Laser beam focus positioning method based on Gaussian energy distribution

Abstract

The invention belongs to the field of laser application, and particularly relates to a Gaussian energy distribution-based laser beam focus positioning method, which comprises the following steps of: constructing a distribution model of laser power along an optical axis direction by using a shading baffle with a through hole, the size of which is slightly smaller than the diameter of a laser spot, and determining the focus of a laser beam by means of synchronously acquired experimental data; and the laser spot position is automatically determined. According to the method, the spot focus can be quickly and automatically positioned, and support is provided for determining the focus position in the application fields of laser processing, detection and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of laser application, and in particular relates to a laser beam focus positioning method based on Gaussian energy distribution. Background Art

[0002] In the application process of lasers, it is crucial to accurately determine the laser focus position. Although the design focus of the lens can provide us with a theoretical reference for the laser focus position, in actual operation, due to the manufacturing imperfections of the laser itself and the fact that the laser beam passes through a variety of optical lenses during transmission, these lenses will have defects in actual processing, which will lead to a certain degree of deviation between the actual laser focus spot and the theoretical focus spot position. Furthermore, there are significant differences in the power distribution and spot morphology at different positions within the laser focus spot, which will directly affect the processing effect on the target component, resulting in huge differences in the component processing results. Therefore, it is particularly important to accurately measure the actual laser spot position.

[0003] For lasers in the invisible light band, manual adjustment is currently widely used at home and abroad to find the spot position. This method mainly relies on the operator's subjective judgment of the degree of component impact to roughly determine the spot position. However, this method is not only cumbersome, but its accuracy is also greatly affected by human factors. Although Zhao Quanzhong and Li Ming et al. have applied for laser micro-nano processing focus alignment systems [CN115488494 A and CN111408835] respectively, these systems usually need to be equipped with image acquisition or imaging systems to collect and process data, which undoubtedly increases the cost of the system and makes these solutions subject to certain limitations in practical applications. Summary of the invention

[0004] In order to overcome the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a method for automatically positioning the focus of a Gaussian spot, which utilizes the step-by-step intensity characteristics of the Gaussian spot in the optical axis and radial directions to realize automatic determination of the laser focal spot position.

[0005] The technical solutions for this program are as follows:

[0006] A laser beam focus positioning method based on Gaussian energy distribution is characterized in that it includes the following steps:

[0007] S1. A light shielding baffle with a through hole is provided, the size of the through hole being slightly smaller than the diameter of the laser spot, and is placed on the path of the laser beam;

[0008] S2. Use the laser power detection module to measure the laser power passing through the through hole of the light shielding baffle to obtain the distribution data of the laser power along the optical axis;

[0009] S 3. The data processing unit processes the collected data according to a preset distribution model of the laser power along the optical axis, and automatically determines the focal position of the laser spot;

[0010] S4. According to the determined laser spot focus position, the position or parameters of the electric displacement platform are adjusted through the control and feedback module to realize automatic positioning of the spot focus.

[0011] Further, the step S1 specifically includes:

[0012] S1.1 The laser power transmitted through the baffle is obtained by integrating the Gaussian beam intensity distribution over the entire baffle hole area, with the baffle hole radius as a variable;

[0013] S1.2 Select appropriate shield radius parameters according to requirements.

[0014] Furthermore, in step S1.1, the Gaussian beam intensity is integrated within the radius of the shielding plate through hole on the laser spot plane to obtain the laser power passing through the shielding plate:

[0015]

[0016] Where r is the spot radius on the laser spot plane, z axis is the optical axis direction, the laser transmission direction is positive, P avg is the laser output power, λ is the laser wavelength, r0 is the laser beam waist radius, and R is the radius of the light shielding baffle hole.

[0017] Further, the step S2 specifically includes:

[0018] The laser, focusing system, shielding plate with through holes and power detector of the light beam to be measured are sequentially placed along the optical path;

[0019] Adjust the optical axis position of the electric displacement platform, use a shielding plate to limit the light beam, and use a power detector to measure the laser power passing through the shielding plate at different optical axis positions;

[0020] The Gaussian distribution spot output by the focusing system passes through the shielding plate with through holes, is received by the power detector and transmitted to the automation controller in real time. Specifically:

[0021] 1) Turn on the laser and preheat it for a while;

[0022] 2) The controller is initialized according to the laser system parameters and the parameters of the perforated shielding plate, and moves the electric translation stage to a suitable position;

[0023] 3) Turn on the laser for a while and use a power detector to collect the signal;

[0024] 4) The controller saves the position signal information and moves the displacement platform to a certain position along the optical axis;

[0025] 5) Repeat steps 3) and 4) until the corresponding collection requirements are met.

[0026] Further, the step s3 includes, the automated controller fitting the data collected in step s2 using formula (3) according to the selected radius parameter of the through hole of the shielding plate to obtain the focal position;

[0027] Among them, the fitting formula of the data processing unit is:

[0028]

[0029] Among them, R hole is the radius of the light shielding plate hole selected in step s1.1, the z axis is the optical axis direction, the laser transmission direction is positive, P0 is the laser output power, λ is the laser wavelength, and r0 is the laser waist radius.

[0030] Compared with the prior art, the technical effect of the present invention is

[0031] (1) In view of the need to determine the focal position when using a laser, the present invention proposes a low-cost and efficient automated device for locating the position of the laser spot. The device is designed according to the transmission direction of the optical path.

[0032] (2) The present invention proposes a method for efficiently determining the laser focus based on the Gaussian distribution characteristics of the light spot, which can quickly and accurately locate the laser focus position and provide technical support for the fields of laser processing detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the measurement optical path;

[0034] Figure 2 The power transmitted through the baffle varies with the direction of the optical axis under different baffle apertures.

[0035] Figure 3 The power formula through the baffle is used to fit the experimental data along the optical axis. DETAILED DESCRIPTION

[0036] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0037] See also Figure 1 , Figure 1Schematic diagram of the measuring optical path, including a laser system for measuring the spot position (including a laser 1-1 and a focusing system 1-2, a shielding plate with a through hole 2, a power detector (including a detection head 3-1 and a data acquisition instrument 3-2), an automatic controller 4, a three-axis electric displacement platform 5, and an optical platform 6.

[0038] The laser beam passes through the focusing system to generate a Gaussian distribution spot that enters the power detector detection lens through a through-hole shielding plate; the power detector is used to detect the power of the laser after it passes through the surface of the shielding original, and is fixed above the displacement platform through a power analyzer bracket. The through-hole shielding plate is used to block a part of the spot energy and is rigidly connected to the power detector; the power detector is fixed above the electric displacement platform to detect the power of the spot after it passes through the through-hole shielding plate, and synchronously transmits the power information to the controller; the controller controls the electric displacement platform to move in the direction of the optical axis, and finally moves the electric displacement platform to the spot position according to the power information of the power detector.

[0039] The focal spot to be measured is a Gaussian beam, and invisible light, such as 10.6μm CO2 laser, can be used.

[0040] The shielding plate has a through hole at its center and is rigidly fixed in front of or above the power detector.

[0041] The power detector can be selected according to the laser band and minimum power parameters.

[0042] A laser beam focus positioning method based on Gaussian energy distribution, comprising:

[0043] aAccording to the intensity expression of Gaussian beam, the laser power expression with the radius of the baffle hole as a variable is obtained. Specifically, according to the energy distribution of Gaussian beam, the laser power expression with the radius of the baffle hole as a variable is obtained. A two-dimensional coordinate system (r, z) of the focus positioning system is established, where the z axis coincides with the direction of the optical axis, the laser transmission direction is positive, r is the radius of the spot in the laser spot plane, and the coordinate origin (0,0) is the center of the focal spot plane at the position of the light wave waist on the optical axis. The intensity distribution of Gaussian beam is expressed as:

[0044]

[0045] Among them, I0=I(0,0), is the irradiance at the center of the light beam waist, Where P is the laser power. r0 is the laser waist radius. e (z) is the intensity drop on the laser spot plane to 1 / e of the axis 2 The spot radius at the axial position z as the cut-off point. The expression is z R is the Rayleigh distance, expressed as, Wherein R is the radius of the through hole of the light shielding baffle.

[0046] Integrate the radius of the shielding plate hole on the laser spot plane to obtain the laser power passing through the shielding plate:

[0047]

[0048] b. Select a baffle with a suitable aperture radius according to the laser power expression. First, based on the laser power expression, obtain the power change in the optical axis direction for different baffle radii. Consider the power change degree and feasibility, and select a baffle with a suitable aperture radius.

[0049] cUse Figure 1 The measurement optical path is used to measure the laser power at different optical axis positions. Specifically: 1) turn on the laser 1-1 to preheat for a period of time, 2) the controller 4 is initialized according to the parameters of the laser system 1 and the parameters of the perforated baffle 2, and moves the electric displacement stage 5 to a suitable position. 3) Turn on the laser 1-1 for a period of time and use the power detector 2 to collect signals, 4) the controller 4 saves this position signal information, and moves the displacement platform to a certain position along the optical axis, 5) repeat steps 3) and 4) until the power meter moves the corresponding distance, thus forming the average power change of the light-shielding baffle in the optical axis direction within a certain distance.

[0050] dUse formula (3) to fit the experimental data and obtain the spot position z0.

[0051]

[0052] Embodiment: Take the example of searching for a 10.6 μm CO2 laser with a focus lens having a spot diameter of 500 μm as an example.

[0053] Step (1) According to the energy distribution of the Gaussian beam, the laser power expression with the radius of the hole of the shielding plate as a variable is obtained. A two-dimensional coordinate system (r, z) of the focus positioning system is established, where the z axis coincides with the direction of the optical axis, the laser transmission direction is positive, r is the radius of the spot in the laser spot plane, and the coordinate origin (0,0) is the center of the focal spot plane at the position of the light wave waist on the optical axis. The intensity distribution of the Gaussian beam is expressed as:

[0054]

[0055] Among them, I0=I(0,0), is the irradiance at the center of the light beam waist, Where P is the laser power. r0 is the laser waist radius. e (z) is the intensity drop on the laser spot plane to 1 / e of the axis 2The spot radius at the axial position z as the cut-off point. The expression is z R is the Rayleigh distance, expressed as, Wherein R is the radius of the through hole of the light shielding baffle.

[0056] Integrate the radius of the shielding plate hole on the laser spot plane to obtain the laser power passing through the shielding plate:

[0057]

[0058] In this example, the laser wavelength λ is 10.6 μm, and the average laser power P avg The power is 30W and the laser spot diameter r0 is 500μm.

[0059] Step (2) Select a baffle with a suitable baffle hole radius according to the laser power expression. First, according to the laser power expression, obtain the power change in the optical axis direction when the baffle radii are different. In this example, the optical axis position is selected from -20mm to 20mm, and a certain data point is taken. The baffle hole radii are selected as 0.5r0, 0.875r0, 1.25r0, 1.675r0, and 2r0 respectively. Figure 2 After comprehensive consideration, an iron shading baffle with a radius of 200 μm is selected.

[0060] Step (3), using Figure 1 The optical path shown is used to measure the laser power at different optical axis positions. Specifically: 1) turn on the laser to preheat for 10 minutes, 2) input the laser system parameters and the parameters of the perforated baffle plate for initialization. 3) Turn on the laser for 1 minute and use the power detector to collect signals, 4) the controller 4 saves this position signal information and moves the displacement platform along the optical axis by 1mm, 5) repeat steps 3) and 4) until the power meter moves a distance of 24mm, thus forming the average power change through the shading baffle in the 2.4cm optical axis direction. Figure 3 Shown

[0061] Step (4), using formula (3), fit the experimental data to obtain the spot position z0 as 10.15 mm.

[0062]

Claims

1. A laser beam focus positioning method based on Gaussian energy distribution, characterized in that: The steps include: S1. A light shielding baffle with a through hole is provided, the size of which is slightly smaller than the diameter of the laser spot, and is placed on the path of the laser beam; S2. Use the laser power detection module to measure the laser power passing through the through hole of the light shielding baffle to obtain the distribution data of the laser power along the optical axis; S3. The collected data is processed by the data processing unit according to the preset distribution model of the laser power along the optical axis, and the focal position of the laser spot is automatically determined; S4. According to the determined laser spot focus position, the position or parameters of the electric displacement platform are adjusted through the control and feedback module to realize automatic positioning of the spot focus.

2. The laser beam focus positioning method based on Gaussian energy distribution according to claim 1, characterized in that: The step S1 specifically includes: S1.1 The laser power transmitted through the baffle is obtained by integrating the Gaussian beam intensity distribution over the entire baffle hole area, with the baffle hole radius as a variable; S1.2 Select appropriate shield radius parameters according to requirements.

3. The laser beam focus positioning method based on Gaussian energy distribution according to claim 2, characterized in that: In step S1.1, the intensity of the Gaussian beam is integrated within the radius of the shielding plate through hole on the laser spot plane to obtain the laser power passing through the shielding plate: Where r is the spot radius on the laser spot plane, z axis is the optical axis direction, the laser transmission direction is positive, P avg is the laser output power, λ is the laser wavelength, r0 is the laser waist radius, and R is the radius of the light shielding baffle hole.

4. The laser beam focus positioning method based on Gaussian energy distribution according to claim 1, characterized in that: The step S2 specifically includes: A laser (1-1) of a light beam to be measured, a focusing system (1-2), a shielding plate with a through hole (2) and a power detector are sequentially placed along the optical path; Adjust the optical axis position of the electric displacement platform, use a shielding plate to limit the light beam, and use a power detector to measure the laser power passing through the shielding plate at different optical axis positions; The Gaussian distribution spot output by the focusing system (1-2) passes through the shielding plate with through holes (2), is received by the power detector (3) and is transmitted to the automatic controller (4) in real time. Specifically: 1) Turn on the laser (1-1) and preheat for a while; 2) The controller (4) is initialized according to the parameters of the laser system (1) and the parameters of the perforated shielding plate (2), and moves the electric translation stage (5) to a suitable position; 3) Turn on the laser (1-1) for a period of time and use the power detector (2) to collect the signal; 4) The controller (4) stores the position signal information and moves the displacement platform to a certain position along the optical axis direction; 5) Repeat steps 3) and 4) until the corresponding collection requirements are met.

5. The laser beam focus positioning method based on Gaussian energy distribution according to claim 1, characterized in that: The step s3 comprises: the automatic controller (4) fits the data collected in step s2 using formula (3) according to the selected shielding plate through hole radius parameter to obtain the focus position; Among them, the fitting formula of the data processing unit is: Among them, R hole is the radius of the light shielding plate hole selected in step s1.1, the z axis is the optical axis direction, the laser transmission direction is positive, P0 is the laser output power, λ is the laser wavelength, and r0 is the laser waist radius.

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