An apparatus and method for material infrared refractive index measurement

Abstract

The application discloses a device and method for measuring infrared refractive index of materials, which comprises an infrared light source assembly, a collimating mirror, a first filter group, a converging lens, a displacement platform and a photoacoustic power assembly arranged in sequence along the horizontal axis direction; the displacement platform carries the material to be measured and can move in the preset range of the focal point of the converging lens along the horizontal axis direction; the infrared light beam is emitted by the infrared light source assembly, the parallel light of a specific spectral band after the collimating mirror and the first filter group is incident to the converging lens, the focused light beam passes through the material to be measured moving in the preset range to form a test light beam, the test light beam enters the photoacoustic power assembly, the photoacoustic power assembly detects and analyzes the change of the light power caused by the movement of the material to be measured, and the infrared refractive index of the material to be measured is given. The application has simple light path, high measurement precision, wide measurement band and strong application in the measurement of the refractive index change of materials.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical measurement, and particularly relates to a device and method for measuring infrared refractive index of a material. BACKGROUND

[0002] The refractive index of a material will generally change with the increase of light intensity acting on the material, and the change of the refractive index of the material at different wavelengths and under the action of light intensity is of great significance for the use of the material in certain technical fields, such as the field of optoelectronics. Especially for the infrared waveband, the change of the infrared refractive index of the material is mainly caused by thermal effect, but it is relatively difficult to detect high-sensitivity photoelectricity in the infrared waveband.

[0003] The current detection of the infrared refractive index of the material basically uses the pyroelectric method. For example, patent CN105004430A discloses a photoelectric sensitive unit of a non-cooled infrared focal plane detector, which comprises a resonant cavity composed of a semi-transparent metal layer, an organic medium layer and a reflective metal layer, and a detector unit fixedly arranged below the resonant cavity for realizing photoelectric signal conversion. At least one of the semi-transparent metal layer, the organic medium layer and the reflective metal layer of the resonant cavity is provided with a hollow line and / or pattern. The scheme effectively reduces the thermal crosstalk of the resonant cavity and improves the spatial resolution of the detector unit by hollowing the corresponding layers of the resonant cavity. However, the device based on the pyroelectric principle is generally expensive, and the measurement accuracy is relatively low.

[0004] The principle of the photoacoustic power detector is photoacoustic effect. At present, photoacoustic spectroscopy technology is mainly used for gas and liquid concentration detection, especially for safety detection of medical and power equipment. Photoacoustic spectroscopy technology is a kind of spectroscopy technology based on photoacoustic effect to detect the concentration of absorbed gas. Compared with gas chromatograph, the technology has the advantages of no need of consumables, rapid measurement and simple operation.

[0005] For example, patent CN109765181A discloses a differential resonant photoacoustic cell for improving the stability of gas photoacoustic spectrum detection. The device comprises a gas chamber for introducing the gas to be detected, a gas inlet, a gas outlet, a reference gas chamber, a resonant photoacoustic cell, a light inlet window, an isolation window, a light outlet window, an acoustic-electric conversion module, a preamplifier circuit and a filter circuit. The scheme combines the differential structure with the resonant structure, effectively isolates the gas to be detected from the acoustic-electric converter, improves the long-term stability and anti-interference of the device, and can measure trace gas to 100% concentration gas. The first-order longitudinal resonant structure realizes the standing wave cooperative amplification of the photoacoustic signal, improves the detection sensitivity of the gas, and is suitable for long-term online monitoring of power and nuclear energy equipment, monitoring of petroleum and chemical raw material production process and other application occasions.

[0006] The photoacoustic spectroscopy technology is only applied to the actual detection of gas concentration, can directly measure the size of the gas absorption light energy, and the sensitivity is much higher than that of the Fourier infrared spectrum under the same gas cell length. The photoacoustic effect of the gas molecules is analyzed, and the photoacoustic effect is generated by the gas molecules absorbing light of a specific wavelength. However, the research on the measurement of the material infrared refractive index is still in blank.

[0007] Therefore, how to design a device and method for measuring the material infrared refractive index based on the photoacoustic spectroscopy technology, so as to realize high measurement precision, wide measurement band and strong application of the material infrared refractive index, is a problem to be solved by the person skilled in the art. SUMMARY

[0008] In view of the defects in the prior art, the present application provides a device and method for measuring the material infrared refractive index based on the photoacoustic spectroscopy technology. The infrared light beam emitted by the infrared light source assembly in the device enters the collimating mirror and then the specific spectral band of the parallel light after the first filter group, and then is incident on the converging lens to form a focused light beam. The focused light beam passes through the to-be-measured material moving in a preset range to form a test light beam. The test light beam enters the photoacoustic power assembly. The photoacoustic power assembly detects and analyzes the change of the light power caused by the movement of the to-be-measured material, determines the absorption range of the absorption medium, and then modulates the wavelength of the infrared light source to enable it to excite a certain specific absorption. At the same time, the proportional relationship between the pressure wave intensity generated after the medium absorbs energy and the light intensity or concentration is determined to give the infrared refractive index of the to-be-measured material.

[0009] The refractive index of the to-be-measured material at different positions in the optical path is different, thereby causing the size of the photoacoustic signal of the photoacoustic power assembly to change with the change of the position of the to-be-measured material in the optical path. The refractive index change of the material can be obtained by processing the photoacoustic signal curve.

[0010] The present application has the advantages of simple optical path, high measurement precision, wide measurement band, and strong application of the measurement of the refractive index change of the material. The photoacoustic spectroscopy-based light power detection response sensitivity is little affected by the wavelength change, and can accurately measure the μW level, especially for the detection of the mid-infrared light power.

[0011] In the first aspect, the present application provides a device for measuring the material infrared refractive index, comprising: an infrared light source assembly, a collimating mirror, a first filter group, a converging lens, a displacement platform and a photoacoustic power assembly arranged in sequence along the horizontal axis direction.

[0012] The displacement platform carries the to-be-measured material and can move in the preset range of the focal point of the converging lens along the horizontal axis direction. The preset range is arranged along the axis of the converging lens, and the center symmetry line of the preset range passes through the focal point of the converging lens.

[0013] The infrared light beam emitted by the infrared light source assembly is incident on the parallel light of a specific spectral band after the collimating mirror and the first filter group, and then enters the converging lens to form a focused light beam.

[0014] Further, the displacement platform further comprises a pinhole diaphragm arranged at the rear end of the material to be measured, and the focused light beam passes through the material to be measured moving in the preset range and forms a changed light spot after passing through the pinhole diaphragm, and the changed light spot is detected and analyzed by the photoacoustic power assembly.

[0015] Further, the photoacoustic power assembly comprises a chopper, a photoacoustic cell, a microphone and a lock-in amplifier, the test light beam passes through the chopper to form a light beam of a specific frequency, the photoacoustic cell collects the light beam of the specific frequency and generates a sound signal transmitted to the microphone, and the microphone converts the sound signal into an electrical signal transmitted to the lock-in amplifier.

[0016] The photoacoustic cell comprises an outer shell, an inner core, an optical absorption medium layer and a second filter group, the outer shell wraps the inner core, the microphone is arranged on the outer shell of the photoacoustic cell, a small hole for collecting photoacoustic signals is arranged at a position close to the microphone mounting position in the inner core, the optical absorption medium layer is coated on the inner wall surface of the inner core, the optical absorption medium layer covers the rear end surface and the side end surface away from the entrance of the light beam of the specific frequency, the optical absorption medium layer of the side end surface extends from the connection with the rear end surface to the position of the small hole, and the second filter group is arranged at the entrance of the photoacoustic cell.

[0017] Further, the radius of the inner core of the photoacoustic cell is 2mm-10mm, the length of the inner core of the photoacoustic cell is 10mm-20mm, and the distance between the outer shell of the photoacoustic cell and the material to be measured is greater than 2 times the focal length of the converging lens.

[0018] Further, the material to be measured is in a sheet structure, the material of the optical absorption medium layer is carbon black, and the wavelength range of the infrared light beam is 1500nm-6500nm.

[0019] In a second aspect, the present application also provides a method for measuring the infrared refractive index of a material, which uses the device for measuring the infrared refractive index of a material as described above, and comprises the following steps:

[0020] Placing the material to be measured on the displacement platform and determining the moving range along the horizontal axis direction;

[0021] Starting the infrared light source assembly to emit an infrared light beam which forms parallel light of a specific spectral band after passing through the collimating mirror and the first filter group;

[0022] The parallel light is incident to the converging lens to form a focused light beam which passes through the material to be measured moving along the horizontal axis at a preset speed to form a test light beam, and the test light beam enters the photoacoustic power assembly which has been pre-calibrated;

[0023] The photoacoustic power assembly detects and analyzes the photoelectric signal to give the infrared refractive index of the material to be measured.

[0024] Further, the pre-calibrated photoacoustic power assembly specifically includes the following steps:

[0025] The infrared light source emits an incident light beam, and the power of the incident light beam is measured and obtained;

[0026] The incident light beam is directly transmitted into the photoacoustic power assembly, and the photoacoustic power is read according to the display data of the photoacoustic power assembly;

[0027] The parameters of the infrared light source are adjusted, and the above process is repeated to form a relationship curve between the power of the incident light beam with different power values and the photoacoustic power, and the pre-calibration of the photoacoustic power assembly is completed.

[0028] Further, the device for measuring the infrared refractive index of the material further comprises a pinhole diaphragm arranged at the rear end of the material to be measured, and the focused light beam passes through the material to be measured moving in a preset range to form a changing light spot on the pinhole diaphragm;

[0029] The photoacoustic power assembly detects and analyzes the photoelectric signal to give the infrared refractive index of the material to be measured, specifically including:

[0030] According to the moving speed of the material to be measured along the horizontal axis and the linear absorption coefficient of the material to be measured, the light intensity of the focused light beam acting on each moving position of the material to be measured is analyzed;

[0031] Combined with the size of the pinhole diaphragm, the transmission power of the focused light beam after passing through the pinhole diaphragm at each moving position of the material to be measured is obtained;

[0032] Based on the initial power of the focused light beam and the light intensity of the focused light beam acting on each moving position of the material to be measured, the transmittance for each moving position of the material to be measured is given, and the transmittance is normalized to obtain a normalized transmittance set;

[0033] The normalized transmittance set and the pre-calibrated transmittance and infrared refractive index corresponding relationship are used to give the infrared refractive index of the material to be measured.

[0034] Further, the light intensity of the focused light beam acting on each moving position of the material to be measured is analyzed, and the specific relationship of the light intensity is as follows:

[0035]

[0036]

[0037] Wherein, I is the light intensity of the focused light beam acting on a certain moving position of the material to be measured, z' is the position of the focused light beam acting in the material to be measured, alpha0 is the linear absorption coefficient of the material to be measured, is the change of the phase of the focused light beam in the material to be measured, Delta n is the change of the refractive index of the material to be measured, and k is the wave vector size of the light wave in the focused light beam.

[0038] The transmission power of the focused light beam after the pinhole diaphragm is obtained for each moving position of the material to be measured, and the specific relationship is as follows:

[0039]

[0040] Wherein, P T is the transmission power of the focused light beam after the pinhole diaphragm for a certain moving position of the material to be measured, R a is the maximum value of the pinhole radius r.

[0041] Based on the transmission power and the light intensity, the transmittance for each moving position of the material to be measured is given, and the transmittance is normalized, and the specific relationship is as follows:

[0042]

[0043] Wherein, T z is the normalized transmittance for a certain moving position of the material to be measured, S is the linear transmittance of the pinhole, T0 is the linear transmittance of the material to be measured, and P i is the initial power of the focused light beam.

[0044] Further, the corresponding relationship between the pre-calibrated transmittance and the infrared refractive index includes the following steps:

[0045] The transmittance of the material to be measured is collected, the transmittance curve is given, and the linear transmittance of the pinhole in the pinhole diaphragm is obtained;

[0046] Based on the parameters of the focused light beam, the transmittance of the material to be measured and the linear transmittance of the pinhole in the pinhole diaphragm, the change of the refractive index of the material to be measured is given, and the relationship of the change of the refractive index of the material to be measured is as follows:

[0047]

[0048] Wherein, Delta n is the change of the refractive index of the material to be measured, Delta T pv is the difference between the peaks and valleys in the transmittance curve, f is the calibration coefficient, S is the linear transmittance of the pinhole, L is the length of the material to be measured, and k is the wave vector size of the light wave in the focused light beam.

[0049] The device and method for measuring the infrared refractive index of the material provided by the application at least have the following beneficial effects:

[0050] (1) The application has simple optical path, high measurement precision, wide measurement waveband and strong application in measuring the change of material refractive index. The response sensitivity of the optical power detection based on photoacoustic spectrum is little affected by the change of wavelength, and can be accurately measured to the level of μW, especially for the detection of optical power in the middle and far infrared.

[0051] (2) The small hole in the core of the photoacoustic cell is used to collect the photoacoustic signal, and the sound signal acquisition has good stability and high sensitivity in combination with the high-sensitivity microphone.

[0052] (3) The power of the infrared light source passing through the small hole diaphragm is received by the photoacoustic power component, and the material infrared refractive index value is obtained through numerical simulation, which improves the measurement accuracy of the infrared refractive index. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 A device structure schematic diagram for measuring the infrared refractive index of materials is provided for the application;

[0054] Figure 2 A photoacoustic power component specific structure schematic diagram of an embodiment provided for the application;

[0055] Figure 3 A relationship curve diagram between the power of the incident light beam and the power of the photoacoustic in an embodiment provided for the application;

[0056] Figure 4 A relationship curve diagram between the change of the infrared refractive index of the material to be measured and the movement of the material to be measured in an embodiment provided for the application;

[0057] Figure 5 A method flowchart for measuring the infrared refractive index of materials is provided for the application.

[0058] 1-Infrared light source component, 2-Collimating mirror, 3-First filter set, 4-Converging lens, 5-Displacement platform, 6-Photoacoustic power component, 7-Photoacoustic cell, 71-Shell, 72-Core, 8-Absorbing medium layer, 9-Second filter set, 10-Chopper, 11-Microphone, 12-Phase-locked amplifier. DETAILED DESCRIPTION

[0059] In order to better understand the above technical solutions, the above technical solutions will be described in detail below in combination with the drawings in the specification and specific embodiments. Obviously, the described embodiments are only part of the embodiments of the application, not all embodiments. Based on the embodiments in the application, all other embodiments obtained by those of ordinary skill in the art without creative labor belong to the scope of protection of the application.

[0060] The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the description of the application and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0061] It is also to be noted that the terms "comprising", "including", and "having" or variations thereof herein, are intended to be broad and encompass the presence of the stated features but do not exclude the presence of additional features.

[0062] The refractive index of the material to be measured at different positions of the light path is different, thereby causing the size of the photoacoustic signal of the photoacoustic power assembly to change with the position of the material to be measured in the light path, and the refractive index change of the material can be obtained according to photoacoustic signal curve processing.

[0063] When the photoacoustic effect is applied to other state materials (except gas), the following two prerequisites must be met. First, the absorption range of the medium to be measured needs to be determined, so that the wavelength of the infrared light source can be modulated to excite a certain specific absorption; second, the proportional relationship between the pressure wave intensity generated after the medium to be measured absorbs energy and the light intensity or concentration needs to be determined. Therefore, by selecting an appropriate wavelength and combining the detection of the intensity of the pressure wave, not only the concentration of the gas can be measured, but also the incident light power can be measured.

[0064] As shown in Figure 1 The application provides a device for measuring the infrared refractive index of a material, which comprises an infrared light source assembly 1, a collimating mirror 2, a first filter set 3, a converging lens 4, a displacement platform 5 and a photoacoustic power assembly 6 arranged in sequence along the horizontal axis direction.

[0065] The displacement platform 5 carries the material to be measured and can move in the preset range of the focal point of the converging lens 4 along the horizontal axis direction. The preset range is arranged along the axis of the converging lens 4, and the center symmetry line of the preset range passes through the focal point of the converging lens 4.

[0066] The infrared light beam emitted by the infrared light source assembly 1 enters the converging lens 4 as parallel light of a specific spectral band after the collimating mirror 2 and the first filter set 3, and the focused light beam formed by the converging lens 4 forms a test light beam after passing through the material to be measured moving in the preset range. The test light beam enters the photoacoustic power assembly 6, the photoacoustic power assembly 6 detects and analyzes the change in light power caused by the movement of the material to be measured, and gives the infrared refractive index of the material to be measured.

[0067] The photoacoustic power component 6 measures the change of the photoacoustic signal based on the photoacoustic spectrum principle, and finally gives the infrared refractive index of the material to be measured.

[0068] The displacement platform 5 further comprises a pinhole diaphragm (not shown in the figure), which is arranged at the rear end of the material to be measured. After the focused light beam passes through the material to be measured moving in a predetermined range, a changing light spot is formed after passing through the pinhole diaphragm, which is detected and analyzed by the photoacoustic power component 6.

[0069] The material to be measured moves near the focal point of the converging lens. After the focused light beam passes through the material to be measured, it enters the pinhole diaphragm and is detected and analyzed by the photoacoustic power component. When the material to be measured moves from one side of the focal point of the converging lens to the other side of the focal point of the converging lens, the photoacoustic power component records the photoacoustic signal value once and analyzes it.

[0070] As shown in Figure 2 The photoacoustic power component 6 comprises a chopper 10, a photoacoustic cell 7, a microphone 11 and a lock-in amplifier 12. The test light beam passes through the chopper 10 to form a light beam of a specific frequency. The photoacoustic cell 7 collects the light beam of the specific frequency and generates a sound signal which is transmitted to the microphone 11. The microphone 11 converts the sound signal into an electrical signal which is transmitted to the lock-in amplifier 12.

[0071] The photoacoustic cell 7 comprises an outer shell 71, an inner core 72, an optical absorption medium layer 8 and a second filter set 9. The outer shell 71 wraps the inner core 72. The microphone 11 is arranged on the outer shell of the photoacoustic cell 7. A small hole for collecting the photoacoustic signal is arranged near the installation position of the microphone 11 in the inner core 72. The optical absorption medium layer 8 is coated on the inner wall surface of the inner core 72. The optical absorption medium layer 8 covers the rear end surface and the side end surface away from the entrance of the light beam of the specific frequency. The optical absorption medium layer of the side end surface extends from the connection with the rear end surface to the position of the small hole. The second filter set 9 is arranged at the entrance of the photoacoustic cell 7. The light beam of the specific frequency enters the photoacoustic cell 7 through the second filter set 9.

[0072] The chopping frequency of the chopper is a specific frequency, so that the infrared light source generates pulsed light of the same frequency. The sound signal detected by the microphone is converted into an electrical signal which is collected by the acquisition card with lock-in amplification function.

[0073] The radius of the inner core 72 of the photoacoustic cell is 2mm-10mm, the length of the inner core 72 of the photoacoustic cell is 10mm-20mm, and the distance between the outer shell 71 of the photoacoustic cell and the material to be measured is ≥2 times the focal length of the converging lens.

[0074] The material to be measured is in a sheet structure, the material of the optical absorption medium layer is carbon black, and the wavelength range of the infrared light beam is 1500nm-6500nm.

[0075] For example, in an embodiment, the light source is selected as a blackbody radiation infrared light source, the filter set is selected as one with a transmission peak of 5275 nm, and the photoacoustic detection chopping frequency is 30 Hz. Placed behind the infrared light source, a brass photoacoustic cell with a radius of 8.5 mm and a length of 18 mm is selected. The microphone sensitivity is about 50 dB / mV.

[0076] The experiment of the embodiment uses a copper sulfate solution to verify the method. The thickness of the material to be measured is 2 mm, the linear transmittance of the material to be measured is 60%, the linear absorption coefficient a0 of the material to be measured is obtained through the linear transmittance, and the moving position range of the displacement platform is -1.6 cm-1.6 cm. The above data is brought into the refractive index-transmittance relationship model to obtain the infrared refractive index change of the material.

[0077] The curve of the small hole transmittance with the sample position of the material to be measured is shown as a solid line in Figure 4 , so that the refractive index change of the material to be measured under different light intensities can be obtained. For the copper sulfate aqueous solution measurement curve, it is a change trend of peak first and valley later, which indicates that a concave lens effect refractive index change is generated, which is mainly because the copper sulfate aqueous solution absorbs infrared light to produce thermal expansion effect.

[0078] As shown in Figure 5 , the application also provides a method for measuring the infrared refractive index of a material, which uses the device for measuring the infrared refractive index of a material as described above, and includes the following steps:

[0079] Placing the material to be measured on the displacement platform, and determining the moving range along the horizontal axis direction;

[0080] Starting the infrared light source assembly to emit an infrared light beam to form a parallel light of a specific spectral band after passing through the collimating mirror and the first filter set;

[0081] The parallel light is incident on the converging lens to form a focused light beam passing through the material to be measured moving along the horizontal axis direction at a preset rate to form a test light beam, and the test light beam enters the pre-calibrated photoacoustic power assembly;

[0082] The photoacoustic power assembly detects and analyzes the photoelectric signal to give the infrared refractive index of the material to be measured.

[0083] The pre-calibrated photoacoustic power assembly specifically includes the following steps:

[0084] The infrared light source emits an incident light beam, and the power of the incident light beam is measured and obtained;

[0085] The incident light beam is directly transmitted into the photoacoustic power assembly, and the photoacoustic power is read according to the display data of the photoacoustic power assembly;

[0086] Adjust the parameters of the infrared light source, repeat the above process, form the power of the incident light beam of different power values and the relationship curve between the power of the photoacoustic, complete the pre-calibration of the photoacoustic power component.

[0087] As shown in Figure 3 The curve of the calibrated photoacoustic power component is given in an embodiment.

[0088] Further, the device for measuring the infrared refractive index of the material also includes a pinhole diaphragm arranged at the rear end of the material to be measured, and the focused light beam passes through the material to be measured moving in a preset range to form a changing light spot on the pinhole diaphragm.

[0089] The photoacoustic power component detects and analyzes the photoelectric signal to give the infrared refractive index of the material to be measured, and specifically includes:

[0090] According to the moving speed of the material to be measured along the horizontal axis direction and the linear absorption coefficient of the material to be measured, the light intensity of the focused light beam acting on each moving position of the material to be measured is analyzed.

[0091] Combined with the size of the pinhole diaphragm, the transmission power of the focused light beam after passing through the pinhole diaphragm at each moving position of the material to be measured is obtained.

[0092] Based on the initial power of the focused light beam and the light intensity of the focused light beam acting on each moving position of the material to be measured, the transmittance for each moving position of the material to be measured is given, and the transmittance is normalized to obtain a set of normalized transmittances.

[0093] The normalized transmittance set is given, and the transmittance and the infrared refractive index corresponding relationship is given, and the infrared refractive index of the material to be measured is given.

[0094] The light beam of the material to be measured near the focal position has the strongest central light, and the light intensity around the periphery decreases with the increase of the distance, so when the material to be measured is near the focal position, the heating is uneven, which leads to uneven temperature distribution, causes the change of refractive index Δn, and finally causes the material to be measured to become a concave lens with a changing focal length, thereby affecting the size of the light spot on the pinhole diaphragm behind the material to be measured, and finally affecting the light power transmitted through the pinhole diaphragm, and finally detected by the photoacoustic power component.

[0095] The light intensity of the focused light beam acting on each moving position of the material to be measured is analyzed, and the specific relationship of the light intensity is as follows:

[0096]

[0097]

[0098] Wherein, I is the light intensity of the focused light beam acting on a certain moving position of the material to be measured, z' is the position of the focused light beam acting in the material to be measured, a0 is the linear absorption coefficient of the material to be measured, is the change of the phase of the focused light beam in the material to be measured, and Δn is the change of the refractive index of the material to be measured, and k is the wave vector size of the light wave in the focused light beam.

[0099] The transmission power of the focused light beam after passing through the pinhole diaphragm at each moving position of the material to be measured is obtained, and the specific relationship is as follows:

[0100]

[0101] Wherein, P T is the transmission power of the focused light beam after passing through the pinhole diaphragm at a certain moving position of the material to be measured, R a is the maximum value of the pinhole radius r.

[0102] Based on the transmission power and the light intensity, the transmittance for each moving position of the material to be measured is given, and the transmittance is normalized, and the specific relationship is as follows:

[0103]

[0104] Wherein, T z is the normalized transmittance for a certain moving position of the material to be measured, S is the linear transmittance of the pinhole, T0 is the linear transmittance of the material to be measured, and P i is the initial power of the focused light beam.

[0105] Further, the corresponding relationship between the pre-calibrated transmittance and the infrared refractive index includes the following steps:

[0106] The transmittance of the material to be measured is collected, the transmittance curve is given, and the linear transmittance of the pinhole in the pinhole diaphragm is obtained;

[0107] Based on the parameters of the focused light beam, the transmittance of the material to be measured and the linear transmittance of the pinhole in the pinhole diaphragm, the change of the refractive index of the material to be measured is given, and the relationship of the change of the refractive index of the material to be measured is as follows:

[0108]

[0109] Wherein, Δn is the change of the refractive index of the material to be measured, ΔT pv is the difference between the peak and the valley in the transmittance curve, f is the calibration coefficient, S is the linear transmittance of the pinhole, L is the length of the material to be measured, and k is the wave vector size of the light wave in the focused light beam.

[0110] The refractive index of the material to be measured at different positions of the light path is different, thereby causing the photoacoustic signal of the photoacoustic power component to change with the position of the material to be measured in the light path, and the refractive index change of the material can be obtained according to photoacoustic signal curve processing.

[0111] The method for measuring the infrared refractive index of the material is very convenient, and has high sensitivity; the acquisition card combined with the phase-locked amplification function can accurately measure to the muW level; in addition, the method is particularly suitable for the measurement of the refractive index change of a material in a wide wave band, especially in a middle and far infrared wave band.

[0112] Although preferred embodiments of the application have been described, those skilled in the art will appreciate that other modifications and variations to the preferred embodiments are possible in light of the above teachings. It is, therefore, contemplated that the appended claims will embrace any such modifications and variations as falling within the scope of the application. Obviously, various modifications and changes are possible in the present application without departing from the scope and spirit of the application. Accordingly, it is intended that the application embrace all modifications and changes that fall within the scope of the claims and their equivalents.

Claims

1. A device for measuring the infrared refractive index of materials, characterized in that, include: The infrared light source assembly, collimating lens, first filter group, converging lens, displacement platform and photoacoustic power assembly are arranged sequentially along the horizontal axis. The displacement platform carries the material to be measured and can move along the horizontal axis within a preset range of the focal point of the converging lens. The preset range is set along the axis of the converging lens, and the central symmetry line of the preset range passes through the focal point of the converging lens. An infrared light beam emitted by an infrared light source component passes through a collimating lens and a first filter group, and parallel light of a specific spectral band is incident on a converging lens. The focused beam formed passes through the test material moving within a preset range to form a test beam. The test beam enters the photoacoustic power component, which detects and analyzes the change in optical power caused by the movement of the test material and provides the infrared refractive index of the test material. The displacement platform also includes a pinhole aperture, which is arranged at the rear end of the material under test. After the focused beam passes through the material under test moving within a preset range, it forms a changing light spot after passing through the pinhole aperture. The changing light spot is detected and analyzed by the photoacoustic power component. The photoacoustic power component includes a chopper, a photoacoustic cell, and a microphone. The test beam is formed into a beam of a specific frequency by the chopper, and the photoacoustic cell collects the beam of the specific frequency and generates a sound signal that is transmitted to the microphone. The photoacoustic cell includes an outer shell, an inner core, a light-absorbing medium layer, and a second filter group. The outer shell encloses the inner core. A microphone is mounted on the outer shell of the photoacoustic cell. A small hole for collecting photoacoustic signals is provided in the inner core near the microphone mounting position. The light-absorbing medium layer is coated on the inner wall surface of the inner core. The light-absorbing medium layer covers the rear end face and side end face away from the beam entrance of a specific frequency. The light-absorbing medium layer on the side end face extends from the connection with the rear end face to the position of the small hole. The second filter group is located at the entrance of the photoacoustic cell. The beam of a specific frequency enters the photoacoustic cell through the second filter group.

2. The apparatus for measuring the infrared refractive index of materials as described in claim 1, characterized in that, The photoacoustic power component also includes a lock-in amplifier, where the microphone converts the sound signal into an electrical signal and transmits it to the lock-in amplifier.

3. The apparatus for measuring the infrared refractive index of materials as described in claim 2, characterized in that, The radius of the inner core of the photoacoustic cell is 2mm to 10mm, the length of the inner core of the photoacoustic cell is 10mm to 20mm, and the distance between the outer shell of the photoacoustic cell and the material under test is ≥ twice the focal length of the converging lens.

4. The apparatus for measuring the infrared refractive index of materials as described in claim 2, characterized in that, The material under test has a sheet-like structure, the light-absorbing medium layer is made of carbon black, and the wavelength range of the infrared beam is 1500nm to 6500nm.

5. A method for measuring the infrared refractive index of materials, characterized in that, Using the apparatus for measuring the infrared refractive index of materials as described in any one of claims 1-4, the method includes the following steps: Place the material to be measured on the displacement platform and determine the range of movement along the horizontal axis. The infrared light source assembly is activated, emitting an infrared beam that passes through a collimating lens and the first filter group to form parallel light in a specific spectral band. Parallel light is incident on the converging lens, and the resulting focused beam passes through the material under test, which is moving along the horizontal axis at a preset rate, to form a test beam. The test beam then enters the photoacoustic power component that has been pre-calibrated. The photoacoustic power component detects and analyzes photoelectric signals to provide the infrared refractive index of the material under test.

6. The method for measuring the infrared refractive index of materials as described in claim 5, characterized in that, The pre-calibrated photoacoustic power component includes the following steps: An infrared light source emits an incident light beam, and the power of the incident light beam is measured and acquired. The incident light beam is directly transmitted to the photoacoustic power component, and the power of the photoacoustic signal is read from the display data of the photoacoustic power component. Adjust the parameters of the infrared light source and repeat the above process to form a curve showing the relationship between the power of the incident beam and the power of the photoacoustic signal at different power values, thus completing the pre-calibration of the photoacoustic power component.

7. The method for measuring the infrared refractive index of materials as described in claim 6, characterized in that, The device for measuring the infrared refractive index of materials also includes a pinhole aperture, which is arranged at the rear end of the material to be measured. After the focused beam passes through the material to be measured moving within a preset range, it forms a changing light spot on the pinhole aperture. The photoacoustic power component detects and analyzes photoelectric signals to provide the infrared refractive index of the material under test, specifically including: Based on the moving speed of the material under test along the horizontal axis and the linear absorption coefficient of the material under test, the light intensity of the focused beam at each moving position of the material under test is analyzed. By combining the size of the pinhole aperture, the transmitted power of the focused beam after passing through the pinhole aperture at each moving position of the material under test can be obtained; Based on the initial power of the focused beam and the light intensity of the focused beam at each moving position of the material under test, the transmittance at each moving position of the material under test is given, and the transmittance is normalized to obtain a set of normalized transmittance. By matching the normalized transmittance set with the pre-calibrated correspondence between transmittance and infrared refractive index, the infrared refractive index of the material under test is given.

8. The method for measuring the infrared refractive index of materials as described in claim 7, characterized in that, The analysis yielded the light intensity of the focused beam at each moving position of the material under test, and the specific relationship of the light intensity is as follows: Where I is the light intensity of the focused beam at a certain moving position of the material under test, z' is the position of the focused beam in the material under test, and α0 is the linear absorption coefficient of the material under test. The phase change of the focused beam in the material under test is given by Δn, where Δn is the change in the refractive index of the material under test, and k is the magnitude of the wave vector of the light wave in the focused beam. The transmitted power of the focused beam at each moving position of the material under test after passing through the pinhole aperture is obtained, and the specific relationship is as follows: Among them, P T R is the transmitted power of the focused beam at a certain moving position of the material under test after passing through the pinhole aperture. a This represents the maximum value of the orifice radius r. Based on transmitted power and light intensity, the transmittance at each moving position of the material under test is given, and the transmittance is normalized. The specific relationship is as follows: Among them, T z To normalize the transmittance of the test material at a specific moving position, S is the linear transmittance of the aperture, T0 is the linear transmittance of the test material, and P... i This represents the initial power of the focused beam.

9. The method for measuring the infrared refractive index of materials as described in claim 7, characterized in that, The pre-defined relationship between transmittance and infrared refractive index includes the following steps: The transmittance of the material to be tested is collected, the transmittance curve is given, and the linear transmittance of the aperture in the pinhole aperture is obtained; Based on the parameters of the focused beam, the transmittance of the material under test, and the linear transmittance of the aperture in the pinhole, the change in the refractive index of the material under test is given. The relationship of the change in the refractive index of the material under test is as follows: Where Δn is the change in refractive index of the material under test, and ΔT pv denoted as , where is the difference between the peaks and valleys in the transmittance curve, f is the calibration coefficient, S is the linear transmittance of the aperture, L is the length of the material under test, and k is the wave vector magnitude of the light wave in the focused beam.

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