Ultraviolet light monitoring device

Abstract

The invention relates to an ultraviolet light monitoring device which comprises a reflection type ultraviolet light fluorescent screen, an imaging lens, an infrared CCD camera and a computer which are sequentially arranged in the light path direction of ultraviolet light, and a fluorescent film and a substrate which are sequentially arranged on the reflection type ultraviolet light fluorescent screen. The fluorescent film comprises vanadium yttrium europium phosphate fluorescent powder, and the vanadium yttrium europium phosphate fluorescent powder is used for converting ultraviolet light into fluorescent light in a visible light wave band. According to the ultraviolet monitoring device, the fluorescent film is manufactured by adopting the vanadium yttrium europium phosphate fluorescent powder, the vanadium yttrium europium phosphate fluorescent powder is high in luminous efficiency, good in color rendering property, stable in chemical property, capable of bearing radiation of high temperature and strong ultraviolet light and better in luminous brightness, and the light intensity is more easily collected by the infrared CCD camera, so that the detection sensitivity is high; the method is very suitable for weak light monitoring of ultraviolet light with the wave band of 190-380 nm, and is suitable for weak ultraviolet light monitoring application scenes in the field of accelerators.

Description

Technical Field

[0001] The present invention relates to the field of ultraviolet light monitoring, and more particularly to an ultraviolet light monitoring device used for position measurement and imaging measurement of spot distribution and shape of ultraviolet light in the field of accelerators. Background Art

[0002] An X-ray free-electron laser (X-ray free-electron laser) is a large-scale scientific research device based on an electron linear accelerator. It produces ultrabright, ultrashort pulses of coherent X-ray radiation with tunable wavelength. It has extensive and crucial applications in fields such as physics, chemistry, materials science, and life sciences. The drive laser system is a crucial component of an X-ray free-electron laser. The drive laser acts on the photocathode electron gun at the front end of the accelerator to generate a high-brightness electron beam. The drive laser system is a key component in determining the quality of the electron beam.

[0003] To ensure the driver laser system maintains optimal performance during beam modulation, laser characteristics at various locations must be monitored during device operation. This includes real-time detection and feedback of the laser spot distribution and position at various monitoring points along the driver laser transmission path, including the virtual cathode, virtual injection mirror, and transmission path. Currently, X-ray free electron lasers use cesium telluride (Cs2Te) as the photocathode material. This photocathode exhibits high quantum efficiency in the ultraviolet region, with a quantum efficiency > 0.5% and a lifetime (the time it takes for the quantum efficiency to decay to 1 / e) > 10 days. While this high quantum efficiency photocathode material can reduce the power requirements of the driver laser, the lifetime of Cs2Te is limited, and photocathode replacement is a tedious and complex task. Therefore, the power of the driver laser's ultraviolet laser must be as high as possible to ensure proper operation even when the quantum efficiency of Cs2Te is low. In addition, the transmittance of optical components in the ultraviolet band is difficult to achieve greater than 95%, and the reflectivity is difficult to achieve greater than 99%. In order to ensure the transmission efficiency of the entire driving laser system, the monitoring light is generally very weak, and the ultraviolet laser light power used for monitoring is generally in the microwatt or even nanowatt level, which brings many difficulties to monitoring.

[0004] There are two existing technologies for ultraviolet light monitoring: the first is direct measurement, which uses an ultraviolet CCD camera to image and monitor ultraviolet light. Ultraviolet CCDs are expensive, and the frequency of beam modulation needs to be frequently changed according to the beam modulation requirements during operation. The light power hitting the ultraviolet CCD will change accordingly, and the ultraviolet CCD is easily damaged. This technology is not well suited for ultraviolet light monitoring applications in the accelerator field. The second is indirect measurement, which converts ultraviolet light into fluorescence using a UV converter for monitoring. The indirect measurement method, which combines a Ce:YAG fluorescent screen and an infrared CCD camera, is limited by the luminous efficiency and color rendering properties of Ce:YAG. During low-frequency and low-power beam modulation, the virtual cathode or virtual injection mirror spot cannot be seen on the infrared CCD camera, which brings many difficulties to the beam modulation operation. Summary of the Invention

[0005] In order to solve the above-mentioned problems in the prior art, the present invention provides an ultraviolet light monitoring device that can measure the spot shape, distribution and position of wide-band ultraviolet light with high sensitivity, solving the problem of low sensitivity of ultraviolet light monitoring in the prior art, and is suitable for weak ultraviolet light monitoring application scenarios in the accelerator field.

[0006] To achieve the above-mentioned objectives, the present invention provides an ultraviolet light monitoring device, comprising a reflective ultraviolet light fluorescent screen, an imaging lens, an infrared CCD camera, and a computer arranged in sequence along the optical path of the ultraviolet light, and a fluorescent film and a substrate arranged in sequence on the reflective ultraviolet light fluorescent screen; the fluorescent film contains yttrium vanadium phosphate europium phosphor powder, and the yttrium vanadium phosphate europium phosphor powder is used to convert ultraviolet light into fluorescence in the visible light band.

[0007] A visible light high reflection film is provided between the fluorescent film and the substrate.

[0008] The substrate is made of sapphire, and the fluorescent film is composed of vanadium yttrium phosphate europium fluorescent powder and an adhesive.

[0009] The mass ratio of the vanadium yttrium europium phosphate phosphor to the binder is m, 3≤m≤20.

[0010] The fluorescent film is made by uniformly mixing vanadium yttrium europium phosphate phosphor and adhesive, coating it on the substrate by blade coating, and then transferring it to a 200-300°C oven and placing it for 5-15 hours. After the organic mixture in the adhesive is fully volatilized, it is sent to a 500-700°C high-temperature furnace and sintered for 10-30 minutes.

[0011] The mixing method is selected from at least one of mechanical stirring, centrifugal dispersion or ultrasonic mixing.

[0012] The substrate is aluminum or stainless steel, and the fluorescent film is formed by mixing vanadium yttrium phosphate europium fluorescent powder and an organic solvent and then precipitating the mixture.

[0013] The median particle size D50 of the vanadium yttrium europium phosphate phosphor is 1-10 μm, and the particle size dispersion distribution coefficient of the vanadium yttrium europium phosphate phosphor is 0.7-1.5.

[0014] The thickness of the fluorescent film is 0.02-0.08 mm, and the thickness of the substrate is between 0.05 mm and 1 mm.

[0015] The incident ultraviolet light and the infrared CCD camera are both located on the front surface of the reflective ultraviolet fluorescent screen; the incident ultraviolet light forms an angle of 90°±1° with the front surface of the reflective ultraviolet fluorescent screen, and the infrared CCD camera forms an angle of 85°±2.5° with the front surface of the reflective ultraviolet fluorescent screen; or, the incident ultraviolet light forms an angle of 85°±2.5° with the front surface of the reflective ultraviolet fluorescent screen, and the infrared CCD camera forms an angle of 90°±1° with the front surface of the reflective ultraviolet fluorescent screen.

[0016] The ultraviolet light monitoring device of the present invention uses vanadium yttrium europium phosphate phosphor to produce a fluorescent film. The vanadium yttrium europium phosphate phosphor has high luminous efficiency, good color rendering, stable chemical properties, can withstand high temperature and strong ultraviolet radiation, has better luminous brightness, and the red light intensity is more easily collected by an infrared CCD camera. The ultraviolet fluorescent screen made of it has the characteristics of high brightness and high-definition display, so it has high detection sensitivity and is very suitable for weak light monitoring of ultraviolet light in the 190-380nm band, and is suitable for weak ultraviolet light monitoring application scenarios in the accelerator field.

[0017] In addition, the present application provides a visible light high reflective film between the fluorescent film and the substrate, so that most of the fluorescence in the visible light band is reflected to the infrared CCD camera, thereby further improving the detection sensitivity of weak light monitoring of ultraviolet light.

[0018] In addition, the reflective ultraviolet fluorescent screen includes a sapphire substrate and a fluorescent film on its front surface. The fluorescent film is composed of vanadium yttrium phosphate europium phosphor and an adhesive. The chemical properties of the vanadium yttrium phosphate europium phosphor are stable and because it is a small spherical particle, the coating is dense, the distribution is more uniform, and the consistency is good. The reflective ultraviolet fluorescent screen made in this way has a simple structure and low cost. Because the coating is dense and the distribution is more uniform, and the sapphire is easy to conduct heat, it can quickly take away the heat generated by UV laser irradiation on the fluorescent screen, preventing heat accumulation, so that it can withstand high-power direct irradiation for a long time without carbonization or other damage to the screen surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 1 is a schematic structural diagram of an ultraviolet light monitoring device according to an embodiment of the present invention.

[0020] Figure 2 yes Figure 1Schematic diagram of the structure of the medium reflective ultraviolet fluorescent screen.

[0021] Figure 3 yes Figure 1 Schematic diagram of three shapes of medium reflective UV fluorescent screens.

[0022] Figure 4 It is a schematic diagram of the layout of a driving laser system of a hard X-ray free electron laser device that adopts the ultraviolet light monitoring device of the present invention.

[0023] Figure 5 It is a schematic diagram of the layout of a driving laser system of a soft X-ray free electron laser device that adopts the ultraviolet light monitoring device of the present invention. DETAILED DESCRIPTION

[0024] Below, in conjunction with the accompanying drawings, a preferred embodiment of the present invention is given, and a detailed description is given to enable a better understanding of the functions and characteristics of the ultraviolet light monitoring device of the present invention.

[0025] First embodiment: UV monitoring device

[0026] like Figure 1 The figure shows an ultraviolet light monitoring device according to the first embodiment of the present invention, which is used to monitor the ultraviolet light in the driving laser system of a hard X-ray free electron laser device. The device comprises: a reflective ultraviolet light fluorescent screen 10, an imaging lens 20, an infrared CCD camera 30 and a computer 40 arranged in sequence along the optical path of the ultraviolet light. Figure 1 and Figure 2 As shown, the reflective ultraviolet fluorescent screen 10 includes a fluorescent film 11, a visible light high reflective film 12 and a substrate 13 arranged in sequence. In this embodiment, the substrate 13 is made of sapphire.

[0027] Thus, incident ultraviolet light strikes the surface of fluorescent film 11 and is absorbed by it. The ultraviolet light (applicable in the wavelength range of 190nm-380nm) is then converted by fluorescent film 11 into visible light fluorescence (wavelength 619nm). The highly reflective visible light film almost completely reflects this fluorescence, with a reflectivity exceeding 99%. The light is then imaged by imaging lens 20 onto infrared CCD camera 30, and finally, computer 40 collects and processes data about the light spot. The incident ultraviolet light from a hard X-ray free electron laser device has a central wavelength of 257.5nm and a bandwidth of <1nm, making it suitable for use in the ultraviolet light monitoring device of the present invention.

[0028] The fluorescent film 11 is composed of vanadium yttrium europium phosphate phosphor and a binder. The vanadium yttrium europium phosphate phosphor has a higher conversion efficiency, allowing it to absorb and convert most ultraviolet light into visible light fluorescence. This allows for highly sensitive measurement of the spot shape, distribution, and position of ultraviolet light in the 190-380nm band, thereby addressing the low sensitivity of ultraviolet light monitoring in existing technologies and facilitating low-light monitoring.

[0029] The mass ratio of vanadium yttrium europium phosphate phosphor and binder is m, 3≤m≤20. The smaller the mass ratio, the stronger the luminous brightness of the fluorescent screen, and the more conducive to weak light detection. When the ultraviolet light power used for monitoring is less than 1 microwatt, in order to obtain the strongest luminous brightness, the optimal mass ratio is m=3. When the ultraviolet light power used for monitoring is greater than 1 microwatt, 3≤m≤20. In practical applications, if the mass ratio m is too small, it will lead to excessive phosphor particles, and the binder will not be able to fully wrap and disperse the particles, forming agglomerates or precipitation. In addition, the binder is insufficient, the film forming property is poor, the mechanical strength of the film layer is low, and it is easy to crack or fall off. In order to take into account both the luminous intensity of the fluorescent screen and the uniformity and adhesion of the fluorescent film, when the mass ratio m is small, the coating process (such as spin coating speed, baking temperature, etc.) can be optimized to enhance the density of the film layer. Vanadium yttrium europium phosphate phosphor (Y(P,V)O4:Eu³⁺) is based on europium ions (i.e. Eu 3+ ) as a YVO4 material for the luminescence center. Preferably, the median particle size D50 of the vanadium yttrium europium phosphate phosphor is 1-10 μm, and the particle size distribution coefficient of the vanadium yttrium europium phosphate phosphor is 0.7-1.5. Due to the small median particle size and the spherical shape of the particles, the roughness is minimal. The thickness of the fluorescent film 11 is 0.02-0.08 mm, with an accuracy of 0.01 mm.

[0030] The fluorescent film 11 is made by mixing vanadium yttrium europium phosphate phosphor and a binder in a specific mass ratio. The mixture is then applied by doctor blade coating onto a substrate 13 pre-coated with a visible light high-reflective film 12. The film is then placed in a 200-300°C oven for 5-15 hours. After the organic mixture in the binder has fully volatilized, the film is then sintered in a 500-700°C furnace for 10-30 minutes. The mixing method is selected from at least one of mechanical stirring, centrifugal dispersion, or ultrasonic mixing. Because the particles are spherical, they are first dissolved in a binder, then uniformly mixed using at least one of mechanical stirring, centrifugal dispersion, or ultrasonic mixing, and then sintered, resulting in a dense coating. The organic mixture is the organic solvent and binder in the adhesive. The organic mixture maintains the film structure during the coating and drying stages and is subsequently removed through high-temperature treatment. The organic solvent, such as ethanol, acts as a liquid medium for dissolving or dispersing the phosphor and binder. It evaporates during the drying stage (200–300°C). The organic binder is used to bond dissimilar materials. Specifically, polymers or resins that provide a temporary bond, such as polyethylene oxide (PEO), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), or epoxy resin, are used. These materials decompose or carbonize during the high-temperature sintering stage (500–700°C) and eventually evaporate or ablate completely, preventing residual impurities from affecting the performance of the phosphor film. Polyethylene oxide (PEO) is readily soluble in water and does not ionize in water. Its aqueous solution is non-ionic, has a low thermal decomposition temperature, sufficient and stable viscosity, and good coating properties, making it widely used. Therefore, the fluorescent film 11 is manufactured by using vanadium yttrium phosphate europium fluorescent powder and adhesive through a sintering process.

[0031] like Figure 3 As shown, the shape and size of the substrate 13 depend on the application and can be round, square, or rectangular, with a thickness ranging from 0.05 mm to 1 mm. At room temperature, sapphire has a thermal conductivity of approximately 20 W / mK, which is better than Ce:YAG (13 W / mK), significantly mitigating the adverse effects of heat accumulation on the material's luminescence properties. Furthermore, sapphire is heat-resistant, hard, and chemically stable, making it a suitable substrate material for fluorescent films, ensuring the mechanical and optical performance of the reflective UV fluorescent screen.

[0032] In this embodiment, the reflectivity of the visible light highly reflective film 12 is above 99%. The material of the visible light highly reflective film 12 is a dielectric film. Dielectric films can be produced using commonly used dielectric film technology in the art. The reflection wavelength range of dielectric films is typically broadband, with a reflection bandwidth typically ranging from 400 nm to 750 nm. Furthermore, the visible light highly reflective film 12 can be single-wavelength. Single-wavelength (or narrow-band) dielectric highly reflective films often have a bandwidth of only ±10 nm to ±20 nm, but can achieve a reflectivity of over 99.8%. In practice, single-wavelength or narrow-band dielectric highly reflective films have higher reflectivity and are more advantageous, but the coating leads to higher prices.

[0033] In hard X-ray free electron laser devices, pulsed UV lasers are characterized by constant energy per pulse. Therefore, higher repetition rates increase their power. Pulsed UV lasers have the physical properties of a low damage threshold and absorption-induced thermal effects. Therefore, when switching to a high frequency, high-power, short-pulse UV light is continuously applied to the existing YAG target. This long-term exposure can cause a halo on the YAG surface, affecting the spot distribution and reducing detection sensitivity. The YAG target needs to be relocated or replaced with a new one. The reflective UV fluorescent screen 10 manufactured by the present invention has a dense coating that provides a more uniform distribution. Furthermore, sapphire is a good thermal conductor, quickly dissipating heat generated by UV laser irradiation on the screen, preventing heat accumulation. Therefore, the screen can withstand high-power direct irradiation for long periods of time without carbonization or other surface damage.

[0034] In this embodiment, a circular sapphire sheet with a thickness of 0.35 mm and a diameter of 50 mm is selected as the substrate for the fluorescent film. The fluorescent film is 0.05 mm thick, and the visible light highly reflective film is 0.002 mm thick, resulting in a total thickness of 0.402 mm for the reflective UV fluorescent screen 10. In other embodiments, the visible light highly reflective film can be a single-layer structure or a multi-layer structure. The thickness of a single-layer structure is 100-200 nm, and the thickness of a multi-layer structure is 1-5 μm.

[0035] The effective luminous surface diameter of the reflective UV fluorescent screen 10 is 45.7 mm. The center height of the zero-order light transmitted by the first grating is 91.8 mm, and the spot diameter is 13 mm. The reflective UV fluorescent screen 10 is a circular disc with a diameter of 50.8 mm and a thickness of 0.402 mm (i.e., according to industry practice, the effective aperture is ≥ 90%, the actual diameter is 50.8 mm, and the effective luminous surface diameter is equal to 50.8 mm × 0.9 ≈ 45.7 mm). The reflective UV fluorescent screen 10 is mounted on a Thorlabs two-dimensional mirror mount with a diameter of 50.8 mm, but it can also be mounted on a one-dimensional mirror mount with a diameter of 50.8 mm. The optimal optical path is one in which the center height of the transmitted zero-order light is at the same level as the center of the reflective UV fluorescent screen 10, the imaging lens 20, and the infrared CCD camera 30. Since the diameter of the reflective UV fluorescent screen 10 is 50.8 mm, which is larger than the diameter of the zero-order light of 13 mm, the center height of the reflective UV fluorescent screen 10 does not need to be consistent with the center height of the zero-order light. It only needs to ensure that the zero-order light is not cut off when it reaches the reflective UV fluorescent screen 10 and is a complete light spot.

[0036] In this embodiment, the incident ultraviolet light (i.e., the zero-order ultraviolet laser pulse train) and the infrared CCD camera 30 are both located on the front surface of the reflective ultraviolet fluorescent screen 10. The incident ultraviolet light forms an angle of 90°±1° with the front surface of the reflective ultraviolet fluorescent screen 10; the infrared CCD camera 30 forms an angle of 85°±2.5° with the front surface of the reflective ultraviolet fluorescent screen 10. The incident ultraviolet light is incident perpendicularly on the fluorescent screen to ensure more accurate measurement of the spot size and to prevent oblique incidence from increasing the size of the ultraviolet spot projected onto the fluorescent screen, affecting measurement accuracy. In other embodiments, if the measured spot parameter is the spot position, the incident ultraviolet light does not need to be incident perpendicularly on the reflective ultraviolet fluorescent screen 10; it can be incident perpendicularly or at a small angle. For example, the incident ultraviolet light forms an angle of 85°±2.5° with the front surface of the reflective ultraviolet fluorescent screen, and the infrared CCD camera forms an angle of 90°±1° with the front surface of the reflective ultraviolet fluorescent screen.

[0037] The distance between the infrared CCD camera 30 and the reflective UV fluorescent screen 10 depends on the focal length of the imaging lens 20 used and the detector size of the infrared CCD camera 30. In this embodiment, the imaging lens 20 uses a C lens with a focal length of 250 mm, and the pixel size of the infrared CCD camera 30 is 4.8 μm × 4.8 μm.

[0038] As a result, the 257.7nm ultraviolet light output by the driving laser system is perpendicularly incident on the surface of fluorescent film 11 and absorbed by it. Under the excitation of the 257.7nm ultraviolet light, fluorescent film 11 emits an intense red light with a main emission peak at 619nm and a relative brightness greater than 100. The 257.7nm ultraviolet light spot is converted into a fluorescent light spot with a wavelength of 619nm in the visible light band. This is then imaged by imaging lens 20 onto infrared CCD camera 30. Finally, a computer collects and processes the light spot data to obtain its parameters, such as its shape, distribution, and center position.

[0039] The UV monitoring device of the present invention is particularly suitable for monitoring weak UV light and is therefore particularly well-suited for use in devices such as hard X-ray free electron lasers and soft X-ray free electron lasers, but is not limited to these two types of devices. Any device that requires UV monitoring, such as one that needs to detect the distribution and position of UV light spots, can be applied to the UV monitoring device of the present invention.

[0040] Second embodiment: UV monitoring device

[0041] According to a second embodiment of the present invention, the structures of the imaging lens, infrared CCD camera, and computer of the UV monitoring device are consistent with those of the prior art, differing only in the specific structure of the reflective UV fluorescent screen. The reflective UV fluorescent screen comprises only a fluorescent film and a substrate. The substrate is aluminum or stainless steel, and the fluorescent film is formed by precipitating a mixture of vanadium yttrium phosphate europium phosphor and an organic solvent. Furthermore, a highly reflective visible light film may be placed between the fluorescent film and the substrate to reflect most visible light.

[0042] Thus, a reflective UV fluorescent screen is manufactured by mixing high-luminous-efficiency, high-color-rendering yttrium europium vanadium phosphate phosphor with an organic solvent and then precipitating it onto a substrate. This allows for highly sensitive detection of UV light spots at low frequencies and low powers. However, this type of screen is susceptible to damage and has poor surface roughness, which affects the accuracy of the actual UV light spot distribution. In this embodiment, the screen is not manufactured using sintering because sintering would cause the phosphor to fuse with the substrate material. Using high-temperature-resistant sapphire as the substrate prevents this fusion.

[0043] Application Example 1: Ultraviolet light monitoring device for hard X-ray free electron laser device

[0044] like Figure 4As shown, the hard X-ray free electron laser device realized based on the ultraviolet light monitoring device described above is a device that is 3.4 kilometers long. The hard X-ray free electron laser device includes a driving laser system 100. Among them, the driving laser system 100 includes an ytterbium-doped fiber laser 101 and a frequency quadrupling device 102 arranged in sequence, and the central wavelength of the ytterbium-doped fiber laser is 1030nm. In addition, the driving laser system also includes transverse and longitudinal shaping, image transmission devices, and various monitoring and diagnostic devices. The ultraviolet light monitoring device of the present invention is only a small part of various monitoring and diagnostic devices, which is used for weak light monitoring.

[0045] Therefore, the ultraviolet light monitoring device of the present invention can realize high-sensitivity weak light monitoring, which can ensure the transmission efficiency of the entire driving laser system, reduce the splitting required for ultraviolet light monitoring, and make the light energy transmitted to the photocathode greater.

[0046] The hard X-ray free electron laser apparatus also includes an electron gun, which includes a photocathode for generating an initial electron beam. In this embodiment, the photocathode is cesium telluride (Cs2Te). Cesium telluride (Cs2Te) photocathodes only have high quantum efficiency in the ultraviolet band. Therefore, a frequency quadrupling device is required to convert 1030nm infrared light into 257.7nm ultraviolet light using a nonlinear crystal. To produce a high-brightness, high-quality electron beam, the 257.7nm ultraviolet light obtained through frequency quadrupling has a Gaussian distribution in both the longitudinal and transverse directions, which is not conducive to optimizing the electron beam emittance. Therefore, spatiotemporal shaping is required to achieve a near-uniform longitudinal and transverse distribution of the ultraviolet laser light. Image transfer is then used to image the shaped laser distribution onto the photocathode surface.

[0047] In this embodiment, the entire transmission optical path from the quadrupling device that outputs ultraviolet light to the photocathode, which drives the laser system, is nearly 40 meters long, requiring 14 meters of vacuum transmission across a floor. The quadrupling device outputs ultraviolet light with a diameter of 2.6 mm and a wavelength of 257.7 nm. This light is then expanded by a 5x beam expander to a 13 mm beam before being transmitted to a grating pulse width device (i.e., a grating stretching pair) for longitudinal shaping.

[0048] To ensure that the entire driver laser system 100 remains in optimal condition during beam modulation, and to promptly identify the source of any malfunction, four UV monitoring devices 200 of the present invention are deployed at various locations along the optical path between the quadrupling frequency device and the photocathode. These devices monitor the expanded beam spot, the spot after longitudinal grating broadening, the virtual cathode, and the virtual injection mirror at different locations. In other embodiments, at least one UV monitoring device 200 as described above is deployed along the optical path between the quadrupling frequency device and the photocathode.

[0049] To ensure transmission efficiency, this embodiment does not add a beam splitter to the main optical path to monitor the expanded light. Instead, the UV monitoring device described in the present invention monitors the zero-order light transmitted through the first grating G1 of the grating expansion pairs G1 and G2, or directly utilizes the backlight of the reflector for weak light monitoring. This monitors the distribution of the expanded light spot and its position changes in real time, thus achieving expanded light spot monitoring. Specifically, the UV monitoring device 200 of the present invention is located in the transmission direction of the first grating G1 and includes a reflective UV fluorescent screen, an imaging lens, and a first infrared CCD camera CCD1.

[0050] Furthermore, a wedge is placed in the transmission optical path downstream of the grating stretcher, enabling low-light monitoring through reflected light from the wedge. Since the light spot size increases downstream of the grating stretcher, the optical power per unit area is lower, making detection more difficult. At certain locations along the optical path, ultraviolet light cannot be detected through monitoring using light transmitted behind the reflector. Therefore, a wedge is placed in the main optical path for spectroscopic monitoring. Specifically, the ultraviolet light monitoring device 200 of the present invention is positioned in the direction of reflection from the wedge and includes a reflective ultraviolet fluorescent screen, an imaging lens, and a second infrared CCD camera (CCD2).

[0051] In this embodiment, the incident UV light (i.e., the zero-order UV laser pulse train) and the infrared CCD camera 30 are both located on the front surface of the reflective UV fluorescent screen 10. The incident UV light forms an angle of 90°±1° with the front surface of the reflective UV fluorescent screen 10; the infrared CCD camera 30 forms an angle of 85°±2.5° with the front surface of the reflective UV fluorescent screen 10. The incident UV light is perpendicularly incident on the fluorescent screen to ensure more accurate spot size measurement and prevent oblique incidence from enlarging the UV spot on the screen, which could affect measurement accuracy.

[0052] In this embodiment, the imaging lens 20 uses a C lens with a focal length of 250mm, and the infrared CCD camera 3 has a pixel size of 4.8μm x 4.8μm. The first grating G1 transmits and outputs 257.7nm ultraviolet light as zero-order light, which is perpendicularly incident on the surface of the fluorescent film and absorbed by the film. Under the excitation of the 257.7nm ultraviolet light, the fluorescent film emits a strong red light with a main emission peak at 619nm and a relative brightness greater than 100. The 257.7nm ultraviolet light spot is converted into a 619nm visible light spot, which is then imaged by the imaging lens onto the infrared CCD camera. Finally, a computer collects and processes the data of the light spot.

[0053] Similarly, the implementation process of grating broadening rear spot monitoring, virtual cathode, and virtual injection mirror monitoring is the same as above and will not be introduced in detail.

[0054] Application Example 2: Ultraviolet light monitoring device for soft X-ray free electron laser device

[0055] like Figure 5 As shown, the soft X-ray free electron laser device implemented based on the ultraviolet light monitoring device described above includes a driving laser system 100'. The driving laser system 100' comprises a laser 101' and a frequency tripler 102' arranged in sequence. This system outputs 266nm ultraviolet laser light through frequency tripler. This light is then broadened to 10ps by a grating stretcher and transmitted to the first motorized mirror mount M1. This light is then transmitted to the photocathode P1 via a shaping aperture A1 and an image transmission optical path. Within the image transmission optical path of the driving laser system 100, a position feedback device is constructed using a combination of two beam splitters B1 and B2, two motorized mirror mounts M1 and M2, and two sets of ultraviolet light monitoring devices 200. Specifically, a beam splitter is positioned downstream of each motorized mirror mount to be adjusted. The beam splitter is used to partially reflect the ultraviolet light toward one of the ultraviolet light monitoring devices 200, thereby forming a position feedback device.

[0056] The laser drive system also includes transverse and longitudinal shaping, image transmission devices, and various monitoring and diagnostic devices. The position feedback device of the present invention is only a small part of these various monitoring and diagnostic devices. It is used for position feedback detection. The purpose of position feedback is to reduce the jitter of ultraviolet light transmitted over long distances to the photocathode due to mechanical vibration, ambient temperature and humidity. This is achieved through measurement and feedback and correction through the high-speed piezoelectric motorized mirror frame.

[0057] In this embodiment, when the UV monitoring device 200 is used to construct a position feedback device, it is only used to detect the center position of the light spot. This application does not specifically require that the incident UV light be incident perpendicularly on the reflective UV fluorescent screen 10; it can be incident perpendicularly or at a slight angle. In this embodiment, due to space limitations on the optical platform, the UV light incident on the UV monitoring device 200 forms an angle of 85°±2.5° with the front surface of the reflective UV fluorescent screen 10, and the infrared CCD camera forms an angle of 90°±1° with the front surface of the fluorescent screen.

[0058] Thus, a 266nm wavelength, 10mm width ultraviolet laser beam from the grating stretcher passes through the first motorized mirror frame M1, then through the shaping aperture A1. A small portion of the light is reflected by the front surface of the first beam splitter B1 and strikes the reflective ultraviolet fluorescent screen 10 of the ultraviolet light monitoring device 200. Excited by the 266nm laser beam, the ultraviolet fluorescent screen emits 619nm infrared light, which is imaged by the imaging lens onto the first infrared CCD camera CCD1'. A computer then collects and processes the data. The center height of the incident ultraviolet light spot coincides with the center height of the first motorized mirror frame M1, shaping aperture A1, first beam splitter B1, reflective ultraviolet fluorescent screen 10, imaging lens, and first infrared CCD camera CCD1'. After grating expansion, the majority of the ultraviolet light passes through the first beam splitter B1 and continues to the second motorized mirror mount M2, then to the second beam splitter B2. A small portion of the light is reflected by the front surface of the second beam splitter B2 onto the reflective ultraviolet fluorescent screen 10. Under the excitation of the 266nm laser, a 619nm infrared light is emitted. This light is imaged by the imaging lens onto the second infrared CCD camera CCD2', and then the data is collected and processed by a computer. The center height of the transmitted ultraviolet light transmitted to the second motorized mirror mount M2 is consistent with the center height of the second motorized mirror mount M2, the second beam splitter B2, the reflective ultraviolet fluorescent screen 10, the imaging lens, and the second infrared CCD camera CCD2'.

[0059] Thus, two ultraviolet light monitoring devices 200 are used to realize position feedback, wherein the two ultraviolet light monitoring devices 200 realize detection and measurement of the center position of the light spot, and realize an efficient feedback loop through the data collected by the ultraviolet light monitoring device 200, and can adjust the motorized mirror frame to realize position feedback and correction, thereby dynamically adjusting and calibrating the optical path in real time, eliminating mechanical vibration, position changes introduced by temperature and humidity changes, ensuring the position stability of the ultraviolet laser reaching the photocathode, and being able to obtain the spatial position, intensity distribution and morphological information of the light beam. Specifically, it is necessary to use an ultraviolet light monitoring device 200 to detect the value of the pixel in the x and y directions corresponding to the center position of the light spot, and then adjust it through the motorized mirror frame (motorized mirror) to keep the center position of the light spot at the initial center position. When the feedback control software detects that the infrared CCD cameras 30 (infrared CCD camera 30 such as Figure 1 ,exist Figure 3 When the X, Y direction deviation of the light spot center of the first infrared CCD camera CCD1' and the second infrared CCD camera CCD2' is 1-5 pixels, the electric mirror frame will be adjusted to make the X, Y direction deviation of the light spot center of the first infrared CCD camera CCD1' and the second infrared CCD camera CCD2' within 1 pixel, thereby ensuring that the jitter of the light spot reaching the photocathode position is less than 10μm.

[0060] Specifically, the first motorized mirror mount M1 is used to adjust the center position of the light spot on the first infrared CCD camera CCD1' in the ultraviolet light monitoring device 200; the second motorized mirror mount M2 is used to adjust the center position of the light spot on the second infrared CCD camera CCD2' in the ultraviolet light monitoring device. When the center position of the light spot on the first infrared CCD camera CCD1' deviates by 1-5 pixels, the first motorized mirror mount M1 automatically adjusts the position of the light spot on the first infrared CCD camera CCD1' to within 1 pixel of the initial center position in both the x and y directions. Similarly, when the center position of the light spot on the second infrared CCD camera CCD2' deviates by 1-5 pixels, the second motorized mirror mount M2 automatically adjusts the position of the light spot on the second infrared CCD camera CCD2' to within 1 pixel of the initial center position in both the x and y directions. The two infrared CCD cameras 30 use the downstream second infrared CCD camera CCD2' as the primary feedback CCD for correction. In this way, when UV is transmitted over long distances, the center position of the UV light on the photocathode can be kept unchanged through the position feedback device.

[0061] In the position feedback device corresponding to the shaping aperture A1, the distance between the reflective UV fluorescent screen 10 of the UV monitoring device 200 and the beam splitter (i.e., the first beam splitter B1) is equal to the distance from the shaping aperture A1 to the beam splitter (i.e., the first beam splitter B1). In the position feedback device corresponding to the photocathode, the distance between the reflective UV fluorescent screen 10 of the UV monitoring device 200 and the beam splitter (i.e., the second beam splitter B2) is equal to the distance from the photocathode P1 to the beam splitter (i.e., the second beam splitter B2).

[0062] The ultraviolet light monitoring device of the present invention uses vanadium yttrium europium phosphate phosphor to produce a fluorescent film. The vanadium yttrium europium phosphate phosphor has high luminous efficiency, good color rendering, stable chemical properties, can withstand high temperature and strong ultraviolet radiation, has better luminous brightness, and the red light intensity is more easily collected by an infrared CCD camera. The ultraviolet fluorescent screen made of it has the characteristics of high brightness and high-definition display, so it has high detection sensitivity and is very suitable for weak light monitoring of ultraviolet light in the 190-380nm band, and is suitable for weak ultraviolet light monitoring application scenarios in the accelerator field.

[0063] In addition, the present invention provides a visible light high reflective film between the fluorescent film and the substrate, so that most of the fluorescence in the visible light band is reflected to the infrared CCD camera, thereby further improving the detection sensitivity of weak light monitoring of ultraviolet light.

[0064] In addition, the reflective ultraviolet fluorescent screen includes a sapphire substrate and a fluorescent film on its front surface. The fluorescent film is composed of vanadium yttrium phosphate europium phosphor and an adhesive. The chemical properties of the vanadium yttrium phosphate europium phosphor are stable and because it is a small spherical particle, the coating is dense, the distribution is more uniform, and the consistency is good. The reflective ultraviolet fluorescent screen made in this way has a simple structure and low cost. Because the coating is dense and the distribution is more uniform, and the sapphire is easy to conduct heat, it can quickly take away the heat generated by UV laser irradiation on the fluorescent screen, preventing heat accumulation, so that it can withstand high-power direct irradiation for a long time without carbonization or other damage to the screen surface.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Various modifications are possible. In other words, any simple, equivalent changes and modifications made in accordance with the claims and description of the present invention are within the scope of protection of the patent claims. Anything not fully described in this invention constitutes conventional technology.

Claims

1. An ultraviolet light monitoring device, characterized in that: The invention comprises a reflective ultraviolet fluorescent screen, an imaging lens, an infrared CCD camera and a computer arranged in sequence along the optical path of ultraviolet light, and a fluorescent film and a substrate arranged in sequence on the reflective ultraviolet fluorescent screen; the fluorescent film contains yttrium europium vanadium phosphate phosphor powder, and the yttrium europium vanadium phosphate phosphor powder is used to convert ultraviolet light into fluorescence in the visible light band.

2. The ultraviolet light monitoring device according to claim 1, characterized in that: A visible light high reflection film is provided between the fluorescent film and the substrate.

3. The ultraviolet light monitoring device according to claim 1, characterized in that: The substrate is made of sapphire, and the fluorescent film is composed of vanadium yttrium phosphate europium fluorescent powder and an adhesive.

4. The ultraviolet light monitoring device according to claim 3, characterized in that: The mass ratio of the vanadium yttrium europium phosphate phosphor to the binder is m, 3≤m≤20.

5. The ultraviolet light monitoring device according to claim 3, characterized in that: The fluorescent film is made by uniformly mixing vanadium yttrium europium phosphate phosphor and adhesive, coating it on the substrate by blade coating, and then transferring it to a 200-300°C oven and placing it for 5-15 hours. After the organic mixture in the adhesive is fully volatilized, it is sent to a 500-700°C high-temperature furnace and sintered for 10-30 minutes.

6. The ultraviolet light monitoring device according to claim 5, characterized in that: The mixing method is selected from at least one of mechanical stirring, centrifugal dispersion or ultrasonic mixing.

7. The ultraviolet light monitoring device according to claim 1, characterized in that: The substrate is aluminum or stainless steel, and the fluorescent film is formed by mixing vanadium yttrium phosphate europium fluorescent powder and an organic solvent and then precipitating the mixture.

8. The ultraviolet light monitoring device according to claim 1, characterized in that: The median particle size D50 of the vanadium yttrium europium phosphate phosphor is 1-10 μm, and the particle size dispersion distribution coefficient of the vanadium yttrium europium phosphate phosphor is 0.7-1.

5.

9. The ultraviolet light monitoring device according to claim 1, characterized in that: The thickness of the fluorescent film is 0.02-0.08 mm, and the thickness of the substrate is between 0.05 mm and 1 mm.

10. The ultraviolet light monitoring device according to claim 1, characterized in that: The incident ultraviolet light and the infrared CCD camera are both located on the front surface of the reflective ultraviolet fluorescent screen; The incident ultraviolet light forms an angle of 90°±1° with the front surface of the reflective ultraviolet fluorescent screen, and the infrared CCD camera forms an angle of 85°±2.5° with the front surface of the reflective ultraviolet fluorescent screen; or, the incident ultraviolet light forms an angle of 85°±2.5° with the front surface of the reflective ultraviolet fluorescent screen, and the infrared CCD camera forms an angle of 90°±1° with the front surface of the reflective ultraviolet fluorescent screen.

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