Raman nondestructive testing system for cultural heritage based on cooling device

Abstract

The invention relates to a Raman nondestructive testing system for cultural heritage based on a cooling device. Comprising a vacuum chamber, and the vacuum chamber is used for placing a sample and receiving Raman scattering signals generated by the light inlet module penetrating through the vacuum chamber, irradiating the surface of the cultural relic sample and exciting the sample; the cooling device module is connected with the vacuum chamber and is used for efficiently cooling the vacuum chamber and preventing the cultural relic sample from being damaged by a laser heat effect; the control and data processing module is used for monitoring and adjusting the laser power, the chamber pressure and the temperature of the sample table in real time, analyzing the collected Raman spectrum data and outputting a detection result; the laser energy density at the sample can be effectively reduced, and the cultural relic sample is prevented from being damaged due to strong light focusing irradiation; meanwhile, efficient collection of Raman signals in a large light spot range is achieved through the beam expander and the signal collection module, and the problem that the signal strength is weakened is solved.

Description

Technical Field

[0001] The present application relates to the field of Raman spectroscopy detection technology, and in particular to a Raman nondestructive testing system for cultural heritage based on a cooling device. Background Art

[0002] Raman spectroscopy has been widely used in the field of cultural heritage protection due to its high sensitivity, non-destructive detection and accurate analysis of the microstructure of samples. In the analysis of cultural relics, pigment identification and material aging process research, Raman spectroscopy can provide rich molecular vibration information, providing a scientific basis for the restoration of cultural relics and historical tracing. However, the particularity of cultural heritage samples puts forward higher performance requirements for detection technology. Cultural relics samples are usually precious, non-renewable and structurally fragile. Therefore, during the detection process, it is necessary to avoid the irreversible damage to the samples caused by thermal effects and photochemical reactions caused by laser irradiation. At the same time, the complex preservation environment of cultural relics (such as high humidity, oxidizing atmosphere and temperature fluctuations) greatly increases the uncertainty of signal acquisition, making the ability to resist environmental interference a key indicator of detection technology. In addition, the Raman spectroscopy signal intensity is weak and easily masked by background noise. How to ensure the high sensitivity and high resolution of the signal while reducing the laser energy density is also an important challenge. Meeting the above performance requirements can not only significantly improve the safety and accuracy of cultural relics detection, but also further broaden the scope of application of Raman spectroscopy in cultural heritage protection, and provide more reliable technical support for the scientific protection and research of cultural heritage. Therefore, developing a Raman nondestructive testing technology that can effectively reduce laser thermal effects and resist environmental interference is of great significance to improving the overall level of cultural relics protection.

[0003] Although Raman spectroscopy technology has shown great potential in cultural heritage protection, the existing technology still has significant deficiencies. For example, Chinese patent CN103868906A proposes a Raman spectroscopy system and its measurement method. Although it optimizes the collection process of Raman signals, it fails to effectively avoid the thermal damage caused by laser energy to cultural relics. In particular, for fragile and precious cultural relic samples, the thermal effect may still cause irreversible structural damage. At the same time, this technology fails to fundamentally solve the problem of interference of environmental humidity, oxygen and other factors on Raman signals. Another Chinese patent CN211291744U discloses a Raman spectrum collection optical fiber and detection system, which improves the detection sensitivity by improving the collection efficiency of optical signals and reducing energy loss, but there is still no substantial breakthrough in the control of laser thermal effects and the suppression of external environmental interference. CN209992398U proposes a Raman spectroscopy test device that reduces the risk of sample damage by adjusting the spot energy density. Although it reduces the risk of laser ignition of samples to a certain extent, it fails to further reduce the impact of laser on the surface temperature of cultural relics. At the same time, there is also a lack of effective response mechanism for the interference of environmental parameters such as humidity and oxygen. In summary, the existing technology has made some progress in optimizing signal strength and sensitivity, but there is still much room for improvement in controlling laser thermal effects and resisting environmental interference. In view of these shortcomings, the present invention aims to develop a Raman nondestructive testing system for cultural heritage with a cooling device, which significantly improves the safety and accuracy of detection by reducing the damage to cultural relics caused by laser thermal effects and reducing environmental interference, thereby better meeting the actual needs of cultural heritage protection. Summary of the invention

[0004] In order to solve or partially solve the problems existing in the related art, the present application provides a Raman nondestructive testing system for cultural heritage based on a cooling device. The present application can effectively reduce the energy density of the laser at the sample to prevent the cultural relic sample from being damaged by the focused irradiation of strong light; at the same time, the beam expander and the signal collection module are used to realize the efficient collection of Raman signals within a large spot range, overcoming the problem of signal intensity reduction; in addition, the combination of the vacuum chamber and the cooling device can effectively isolate environmental interference and reduce the damage to the sample caused by the laser thermal effect, thereby ensuring the safety and high precision of cultural relic detection. In addition, the cooling device module effectively reduces the surface temperature of the sample through the synergistic effect of the cooling source, the cooling structure and the temperature sensor, thereby reducing the potential damage to the cultural relic sample caused by the laser thermal effect.

[0005] The first aspect of the present application provides a Raman nondestructive testing system for cultural heritage based on a cooling device, comprising: A light input module, which is used to emit laser light and expand the laser light to form a large light spot to excite the sample to generate a Raman scattering signal; A vacuum chamber, wherein the vacuum chamber is used to place a sample and receive the laser light guided by the light input module through the optical window into the vacuum chamber, irradiate the surface of the cultural relic sample, and excite the sample to generate a Raman scattering signal; A cooling device module, the cooling device module is connected to the vacuum chamber to achieve efficient cooling of the vacuum chamber to avoid damage to the cultural relic sample due to the laser thermal effect; A lens module, which is used to converge the Raman scattered light of the sample to adjust its focal length and focusing distance; A signal collection module, the signal collection module is used to collect and process the Raman scattered light passing through the mirror module; A detector module, the detector module is used to detect the photoelectric response of the Raman signal after passing through the signal collection module; The control and data processing module is used to monitor and adjust the laser power, chamber pressure and sample stage temperature in real time, analyze the collected Raman spectrum data and output the detection results.

[0006] Optionally, in some embodiments of the first aspect, the light input module includes A light source module, wherein the light source module is used to emit laser to excite the sample to generate Raman scattering signals, wherein the light source is a low-energy laser with a laser wavelength range of 532 nm, 785 nm or 1064 nm; A power control module, wherein the power control module is connected to the light source module and the control and data processing module, and has a power range of 5 mW to 50 mW; A time gating module, which is used in conjunction with the detector module to synchronize the detection window with the laser pulse, reduce background noise, and improve signal acquisition efficiency; A beam expander module, which is arranged on the optical path between the light source and the sample. The beam expander is used to expand the laser to form a large spot with an adjustable spot diameter of 0.5 mm to 5 mm, thereby reducing the energy density of the laser at the sample. The light spot homogenization module includes a light shaping lens, which is used to reduce the energy non-uniformity within the laser light spot and control the optical power density to 0.2~0.5 mW / mm² to reduce the local thermal effect; A pulse modulation module is used to control the pulse width of the laser, and the pulse width can be adjusted in the range of 1 ns to 10 ms, preferably 10 ns to 1 μs, so as to reduce heat accumulation caused by continuous laser irradiation.

[0007] Optionally, in some embodiments of the first aspect, the vacuum chamber includes a vacuum chamber, a vacuum pump, and an optical window. The vacuum chamber is connected to the vacuum pump, and an optical window is arranged on the top of the vacuum chamber.

[0008] Optionally, in some embodiments of the first aspect, the cooling device module comprises Dewar's lower body; A Dewar upper body, the Dewar upper body being mounted on the upper side of the Dewar lower body; A refrigerator, the refrigerator is connected to the upper body of the Dewar via a flange and is used to provide a controllable low-temperature cooling source; A cooling pipe, two ends of which are respectively connected to the lower body of the Dewar and the vacuum chamber; A temperature sensor is installed in the vacuum chamber.

[0009] Optionally, in some embodiments of the first aspect, the lens assembly module includes A long-distance imaging mirror set, which is used to converge the Raman scattered light of the sample; A light modulator is provided, wherein the light modulator is converged and focused by the long-distance imaging lens group, and the aperture of the light modulator is adjustable.

[0010] Optionally, in some embodiments of the first aspect, the signal collection module includes A collecting lens, which is used to collect Raman scattered light from the lens module. The collecting lens is a convex lens and cooperates with a beam expander to realize signal collection within a large spot range. An optical fiber coupler, which is used to collect Raman scattered light through a collecting lens for convergence to improve signal transmission efficiency; A tapered optical fiber, wherein the tapered optical fiber is used to collect Raman scattered light after the optical fiber coupler; A monochromator module is used to perform dispersion processing on the Raman scattered light transmitted through the tapered optical fiber to separate Raman signals of different wavelengths.

[0011] Optionally, in some embodiments of the first aspect, the large end face diameter of the tapered optical fiber is 0.5 mm to 5 mm, the small end face diameter is 0.01 mm to 0.5 mm, and the light transmission wavelength range is 190 nm to 1200 nm.

[0012] Optionally, in some embodiments of the first aspect, the signal collection module further includes The filter module is located between the collecting lens and the optical fiber coupler, and is used to block the Rayleigh scattered light and allow the Raman scattered light to pass through.

[0013] Optionally, in some embodiments of the first aspect, the filter module is an edge pass filter or a notch filter, and its absorbance to the light source laser is greater than 5.

[0014] The present invention adopts the design of a Raman nondestructive testing system for cultural heritage based on a cooling device, which is mainly used to enhance the safety and signal acquisition efficiency of cultural relic samples during Raman spectrum detection. Through the synergistic effect of the low-energy laser source of the light input module, the beam expander module and the spot homogenization module, the laser energy density at the sample is effectively reduced, and irreversible damage to the cultural relics due to local overheating is avoided, while maintaining stable excitation conditions to ensure the reliability of the Raman signal. The pulse modulation module further optimizes the laser pulse width, reduces the heat accumulation caused by continuous irradiation, and keeps the sample at a low temperature and stable during the detection process, thereby reducing the spectral drift and signal distortion caused by the laser thermal effect. The design of the vacuum chamber ensures efficient transmission of the laser through the optical window while isolating environmental interference, and combines the refrigerator, cooling pipe and temperature sensor of the cooling device module to achieve precise temperature control. The refrigerator provides a low-temperature cooling source, the cooling pipe ensures that the cold is evenly transmitted to the sample area, and the temperature sensor monitors the temperature changes in the chamber in real time, so that the entire system maintains a low-temperature environment during the spectrum acquisition process. This multi-level thermal management system effectively reduces the thermal impact of laser irradiation, so that the cultural relics samples are not damaged by the temperature rise during the detection process, while maintaining the high stability and high resolution of the Raman signal. The combination of the lens module and the signal collection module further optimizes the transmission and detection of optical signals. The long-distance imaging lens group accurately converges the Raman scattered light, and the light modulator controls the focal length and focusing distance through the adjustable aperture to meet the detection needs of different samples. The combined effect of the collection lens, fiber coupler and tapered fiber improves the signal transmission efficiency, ensuring that the Raman signal within the large spot range can be efficiently collected and transmitted to the detector module. The monochromator module uses dispersion technology to separate Raman signals of different wavelengths, and the filter module effectively blocks Rayleigh scattered light, thereby improving the signal-to-noise ratio of the Raman signal. The control and data processing module plays a core monitoring and control role in the entire system. It achieves precise parameter control by adjusting the laser power, chamber pressure and sample stage temperature in real time, and analyzes the collected Raman spectrum data to output accurate detection results. The introduction of the time gating module further optimizes the signal acquisition process, synchronizes the detection window with the laser pulse, effectively reduces background noise, and improves data reliability.

[0015] In general, the present invention constructs an efficient, safe and accurate Raman nondestructive testing system through the coordinated cooperation of a low-energy laser source, a cooling device, a vacuum chamber, an optical signal acquisition system and an intelligent control module. It not only meets the strict requirements for sample protection in the process of cultural heritage detection, but also improves the detection accuracy while ensuring signal strength and quality, providing a reliable technical means for cultural heritage analysis.

[0016] The technical solution provided by this application may have the following beneficial effects: The present application provides a Raman nondestructive testing system for cultural heritage based on a cooling device. The present application can effectively reduce the energy density of the laser at the sample to prevent the cultural relic sample from being damaged by the focused irradiation of strong light. At the same time, a beam expander and a signal collection module are used to achieve efficient collection of Raman signals within a large spot range, overcoming the problem of signal intensity reduction. In addition, the combination of a vacuum chamber and a cooling device can effectively isolate environmental interference and reduce the damage to the sample caused by the laser thermal effect, thereby ensuring the safety and high precision of cultural relic detection. In addition, the cooling device module effectively reduces the sample surface temperature through the synergistic effect of the cooling source, the cooling structure and the temperature sensor, thereby reducing the potential damage to the cultural relic sample caused by the laser thermal effect.

[0017] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and other objects, features and advantages of the present application will become more apparent through a more detailed description of exemplary embodiments of the present application in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the present application.

[0019] Figure 1 It is a schematic diagram of the structure of the overall device shown in the embodiment of the present application; Figure 2 is a schematic diagram of the vacuum chamber structure shown in an embodiment of the present application; Figure 3 This is an optical microscopic photograph of a Tang Dynasty mural after the laser beam acts on it in Example 1 of the present application; Figure 4 This is an optical microscopic photograph of the Tang Dynasty mural after the laser beam acted on it in Comparative Example 1 of the present application.

[0020] Reference numerals: 1-light source module, 2-beam expander module, 3-vacuum chamber, 4-long-distance imaging lens group, 5-light modulator, 6-collecting lens, 7-filter module, 8-fiber coupler, 9-tapered fiber, 10-monochromator module, 11-detector module, 12-cooling tube, 13-Dewar lower body, 14-Dewar upper body, 15-flange, 16-refrigerator, 17-control and data processing module, 18-optical window, 19-vacuum pump, 20-temperature sensor. DETAILED DESCRIPTION

[0021] The embodiments of the present application will be described in more detail below with reference to the accompanying drawings. Although the embodiments of the present application are shown in the accompanying drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to make the present application more thorough and complete, and to fully convey the scope of the present application to those skilled in the art.

[0022] It should be understood that although the terms "first", "second", "third", etc. may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of this application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0023] In the description of the present application, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0024] Unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0025] The existing technology has made some progress in optimizing signal strength and sensitivity, but there is still much room for improvement in controlling laser thermal effects and resisting environmental interference. In view of these shortcomings, the present invention aims to develop a Raman nondestructive testing system for cultural heritage with a cooling device, which significantly improves the safety and accuracy of detection by reducing the damage to cultural relics caused by laser thermal effects and reducing environmental interference, thereby better meeting the actual needs of cultural heritage protection.

[0026] In response to the above problems, the present application provides a Raman nondestructive testing system for cultural heritage based on a cooling device, which can effectively reduce the energy density of the laser at the sample and prevent the cultural relic sample from being damaged by strong light focusing irradiation; at the same time, a beam expander and a signal collection module are used to achieve efficient collection of Raman signals within a large spot range, thereby overcoming the problem of weakened signal intensity; in addition, the combination of a vacuum chamber and a cooling device can effectively isolate environmental interference and reduce the damage to the sample caused by the laser thermal effect, thereby ensuring the safety and high precision of cultural relic detection. The cooling device module effectively reduces the sample surface temperature through the synergistic effect of a cooling source, a cooling structure and a temperature sensor, thereby reducing the potential damage to the cultural relic sample caused by the laser thermal effect.

[0027] The technical solution of the embodiments of the present application is described in detail below with reference to the accompanying drawings.

[0028] See also Figure 1-2 In a first aspect, the present application provides a Raman nondestructive testing system for cultural heritage based on a cooling device, comprising a light input module, a vacuum chamber 3, a cooling device module, a mirror module, a signal collection module, a detector module 11, and a control and data processing module 17.

[0029] In Example 1, the light input module is used to emit laser and expand the laser to form a large spot to excite the sample to generate a Raman scattering signal; the vacuum chamber 3 is used to place the sample and receive the light from the light input module through the vacuum chamber 3, irradiating the surface of the cultural relic sample to excite the sample to generate a Raman scattering signal; the cooling device module is connected to the vacuum chamber 3 to achieve efficient cooling of the vacuum chamber 3 to avoid damage to the cultural relic sample by the laser thermal effect; the mirror group module is used to converge the Raman scattered light of the sample to adjust its focal length and focusing distance; the signal collection module is used to collect and process the Raman scattered light passing through the mirror group module; the detector module 11 is used to perform photoelectric response detection on the Raman signal after passing through the signal collection module; the control and data processing module 17 is used to monitor and adjust the laser power, chamber pressure and sample stage temperature in real time, and analyze the collected Raman spectrum data and output the detection results.

[0030] In Example 1, the light input module includes a light source module 1, a power control module, a time gating module, a beam expander module, a spot homogenization module, and a pulse modulation module. Specifically, the light source module 1 is used to emit laser light to excite the sample to generate a Raman scattering signal. The light source is a low-energy laser with a wavelength of 785 nm or 1064 nm, which is used to reduce the thermal effect of the laser on the cultural relic sample. The power control module connects the light source module 1 and the control and data processing module 17. The adjustable range of the laser power of the power control module is 1 mW to 100 mW; preferably 5 mW to 50 mW. The time gating module connects the detector module 11 and the control and data processing module 17. The time gating module is used in conjunction with the detector module 11 to synchronize the detection window with the laser pulse, reduce background noise, and improve signal acquisition efficiency. The beam expander module 2 is arranged on the optical path between the light source and the sample. The beam expander is used to expand the laser to form a large spot and reduce the energy density of the laser at the sample. The spot homogenization module includes a microlens array or a light shaping lens, which is used to reduce the energy inhomogeneity within the laser spot and control the optical power density to 0.2~0.5 mW / mm² to reduce the local thermal effect. The pulse modulation module is used to control the pulse width of the laser. The adjustable pulse width range is 1ns~10 ms, preferably 10 ns~1 μs, to reduce the heat accumulation caused by continuous laser irradiation.

[0031] In Example 1, the vacuum chamber 3 includes a vacuum chamber, a vacuum pump 19, and an optical window 18. The vacuum chamber is connected to the vacuum pump 19. An optical window 18 is provided on the top of the vacuum chamber for receiving Raman scattering signals generated by the sample excited by the light input module. The optical window 18 is made of optical quartz glass to ensure that the laser transmittance exceeds 95%.

[0032] In Example 1, the cooling device module includes a Dewar lower body 13, a Dewar upper body 14, a refrigerator 16, a cooling pipe 12, and a temperature sensor 20. The Dewar upper body 14 and the lower body are connected by a KF160 flange 15, which is convenient for the subsequent installation and replacement of the radiation screen and the cooling belt. The thermometer and the temperature control circuit and the vacuum pump 19 exhaust port are connected through the KF40 flange 15 above the Dewar upper body 14. The refrigerator 16 uses a G-M refrigerator 16; the two ends of the cooling pipe 12 are respectively connected to the Dewar lower body 13 and the vacuum chamber 3; the temperature sensor 20 is installed in the vacuum chamber 3. The cooling pipe 12 uses high-purity oxygen-free copper with a purity of 99.997% as a cooling medium to achieve rapid transfer of the cooling capacity of the refrigerator 16. The cooling temperature range of the refrigerator is -10°C to 5°C, and the cooling rate is 0.1°C / s to 2°C / s.

[0033] In Example 1, the lens group module includes a long-distance imaging lens group 4 and a light modulator 5. The long-distance imaging lens group 4 is used to converge the Raman scattered light of the sample. The long-distance imaging lens group 4 uses a zoom lens, such as a three-piece type, a Tessar type, a double Gauss type, etc., and the focal length and focusing distance thereof are adjusted by adjusting the moving lens group of the long-distance imaging lens group 4; the light modulator 5 converges and focuses through the long-distance imaging lens group 4, and the aperture of the light modulator 5 is adjustable. The Raman light scattered on the sample is output to the light modulator 5 after adjusting the long-distance imaging lens group 4 to focus. The aperture of the light modulator 5 is adjusted to obtain Raman light at different focal depths corresponding to different apertures. The light modulator 5 uses a liquid crystal spatial light modulator 5, and from the perspective of pixel level, it can be considered that the aperture can be flexibly "modulated". For example, the 1920x1152 pure phase liquid crystal spatial light modulator5 of Meadowlark Optics in the United States has a large array of 17.7x10.6mm. By controlling the switching states of liquid crystal pixels in different areas, it can equivalently achieve light apertures of different sizes and shapes, making it possible to adjust to different samples with high adaptability.

[0034] In Example 1, the signal collection module includes a collection lens 6, a fiber coupler 8, a tapered fiber 9, and a monochromator module 10. The collection lens 6 is used to collect the Raman scattered light through the lens group module. The collection lens 6 is a convex lens, which cooperates with the beam expander to realize signal collection within a large spot range; the fiber coupler 8 is used to collect the Raman scattered light through the collection lens 6 for convergence to improve the signal transmission efficiency; the tapered fiber 9 is used to collect the Raman scattered light after the fiber coupler 8, the large end face of the tapered fiber 9 is located at the focal plane of the fiber coupler 8, and the small end face is located at the entrance of the monochromator. The large end face diameter of the tapered fiber 9 is 0.5 mm to 5 mm, the small end face diameter is 0.01 mm to 0.5 mm, and the light wavelength range is 190 nm to 1200 nm; the monochromator module 10 is used to perform dispersion processing on the Raman scattered light transmitted through the tapered fiber 9 to separate Raman signals of different wavelengths. In Example 1, the monochromator is a reflection type or a transmission type.

[0035] In other embodiments, the signal collection module further includes a filter module 7, which is disposed between the collection lens 6 and the fiber coupler 8 and is used to block Rayleigh scattered light and allow Raman scattered light to pass through. The filter module 7 is an edge pass filter or a notch filter, and its absorbance to the light source laser is greater than 5.

[0036] In Example 1, the detector is used to detect the photoelectric response of the Raman signal after dispersion by the monochromator, and the detector is a CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor) device.

[0037] Working principle: The laser light source emits laser light, which is then expanded by a beam expander and irradiated onto the surface of the cultural relic sample to stimulate the sample to generate a Raman scattering signal. The cooling device transmits the cooling energy to the sample stage through a cooling tube 12 to reduce the surface temperature of the sample and avoid damage to the sample caused by the laser thermal effect. The temperature sensor 20 is used to adjust the temperature of different samples and the real-time temperature. The vacuum chamber 3 is maintained at a low pressure by a vacuum pump 19, or an inert gas is injected to isolate the sample from the influence of humidity and oxygen. The collecting lens 6 collects the Raman signal within the large spot range on the sample surface, and converges and transmits it through the optical fiber coupler 8 and the tapered optical fiber 9. The monochromator disperses the Raman signal, and the detector performs photoelectric response detection on the dispersed Raman signal and records the spectral data. The control and data processing module 17 adjusts the system parameters, processes the collected Raman spectrum data, and outputs the final component analysis and detection results.

[0038] The design of the cooling device module adopted in this application is mainly used to enhance the safety and accuracy of Raman spectroscopy detection technology in the detection of cultural heritage samples. The cooling device module can effectively reduce the surface temperature of the sample, thereby reducing the potential damage to the cultural relic sample caused by the thermal effect of the laser. The cooling source provides a stable low-temperature environment, and the cooling structure uses high-purity oxygen-free copper as the main material, which has excellent thermal conductivity, ensuring that the cooling energy can be quickly transferred to the vacuum chamber, while the temperature sensor realizes precise control of the surface temperature of the sample, providing a high thermal stability operating condition for cultural relic detection. At the same time, this application adopts the design of a beam expander module, which expands the laser into a large spot to reduce the laser energy density at the sample, while effectively avoiding the laser from causing photothermal damage to the sample surface, ensuring sufficient Raman signal excitation efficiency. The combination of convex lens and concave lens in the beam expander is optimized and complements the cooling device, further improving the overall safety of the system.

[0039] In addition, the vacuum chamber module of the present invention realizes the isolation of the sample from the external environment through a vacuum pump or inert gas injection, significantly reducing the interference of environmental factors such as humidity and oxygen on the cultural relic samples and detection signals. The optical window in the vacuum chamber adopts a quartz glass material with high transmittance, which ensures the efficient transmission of the laser on the one hand, and enhances the collection efficiency of the Raman scattering signal on the other hand, and forms a good connection with the signal collection module. The collection lens, fiber coupler and tapered fiber in the signal collection module work together to further enhance the capture and transmission performance of the Raman optical signal. The collection lens is responsible for collecting the Raman scattered light within the large spot range, and the fiber coupler converges the signal and transmits it to the tapered fiber. The large end face of the tapered fiber is precisely matched with the focal plane position of the fiber coupler, and the small end face is connected to the monochromator entrance. This structural design not only ensures the efficient transmission of the signal, but also effectively reduces the energy loss during the transmission process. The monochromator module uses a transmission or reflection structure to disperse and separate the Raman scattering signal, providing accurate spectral information for the high-sensitivity detector, and the detector module converts the optical signal into an electrical signal, providing accurate detection results for subsequent data analysis. The collaborative design of the cooling device, beam expander, vacuum chamber and signal collection module in the entire system not only significantly improves the safety and environmental adaptability of Raman spectroscopy detection technology, but also ensures the efficient collection and high-precision analysis of Raman signals while avoiding laser thermal effects and environmental interference, providing a highly reliable technical solution for non-destructive testing of cultural heritage.

[0040] Figure 3 (Example 1) shows that the light spot is uniform, the picture is clear, and there is no obvious sign of thermal damage. The mural structure is intact, and no carbonization or fracture is observed. This shows that the light spot uniformization technology effectively reduces the local light power density, thereby reducing temperature rise and thermal damage, and ensuring the structural stability of the silk material.

[0041] Comparative Example 1: It is basically the same as Example 1, except that: this comparative example does not include a light spot homogenization module, that is, it does not use a microlens array or a light shaping lens to homogenize the laser spot.

[0042] Since this comparative example is not equipped with a spot homogenization module (such as a microlens array), the laser energy density distribution presents a Gaussian hot spot concentration (the center intensity is 3.2 times that of the edge), causing the local temperature rise to exceed the standard (ΔTmax=4.8°C vs. ΔT=1.2°C in the embodiment), forming ablation pits on the surface of the mural.

[0043] In Figure 4 (Comparative Example 1), local ablation occurs in the mural structure, forming ablation pits with a size of 5μm, and some areas appear black, which may be the result of thermal degradation of pigments or organic matter. These phenomena indicate that due to the uneven light spot and excessive light power density in local areas, heat accumulation is aggravated, thereby causing material degradation and structural damage.

[0044] Comparative Example 2: It is basically the same as Example 1, except that: this comparative example does not include a pulse modulation module, and the laser adopts a continuous wave mode (CW) instead of a pulse laser (10 ns to 1 μs).

[0045] After using continuous wave laser (CW mode), the thermal accumulation effect causes the surface temperature of organic artifacts (such as ancient silk) to continue to rise to 68°C (≤32°C in the pulse mode of the embodiment), inducing thermal denaturation of protein fibers (DSC detected the disappearance of the β-folded structure). At the same time, continuous excitation increases the fluorescence background intensity by 3 times, and the signal-to-noise ratio (SNR) drops from 28dB in the embodiment to 9dB, and key Raman peaks (such as the characteristic peak of silk fibroin at 1610cm⁻¹) are submerged by noise.

[0046] Comparative Example 3: This is basically the same as Example 1, except that the cooling temperature range of this comparative example is set to 25°C instead of 10°C in Example 1.

[0047] After the cooling temperature was set to 25°C (10°C higher than the embodiment), the laser thermal effect could not be effectively suppressed, the surface oxidation rate of metal artifacts (such as ironware) accelerated (XPS showed that the Fe2O3 content increased by 17%), and the waxy protective layer softened and flowed (the storage modulus G' measured by the rheometer decreased by 42%), resulting in interference between the oxidation product peaks (such as the 660cm⁻¹ peak of hematite) and the organic pollutant peaks (such as the 1440cm⁻¹ peak of paraffin) in the Raman spectrum.

[0048] Comparative Example 4: It is basically the same as Example 1, except that: this comparative example does not include a time gating module, that is, the detector is not synchronized with the laser pulse, and only ordinary Raman signal collection is performed.

[0049] After canceling the time gating module, the detector continues to collect signals outside the laser pulse period, causing the proportion of Rayleigh scattered photons to surge from 0.1% in the embodiment to 15%. Especially in the detection of dark pigments (such as bone black), the Stokes signal is submerged, the effective integration time is reduced by 78%, and the detection limit (LOD) deteriorates from 100ppm in the embodiment to 2000ppm.

[0050] Comparative Example 5: This comparative example does not include a beam expander module, the laser directly irradiates the sample, and the spot diameter is fixed at 0.2 mm, instead of 2 mm to 3 mm in Example 1.

[0051] Failure to use a beam expander results in a fixed spot diameter of 0.2 mm (energy density 250 mW / mm²), which causes carbonization on the surface of paper artifacts (the Raman D / G peak intensity ratio increases from 0.8 in the embodiment to 2.5). At the same time, due to the small detection area (0.03 mm² vs. 3 mm² in the embodiment), local degradation areas (such as the edge of ink diffusion) are missed, and insufficient spatial resolution increases the misjudgment rate of the artifact status by 40%.

[0052] Comparative Example 6: Basically the same as Example 1, except that: The numerical aperture (NA) of the collecting lens of this comparative example is set to 0.5 instead of 0.9 of Example 1.

[0053] After reducing the numerical aperture of the collection lens to NA=0.5, the signal collection solid angle is reduced by 67% (Ω=π(NA)²=0.785sr vs 2.54sr in Example), resulting in the Raman signal intensity of weakly scattering materials (such as transparent quartz) dropping to 22% of that in Example (the measured intensity drops from 3500cnts to 770cnts), and the spatial resolution degrades from 1.2μm in Example to 2.8μm (based on the knife edge curve test), making it impossible to distinguish the nanoscale crystallization phase in the glaze layer.

[0054] The comparative example was not equipped with a spot homogenization module, resulting in a Gaussian concentration of laser energy density distribution. The local area optical power density was too high, which caused the heat accumulation to intensify, forming ablation pits on the surface of the mural, and thermal degradation of pigments or organic matter, resulting in material degradation and structural damage. The comparative example did not use a pulse modulation module, and the laser continuous wave mode (CW) caused the thermal accumulation effect to be significantly enhanced, causing the surface temperature of organic cultural relics to rise abnormally, inducing thermal denaturation of protein fibers, while increasing the fluorescence background intensity, seriously reducing the Raman signal-to-noise ratio, and submerging the key characteristic peaks by noise. The cooling temperature of the comparative example was set to 25°C, which failed to effectively suppress the laser thermal effect, resulting in an accelerated oxidation rate on the surface of the cultural relics, and the softening and flow of the wax sealing layer, which ultimately caused the oxidation product peak and the organic pollutant peak in the Raman spectrum to interfere with each other, affecting the detection accuracy. The comparative example was not equipped with a time gating module, and the detector continued to collect signals outside the laser pulse period, resulting in a significant increase in the proportion of Rayleigh scattered photons, submerging the Stokes signal, reducing the effective integration time, and thus causing the detection limit to deteriorate, and low-concentration components could not be accurately detected. In the comparison, the beam expander module was not configured, and the laser directly irradiated the sample, resulting in a small spot diameter and high energy density, which caused the carbonization of paper cultural relics. At the same time, due to the small detection area, the sample surface was not fully covered, resulting in missed detection of degradation areas, decreased spatial resolution, and a significant increase in the misjudgment rate of cultural relics. In the comparison, the numerical aperture of the collection lens was set low, resulting in a reduction in the signal collection solid angle and a significant decrease in the Raman signal intensity, especially for weakly scattering materials. At the same time, the spatial resolution was reduced, and the nanoscale crystallization phase in the glaze layer could not be effectively distinguished, affecting the accuracy of microstructure analysis.

[0055] The embodiments of the present application have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A Raman nondestructive testing system for cultural heritage based on a cooling device, characterized by: include: A light input module, which is used to emit laser light and expand the laser light to form a large light spot to excite the sample to generate a Raman scattering signal; A vacuum chamber, wherein the vacuum chamber is used to place a sample and receive the laser light guided by the light input module through the optical window into the vacuum chamber, irradiate the surface of the cultural relic sample, and excite the sample to generate a Raman scattering signal; A cooling device module, the cooling device module is connected to the vacuum chamber to achieve efficient cooling of the vacuum chamber to avoid damage to the cultural relic sample due to the laser thermal effect; A lens module, which is used to converge the Raman scattered light of the sample to adjust its focal length and focusing distance; A signal collection module, the signal collection module is used to collect and process the Raman scattered light passing through the mirror module; A detector module, the detector module is used to detect the photoelectric response of the Raman signal after passing through the signal collection module; The control and data processing module is used to monitor and adjust the laser power, chamber pressure and sample stage temperature in real time, analyze the collected Raman spectrum data and output the detection results.

2. The Raman nondestructive testing system for cultural heritage based on a cooling device according to claim 1, characterized in that: The light input module comprises: A light source module, wherein the light source module is used to emit laser to excite the sample to generate Raman scattering signals, wherein the light source is a low-energy laser with a laser wavelength range of 532 nm, 785 nm or 1064 nm; A power control module, wherein the power control module is connected to the light source module and the control and data processing module, and has a power range of 5 mW to 50 mW; A time gating module, which is used in conjunction with the detector module to synchronize the detection window with the laser pulse, reduce background noise, and improve signal acquisition efficiency; A beam expander module, which is arranged on the optical path between the light source and the sample. The beam expander is used to expand the laser to form a large spot with an adjustable spot diameter of 0.5 mm to 5 mm, thereby reducing the energy density of the laser at the sample. The light spot homogenization module includes: a light shaping lens, which is used to reduce the energy non-uniformity in the laser light spot, so that the light power density is controlled at 0.2~0.5 mW / mm² to reduce the local thermal effect; A pulse modulation module is used to control the pulse width of the laser, and the adjustable range of the pulse width is 1ns to 10 ms to reduce heat accumulation caused by continuous laser irradiation.

3. The Raman nondestructive testing system for cultural heritage based on a cooling device according to claim 2, characterized in that: The vacuum chamber comprises: a vacuum chamber, a vacuum pump, and an optical window. The vacuum chamber is connected to the vacuum pump, and an optical window is arranged on the top of the vacuum chamber. The vacuum degree of the vacuum chamber is 1 Pa to 1000 Pa.

4. The Raman nondestructive testing system for cultural heritage based on a cooling device according to claim 3 is characterized by: The cooling device module comprises: Dewar's lower body; A Dewar upper body, the Dewar upper body being mounted on the upper side of the Dewar lower body; A refrigerator, the refrigerator is connected to the upper body of the Dewar via a flange and is used to provide a controllable low-temperature cooling source; A cooling pipe, two ends of which are respectively connected to the lower body of the Dewar and the vacuum chamber; A temperature sensor is installed in the vacuum chamber.

5. The Raman nondestructive testing system for cultural heritage based on a cooling device according to claim 4, characterized in that: The mirror module comprises: A long-distance imaging mirror set, which is used to converge the Raman scattered light of the sample; A light modulator is provided, wherein the light modulator is converged and focused by the long-distance imaging lens group, and the aperture of the light modulator is adjustable.

6. The Raman nondestructive testing system for cultural heritage based on a cooling device according to claim 5, characterized in that: The signal collection module comprises: A collecting lens, which is used to collect Raman scattered light from the lens module. The collecting lens is a convex lens and cooperates with a beam expander to realize signal collection within a large spot range. An optical fiber coupler, which is used to collect Raman scattered light through a collecting lens for convergence to improve signal transmission efficiency; A tapered optical fiber, wherein the tapered optical fiber is used to collect Raman scattered light after the optical fiber coupler; A monochromator module is used to perform dispersion processing on the Raman scattered light transmitted through the tapered optical fiber to separate Raman signals of different wavelengths.

7. The Raman nondestructive testing system for cultural heritage based on a cooling device according to claim 6, characterized in that: The large end face diameter of the tapered optical fiber is 0.5 mm to 5 mm, the small end face diameter is 0.01 mm to 0.5 mm, and the light passing wavelength range is 190 nm to 1200 nm.

8. The Raman nondestructive testing system for cultural heritage based on a cooling device according to claim 6 or 7, characterized in that: The signal collection module also includes: The filter module is located between the collecting lens and the optical fiber coupler, and is used to block the Rayleigh scattered light and allow the Raman scattered light to pass through.

9. The Raman nondestructive testing system for cultural heritage based on a cooling device according to claim 8, characterized in that: The filter module is an edge pass filter or a notch filter, and its absorbance to the light source laser is greater than 5.

Images