CN212646516U - Single-beam photothermal measuring device for absorption defects - Google Patents
Single-beam photothermal measuring device for absorption defects Download PDFInfo
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- CN212646516U CN212646516U CN202020764330.9U CN202020764330U CN212646516U CN 212646516 U CN212646516 U CN 212646516U CN 202020764330 U CN202020764330 U CN 202020764330U CN 212646516 U CN212646516 U CN 212646516U
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Abstract
A single-beam photothermal measuring device for absorptive defects comprises a common-path structure and a non-common-path structure. The utility model discloses light path simple structure, the installation and debugging of being convenient for. The measurement result is stable, and the measurement signal abnormity caused by environmental vibration and sample inclination is avoided. By detecting the power change of the light beam at the edge of the light spot, the measurement sensitivity of the system is obviously improved.
Description
Technical Field
The utility model relates to a defect detection field, especially a measuring device to optical element surface absorptivity defect.
Background
The problem of damage to the optical components used in intense laser systems has been a central factor limiting the increase in device output flux. The metal impurities in the solution introduced in the growth process of the optical material, the metal and nonmetal impurities such as polishing solution and magnetorheological fluid remained on the surface after grinding, polishing and shaping, and the nodule defects in the film layer after film coating have higher absorption than that of the optical element. These defects act as light absorption centers, and strongly absorb laser light under high-energy laser irradiation, and exceed the tolerable range of the element, thereby causing element damage.
Current methods for defect detection mainly include microscopic scattering dark-field imaging, fluorescence microscopy and photothermal scanning imaging. The microscopic scattering dark field imaging method mainly aims at structural defects such as scratches, pits and the like, and utilizes scattered light generated by the defects to carry out imaging detection. The defects such as metal, nonmetal and other impurity ions hardly scatter incident light, and the microscopic scattering dark field imaging method cannot effectively detect the defects which are invisible visually. The fluorescence microscopic imaging method utilizes the fluorescence generated by the defect under the excitation of short wavelength laser to carry out imaging, has low detection sensitivity and can not detect the absorption defect which does not emit light under the irradiation of the laser. The traditional photothermal scanning imaging technology is based on the photothermal effect, the pumping light irradiates the surface of an element to cause the element to generate thermal deformation, and the probe light measures the thermal deformation degree of the region. The method can detect the absorption defects, has high sensitivity, but has complex measuring light path, large adjusting difficulty and large influence of the overlapping degree of the two light spots on the detection sensitivity, and particularly when the surface of an element with larger size is scanned, the overlapping degree of the two light spots can be obviously changed by environmental vibration and sample inclination, even the overlapping degree of the two light spots can not be overlapped, so that the measuring signals are uneven or have no signals, and the absorption defects are easy to miss detection or mistakenly identified.
SUMMERY OF THE UTILITY MODEL
In order to overcome the defects of the prior art, the utility model provides an absorptive defect single-beam photothermal measuring device and a measuring method. The light path structure of the measuring device is simple, and the installation and debugging are convenient. The measurement result is stable, and the measurement signal abnormity caused by environmental vibration and sample inclination is avoided. By detecting the power change of the light beam at the edge of the light spot, the measurement sensitivity of the system is obviously improved.
The method can detect the absorption abnormality of the defect area by a single light beam by utilizing the absorption difference between the defect and the material substrate.
In order to achieve the above purpose, the utility model adopts the following technical scheme:
the utility model discloses absorptive defect single beam light and heat is measured including being total to light path type and non-two kinds of light path type altogether:
a common-path type single-beam photothermal measuring device for absorption defects is characterized by comprising a laser, a beam expander, a power regulator, a beam splitter, a power meter, a chopper, a polarization beam splitter, a quarter-wave plate, a reflecting mirror, a galvanometer scanner, a scanning lens, a converging lens, a baffle diaphragm, a photoelectric detector, a phase-locked amplifier, an XYZ displacement platform and a computer, wherein a sample to be measured is placed on the XYZ displacement platform;
the beam expander, the power regulator and the beam splitter are sequentially arranged along the direction of a light beam emitted by the laser, an incident light beam is divided into weak reflection light and strong transmission light with different intensities by the beam splitter, the power meter is arranged along the direction of the weak reflection light, and the chopper, the polarization beam splitter, the quarter-wave plate, the reflector, the galvanometer scanner and the scanning lens are sequentially arranged along the direction of the strong transmission light;
said strongly transmitted beam is modulated by said chopper; modulating incident light and outputting p polarized light after passing through the polarization beam splitter, wherein the p polarized light outputs circularly polarized light after passing through the quarter wave plate; the circularly polarized light is focused and incident to the surface of a sample to be measured after passing through the galvanometer scanner and the scanning lens; the surface of the sample to be measured generates thermal deformation under the irradiation of laser; the reflected light modulated by thermal deformation passes through the scanning lens, the galvanometer scanner, the reflecting mirror and the quarter-wave plate in sequence to become s-polarized light; the s-polarized light is reflected by the polarization beam splitter and then is focused by the convergent lens; after the focused light beam passes through the baffle diaphragm, the light beam at the edge of the light spot is received by the photoelectric detector;
the modulation frequency of the chopper is used as a reference signal and is input into the second input end of the phase-locked amplifier through a cable; the signal collected by the photoelectric detector is used as a measuring signal and is input into the first input end of the phase-locked amplifier;
the control signal output end of the computer is respectively connected with the control end of the XYZ displacement platform and the control end of the galvanometer scanner, and the output end of the phase-locked amplifier is connected with the input end of the computer.
A non-common-path type single-beam photothermal measuring device for absorption defects is characterized by comprising a laser, a beam expander, a power regulator, a beam splitter, a power meter, a chopper, a converging lens, a baffle diaphragm, a photoelectric detector, a phase-locked amplifier, an XYZ displacement platform, a computer and a second converging lens, wherein a sample to be measured is placed on the XYZ displacement platform;
the beam expander, the power regulator and the beam splitter are sequentially arranged along the direction of a light beam emitted by the laser, the beam splitter divides an incident light beam into weak reflected light and strong transmitted light with different intensities, the power meter is arranged along the direction of the weak reflected light, the chopper is arranged along the direction of the strong transmitted light, the strong transmitted light is modulated by the chopper and then is focused by the second converging lens to irradiate the sample to be detected, the baffle diaphragm, the converging lens and the photoelectric detector are sequentially arranged along the direction of the reflected light of the sample to be detected, the output end of the photoelectric detector is connected with the first input end of the phase-locked amplifier, the modulation frequency of the chopper is used as a reference signal, the output end of the reference signal is connected with the second input end of the phase-locked amplifier through a cable, and the output end of the phase-locked amplifier is connected with the input end of the computer, the control signal output end of the computer is connected with the control end of the XYZ displacement platform.
The baffle diaphragm is manufactured in a mode that a circular aluminum film or chromium film is plated on the surface of circular fused quartz glass with the thickness of 0.5 mm; the transmittance of the film coating area is less than or equal to 0.01 percent; the radius of the coating area is larger than the beam waist radius of the light spot incident to the baffle diaphragm, so that the power of the light beam passing through is smaller than 1% of the power of the light beam incident to the baffle diaphragm;
a method for measuring the absorption defects on the surface of an optical element by using a common-path type absorption defect single-beam photothermal measuring device comprises the following steps:
1) placing the sample to be measured on an XYZ displacement platform, and driving the XYZ displacement platform by the computer to move the sample to be measured along the Z direction so that the surface of the sample to be measured is positioned near the focus of the scanning lens;
2) setting the modulation frequency of the chopper as f, and setting the demodulation frequency of the lock-in amplifier as 2 times of the modulation frequency of the chopper, namely 2 f;
3) the computer drives an internal scanning reflector of the galvanometer scanner to enable a focusing light spot to move on the surface of the sample along the X direction and the Y direction so as to form raster scanning; the stepping amount of the light spot moving along the X and Y directions is the diameter of the light spot focused on the surface of the sample to be measured;
4) at the measuring point, the measuring signal of the photoelectric detector is input into the phase-locked amplifier, and the amplitude of the second harmonic (2f) of the measuring signal is output to the computer after the signal is demodulated by the phase-locked amplifier; the computer records the amplitude of the measuring point in real time;
5) under the control of the computer, the XYZ displacement platform moves the sample to be measured to the next measuring area along the X or Y direction, and the step 3) is returned until all the measurements of the sample to be measured are completed;
6) and the computer draws the recorded signal amplitude into a two-dimensional distribution map of the absorption defects and analyzes the two-dimensional distribution map, gives an analysis report and completes the absorption defect test of the sample to be tested.
A method for measuring the absorption defects on the surface of an optical element by using a non-common-path type absorption defect single-beam photothermal measuring device comprises the following steps:
1) placing the sample to be measured on an XYZ displacement platform, and moving the sample to be measured along the Z direction on the XYZ displacement platform under the control of the computer to enable the surface of the sample to be measured to be positioned near the focus of the second convergent lens;
2) setting the modulation frequency of the chopper as f, and setting the demodulation frequency of the lock-in amplifier as 2 times of the modulation frequency of the chopper, namely 2 f;
3) the computer drives the XYZ displacement platform to move, so that a focused light spot output by the second converging lens moves on the surface of the sample to be detected along the X direction and the Y direction, and the moving stepping amount of the light spot along the X direction and the Y direction is the diameter of the light spot focused on the surface of the sample to be detected;
4) at the measuring point, the measuring signal of the photoelectric detector is input into the phase-locked amplifier, and the amplitude of the second harmonic (2f) of the measuring signal is output to the computer after the signal is demodulated by the phase-locked amplifier; the computer records the amplitude of the measuring point in real time;
5) under the control of the computer, the XYZ displacement platform moves the sample to be measured to the next measuring point along the X or Y direction, and the step 4) is returned until all the measurements of the sample to be measured are completed;
6) and the computer draws the recorded signal amplitude into a two-dimensional distribution map of the absorption defects and analyzes the two-dimensional distribution map, gives an analysis report and completes the absorption defect test of the sample to be tested.
The utility model has the advantages as follows:
the utility model discloses single beam photothermal measuring device of absorption defect's light path simple structure, the installation and debugging of being convenient for. The measurement result is stable, and the measurement signal abnormity caused by environmental vibration and sample inclination is avoided. By detecting the power change of the light beam at the edge of the light spot, the measurement sensitivity of the system is obviously improved.
Drawings
FIG. 1 is a schematic view of the single-beam photothermal measuring device for common-path absorption defects of the present invention
FIG. 2 is a schematic view of the baffle diaphragm structure provided by the present invention
FIG. 3 is a schematic view of the non-common-path type single-beam photothermal measuring device for absorption defects of the present invention
In the figure: 1-a laser; 2-a beam expander; 3-a power regulator; 4-a beam splitter; 5-a power meter; 6-a chopper; 7-a polarizing beam splitter; 8-quarter wave plate; 9-a mirror; 10-galvanometer scanner; 11-a scanning lens; 12-the sample; 13-a converging lens; 14-baffle diaphragm; 15-a photodetector; 16-a lock-in amplifier; 17-XYZ stage; 18-a computer; 19-second converging lens.
Detailed Description
The present invention will be described in further detail with reference to the following drawings and examples, which should not be construed as limiting the scope of the present invention.
Example 1
Fig. 1 is a schematic diagram of a common-path type single-beam photo-thermal measurement apparatus for absorption defects in embodiment 1 of the present invention, which is shown in the figure, and includes a laser 1, a beam expander 2, a power regulator 3, a beam splitter 4, a power meter 5, a chopper 6, a polarization beam splitter 7, a quarter wave plate 8, a reflector 9, a galvanometer scanner 10, a scanning lens 11, a converging lens 13, a baffle diaphragm 14, a photodetector 15, a lock-in amplifier 16, an XYZ displacement platform 17 and a computer 18, wherein a sample 12 to be measured is placed on the XYZ displacement platform 17;
the beam expander 2, the power regulator 3 and the beam splitter 4 are sequentially arranged along the direction of a light beam emitted by the laser 1, the beam splitter 4 divides an incident light beam into weak reflection light and strong transmission light with different intensities, the power meter 5 is arranged along the direction of the weak reflection light, the power meter 5 is used for monitoring the incident light power and stability, and the chopper 6, the polarization beam splitter 7, the quarter-wave plate 8, the reflecting mirror 9, the galvanometer scanner 10 and the scanning lens 11 are sequentially arranged along the direction of the strong transmission light;
said strongly transmitted beam is modulated by said chopper 6; modulating incident light, outputting p-polarized light after passing through the polarization beam splitter 7, and outputting circularly polarized light after passing through the quarter-wave plate 8; the circularly polarized light passes through the galvanometer scanner 10 and the scanning lens 11 and then is focused to be incident on the surface of a sample 12 to be measured; the surface of the sample 12 to be measured is thermally deformed under the irradiation of laser; the reflected light modulated by thermal deformation passes through the scanning lens 11, the galvanometer scanner 10, the reflecting mirror 9 and the quarter-wave plate 8 in sequence to become s-polarized light; the s-polarized light is reflected by the polarization beam splitter 7 and then focused by the converging lens 13; after the focused light beam passes through the baffle diaphragm 14, the light beam at the edge of the light spot is received by the photoelectric detector 15 as a measurement signal;
the modulation frequency of the chopper 6 is used as a reference signal and is input into a second input end of the phase-locked amplifier 16 through a cable; the measuring signal output by the photodetector 15 is input to a first input end of the lock-in amplifier 16;
the control signal output end of the computer 18 is respectively connected with the control end of the XYZ displacement platform 17 and the control end of the galvanometer scanner 10, and the output end of the lock-in amplifier 16 is connected with the input end of the computer 18.
FIG. 2 is a schematic view of the baffle diaphragm 14, which is fabricated by plating a circular aluminum film or chromium film on a circular 0.5mm thick fused silica glass surface; the transmittance of the film coating area is less than or equal to 0.01 percent; the radius of the coating area is larger than the beam waist radius of the light spot incident on the baffle diaphragm 14, so that the power of the passing light beam is smaller than 1% of the power of the light beam incident on the baffle diaphragm 14.
The method for measuring the surface absorption defects of the optical element by using the common-path type absorption defect single-beam photothermal measuring device is characterized by comprising the following steps of:
1) placing the sample 12 on an XYZ stage 17, wherein under the control of the computer, the XYZ stage 17 moves the sample 12 along the Z direction to make the surface of the sample 12 near the focus of the scanning lens 11, and adjusting the beam expander 2 to make the diameter of the beam expanded by the beam expander 2 meet the entrance pupil requirement of the galvanometer scanner 10;
2) setting the modulation frequency of the chopper 6 as f, and setting the demodulation frequency of the lock-in amplifier 16 as 2 times, namely 2f, of the modulation frequency of the chopper 6;
3) the computer 18 drives the internal scanning reflector of the galvanometer scanner 10 to move the focused light spot on the surface of the sample along the X and Y directions to form raster scanning; the step amount of the light spot moving along the X and Y directions is the diameter of the light spot focused on the surface of the sample 12 to be measured;
4) at the measuring point, the measuring signal of the photodetector 15 is input into the lock-in amplifier 16, and the amplitude of the second harmonic (2f) is output to the computer 18 after being demodulated by the lock-in amplifier 16; the computer 18 records the amplitude of the measuring point in real time;
5) the XYZ displacement platform 17 moves the sample 12 to be measured to the next measuring area along the X or Y direction, and returns to the step 3) until all the measurements of the sample to be measured are completed;
6) the computer 18 plots the recorded signal amplitude into a two-dimensional absorption defect distribution map and analyzes the two-dimensional absorption defect distribution map to give an analysis report, thereby completing the absorption defect test of the sample 12 to be tested.
Example 2
Fig. 3 is a schematic diagram of a non-common-path type absorption defect single-beam photothermal measurement device according to embodiment 2 of the present invention, and it can be seen from the figure that the non-common-path type absorption defect single-beam photothermal measurement device includes a laser 1, a beam expander 2, a power regulator 3, a beam splitter 4, a power meter 5, a chopper 6, a converging lens 13, a baffle diaphragm 14, a photodetector 15, a lock-in amplifier 16, an XYZ displacement platform 17, a computer 18, and a second converging lens 19, and a sample 12 to be measured is placed on the XYZ displacement platform 17;
the beam expander 2, the power regulator 3 and the beam splitter 4 are sequentially arranged along the direction of the light beam emitted by the laser 1, the beam splitter 4 divides the incident light beam into weak reflected light and strong transmitted light with different intensities, the power meter 5 is arranged along the direction of the weak reflected light, and the power meter 5 is used for monitoring the incident light power and stability; the chopper 6 is arranged along the direction of the strong transmission light, the strong transmission light is modulated by the chopper and then is focused and irradiated on the sample 12 to be measured through the second converging lens 19, the baffle diaphragm 14, the converging lens 13 and the photoelectric detector 15 are sequentially arranged in the direction of the reflection light of the sample 12 to be measured, the output end of the photoelectric detector 15 is connected with the first input end of the phase-locked amplifier 16, the modulation frequency of the chopper 6 serves as a reference signal, the reference signal output end is connected with the second input end of the phase-locked amplifier 16 through a cable, the output end of the phase-locked amplifier 16 is connected with the input end of the computer 18, and the control signal output end of the computer 18 is connected with the control end of the XYZ displacement platform 17.
The baffle diaphragm 14 is manufactured by plating a circular aluminum film or chromium film on the surface of circular fused quartz glass with the thickness of 0.5 mm; the transmittance of the film coating area is less than or equal to 0.01 percent; the radius of the coating area is larger than the beam waist radius of the light spot incident to the baffle diaphragm 14, so that the power of the passing light beam is smaller than 1% of the power of the light beam incident to the baffle diaphragm 14;
the method for measuring the surface absorption defects of the optical element by using the non-common-path type absorption defect single-beam photothermal measuring device comprises the following steps of:
1) placing the sample 12 on an XYZ stage 17, wherein the XYZ stage 17 moves the sample 12 along the Z direction under the control of the computer, so that the surface of the sample 12 is near the focus of the second converging lens 19;
2) setting the modulation frequency of the chopper 6 as f, and setting the demodulation frequency of the lock-in amplifier 16 as 2 times, namely 2f, of the modulation frequency of the chopper 6;
3) the computer 18 drives the XYZ displacement stage 17 to move, so that the focused light spot output by the second converging lens 19 moves on the surface of the sample to be measured along the X and Y directions, and the moving step amount of the light spot along the X and Y directions is the diameter of the light spot focused on the surface of the sample to be measured 12;
4) at the measuring point, the measuring signal of the photodetector 15 is input into the lock-in amplifier 16, and the amplitude of the second harmonic (2f) is output to the computer 18 after being demodulated by the lock-in amplifier 16; the computer 18 records the amplitude of the measuring point in real time;
5) under the control of the computer, the XYZ stage 17 moves the sample 12 to be measured to the next measurement point along the X or Y direction, and returns to step 4) until all measurements of the sample to be measured are completed;
6) the computer 18 plots the recorded signal amplitude into a two-dimensional absorption defect distribution map and analyzes the two-dimensional absorption defect distribution map to give an analysis report, thereby completing the absorption defect test of the sample 12 to be tested.
The experiment shows that the utility model discloses absorptive defect single beam light thermal measurement device's light path simple structure, the installation and debugging of being convenient for. The measurement result is stable, and the measurement signal abnormity caused by environmental vibration and sample inclination is avoided. By detecting the power change of the light beam at the edge of the light spot, the measurement sensitivity of the system is obviously improved.
Claims (3)
1. The single-beam photothermal measuring device for the absorptive defect is characterized by comprising a laser (1), a beam expander (2), a power regulator (3), a beam splitter (4), a power meter (5), a chopper (6), a polarization beam splitter (7), a quarter wave plate (8), a reflecting mirror (9), a galvanometer scanner (10), a scanning lens (11), a converging lens (13), a baffle diaphragm (14), a photoelectric detector (15), a phase-locked amplifier (16), an XYZ displacement platform (17) and a computer (18), wherein a sample (12) to be measured is placed on the XYZ displacement platform (17);
the beam expander (2), the power regulator (3) and the beam splitter (4) are sequentially arranged along the direction of a light beam emitted by the laser (1), the beam splitter (4) divides an incident light beam into weak reflected light and strong transmitted light with different intensities, the power meter (5) is arranged along the direction of the weak reflected light, and the chopper (6), the polarization beam splitter (7), the quarter-wave plate (8), the reflector (9), the galvanometer scanner (10) and the scanning lens (11) are sequentially arranged along the direction of the strong transmitted light;
said strongly transmitted beam is modulated by said chopper (6); modulating incident light, outputting p-polarized light after passing through the polarization beam splitter (7), and outputting circularly polarized light after passing through the quarter-wave plate (8); the circularly polarized light passes through the galvanometer scanner (10) and the scanning lens (11) and then is focused to be incident on the surface of a sample (12) to be measured; the surface of the sample (12) to be measured generates thermal deformation under the irradiation of laser; the reflected light modulated by thermal deformation passes through the scanning lens (11), the galvanometer scanner (10), the reflecting mirror (9) and the quarter-wave plate (8) in sequence to become s-polarized light; the s-polarized light is reflected by the polarization beam splitter (7) and then focused by the convergent lens (13); after the focused light beam passes through the baffle diaphragm (14), the light beam at the edge of the light spot is received by the photoelectric detector (15);
the modulation frequency of the chopper (6) is used as a reference signal and is input into a second input end of the phase-locked amplifier (16) through a cable; the signal collected by the photoelectric detector (15) is used as a measuring signal and is input into a first input end of the phase-locked amplifier (16);
the control signal output end of the computer (18) is respectively connected with the control end of the XYZ displacement platform (17) and the control end of the galvanometer scanner (10), and the output end of the phase-locked amplifier (16) is connected with the input end of the computer (18).
2. The single-beam photothermal measuring device for the absorptive defect is characterized by comprising a laser (1), a beam expander (2), a power regulator (3), a beam splitter (4), a power meter (5), a chopper (6), a converging lens (13), a baffle diaphragm (14), a photoelectric detector (15), a phase-locked amplifier (16), an XYZ displacement platform (17), a computer (18) and a second converging lens (19), wherein a sample (12) to be measured is placed on the XYZ displacement platform (17);
the beam expander (2), the power regulator (3) and the beam splitter (4) are sequentially arranged along the direction of a light beam emitted by the laser (1), the beam splitter (4) divides an incident light beam into weak reflected light and strong transmitted light with different intensities, the power meter (5) is arranged along the direction of the weak reflected light, the chopper (6) is arranged along the direction of the strong transmitted light, the strong transmitted light is modulated by the chopper (6) and then is focused by the second converging lens (19) to irradiate the sample (12) to be detected, the baffle diaphragm (14), the converging lens (13) and the photoelectric detector (15) are sequentially arranged along the direction of the reflected light of the sample (12) to be detected, the output end of the photoelectric detector (15) is connected with the first input end of the phase-locked amplifier (16), and the modulation frequency of the chopper (6) is used as a reference signal, the reference signal output end is connected with the second input end of the phase-locked amplifier (16) through a cable, the output end of the phase-locked amplifier (16) is connected with the input end of the computer (18), and the control signal output end of the computer (18) is connected with the control end of the XYZ displacement platform (17).
3. The single-beam photothermal measuring device for absorption defects according to claim 1 or 2, wherein said stop plate diaphragm (14) is made by plating a circular aluminum or chromium film on the surface of a circular 0.5mm thick fused silica glass; the transmittance of the film coating area is less than or equal to 0.01 percent; the radius of the film coating area is larger than the beam waist radius of the light spot incident to the baffle diaphragm (14), so that the power of the passing light beam is smaller than 1% of the power of the light beam incident to the baffle diaphragm (14).
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