A high-sensitivity photothermal near-field detection system and method for a high-power laser element

Abstract

The application discloses a high-sensitivity photothermal near-field detection system and method of a strong laser element, relates to the field of optical absorption coefficient and absorption defect detection of optical materials, and the whole system comprises a pump laser irradiation module, a detection laser module, a pinhole filter, a 4f imaging lens group and a photoelectric detector. Based on the scalar angular spectrum diffraction theory, it is found that there is a maximum value in the change of the electric field intensity in the near-field diffraction area of the thermal-induced phase modulation, and the detection sensitivity of the optical absorption coefficient and the absorption defect can be greatly improved by detecting at the position, and the sensitivity is improved by several orders of magnitude compared with the traditional far-field photothermal detection.

Description

Technical Field

[0001] This invention relates to the field of light absorption coefficient and absorption defect detection of high-power laser elements, and more specifically, to a high-sensitivity photothermal near-field detection system and method for high-power laser elements. Background Technology

[0002] Laser-induced photothermal technology is an effective method for detecting the optical absorption coefficient and absorption defects of high-power laser components. This technology uses a high-power pump laser to irradiate the optical component. Valence band electrons in the component absorb laser energy and transition to the conduction band, generating free electrons. These electrons generate heat through lattice collisions or electron-phonon interactions, causing a localized temperature rise in the pump laser irradiation region. This temperature rise leads to thermoelastic deformation on the component surface and a refractive index gradient (i.e., thermal lensing) within the component. Irradiating the temperature-rising region with a low-power probe beam of a different wavelength causes a phase delay in the probe beam's wavefront due to the thermoelastic deformation and thermal lensing, resulting in diffraction and intensity changes during propagation. A photodetector converts these intensity changes into electrical signal changes; the amplitude of this signal change is called the photothermal signal. On the one hand, the optical absorption coefficient of a high-power laser component generally has a linear relationship with the photothermal signal; on the other hand, absorption defects in high-power laser components cause dramatic temperature rises, significantly enhancing the photothermal signal. Therefore, the detection sensitivity of the photothermal signal determines the detection sensitivity of the optical absorption coefficient and absorption defects of the high-power laser component.

[0003] Currently, methods to improve the sensitivity of photothermal signal detection mainly include: 1) increasing the power density of the pump laser, such as increasing the pump laser power or reducing the pump beam diameter; 2) adding a pinhole filter to the probe beam to filter out the local area with the largest intensity change on the probe beam cross-section; 3) optimizing the ratio of the pump beam diameter to the probe beam diameter; 4) optimizing the distance from the probe beam waist to the thermoelastic deformation and thermal lens; and 5) using a shorter wavelength probe beam. Based on the above methods, the sensitivity of existing photothermal detection has reached ppm (i.e., 10). -6 ) magnitude.

[0004] However, with the power of various laser devices constantly increasing and the growth and processing technology of high-power laser components constantly improving, the existing light absorption coefficient and the detection sensitivity of absorption defects can no longer meet the development needs of high-power laser devices. Summary of the Invention

[0005] To address the problems in related technologies, this invention proposes a high-sensitivity photothermal near-field detection system and method for high-power laser elements, in order to overcome the aforementioned technical problems existing in the prior art.

[0006] The technical solution of this invention is implemented as follows:

[0007] One aspect of the present invention:

[0008] A high-sensitivity photothermal near-field detection system for a high-power laser element includes: a pump laser irradiation module, a detection laser module, a pinhole filter, a 4f imaging mirror group, and a photodetector.

[0009] The pump laser irradiation module is used to output a high-power pump laser to irradiate a designated area of ​​the device under test, causing thermoelastic deformation on the surface of the device under test and forming a thermal lens effect inside.

[0010] The detection laser module is used to output a detection laser, which is incident at an inclined angle onto the irradiation area of ​​the component under test. After being reflected and transmitted by the component, the detection laser carries the phase modulation information corresponding to thermoelastic deformation and thermal lens, respectively.

[0011] The pinhole filter is positioned at the location of the maximum near-field diffraction intensity difference of the light emitted from the device under test.

[0012] The 4f imaging lens group is used to coincide with the plane where the pinhole filter is located, so as to relay the near-field diffraction pattern to the photodetector target surface without distortion.

[0013] The photodetector is arranged on the rear focal plane of the 4f imaging lens group to receive the near-field diffracted light field relayed by the 4f imaging lens group and convert the light intensity signal into an electrical signal.

[0014] Furthermore, it also includes: a lens module, which comprises a pump laser focusing lens and a probe laser focusing objective;

[0015] The pump laser focusing lens is disposed between the pump laser irradiation module and the device under test, and is used to focus the pump laser onto the surface of the device under test;

[0016] The probe laser focusing objective is located between the probe laser module and the device under test, and is used to focus the probe laser onto the same area on the device under test that is irradiated by the pump laser.

[0017] Furthermore, the 4f imaging lens group consists of two convex lenses. The front focal plane of the front convex lens coincides with the plane where the pinhole filter is located, and the rear focal plane of the rear convex lens holds the photodetector array, which is used to relay the near-field diffraction pattern to the photodetector target surface without distortion.

[0018] Furthermore, the detection laser includes reflected detection light and transmitted detection light;

[0019] The reflected probe light is used to detect the thermoelastic deformation information of the surface of the component under test.

[0020] The transmitted probe light is used to detect thermal lens information inside the component under test.

[0021] Another aspect of the present invention:

[0022] A high-sensitivity photothermal near-field detection method for a high-power laser element, used in the aforementioned high-sensitivity photothermal near-field detection system for a high-power laser element, includes the following steps:

[0023] When the pump laser irradiation module is activated, the pump laser is focused by the pump laser focusing lens and then vertically irradiates a designated area on the surface of the component under test. The component under test absorbs the pump laser energy and generates a local temperature rise, which in turn forms thermoelastic deformation on the surface of the component and generates a thermal lensing effect inside.

[0024] The probe laser module is activated. After being focused by the probe laser focusing objective, the probe laser is incident on the same irradiation area of ​​the device under test at an angle deviating from that of the pump laser. Part of the probe laser is reflected by the surface of the device to form a reflected light field, carrying phase modulation information of the surface thermoelastic deformation; the other part penetrates the device to form a transmitted light field, carrying phase modulation information of the internal thermal lens.

[0025] Based on the scalar angular spectrum diffraction theory, the light intensity distribution of the phase-modulated probe light field at different propagation distances in free space is calculated. The intensity difference is calibrated as the difference in total light intensity at the same position when there is pumped laser irradiation and when there is no pumped laser irradiation, and the location of the maximum value of the intensity difference in the near field is determined.

[0026] A pinhole filter and a 4f imaging lens group are arranged at the location of the maximum intensity difference, so that the front focal plane of the 4f imaging lens group coincides with the plane at that location.

[0027] The light intensity signals under two conditions, namely unpumped laser and pumped laser, are collected by a photodetector. The change in photothermal signal is obtained by calculating the difference in light intensity. Based on the photothermal signal, the light absorption coefficient and absorption defects of the high-power laser element under test are detected.

[0028] The phase modulation of the reflected probe light is expressed as:

[0029] ;

[0030] In the formula, k is the wavenumber of the probe light, and λ is the wavelength of the probe light. The surface thermoelastic deformation distribution function;

[0031] The phase modulation of the transmitted probe light is represented as:

[0032] ;

[0033] In the formula, d is the thermo-optic coefficient of the material, and d is the thickness of the component. This is the temperature rise distribution function.

[0034] The determination of the location of the maximum intensity difference within the near field range includes the following steps:

[0035] Obtain the propagation distance of the modulated light field in free space The resulting light field distribution is represented as:

[0036] ;

[0037] In the formula, f x and f y This refers to the spatial frequency.

[0038] Calibrated strength difference The difference between the total light intensity passing through the pinhole filter when irradiated by a pumped laser and when irradiated by an unpumped laser:

[0039] ;

[0040] In the formula, The intensity distribution at position z when irradiated by a pumped laser. This represents the light intensity distribution at position z under unpumped laser irradiation.

[0041] The beneficial effects of this invention are:

[0042] 1. Based on the scalar angular spectrum diffraction theory, this invention obtains the maximum value of the electric field intensity change in the near-field diffraction region of thermal phase modulation. Calibrating the detection at this position can significantly improve the detection sensitivity of the light absorption coefficient and absorption defects. Its sensitivity is several orders of magnitude higher than that of traditional far-field photothermal detection.

[0043] 2. To address the problem that the near-field maximum region is close to the surface of the element and is difficult to detect directly, this invention introduces a 4f imaging lens group to relay the near-field diffraction pattern to the distant detector plane without distortion. This not only preserves the near-field enhancement effect but also solves the spatial limitation, making the system layout flexible and easy to implement.

[0044] 3. The present invention has two detection modes, reflection and transmission, which can respectively obtain information on surface thermoelastic deformation and internal thermal lensing. They can also be used in combination to achieve comprehensive detection of the all-round light absorption characteristics of high-power laser elements. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a schematic diagram of the optical path of a high-sensitivity photothermal near-field detection system for a high-power laser element according to an embodiment of the present invention;

[0047] Figure 2 This is a schematic diagram of a scenario in which a high-sensitivity photothermal near-field detection system with a high-power laser element is used for existing far-field detection according to an embodiment of the present invention.

[0048] Figure 3 This is a schematic diagram of the optical path used for near-field detection by a high-sensitivity photothermal near-field detection system of a high-power laser element according to an embodiment of the present invention, using a 4f imaging lens group.

[0049] Figure 4 This is a graph showing the intensity difference as a function of propagation distance measured by photodetectors under pinhole filters of multiple different pinhole diameters in a high-sensitivity photothermal near-field detection system of a high-power laser element according to an embodiment of the present invention.

[0050] Figure 5 This is a graph showing the intensity difference measured by a photodetector as a function of propagation distance when the element of a high-sensitivity photothermal near-field detection system for a high-power laser element is located at different distances from the waist of the detection laser beam, according to an embodiment of the present invention.

[0051] Figure 6 This is a graph showing the intensity difference measured by the photodetector as a function of propagation distance when the ratio of the diameter of the pump laser spot and the probe laser spot on the front surface of the element in a high-sensitivity photothermal near-field detection system of a high-power laser element according to an embodiment of the present invention is different. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0053] According to an embodiment of the present invention, a high-sensitivity photothermal near-field detection system using a high-power laser element is provided.

[0054] like Figures 1-6 As shown, the high-sensitivity photothermal near-field detection system for a high-power laser element according to an embodiment of the present invention includes: a pump laser irradiation module 1, a detection laser module 3, a lens module 2, a pinhole filter 5, a 4f imaging mirror group 6, and a photodetector 7.

[0055] The pump laser irradiation module 1 is used to generate a high-power pump laser and irradiate a predetermined area on the surface of the component under test 4 to excite thermoelastic deformation and thermal lensing effect.

[0056] Specifically, for the aforementioned device under test 4, its high-power pump laser irradiation will cause a local temperature rise in the optical device 4. The temperature rise will cause thermoelastic deformation on the surface of the device 4 on the one hand, and thermal lenses will be generated inside the device 4 on the other hand.

[0057] The detection laser module 3 is used to generate and output a detection laser, which is incident on the element 4 at a certain angle and in the same area as the pump laser. After being reflected and transmitted by the element, the detection laser carries the phase modulation information corresponding to thermoelastic deformation and thermal lens, respectively.

[0058] Specifically, the detection laser converts the deformation and refractive index change of element 4 caused by temperature rise into an optical signal that can be received by photodetector 7.

[0059] The lens module 2 includes two parts: a pump laser focusing lens 21 and a probe laser focusing objective lens 22.

[0060] Among them, the pump laser focusing lens 21 is disposed between the pump laser irradiation module 1 and the device under test 4, and is used to focus the pump laser onto the surface of the device under test 4;

[0061] The probe laser focusing objective 22 is disposed in the probe laser module 3, located between the probe laser module 3 and the device under test 4, and is used to focus the probe laser onto the same area of ​​the device under test 4 to form a probe spot that matches the pump laser spot.

[0062] The pinhole filter 5 is positioned at the location of the maximum near-field diffraction intensity change of the light emitted from the device under test. Place;

[0063] The 4f imaging lens group 6 consists of two convex lenses. The front focal plane of the front convex lens coincides with the plane where the pinhole filter 5 is located, and the rear focal plane of the rear convex lens is used to place the photodetector 7 array to relay the near-field diffraction pattern to the target surface of the photodetector 7 without distortion.

[0064] The photodetector 7 is arranged on the back focal plane of the 4f imaging lens group 6, and is used to receive the near-field diffracted light field relayed by the 4f imaging lens group 6, and convert the light intensity signal into an electrical signal.

[0065] like Figure 2 As shown, in traditional far-field detection methods, photodetector 7 detects the intensity of far-field diffracted light at a relatively far distance from element 4. However, the intensity difference at this far-field location is not at its maximum, thus limiting the detection sensitivity.

[0066] like Figure 3 As shown, the present invention addresses the location of the maximum near-field diffraction intensity variation. A 4f imaging lens group 6 is installed at the location, which consists of two convex lenses. The front focal plane of the convex lens is... With the planes overlapping, the back focal plane of the convex lens is used to place the photodetector 7 array, which relays the near-field diffraction pattern to the target surface of the photodetector 7 without distortion, so that the photodetector 7 can still obtain a high-sensitivity signal at the near-field maximum value under the condition that the physical space is not restricted.

[0067] like Figure 4 As shown, the total intensity difference of the probe light passing through the pinhole filter 5 varies with the propagation distance z under different pinhole diameters. According to Gaussian beam theory, the probe laser on the focal plane... The beam diameter is given by the following formula:

[0068] ;

[0069] Where λ=532nm is the probe wavelength, f=0.2m is the lens focal length, and D=10mm is the probe beam diameter at the lens. The calculated focused probe spot diameter is 2w0≈13.55μm, and the Rayleigh length is... z was calculated R ≈0.27mm.

[0070] Specifically, in the simulation, the fixed element is located at the waist of the probe laser beam, z0, which corresponds to a length of 2 Rayleigh ohms. The full width at half maximum (FWHM) of the phase modulation space is fixed at 2 μm, and the peak height is 20 nm. The pinhole diameter D is set accordingly. p The ratios to the focused spot diameter 2w0 were 1, 5, 10, 15 and 20, respectively. The intensity difference at each position within a range of 100 mm from the element surface was recorded. The results showed that the maximum value occurred at a ratio of 20 and z=8.08 mm.

[0071] like Figure 5 As shown, the total intensity difference of the probe light passing through the pinhole filter 5 varies with the propagation distance z when the element is located at different defocus positions in front of the probe laser beam waist. In the simulation, the ratio of the pinhole diameter to the focused spot diameter is fixed at 20, the half-width at half-maximum (FWHM) of the phase modulation is fixed at 2μm, and the peak height is 20nm. The element is placed at different positions in front of the probe laser beam waist, i.e., z0 / z R Using values ​​of 0, 2, 4, 6, and 8 respectively, the intensity difference at various locations within a 100mm radius from the component surface was recorded. The results show that the maximum value occurs at z0=2z. R At z=8.08mm;

[0072] like Figure 6As shown, when the ratio of the pump laser spot diameter to the probe laser spot diameter is different, the total intensity difference of the probe light passing through the pinhole filter 5 varies with the propagation distance z. The probe spot radius at the modulation surface where the element is located is calculated using the Gaussian beam propagation formula:

[0073] ;

[0074] In the simulation, fixed element 4 is located at the waist of the probe laser beam with a position z0 of 0.54 mm. The spot diameter 2w1≈30.19 μm, the peak height of phase modulation is fixed at 20 nm, and the pinhole diameter is set to 20 times the diameter of the probe spot. When the ratio of the spatial half-width W of phase modulation to the spot diameter W / 2w1 is set to 0.1, 0.3, 0.5, 0.7, and 0.9, the intensity difference at each position within a range of 100 mm from the surface of element 4 is recorded. The results show that the maximum value occurs at a ratio of 0.1 and z=9.09 mm.

[0075] This invention utilizes a pump laser to irradiate a high-power laser element, inducing thermoelastic deformation and thermal lensing on the element's surface and interior, respectively. This thermoelastic deformation and thermal lensing cause a phase delay on the wavefront of a probe beam, resulting in diffraction of the probe beam during transmission. Based on the scalar angular spectrum propagation theory of electromagnetic waves, a maximum value of electric field intensity change is found in the near-field diffraction region of the thermoelastic deformation and thermal lensing. Unlike traditional far-field photothermal detection methods, this invention performs photothermal detection in the near-field diffraction region, significantly improving the light absorption coefficient and detection sensitivity of absorption defects in high-power laser elements.

[0076] According to an embodiment of the present invention, a high-sensitivity photothermal near-field detection method for a high-power laser element is provided.

[0077] A high-sensitivity photothermal near-field detection method for a high-power laser element according to an embodiment of the present invention includes the following steps:

[0078] Step S1: The pump laser is perpendicularly irradiated onto a certain area of ​​the surface of the high-power laser element under test. After the pump laser is absorbed by the element, it produces thermoelastic deformation on the surface and a thermal lensing effect inside.

[0079] Step S2: Irradiate the same area described in step S1 with a probe laser at an incident angle deviating from that of the pump laser. After reflection from the component surface, the light carries surface deformation information. The phase modulation experienced by the reflected light wavefront is expressed as:

[0080] ;

[0081] In the formula, To detect the light wavenumber, λ is the wavelength of the light being detected. This is the surface thermoelastic deformation distribution function.

[0082] The probe light also transmits through the element, and the outgoing light carries information from the internal thermal lens. The phase modulation experienced by the transmitted light wavefront is represented as:

[0083] ;

[0084] In the formula, d is the thermo-optic coefficient of the material, and d is the thickness of the component. This is the temperature rise distribution function.

[0085] The two modulated probe light fields can be uniformly represented as:

[0086] ;

[0087] In the formula, Let be the initial complex amplitude function of the incident probe light field. According to different detection modes or .

[0088] Step S3: Based on the scalar angular spectrum diffraction theory, the propagation distance of the modulated light field in free space is... The resulting light field distribution is represented as follows:

[0089] ;

[0090] In the formula, f x and f y This refers to the spatial frequency.

[0091] Calibrated strength difference The difference in total light intensity passing through pinhole filter 5 between pumped laser irradiation and unpumped laser irradiation:

[0092] ;

[0093] In the formula, The intensity distribution at position z when irradiated by a pumped laser. This represents the light intensity distribution at position z under unpumped laser irradiation.

[0094] Numerical simulations show that in the near-field region immediately adjacent to the modulation surface, the intensity difference is significant for reflective devices (i.e., the front surface of the element) and for transmissive devices (i.e., the rear surface of the element). There exists a maximum value, and the location of this maximum value is... Typically, they are only a few millimeters to tens of millimeters in size.

[0095] Step S4, at the maximum value position A 4f imaging lens group 6 is installed at the location. This 4f imaging lens group 6 consists of two convex lenses, with the front focal plane aligned with... The planes they are on coincide, and a photodetector 7 is placed at the back focal plane.

[0096] Step S5, 4f imaging lens group 6 will locate the maximum value The near-field diffraction pattern at the plane is relayed to the detector target surface. The light intensity when the pump laser is irradiated and the light intensity when the un-pump laser is irradiated are recorded by the photodetector 7, and the intensity difference is calculated to obtain the change in the photothermal signal.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Those skilled in the art, upon considering the disclosure in the specification and embodiments, will readily conceive of other embodiments of this disclosure. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

[0098] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A high-sensitivity photothermal near-field detection system for a high-power laser element, characterized in that, include: Pumped laser irradiation module (1), detection laser module (3), pinhole filter (5), 4f imaging lens group (6) and photodetector (7); The pump laser irradiation module (1) is used to output a high-power pump laser to irradiate a designated area of ​​the device under test, causing thermoelastic deformation on the surface of the device under test and forming a thermal lens effect inside. The detection laser module (3) is used to output a detection laser, which is incident at an inclined angle onto the irradiation area of ​​the component under test. After being reflected and transmitted by the component, the detection laser carries the phase modulation information corresponding to the thermoelastic deformation and the thermal lens, respectively. The pinhole filter (5) is located at the position of the maximum near-field diffraction intensity difference of the light emitted from the device under test; The 4f imaging mirror group (6) is used to coincide with the plane where the pinhole filter (5) is located, so as to relay the near-field diffraction pattern to the target surface of the photodetector (7) without distortion; The photodetector (7) is arranged on the back focal plane of the 4f imaging mirror group (6) to receive the near-field diffraction light field relayed by the 4f imaging mirror group (6) and convert the light intensity signal into an electrical signal.

2. The high-sensitivity photothermal near-field detection system for a high-power laser element according to claim 1, characterized in that, Also includes: Lens module (2), which includes a pump laser focusing lens (21) and a probe laser focusing objective (22); The pump laser focusing lens (21) is disposed between the pump laser irradiation module (1) and the device under test, and is used to focus the pump laser onto the surface of the device under test; The probe laser focusing objective (22) is located between the probe laser module (3) and the device under test, and is used to focus the probe laser onto the same area on the device under test that is irradiated by the pump laser.

3. The high-sensitivity photothermal near-field detection system for a high-power laser element according to claim 1, characterized in that, The 4f imaging lens group (6) consists of two convex lenses. The front focal plane of the front convex lens coincides with the plane of the pinhole filter (5), and the rear focal plane of the rear convex lens holds the photodetector (7) array, which is used to relay the near-field diffraction pattern to the target surface of the photodetector (7) without distortion.

4. The high-sensitivity photothermal near-field detection system for a high-power laser element according to claim 1, characterized in that, The detection laser includes reflected detection light and transmitted detection light; The reflected probe light is used to detect the thermoelastic deformation information of the surface of the component under test. The transmitted probe light is used to detect thermal lens information inside the component under test.

5. A high-sensitivity photothermal near-field detection method for a high-power laser element, used in the detection method of the high-sensitivity photothermal near-field detection system for a high-power laser element as described in any one of claims 1-4, characterized in that, Includes the following steps: When the pump laser irradiation module is activated, the pump laser is focused by the pump laser focusing lens and then vertically irradiates a designated area on the surface of the component under test. The component under test absorbs the pump laser energy and generates a local temperature rise, which in turn forms thermoelastic deformation on the surface of the component and generates a thermal lensing effect inside. The probe laser module is activated. After being focused by the probe laser focusing objective, the probe laser is incident on the same irradiation area of ​​the device under test at an angle deviating from that of the pump laser. Part of the probe laser is reflected by the surface of the device to form a reflected light field, carrying phase modulation information of the surface thermoelastic deformation; the other part penetrates the device to form a transmitted light field, carrying phase modulation information of the internal thermal lens. Based on the scalar angular spectrum diffraction theory, the light intensity distribution of the phase-modulated probe light field at different propagation distances in free space is calculated. The calibrated intensity difference is the difference in total transmitted light intensity at the same position when there is pumped laser irradiation and when there is no pumped laser irradiation. This value has a maximum value position in the near-field diffraction range. A pinhole filter and a 4f imaging lens group are arranged at the location of the maximum intensity difference, so that the front focal plane of the 4f imaging lens group coincides with the plane at that location. The light intensity signals under two conditions, namely unpumped laser and pumped laser, are collected by a photodetector. The change in photothermal signal is obtained by calculating the difference in light intensity. Based on the photothermal signal, the light absorption coefficient and absorption defects of the high-power laser element under test are detected.

6. The high-sensitivity photothermal near-field detection method for high-power laser elements according to claim 5, characterized in that, The phase modulation of the reflected probe light is represented as: ； In the formula, k is the wavenumber of the probe light, and λ is the wavelength of the probe light. The surface thermoelastic deformation distribution function; The phase modulation of the transmitted probe light is represented as: ； In the formula, d is the thermo-optic coefficient of the material, and d is the thickness of the component. This is the temperature rise distribution function.

7. The high-sensitivity photothermal near-field detection method for high-power laser elements according to claim 5, characterized in that, Determining the location of the maximum intensity difference within the near field includes the following steps: Obtain the propagation distance of the modulated light field in free space The resulting light field distribution is represented as: ； In the formula, f x and f y Spatial frequency; Calibrated strength difference The difference between the total light intensity passing through the pinhole filter when irradiated by a pumped laser and when irradiated by an unpumped laser: ； In the formula, The intensity distribution at position z when irradiated by a pumped laser. This represents the light intensity distribution at position z under unpumped laser irradiation.

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