A propagation light field detection system and method

Abstract

A propagating light field detection system and method are disclosed. The detection system includes a housing, a linear displacement stage, a knife-edge detector, a light-transmitting aperture, and a control center. Both the linear displacement stage and the knife-edge detector are mounted inside the housing, and the light-transmitting aperture is located on the side of the housing. The linear displacement stage is used for high-precision scanning along the beam propagation direction, and the knife-edge detector is used to scan the light field distribution across the transverse cross-section of the beam. Using the detection system and method of this invention, the spatial propagation characteristics of a laser light field can be accurately measured, and the depth of focus and focal point size can be detected, demonstrating significant potential application value in laser processing and laser optics.

Description

Technical Field

[0001] This invention relates to the field of laser application technology, and specifically to a propagation light field detection system and method. Background Technology

[0002] With the rapid development of laser technology, lasers have been widely applied in fields such as information and communication, healthcare and life sciences, national defense, and laser manufacturing, playing a significant role in promoting socio-economic development. Among these applications, laser manufacturing is the leading and fastest-growing area of ​​laser technology, with the greatest economic impact. Laser manufacturing uses photons as energy carriers, inducing a series of physical and chemical changes through the interaction of photons with materials, thereby enabling the preparation, shaping, modification, joining, and cutting of materials. In laser manufacturing technology, it is generally necessary to focus the laser to obtain a high laser power density, and accurately measure the intensity distribution of the focused spot to rationally plan and utilize laser energy while ensuring processing precision.

[0003] Currently, lasers are generally evaluated using parameters such as propagation optical field and focal depth. The propagation optical field reflects the energy distribution of the laser beam as it travels over distance, while the focal depth of a laser focusing system refers to the distance from the focal point to which the light intensity at a given point on the optical axis decreases to half that at the focal point. There are currently no effective methods for measuring the propagation optical field and focal depth of an actual laser transmission system. The actual focal depth is typically determined through software simulation combined with measurements of process parameters, which is time-consuming, labor-intensive, and lacks definitive evaluation standards. This invention aims to provide a propagation optical field detection system and method that enables visualized measurement of the propagation optical field and accurate assessment of the propagation characteristics of laser energy. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned shortcomings of the prior art and provide a propagation light field detection system and method that can accurately measure the spatial propagation characteristics of laser light fields and detect the depth of focus and the size of the focal point.

[0005] The technical solution of the present invention is as follows: First, a propagating light field detection system is provided, including a housing, a linear displacement stage, a knife-edge detector, a light-transmitting aperture, and a control center; the linear displacement stage and the knife-edge detector are both installed inside the housing, and the light-transmitting aperture is set on the side of the housing. The linear displacement stage is used to perform high-precision scanning in the direction of beam propagation, and the knife-edge detector is used to scan the light field distribution of the transverse cross section of the beam. The control center includes light field scanning control and calculation software. The linear displacement stage and the knife-edge detector are both connected to the control center and work together under the control of the control center.

[0006] Furthermore, the knife-edge detector is a photodetector and includes two mutually perpendicular narrow slits, which scan in corresponding directions.

[0007] Furthermore, the slit widths are A um and B um, respectively. Each scan is performed on an A um * B um pixel block, the value of which is the intensity value of the light spot at the corresponding position. The resulting M*N data matrix is ​​stored in the control center, and the data value in the i-th row and j-th column of the data matrix is ​​denoted as M. ij .

[0008] Furthermore, the control center stitches together the data from all the data matrices to display the propagated light field obtained after scanning.

[0009] The present invention also provides a method for detecting a propagating light field, utilizing the above-mentioned detection system, comprising the following steps:

[0010] S1, Laser alignment;

[0011] The purpose of alignment is to make the direction of light field measurement perpendicular to the detector, that is, to ensure that the measured light field is an axially propagating light field.

[0012] S2. Define the scan length and differential length, and estimate the focal position by continuous scanning;

[0013] After laser alignment, a linear displacement stage is used for scanning. Based on the scanning results, the focal point position Pf is initially estimated. When defining the scanning length, the focal depth length DOF is estimated according to the focal depth calculation formula (1). The scanning length is selected to be no more than 6 times DOF ​​for scanning, that is, the scanning interval is (P... f - 3*DOF, P f + 3*DOF), where P f The estimated focal position;

[0014] (1)

[0015] In the formula: λ is the laser wavelength; f is the focal length of the focusing lens; D is the radius of the laser beam incident on the surface of the focusing lens;

[0016] When determining the differential length, it is inversely proportional to the scanning time, and should be greater than the single-step accuracy of the displacement stage. For example, if the single-step displacement accuracy of a linear displacement stage is 1µm, then in practical applications, a scanning accuracy that is an integer multiple of 10µm can be selected.

[0017] S3. Perform a transverse slice scan of the beam.

[0018] Lateral slicing of the light beam is typically accomplished using a photodetector, which scans the light field distribution perpendicular to the beam propagation direction to obtain the lateral light field at a specific location. This invention employs a knife-edge detector, consisting of two mutually perpendicular narrow slits. These slits scan in corresponding directions, with widths of Aum and Bum, respectively. Each scan covers an Aum * Bum pixel block, whose value corresponds to the intensity of the light spot at that location. Because the photodetector's scanning time is very short and the single-step length of the linear displacement stage is sufficiently small, real-time scanning can be achieved during the movement. After scanning, an M*N data matrix is ​​obtained and stored in the control center, where the data value in the i-th row and j-th column is M. ij .

[0019] S4. Concatenate the sliced ​​data obtained in the previous step;

[0020] After the previous scan is completed, the sliced ​​data is stitched together. The stitching process follows a specific algorithm, the principle of which is as follows:

[0021] Since the obtained single-piece data is an M * N array, where M = N in general, assuming the displacement stage scanning length is L and the number of scans in the propagation direction is T, the single-step scanning accuracy is L / (T-1). Therefore, the total data stored in the control center is an M * N * T matrix, where the value in the i-th row and j-th column of the k-th scan is the element's light field intensity P. ijk Slicing and splicing is the process of combining the data from the i-th row or j-th column of individual data from T scans into an N*T or M*T matrix.

[0022] S5, Displays the propagating light field;

[0023] Displaying the propagating light field involves visualizing the stitched N*T or M*T matrix; the display accuracy is related to the scanning accuracy of the linear displacement stage—higher scanning accuracy results in finer detail. The control center provides filtering and data averaging algorithm modules. Filtering uses Gaussian filtering to remove noise from a certain detector, while averaging integrates a Lagrange averaging algorithm.

[0024] The data along the Z-axis (i.e., the direction of light propagation) consists of T discrete data points. The larger T is, the finer the image, but it remains discrete. The control center of this invention integrates a Z-axis interpolation smoothing algorithm. The algorithm's logic is to use adjacent data points from two adjacent slice data matrices, T1 and T2. and Lagrange polynomials are used for interpolation to obtain a smooth propagation light field pattern that does not change the properties of the original data.

[0025] At the same time, it can be used to measure the strength P ijk Performing diffraction mapping allows for a more intuitive assessment of the light field distribution, such as...Figure 4 This is a display effect that maps intensity to a heatmap. The horizontal axis in the graph represents the propagation distance (Z), the Y axis represents the width of the light spot at the slice location, and the color intensity represents the energy level. The control center provides a hover display function, allowing you to hover the mouse over a point on the graph to display the location and intensity information of the element of interest. Similarly, it can also be mapped to a grayscale image or a rainbow image for display.

[0026] S6. Find the maximum value of the light field to determine the focal point;

[0027] First, the control center's calculation software analyzes the M*N*T horizontal slice matrix to find the maximum value I of the matrix. max At this point, the location of the focal point Ps is located. Then, the calculation software locates the two-dimensional matrix M*N where Ps is located, and then calculates the size of the focal point based on the light field.

[0028] like Figure 5 As shown, there are two methods for calculating the focal point. One method is to define the focal point size as the area enclosed by the light intensity decreasing to half of the center light intensity (maximum light intensity), which is called the full width at half maximum (FWHM) diameter. The other method is to define the focal point size as the area enclosed by the light intensity decreasing to half of the maximum light intensity (e). 2 The size enclosed by the focal point is called the Gaussian Diameter.

[0029] S7. Slice along the optical axis to determine the depth of focus;

[0030] The depth of focus is calculated by slicing the propagating light field twice. Slicing the light field around the optical axis yields a planar light field distribution. Slicing again around the optical axis results in a light field distribution curve along the optical axis. The distance covered when the light intensity drops to half of its maximum intensity is the depth of focus. The algorithm used in this invention is a positioning I... max In P s The position of the slice matrix is ​​[i,j]. Then, the matrix M * N * T is traversed to obtain the light intensity distribution matrix [p,z] along the optical axis, where p is the intensity of the i-th row and j-th column of the slice matrix M * N, and z is the slice position in the propagation direction. This gives the light intensity at each point along the optical axis, and then the slice closest to 1 / 2 I is found. max The corresponding positions Z1, Z2, such as Figure 6 As shown.

[0031] Furthermore, precise measurement of various parameters is only possible after laser alignment, as in step S1, such as... Figure 3 As shown, the specific steps for laser alignment are as follows:

[0032] The first step is to detect the center position P of the light spot. x1 , P y1 ;

[0033] The second step is to move the light spot a distance d, where d > 10 times the spot width; then, the center position P of the light spot is detected again. x2 , P y2 ;

[0034] The third step is to make ;

[0035] Then determine whether ΔPx and ΔPy simultaneously satisfy formulas (2.1) and (2.2);

[0036]

[0037] If both conditions cannot be met simultaneously, adjust the direction and pitch angle of the laser device to make P x2 =P x1 , P y2 = P y1 Return to step two;

[0038] If both conditions are met simultaneously, the laser alignment operation is complete.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows: A laser propagation light field testing system and software can accurately measure the spatial propagation characteristics of the laser light field and detect the depth of focus and the size of the focal point, which has significant potential application value in the fields of laser processing and laser optics. Attached Figure Description

[0040] Figure 1 This is a three-dimensional schematic diagram of the detection system of the present invention;

[0041] Figure 2 This is a schematic diagram of the overall process of the detection method in this invention;

[0042] Figure 3 This is a schematic diagram of the laser alignment process in the detection method of the present invention;

[0043] Figure 4 This is an illustration of the effect of mapping intensity to a grayscale image when displaying a propagating light field, according to the present invention.

[0044] Figure 5 This is a schematic diagram of the focus calculation method in this invention;

[0045] Figure 6 This is a schematic diagram illustrating the calculation of focal depth in this invention;

[0046] In the diagram: 1-outer shell, 2-linear displacement stage, 3-knife edge controller, 4-light transmission hole. Detailed Implementation

[0047] The present invention will be further described in detail below with reference to specific embodiments. Methods or functional components not specifically described in the embodiments are all prior art. Example

[0048] like Figure 1 As shown, this embodiment is a propagation light field detection system, including a housing, a linear displacement stage, a knife-edge detector, a light-transmitting aperture, and a control center. The linear displacement stage and the knife-edge detector are both installed inside the housing, and the light-transmitting aperture is located on the side of the housing. The linear displacement stage is used for high-precision scanning in the beam propagation direction, and the knife-edge detector is used to scan the light field distribution across the transverse cross-section of the beam. The knife-edge detector is installed on the linear displacement stage and can move horizontally along the length of the linear displacement stage. The control center includes light field scanning control and calculation software. The linear displacement stage and the knife-edge detector are both connected to the control center and work collaboratively under its control. The knife-edge detector is a photodetector and includes two mutually perpendicular narrow slits. The two narrow slits scan in corresponding directions, and each slit has a width of 5 μm. Each scan can scan a 5 μm * 5 μm pixel, whose value is the intensity value of the light spot at the corresponding position. The scanned data matrix is ​​stored in the control center, and the data value in the i-th row and j-th column of the data matrix is ​​denoted as M. ij The control center stitches together the data from all the data matrices to display the propagated light field obtained after scanning.

[0049] The detection system in this embodiment can accurately measure the spatial propagation characteristics of a laser light field. The specific method includes the following steps:

[0050] S1, Laser alignment;

[0051] Specifically Figure 3 Follow the steps shown.

[0052] S2. Define the scan length and differential length, and estimate the focal position by continuous scanning;

[0053] After laser alignment, a linear displacement stage is used for scanning, and the position P of the focal point is initially estimated based on the scanning results. f When defining the scan length, estimate the depth of focus (DOF) according to the depth of focus calculation formula (1). Select a scan length no greater than 6 times the DOF for scanning, that is, the scan interval is (P f - 3*DOF, P f (+3*DOF);

[0054] (1)

[0055] In the formula: λ is the laser wavelength; f is the focal length of the focusing lens; D is the radius of the laser beam incident on the surface of the focusing lens;

[0056] When determining the differential length, it is inversely proportional to the scanning time, and should be greater than the single-step accuracy of the displacement stage. For example, if the single-step displacement accuracy of a linear displacement stage is 1µm, then in practical applications, a scanning accuracy that is an integer multiple of 10µm can be selected.

[0057] S3. Perform a transverse slice scan of the beam.

[0058] Lateral slicing of the light beam is typically accomplished using a photodetector, which scans the light field distribution perpendicular to the beam propagation direction to obtain the lateral light field at a specific location. This invention employs a knife-edge detector, consisting of two mutually perpendicular narrow slits. These slits scan in corresponding directions, with widths of Aum and Bum, respectively. Each scan covers an Aum * Bum pixel, whose value corresponds to the intensity of the light spot. Because the photodetector's scanning time is very short and the linear displacement stage's single-step length is sufficiently small, real-time scanning can be achieved during movement. After scanning, an M*N data matrix is ​​obtained and stored in the control center, where the data value in the i-th row and j-th column is M. ij .

[0059] S4. Concatenate the sliced ​​data obtained in the previous step;

[0060] After the previous scan is completed, the sliced ​​data is stitched together. The stitching process follows a specific algorithm, the details of which are as follows:

[0061] Since the obtained single-piece data is an M * N array, where M = N in general, assuming the displacement stage scanning length is L and the number of scans in the propagation direction is T, the single-step scanning accuracy is L / (T-1). Therefore, the total data stored in the control center is an M * N * T matrix, where the value in the i-th row and j-th column of the k-th scan is the element's light field intensity P. ijk Slicing and splicing is the process of combining the data from the i-th row or j-th column of individual data from T scans into an N*T or M*T matrix.

[0062] S5, Displays the propagating light field;

[0063] Displaying the propagating light field involves visualizing the stitched N*T or M*T matrix; the display accuracy is related to the scanning accuracy of the linear displacement stage—higher scanning accuracy results in finer detail. The control center provides filtering and data averaging algorithm modules. Filtering uses Gaussian filtering to remove noise from a certain detector, while averaging integrates a Lagrange averaging algorithm.

[0064] The data along the Z-axis (i.e., the direction of light propagation) consists of T discrete data points. The larger T is, the finer the image, but it remains discrete. The control center of this invention integrates a Z-axis interpolation smoothing algorithm. The algorithm's logic is to use adjacent data points from two adjacent slice data matrices, T1 and T2. and Lagrange polynomials are used for interpolation to obtain a smooth propagation light field pattern that does not change the properties of the original data.

[0065] At the same time, it can be used to measure the strength P ijk Performing diffraction mapping allows for a more intuitive assessment of the light field distribution, such as... Figure 4 This is a display effect that maps intensity to a heatmap. The horizontal axis in the graph represents the propagation distance (Z), the Y axis represents the width of the light spot at the slice location, and the color intensity represents the energy level. The control center provides a hover display function, allowing you to hover the mouse over a point on the graph to display the location and intensity information of the element of interest. Similarly, it can also be mapped to a grayscale image or a rainbow image for display.

[0066] S6. Find the maximum value of the light field to determine the focal point;

[0067] First, the calculation software in the control center analyzes the horizontal slice matrix of M*N*T and finds the maximum value Imax of the matrix. At this time, the position Ps of the focal point is located. Then, the calculation software locates the two-dimensional matrix M*N where Ps is located, and then calculates the size of the focal point based on the light field.

[0068] like Figure 5 As shown, there are two methods for calculating the focal point. One method is to define the focal point size as the area enclosed by the light intensity decreasing to half of the center light intensity (maximum light intensity), which is called the full width at half maximum (FWHM) diameter. The other method is to define the focal point size as the area enclosed by the light intensity decreasing to half of the maximum light intensity (e). 2 The size enclosed by the focal point is called the Gaussian Diameter.

[0069] S7. Slice along the optical axis to determine the depth of focus;

[0070] The depth of focus is calculated by slicing the propagating light field twice. Slicing the light field around the optical axis yields a planar light field distribution. Slicing again around the optical axis results in a light field distribution curve along the optical axis. The distance covered when the light intensity drops to half of its maximum intensity is the depth of focus. The algorithm used in this invention is a positioning I... max In P sThe position of the slice matrix is ​​[i,j]. Then, the matrix M * N * T is traversed to obtain the light intensity distribution matrix [p,z] along the optical axis, where p is the intensity of the i-th row and j-th column of the slice matrix M * N, and z is the slice position in the propagation direction. This gives the light intensity at each point along the optical axis, and then the slice closest to 1 / 2 I is found. max The corresponding positions Z1, Z2, such as Figure 6 As shown.

[0071] The above are only some embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various combinations and modifications of the aforementioned technical features. Any improvements, modifications, equivalent substitutions, or applications of the structure or method of the present invention to other fields to achieve the same effect without departing from the spirit and scope of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for detecting a propagating light field, comprising a propagating light field detection system including a housing, a linear displacement stage, a knife-edge detector, a light-transmitting aperture, and a control center; the linear displacement stage and the knife-edge detector are both installed inside the housing, and the light-transmitting aperture is located on the side of the housing; the linear displacement stage is used for high-precision scanning in the direction of beam propagation, the knife-edge detector is used for scanning the light field distribution of the transverse cross section of the beam, and the control center includes light field scanning control and calculation software; the linear displacement stage and the knife-edge detector are both connected to the control center and work collaboratively under the control of the control center; the knife-edge detector is a photodetector, the main structure of which includes two mutually perpendicular narrow slits and a detection chip; the two slits scan in corresponding directions, and each scan detects one pixel; the knife-edge detector receives the light intensity value of the pixel region. The widths of the narrow slits are A um and B um, respectively. Each scan scans an A um * B um pixel, whose value is the light intensity at that pixel location. The resulting M*N data matrix is ​​stored in the control center, and the data value in the i-th row and j-th column of the data matrix is ​​denoted as M. ij Its characteristics are, Includes the following steps: S1, Laser alignment; The purpose of alignment is to make the direction of light field measurement perpendicular to the detector, that is, to ensure that the measured light field is the axial propagation light field; S2. Define the scan length and differential length, and estimate the focal position by continuous scanning; After laser alignment, a linear displacement stage is used for scanning, and the position P of the focal point is initially estimated based on the scanning results. f ; S3. Perform a transverse slice scan of the beam. The transverse light field at a specific location is obtained by scanning the light field distribution perpendicular to the beam propagation direction; S4. Concatenate the sliced ​​data obtained in the previous step; The control center stitches together the sliced ​​data, following this algorithm: Since the sliced ​​data is an M*N array, assuming the displacement stage scanning length is L and the number of scans in the propagation direction is T, the single-step scanning accuracy is L / (T-1). The total data stored in the control center is an M*N*T matrix, where the value in the i-th row and j-th column of the k-th scan is the element's light field intensity P. ijk ; Slice stitching is the process of stitching together the data from the i-th row or j-th column of individual data from T scans into an N*T or M*T matrix; S5, Displays the propagating light field; Displaying the propagating light field means visualizing the spliced ​​N*T or M*T matrix; S6. Find the maximum value of the light field to determine the focal point; First, the control center's calculation software analyzes the M*N*T horizontal slice matrix to find the maximum value I of the matrix. max At this point, the location of the focal point Ps is located. Then, the calculation software locates the two-dimensional matrix M*N where Ps is located, and then calculates the size of the focal point based on the light field. S7. Slice along the optical axis, iterate through the light field intensity at the optical axis of each slice, and determine the depth of focus. After slicing the light field with the optical axis as the center, a light field distribution on a surface is obtained. Then, slicing with the optical axis as the center again, a light field distribution curve on the optical axis is obtained. The distance covered when the light intensity drops to half of the maximum light intensity is the depth of focus.

2. The detection method according to claim 1, characterized in that: In step S1, the specific steps for laser alignment are as follows: The first step is to detect the center position P of the light spot. x1 , P y1 ; The second step involves moving the displacement stage to move the knife-edge detector a distance d, where d > 10 times the spot width; then, the center position P of the spot is detected again. x2 , P y2 ; The third step is to make ; Determine whether ΔPx and ΔPy simultaneously satisfy formulas (2.1) and (2.2); ； If both conditions cannot be met simultaneously, adjust the direction and pitch angle of the laser device to make P x2 = P x1 , P y2 = P y1 Return to step two; If both conditions are met simultaneously, the laser alignment process ends.

3. The detection method according to claim 1, characterized in that: In step S2, when defining the scan length, the depth of focus (DOF) is estimated according to the depth of focus calculation formula (1), and the scan length is selected to be no more than 6 times the DOF for scanning, that is, the scan interval is (P f - 3*DOF, P f + 3*DOF), where P f The estimated focal position; （1） In the formula: λ is the laser wavelength; f is the focal length of the focusing lens; and D is the radius of the laser beam incident on the surface of the focusing lens.

4. The detection method according to claim 1, characterized in that: In step S2, when determining the differential length, the differential length is inversely proportional to the scanning time, and the differential length is greater than the single-step accuracy of the displacement stage.

5. The detection method according to claim 1, characterized in that: In step S3, the cross-section of the laser beam is scanned by a blade detector, and an M*N data matrix is ​​obtained by slicing the beam horizontally each time. All data matrices are then stored in the control center.

6. The detection method according to claim 1, characterized in that: In step S6, there are two methods for calculating the focal point: one is that the size of the area enclosed by the light intensity decreasing to half of the center light intensity is the focal point size; the other is that the maximum light intensity decreases to 1 / e of the maximum light intensity. 2 The size enclosed is the size of the focal point.

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