A high-sensitivity photothermal deflection spectrum test device and calibration method

Abstract

The present invention discloses a high-sensitivity photothermal deflection spectrum test device and calibration method, comprising mutually perpendicular detection light path and pump light path, wherein a pump light source, a monochromator, an optical chopper, a pump light lens group and an absorption cell are sequentially arranged along the pump light path; a detection light source, a spatial filtering system, a detection light focusing lens, an absorption cell and a position-sensitive detector are sequentially arranged along the detection light path; the signal output end of the position-sensitive detector is connected to the signal input end of a phase-locked amplifier, and the output end of the phase-locked amplifier is connected to a computer; the signal control end of the monochromator is connected to a computer, and the signal output end of the optical chopper is connected to the signal input end of the phase-locked amplifier; the spatial filtering system comprises a spatial filtering focusing lens, a micropore, a spatial filtering collimating lens and an aperture arranged along the light path. By utilizing the present invention, the test sensitivity of the photothermal deflection spectrum can be improved, so that the test accuracy of the thin film absorbance can reach 10 <supgt;‑5< / supgt;~10<supgt;‑4< / supgt;。

Description

Technical Field

[0001] The present invention belongs to the technical field of spectrum detection, and in particular relates to a high-sensitivity photothermal deflection spectrum testing device and a calibration method. Background Art

[0002] Thin films are the cornerstone of the development of optoelectronic devices, and the defect state of thin films plays a decisive role in the performance of thin films. Currently commercial thin film characterization methods based on light absorption, such as UV-visible absorption spectroscopy, are often not very sensitive and cannot be used to characterize thin film defect states with weak absorption (absorption rate less than 0.5%). Therefore, the development of a highly sensitive thin film characterization method is of great significance for guiding the research and development of optoelectronic devices.

[0003] Photothermal deflection spectroscopy establishes the photothermal effect and the correlation between the temperature and refractive index of the medium. When light is irradiated onto the film, the film absorbs light energy and converts it into heat energy. The temperature of the micro-area of ​​the film rises, and the heat diffuses from the film with a higher temperature to the nearby area with a relatively lower temperature, thus forming a temperature field. The higher the temperature of the medium, the lower the refractive index, thus forming a refractive index field corresponding to the temperature field. After the detection light passes through the refractive index field of the adjacent film surface, the direction of the light path is deflected. The deflection angle of the detection light is proportional to the heat released by the film after absorbing light, so the light absorption characteristic information of the film can be extracted from the detection light deflection signal.

[0004] For example, the Chinese patent document with publication number CN113109282A discloses a photothermal deflection spectrum test device with wide wavelength coverage, including a pump light source, a monochromator, an optical chopper and a beam splitter arranged in sequence along the optical path; a photodetector is arranged on the reflected light path of the beam splitter, and an absorption cell is arranged on the transmitted light path of the beam splitter; the signal output end of the photodetector is connected to a computer; the absorption cell is respectively provided with a detection light source and a position-sensitive detector on the two sides perpendicular to the transmitted light path of the beam splitter; the signal output end of the position-sensitive detector is connected to a phase-locked amplifier and a computer in sequence; the absorption cell is used to contain a heat-conducting medium, and a sample stage is fixed at the bottom, and the sample stage is used to fix the film to be tested; a focusing lens is provided between the absorption cell and the beam splitter, and the pump light transmitted through the beam splitter enters the absorption cell through the focusing lens; the pump light source adopts a laser-driven broadband light source, which is used to emit pump light of 170nm to 2100nm. By using this invention, the testing requirements from narrow bandgap materials to wide bandgap materials can be met at the same time.

[0005] The sensitivity of the photothermal deflection spectrum is directly related to the output power and power density of the pump light source. The higher the output power and power density of the pump light source, the higher the sensitivity of the device. Therefore, in the reported applications based on photothermal deflection signals, high-power lasers are often used as pump lights to improve the sensitivity of the test device, but this single-wavelength test of thin film samples cannot provide effective guidance information for the preparation of optoelectronic devices. For broadband light sources such as xenon lamps, the intensity of high-output power and high-power density white light is greatly reduced after being monochromated by a monochromator. With a simple optical path that is not optimized, the sensitivity of the test device is far from meeting the requirements for testing weak absorption signals. On the other hand, based on the quantitative relationship between the photothermal effect and the deflection signal, a xenon lamp with a power of tens to hundreds of watts equipped with a suitable monochromator can meet the needs of high-sensitivity photothermal deflection spectrum testing, but it has high requirements for the accuracy of the optical path. Summary of the invention

[0006] In order to solve the problem that the existing technology cannot accurately test the weak absorption of thin films, the present invention provides a high-sensitivity photothermal deflection spectrum testing device and calibration method, so that the film absorbance test accuracy can reach 10 -5 ~10 -4 .

[0007] A photothermal deflection spectrum testing device comprises a mutually perpendicular detection light path and a pump light path, wherein a pump light source, a monochromator, an optical chopper, a pump light lens group and an absorption cell are sequentially arranged along the pump light path; a detection light source, a spatial filtering system, a detection light focusing lens, an absorption cell and a position-sensitive detector are sequentially arranged along the detection light path;

[0008] The signal output end of the position-sensitive detector is connected to the signal input end of the phase-locked amplifier, and the output end of the phase-locked amplifier is connected to the computer; the signal control end of the monochromator is connected to the computer, and the signal output end of the optical chopper is connected to the signal input end of the phase-locked amplifier;

[0009] The spatial filtering system comprises a spatial filtering focusing lens, a micro-aperture, a spatial filtering collimating lens and an aperture arranged along the optical path; the detection light is focused by the spatial filtering focusing lens, passes through the micro-aperture, and then is converted into parallel light after passing through the spatial filtering collimating lens, and then passes through the aperture to filter out the interference fringes of the detection light;

[0010] The absorption cell includes a sample rack, a sample dish and a high-precision displacement stage. The sample rack is used to fix a film substrate coated with a film to be tested. The sample rack is placed in a sample dish. The sample dish is used to contain a heat-conducting medium. The position of the sample dish is controlled by the displacement stage. The pump light and the detection light are focused respectively and then intersect on the surface of the film to be tested.

[0011] When the present invention is testing, the incident slit width and the exit slit width of the monochromator are determined according to the sample test band, and a suitable filter is selected; the wide-spectrum white light of the pump light source is introduced into the monochromator through the incident slit, and the monochromatic light of a specific band is derived from the exit slit; the monochromatic light is modulated in intensity by an optical chopper, and the modulation frequency of the chopper is introduced into a phase-locked amplifier as a reference signal; the pump light is converted from divergent light into parallel light after passing through a pump light collimating lens, and is introduced into an absorption cell through a pump light focusing lens to be focused on a film to be tested fixed on a sample holder; the sample holder is placed in a container filled with a heat-conducting medium and strictly The sample dish is limited; the intensity of the detection light source is adjusted to make the brightness signal measured by the position-sensitive detector close to the upper limit of the instrument test signal; the detection light is expanded by the spatial filtering system, and is introduced into the absorption cell through the detection light focusing lens, and passes over the film; the three-dimensional displacement stage and the rotating stage of the absorption cell are adjusted to make the film surface parallel to the detection light, and the film surface is made as close to the detection light as possible without contacting the film surface with the detection light; the three-dimensional displacement stage of the pump light focusing lens is adjusted to maximize the contact distance between the pump light and the detection light; the detection signal of the position-sensitive detector is transmitted to the computer after being demodulated by the phase-locked amplifier.

[0012] Preferably, a periscope is arranged between the optical chopper and the pump light lens group in the pump light path, and the light spot emitted by the monochromator is rotated through the periscope to maximize the size of the light spot along the pump light PP direction.

[0013] Furthermore, the monochromator is equipped with a filter set for filtering out stray light, and the transmittance of each filter in the transmission band is above 90%. The pump light emitted by the monochromator contains a certain proportion of stray light. According to the test band and the light absorption characteristics of the sample, a suitable filter is selected to filter out the stray light.

[0014] In this system, the pump light spot shape emitted by the monochromator is a vertical strip, while the detection light is in the horizontal direction. In order to maximize the intersection distance between the pump light and the detection light and improve the test signal, the pump light is rotated 90° around the optical axis using a periscope, and the pump light spot shape is transformed into a horizontal strip. The light spot emitted by the monochromator is rotated through the periscope to maximize the size of the light spot along the PP direction of the pump light.

[0015] Furthermore, the pump light lens group includes a pump light collimating lens and a pump light focusing lens. The pump light is first converted into parallel light by the pump light collimating lens and then focused by the pump light focusing lens. The power density is about 50-1000mW cm -2 The pump light lens group ensures the light collection efficiency while ensuring that the power density of the pump light spot focused on the sample surface is high enough to enhance the deflection signal.

[0016] The spatial filtering system needs to ensure a high degree of optical path stability. Preferably, the spatial filtering system adopts a cage structure, and the relative positions of the spatial filtering focusing lens, the micropore and the spatial filtering collimating lens are fixed. Among them, the focal length of the spatial filtering collimating lens is greater than the focal length of the spatial filtering focusing lens, the focal length of the spatial filtering collimating lens is 150-300mm, and the focal length of the spatial filtering focusing lens is 30-50mm; the diameter of the micropore is 15-100μm.

[0017] Preferably, the focal length of the detection light focusing lens is 100-300 mm.

[0018] After the detection light PB emitted by the detection light source passes through the spatial filtering system and the detection light focusing lens, the spot diameter at the focus is 10-100μm and is 10-100μm away from the outer surface of the film to be tested.

[0019] Furthermore, the translation stage is composed of three high-precision linear translation axes X, Y, and Z and a high-precision rotation stage, and the translation stage is provided with a limiting groove for mounting a sample dish.

[0020] Furthermore, the position sensitive detector is equipped with a bandpass filter that matches the wavelength of the detection light PB emitted by the detection light source; during the test, the power of the detection light PB reaching the position sensitive detector is close to the detection power upper limit of the position sensitive detector.

[0021] Preferably, the reflectivity of each reflector in the periscope is above 90% in the ultraviolet region and the visible light region. The transmittance of the lens in the pump light lens group and the sample dish in the ultraviolet region and the visible light region is above 90%.

[0022] The present invention also provides a method for calibrating a photothermal deflection spectrum, based on the above-mentioned high-sensitivity photothermal deflection spectrum testing device, comprising the following steps:

[0023] A black film with an absorbance of more than 98% in the ultraviolet, visible and near-infrared regions is used as a reference sample, placed on the film substrate in the absorption cell, and the corresponding reference signal is obtained by testing;

[0024] The test film sample signal is divided by the reference signal to obtain a relative absorption spectrum;

[0025] An arbitrary point in the strong absorption band of the UV-visible spectrum is taken as a reference for the absolute absorbance, and then the relative absorption spectrum is converted into an absolute absorption spectrum.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. Based on the principle of photothermal effect, the present invention comprehensively considers the influence of various factors on the photothermal deflection spectrum signal, and makes a series of targeted optimization adjustments to the light source and the optical path, such as using a periscope to flip the direction of the pump light spot, using a spatial filtering system to reduce the size of the spot at the focus of the detection light, improving the intensity of the detection light, using high-transmittance lenses and high-reflectivity mirrors, and equipping key optical path components with high-precision translation stages, etc., which greatly improves the detection light deflection signal; at the same time, the present invention uses high-quality fused quartz with ultra-low absorption characteristics in the ultraviolet-visible light region as the substrate, which greatly reduces the substrate signal; the photothermal deflection spectrum test device demonstrated by the present invention has achieved 10 4 -10 5 The signal-to-noise ratio meets the demand for high-sensitivity detection of weakly absorbing samples.

[0028] 2. The present invention proposes a calibration method for photothermal deflection spectrum, using a black film with an absorption rate of more than 98% in the ultraviolet-visible-near infrared region as a 100% absorption reference sample, and correcting the pump light spectrum intensity term coupled in the deflection signal of the test sample to obtain a relative absorption spectrum, which can correspond one-to-one with the ultraviolet-visible absorption spectrum result, and verify the test accuracy.

[0029] 3. The installation and operation of the device of the present invention have good repeatability, and its detection sensitivity for the absorbance of thin film samples is generally one order of magnitude higher than that of conventional commercial detection methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the overall structure of a high-sensitivity photothermal deflection spectrum testing device of the present invention;

[0031] Figure 2 It is a schematic diagram of the structure of the absorption tank in the present invention;

[0032] Figure 3 A schematic diagram of the intersection of pump light and detection light in the present invention;

[0033] Figure 4 It is a schematic diagram of the structure of the pump light lens group in the present invention;

[0034] Figure 5 It is a structural schematic diagram of the spatial filtering system in the present invention;

[0035] Figure 6 This is a comparison diagram of the photothermal deflection spectra of the black film and the high-quality fused quartz substrate in the embodiment of the present invention;

[0036] Figure 7 This is a graph showing the theoretical signal-to-noise ratio of the photothermal deflection spectrum in an embodiment of the present invention;

[0037] Figure 8This is a comparison chart of the ultraviolet-visible absorption spectrum and the photothermal deflection spectrum of the green light quantum dots, a weak absorption material in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0039] like Figure 1 As shown, a highly sensitive photothermal deflection spectroscopy test device includes a pump light source 1, a monochromator 2, an optical chopper 3, a periscope 4, a pump light lens group 5, a detection light source 6, a spatial filtering system 7, a detection light focusing lens 8, an absorption cell 9, a position-sensitive detector 10, a phase-locked amplifier 11, and a computer 12. The entire system is built on a seismic isolation platform and is covered with a dark box during testing. It should be pointed out that Figure 1 The periscope 4 is only used to optimize the shape of the light spot emitted by the monochromator 2 in this embodiment and is not necessary.

[0040] The pump light path is sequentially arranged with a pump light source 1, a monochromator 2, an optical chopper 3, a periscope 4, a pump light lens group 5, and an absorption cell 9; the signal control end of the monochromator 2 is connected to a computer 12; and the output signal of the optical chopper 3 is used as a reference signal of a phase-locked amplifier 11.

[0041] The detection light PB optical path is perpendicular to the pump light PP optical path and intersects at the absorption cell 9; along the detection light optical path, the detection light source 6, the spatial filtering system 7, the detection light focusing lens 8, the absorption cell 9 and the position-sensitive detector 10 are arranged in sequence; the signal output end of the position-sensitive detector 10 is connected to the signal input end of the phase-locked amplifier 9, and the detection signal is demodulated by the phase-locked amplifier 11 and transmitted to the computer 12.

[0042] The wide spectrum white light of the pump light source 1 is introduced into the monochromator 2 controlled by the computer 12 through the incident slit, and the monochromatic light of a specific wavelength band is extracted from the exit slit. The monochromatic light is modulated by the optical chopper 3, and the modulation frequency of the chopper 3 is introduced into the phase-locked amplifier 11 as a reference signal.

[0043] like Figure 2 and Figure 3 As shown, in the absorption cell 9, the pump light is focused on the film 91 to be tested fixed on the sample holder 93. In order to reduce the interference signal absorbed by the substrate, the film substrate 92 is made of high-quality fused quartz with an absorption rate of less than 10 -5. The sample holder 93 is placed in a sample dish 95 filled with a heat-conducting medium 94 and strictly limited. The position of the sample dish 95 is adjusted by a high-precision displacement stage 96 so that the detection light PB passes over the upper surface of the film 91 at a distance d≈50μm. The film 91 absorbs part of the pump light PP, converts the light energy into heat energy, and generates a temperature field and a corresponding refractive index field through thermal diffusion. After passing through the refractive index field of the adjacent film surface, the detection light PB deflects its direction of travel and finally irradiates the light-receiving surface of the position-sensitive detector 10 placed on the output light path. The deflection signal is input to the phase-locked amplifier 11 for demodulation; the demodulated signal is transmitted to the computer 12 for data acquisition and analysis.

[0044] Taking the black film signal as a reference, the sample signal is divided by the black film signal to obtain the relative absorption spectrum; taking a point in the strong absorption band of the UV-visible spectrum as a reference for the absolute absorbance rate, the relative absorption spectrum can be converted into an absolute absorption spectrum.

[0045] like Figure 4 As shown, the pump light lens group 5 includes a pump light collimating lens 51 and a pump light focusing lens 52. In order to reduce the pump light PP spot to a suitable size and improve the light collection efficiency, the pump light PP is converted from divergent light to parallel light after passing through the pump light collimating lens 51, and then introduced into the absorption cell 9 through the pump light focusing lens 52.

[0046] In this embodiment, the spot size of the detection light PB at the focus is negatively correlated with the spot size of the detection light PB before passing through the detection light focusing lens 8. Under the premise of comprehensively considering factors such as the size of the film substrate 92, the deflection distance of the detection light PB, and the light receiving area of ​​the position sensitive detector 10, the detection light PB first passes through the spatial filtering system 7 to enlarge the parallel light spot to a certain size.

[0047] like Figure 5 As shown, the spatial filtering system 7 includes a spatial filtering focusing lens 71, a micro-hole 72, a spatial filtering collimating lens 73 and an aperture 74 arranged along the optical path; the detection light is focused by the spatial filtering focusing lens 71 and passes through the micro-hole 72, and then is converted into parallel light after passing through the spatial filtering collimating lens 73, and then passes through the aperture 74 to filter out the interference fringes of the detection light. The detection light PB after the spot size is enlarged is introduced into the absorption cell 9 through the detection light focusing lens 8.

[0048] In this embodiment, after the detection light passes through the spatial filtering system 7 and the detection light focusing lens 8, the spot diameter at the focus is reduced to 35μm, ensuring that the overall deflection phase of the detection light spot is consistent during the test and the detection light can be closer to the film; the detection light passes by at a distance of 50μm from the outer surface of the film to be tested, ensuring that the detection light passes through a larger refractive index field, generating a larger deflection signal, and improving the test sensitivity.

[0049] The displacement stage in the absorption cell 9 is composed of three high-precision linear displacement axes of X, Y, and Z and a high-precision rotational displacement stage. The linear displacement accuracy reaches 0.1μm and the rotation angle resolution is 0.017°, which ensures the precise control of each degree of freedom of movement of the sample dish 95; the sample dish limiting groove is installed on the displacement stage to avoid mechanical vibration causing the optical path of the sample dish to deviate, thereby reducing the test error.

[0050] The film substrate 92 is made of high quality fused quartz; the absorbance of the fused quartz substrate is less than 10 -5 , reducing the background signal caused by the substrate and ensuring accurate testing of weak absorption signals.

[0051] The position-sensitive detector 10 is equipped with a bandpass filter that matches the wavelength of the detection light, which reduces the interference of the scattered pump light on the deflection signal. The detection light reaches the position-sensitive detector 10 through a series of optical paths, and the detection light power can still reach the detection power upper limit of the position-sensitive detector 10. Within the range, the deflection signal obtained by the position-sensitive detector 10 is proportional to the detection light power. Increasing the detection light power can enhance the deflection signal and improve the signal-to-noise ratio.

[0052] The detection light focusing lens 8 and the position-sensitive detector 10 are used in conjunction with a high-precision three-dimensional translation stage (XYZ), and the linear displacement accuracy of each degree of freedom reaches 0.1 μm, ensuring precise control of the optical path.

[0053] The entire device is covered by a dark box to isolate the device from external air flow and stray light, thereby improving the signal-to-noise ratio.

[0054] The reflectivity of each reflector in the periscope 4 in the ultraviolet light region and the visible light region is above 90%, and the transmittance of the lens in the pump light lens group and the sample dish in the ultraviolet light region and the visible light region is above 90%, ensuring that the pump light intensity has no obvious attenuation and improving the test signal-to-noise ratio.

[0055] The calibration method of the photothermal deflection spectrum of the present invention comprises the following steps: using a black film (e.g., Acktar Company, MV-20X030-1-01) with an absorbance of more than 98% in the ultraviolet, visible and near-infrared regions as a reference sample to obtain a reference signal that is approximately equal to 100% absorbance; in the band corresponding to the strong absorption band of the ultraviolet-visible spectrum, the sample signal is divided by the black film signal to obtain a relative absorption spectrum.

[0056] like Figure 6 , which is a comparison diagram of the light-thermal deflection spectra of the black film in this embodiment and the high-quality fused silica substrate; Figure 7Figure 2 is the photothermal deflection spectrum signal-to-noise ratio diagram. It can be seen that in the wavelength range of 470-600nm, the photothermal deflection signal of the black film is 20-100mV, and the corresponding photothermal deflection signal of the high-quality fused quartz substrate is <3μV, and the average background noise is about 1.6μV. The theoretical signal-to-noise ratio of the photothermal deflection spectrum test device in this band is calculated to be 1.6×10 4 ~6×10 4 , much higher than 10 of the commercial UV-visible spectrum 3 signal-to-noise ratio.

[0057] like Figure 8 As shown, the UV-visible absorption spectrum and photothermal deflection spectrum of the weak absorption material green light quantum dots in the embodiment are compared. Since the photothermal conversion factor of the sample is not corrected in the figure, the absolute value of the absorption spectrum converted from the photothermal deflection spectrum at around 525nm deviates from the true value. From the overall spectrum, the signal-to-noise ratio of the absorption spectrum converted from the photothermal deflection spectrum is significantly better than that of the UV-visible absorption spectrum, and the absorbance test range has been expanded by an order of magnitude, proving the high sensitivity of the photothermal deflection spectrum device of the present invention.

[0058] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A highly sensitive photothermal deflection spectroscopy test device, It is characterized in that It comprises a mutually perpendicular detection light path and a pump light path, wherein a pump light source (1), a monochromator (2), an optical chopper (3), a pump light lens group (5) and an absorption cell (9) are sequentially arranged along the pump light path; and a detection light source (6), a spatial filtering system (7), a detection light focusing lens (8), an absorption cell (9) and a position-sensitive detector (10) are sequentially arranged along the detection light path; The pump light optical path is further provided with a periscope (4) between the optical chopper (3) and the pump light lens group (5), and the light spot emitted by the monochromator (2) is rotated through the periscope (4) so ​​that the size of the light spot along the pump light PP direction is maximized; The signal output end of the position-sensitive detector (10) is connected to the signal input end of the phase-locked amplifier (11), and the output end of the phase-locked amplifier (11) is connected to the computer (12); the signal control end of the monochromator (2) is connected to the computer (12), and the signal output end of the optical chopper (3) is connected to the signal input end of the phase-locked amplifier (11); The spatial filtering system (7) comprises a spatial filtering focusing lens (71), a micro-aperture (72), a spatial filtering collimating lens (73) and an aperture (74) arranged along the optical path; the detection light is focused by the spatial filtering focusing lens (71) and passes through the micro-aperture (72), and then is converted into parallel light after passing through the spatial filtering collimating lens (73), and then passes through the aperture (74) to filter out interference fringes of the detection light; The spatial filtering system (7) adopts a cage structure, and the relative positions of the spatial filtering focusing lens (71), the micropore (72) and the spatial filtering collimating lens (73) are fixed; wherein the focal length of the spatial filtering collimating lens (73) is greater than the focal length of the spatial filtering focusing lens (71), the focal length of the spatial filtering collimating lens (73) is 150-300 mm, and the focal length of the spatial filtering focusing lens (71) is 30-50 mm; the diameter of the micropore (72) is 15-100 μm; The absorption cell (9) comprises a sample holder (93), a sample dish (95) and a displacement stage (96); the sample holder (93) is used to fix a film substrate (92) coated with a film to be tested (91); the film substrate (92) is high-quality fused quartz; the sample holder (93) is placed in a sample dish (95); the sample dish (95) is used to contain a heat-conducting medium (94); the position of the sample dish (95) is controlled by the displacement stage (96); the pump light and the detection light are focused and intersect on the surface of the film to be tested (91).

2. The high-sensitivity photothermal deflection spectroscopy testing device according to claim 1, It is characterized in that The monochromator (2) is equipped with a filter set, and the transmittance of each filter in the transmission band is above 90%.

3. The high-sensitivity photothermal deflection spectroscopy testing device according to claim 1, It is characterized in that The pump light lens group (5) comprises a pump light collimating lens (51) and a pump light focusing lens (52). The pump light is first converted into parallel light by the pump light collimating lens (51) and then focused by the pump light focusing lens (52). The power density is 50-1000 mW cm -2 .

4. The high-sensitivity photothermal deflection spectroscopy testing device according to claim 1, It is characterized in that The focal length of the detection light focusing lens (8) is 100-300 mm.

5. The high-sensitivity photothermal deflection spectroscopy testing device according to claim 1, It is characterized in that After the detection light PB emitted by the detection light source (6) passes through the spatial filtering system (7) and the detection light focusing lens (8), the diameter of the light spot at the focus is 10-100 μm and the distance from the outer surface of the film (91) to be tested is 10-100 μm.

6. The high-sensitivity photothermal deflection spectroscopy testing device according to claim 1, It is characterized in that The position-sensitive detector (10) is equipped with a bandpass filter that matches the wavelength of the detection light PB emitted by the detection light source (6); during the test, the power of the detection light PB reaching the position-sensitive detector (10) is close to the detection power upper limit of the position-sensitive detector (10).

7. The high-sensitivity photothermal deflection spectroscopy testing device according to claim 1, It is characterized in that The reflectivity of each reflector in the periscope (4) in the ultraviolet region and the visible light region is greater than 90%; The transmittance of the lens in the pump light lens group (5) and the sample dish (95) in the ultraviolet region and the visible light region is both above 90%.

8. A calibration method for photothermal deflection spectroscopy, It is characterized in that The high-sensitivity photothermal deflection spectroscopy testing device according to any one of claims 1 to 7 comprises the following steps: A black film with an absorbance of more than 98% in the ultraviolet, visible and near-infrared regions is used as a reference sample, placed on the film substrate in the absorption cell, and the corresponding reference signal is obtained by testing; The test film sample signal is divided by the reference signal to obtain a relative absorption spectrum; An arbitrary point in the strong absorption band of the UV-visible spectrum is taken as a reference for the absolute absorbance, and then the relative absorption spectrum is converted into an absolute absorption spectrum.

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