Optothermal Surface Deformation Detection and Calibration Device and Method Based on Wavelength-Shifting Interference

Abstract

The present invention discloses a photothermal surface deformation detection and calibration device and method based on wavelength-shifting interference. The photothermal surface deformation detection and calibration device includes a pump light source, a detection light source, a photoelectric detector, and a wavelength-tunable light source, all of which are respectively oriented towards the surface of the sample to be measured. Between the wavelength-tunable light source and the sample to be measured, a tunable light source beam splitter device, a tunable light source focusing device, a beam collimation device, and a reference mirror are sequentially arranged. The interference light focusing device is oriented towards the tunable light source beam splitter device. The light reflected back from the surface of the reference mirror and the surface of the sample to be measured undergoes interference. The interference light sequentially passes through the beam collimation device, the tunable light source focusing device, the tunable light source beam splitter device, and the interference light focusing device and then enters the interference light intensity detection device. The present invention combines the wavelength-shifting interference method and the photoinduced surface thermal deformation method to achieve quantitative detection and calibration of the surface thermal deformation amount caused by the absorption of light energy by materials, and the measurement process is simple and fast, and is easy to promote.

Description

Technical Field

[0001] The present invention relates to the field of optical material detection, and specifically to a photothermal surface deformation detection and calibration device and method based on wavelength-shifting interference. Background Art

[0002] When the surface of a material is irradiated with light, it absorbs the light energy, causing a local temperature rise and thus surface deformation. This effect is also known as the "photoinduced surface thermal deformation" effect. Since the magnitude of the resulting surface thermal deformation is related to the optical absorption, thermal expansion coefficient, thermal conductivity, and other properties of the material, it is often used as a method for measuring parameters such as the absorption rate and thermal conductivity of the material. Taking the measurement of the material absorption rate as an example, the basic principle of this method is to irradiate the surface of the sample to be measured with a beam of light (usually a laser). After the material absorbs the light energy, surface thermal deformation occurs, which is equivalent to adding a new "lens" to the surface of the sample. Therefore, this effect is also called the surface thermal "lens" effect. Due to this newly added thermal "lens", the propagation characteristics of the light reflected from the material surface will change, resulting in a converging or diverging effect. A beam of probe light can be used to measure this surface thermal deformation. For example, a spatial filter is added to the optical path of the reflected probe light. The energy of the probe light reaching the detector after passing through the spatial filter will change due to the converging or diverging effect of the surface thermal deformation on the probe light. The greater the absorption, the greater the measured signal. Within a certain range of pump laser power, the absorption is linearly related to the measured photothermal signal. The detection sensitivity for surface absorption using this method can reach 10 -8 , which is particularly suitable for the detection and analysis of weakly absorbing materials. However, when using this method to accurately quantitatively measure the surface absorption rate of a material, calibration is required. Generally, this is achieved by making a calibration sample, that is, a sample with a known absorption rate is prepared in advance, and the absorption rate value of the sample to be measured is obtained by comparing the photothermal signals of the sample to be measured and the calibration sample. This method has certain limitations and requires the calibration sample and the sample to be measured to have the same thermophysical properties. Therefore, different calibration samples need to be made separately for different types of samples to be measured, which is not conducive to the popularization and application of this method.

[0003] Since surface thermal deformation is related to thermophysical parameters such as the absorption, thermal conductivity, and thermal expansion coefficient of the material, if the amount of surface thermal deformation caused can be directly measured, the absorption rate, thermal conductivity, thermal expansion coefficient, and other parameters of the sample to be measured can be directly obtained, eliminating the need to use a calibration sample and thus simplifying the measurement process.

[0004] For weakly absorbing materials, the surface thermal deformation induced by laser is very small, generally at the sub-micron or even nano scale. Interferometric measurement technology is a commonly used technology for measuring the surface shape of an object. In particular, the Fizeau interferometer has very high surface shape measurement accuracy. In the measurement process of a general Fizeau interferometer, a mechanical phase-shifting method is used to achieve fine adjustment of the phase of the measurement beam. This phase-shifting method is limited by the errors caused by the movement of the hardware, thus restricting the measurement accuracy. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an optical-thermal surface deformation detection and calibration device and method based on wavelength-shifting interference, which solves the problem that the traditional optical-induced surface thermal deformation measurement method needs to separately manufacture calibration samples for different types of samples, resulting in a complex measurement process and being not conducive to popularization and application.

[0006] The technical solution of the present invention is as follows:

[0007] An optical-thermal surface deformation detection and calibration device based on wavelength-shifting interference includes a pump light source, a detection light source, a photodetector, and a wavelength-tunable light source respectively facing the surface of the sample to be measured. A pump light focusing device is arranged between the pump light source and the sample to be measured. A first detection light focusing device is arranged between the detection light source and the sample to be measured. A second detection light focusing device is arranged between the photodetector and the sample to be measured. A tunable light source beam splitting device, a tunable light source focusing device, a beam collimation device, and a reference mirror are sequentially arranged between the wavelength-tunable light source and the sample to be measured. The interference light focusing device faces the tunable light source beam splitting device. The light reflected from the surface of the reference mirror and the surface of the sample to be measured interferes, and the interference light sequentially passes through the beam collimation device, the tunable light source focusing device, the tunable light source beam splitting device, and the interference light focusing device and then enters the interference light intensity detection device.

[0008] A pump beam modulation device is arranged between the pump light source and the pump light focusing device.

[0009] A detection light beam splitting device, a detection light spatial filtering device, and a filtering device are sequentially arranged between the second detection light focusing device and the photodetector.

[0010] A detection light power monitoring device is arranged in the optical path between the second detection light focusing device and the photodetector.

[0011] The pump light reflected from the surface of the sample to be measured is collected by a pump light collection device.

[0012] A calibration method for detecting photothermal surface deformation based on wavelength-shifted interference includes the following steps: First, when the surface of the sample to be measured does not generate surface thermal deformation, the wavelength-tunable light source starts from a selected starting wavelength λ0 and sequentially changes the wavelength at a certain wavelength step Δλ. The interference light intensity detection device records the interference results at different wavelengths, and the initial surface shape result W0 of the sample to be measured is measured according to the weighted multi-step wavelength-shifted phase-shifting algorithm. Then, the pump light source is used to excite the surface of the sample to be measured to generate thermal deformation. The wavelength-tunable light source starts from the selected starting wavelength λ0 again and sequentially changes the wavelength at a certain wavelength step Δλ. The interference light intensity detection device records the interference results at different wavelengths, and the surface shape result W1 of the sample to be measured under the irradiation of the pump laser is measured according to the weighted multi-step wavelength-shifted phase-shifting algorithm. Finally, through the comparison and analysis of the surface shape result W1 and the initial surface shape result W0, the surface thermal deformation amount h of the sample to be measured caused by laser induction is obtained. According to the surface thermal deformation amount h and combined with the thermophysical parameters of the sample to be measured, the actual absorption rate result of the sample to be measured is obtained.

[0013] The specific process of the pump light source exciting the surface of the sample to be measured to generate thermal deformation is as follows: The pump beam emitted by the pump light source is modulated after passing through the pump beam modulation device, and then focused on the surface of the sample to be measured through the pump light focusing device to excite the generation of surface thermal deformation; the detection beam emitted by the detection light source is also focused on the surface of the sample to be measured through the first detection light focusing device and coincides with the pump spot; the detection light reflected from the surface of the sample to be measured is collected by the second detection light focusing device, and then sequentially passes through the detection light beam splitting device, the detection light spatial filtering device and the filtering device, and then enters the photodetector for detection. The output signal of the photodetector is detected by using the phase-locked detection technology, and an AC signal with the same modulation frequency as the modulated pump beam is used as the reference signal for phase-locked detection. Only the optothermal signal induced by the pump beam can be detected by the lock-in amplifier, and other external noises are filtered out.

[0014] The beam emitted by the wavelength-tunable light source sequentially passes through the tunable light source beam splitting device, the tunable light source focusing device and the beam collimating device and then reaches the reference mirror. A part of the light is reflected back from the surface of the reference mirror, and another part of the light passes through the reference mirror and reaches the surface of the sample to be measured and is reflected back. The light reflected back from the surface of the reference mirror and the surface of the sample to be measured interferes, and then passes through the beam collimating device, the tunable light source beam splitting device, the tunable light source focusing device, and the interference light focusing device in sequence and then enters the interference light intensity detection device to record the interference results at different wavelengths.

[0015] The detection light reflected from the surface of the sample to be measured is used by the detection light power monitoring device to monitor the power of the detection light in real time.

[0016] Advantages of the present invention:

[0017] The measurement and calibration of the photothermal surface deformation caused by light induction in the present invention are realized by the Fizeau interference measurement method based on wavelength phase shifting. By combining the wavelength phase shifting interference method with the photothermal surface deformation method, a wavelength tunable laser is used as the light source. By continuously changing its wavelength, the function of a phase shifter is achieved, eliminating the need to drive hardware to realize phase shifting, greatly simplifying the mechanical structure of the interference measurement system. Moreover, during the measurement, the mechanical part of the system remains stationary, eliminating the errors caused by the movement of the hardware and further improving the accuracy of the measurement and calibration. Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of the photothermal surface deformation detection and calibration device of the present invention. Detailed Embodiments

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0020] See Figure 1 , a photothermal surface deformation detection and calibration device based on wavelength phase shifting interference, including a pump light source 1, a detection light source 6, a photodetector 13, and a wavelength tunable light source 14 respectively facing the surface of the sample to be measured 4. The pump light reflected from the surface of the sample to be measured 4 is collected by the pump light collection device 5. A pump beam modulation device 2 and a pump light focusing device 3 are sequentially arranged between the pump light source 1 and the sample to be measured 4. A first detection light focusing device 7 is arranged between the detection light source 6 and the sample to be measured 4. A second detection light focusing device 8, a detection light beam splitting device 9, a detection light spatial filtering device 11, and a filtering device 12 are sequentially arranged between the sample to be measured 4 and the photodetector 13. A detection light power monitoring device 10 is arranged in the optical path between the second detection light focusing device 8 and the photodetector 13. An adjustable light source beam splitting device 15, an adjustable light source focusing device 16, a beam collimation device 17, and a reference mirror 18 are sequentially arranged between the wavelength tunable light source 14 and the sample to be measured 4. An interference light focusing device 19 faces the adjustable light source beam splitting device 15. The light reflected from the surface of the reference mirror 18 and the surface of the sample to be measured 4 interferes, and the interference light sequentially passes through the beam collimation device 17, the adjustable light source focusing device 16, the adjustable light source beam splitting device 15, the interference light focusing devices 19 and 20 and then enters the interference light intensity detection device 21.

[0021] A calibration method for detecting the surface thermal deformation based on wavelength-shifting interference includes the following steps: First, when the surface of the sample to be measured 4 does not generate surface thermal deformation, the wavelength-tunable light source 14 starts from the selected initial wavelength λ0 and sequentially changes the wavelength with a certain wavelength step Δλ. The interference light intensity detection device 21 records the interference results at different wavelengths, and the initial surface shape result W0 of the sample to be measured 4 is measured according to the weighted multi-step wavelength-shifting algorithm. Then, the pump light source 1 is used to excite the surface of the sample to be measured to generate thermal deformation. The wavelength-tunable light source 14 starts from the selected initial wavelength λ0 again and sequentially changes the wavelength with a certain wavelength step Δλ. The interference light intensity detection device 21 records the interference results at different wavelengths, and the surface shape result W1 of the sample to be measured 4 under the irradiation of the pump laser is measured according to the weighted multi-step wavelength-shifting algorithm. Finally, through the comparison and analysis of the surface shape result W1 and the initial surface shape result W0, the surface thermal deformation amount h caused by laser induction is obtained. According to the surface thermal deformation amount h and the thermophysical parameters of the sample to be measured, the actual absorption rate result of the sample to be measured is obtained.

[0022] Among them, the specific process of the pump light source 1 exciting the surface of the sample to be measured to generate thermal deformation is as follows: The pump beam emitted by the pump light source 1 is modulated after passing through the pump beam modulation device 2, and then focused on the surface of the sample to be measured 4 through the pump light focusing device 3 to excite the generation of surface thermal deformation; the detection beam emitted by the detection light source 6 is also focused on the surface of the sample to be measured after passing through the detection light focusing device 7 and coincides with the pump spot; the detection light reflected from the surface of the sample to be measured 4 is collected by the second detection light focusing device 8, and then sequentially passes through the detection light beam splitting device 9, the detection light spatial filtering device 11 and the filtering device 12, and then enters the photodetector 13 for detection. The output signal of the photodetector 13 is detected by using the phase-locked detection technology, and an AC signal with the same modulation frequency as the modulated pump beam is used as the reference signal for phase-locked detection. Only the optothermal signal induced by the pump beam can be detected by the lock-in amplifier, and other external noises are filtered out; among them, the detection light reflected from the surface of the sample to be measured 4 is used by the detection light power monitoring device 10 to monitor the power of the detection light in real time.

[0023] The process of detecting and calibrating the optically induced surface thermal deformation amount is specifically as follows: The light beam emitted by the wavelength-tunable light source 14 sequentially passes through the tunable light source beam splitting device 15, the tunable light source focusing device 16 and the beam collimation device 17 and then reaches the reference mirror 18. A part of the light is reflected back from the surface of the reference mirror 18, and the other part of the light passes through the reference mirror 18 and then reaches the surface of the sample to be measured 4 and is reflected back. The light reflected back from the surface of the reference mirror 18 and the surface of the sample to be measured 4 interferes, and then sequentially passes through the beam collimation device 17, the tunable light source focusing device 16, the tunable light source beam splitting device 15, the interference light focusing device 19 and 20 and then enters the interference light intensity detection device 21 to record the interference results at different wavelengths.

[0024] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A calibration device for detecting and calibrating the surface deformation of a photothermal object based on wavelength-shifting interference, characterized in that: It includes a pump light source, a detection light source, a photodetector, and a wavelength tunable light source that are respectively oriented towards the surface of the sample to be measured. A pump light focusing device is provided between the pump light source and the sample to be measured, and a first detection light focusing device is provided between the detection light source and the sample to be measured. A second detection light focusing device, a detection light beam splitting device, a detection light spatial filtering device, and a filtering device are sequentially arranged between the sample to be measured and the photodetector. A detection light power monitoring device is arranged in the optical path between the second detection light focusing device and the photodetector. A tunable light source beam splitting device, a tunable light source focusing device, a beam collimating device, and a reference mirror are sequentially arranged between the wavelength tunable light source and the sample to be measured. The interference light focusing device is oriented towards the tunable light source beam splitting device. The light reflected back from the surface of the reference mirror and the surface of the sample to be measured interferes, and the interference light enters the interference light intensity detection device after passing through the beam collimating device, the tunable light source focusing device, the tunable light source beam splitting device, and the interference light focusing device in sequence.

2. The calibration device for detecting and calibrating the photothermal surface deformation based on wavelength-shifted interference according to claim 1, wherein: A pump light beam modulation device is provided between the pump light source and the pump light focusing device.

3. The calibration device for photothermal surface deformation detection based on wavelength-shifting interference according to claim 1, characterized in that: The pump light reflected from the surface of the sample to be measured is collected by a pump light collection device.

4. The detection and calibration method of the optical thermal surface deformation detection and calibration device based on wavelength-shifted interference according to claim 1, characterized in that: It includes the following steps: First, when the surface of the sample to be measured does not generate surface thermal deformation, the wavelength tunable light source starts from a selected starting wavelength λ0 and sequentially changes the wavelength at a certain wavelength step Δλ. The interference light intensity detection device records the interference results at different wavelengths, and the initial surface shape result W0 of the sample to be measured is measured according to the weighted multi-step wavelength phase-shifting algorithm. Then, the pump light source is used to excite the surface of the sample to be measured to generate thermal deformation. The wavelength tunable light source starts from the selected starting wavelength λ0 again and sequentially changes the wavelength at a certain wavelength step Δλ. The interference light intensity detection device records the interference results at different wavelengths, and the surface shape result W1 of the sample to be measured under the irradiation of the pump laser is measured according to the weighted multi-step wavelength phase-shifting algorithm. Finally, through the comparison and analysis of the surface shape result W1 and the initial surface shape result W0, the surface thermal deformation amount h caused by laser induction is obtained. According to the surface thermal deformation amount h and combined with the thermophysical parameters of the sample to be measured, the actual absorption rate result of the sample to be measured is obtained.

5. The detection and calibration method according to claim 4, characterized in that: The specific process of the pump light source exciting the surface of the sample to be measured to generate thermal deformation is as follows: The pump light beam emitted by the pump light source is modulated after passing through the pump light beam modulation device, and then focused on the surface of the sample to be measured through the pump light focusing device to excite the generation of surface thermal deformation; the detection light beam emitted by the detection light source is also focused on the surface of the sample to be measured through the first detection light focusing device and coincides with the pump light spot; the detection light reflected from the surface of the sample to be measured is collected by the second detection light focusing device, and then enters the photodetector for detection after passing through the detection light beam splitting device, the detection light spatial filtering device, and the filtering device in sequence. The output signal of the photodetector is detected using the phase-locked detection technique, and an AC signal with the same modulation frequency as the modulated pump light beam is used as the reference signal for phase-locked detection. Only the optothermal signal induced by the pump light beam can be detected by the lock-in amplifier, and other external noises are filtered out.

6. The detection and calibration method according to claim 4, wherein: The light beam emitted by the wavelength tunable light source sequentially passes through a tunable light source beam splitting device, a tunable light source focusing device, and a beam collimating device and then reaches the reference mirror. A part of the light is reflected back from the surface of the reference mirror, and another part of the light passes through the reference mirror and then reaches the surface of the sample to be measured and is reflected back. The light reflected back from the surface of the reference mirror and the surface of the sample to be measured interferes, and sequentially passes through the beam collimating device, the tunable light source beam splitting device, the tunable light source focusing device, and the interference light focusing device and then enters the interference light intensity detection device to record the interference results at different wavelengths.

7. The detection and calibration method according to claim 5, characterized in that: The detection light reflected from the surface of the sample to be measured is used by the detection light power monitoring device to monitor the power of the detection light in real time.

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