between the noise point and the surrounding area, the noise is divided into salt and pepper noise and independent Gaussian noise outside the spot.

[0012] Preferably, an adaptive median filtering method is used to filter out salt and pepper noise in the spot image.

[0013] Preferably, a Gaussian filtering method is used to filter out independent Gaussian noise outside the light spot in the light spot image.

[0014] Preferably, the grayscale threshold is the grayscale of the Gaussian peak of the spot. .

[0015] Preferably, any position in the spot image after grayscale threshold assignment Grayscale of pixel at for: ; in, Indicates that before the grayscale threshold is assigned The grayscale of the pixel at Indicates the Gaussian peak grayscale of the light spot.

[0016] Preferably, any position in the spot image after the distance threshold is assigned Grayscale of pixel at for: ; Among them, R represents the value before the distance threshold is assigned. The distance between the pixel point at and the initial coordinates of the center of mass of the light spot, Indicates the distance threshold.

[0017] Preferably, the final coordinates of the centroid of the light spot are calculated based on the light spot image after the distance threshold is assigned, including: The grayscale of the pixels in the spot image after the distance threshold is assigned is used as the weight, and the final coordinates of the spot centroid are obtained through weighted average calculation.

[0018] Preferably, the calculation formula for obtaining the final coordinates of the center of mass of the light spot by weighted average calculation is: ; in, Indicates the x-axis coordinate of the final center of mass of the light spot, Indicates the y-axis coordinate of the final center of mass of the light spot.

[0019] Another aspect of the present invention provides a photoacoustic measurement system, comprising: a light source that emits pump light and probe light, and an imaging module for collecting spot images, wherein the imaging module uses a spot recognition method during the photoacoustic measurement process to identify the centroid coordinates of the pump light and probe light spot images.

[0020] Preferably, it also includes: A pump light reflector for adjusting the direction of the pump light; a detection light reflector for adjusting the direction of the detection light; The distance between the centroids of the pump light spot and the probe light spot is determined based on the centroid coordinates of the pump light spot and the probe light spot. The pump light reflector and / or the probe light reflector are regulated based on the centroid distance to improve the overlap of the pump light and the probe light.

[0021] Compared with the prior art, the present invention can achieve the following beneficial effects: The present invention achieves precise positioning of the centroid of the light spot through dual segmentation using a grayscale threshold and a distance threshold, facilitating subsequent spot calibration and ensuring the accuracy of spot calibration. Because the angles of incidence of the excitation light and the detection light on the sample surface differ when they are focused and overlap, the excitation light spot and the detection light spot on the sample surface are elliptical spots with slightly different angles during actual measurement. Therefore, the pump light and detection light spots are generally elliptical, which makes it difficult to locate the centroid and calibrate the spot. Therefore, the present invention innovatively proposes a distance threshold for image segmentation, processing the elliptical spot into a circular spot, achieving high-precision positioning of the spot centroid.

[0022] Furthermore, the present invention effectively removes noise interference in the spot image through noise detection and classification, adaptive median filtering and Gaussian filtering, and further suppresses Gaussian noise through grayscale thresholding.

[0023] The photoacoustic measurement system of the present invention adds an imaging module on the basis of the traditional basic system. The imaging module is used to obtain the image of the light spot in the optical path, and the light spot recognition method is used to accurately locate the execution. The light spot position is then dynamically calibrated according to the center of mass distance, thereby improving the overlap of the pump light spot and the detection light spot on the sample, reducing the noise caused by the light spot jitter caused by external factors such as mechanical vibration, and thus significantly improving the signal-to-noise ratio of the photoacoustic measurement signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings: Figure 1 This is a process of a light spot recognition method in a photoacoustic measurement process according to an embodiment of the present invention; Figure 2 is a framework diagram of a photoacoustic measurement system provided according to an embodiment of the present invention; Figure 3 4 is a flow chart of threshold segmentation provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with 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 use associated similar element numbers. In the following embodiments, many detailed descriptions are intended to enable the present invention to be better understood. 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, or methods. In some cases, some operations related to the present invention are not shown or described in the specification. This is to avoid the core part of the present invention being overwhelmed by too much description. For those skilled in the art, it is not necessary to describe these related operations in detail. They can fully understand the related operations based on the description in the specification and the general technical knowledge in the art.

[0026] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other to form various implementation methods. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various orders in the description and the drawings are only for the purpose of clearly describing a certain embodiment and are not intended to be a required order, unless otherwise specified that a certain order must be followed.

[0027] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are 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 on the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0028] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0029] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0030] See also Figure 1 In one embodiment of the present invention, a method for spot identification during photoacoustic measurement is provided. This method is primarily used to accurately identify the centroids of pump and probe light spots during photoacoustic measurement. This method can be applied to scenarios such as film thickness measurement, defect detection, and material property testing, aiming to address the issue of low centroid accuracy during spot calibration during photoacoustic measurement.

[0031] The photoacoustic measurement system used in the photoacoustic measurement process can be found in Figure 2 , whose structure includes: The standard sample is a reference sample used to calibrate the system. Its primary function is to ensure measurement accuracy and to enable self-calibration of the device when no sample is available. The sample to be measured is the actual sample whose film thickness is to be measured. The standard sample and the sample to be measured are not inherently part of the system structure.

[0032] Laser module: It is the light source for photoacoustic measurement, used to provide laser to irradiate the sample to be measured.

[0033] The spectrometer is installed on the rear optical path of the laser module to split the light emitted by the laser module into two paths. One path is the pump light, which is used to excite the sample to be tested and stimulate ultrasonic waves in the sample to be tested; the other path is the detection light, which is used to detect the deformation or reflectivity change caused by ultrasonic waves.

[0034] In some embodiments, the laser module may include two separate sub-light sources, which respectively emit pump light and probe light. In this case, the light splitting module may be omitted.

[0035] Reflectors in the pump light path and the probe light path, as well as controllers for the two reflectors, are used to adjust the reflection directions of the pump light and the probe light, respectively. The pump light reflector controller and the probe light reflector controller enable real-time adjustment of the motion parameters of the pump light reflector and the probe light reflector, including the coordinates of the deflection center of the reflective surface, the equilibrium position of the periodic motion, the mirror rotation amplitude, and the frequency. These parameters can be specifically represented as a reflector motion control curve.

[0036] Photoelectric conversion module: It is used to receive the detection light reflected by the sample to be tested, that is, the photoacoustic measurement signal, convert the fluctuation of the received detection light intensity into the fluctuation of the electrical signal, obtain the photoacoustic signal that can represent the information of the sample to be tested, and finally transmit it to the signal processing module.

[0037] Signal processing module: It is used to process and compensate the photoacoustic signal, calculate the film thickness measurement value of the sample to be measured, and solve the measurement result of the film thickness of the sample to be measured.

[0038] Imaging module: used to obtain spot images, identify and calibrate the spot centroid coordinates in the pump light and detection light spot images.

[0039] During the photoacoustic measurement process, since the pump light and the detection light are incident on the sample at different angles, elliptical spots of different shapes and angles are formed. It is difficult to achieve precise alignment of elliptical spots of different shapes and angles. Therefore, traditional methods cannot accurately determine the center of mass position, which affects the measurement accuracy.

[0040] To solve this problem, the embodiment of the present invention realizes the accurate positioning of the centroid of the light spot through double segmentation of grayscale threshold and distance threshold, which facilitates the subsequent light spot calibration. Specifically, the light spot recognition process is as follows: First, in a photoacoustic measurement system, an imaging device is used to capture the light spot image along the photoacoustic measurement optical path. This can include capturing light spot images on the surfaces of optical components in the optical path, such as the pump and probe light reflectors, or the pump and probe light reflector controllers. It can also capture light spot images on samples requiring film thickness measurement or standard samples used for optical path calibration. The imaging device can be an optical device such as a microscope.

[0041] After acquiring the spot image, further threshold segmentation is performed on the spot image to remove irrelevant noise and pixels in non-spot areas, optimize the spot image and extract the feature information of the spot. Figure 3 , the threshold segmentation process mainly includes: First, the initial center of mass coordinates of the light spot are obtained based on the pixel size and two-dimensional Gaussian fitting calculation and the Gaussian peak grayscale of the spot According to the common definition of Gaussian beam width, the peak grayscale The ratio is used as the grayscale threshold of the light spot, which can represent the effective boundary of the light spot. The grayscale threshold is expressed as .

[0042] According to the gray threshold Re-assign the grayscale of all pixels in the entire spot image: the grayscale of pixels below the grayscale threshold is assigned to 0, and the grayscale of pixels above the grayscale threshold remains unchanged. Grayscale of pixel at for: ; in, Indicates that before the grayscale threshold is assigned The grayscale of the pixel at .

[0043] After the grayscale threshold is assigned and segmented, the spot shape needs to be further processed. Since the pump light and the detection light are usually incident on the sample to be measured and the surface of the optical path element at different angles, there are certain differences in the incident angles, so the pump light spot and the detection light spot on the surface of the sample to be measured during actual measurement are two elliptical spots with slightly different angles and shapes. However, two elliptical spots of different angles and shapes cannot be completely overlapped, and are not convenient for center of mass identification. Therefore, the embodiment of the present invention also proposes to design a distance threshold to process the elliptical spot, optimize the elliptical spot into a circular spot that can characterize the actual characteristics and position of the spot, and calculate the center of mass coordinates based on the circular spot. Specifically, edge detection is performed on the spot image after the grayscale threshold is assigned, and the coordinates of the spot edge pixel points in the spot image are recorded to form a spot edge coordinate point set U. Then calculate the distance R between the initial spot center of mass coordinates obtained by two-dimensional Gaussian fitting and each pixel point in the spot edge coordinate point set U. The calculation formula for R is: .

[0044] The minimum value of the interval is selected as the distance threshold, which is expressed as .

[0045] Based on distance threshold Reassign the grayscale of all pixels in the entire spot image: and the initial spot centroid coordinates Distance greater than distance threshold The grayscale of the pixel is assigned to 0, which is consistent with the initial coordinates of the centroid of the light spot. The grayscale of pixels whose distance is less than the grayscale threshold remains unchanged. Grayscale of pixel at for: ; Among them, R represents the value before the distance threshold is assigned. The distance between the pixel point at and the initial center of mass coordinates of the light spot.

[0046] After the light spot distance threshold segmentation is completed, the light spot shape becomes circular, and the grayscale of each pixel on the light spot is , where x and y are the coordinates of the spot pixel in the x and y directions, and the spot radius is .

[0047] After the threshold segmentation process is completed, the grayscale of the pixel in the spot image after the distance threshold is assigned is used as the weight, and the final spot centroid coordinates are calculated by the weighted average method. , the specific calculation formula is: .

[0048] in, Indicates the x-axis coordinate of the final center of mass of the light spot, Indicates the y-axis coordinate of the final center of mass of the light spot.

[0049] The above processing can accurately obtain the coordinates of the center of mass of the light spot, facilitate the subsequent light spot calibration, improve the overlap of the pump light spot and the detection light spot on the sample, and improve the signal-to-noise ratio of the photoacoustic measurement signal.

[0050] As an optional embodiment, the light spot image is assigned a segmentation process based on a distance threshold and a grayscale threshold, and a division extraction method can also be used. Specifically, after determining the grayscale threshold based on the grayscale of the light spot Gaussian peak, all pixels in the light spot image with a grayscale greater than the grayscale threshold can be extracted to form a first light spot image point set. Then, the light spot edge coordinate point set of the light spot image corresponding to the first light spot image point set is calculated, and the minimum value of the distance between the initial light spot centroid coordinates and the pixels in the light spot edge coordinate point set is calculated. This minimum value is used as the distance threshold, and the pixels in the first light spot image point set whose distance from the initial light spot centroid coordinates is less than the distance threshold are extracted. These pixels are combined into a second light spot image point set. The light spot image formed by the second light spot image point set is the final processed light spot image, and the light spot centroid coordinates can be calculated using this light spot image.

[0051] As an optional embodiment, based on the principle of photoacoustic film thickness measurement, the overlap between the pump light spot and the probe light spot directly affects the strength of the probe light reflection signal. The presence of noise in the spot image can interfere with spot edge extraction and centroid coordinate calculation, leading to errors in spot edge extraction or offsets in centroid coordinate calculation due to noise. Therefore, when processing the spot image, it is important to ensure that the spot edge is clear while removing as much noise as possible and that the centroid coordinate calculation is accurate. Therefore, after acquiring the spot image, noise detection and classification can be performed before image processing using grayscale and distance thresholds. Specifically, noise detection and classification are first performed on the spot image. In this embodiment of the present invention, the grayscale difference between the noise point and the surrounding area is calculated to classify the noise into salt and pepper noise and independent Gaussian noise outside the main spot area. If the grayscale value of a pixel differs from that of surrounding pixels by more than a certain threshold, and the pixel's grayscale value is close to the maximum or minimum value of the image, the pixel is determined to be salt and pepper noise. Gaussian noise, whose grayscale values ​​follow a Gaussian distribution, is typically introduced by the imaging device or optical path components themselves. It can be identified by analyzing the image's grayscale histogram. Based on the noise classification, different filtering methods can be used to reduce spot noise while maintaining edge clarity.

[0052] As an optional embodiment, the photoacoustic signal indicated by the position of the signal processing module may be collected by the imaging module, and further adjustment and compensation may be performed based on the photoacoustic signal diagram.

[0053] An adaptive median filtering method is used to deal with salt and pepper noise. The size of the median filter window is determined according to the overall noise level of the image, and the grayscale value of the noise pixel is replaced by the median grayscale value of the surrounding pixels, thereby retaining the edge information of the image.

[0054] The Gaussian filtering method is used for Gaussian noise, which smoothes the noise in the background area while minimizing the impact on the edge of the light spot.

[0055] In view of the above-mentioned spot recognition method in the photoacoustic measurement process, the embodiment of the present invention applies it to a specific photoacoustic measurement system and specially designs the imaging module. Specifically, the imaging module obtains the spot images on the optical paths of the pump light and the probe light, and identifies the coordinates of the center of mass of the spot in the pump light and the probe light spot images. The acquired spot images and the coordinates of the center of mass of the spot are used to calculate the parameters such as the spot position, the jitter of the spot spacing, and the coincidence of the spot. The motion of the pump light reflector and the probe light reflector is controlled according to the acquired parameters to suppress the jitter of the spot and solve the influence of external disturbance on the signal-to-noise ratio of the film thickness photoacoustic measurement signal. The imaging module obtains the images of the pump light and the probe light spots, identifies the coordinates of the center of mass, determines the distance between the center of mass of the pump light spot and the center of mass of the probe light spot, and designs the motion control curves of the pump light reflector and the probe light reflector based on the distance between the centers of mass. The pump light reflector controller and the probe light reflector controller control the motion of the reflectors according to the motion control curves of the pump light reflector and the probe light reflector, respectively. The detection light reflector and the pump light reflector can reflect the detection light and the pump light onto the sample to be tested, ultrasonically excite the surface of the sample to be tested by the pump light, and then use the detection light to obtain the photoacoustic measurement signal, thereby obtaining the film thickness information of the surface of the sample to be tested.

[0056] In short, the above description is only a preferred embodiment of this specification and is not intended to limit the scope of protection of this specification. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this specification shall be included in the scope of protection of this specification.

[0057] The systems, devices, modules, or units described in one or more of the above embodiments may be implemented by a computer chip or entity, or by a product having a certain function. A typical implementation device is a computer. Specifically, the computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smartphone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0058] It should also be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or includes elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, commodity, or apparatus that includes the element.

[0059] The various embodiments in this specification are described in a progressive manner. Similar parts between the various embodiments can be referred to in conjunction with each other. Each embodiment focuses on the differences between the other embodiments. In particular, the system embodiments are generally similar to the method embodiments, so the description is relatively simple. For relevant parts, refer to the description of the method embodiments.

[0060] The foregoing description of this specification describes specific embodiments. 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 from that described in the embodiments and still achieve the desired results. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the specific order shown or the sequential order to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A method for spot recognition in a photoacoustic measurement process, characterized in that: include: Collect the spot image on the photoacoustic measurement optical path, calculate the initial spot centroid coordinates and the spot Gaussian peak grayscale, determine the grayscale threshold based on the spot Gaussian peak grayscale, and assign the grayscale of the pixels in the spot image with a grayscale less than the grayscale threshold to 0; Obtain the spot edge coordinate point set of the spot image after grayscale threshold assignment, obtain the minimum value of the distance between the initial spot centroid coordinate and the pixel points in the spot edge coordinate point set, use this minimum value as the distance threshold, and assign the grayscale value of the pixel points in the spot image whose distance from the initial spot centroid coordinate is greater than the distance threshold to 0; According to the spot image after the distance threshold is assigned, the final spot centroid coordinates are calculated.

2. The method for spot recognition during photoacoustic measurement according to claim 1, characterized in that: An imaging module is added during the photoacoustic measurement process, and the imaging module is used to collect a light spot image on the photoacoustic measurement light path.

3. The method for spot recognition during photoacoustic measurement according to claim 1, characterized in that: The calculating and obtaining the preliminary coordinates of the centroid of the light spot and the Gaussian peak grayscale of the light spot includes: calculating and obtaining the preliminary coordinates of the centroid of the light spot and the Gaussian peak grayscale of the light spot by two-dimensional Gaussian fitting.

4. The method for spot recognition during photoacoustic measurement according to claim 1, wherein: Before calculating the initial coordinates of the centroid of the light spot and the Gaussian peak grayscale of the light spot, the method further includes: Noise detection is performed on the spot image. By calculating the grayscale difference between the noise point and the surrounding area, the noise is divided into salt and pepper noise and independent Gaussian noise outside the spot.

5. The method for spot recognition during photoacoustic measurement according to claim 4, characterized in that: Adaptive median filtering method is used to filter out salt and pepper noise in the spot image.

6. The method for spot recognition during photoacoustic measurement according to claim 4 or 5, characterized in that: The Gaussian filtering method is used to filter out the independent Gaussian noise outside the spot in the spot image.

7. The method for spot recognition during photoacoustic measurement according to claim 1, characterized in that: The grayscale threshold is the grayscale of the Gaussian peak of the spot. .

8. The method for spot recognition during photoacoustic measurement according to claim 7, characterized in that: Any position in the spot image after grayscale threshold assignment Grayscale of pixel at for: ； in, Indicates that before the grayscale threshold is assigned The grayscale of the pixel at Indicates the Gaussian peak grayscale of the light spot.

9. The method for spot recognition during photoacoustic measurement according to claim 8, characterized in that: Any position in the spot image after distance threshold assignment Grayscale of pixel at for: ； Among them, R represents the value before the distance threshold is assigned. The distance between the pixel point at and the initial coordinates of the center of mass of the light spot, Indicates the distance threshold.

10. The method for spot recognition during photoacoustic measurement according to claim 1, characterized in that: The calculation of the final coordinates of the centroid of the light spot based on the light spot image after the distance threshold is assigned includes: The grayscale of the pixels in the spot image after the distance threshold is assigned is used as the weight, and the final coordinates of the spot centroid are obtained through weighted average calculation.

11. The method for spot recognition during photoacoustic measurement according to claim 10, characterized in that: The final calculation formula for the center of mass coordinates of the light spot obtained by weighted average calculation is: ； in, Indicates the x-axis coordinate of the final center of mass of the light spot, Indicates the y-axis coordinate of the final center of mass of the light spot.

12. A photoacoustic measurement system, comprising a light source, the light source emitting pump light and probe light, characterized in that: Also includes: An imaging module for collecting spot images, wherein the imaging module uses the spot recognition method in the photoacoustic measurement process according to any one of claims 1 to 9 to identify the centroid coordinates of the pump light and probe light spot images.

13. The photoacoustic measurement system according to claim 12, wherein: Also includes: A pump light reflector for adjusting the direction of the pump light; a detection light reflector for adjusting the direction of the detection light; The distance between the centroids of the pump light spot and the probe light spot is determined based on the centroid coordinates of the pump light spot and the probe light spot. The pump light reflector and / or the probe light reflector are regulated based on the centroid distance to improve the overlap of the pump light and the probe light.

Images