Detection device for photothermal oscillation spectrum and detection method thereof

Abstract

The application provides a photothermal vibration spectrum detection device and a detection method thereof, and relates to the field of material photothermal vibration spectrum detection, aiming to improve the sensitivity, accuracy, reliability and noise suppression capability of detection. In the detection device, the first laser is configured to emit first laser, and the first light path is configured to propagate the first laser to the detection sample. The second laser is configured to emit second laser, and the second light path is configured to propagate the second laser to the detection sample to generate reflected light, and collect the reflected light. The reflected light is frequency shifted compared with the second laser. The third light path is configured to frequency shift the second laser to generate third laser. The photodetector is configured to receive the reflected light and the third laser, and convert the beat frequency signal generated by the interference of the reflected light and the third laser into an electrical signal. The signal processor is configured to determine the photothermal vibration frequency and vibration intensity of the detection sample according to the electrical signal.

Description

Technical Field

[0001] This application relates to the field of photothermal vibration spectrum detection of materials, and in particular to a photothermal vibration spectrum detection device and method thereof. Background Technology

[0002] Photothermal vibrational spectroscopy is a molecular vibrational spectral analysis method based on the photothermal effect. It combines vibrational spectroscopy with the photothermal effect, and obtains molecular vibrational information by analyzing the local temperature changes caused by the absorption of light of a specific frequency by the sample.

[0003] Currently used photothermal spectroscopy detection techniques directly detect photothermal signals using probe light. However, the signals generated by the photothermal effect are usually relatively weak, especially when the sample has low absorption capacity, resulting in a low signal-to-noise ratio. Commonly used detection equipment struggles to capture minute temperature changes. Furthermore, thermal noise from the external environment (such as temperature fluctuations and environmental radiation) can also interfere with the detection results, thereby reducing the reliability and accuracy of the signal. Summary of the Invention

[0004] This application proposes a detection device and method for photothermal vibration spectrum, aiming to improve the detection sensitivity, accuracy, reliability and noise suppression capability.

[0005] To achieve the above objectives, embodiments of this application provide the following technical solutions:

[0006] On one hand, a device for detecting photothermal vibrational spectra is provided. This device includes a first laser, a first optical path, a second laser, a second optical path, a third optical path, a photodetector, and a signal processor. The first laser is configured to emit a first laser beam. The first optical path is connected to the first laser and configured to propagate the first laser beam to a sample for testing. The second laser is configured to emit a second laser beam. The second optical path is connected to the second laser and configured to propagate the second laser beam to the sample for testing, generating reflected light and collecting the reflected light, which has a frequency shift relative to the second laser beam. The third optical path is connected to the second laser and configured to cause the second laser beam to undergo a frequency shift, generating a third laser beam. The photodetector is connected to the second and third optical paths and configured to receive the reflected light and the third laser beam, converting the beat frequency signal generated by the interference of the reflected light and the third laser beam into an electrical signal. The signal processor is electrically connected to the photodetector and configured to determine the photothermal vibrational frequency and vibrational intensity of the sample for testing based on the electrical signal.

[0007] The detection device provided in the above embodiments of this application emits a first laser beam through a first laser and propagates the first laser beam to the detection sample through a first optical path, causing the detection sample to generate periodic photothermal vibrations. These photothermal vibrations have minute displacements and vibration velocities, as well as minute temperature and stress field changes. A second laser beam is emitted through a second laser and propagates to a second optical path as a probe beam. The second optical path propagates the probe beam to the detection sample, detecting the area of ​​the detection sample affected by the first laser. The minute displacements or vibration velocities, and minute temperature or stress field changes in this area cause a frequency shift in the second laser beam, resulting in higher detection sensitivity and superior performance in detecting samples with weak signals.

[0008] After the second laser generates a frequency shift, it is reflected back by the sample to generate reflected light. This reflected light carries the vibration information of the sample and is collected by the second optical path. This enables real-time monitoring of the dynamic response of the sample's photothermal vibration. Its high-speed data acquisition capability allows the instantaneous thermal response and vibration of the sample when it is irradiated by the pump light (first laser) to be recorded in real time, improving the detection efficiency and accuracy in the dynamic process.

[0009] Furthermore, the second laser beam propagates through the third optical path as a reference beam. The third optical path causes a frequency shift in the second laser beam, generating a third laser beam. A stable frequency difference exists between the third laser beam and the reflected light. A photodetector receives both the reflected light and the third laser beam. The interference between the reflected light and the third laser beam on the photodetector generates a beat frequency signal. The frequency of this beat frequency signal is the frequency difference between the third laser beam and the reflected light, thus carrying vibration information of the sample. The interference between the reflected light and the third laser beam is known as "heterodyne interferometry." Heterodyne interferometry not only determines the direction of photothermal vibration of the sample but also enhances noise suppression capabilities and improves measurement accuracy.

[0010] In addition, the photodetector can convert the beat frequency signal into an electrical signal, and the signal processor can determine the photothermal vibration frequency and vibration intensity of the sample based on the electrical signal.

[0011] In some embodiments, the third optical path includes an acousto-optic modulator configured to cause a frequency shift in the second laser to generate the third laser.

[0012] In some embodiments, the detection device further includes a first beam splitter and a second beam splitter. The first beam splitter is connected to the second laser and is configured to split the second laser into two beams. The third optical path further includes a first reflector connected to the first beam splitter and an acousto-optic modulator. The first reflector is configured to reflect one beam of the second laser into the acousto-optic modulator. The second beam splitter is connected to the acousto-optic modulator and a photodetector, and is configured to propagate the third laser to the photodetector.

[0013] In some embodiments, the detection device further includes a first beam splitter and a second beam splitter. The first beam splitter is connected to the second laser and is configured to split the second laser into two beams. The second optical path includes a third beam splitter, a first dichroic mirror, and a reflecting objective. The third beam splitter is connected to the first beam splitter, the second beam splitter, and the first dichroic mirror, and is configured to propagate another beam of the second laser to the first dichroic mirror. The reflecting objective is connected to the first dichroic mirror, and the first dichroic mirror is configured to propagate the second laser to the reflecting objective. The reflecting objective is configured to propagate the second laser to the detection sample to generate reflected light and collect the reflected light.

[0014] The first dichroic mirror is also configured to propagate reflected light from the reflecting objective to a third beam splitter, which in turn is configured to propagate the reflected light to a second beam splitter. The second beam splitter is also connected to a photodetector and is configured to propagate the reflected light to the photodetector.

[0015] In some embodiments, the signal processor includes a lock-in amplifier and a controller. The lock-in amplifier is electrically connected to a photodetector and is configured to determine a vibration velocity signal of the sample based on an electrical signal. The controller is electrically connected to the lock-in amplifier and is configured to determine the photothermal vibration frequency and vibration intensity of the sample based on the vibration velocity signal.

[0016] In some embodiments, the detection device further includes a vibration meter, which comprises a second laser, a first beam splitter, a second beam splitter, a third beam splitter, a first reflector, an acousto-optic modulator, and a photodetector. The second laser, the first beam splitter, the first reflector, the acousto-optic modulator, the second beam splitter, the photodetector, and the signal processor are connected in sequence. The third beam splitter is connected to the first beam splitter, the second beam splitter, and the first optical path.

[0017] In some embodiments, the first optical path includes a second reflecting mirror, a second dichroic mirror, a first dichroic mirror, and a reflective objective lens. The second reflecting mirror is connected to the first laser and the second dichroic mirror, and is configured to reflect the first laser to the second dichroic mirror. The first dichroic mirror is connected to the second dichroic mirror and the reflective objective lens. The second dichroic mirror is configured to propagate the first laser to the first dichroic mirror, and the first dichroic mirror is configured to propagate the first laser to the reflective objective lens. The reflective objective lens is configured to propagate the first laser to the sample to be detected.

[0018] In some embodiments, the detection device further includes a fourth optical path connected to the first optical path, and the fourth optical path is configured to calibrate the first optical path, the second optical path, and the third optical path.

[0019] In some embodiments, the first laser is further configured to lock the frequency of the first laser, change the wavelength of the first laser, and the first optical path is further configured to propagate the first laser of different wavelengths to the detection sample. The signal processor is further configured to determine the photothermal vibration frequency and vibration intensity of the detection sample when the detection sample is irradiated by the first laser of different wavelengths, thereby obtaining a photothermal vibration spectrum.

[0020] In some embodiments, the signal processor is also connected to a first laser and is configured to control the first laser to lock onto the wavelength of the first laser based on the photothermal vibration spectrum. The detection device also includes a displacement stage for carrying the detection sample and driving the sample to perform scanning motion. The signal processor is further configured to determine the vibration intensity at different locations on the detection sample when the first laser irradiates the sample, thereby obtaining a photothermal vibration image.

[0021] On the other hand, a method for detecting photothermal vibration spectra is provided, the method comprising: a first laser propagating to a sample for detection via a first optical path; a second laser propagating to the sample for detection via a second optical path and generating reflected light, the reflected light having a frequency shift relative to the second laser; the second laser also having a frequency shift via a third optical path, generating a third laser; the reflected light and the third laser being transmitted to a photodetector and interfering to generate a beat frequency signal, the beat frequency signal being converted into an electrical signal by the photodetector; and the electrical signal being transmitted to a signal processor to determine the photothermal vibration frequency and vibration intensity of the sample for detection.

[0022] The detection method provided in the above embodiments of this application involves a first laser propagating through a first optical path to the sample, causing periodic photothermal vibrations in the sample. These vibrations exhibit minute displacements and vibration velocities, as well as minute temperature and stress field changes. A second laser propagates through a second optical path to the sample, detecting the area of ​​the sample affected by the first laser. The minute displacements or vibration velocities, and minute temperature or stress field changes in this area cause a frequency shift in the second laser, resulting in higher detection sensitivity and superior performance in detecting samples with weak signals.

[0023] After the second laser generates a frequency shift, it is reflected back by the sample to generate reflected light. This reflected light carries the vibration information of the sample and is collected by the second optical path. This enables real-time monitoring of the dynamic response of the sample's photothermal vibration. Its high-speed data acquisition capability allows the instantaneous thermal response and vibration of the sample when it is irradiated by the pump light (first laser) to be recorded in real time, improving the detection efficiency and accuracy in the dynamic process.

[0024] Furthermore, the second laser undergoes a frequency shift via the third optical path, generating a third laser. This third laser has a stable frequency difference with the reflected light. The reflected light and the third laser are transmitted to a photodetector, where they interfere and generate a beat frequency signal. The frequency of this beat frequency signal is the frequency difference between the third laser and the reflected light, thus carrying vibration information of the sample. The interference between the reflected light and the third laser is known as "heterodyne interferometry." Heterodyne interferometry not only determines the direction of photothermal vibration of the sample but also enhances noise suppression and improves measurement accuracy.

[0025] In addition, the beat frequency signal is converted into an electrical signal by a photodetector, and the electrical signal is transmitted to a signal processor to determine the photothermal vibration frequency and vibration intensity of the sample being tested.

[0026] In some embodiments, the second laser undergoes a frequency shift via an acousto-optic modulator in the third optical path to generate the third laser.

[0027] In some embodiments, after determining the photothermal vibration frequency and vibration intensity of the sample, the frequency of the first laser is locked, and the wavelength of the first laser is changed. First lasers of different wavelengths propagate to the sample through the first optical path. With the sample irradiated by first lasers of different wavelengths, the photothermal vibration frequency and vibration intensity of the sample are determined, and a photothermal vibration spectrum is obtained.

[0028] In some embodiments, after obtaining the photothermal vibration spectrum, the wavelength of the first laser is locked based on the photothermal vibration spectrum. With the first laser irradiating the test sample, the test sample is subjected to scanning motion to determine the vibration intensity at different locations on the test sample, thereby obtaining a photothermal vibration image.

[0029] In some embodiments, locking the wavelength of the first laser according to the photothermal vibration spectrum includes: selecting a target wavelength corresponding to the peak value of the vibration intensity in the photothermal vibration spectrum, so that the wavelength of the first laser is locked at the target wavelength. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in this application, the accompanying drawings used in some embodiments of this application will be briefly described below. Obviously, the drawings described below are only drawings of some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings. In addition, the drawings described below can be regarded as schematic diagrams and are not actual dimensions of the products or actual processes of the methods involved in the embodiments of this application.

[0031] Figure 1 A structural diagram of the photothermal vibration spectrum detection device provided in an embodiment of this application;

[0032] Figure 2A flowchart of a photothermal vibration spectrum detection method provided in an embodiment of this application. Detailed Implementation

[0033] The technical solutions in some embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application are within the scope of protection of this application.

[0034] Unless the context otherwise requires, throughout the specification and claims, the term "comprising" is interpreted as open and encompassing, that is, "including, but not limited to".

[0035] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this application, unless otherwise stated, "a plurality of" means two or more.

[0036] In describing some embodiments, the term "connection" and its derivative expressions may be used. The term "connection" should be interpreted broadly; for example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a direct connection or an indirect connection through an intermediate medium. For example, in describing some embodiments, the term "connection" may be used to indicate that two or more components have direct physical or electrical contact with each other.

[0037] In addition, the use of “based on” implies openness and inclusivity, because processes, steps, calculations or other actions “based on” one or more of the stated conditions or values ​​may in practice be based on additional conditions or values ​​beyond those stated.

[0038] It should be understood that when a layer or element is referred to as being on another layer or substrate, it can mean that the layer or element is directly on the other layer or substrate, or that there is an intermediate layer between the layer or element and the other layer or substrate.

[0039] Embodiments of this application provide a device for detecting photothermal vibrational spectra. Figure 1 This is a structural diagram of the photothermal vibration spectrum detection device provided in an embodiment of this application.

[0040] See Figure 1 The detection device 1 includes a first laser 2, a first optical path 3, a second laser 4, a second optical path 5, a third optical path 6, a photodetector 7, and a signal processor 8.

[0041] The first laser 2 is configured to emit a first laser. For example, the first laser 2 can be a mid-infrared quantum cascade laser (QCL), and the first laser emitted is a tunable mid-infrared pulsed laser.

[0042] The first optical path 3 is connected to the first laser 2. The first optical path 3 is configured to propagate the first laser emitted by the first laser 2 to the detection sample 9, so that the first laser acts on the upper surface or interior of the detection sample 9. The detection sample 9 absorbs the first laser, causing its local temperature to rise, thereby generating a periodic photothermal vibration signal in the area of ​​the detection sample 9 irradiated by the first laser. The thermal expansion coefficient, infrared absorption (IR absorption) and refractive index of this area will change with time.

[0043] For example, the first optical path 3 includes a second reflector 31, a second dichroic mirror 32, a first dichroic mirror 33 and a reflective objective lens 34. The second reflector 31 is connected to the first laser 2 and the second dichroic mirror 32. The second reflector 31 is configured to reflect the first laser emitted by the first laser 2 to the second dichroic mirror 32.

[0044] The first dichroic mirror 33 is connected to the second dichroic mirror 32 and the reflecting objective 34. The second dichroic mirror 32 is configured to propagate the first laser to the first dichroic mirror 33, and the first dichroic mirror 33 is configured to propagate the first laser to the reflecting objective 34. The reflecting objective 34 is configured to propagate the first laser to the test sample 9. For example, the reflecting objective 34 can focus the first laser onto the test sample 9.

[0045] The second laser 4 is configured to emit a second laser. For example, the second laser 4 can be a helium-neon laser, which emits polarized light with a frequency of f0.

[0046] The second optical path 5 is connected to the second laser 4. The second optical path 5 is configured to propagate the second laser emitted by the second laser 4 to the detection sample 9, and to detect the area of ​​the detection sample 9 that has been affected by the first laser. The photothermal vibration of this area will cause the second laser to undergo a frequency shift (f). v = 2v / λ, where v is the rate of change of the photothermal vibration of the sample 9 over time, and λ is the wavelength of the first laser. The second laser, after undergoing a frequency shift, is reflected back by the sample 9 to generate reflected light (frequency f0 ± f). v The reflected light carries the vibration information of the sample 9 (the speed v of the change of photothermal vibration over time), and the reflected light will be collected by the second optical path 5.

[0047] For example, the detection device 1 further includes a first beam splitter 10 and a second beam splitter 11. The first beam splitter 10 is connected to the second laser 4 and is configured to split the second laser emitted by the second laser 4 into two beams, one of which is used as a probe beam and the other as a reference beam.

[0048] The second optical path 5 includes a third beam splitter 12, the aforementioned first dichroic mirror 33, and the aforementioned reflective objective lens 34. The third beam splitter 12 is connected to the first beam splitter 10, the second beam splitter 11, and the first dichroic mirror 33. The third beam splitter 12 is configured to propagate the second laser (probe light) to the first dichroic mirror 33. The reflective objective lens 34 is connected to the first dichroic mirror 33, and the first dichroic mirror 33 is also configured to propagate the second laser (probe light) to the reflective objective lens 34. The reflective objective lens 34 is also configured to propagate the second laser (probe light) to the detection sample 9.

[0049] In the above embodiments, the probe light is used to measure the expansion displacement / velocity change of the test sample 9. After being reflected by the surface of the test sample 9, the probe light is reflected to form reflected light (frequency-shifted scattering field). In this case, the test sample 9 may include an opaque material. Alternatively, the probe light passes through the expansion region of the test sample 9 and is reflected to form reflected light. In this case, the test sample 9 may include a transparent material. Furthermore, the embodiments of this application do not limit the shape and thickness of the test sample 9, thus improving the flexibility of the detection.

[0050] The first dichroic mirror 33 is also configured to propagate reflected light from the reflecting objective lens 34 to the third beam splitter 12, which is further configured to propagate the reflected light to the second beam splitter 11. The second beam splitter 11 is also connected to the photodetector 7 and is configured to propagate the reflected light to the photodetector 7.

[0051] The third optical path 6 is connected to the second laser 4. The third optical path 6 is configured to cause a frequency shift (f) in the second laser (reference light) emitted by the second laser 4, generating a third laser (frequency f0+f). The frequency difference between the third laser and the reflected light is f±f. v .

[0052] By changing the frequency of the reference light to create a frequency difference between it and the probe light, the interference of the subsequent reflected light with the third laser is called "heterodyne interferometry". Heterodyne interferometry can not only determine the direction of photothermal vibration of the sample 9, but also enhance the ability to suppress noise and improve the measurement accuracy.

[0053] For example, the third optical path 6 includes an acousto-optic modulator 13, which is configured to cause the second laser 4 to emit a second laser beam with a frequency shift, thereby generating a third laser beam. The acousto-optic modulation technique employed by the acousto-optic modulator 13 is an external modulation technique, which does not change the parameters of the second laser 4, but achieves the modulation purpose by changing the parameters of the second laser 4 that has already emitted the second laser beam. Furthermore, the acousto-optic modulation technique has a high modulation frequency and produces a stable frequency shift.

[0054] For example, the third optical path 6 further includes a first reflector 14, which is connected to the first beam splitter 10 and the acousto-optic modulator 13. The first reflector 14 is configured to reflect the second laser (reference light) into the acousto-optic modulator 13, so that the second laser is frequency-shifted by acousto-optic modulation to generate the third laser. The second beam splitter 11 is connected to the acousto-optic modulator 13 and the photodetector 7, and the second beam splitter 11 is also configured to propagate the third laser to the photodetector 7.

[0055] Photodetector 7 is connected to the second optical path 5 and the third optical path 6. Photodetector 7 is configured to receive reflected light from the second optical path 5 and third laser light from the third optical path 6. The reflected light and third laser light interfere on photodetector 7, generating a time-varying beat frequency signal (frequency f±f) at the modulation frequency. v The frequency of the beat frequency signal is the frequency difference between the third laser and the reflected light. The beat frequency signal also carries the vibration information of the sample 9 (the intensity of the beat frequency signal corresponds one-to-one with the velocity v of the sample 9). Furthermore, the photodetector 7 can convert the beat frequency signal into an electrical signal.

[0056] The signal processor 8 is electrically connected to the photodetector 7 and is configured to determine the photothermal vibration frequency and vibration intensity of the sample 9 based on the electrical signal from the photodetector 7.

[0057] For example, the signal processor 8 includes a lock-in amplifier 81 and a controller 82. The lock-in amplifier 81 is electrically connected to the photodetector 7 and is configured to determine the vibration velocity signal of the sample 9 (which includes the velocity v of photothermal vibration changing over time) based on the electrical signal from the photodetector 7. The lock-in amplifier 81 can also amplify the electrical signal from the photodetector 7, which can reduce the influence of environmental noise and system errors on the signal, thereby making the detection results more accurate and stable.

[0058] The controller 82 is electrically connected to the lock-in amplifier 81. The controller 82 is configured to determine the photothermal vibration frequency and vibration intensity of the sample 9 based on the vibration velocity signal from the lock-in amplifier 81. For example, the controller 82 uses a Fourier transform to convert the vibration velocity signal into information between the photothermal vibration frequency and vibration intensity.

[0059] The controller 82 described above can be, for example, a control computer, which is equipped with control software and is electrically connected to the lock-in amplifier 81 via a network cable. The control computer is also electrically connected to the first laser 2 via a network cable to control the first laser 2 to emit the first laser beam.

[0060] The detection device 1 provided in the above embodiments of this application emits a first laser beam through a first laser and propagates the first laser beam to the detection sample 9 through a first optical path 3, causing the detection sample 9 to generate periodic photothermal vibrations. These photothermal vibrations have minute displacements and vibration velocities, as well as minute temperature and stress field changes. A second laser beam is emitted through a second laser beam 4 and propagates to a second optical path 5 as a probe beam. The second optical path 5 propagates the probe beam to the detection sample 9, detecting the area of ​​the detection sample 9 affected by the first laser beam. The minute displacements or vibration velocities, and minute temperature or stress field changes in this area cause a frequency shift in the second laser beam, resulting in higher detection sensitivity and better performance in detecting weak signal detection samples 9.

[0061] After the second laser generates a frequency shift, it is reflected back by the test sample 9 to generate reflected light. This reflected light carries the vibration information of the test sample 9. The reflected light is collected by the second optical path 5, realizing real-time monitoring of the dynamic response of the photothermal vibration of the test sample 9. Its high-speed data acquisition capability enables the instantaneous thermal response and vibration of the test sample 9 when it is irradiated by the pump light (first laser) to be recorded in real time, improving the detection efficiency and accuracy in the dynamic process.

[0062] Furthermore, the second laser beam propagates to the third optical path 6 as a reference light. The third optical path 6 causes a frequency shift in the second laser beam, generating a third laser beam. A stable frequency difference exists between the third laser beam and the reflected light. The photodetector 7 receives both the reflected light and the third laser beam. The interference between the reflected light and the third laser beam on the photodetector 7 generates a beat frequency signal. The frequency of this beat frequency signal is the frequency difference between the third laser beam and the reflected light, thus carrying vibration information from the sample 9. The interference between the reflected light and the third laser beam constitutes "heterodyne interferometry." Heterodyne interferometry not only determines the direction of photothermal vibration of the sample 9 but also enhances noise suppression capabilities and improves measurement accuracy.

[0063] In addition, the photodetector 7 can convert the beat frequency signal into an electrical signal, and the signal processor 8 can determine the photothermal vibration frequency and vibration intensity of the sample 9 based on the electrical signal.

[0064] In some embodiments, see Figure 1The detection device 1 also includes a vibration meter 15, which includes the aforementioned second laser 4, first beam splitter 10, second beam splitter 11, third beam splitter 12, first reflector 14, acousto-optic modulator 13 and photodetector 7. The second laser 4, first beam splitter 10, first reflector 14, acousto-optic modulator 13, second beam splitter 11 and photodetector 7 are connected in sequence. The third beam splitter 12 is connected to the first beam splitter 10, the second beam splitter 11 and the first optical path 3.

[0065] For example, the vibration meter 15 also includes the aforementioned lock-in amplifier 81, which is electrically connected to the photodetector 7 via a data line.

[0066] For example, the vibration meter 15 can be a laser Doppler vibration meter, which is connected to the first dichroic mirror 33 in the first optical path 3 to realize the connection between the vibration meter 15 and the first optical path 3.

[0067] In the above embodiments of this application, the vibration meter 15 employs a laser Doppler vibration meter. Compared to current probe light detection technology, the laser Doppler vibration meter, by measuring the minute displacements and vibration velocities generated on the surface of the sample 9 under the photothermal effect, has higher sensitivity, especially in the presence of minute temperature changes and stress fields. Furthermore, the laser Doppler vibration meter can capture even smaller displacement signals, thus performing better in the detection of weak signal samples. The laser Doppler vibration meter can monitor the dynamic response of sample surface vibration in real time, which is particularly important for vibration signals induced by the photothermal effect. Its high-speed data acquisition capability allows for real-time recording of the instantaneous thermal response and vibration of the sample when irradiated by pump light, improving detection efficiency and accuracy in dynamic processes. Moreover, the laser Doppler vibration meter can amplify and detect minute displacement and vibration signals, reducing the influence of environmental noise and system errors on the signal, thereby making the detection results more accurate and stable.

[0068] In some embodiments, see Figure 1 The first laser 2 is also configured to lock the frequency of the first laser and change the wavelength of the first laser, and the first optical path 3 is also configured to propagate the first laser of different wavelengths to the detection sample 9.

[0069] For example, the vibration frequency of the test sample 9 can be locked in the frequency domain of the vibration measurement result by the lock-in amplifier 81. The vibration frequency of the test sample 9 is the same as the frequency of the first laser, thereby locking the frequency of the first laser and keeping it constant. By changing its wavelength, the first optical path 3 propagates the first laser of different wavelengths to the test sample 9. At the selected photothermal vibration frequency, the vibration intensity generated by the test sample 9 under the irradiation of the first laser of different wavelengths also changes accordingly.

[0070] For example, the wavelength of the first laser emitted by the first laser 2 changes linearly with time.

[0071] For example, the first laser 2 can be controlled by a computer so that the frequency of the first laser emitted by the first laser 2 remains constant while the wavelength changes.

[0072] See also Figure 1 The signal processor 8 is also configured to determine the photothermal vibration frequency and vibration intensity of the test sample 9 under the condition that the test sample 9 is irradiated by a first laser of different wavelengths, and obtain the photothermal vibration spectrum.

[0073] It is understandable that through the coordinated work of the first laser 2, the first optical path 3, the second laser 4, the second optical path 5, the third optical path 6, the photodetector 7, and the signal processor 8, at the selected photothermal vibration frequency, a single fixed coordinate position in the detection sample 9 is irradiated by the first laser of different wavelengths. The vibration intensity of this coordinate position also changes accordingly. The vibration intensity corresponding to the first laser of different wavelengths irradiated by the detection sample 9 can be determined. The complete photothermal vibration spectrum of the detection sample 9 can be obtained by software.

[0074] Furthermore, by using the above setup, the molecular fingerprint spectrum of the material of sample 9 can be measured, and the chemical composition (chemical bonds or functional groups) of the material can be obtained.

[0075] In some embodiments, see Figure 1 The signal processor 8 is also connected to the first laser 2; for example, the controller 82 in the signal processor 8 is connected to the first laser 2. The signal processor 8 is also configured to control the first laser 2 to lock the wavelength of the first laser based on the obtained photothermal vibration spectrum.

[0076] The detection device 1 also includes a displacement stage 19, which carries the detection sample 9 and drives the detection sample 9 to perform scanning motion. The signal processor 8 is also configured to determine the vibration intensity at different positions on the detection sample 9 when the first laser irradiates the detection sample 9, thereby obtaining a photothermal vibration image.

[0077] In the above embodiments, a target wavelength corresponding to a specific vibration intensity is selected from the photothermal vibration spectrum. The wavelength of the first laser emitted by the first laser 2 is controlled by the signal processor 8 to remain unchanged at the target wavelength. The detection sample 9 is driven to perform scanning motion by the displacement stage 19. The vibration intensity at different coordinate positions also changes accordingly. The vibration intensity at different coordinate positions can be determined. The photothermal vibration image of the detection sample 9 can be drawn by the software.

[0078] For example, the displacement stage 19 is an electrically controlled three-dimensional displacement stage. The electrically controlled three-dimensional displacement stage is electrically connected to the controller 82 via a network cable. The controller 82 controls the displacement stage 19 to perform two-dimensional / three-dimensional motion, thereby driving the test sample 9 to perform two-dimensional / three-dimensional scanning motion. Through the above settings, two-dimensional / three-dimensional photothermal vibration images of the test sample 9 can be obtained.

[0079] In some embodiments, see Figure 1 The detection device 1 also includes a fourth optical path 16, which is connected to the first optical path 3. Before detection, the fourth optical path 16 is configured to calibrate the first optical path 3, the second optical path 5 and the third optical path 6 so that the four optical paths are coaxial and focused at a point.

[0080] For example, the fourth optical path 16 includes a focusing lens 17 and a charge-coupled device (CCD) 18. The focusing lens 17 is positioned relative to and connected to the second dichroic mirror 32. The charge-coupled device 18 is connected to the focusing lens 17. The detection area of ​​the sample 9 is found by observing through the CCD.

[0081] Embodiments of this application also provide a method for detecting photothermal vibrational spectra. Figure 2 A flowchart of a photothermal vibration spectrum detection method provided in an embodiment of this application.

[0082] See Figure 2 The detection method for photothermal vibrational spectra includes the following steps S1 to S5:

[0083] S1: The first laser propagates to the test sample 9 through the first optical path 3, so that the first laser acts on the upper surface or interior of the test sample 9. The test sample 9 absorbs the first laser and locally heats it to generate periodic photothermal vibration signals, causing the refractive index (Δn) and thermal expansion coefficient (Δl) of the test sample 9 to change.

[0084] For example, a first laser 2 can be used to emit a first laser. For instance, the first laser 2 can be a mid-infrared quantum cascade laser (QCL), which emits a tunable mid-infrared pulsed laser.

[0085] S2: The second laser propagates to the detection sample 9 through the second optical path 5 and detects the area of ​​the detection sample 9 that was affected by the first laser. The photothermal vibration of this area will cause the scattered field to change (Δs), causing the second laser to generate a frequency shift (Δf). After the second laser generates a frequency shift, it is reflected back by the detection sample 9 to generate reflected light (detection light). This reflected light carries the vibration information of the detection sample 9.

[0086] For example, a second laser 4 can be used to emit a second laser. For instance, the second laser 4 can be a helium-neon laser, which emits polarized light as the second laser.

[0087] S3: The second laser also undergoes a frequency shift via the third optical path 6, generating a third laser (reference light). There is a frequency difference between the third laser and the reflected light. By changing the frequency of the reference light, a frequency difference is generated between it and the probe light. The subsequent interference between the reflected light and the third laser is called "heterodyne interferometry". Heterodyne interferometry can not only determine the direction of photothermal vibration of the sample 9, but also enhance the ability to suppress noise and improve the measurement accuracy.

[0088] For example, a second laser 4 can be used to emit a second laser. For instance, the second laser 4 can be a helium-neon laser, which emits polarized light as the second laser.

[0089] For example, the second laser undergoes a frequency shift via the acousto-optic modulator 13 in the third optical path 6 to generate the third laser. The acousto-optic modulation technique employed by the acousto-optic modulator 13 is an external modulation technique, which does not change the parameters of the second laser 4, but achieves the modulation purpose by changing the parameters of the second laser already output by the second laser 4. Furthermore, the acousto-optic modulation technique has a high modulation frequency and produces a stable frequency shift.

[0090] S4: The reflected light and the third laser are transmitted to the photodetector 7 and interfere with each other, generating a beat frequency signal that varies with time at the modulation frequency. The frequency of the beat frequency signal is the frequency difference between the third laser and the reflected light. The beat frequency signal also carries the vibration information of the sample 9. Furthermore, the photodetector 7 can convert the beat frequency signal into an electrical signal.

[0091] S5: The electrical signal is transmitted to the signal processor 8 to determine the photothermal vibration frequency and vibration intensity of the sample 9.

[0092] For example, S5 above includes the following S51 to S52:

[0093] S51: The electrical signal is transmitted to the lock-in amplifier 81 in the signal processor 8, which can determine the vibration velocity (v) signal of the detection sample 9.

[0094] S52: The vibration velocity signal is transmitted to the controller 82 in the signal processor 8. The controller 82 uses the Fast Fourier Transform (FFT) method to convert the vibration velocity signal into information between the photothermal vibration frequency and the vibration intensity.

[0095] The detection method provided in the above embodiments of this application involves a first laser propagating through a first optical path 3 to the detection sample 9, causing the detection sample 9 to generate periodic photothermal vibrations. These photothermal vibrations have minute displacements and vibration velocities, as well as minute temperature and stress field changes. A second laser propagates through a second optical path 5 to the detection sample 9, detecting the area of ​​the detection sample 9 affected by the first laser. The minute displacements or vibration velocities, and minute temperature or stress field changes in this area cause a frequency shift in the second laser, resulting in higher detection sensitivity and better performance in detecting weak signal detection samples 9.

[0096] After the second laser generates a frequency shift, it is reflected back by the test sample 9 to generate reflected light. This reflected light carries the vibration information of the test sample 9. The reflected light is collected by the second optical path 5, realizing real-time monitoring of the dynamic response of the photothermal vibration of the test sample 9. Its high-speed data acquisition capability enables the instantaneous thermal response and vibration of the test sample 9 when it is irradiated by the pump light (first laser) to be recorded in real time, improving the detection efficiency and accuracy in the dynamic process.

[0097] Furthermore, the second laser undergoes a frequency shift via the third optical path 6, generating a third laser. This third laser has a stable frequency difference with the reflected light. The reflected light and the third laser are transmitted to the photodetector 7, where they interfere and generate a beat frequency signal. The frequency of this beat frequency signal is the frequency difference between the third laser and the reflected light, thus carrying vibration information from the sample 9. The interference between the reflected light and the third laser is known as "heterodyne interferometry." Heterodyne interferometry not only determines the direction of photothermal vibration of the sample 9 but also enhances noise suppression and improves measurement accuracy.

[0098] In addition, the beat frequency signal is converted into an electrical signal by the photodetector 7, and the electrical signal is transmitted to the signal processor 8 to determine the photothermal vibration frequency and vibration intensity of the sample 9.

[0099] In some embodiments, after determining the photothermal vibration frequency and vibration intensity of the test sample 9 in step S5, the detection method further includes the following S6:

[0100] S6: Lock the frequency of the first laser, change the wavelength of the first laser, and the first laser of different wavelengths propagates to the test sample 9 through the first optical path 3. Under the condition of the first laser of different wavelengths irradiating the test sample 9, determine the photothermal vibration frequency and vibration intensity of the test sample 9, and obtain the photothermal vibration spectrum.

[0101] For example, the vibration frequency of the test sample 9 can be locked in the frequency domain of the vibration measurement result by the lock-in amplifier 81. The vibration frequency of the test sample 9 is the same as the frequency of the first laser, so the frequency of the first laser can be locked and kept constant, so that its wavelength changes linearly with time. At the selected photothermal vibration frequency, the vibration intensity corresponding to the test sample 9 being irradiated by the first laser of different wavelengths can be determined. The complete photothermal vibration spectrum of the test sample 9 can be obtained by software.

[0102] In some embodiments, after obtaining the photothermal vibration spectrum in step S6, the detection method further includes the following S7:

[0103] S7: Based on the photothermal vibration spectrum, lock the wavelength of the first laser. Under the condition that the first laser irradiates the test sample 9, make the test sample 9 perform scanning motion to determine the vibration intensity at different positions on the test sample 9 and obtain the photothermal vibration image.

[0104] In the above embodiments, a target wavelength corresponding to a specific vibration intensity is selected from the photothermal vibration spectrum, so that the wavelength of the first laser is kept constant at the target wavelength, and the detection sample 9 is made to perform scanning motion. The vibration intensity at different coordinate positions also changes accordingly, so the vibration intensity at different coordinate positions can be determined, and the photothermal vibration image of the detection sample 9 can be drawn by software.

[0105] For example, in the photothermal vibration spectrum, different types of materials have different vibration peaks (peak values ​​of vibration intensity). The first target wavelength corresponding to the peak value of the vibration intensity of the first target material is selected from the photothermal vibration spectrum, and the wavelength of the first laser is locked as the first target wavelength. When the first laser irradiates the test sample 9, the test sample 9 is made to perform scanning motion to determine the vibration intensity at different coordinate positions. In this way, the vibration intensity at different positions can be compared with the vibration peak of the first target material to determine whether the first target material is present at each position of the test sample 9.

[0106] Based on the above method, the second target wavelength corresponding to the peak vibration intensity of the second target material is selected from the photothermal vibration spectrum, and the wavelength of the first laser is locked as the second target wavelength. While the first laser irradiates the test sample 9, the test sample 9 is made to perform a scanning motion to determine the vibration intensity at different coordinate positions. Thus, by comparing the vibration intensity at different positions with the vibration peak of the second target material, it can be determined whether the second target material is present at each position of the test sample 9. By repeating this measurement cycle, the material at each position of the test sample 9 can be determined, and a photothermal vibration image of the test sample 9 can be obtained.

[0107] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A device for detecting photothermal vibrational spectra, characterized in that, include: The first laser is configured to emit the first laser; A first optical path, connected to the first laser, is configured to propagate the first laser to the sample to be detected; A second laser is configured to emit a second laser. The second optical path, connected to the second laser, is configured to propagate the second laser to the detection sample to generate reflected light and collect the reflected light; The reflected light undergoes a frequency shift compared to the second laser; The third optical path is connected to the second laser and is configured to cause a frequency shift in the second laser to generate the third laser. A photodetector, connected to the second optical path and the third optical path, is configured to receive the reflected light and the third laser, and convert the beat frequency signal generated by the interference of the reflected light and the third laser into an electrical signal; A signal processor, electrically connected to the photodetector, is configured to determine the photothermal vibration frequency and vibration intensity of the sample to be detected based on the electrical signal.

2. The detection device according to claim 1, characterized in that, The third optical path includes an acousto-optic modulator configured to cause a frequency shift in the second laser to generate the third laser.

3. The detection device according to claim 2, characterized in that, The detection device further includes a first beam splitter and a second beam splitter, wherein the first beam splitter is connected to the second laser and is configured to split the second laser into two beams. The third optical path further includes a first reflector, which is connected to the first beam splitter and the acousto-optic modulator. The first reflector is configured to reflect a second laser beam into the acousto-optic modulator. The second beam splitter is connected to the acousto-optic modulator and the photodetector, and the second beam splitter is configured to propagate the third laser to the photodetector.

4. The detection device according to claim 1, characterized in that, The detection device further includes a first beam splitter and a second beam splitter, wherein the first beam splitter is connected to the second laser and is configured to split the second laser into two beams. The second optical path includes a third beam splitter, a first dichroic mirror, and a reflective objective lens. The third beam splitter is connected to the first beam splitter, the second beam splitter, and the first dichroic mirror. The third beam splitter is configured to propagate another second laser beam to the first dichroic mirror. The reflective objective lens is connected to the first dichroic mirror. The first dichroic mirror is configured to propagate the second laser beam to the reflective objective lens. The reflective objective lens is configured to propagate the second laser beam to the detection sample to generate reflected light and collect the reflected light. The first dichroic mirror is further configured to propagate reflected light from the reflective objective to the third beam splitter, which is further configured to propagate the reflected light to the second beam splitter; the second beam splitter is also connected to the photodetector and is configured to propagate the reflected light to the photodetector.

5. The detection device according to claim 1, characterized in that, The signal processor includes a lock-in amplifier and a controller. The lock-in amplifier is electrically connected to the photodetector and is configured to determine the vibration velocity signal of the detected sample based on the electrical signal. The controller is electrically connected to the lock-in amplifier, and the controller is configured to determine the photothermal vibration frequency and vibration intensity of the test sample based on the vibration velocity signal.

6. The detection device according to claim 1, characterized in that, The detection device further includes a vibration meter, which comprises a second laser, a first beam splitter, a second beam splitter, a third beam splitter, a first reflector, an acousto-optic modulator, and the photodetector. The second laser, the first beam splitter, the first reflector, the acousto-optic modulator, the second beam splitter, the photodetector, and the signal processor are connected in sequence; the third beam splitter is connected to the first beam splitter, the second beam splitter, and the first optical path.

7. The detection device according to claim 1, characterized in that, The first optical path includes a second reflector, a second dichroic mirror, a first dichroic mirror, and a reflective objective lens. The second reflector is connected to the first laser and the second dichroic mirror, and the second reflector is configured to reflect the first laser to the second dichroic mirror. The first dichroic mirror is connected to the second dichroic mirror and the reflective objective lens. The second dichroic mirror is configured to propagate the first laser to the first dichroic mirror, the first dichroic mirror is configured to propagate the first laser to the reflective objective lens, and the reflective objective lens is configured to propagate the first laser to the test sample.

8. The detection device according to claim 1, characterized in that, The detection device further includes a fourth optical path, which is connected to the first optical path and configured to calibrate the first optical path, the second optical path, and the third optical path.

9. The detection device according to claim 1, characterized in that, The first laser is further configured to lock the frequency of the first laser and change the wavelength of the first laser; the first optical path is further configured to propagate the first laser of different wavelengths to the detection sample; The signal processor is further configured to determine the photothermal vibration frequency and vibration intensity of the test sample when the test sample is irradiated by a first laser of different wavelengths, thereby obtaining a photothermal vibration spectrum.

10. The detection device according to claim 9, characterized in that, The signal processor is also connected to the first laser, and the signal processor is further configured to control the first laser to lock the wavelength of the first laser according to the photothermal vibration spectrum; The detection device further includes a displacement stage for carrying the detection sample and driving the detection sample to perform scanning motion; the signal processor is also configured to determine the vibration intensity at different positions on the detection sample when the first laser irradiates the detection sample, and obtain a photothermal vibration image.

11. A method for detecting photothermal vibrational spectra, characterized in that, include: The first laser beam propagates to the sample being tested via the first optical path; The second laser propagates to the detection sample via the second optical path and generates reflected light, which has a frequency shift compared to the second laser. The second laser also undergoes a frequency shift via a third optical path to generate a third laser; The reflected light and the third laser are transmitted to the photodetector and interfere to generate a beat frequency signal; the beat frequency signal is converted into an electrical signal by the photodetector. The electrical signal is transmitted to a signal processor to determine the photothermal vibration frequency and vibration intensity of the sample being tested.

12. The detection method according to claim 11, characterized in that, The second laser undergoes a frequency shift via an acousto-optic modulator in the third optical path to generate the third laser.

13. The detection method according to claim 11, characterized in that, After determining the photothermal vibration frequency and vibration intensity of the sample to be tested, the detection method further includes: The frequency of the first laser is locked, and the wavelength of the first laser is changed. The first laser of different wavelengths propagates to the detection sample through the first optical path. By irradiating the test sample with a first laser of different wavelengths, the photothermal vibration frequency and vibration intensity of the test sample are determined, and the photothermal vibration spectrum is obtained.

14. The detection method according to claim 13, characterized in that, After obtaining the photothermal vibration spectrum, the detection method further includes: Based on the photothermal vibration spectrum, the wavelength of the first laser is locked; When the test sample is irradiated by the first laser, the test sample is made to perform a scanning motion to determine the vibration intensity at different positions on the test sample and obtain a photothermal vibration image.

15. The detection method according to claim 14, characterized in that, Based on the photothermal vibration spectrum, the wavelength of the first laser is locked, including: The target wavelength corresponding to the peak value of the vibration intensity is selected from the photothermal vibration spectrum, so that the wavelength of the first laser is locked at the target wavelength.

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