Laser irradiation substance reflected light power measuring device and method

Abstract

The invention provides a laser irradiation substance reflected light power measuring device which can be applied to the technical field of laser. The device comprises a laser used for generating and emitting a laser beam; the beam adjusting device is used for adjusting parameters of the laser beams; a target material is placed in the hemispherical light-transmitting cover, so that the laser beam irradiates the surface of the target material after penetrating through the hemispherical light-transmitting cover and generates reflected laser, and the reflected laser is further reflected by the hemispherical light-transmitting cover to form converged reflected light; the rotating paraboloid-shaped reflecting mirror is used for converting reflected light from the hemispherical light-transmitting cover into parallel light beams; the diffuse reflection standard plate is used for carrying out diffuse reflection on the parallel light beams; the band-pass filter is arranged on a diffuse reflection light path of the diffuse reflection standard plate and is used for selectively transmitting light with the wavelength consistent with that of the laser beam; and the optical detector is used for collecting the optical signal passing through the band-pass filter and outputting an electric signal corresponding to the power of the reflected light.

Description

Technical Field

[0001] This invention relates to the field of laser application technology, and more specifically to a device and method for measuring the reflected light power of a material irradiated by a laser. Background Technology

[0002] The study of optical, thermal, mechanical, and mass transfer effects resulting from the interaction of lasers with matter has broad applications in numerous fields, including industrial processing, scientific research, and defense technology. Whether it's material processing techniques such as laser cutting, welding, and marking, or advanced technologies like laser ranging, composition detection, and additive manufacturing (3D printing), the essence of the process involves the absorption of laser energy by matter, triggering a series of physicochemical changes. In this process, the absorptivity and reflectivity of the target material to the incident laser are among the most critical parameters, directly determining the energy coupling efficiency and consequently affecting the target material's heating rate, phase transition process, vaporization, and even plasma generation.

[0003] Specifically, when lasers irradiate non-transparent materials such as metals, part of the energy is absorbed by the material, while the other part is reflected by its surface. The absorption and reflection characteristics of a material are not fixed but are influenced by a complex interplay of factors, including laser parameters (such as wavelength, power density, and pulse width), the material's inherent properties (such as material composition, surface roughness, and oxidation state), and the real-time state of the target surface during the irradiation process (such as temperature rise, melting, vaporization, and plasma plume formation). Therefore, achieving accurate measurement of the transient reflection coefficient (or absorption coefficient) of the target material during laser irradiation is crucial for a deeper understanding of the interaction mechanism, predicting and controlling the force-thermal-mass migration effect, and optimizing relevant application process parameters.

[0004] Currently, one of the conventional methods for measuring reflected light power is the integrating sphere method. This method utilizes the high diffuse reflection characteristics of the inner wall of the integrating sphere to collect reflected light incident from the target surface into the entire hemispherical space, and calculates the total reflected energy by measuring the light intensity at the exit of the integrating sphere. However, this method has the following inherent limitations:

[0005] Low temporal resolution: Inside the integrating sphere, reflected light from different directions on the target surface needs to undergo multiple diffuse reflections before reaching the detector. The optical paths are different and generally long, which causes the signal to be severely broadened in time, making it difficult to achieve high-speed, real-time measurement of transient processes (such as rapid changes on the order of nanoseconds or microseconds).

[0006] Susceptible to damage: When the incident laser power is high, the focused reflected light energy may directly act on the diffuse reflection coating on the inner wall of the integrating sphere, causing coating ablation, performance degradation or even permanent damage, affecting the accuracy of measurement and limiting its application in high-power scenarios.

[0007] System complexity: To achieve accurate measurements, the integrating sphere usually needs to be tightly coupled to the target surface, which is difficult to achieve in some online measurements or complex operating conditions.

[0008] Therefore, existing technologies lack an effective device and method for high-intensity, high-temporal-resolution, and real-time measurement of the dynamically changing laser power reflected from the target surface during high-power laser irradiation of the target material. Summary of the Invention

[0009] (a) Technical problems to be solved

[0010] To address at least one of the aforementioned problems, this invention provides a device and method for measuring the reflected light power of laser-irradiated materials. By employing an optical path design combining a hemispherical transparent cover, a rotating parabolic reflector, and a diffuse reflection standard plate, the target material is positioned near the center of the transparent cover. This allows reflected light from all directions to be transmitted through similar optical paths and undergo three attenuations before being received and processed by an adjustable photodetector. This achieves high temporal resolution and real-time accurate measurement of the reflected light power of the target surface during high-power laser irradiation, while significantly reducing the requirements for the target surface condition and effectively suppressing background interference.

[0011] (II) Technical Solution

[0012] To address the aforementioned technical problems, embodiments of the present invention provide a device and method for measuring the reflected light power of laser-irradiated materials.

[0013] According to a first aspect of the present invention, a device for measuring the reflected light power of laser-irradiated material is provided, comprising: a laser for generating and emitting a laser beam; a beam adjustment device for adjusting parameters of the laser beam; a hemispherical light-transmitting cover disposed in the optical path of the laser beam, wherein a target placement area is disposed inside the hemispherical light-transmitting cover for placing a target, such that the laser beam irradiates the surface of the target after passing through the hemispherical light-transmitting cover and generates reflected laser light, the reflected laser light being further reflected by the hemispherical light-transmitting cover to form converged reflected light; and a rotating parabolic reflector disposed in the hemispherical light-transmitting cover. Within the converging region of the reflected light from the spherical light-transmitting mask, a device is used to convert the reflected light from the hemispherical light-transmitting mask into a parallel beam. The optical focus of the rotating parabolic reflector and the laser irradiation point of the target material are symmetrical about the center of the hemispherical light-transmitting mask. A diffuse reflection standard plate is placed in the optical path of the parallel beam to diffusely reflect it. A bandpass filter is placed in the diffuse reflection optical path of the diffuse reflection standard plate to selectively transmit light with the same wavelength as the laser beam. A photodetector collects the optical signal passing through the bandpass filter and outputs an electrical signal corresponding to the reflected light power.

[0014] In some exemplary embodiments, the target placement area is configured such that the laser irradiation point of the target is located between the center of the hemispherical light-transmitting cover and the apex of the spherical cap.

[0015] In some exemplary embodiments, the position and / or angle of the photodetector's detection surface relative to the diffuse reflection standard plate can be adjusted. By adjusting the position and / or angle, the photodetector can collect light signals reflected from different points in the area illuminated by the parallel beam on the diffuse reflection standard plate with consistent efficiency.

[0016] In some exemplary embodiments, the measuring device further includes a light-absorbing material disposed on the non-optical signal acquisition path within the cavity formed by the hemispherical light-transmitting cover, the rotating parabolic reflector and the diffuse reflection standard plate, for absorbing stray light to prevent stray light from entering the photodetector.

[0017] In some exemplary embodiments, the beam adjustment device includes a beam splitter and an incident light power monitoring detector. The beam splitter is disposed in the output light path of the laser and is used to guide a portion of the incident laser branch to the incident light power monitoring detector to achieve synchronous monitoring of the laser power incident on the target.

[0018] In some exemplary embodiments, the bandpass filter is mounted on an adjustable bracket, and the angle of the bandpass filter can be continuously adjusted so that the transmission band of the bandpass filter matches the output wavelength of the laser.

[0019] According to a second aspect of the present invention, a method for measuring the reflected light power of a laser-irradiated material based on the above-described laser-irradiated material reflected light power measuring device is provided, comprising: generating a laser beam, adjusting it by a beam adjustment device, and irradiating it through a hemispherical light-transmitting cover onto a target material placed inside the hemispherical light-transmitting cover; collecting a parallel reflected beam formed by reflection from the target material, reflection and convergence by the hemispherical light-transmitting cover, and collimation by a rotating parabolic reflector; guiding the parallel reflected beam to a diffuse reflection standard plate for diffuse reflection; filtering the diffuse reflected light using a bandpass filter to selectively transmit light with the same wavelength as the incident laser; receiving the filtered light signal using a photodetector, and determining the reflected light power of the target material based on the light signal and a pre-calibrated conversion coefficient.

[0020] In some exemplary embodiments, the method for obtaining the pre-calibrated conversion coefficient includes: installing a standard mirror with known reflectivity in the target placement area; irradiating the standard mirror with a laser of known power and measuring the reference reflected power in the reflected optical path of the hemispherical light-transmitting cover using a standard power meter, while recording the reference voltage signal output by the photodetector; and calculating the conversion coefficient between the optical power and the voltage signal based on the reference reflected power and the reference voltage signal.

[0021] In some exemplary embodiments, receiving the filtered optical signal using a photodetector includes: adjusting the relative position between the photodetector and the diffuse reflection standard plate so that the detection surface of the photodetector satisfies the condition of uniformity in collecting reflected light from each point on the diffuse reflection standard plate.

[0022] In some exemplary embodiments, the spatial size of the region where the reflected light converges is constrained by controlling the offset distance of the laser irradiation point of the target material relative to the center of the hemispherical light-transmitting cover, thereby controlling the maximum optical path difference in the entire detection optical path within a preset range.

[0023] (III) Beneficial Effects

[0024] As can be seen from the above technical solutions, the laser-irradiated material reflected light power measurement device and method provided in the embodiments of the present invention have at least the following beneficial effects:

[0025] (1) By setting the target material near the center of the hemispherical light-transmitting cover, the optical path of the light reflected from all directions of the target surface to the light-transmitting cover is basically the same, the maximum optical path difference of the system is controlled at the centimeter level, and the corresponding time delay is less than 0.133 nanoseconds, which meets the real-time measurement requirements of the transient reflection process.

[0026] (2) The reflected light passes through the transmission attenuation of the hemispherical light-transmitting cover, the reflection attenuation of the rotating parabolic reflector, and the diffuse reflection attenuation of the diffuse reflection standard plate in sequence. The total attenuation factor is sufficient to reduce the high-power reflected light to the safe range of the detector, while avoiding damage to the optical components.

[0027] (3) By adjusting the position of the photodetector relative to the diffuse reflection standard plate, the signal acquisition efficiency of the detector on different areas of the diffuse reflection standard plate is kept consistent, thus realizing the accurate measurement of the total power of the non-uniform light spot and overcoming the measurement error caused by the uneven distribution of light intensity in the traditional method.

[0028] (4) A bandpass filter was set in the optical path to effectively filter out background noise such as target thermal radiation and plasma emission, ensuring that the detector only receives optical signals with the same wavelength as the laser. Combined with the calibration method, a quantitative conversion relationship between electrical signals and optical power was established, and the accurate inversion of reflectivity was realized.

[0029] (5) Due to the optical path design, the reflected light from different directions eventually reaches the detector at the same time, which reduces the requirement for the flatness of the target surface and enables the device to adapt to the measurement scenario where the target surface shape changes continuously during the laser action, thus improving the practicality and applicability of the system. Attached Figure Description

[0030] The above-described features, other objects, and advantages of the present invention will become clearer from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0031] Figure 1 This schematic diagram illustrates the structure of a laser-irradiated material reflected light power measuring device according to an embodiment of the present invention;

[0032] Figure 2 A flowchart illustrating a method for measuring the reflected light power of a material irradiated by a laser according to an embodiment of the present invention is shown schematically.

[0033] Figure 3 A schematic diagram of an apparatus for a power calibration method according to an embodiment of the present invention is shown.

[0034] Figure 4 A schematic diagram illustrating the calculation of the laser reflection point of the light-transmitting mask according to an embodiment of the present invention is shown; and

[0035] Figure 5 A schematic diagram illustrating the determination of the position of a photodetector according to an embodiment of the present invention is shown.

[0036] Figure label:

[0037] 1. Laser, 2. Beam adjustment device, 3. Hemispherical light-transmitting cover, 4. Target placement area, 5. Rotating parabolic reflector, 6. Light-absorbing material, 7. Diffuse reflection standard plate, 8. Photodetector, 9. Bandpass filter, 10. High reflectivity reflector, 11. Turntable. Detailed Implementation

[0038] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0039] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0040] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0041] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0042] Figure 1 The diagram schematically illustrates a structural diagram of a laser-irradiated material reflected light power measuring device according to an embodiment of the present invention.

[0043] like Figure 1 As shown, a laser-irradiated material reflected light power measuring device according to an embodiment of the present invention includes: a laser 1 for generating and emitting a laser beam; a beam adjustment device 2 for adjusting the parameters of the laser beam; a hemispherical light-transmitting cover 3 disposed in the optical path of the laser beam, wherein a target placement area 4 is disposed inside the hemispherical light-transmitting cover 3 for placing a target material, such that the laser beam irradiates the surface of the target material after passing through the hemispherical light-transmitting cover 3 and generates reflected laser light, the reflected laser light is further reflected by the hemispherical light-transmitting cover 3 to form converged reflected light; and a rotating parabolic reflector 5 disposed in the hemispherical light-transmitting cover 3. Within the convergence area of ​​the reflected light from the light-transmitting cover 3, the reflected light from the hemispherical light-transmitting cover 3 is converted into a parallel beam. The optical focus of the rotating parabolic reflector 5 and the laser irradiation point of the target material are symmetrical about the center of the hemispherical light-transmitting cover 3. The diffuse reflection standard plate 7 is placed in the optical path of the parallel beam and is used to diffusely reflect the parallel beam. The bandpass filter 9 is placed in the diffuse reflection optical path of the diffuse reflection standard plate 7 and is used to selectively transmit light with the same wavelength as the laser beam. The photodetector 8 is used to collect the optical signal passing through the bandpass filter 9 and output an electrical signal corresponding to the reflected light power.

[0044] In an embodiment of the invention, the incident laser passes through a hemispherical light-transmitting cover 3 and irradiates the target material. The laser reflected by the target surface is reflected by the light-transmitting cover and the rotating parabolic reflector 5 to form parallel light. The parallel light irradiates a certain area of ​​the diffuse reflection standard plate 7 and emits a diffuse reflection signal into space. The diffuse reflection signal is collected by the photodetector 8 to obtain the real-time change of the reflected light power of the target surface from the incident laser. Through the optical path design of the combination of the hemispherical light-transmitting cover 3, the rotating parabolic reflector 5, and the diffuse reflection standard plate 7, multiple attenuations of the reflected laser power can be achieved, so that the attenuated light power meets the detection range requirements of the photodetector 8, enabling the measurement of the reflected light power of high-power lasers.

[0045] In an embodiment of the invention, the target placement area 4 is configured such that the laser irradiation point of the target is located between the center and the apex of the hemispherical light-transmitting cover 3. Light reflected in all directions of the hemispherical space after laser irradiation (target surface reflected light) reaches the hemispherical light-transmitting cover 3 through substantially the same optical path, undergoing transmission and reflection (light-transmitting cover reflected light). Since the laser ablation point is located near the center of the hemispherical cover, the light reflected in all directions of the hemispherical space is reflected by the light-transmitting cover at an incident angle close to 0 degrees, resulting in substantially the same reflectivity. This achieves attenuation (transmission portion) and collection (reflection portion) of the target surface reflected light. The laser light reflected from the target surface in all directions of the hemispherical space can simultaneously reach the detector after passing through this optical path; that is, the light reflected in all directions of the hemispherical space after laser irradiation travels approximately the same optical path until reaching the detection area.

[0046] In embodiments of the present invention, the position and / or angle of the detection surface of the photodetector 8 relative to the diffuse reflection standard plate 7 can be adjusted. By adjusting the position and / or angle, the photodetector 8 can achieve consistent light signal acquisition efficiency from different points within the area illuminated by the parallel beam on the diffuse reflection standard plate 7. The light intensity reflected from the target surface in different directions is typically different and changes continuously over time. Therefore, in the reflected light path after reflection by the rotating parabolic mirror, the light intensity at different positions on the beam cross-section is different and changes continuously over time. Detecting the reflected light power requires measuring the summation of the light intensities at different positions on the beam cross-section after proportional attenuation. By using the diffuse reflection standard plate 7 to diffusely reflect the light after reflection by the rotating parabolic mirror, and by changing the detector position, the optical path and luminous flux of the light reflected from the laser spot area on the diffuse reflection standard plate 7 in different directions can be adjusted. In particular, by adjusting the detector position, the light intensity ratio of the light reflected from different areas on the diffuse reflection standard plate 7 can be made approximately consistent when reaching the detector position.

[0047] In an embodiment of the present invention, the measuring device may further include a light-absorbing material 6, which is disposed on the non-optical signal acquisition path within the cavity formed by the hemispherical light-transmitting cover 3, the rotating parabolic reflector 5, and the diffuse reflection standard plate 7, for absorbing stray light to prevent stray light from entering the photodetector 8.

[0048] In an embodiment of the present invention, the beam adjustment device 2 includes a beam splitter and an incident light power monitoring detector. The beam splitter is disposed in the output light path of the laser 1 and is used to guide a portion of the incident laser branch to the incident light power monitoring detector in order to realize synchronous monitoring of the laser power incident on the target.

[0049] In an embodiment of the present invention, the bandpass filter 9 is mounted on an adjustable bracket, and the angle of the bandpass filter 9 can be continuously adjusted so that the transmission band of the bandpass filter 9 matches the output wavelength of the laser 1.

[0050] Figure 2 A flowchart illustrating a method for measuring the reflected light power of a material irradiated by a laser, according to an embodiment of the present invention, is shown schematically.

[0051] like Figure 2 As shown, a method for measuring the reflected light power of a laser-irradiated material according to an embodiment of the present invention includes steps S110 to S150.

[0052] In step S110, a laser beam is generated, and after being adjusted by the beam adjustment device 2, it irradiates the target material placed inside the hemispherical light-transmitting cover 3 through the hemispherical light-transmitting cover 3.

[0053] Specifically, laser 1 emits a high-power laser beam, which, after the beam parameters are adjusted by beam adjustment device 2, reaches hemispherical light-transmitting cover 3, where reflection, absorption, and transmission occur, with the transmitted light irradiating a certain area of ​​the target surface.

[0054] In step S120, a parallel reflected beam is collected, which is reflected by the target material, reflected and converged by the hemispherical light-transmitting cover 3, and then collimated by the rotating parabolic reflector 5.

[0055] Specifically, during the interaction between the laser and the target material, depending on the differences in laser energy density and interaction time, the target material undergoes various physical processes such as heating, melting, generating high-temperature steam, and generating plasma. During this interaction, the irradiated area and its surroundings on the target surface undergo changes in state of matter or configuration, and the direction of the reflected laser changes within a half-space. By setting the irradiated area at a specific position within the hemispherical light-transmitting cover 3, reflected light from all directions can be concentrated in a certain area near a position symmetrical about the center of the irradiated area (when the size of the light-transmitting cover is fixed, the size of the focused area depends on the target material's eccentricity). In this process, most of the light reflected from the target surface is transmitted when it reaches the hemispherical light-transmitting cover 3, achieving attenuation of the laser reflected from the target surface. A rotating parabolic reflector 5 is placed below the area, with the focal point of the reflector symmetrical to the target irradiation point. Due to the properties of a parabola, the beam will exit approximately horizontally after reflection by the reflector.

[0056] In step S130, the parallel reflection beam is guided to the diffuse reflection standard plate 7 for diffuse reflection.

[0057] The intensity of the reflected light is significantly attenuated after passing through this series of optical paths, reaching the detection range of photodetector 8. By adjusting the detection position of photodetector 8, the proportion of light intensity reflected from each position on the reflector plate to the detector is made approximately the same. In this measuring device, the laser reflection direction has little impact on the optical path, which reduces the flatness requirement of the target material while ensuring the real-time detection of reflected light power.

[0058] In step S140, the diffuse reflection light is filtered by the bandpass filter 9, and light with the same wavelength as the incident laser is selectively transmitted.

[0059] In step S150, the filtered optical signal is received using photodetector 8, and the reflected optical power of the target material is determined based on the optical signal and the pre-calibrated conversion coefficient.

[0060] In some exemplary embodiments, receiving the filtered optical signal using the photodetector 8 includes: adjusting the relative position between the photodetector 8 and the diffuse reflection standard plate 7 so that the detection surface of the photodetector 8 meets the condition of uniformity in collecting reflected light from each point on the diffuse reflection standard plate 7.

[0061] In some exemplary embodiments, the method for obtaining the pre-calibrated conversion coefficient includes: installing a standard reflector with known reflectivity in the target placement area 4; irradiating the standard reflector with a laser of known power and measuring the reference reflected power in the reflected light path of the hemispherical light-transmitting cover 3 using a standard power meter, while recording the reference voltage signal output by the photodetector 8; and calculating the conversion coefficient between the optical power and the voltage signal based on the reference reflected power and the reference voltage signal.

[0062] Figure 3 A schematic diagram of an apparatus for a power calibration method according to an embodiment of the present invention is shown.

[0063] like Figure 3 As shown, the power calibration method according to an embodiment of the present invention includes: installing a high-reflectivity mirror 10 in a certain area of ​​the target material. First, the output power of the laser 1 is controlled at a low level. The position of the target material is adjusted by the turntable 11 so that the laser hits the mirror. Since the mirror has a high reflectivity, the incident laser is almost completely reflected. Laser power meters are placed at EM1 and EM2 respectively to detect the laser reflection power at the two reflection positions, thereby obtaining the reflection-transmittance ratio of the hemispherical light-transmitting cover 3. Then, the power meter is removed, and the voltage signal detected by the photodetector 8 is the reference voltage waveform under the condition of total laser reflection. The power-to-voltage conversion coefficient is obtained by calculating the ratio of the laser power measured by EM2 to the dimensionless value obtained by integrating the voltage waveform. The turntable 11 is moved so that the low-energy pulsed laser hits the target material. The photodetector 8 detects the voltage signal, and the transient change information of reflectivity can be obtained by the power-to-voltage conversion relationship obtained by calibration.

[0064] Note: The above calibration method is only one feasible solution. Other methods can also be used for calibration. For example, in actual operation, turntable 11 may not be necessary, and the reflector can be moved away in other ways; or the reflectivity of the light-transmitting cover can be calibrated before installation.

[0065] In an embodiment of the present invention, the spatial size of the convergent reflected light area is constrained by controlling the offset distance of the laser irradiation point of the target material relative to the center of the hemispherical light-transmitting cover 3, thereby controlling the maximum optical path difference in the entire detection optical path within a preset range.

[0066] The following calculations further illustrate that the optical path difference of the apparatus and method in the embodiments of the present invention is small.

[0067] Calculation of optical path difference:

[0068] As the laser incident angle changes, the subsequent detection optical path will also change. The main differences in optical path are in the following parts: inside the hemispherical transparent cover, inside the rotating parabolic reflector 5, at the diffuse reflection standard plate 7, and on the detection optical path of the photodetector 8.

[0069] Assuming the distance from the incident point to the center of the hemispherical light-transmitting cover is *d*, the width of the irradiated area on the diffuse reflection standard plate 7 is *w*, and the tilt angle of the reflector is *θ*, the optical path difference within the hemispherical light-transmitting cover is first calculated. The calculation method is shown in Appendix 1. The results show that the maximum optical path difference of the reflected light in different directions after the laser irradiates the target surface is approximately 4 *d*. Then, according to the definition of a parabola, the optical path of light emitted from the focal point is equal. Since the size of the convergence area of ​​the reflected light from the light-transmitting cover is very small (e.g., when the radius of the spherical cover is 25 cm and *d* = 1 cm, the size of the focal area is approximately 0.1 *d*), the optical path difference at the rotating parabolic reflector 5 can be ignored. Assuming the photodetector 8 is positioned on the normal line passing through the center of the light spot on the diffuse reflection standard plate 7, the maximum optical path difference between the diffuse reflection standard plate 7 and the path of the photodetector 8 can be calculated based on the triangle theorem and the structure of the diffuse reflection standard plate 7. The optical path difference can be further shortened by adjusting the position of photodetector 8. Therefore, the maximum optical path difference in the entire optical path is 4d+. In one embodiment, d = 1 cm, and the position of the photodetector 8 can be adjusted to... If the total optical path difference of the detection system is less than 4 cm, then according to the speed of light c = 3 × 10⁻⁶, the total optical path difference is less than 4 cm. 8 Calculated in m / s, the delay time introduced by the optical path difference is less than 0.1333 ns.

[0070] Calculation of laser reflection point and optical path for hemispherical light-transmitting cover 3:

[0071] Figure 4 The diagram illustrates a calculation of the laser reflection point of the light-transmitting mask according to an embodiment of the present invention.

[0072] like Figure 4As shown, the target is placed below the hemispherical light-transmitting cover 3 at a certain position offset to the left of the sphere's center. The eccentricity varies depending on the viewing angle. The plane with the largest eccentricity is selected as the reference plane. The following calculations determine the maximum convergence area and maximum optical path difference of light reflected from the target surface in different directions using this method. A coordinate system is established as shown in the figure below, with the center O of the spherical mirror as the origin. The main calculation approach is to determine the equation of the reflected ray by using the laser incident angle and the irradiation point. By simultaneously solving the equation of the circle of the light-transmitting cover's cross-section, the coordinates of the reflection point of the light-transmitting cover can be obtained, and thus the normal passing through that point can be obtained. By simultaneously solving the equation of the reflected light from the light-transmitting cover, the landing point and optical path of the reflected light can be determined.

[0073] The specific calculation process is as follows:

[0074] A laser beam irradiates a target at point A(-d,0), and is reflected in all directions. One of the reflected beams exits at a reflection angle α. The slope of line segment AB is... Therefore, the equation of line AB can be obtained as follows: Solve the equations of line AB and the circle simultaneously:

[0075] (1)

[0076] The coordinates of point B can be obtained from equation (1):

[0077] (2)

[0078] in:

[0079] (3)

[0080] Furthermore, based on optical principles and the properties of a circle, we know that line OB is the angle bisector of the incident ray AB and the reflected ray BC, and the slope of line OB is... Then, by the properties of angle bisectors, we can obtain:

[0081] (4)

[0082] The slope of the reflected ray BC can be obtained from equation (4). Then the equation of the reflected ray BC is:

[0083] (5)

[0084] The point of impact of the beam can be obtained The optical path can then be calculated based on the B and C coordinates:

[0085] (6)

[0086] Based on the determined dimensions of the hemispherical light-transmitting cover 3 and the position of the incident target, the size of the area where the reflected light falls can be calculated, and then the size and position of the subsequent reflector can be determined.

[0087] The detection range of photodetector 8 is determined:

[0088] Figure 5 A schematic diagram illustrating the position determination of the photodetector 8 according to an embodiment of the present invention is shown.

[0089] like Figure 5 As shown, the diffuse reflection standard plate 7 in this embodiment of the invention is an approximately ideal Lambertian body. When incident light hits the plate surface, it will produce diffuse reflection in all directions in the entire hemispherical space from the point of incidence, satisfying the Lambertian cosine theorem, that is, the radiation intensity of the radiating surface in a certain direction varies with the cosine of the angle between that direction and the surface normal.

[0090] When parallel light irradiates the diffuse reflection standard plate 7, the irradiated area is as shown in the figure above, with a width of w. Placing the photodetector 8 above point O, the center of the irradiated area, allows for the simultaneous collection of signals from each beam of light. Assuming the incident parallel light intensity is the same, let the intensity of the light reflected from point O to the photodetector 8 at a distance r along the OA direction be... Then the light intensity signal received by photodetector 8 from point O is... , l OA This represents the distance from point A to the center point O. Point O2 is the point farthest from point O in the diffuse reflection standard plate 7 irradiation area of ​​the parallel light. According to Lambert's cosine theorem, the intensity of the light collected at a distance r from point O2 along the O2A direction and reflected from point O2 to the photodetector 8 is... Then photodetector 8 receives the light intensity signal reflected from point O2. The photodetector 8 collects the ratio of the intensity of the reflected light from the two irradiation points. By adjusting the placement of the photodetector 8, the proportion of laser light intensity collected by the photodetector 8 and reflected from the target surface in different directions can be changed. When the photodetector 8 is far enough away from the diffuse reflection standard plate 7, such as hour, This allows us to approximate that the proportion of laser intensity reflected from the target surface in different directions is the same.

[0091] Those skilled in the art will understand that the features described in the various embodiments of the present invention can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in the present invention. In particular, the features described in the various embodiments of the present invention can be combined and / or combined in various ways without departing from the spirit and teachings of the present invention. All such combinations and / or combinations fall within the scope of the present invention.

Claims

1. A device for measuring the reflected light power of a material irradiated by a laser, characterized in that, include: A laser is used to generate and emit laser beams; A beam adjustment device for adjusting the parameters of the laser beam; A hemispherical light-transmitting cover is disposed in the optical path of the laser beam. The interior of the hemispherical light-transmitting cover is provided with a target placement area for placing the target material. The laser beam passes through the hemispherical light-transmitting cover and irradiates the surface of the target material, generating reflected laser light. The reflected laser light is further reflected by the hemispherical light-transmitting cover to form converged reflected light. A rotating parabolic reflector is disposed in the converging region of the reflected light from the hemispherical light-transmitting cover, for converting the reflected light from the hemispherical light-transmitting cover into a parallel beam; wherein, the optical focal point of the rotating parabolic reflector and the laser irradiation point of the target material are symmetrical about the center of the hemispherical light-transmitting cover. A diffuse reflection standard plate is placed in the optical path of the parallel beam to diffusely reflect the parallel beam. A bandpass filter is disposed in the diffuse reflection optical path of the diffuse reflection standard plate to selectively transmit light with the same wavelength as the laser beam; A photodetector is used to collect the optical signal passing through the bandpass filter and output an electrical signal corresponding to the reflected light power.

2. The laser-irradiated material reflected light power measuring device according to claim 1, characterized in that, The target placement area is configured such that the laser irradiation point of the target is located between the center of the hemispherical light-transmitting cover and the apex of the spherical cap.

3. The laser-irradiated material reflected light power measuring device according to claim 1, characterized in that, The position and / or angle of the detection surface of the photodetector relative to the diffuse reflection standard plate can be adjusted. By adjusting the position and / or angle, the photodetector can collect light signals reflected from different points in the area illuminated by the parallel beam on the diffuse reflection standard plate with consistent efficiency.

4. The laser-irradiated material reflected light power measuring device according to claim 1, characterized in that, The measuring device also includes a light-absorbing material disposed on the non-optical signal acquisition path within the cavity formed by the hemispherical light-transmitting cover, the rotating parabolic reflector, and the diffuse reflection standard plate, for absorbing stray light to prevent the stray light from entering the photodetector.

5. The laser-irradiated material reflected light power measuring device according to claim 1, characterized in that, The beam adjustment device includes a beam splitter and an incident light power monitoring detector. The beam splitter is disposed in the output light path of the laser and is used to guide a portion of the incident laser branch to the incident light power monitoring detector in order to realize synchronous monitoring of the laser power incident on the target.

6. The laser-irradiated material reflected light power measuring device according to claim 1, characterized in that, The bandpass filter is mounted on an adjustable bracket, and the angle of the bandpass filter can be continuously adjusted so that the transmission band of the bandpass filter matches the output wavelength of the laser.

7. A method for measuring the reflected light power of laser-irradiated material based on the laser-irradiated material reflected light power measuring device according to any one of claims 1-6, characterized in that, include: A laser beam is generated, and after being adjusted by a beam adjustment device, it irradiates the target material placed inside the hemispherical light-transmitting cover through the hemispherical light-transmitting cover. Collects parallel reflected beams formed by the target material, which are reflected and converged by the hemispherical light-transmitting cover and then collimated by the rotating parabolic reflector; The parallel reflected beam is guided to the diffuse reflection standard plate for diffuse reflection; By using a bandpass filter to filter diffuse reflection light, light with the same wavelength as the incident laser is selectively transmitted. The filtered optical signal is received using a photodetector, and the reflected optical power of the target material is determined based on the optical signal and a pre-calibrated conversion coefficient.

8. The method based on claim 7, characterized in that, The method for obtaining the pre-calibrated conversion coefficients includes: A standard reflector with known reflectivity is installed in the target placement area; The standard reflector is irradiated with a laser of known power, and the reference reflected power is measured in the reflected optical path of the hemispherical light-transmitting cover using a standard power meter, while the reference voltage signal output by the photodetector is recorded. The conversion coefficient between optical power and voltage signal is calculated based on the reference reflected power and the reference voltage signal.

9. The method based on claim 7, characterized in that, The step of receiving the filtered optical signal using a photodetector includes: adjusting the relative position between the photodetector and the diffuse reflection standard plate so that the detection surface of the photodetector meets the condition of uniform collection of reflected light from each point on the diffuse reflection standard plate.

10. The method based on claim 8, characterized in that, By controlling the offset distance of the laser irradiation point of the target material relative to the center of the hemispherical light-transmitting cover, the spatial size of the converging reflected light area is constrained, thereby controlling the maximum optical path difference in the entire detection optical path within a preset range.

Images