An ultraviolet light monitoring device

Abstract

The present application relates to a kind of ultraviolet light monitoring devices, including the reflective ultraviolet light fluorescent screen, imaging lens, infrared CCD camera and computer in turn arranged along the light path of ultraviolet light, reflective ultraviolet light fluorescent screen is arranged in turn fluorescent film and substrate;The fluorescent film contains vanadium phosphorus yttrium europium fluorescent powder, vanadium phosphorus yttrium europium fluorescent powder is used to convert ultraviolet light into the fluorescent of visible light band.The ultraviolet light monitoring device of the present application uses vanadium phosphorus yttrium europium fluorescent powder to make fluorescent film, vanadium phosphorus yttrium europium fluorescent powder high luminous efficiency, good color rendering, chemical stability, can withstand high temperature and strong ultraviolet light radiation, luminous brightness is better and light intensity is more easily collected by infrared CCD camera, so detection sensitivity is high, very suitable for 190-380nm waveband ultraviolet light weak light monitoring, applicable to accelerator field weak ultraviolet light monitoring application scene.

Description

TECHNICAL FIELD

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

[0002] X-ray free electron laser is a large scientific research device based on electron linear accelerator, which can produce super-high brightness, ultra-short pulse, wavelength adjustable coherent X-ray radiation, and has very wide and extremely important applications in physics, chemistry, materials, life science and other fields. The driving laser system is an important part of the X-ray free electron laser, which produces high-brightness electron beams by acting on the photocathode electron gun at the front end of the accelerator. The driving laser system is the key part that determines the quality of the electron beam.

[0003] In order to ensure that the driving laser system is in the best state during the beam tuning operation, the laser characteristics at different positions need to be monitored during the operation of the device, including real-time detection and feedback of the laser spot distribution and position of the driving laser virtual cathode, virtual injection mirror, and different monitoring points of the driving laser transmission optical path. At present, cesium telluride (Cs2Te) is used as the photocathode material in the X-ray free electron laser device. The cesium telluride (Cs2Te) photocathode is a high quantum efficiency photocathode material responding in the ultraviolet band, with quantum efficiency > 0.5% and lifetime (time required for quantum efficiency to decay to 1 / e) > 10 days. Although the high quantum efficiency photocathode material can reduce the power requirement of the driving laser, the lifetime of cesium telluride is limited, and the replacement of the photocathode is also a tedious and complex work. Therefore, the power of the ultraviolet laser of the driving laser still needs to be as large as possible, and the driving laser can also work normally when the quantum efficiency of cesium telluride is low. In addition, the transmittance of optical components in the ultraviolet band is difficult to be greater than 95%, and the reflectivity is difficult to be 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 monitoring ultraviolet laser power is generally in the order of microwatt or even nanowatt, which brings many difficulties to the monitoring.

[0004] The prior art of ultraviolet light monitoring has two kinds: one is direct measurement method, which uses ultraviolet CCD camera to image monitor ultraviolet light. The price of ultraviolet CCD is expensive, and the frequency needs to be changed frequently during beam tuning, and the light power hitting the ultraviolet CCD will change, so the ultraviolet CCD is easy to be damaged. This technology is not suitable for the application of ultraviolet light monitoring in the field of accelerators. The second is indirect measurement method, which converts ultraviolet light into fluorescence through UV converter for monitoring. The indirect measurement method combined with Ce:YAG fluorescent screen and infrared CCD camera is limited by the luminous efficiency and color rendering performance of Ce:YAG. When the beam is low in frequency and power, the virtual cathode or virtual injection mirror spot cannot be seen on the infrared CCD camera, which brings many difficulties to the beam tuning work. SUMMARY

[0005] To solve the above problems in the prior art, the present application provides an ultraviolet light monitoring device to measure the spot shape, distribution and position of wide-band ultraviolet light with high sensitivity, solve 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 field of accelerators.

[0006] In order to achieve the above purpose, the present application provides an ultraviolet light monitoring device, which comprises a reflective ultraviolet light fluorescent screen, an imaging lens, an infrared CCD camera and a computer arranged in sequence along the light path of ultraviolet light. The reflective ultraviolet light fluorescent screen is arranged in sequence with a fluorescent film and a substrate; the fluorescent film contains vanadium phosphoric acid yttrium europium fluorescent powder, and the vanadium phosphoric acid yttrium europium fluorescent powder is used to convert ultraviolet light into visible light band fluorescence.

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

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

[0009] The mass ratio of the vanadium phosphoric acid yttrium europium fluorescent powder and the adhesive is m, and 3≤m≤20.

[0010] The fluorescent film is made by uniformly mixing the vanadium phosphoric acid yttrium europium fluorescent powder and the adhesive, coating on the substrate by scraping method, then transferring to a 200-300℃ oven for 5-15 hours, and then sending to a 500-700℃ high temperature furnace for sintering for 10-30min.

[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 precipitating the mixture of vanadium phosphoric acid yttrium europium fluorescent powder and organic solvent.

[0013] The vanadium yttrium phosphate europium fluorescent powder has a median particle size D50 of 1-10 microns, and a particle size discrete distribution coefficient of 0.7-1.5.

[0014] The fluorescent film has a thickness of 0.02-0.08 mm, and the substrate has a thickness of 0.05-1 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 monitoring device of the present application adopts vanadium yttrium phosphate europium fluorescent powder to make the fluorescent film, the vanadium yttrium phosphate europium fluorescent powder has high luminous efficiency, good color rendering property, stable chemical property, can withstand high temperature and strong ultraviolet radiation, has better luminous brightness, and the red light intensity is easier to be collected by the infrared CCD camera, the ultraviolet fluorescent screen made of the vanadium yttrium phosphate europium fluorescent powder has the characteristics of high brightness and high definition display, so the detection sensitivity is high, and it is very suitable for weak light monitoring of ultraviolet light in the 190-380 nm wave band, and is suitable for weak ultraviolet monitoring application scenarios in the field of accelerators.

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

[0018] In addition, the reflective ultraviolet fluorescent screen includes a sapphire substrate and a fluorescent film on the front surface thereof, the fluorescent film is composed of vanadium yttrium phosphate europium fluorescent powder and a binder, the vanadium yttrium phosphate europium fluorescent powder has stable chemical property, and because it is a spherical small particle, the coating is dense, the distribution is more uniform, and the consistency is good, the reflective ultraviolet fluorescent screen made of the vanadium yttrium phosphate europium fluorescent powder has simple structure and low cost, because the coating is dense and the distribution is more uniform, and the sapphire is easy to conduct heat, can quickly take away the heat generated by the UV laser irradiated on the fluorescent screen, prevents heat accumulation, thereby can withstand high-power direct irradiation for a long time, and will not cause screen surface damage such as carbonization. BRIEF DESCRIPTION OF DRAWINGS

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

[0020] Figure 2 is Figure 1Structure diagram of the reflecting ultraviolet light fluorescent screen.

[0021] Figure 3 Is Figure 1 Structure diagram of three shapes of the reflecting ultraviolet light fluorescent screen.

[0022] Figure 4 Is the layout diagram of the driving laser system of the hard X-ray free electron laser device using the ultraviolet light monitoring device of the application.

[0023] Figure 5 Is the layout diagram of the driving laser system of the soft X-ray free electron laser device using the ultraviolet light monitoring device of the application. DETAILED DESCRIPTION

[0024] The preferred embodiments of the application are described below in conjunction with the accompanying drawings, and the functions and features of the ultraviolet light monitoring device of the application are better understood by the detailed description.

[0025] First embodiment: ultraviolet light monitoring device

[0026] As Figure 1 The ultraviolet light monitoring device of the first embodiment of the application is used for monitoring the ultraviolet light in the driving laser system of the hard X-ray free electron laser device, which comprises, in sequence along the light path of the ultraviolet light, a reflecting ultraviolet light fluorescent screen 10, an imaging lens 20, an infrared CCD camera 30 and a computer 40. Figure 1 And Figure 2 The reflecting ultraviolet light fluorescent screen 10 comprises, in sequence, a fluorescent film 11, a visible light high reflection film 12 and a substrate 13. In this embodiment, the material of the substrate 13 is sapphire.

[0027] Thus, the incident ultraviolet light is incident on the surface of the fluorescent film 11, is absorbed by the fluorescent film 11, and then the ultraviolet light (wavelength range of 190nm-380nm) is converted into fluorescent light (wavelength of 619nm) in the visible light waveband by the fluorescent film 11, and almost all of the fluorescent light in the visible light waveband is reflected by the visible light high reflection film, and the reflectivity of the visible light high reflection film is above 99%. Then, the imaging lens 20 is used for imaging on the infrared CCD camera 30, and finally the computer 40 is used for data acquisition and processing of the light spot. The central wavelength of the incident ultraviolet light of the hard X-ray free electron laser device is 257.5nm, and the bandwidth is <1nm, so the ultraviolet light monitoring device of the application is suitable.

[0028] The fluorescent film 11 is composed of yttrium vanadate phosphor and adhesive. The conversion efficiency of yttrium vanadate phosphor is higher, so that most of the ultraviolet light can be absorbed and converted into fluorescent light in the visible light band, and the spot shape, distribution and position of the ultraviolet light in the 190-380nm band can be measured with high sensitivity, thereby solving the problem of low sensitivity of ultraviolet light monitoring in the prior art, and facilitating weak light monitoring.

[0029] The mass ratio of yttrium vanadate phosphor to adhesive is m, 3≤m≤20. The smaller the mass ratio, the stronger the luminous intensity of the fluorescent screen, and the more conducive to weak light detection. When the power of the monitoring ultraviolet light is less than 1 micro watt, in order to obtain the strongest luminous intensity, the optimal mass ratio is m=3. When the power of the monitoring ultraviolet light is greater than 1 micro watt, 3≤m≤20. In practical application, too small mass ratio m will result in too many fluorescent powder particles, and the adhesive is not enough to fully wrap and disperse the particles, forming agglomeration or precipitation. In addition, the adhesive 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 balance the luminous intensity of the fluorescent screen and the film forming uniformity and adhesion of the fluorescent film, when the mass ratio m is small, the film layer density can be enhanced by optimizing the coating process (such as spin coating speed, baking temperature, etc.). Yttrium vanadate phosphor (Y(P,V)O4:Eu³⁺) is a YVO4 substance with europium ions (Eu³⁺) as the light center. Preferably, the median particle size D50 of the yttrium vanadate phosphor is 1-10μm, and the particle size dispersion distribution coefficient of the yttrium vanadate phosphor is 0.7-1.5. Because the median particle size is small and spherical, the roughness is small. The thickness of the fluorescent film 11 is 0.02-0.08mm, and the precision is 0.01mm. 3+ )as the light center. Preferably, the median particle size D50 of the yttrium vanadate phosphor is 1-10μm, and the particle size dispersion distribution coefficient of the yttrium vanadate phosphor is 0.7-1.5. Because the median particle size is small and spherical, the roughness is small. The thickness of the fluorescent film 11 is 0.02-0.08mm, and the precision is 0.01mm.

[0030] The fluorescent film 11 is made by mixing the yttrium vanadate phosphor and the adhesive in a certain mass ratio, coating the mixture on the substrate 13 with a high-reflective visible light film 12 pre-plated on it by using a doctor blade method, then transferring it to an oven at 200-300°C and placing it for 5-15 hours, and then sending it to a high-temperature furnace at 500-700°C for sintering for 10-30 minutes. The mixing method is at least one of mechanical stirring, centrifugal dispersion or ultrasonic mixing. Because the particles are spherical, the mixture is dissolved in the adhesive and then mixed uniformly by using at least one of mechanical stirring, centrifugal dispersion or ultrasonic mixing, and then sintered, so that the coating is dense. The organic mixture is the organic solvent and the organic binder in the adhesive. The organic mixture maintains the film structure during the coating and drying stages and is removed by high-temperature treatment. The organic solvent is used as a liquid medium for dissolving or dispersing the fluorescent powder and the adhesive, such as ethanol, which volatilizes during the drying stage (200-300°C). The organic binder is used to bond heterogeneous materials, and can be a polymer or a resin that provides temporary bonding, such as polyethylene oxide (PEO), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP) or epoxy resin. These substances decompose or carbonize during the high-temperature sintering stage (500-700°C) and eventually volatilize or ablate completely, avoiding the presence of impurities that affect the performance of the fluorescent film. Polyethylene oxide (PEO) is easily 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, good coating performance, and has been widely used. Therefore, the fluorescent film 11 is made by using a sintering process with the yttrium vanadate phosphor and the adhesive.

[0031] As shown in Figure 3 The shape and size of the substrate 13 depend on the application and can be circular, square or rectangular, with a thickness of 0.05mm to 1mm. At room temperature, the thermal conductivity of sapphire is about 20W / mK, which is better than that of Ce:YAG (thermal conductivity 13W / mK), which can greatly reduce the adverse effects of heat accumulation on the luminescence performance of the material. In addition, sapphire is resistant to high temperature, has high hardness and good chemical stability, and is used as a substrate material for fluorescent films, which can ensure the mechanical and optical performance of the reflective ultraviolet fluorescent screen.

[0032] In the embodiment, the reflectivity of the visible light high reflectance film 12 is above 99%. The material of the visible light high reflectance film 12 is a dielectric film. The dielectric film can be realized by using the dielectric film technology in the art, and the reflection wavelength range of the dielectric film is usually wideband, and the reflection bandwidth is usually 400 nm-750 nm. In addition, the visible light high reflectance film 12 can be single-wavelength, and the single-wavelength (or narrowband) dielectric high reflectance film has a bandwidth of only about ±10 nm-±20 nm, but the reflectivity can be as high as above 99.8%. In fact, the reflectivity of the single-wavelength or narrowband dielectric high reflectance film is higher, which is more advantageous, but the plating film leads to a higher price.

[0033] In the hard X-ray free electron laser device, the pulse ultraviolet laser has the characteristics of constant single pulse energy, so the higher the repetition frequency, the higher the power, and the pulse ultraviolet laser has the physical characteristics of low damage threshold and absorption leading to thermal effect, so when switching at a high frequency, the high-power short pulse width UV light is long-term irradiated on the existing YAG target, and long-time irradiation will cause a halo on the surface of the YAG, which will affect the spot distribution and reduce the detection sensitivity, and the YAG target needs to be replaced or directly replaced with a new one. The reflective ultraviolet fluorescent screen 10 prepared in the application has a dense coating and a more uniform distribution, and in addition, the sapphire is easy to conduct heat and can quickly take away the heat generated by the UV laser irradiated on the fluorescent screen, thereby preventing heat accumulation and being able to withstand long-term high-power direct irradiation without damaging the screen surface due to carbonization.

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

[0035] The effective emitting surface diameter of the reflective ultraviolet light 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 ultraviolet light screen 10 is a circular sheet with a diameter of 50.8 mm and a thickness of 0.402 mm (i.e., according to industry convention, the effective aperture is greater than or equal to 90%, the actual diameter is 50.8 mm, and the effective emitting surface diameter is equal to 50.8 mm x 0.9 ≈ 45.7 mm). The reflective ultraviolet light screen 10 is mounted on a two-dimensional mirror frame with a diameter of 50.8 mm from Thorlabs, and can also be mounted on a one-dimensional mirror frame with a diameter of 50.8 mm. The optimal optical path is that the center height of the transmitted zero-order light is at the same horizontal level as the reflective ultraviolet light screen 10, the imaging lens 20, and the infrared CCD camera 30. Since the diameter of the reflective ultraviolet light screen 10 is 50.8 mm, which is larger than the diameter of the zero-order light (13 mm), the center height of the reflective ultraviolet light screen 10 does not need to be consistent with the center height of the zero-order light, but only needs to ensure that the zero-order light reaches the reflective ultraviolet light screen 10 without being cut off and is a complete spot.

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

[0037] The distance between the infrared CCD camera 30 and the reflective ultraviolet light 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 um x 4.8 um.

[0038] Thus, the 257.7 nm ultraviolet light output by the driving laser system is perpendicularly incident on the surface of the fluorescent film 11 and is absorbed by the fluorescent film 11. Under the excitation of the 257.7 nm ultraviolet light, the fluorescent film 11 emits strong red light with a main emission peak of 619 nm and a relative brightness greater than 100. The 257.7 nm ultraviolet light spot is converted into a fluorescent light spot of another wavelength, i.e., the 619 nm visible light band, and then imaged on the infrared CCD camera 30 through the imaging lens 20. Finally, the light spot is subjected to data acquisition and processing by the computer to obtain the parameters of the light spot, such as the shape, distribution and central position of the light spot.

[0039] The ultraviolet light monitoring device of the present application is particularly suitable for weak ultraviolet light monitoring and is particularly suitable for application in hard X-ray free electron laser devices, soft X-ray free electron laser devices and the like, and is not limited to these two types of devices. As long as the device involves ultraviolet light monitoring, for example, a device that needs to detect the spot distribution and position of ultraviolet light, the ultraviolet light monitoring device of the present application can be applied.

[0040] Second embodiment: ultraviolet light monitoring device

[0041] According to the second embodiment of the present application, the structures of the imaging lens, the infrared CCD camera and the computer of the ultraviolet light monitoring device are consistent with those of the prior art, and the only difference lies in the specific structure of the reflective ultraviolet light fluorescent screen. The reflective ultraviolet light fluorescent screen only includes a fluorescent film and a substrate. The substrate is made of aluminum or stainless steel, and the fluorescent film is formed by precipitating a mixture of vanadium phosphovanadate europium fluorescent powder and an organic solvent. In addition, a visible light high reflection film can be arranged between the fluorescent film and the substrate to reflect most of the visible light.

[0042] Thus, the reflective ultraviolet light fluorescent screen is made by precipitating the vanadium phosphovanadate europium fluorescent powder with high luminous efficiency and high color rendering performance and the organic solvent on the substrate, so that the ultraviolet light spot can be monitored with high sensitivity at low frequency and low power. However, such a fluorescent screen is easy to be damaged and has poor surface roughness, which affects the judgment of the actual ultraviolet light spot distribution. In this embodiment, the reason why sintering is not used to prepare the fluorescent screen is that sintering will cause the fluorescent powder to be fused with the substrate material, and the use of sapphire as a substrate with high temperature resistance can avoid the fusion of the fluorescent powder and the substrate material.

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

[0044] As Figure 4As shown, the hard X-ray free electron laser device based on the above-mentioned ultraviolet light monitoring device is a 3.4 km long device. The hard X-ray free electron laser device includes a driving laser system 100. The driving laser system 100 includes, in sequence, a ytterbium-doped fiber laser 101 and a four-fold frequency device 102, and the center wavelength of the ytterbium-doped fiber laser is 1030 nm. In addition, the driving laser system also includes transverse and longitudinal shaping, image transfer devices, and various monitoring and diagnostic devices. The ultraviolet light monitoring device of the present application is only a small part of the various monitoring and diagnostic devices, and is used for weak light monitoring.

[0045] Thus, the ultraviolet light monitoring device of the present application realizes high-sensitivity weak light monitoring, can ensure the transmission efficiency of the entire driving laser system, can reduce the required light splitting for ultraviolet light monitoring, and can make the light energy transmitted to the photocathode larger.

[0046] The hard X-ray free electron laser device also includes an electron gun including a photocathode for generating an initial electron beam. In the present embodiment, the photocathode is cesium telluride (Cs2Te), and the photocathode of cesium telluride (Cs2Te) has high quantum efficiency only in the ultraviolet band. Therefore, a four-fold frequency device is used to convert 1030 nm infrared light into 257.7 nm ultraviolet light through a nonlinear crystal. In order to generate an electron beam with high brightness and high quality, the ultraviolet light with a wavelength of 257.7 nm obtained by four-fold frequency is a Gaussian distribution in both the longitudinal direction and the transverse direction, which is not conducive to the optimization of the emission degree of the electron beam. Therefore, it is necessary to space-time shape the ultraviolet light so that the longitudinal and transverse distributions of the ultraviolet light are close to average distributions, and to image the shaped light distribution to the photocathode surface through image transfer.

[0047] In the present embodiment, the entire transmission light path from the four-fold frequency device outputting ultraviolet light to the photocathode is as long as nearly 40 m, and needs to be transmitted in vacuum across floors for 14 m. The four-fold frequency device outputs ultraviolet light with a wavelength of 257.7 nm and a diameter of 2.6 mm, which is expanded to 13 mm ultraviolet light through a 5-fold beam expander, and then transmitted to a grating pulse width device (i.e., grating stretching pair) for longitudinal shaping.

[0048] In order to ensure that the entire driving laser system 100 is in an optimal state during beam shaping operation, and to determine the problem in time when a fault occurs, four ultraviolet light monitoring devices 200 of the present application are arranged at different positions of the light path between the four-fold frequency device and the photocathode, so as to respectively monitor the expanded beam spot, the beam spot after grating longitudinal stretching, the virtual photocathode, and the virtual injection mirror. In other embodiments, at least one ultraviolet light monitoring device 200 described above is arranged on the light path between the four-fold frequency device and the photocathode.

[0049] In order to ensure transmission efficiency, in the embodiment, the beam splitter is not added to the main light path to monitor the expanded beam, but the ultraviolet monitoring device is used to monitor the zero-order light of the first grating G1 transmitted by the grating expansion device or the weak light monitoring is directly performed by using the back light of the reflector, so that the expanded beam spot monitoring is realized. Specifically, the ultraviolet monitoring device 200 is arranged in the transmission direction of the first grating G1 and includes a reflective ultraviolet fluorescent screen, an imaging lens and a first infrared CCD camera CCD1.

[0050] In addition, the weak light monitoring is realized by arranging a wedge in the transmission light path downstream of the grating expansion device. Since the spot is large and the unit area light power is low downstream of the grating expansion device, the detection is more difficult, and the ultraviolet light cannot be detected by monitoring the light transmitted through the back of the reflector at some positions of the light path. Therefore, the light monitoring is performed by arranging the wedge in the main light path. Specifically, the ultraviolet monitoring device 200 is arranged in the reflection direction of the wedge and includes a reflective ultraviolet fluorescent screen, an imaging lens and a second infrared CCD camera CCD2.

[0051] In the embodiment, the incident ultraviolet light (i.e. zero-order light ultraviolet laser pulse train) and the infrared CCD camera 30 are located on the front surface of the reflective ultraviolet fluorescent screen 10, and 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 perpendicular incidence of the incident ultraviolet light on the fluorescent screen is to ensure that the measurement of the spot size is more accurate, and to prevent the measurement accuracy from being affected by the large ultraviolet spot projected on the fluorescent screen due to the oblique incidence.

[0052] In the embodiment, the imaging lens 20 is a C lens with a focal length of 250 mm, and the pixel size of the infrared CCD camera 3 is 4.8um×4.8um. The 257.7nm ultraviolet light transmitted by the first grating G1 and output as zero-order light is vertically incident on the surface of the fluorescent film and is absorbed by the fluorescent film. Under the excitation of the 257.7nm ultraviolet light, the fluorescent film emits strong red light with a main emission peak of 619nm and a relative brightness greater than 100. The 257.7nm ultraviolet spot is converted into another wavelength 619nm visible light spot, then imaged on the infrared CCD camera through the imaging lens, and finally the light spot is collected and processed by the computer.

[0053] Similarly, the light spot monitoring after the grating expansion device, the virtual cathode and the virtual injection mirror monitoring are implemented in the same way as above, and will not be described in detail.

[0054] Application Example 2: Ultraviolet Monitoring Device for Soft X-ray Free Electron Laser Device

[0055] like Figure 5 As shown, the soft X-ray free-electron laser device based on the ultraviolet light monitoring device described above includes a driving laser system 100'. The driving laser system 100' includes a laser 101' and a third-harmonic generation device 102' arranged sequentially, thereby outputting 266nm ultraviolet laser light through third-harmonic generation. After being broadened to 10ps by a grating stretcher, the laser light is transmitted to the first motorized mirror mount M1, and then transmitted to the photocathode P1 through a shaping aperture A1 and an image transmission optical path. In the image transmission optical path of the driving laser system 100, 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 is used to construct a position feedback device. Specifically, a beam splitter is located downstream of each motorized mirror mount to be adjusted. The beam splitter reflects a portion of the ultraviolet light to an ultraviolet light monitoring device 200, thereby forming a position feedback device.

[0056] In addition, the driving laser system also includes lateral and longitudinal shaping, image transmission devices, and various monitoring and diagnostic devices. The position feedback device of this invention is only a small part of the various monitoring and diagnostic devices. It is used for position feedback detection. The role of position feedback is to reduce the jitter caused by mechanical vibration and environmental temperature and humidity in the ultraviolet light transmitted over long distances to the photocathode. This is achieved through measurement and high-speed piezo motion via an electric frame.

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

[0058] Thus, the 266nm wavelength, 10mm width ultraviolet laser light from the grating-stretched image passes through the first motorized lens mount M1, then through the shaping aperture A1, and is reflected off the front surface of the first beam splitter B1, splitting off a small portion of the light that strikes the reflective ultraviolet fluorescent screen 10 of the ultraviolet light monitoring device 200. The ultraviolet fluorescent screen, excited by the 266nm laser, emits 619nm infrared light, which is then imaged onto the first infrared CCD camera CCD1' by the imaging lens. Data is then acquired and processed by a computer. The center height of the incident ultraviolet light spot is consistent with the center heights of the first motorized lens mount M1, the shaping aperture A1, the first beam splitter B1, the reflective ultraviolet fluorescent screen 10, the imaging lens, and the first infrared CCD camera CCD1'. Most of the ultraviolet light after grating broadening passes through the first beam splitter B1 and continues to the second motorized lens mount M2, then to the second beam splitter B2. A small portion of the light is reflected from the front surface of the second beam splitter B2 onto the reflective ultraviolet phosphor screen 10. Under 266nm laser excitation, it also emits 619nm infrared light, which is imaged onto the second infrared CCD camera CCD2' through the imaging lens. Data is then acquired and processed by a computer. The center height of the transmitted ultraviolet light to the second motorized lens mount M2 is consistent with the center heights of the second motorized lens mount M2, the second beam splitter B2, the reflective ultraviolet phosphor screen 10, the imaging lens, and the second infrared CCD camera CCD2'.

[0059] Therefore, two ultraviolet (UV) light monitoring devices 200 are used to achieve position feedback. These devices detect and measure the center position of the light spot, and the data collected by the UV monitoring devices 200 forms an efficient feedback loop. This loop allows for adjustment of the motorized mirror frame, enabling position feedback and correction. This dynamically adjusts and calibrates the optical path in real time, eliminating position changes caused by mechanical vibration and temperature / humidity variations, ensuring the positional stability of the UV laser reaching the photocathode, and obtaining information on the spatial position, intensity distribution, and shape of the beam. Specifically, the UV monitoring devices 200 detect the pixel values ​​in the x and y directions corresponding to the center position of the light spot, and the motorized mirror frame is then adjusted to maintain the center position of the light spot at its initial position. When the feedback control software detects the infrared CCD cameras 30 of each of the two UV monitoring devices 200 (such as...), the feedback control software... Figure 1 ,exist Figure 3 When the X and Y direction deviations of the light spot centers of the first infrared CCD camera (CCD1') and the second infrared CCD camera (CCD2') are 1-5 pixels, the motorized lens frame is adjusted to ensure that the X and Y direction deviations of the light spot centers of the first infrared CCD camera (CCD1') and the second infrared CCD camera (CCD2') are within 1 pixel, thereby ensuring that the jitter at the photocathode position is less than 10μm.

[0060] That is, 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, and 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 position deviation of the light spot center on the first infrared CCD camera CCD1' is 1-5 pixels, the first motorized mirror mount M1 will automatically adjust through the feedback loop to correct the position of the light spot center on the first infrared CCD camera CCD1' to within 1 pixel of the initial center position in both x and y directions. Similarly, when the position deviation of the light spot center on the second infrared CCD camera CCD2' is 1-5 pixels, the second motorized mirror mount M2 will automatically adjust through the feedback loop to correct the position of the light spot center on the second infrared CCD camera CCD2' to within 1 pixel of the initial center position in both x and y directions. The second infrared CCD camera CCD2' downstream of the two infrared CCD cameras 30 is the main feedback CCD for correction. In this way, when the UV is transmitted over a long distance, the position feedback device can be used to keep the center position of the UV light on the photocathode unchanged.

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

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

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

[0064] In addition, the reflective ultraviolet light fluorescent screen comprises a sapphire substrate and a fluorescent film on the front surface of the sapphire substrate, the fluorescent film is composed of vanadium yttrium phosphate europium fluorescent powder and a binder, the vanadium yttrium phosphate europium fluorescent powder has stable chemical properties and is in the form of spherical small particles, so that the coating is dense and uniformly distributed and has good consistency, the reflective ultraviolet light fluorescent screen made in this way has simple structure and low cost, the coating is dense and uniformly distributed, the sapphire is easy to conduct heat, and the heat generated by the UV laser irradiated on the fluorescent screen can be quickly taken away, so that the heat accumulation is prevented, the long-term high-power direct irradiation can be withstood, and the screen surface will not be damaged due to carbonization and the like.

[0065] The above is only a preferred embodiment of the present application, and is not intended to limit the scope of the present application. The above embodiment of the present application can be variously changed. Any simple, equivalent change and modification made according to the content of the claims and the specification of the present application falls within the scope of protection of the present application. The present application is not described in detail.

Claims

1. An ultraviolet light monitoring device, characterized by, The application relates to a reflective ultraviolet light fluorescence screen, an imaging lens, an infrared CCD camera and a computer which are arranged in sequence along the light path of ultraviolet light; the reflective ultraviolet light fluorescence screen is sequentially provided with a fluorescence film and a substrate; the fluorescence film contains vanadium phosphor yttrium europium fluorescent powder which is used for converting ultraviolet light into visible light of a wavelength of 619 nm; a visible light high-reflection film is arranged between the fluorescence film and the substrate; the substrate is made of sapphire; the fluorescence film is composed of vanadium phosphor yttrium europium fluorescent powder and a binder; the mass ratio of the vanadium phosphor yttrium europium fluorescent powder and the binder is m, 3<=m<=20; the median particle size D50 of the vanadium phosphor yttrium europium fluorescent powder is 1-10 mu m; and the particle size discrete distribution coefficient of the vanadium phosphor yttrium europium fluorescent powder is 0.7-1.

5. The fluorescence film is made by uniformly mixing vanadium phosphor yttrium europium fluorescent powder and a binder, coating the mixture on the substrate by means of scraping, transferring the coated substrate into a 200-300 DEG C oven and placing the substrate for 5-15 hours, fully volatilizing the organic mixture in the binder, transferring the substrate into a 500-700 DEG C high-temperature furnace and sintering the substrate for 10-30 minutes. The mixing method is at least one of mechanical stirring, centrifugal dispersion or ultrasonic mixing.

2. The ultraviolet light monitoring device of claim 1, wherein, The thickness of the fluorescence film is 0.02-0.08 mm, and the thickness of the substrate is 0.05-1 mm.

3. The ultraviolet light monitoring device of claim 2, wherein, The incident ultraviolet light and the infrared CCD camera are located on the front surface of the reflective ultraviolet light fluorescence screen.

4. The ultraviolet light monitoring device of claim 1, wherein, The incident ultraviolet light and the infrared CCD camera are located on the front surface of the reflective ultraviolet light fluorescence screen.

5. The ultraviolet light monitoring device of claim 1, wherein, The incident ultraviolet light and the infrared CCD camera are located on the front surface of the reflective ultraviolet light fluorescence screen. ​

Images