An ultraviolet filter and a preparation method and application thereof

Abstract

The application discloses an ultraviolet filter and a preparation method and application thereof, wherein the ultraviolet filter comprises a substrate, a first film layer and a second film layer; the substrate has a first surface and a second surface arranged oppositely; the first film layer is arranged on the first surface, the first film layer is formed by alternately arranging a plurality of first high-refractive-index material layers and a plurality of first low-refractive-index material layers, and the first film layer is formed by the first high-refractive-index material layers on the side close to the first surface and on the side far from the first surface; and the second film layer is arranged on the second surface, the second film layer is formed by alternately arranging a plurality of second high-refractive-index material layers and a plurality of second low-refractive-index material layers. The ultraviolet filter has the advantages that the reflection band is divided into two parts by arranging the high-refractive-index material layers and the low-refractive-index material layers alternately on the opposite sides of the substrate, the overall film layer distribution is more reasonable, the surface stress on the opposite sides of the substrate is relatively uniform, and the film cracking phenomenon caused by excessive single surface stress is avoided.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical elements and gas detection, and particularly relates to an ultraviolet filter and a preparation method and application thereof. BACKGROUND

[0002] At present, the detection light source generally used in the SO2 gas concentration detection system is a zinc lamp. A collimating lens is added behind the zinc lamp light source to collimate the light beam, and a transmission interference filter is used to filter light to obtain a light beam of an effective excitation wavelength. The light beam enters a measuring cavity to detect the concentration of SO2 gas.

[0003] In the detection of SO2 gas concentration by ultraviolet fluorescence spectroscopy, ultraviolet light (near 213 nm-214 nm) is needed as excitation light to make the measured SO2 gas emit fluorescence (300 nm-420 nm). Due to the optical characteristics of the ultraviolet wavelength, the ultraviolet light source with a wavelength of 213 nm is expensive. Therefore, a filter is used to filter out other wavelength components from the zinc lamp containing the 213 nm light source, and only the required effective wavelength is retained. At present, a transmission interference filter is commonly used. Although the transmission interference filter is small in size and easy to integrate, the filter is high in price, low in light transmission efficiency, and usually has only 10-20% transmittance of the effective wavelength. In addition, the transmission interference filter has a short service life and low spectral purity (mainly due to the pinhole light leakage caused by the non-uniformity of the film layer). At the same time, the transmission interference filter is one of the most important consumables in the instrument. SUMMARY

[0004] Therefore, one object of the present application is to provide an ultraviolet filter. The filter is provided with different high-refractive-index material layers and low-refractive-index material layers arranged alternately on opposite sides of a substrate. The reflection band is divided into two parts. The overall film layer distribution is more reasonable. The surface stress on opposite sides of the substrate is relatively uniform. In addition, the phenomenon of film cracking caused by excessive stress on a single side is avoided.

[0005] Another object of the present application is to provide a preparation method of the ultraviolet filter.

[0006] Still another object of the present application is to provide a light filtering device.

[0007] Still another object of the present application is to provide a light filtering method.

[0008] Still another object of the present application is to provide an application of the light filtering method in the detection of sulfur dioxide gas concentration.

[0009] To achieve the above objects, the first aspect of the present application provides an ultraviolet filter, which comprises

[0010] a substrate having a first surface and a second surface arranged oppositely;

[0011] a first film layer arranged on the first surface, the first film layer being alternately arranged by a plurality of first high-refractive-index material layers and a plurality of first low-refractive-index material layers, the first film layer being the first high-refractive-index material layer on the side close to the first surface and on the side away from the first surface;

[0012] a second film layer arranged on the second surface, the second film layer being alternately arranged by a plurality of second high-refractive-index material layers and a plurality of second low-refractive-index material layers, the second film layer being the second low-refractive-index material layer on the side close to the second surface and being the second high-refractive-index material layer on the side away from the second surface.

[0013] The ultraviolet filter according to the embodiment of the present application divides the reflection band into two parts by arranging the high-refractive-index material layers and the low-refractive-index material layers alternately on the opposite sides of the substrate, and the overall film layer distribution is more reasonable, and the surface stress on the opposite sides of the substrate is relatively uniform, and the film cracking phenomenon caused by excessive single surface stress is avoided.

[0014] In some embodiments of the present application, the unit thickness of the first high-refractive-index material layer is 27-33 nm, and the thickness of the first high-refractive-index material layer is 20-43.9 nm; the unit thickness of the first low-refractive-index material layer is 35-41 nm, and the thickness of the first low-refractive-index material layer is 32.66-53.78 nm; the unit thickness of the second high-refractive-index material layer is 27-33 nm, and the thickness of the second high-refractive-index material layer is 22.91-43.09 nm; the unit thickness of the second low-refractive-index material layer is 35-41 nm, and the thickness of the second low-refractive-index material layer is 30.63-84.54 nm.

[0015] In some embodiments of the present application, the total number of the first high-refractive-index material layers and the first low-refractive-index material layers in the first film layer is 19-39 layers; and the total number of the second high-refractive-index material layers and the second low-refractive-index material layers in the second film layer is 18-38 layers.

[0016] In some embodiments of the present application, the material of the substrate is ultraviolet fused quartz or calcium fluoride; the material of the first high-refractive-index material layer and the second high-refractive-index material layer is hafnium dioxide or aluminum oxide; and the material of the first low-refractive-index material layer and the second low-refractive-index material layer is aluminum fluoride or magnesium fluoride.

[0017] To achieve the above-mentioned purpose, the second aspect of the present application provides a preparation method of an ultraviolet filter, comprising pretreating the substrate;

[0018] sequentially pre-melting and sintering the first high-refractive-index material layer material, the first low-refractive-index material layer material, the second high-refractive-index material layer material and the second low-refractive-index material layer material;

[0019] The first film layer and the second film layer are formed on the first surface and the second surface of the pretreated substrate respectively by vacuum evaporation.

[0020] The preparation method of the ultraviolet filter according to the embodiments of the present application is simple in process, and the film layer formed has strong bonding force with the substrate, is more firm and does not contain impurities.

[0021] In some embodiments of the present application, the pretreatment method is: ultrasonic cleaning of the substrate, inert gas blowing and drying, and then high-energy ion treatment by an ion source.

[0022] In some embodiments of the present application, the pre-melting method of the first high-refractive-index material layer material and the second high-refractive-index material layer material is: pre-melting by an electron gun under the condition of a current of 0.1-180 mA, and repeatedly pre-melting the surface of the first high-refractive-index material layer material or the second high-refractive-index material layer material by increasing the current by 30 mA from 0.1 mA each time until all the particles of the first high-refractive-index material layer material or the second high-refractive-index material layer material are completely melted and the surface of the first high-refractive-index material layer material or the second high-refractive-index material layer material is completely melted flat.

[0023] In some embodiments of the present application, the pre-melting method of the first low-refractive-index material layer material and the second low-refractive-index material layer material is: repeatedly pre-melting by an electron gun under the condition of a current of 0.1-15 mA and a scanning radius of 10-20 mm.

[0024] In some embodiments of the present application, the process conditions of vacuum evaporation of the first high-refractive-index material layer material and the second high-refractive-index material layer material are: vacuum degree (0.5×10 -3 )-(2×10 -3 ) Pa, evaporation rate 1-3 nm / s, baking temperature 270-310 ℃, and baking time 30-60 min.

[0025] In some embodiments of the present application, the process conditions of vacuum evaporation of the first low-refractive-index material layer material and the second low-refractive-index material layer material are: vacuum degree (0.5×10 -3 )-(2×10 -3Pa, evaporation rate 0.3-1.3 nm / s, baking temperature 270-310 DEG C, baking time 30-60 min.

[0026] To achieve the above object, the third aspect of the present application provides a light filtering device, comprising a light source, a collimating lens and at least two pieces of the ultraviolet filter according to the embodiments of the present application arranged in sequence, and the light beam emitted by the light source is incident on each piece of the ultraviolet filter at the same angle.

[0027] The light filtering device according to the embodiments of the present application has the beneficial effects of the ultraviolet filter according to the embodiments of the present application, and further has the beneficial effects that the light source is collimated by the collimating lens and then filtered by the multiple pieces of the ultraviolet filter in sequence, the comprehensive reflectivity of the reflected light emitted after each filtering decreases according to the power index of the number of filtering, and the spectral intensity and full width at half maximum are reduced and converged.

[0028] In some embodiments of the present application, the first film layer of the ultraviolet filter is the incident surface of the light beam.

[0029] In some embodiments of the present application, the incident angle of the light beam is 22.5-45 DEG, and the number of the ultraviolet filters is four.

[0030] In some embodiments of the present application, an optoelectronic detector is arranged behind each piece of the ultraviolet filter, and the optoelectronic detector is arranged perpendicularly to the transmission direction of the light beam.

[0031] To achieve the above object, the fourth aspect of the present application provides a light filtering method, which is applied to the light filtering device according to the embodiments of the present application, and comprises

[0032] The light beam emitted by the light source is collimated by the collimating lens to obtain collimated light;

[0033] The collimated light is reflected and filtered by each piece of the ultraviolet filter in sequence at the same incident angle to obtain a light source light beam with a convergent spectral range.

[0034] The light filtering method according to the embodiments of the present application has basically the same beneficial effects as the light filtering device according to the embodiments of the present application, and thus the detailed description is omitted here.

[0035] In some embodiments of the present application, the light filtering method further comprises that each optoelectronic detector synchronously detects the transmission intensity of the corresponding ultraviolet filter and corrects the reference light intensity of the ultraviolet filter.

[0036] To achieve the above object, the fifth aspect of the present application provides the application of the light filtering method according to the embodiments of the present application in the detection of sulfur dioxide gas concentration, which comprises

[0037] The light source is a zinc lamp or a flashing xenon lamp;

[0038] The incident angle of the light beam is 22.5-45°;

[0039] The number of the ultraviolet filters is four;

[0040] The spectral range of the light source filtered by all the ultraviolet filters converges to 200-230 nm.

[0041] The application of the light filtering method in the detection of sulfur dioxide gas concentration, by using ultraviolet light of a specific angle (22.5-45°) irradiated on an ultraviolet filter with high reflectivity characteristics, combined with multiple filtering, the spectral range of the ultraviolet light is overall covered with the 200-230 nm waveband absorption cross section of SO2 molecules, while the noise waveband after 230 nm is suppressed, the light emitting efficiency of the light source is detected in real time by using the transmission light intensity after each filtering, the light source voltage fluctuation is corrected in time, the background signal interference is reduced, the SO2 detection limit is reduced, and through long-term testing and Allen variance calculation, the lower limit of SO2 gas detection can be reduced to 85 ppt.

[0042] Additional aspects and advantages of the application will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and / or can be learned by practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0043] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, taken in conjunction with the accompanying drawings, in which:

[0044] Figure 1 It is a simple structure schematic diagram of the ultraviolet filter according to one embodiment of the present application.

[0045] Figure 2 It is a reflection characteristic principle diagram of the ultraviolet filter according to one embodiment of the present application.

[0046] Figure 3 It is a reflection characteristic principle diagram of the ultraviolet filter according to one embodiment of the present application within the incident angle range of 22.5-45°.

[0047] Figure 4 It is a reflectivity curve of the ultraviolet filter according to one embodiment of the present application within the waveband of 200-700 nm.

[0048] Figure 5 It is a flowchart of the film layer design and preparation method of the ultraviolet filter according to one embodiment of the present application.

[0049] Figure 6 It is a simple structure schematic diagram of the light filtering device according to one embodiment of the present application.

[0050] Figure 7 A simple structure diagram of the light filtering device according to another embodiment of the present application.

[0051] Figure 8 A cross section diagram of the absorption of the ultraviolet wave band of sulfur dioxide gas.

[0052] Figure 9 A comparison diagram of the conventional transmission type light filtering and the reflection type light filtering according to Embodiment 3 of the present application.

[0053] Figure 10 A diagram of the intensity of the ultraviolet light source after multiple reflections.

[0054] Figure 11 A diagram of the lower limit of the sulfur dioxide gas concentration detection result calculated by the Allen variance according to Embodiment 3 of the present application.

[0055] Reference signs:

[0056] 1 - substrate; 101 - first surface; 102 - second surface; 2 - first film layer; 201 - first high refractive index material layer; 202 - first low refractive index material layer; 3 - second film layer; 301 - second high refractive index material layer; 302 - second low refractive index material layer; 4 - light source; 5 - collimating lens; 6 - ultraviolet filter; 7 - photodetector; 8 - reflected light beam; 9 - projected light beam. DETAILED DESCRIPTION

[0057] The embodiments of the present application are described in detail below with reference to the accompanying drawings. The embodiments described below by reference to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0058] The inventors found that the current SO2 gas concentration detection system has the problems that the output voltage of the ultraviolet light source is unstable when the voltage is boosted and flickers, and after the optical shaping and light filtering treatment, the relative intensity of the effective ultraviolet excitation light spectrum retained is low, the effective excitation spectrum region covered is incomplete, and the relative intensity of the invalid ultraviolet light transmitted is high, which introduces a large amount of background noise, increases the background signal of the measurement system, causes zero drift, and obscures the characteristic signal of SO2 gas, resulting in the problem that the measurement system cannot accurately measure the trace concentration of SO2 gas. Based on the above, the present application designs an ultraviolet filter, provides a preparation method of the ultraviolet filter, a light filtering device, a light filtering method, and the application thereof in the detection of the concentration of sulfur dioxide gas.

[0059] The ultraviolet filter, the preparation method of the ultraviolet filter, the light filtering device, and the light filtering method of the embodiments of the present application are described below with reference to the accompanying drawings.

[0060] Figure 1This is a simplified structural diagram of an ultraviolet filter according to an embodiment of the present invention.

[0061] like Figure 1 As shown, the ultraviolet filter of this embodiment includes a substrate 1, a first film layer 2, and a second film layer 3. The substrate 1 has a first surface 101 and a second surface 102 disposed opposite to each other. The first film layer 2 is disposed on the first surface 101 and is formed by alternatingly distributing a plurality of first high refractive index material layers 201 and a plurality of first low refractive index material layers 202. The side of the first film layer 2 closest to the first surface 101 and the side furthest from the first surface 101 are both first high refractive index material layers 201. The second film layer 3 is disposed on the second surface 102 and is formed by alternatingly distributing a plurality of second high refractive index material layers 301 and a plurality of second low refractive index material layers 302. The side of the second film layer 3 closest to the second surface 102 is a second low refractive index material layer 302, and the side of the second film layer 3 furthest from the second surface 102 is a second high refractive index material layer 301.

[0062] The ultraviolet filter of this invention divides the reflection band in two by setting different alternating high-refractive-index material layers and low-refractive-index material layers on opposite sides of the substrate. This results in a more reasonable overall film layer distribution and relatively uniform surface stress on opposite sides of the substrate, while avoiding film cracking caused by excessive stress on one side. Specifically, the first film layer has a first high-refractive-index material layer on both the side closest to the first surface and the side furthest from the first surface. The second film layer has a second low-refractive-index material layer on the side closest to the second surface and a second high-refractive-index material layer on the side furthest from the second surface. This design effectively suppresses and reduces background stray light reflected from the surface opposite the beam incident surface.

[0063] In the ultraviolet filter of this embodiment, the first surface and the second surface can be the front surface and the back surface of the substrate, or the upper surface and the lower surface, or the left surface and the right surface, etc.

[0064] Optionally, the substrate 1 is made of quartz or calcium fluoride; the first high refractive index material layer 201 and the second high refractive index material layer 301 are both made of hafnium dioxide or aluminum oxide; the first low refractive index material layer 202 and the second low refractive index material layer 302 are both made of aluminum fluoride or magnesium fluoride.

[0065] The design concept of the ultraviolet filter in this embodiment of the invention is as follows:

[0066] By analyzing the ultraviolet absorption cross section of SO2 gas, the ground state of SO2 is... In the ultraviolet spectral region, there are two absorption regions in the 185nm-320nm range, and a spectral region in the 270nm-320nm range with absorption intensity below 1e-18. The strongest absorption occurs around 290nm, where the vibrational-rotational structure is relatively complex. The 195nm-230nm range is the strongest absorption band, exhibiting continuous absorption peaks with absorption intensities between 1e-18 and 1.4e-17. From 200nm to 230nm, absorption gradually increases as the wavelength shortens, with absorption intensities exceeding the 1e-17 order of magnitude in the 200nm-212nm range. Figure 8 As shown.

[0067] Among the electronic transitions involved in the 200nm-230nm wavelength range, there is only one excited state that is 5.279 eV higher than the ground state. Vibrational rotation structures are relatively simple, and transition assignments are... This results in the emission of a fluorescence signal. In this embodiment of the ultraviolet filter, a first high-refractive-index material layer, a first low-refractive-index material layer, a second high-refractive-index material layer, and a second low-refractive-index material layer are alternately disposed on opposite sides of the substrate. Through fitting and simulation calculations of the optical constants of the film materials, the reflection band is divided into two. The first film layer achieves high reflection at 200-230nm and high transmission at 230-700nm, while the second film layer achieves reflection at 220-290nm and high transmission at 290nm-700nm. 235nm-290nm is the transition band between transmission and reflection. Dividing the reflection band into two makes the overall film layer distribution more reasonable, and the stress of the first and second film layers is relatively uniform, while avoiding the film cracking phenomenon caused by excessive stress on one side. The initial unit design of the film system is as follows: where 210nm-214nm is used as the reference wavelength, H represents the high-refractive-index material, L represents the low-refractive-index material, S represents the period number, and Air represents air.

[0068] Sub|(0.5HL 0.5H) s |Air;

[0069] The first film layer structure: the unit thickness of the first high refractive index material layer is 27-33 nm, for example 30 nm; the unit thickness of the first low refractive index material layer is 35-41 nm, for example 38 nm;

[0070] Sub|(0.5HL 0.5H) 7 1.15 (0.5HL 0.5H) 7 |Air;

[0071] The second film layer structure: the unit thickness of the second high refractive index material layer is 27-33 nm, for example 30 nm; the unit thickness of the second low refractive index material layer is 35-41 nm, for example 38 nm;

[0072] Sub | 0.85 (0.5H L 0.5H) 7 (0.5H L 0.5H) 7 |Air.

[0073] The film system structure of the first film layer and the second film layer is optimized respectively, and after optimization:

[0074] In some embodiments, the total number of the first high-refractive-index material layers 201 and the first low-refractive-index material layers 202 in the first film layer 2 is 19-39 layers, the thickness of the first high-refractive-index material layers 201 is between 20-43.9 nm, and the thickness of the first low-refractive-index material layers 202 is between 32.66-53.78 nm.

[0075] In some embodiments, the total number of the second high-refractive-index material layers 301 and the second low-refractive-index material layers 302 in the second film layer 3 is 18-38 layers, the thickness of the second high-refractive-index material layers 301 is between 22.91-43.09 nm, and the thickness of the second low-refractive-index material layers 302 is between 30.63-84.54 nm.

[0076] It should be noted that in the ultraviolet filter of the embodiments of the present application, the number of layers of the first high-refractive-index material layers and the first low-refractive-index material layers in the first film layer and the number of layers of the second high-refractive-index material layers and the second low-refractive-index material layers in the second film layer are selected in relation to the period number S, and the greater the period number S, the higher the reflectivity and the more the number of layers. Here, the period number S refers to the number of times of alternately arranging the first high-refractive-index material layers and the first low-refractive-index material layers for the first film layer, and refers to the number of times of alternately arranging the second high-refractive-index material layers and the second low-refractive-index material layers for the second film layer.

[0077] The ultraviolet filter of the embodiments of the present application takes the first film layer as the incident light side, and its reflection characteristic principle diagram is as shown in Figure 2 When the light source with a wavelength between 200-700 nm is incident to the first film layer, the light beam with a wavelength between 200-230 nm is reflected by the first film layer, the light beam with a wavelength between 220-290 nm is reflected by the second film layer, and the light beam with a wavelength between 290-700 nm is transmitted. When the incident angle of the light source on the first film layer is within the angle range of 22.5-45°, the reflection characteristic principle diagram of the ultraviolet filter of the embodiments of the present application is as shown in Figure 3 Within the angle range of 22.5-45°, the reflectivity of 200 nm-230 nm is all over 60%, the reflectivity near 214 nm is over 80%, the reflectivity of 230 nm-290 nm is all below 30%, and the reflectivity of 290 nm-700 nm is not more than 10%. It can be seen that there is a huge difference in reflectivity of the ultraviolet filter of the embodiments of the present application before and after 230 nm wavelength.

[0078] After the overall film system structure design is optimized, the ultraviolet filter of the embodiment is prepared. The preparation method of the ultraviolet filter of the embodiment includes but is not limited to a chemical vapor deposition (CVD) process, an atomic layer deposition (ALD) process, a physical vapor deposition (PVD) process or other suitable processes. For example, the physical vapor deposition process can be vacuum evaporation or sputtering.

[0079] As a possible example, as shown in FIG. 1, the preparation method of the ultraviolet filter of the embodiment adopts a double-sided split vacuum evaporation method, which includes the following steps. Figure 5

[0080] The substrate is pretreated.

[0081] The first high-refractive-index material layer material, the first low-refractive-index material layer material, the second high-refractive-index material layer material and the second low-refractive-index material layer material are sequentially pre-melted and sintered.

[0082] The first film layer and the second film layer are respectively formed on the first surface and the second surface of the pretreated substrate by a vacuum evaporation method.

[0083] In the preparation method of the ultraviolet filter of the embodiment, the purpose of pretreatment is to remove impurities adsorbed on the surface of the substrate, fill the recesses on the surface of the substrate, activate the surface particles and improve the bonding force between the substrate and the film material molecules, so that the film layer is more firm. The pretreatment method includes but is not limited to ultrasonic cleaning, ion source treatment, etc. As a possible example, the pretreatment method is as follows: the substrate is ultrasonically cleaned, then dried by blowing inert gas, and then treated by high-energy ion of an ion source. Optionally, the ultrasonic cleaning is performed twice, the first time is to place the substrate in a solution mixed with alcohol and diethyl ether, and the second time is to place the substrate after the first cleaning in deionized water, and the first cleaning time and the second cleaning time are both 5-15 min. Optionally, the inert gas can be one or more of nitrogen, argon and helium. Optionally, the high-energy ion of the ion source is an anode ion source high-energy ion, a Hall ion source high-energy ion, etc.

[0084] In the preparation method of the ultraviolet filter of the embodiment, the first high-refractive-index material layer material, the second high-refractive-index material layer material, the first low-refractive-index material layer material and the second low-refractive-index material layer material are sintered and pre-melted to remove the gas and impurities adsorbed in the gaps between the film materials and on the surface.

[0085] ​In some embodiments, the method for pre-melting the first high-refractive-index material layer material and the second high-refractive-index material layer material is that: the electron gun is used to pre-melt under the condition that the current is from 0.1 mA to 180 mA, and the surface of the first high-refractive-index material layer material or the second high-refractive-index material layer material is repeatedly pre-melted by increasing the current by 30 mA from 0.1 mA until all the particles of the first high-refractive-index material layer material or the second high-refractive-index material layer material are melted and the surface of the first high-refractive-index material layer material or the second high-refractive-index material layer material is completely melted.

[0086] In some embodiments, the method for pre-melting the first low-refractive-index material layer material and the second low-refractive-index material layer material is that: the electron gun is used to repeatedly pre-melt under the condition that the current is from 0.1 mA to 15 mA and the scanning radius is from 10 mm to 20 mm.

[0087] It should be noted that the pre-melting of the first high-refractive-index material layer material and the second high-refractive-index material layer material and the pre-melting of the first low-refractive-index material layer material and the second low-refractive-index material layer material are both performed by connecting the electric gun to a 220 V voltage.

[0088] In some embodiments, the process conditions for vacuum evaporation of the first high-refractive-index material layer material and the second high-refractive-index material layer material are that: the vacuum degree is from (0.5×10 -3 ) Pa to (2×10 -3 ) Pa, the evaporation rate is from 1 nm / s to 3 nm / s, the baking temperature is from 270 ℃ to 310 ℃, and the baking time is from 30 min to 60 min.

[0089] In some embodiments, the process conditions for vacuum evaporation of the first low-refractive-index material layer material and the second low-refractive-index material layer material are that: the vacuum degree is from (0.5×10 -3 ) Pa to (2×10 -3 ) Pa, the evaporation rate is from 0.3 nm / s to 1.3 nm / s, the baking temperature is from 270 ℃ to 310 ℃, and the baking time is from 30 min to 60 min.

[0090] In some embodiments, the sintering temperature of the first high-refractive-index material layer material is from 1650 ℃ to 1950 ℃, and the holding time is from 200 min to 300 min; the sintering temperature of the second high-refractive-index material layer material is from 1650 ℃ to 1950 ℃, and the holding time is from 200 min to 300 min; the sintering temperature of the first low-refractive-index material layer material is from 1250 ℃ to 1350 ℃, and the holding time is from 250 min to 350 min; and the sintering temperature of the second low-refractive-index material layer material is from 1250 ℃ to 1350 ℃, and the holding time is from 250 min to 350 min.

[0091] Based on the filtering characteristics of the ultraviolet filter according to the embodiments of the present application, multiple groups of the ultraviolet filter according to the embodiments of the present application can be arranged to filter light.

[0092] The inventive concept of the light filtering device and the light filtering method of the embodiment of the present application is:

[0093] The ultraviolet filter of the embodiment of the present application has a huge difference in reflectivity around the wavelength of 230 nm. The transmission mode of multiple reflection filtering of the light beam makes the low reflectivity wavelength in the light beam form exponential decay of light intensity, so that the high reflectivity spectral region of the light beam gradually converges and compresses, and the overall reflectivity R of the overall spectrum of the light beam 总 is in an exponential decreasing relationship with the number of reflections (N = 1, 2, 3, 4, …). 总 单 N ), so that the overall spectrum intensity I and the full width at half maximum (FWHM) are reduced and converged after multiple filtering, the wavelength band after 230 nm is gradually suppressed, and finally the ultraviolet light of the effective wavelength band of 200 nm-230 nm with high intensity is reserved. The ultraviolet light of the wavelength band of 200 nm-230 nm overall covers the strong absorption region and the weak absorption region of the SO2 gas absorption cross section, which can maximize the excitation of the SO2 gas radiation fluorescence signal.

[0094] Based on the above concept, as shown in Figure 6 and Figure 7 , the light filtering device of the embodiment of the present application comprises a light source 4, a collimating lens 5 and at least two pieces of the ultraviolet filter 6 of the embodiment of the present application arranged in sequence. The light beam emitted by the light source 4 is incident on each piece of the ultraviolet filter 6 at the same angle in sequence.

[0095] Optionally, the light source 4 is a zinc lamp or a flickering xenon lamp. The light source 4, the collimating lens 5 and the multiple ultraviolet filters have a spacing between adjacent two. It should be noted that as long as the light beam emitted by the light source can be incident on each piece of the ultraviolet filter at the same angle in sequence, the setting position of each ultraviolet filter is not limited. At the same time, based on the light filtering characteristics of the ultraviolet filter of the embodiment of the present application, the number of ultraviolet filters can be set according to the light filtering requirement. The specific principle is that the more the number of light filtering times is, the more the number of ultraviolet filters needs to be if the lower the overall reflectivity of the reflected light emitted by the light source after the light filtering device is needed. As a possible example, the light source is a zinc lamp, the incident angle of the light beam emitted by the light source is 22.5-45°, and the number of ultraviolet filters 6 is 4.

[0096] Optionally, the first film layer 2 of the ultraviolet filter is the incident surface of the light beam.

[0097] ​Optionally, as a possible implementation of the present application, when the light source is a zinc lamp, due to the pulse triggering characteristics of the ultraviolet light source, the output light intensity is unstable when the light source flashes with voltage boost, and long-time continuous voltage boost will cause damage to the light source, resulting in a decrease in luminous efficiency under the same voltage, so it is necessary to monitor the intensity of the light source in real time to regulate the voltage boost range of the light source, and when the luminous efficiency of the light source decreases, the voltage boost is adjusted in time to keep the luminous efficiency of the light source consistent with the loss before, reduce the zero drift of the measurement system, and use the ultraviolet filter to filter multiple times while adding a photodetector 7 vertically behind each ultraviolet filter along the direction of light beam transmission to synchronously detect the transmission spectrum intensity I of each ultraviolet filter T , the light signal intensity detected by each photodetector continuously corrects the pulse voltage boost range of the ultraviolet light source, so that the luminous efficiency of the light source is stable and the intensity range converges. The light intensity change of the wavelength band with the highest transmittance of the corresponding filter is detected by the photodetector behind each ultraviolet filter, and the reference light intensity after filtering at each stage is compared and corrected in real time. Taking the number of ultraviolet filters as 4 as an example, the four ultraviolet filters are defined as the first ultraviolet filter, the second ultraviolet filter, the third ultraviolet filter and the fourth ultraviolet filter in the order of light source incidence, and the corresponding photodetectors are the first photodetector, the second photodetector, the third photodetector and the fourth photodetector, respectively. The 400-700nm spectrum intensity after one-time filtering is I T1 , the 230-290nm spectrum intensity after two-time filtering is I T2 , the 230-290nm spectrum intensity after three-time filtering is I T3 , and the 200-230nm spectrum intensity after four-time filtering is I T4 , the relative intensity I T1 -I T4 is compared with the standard light intensity in real time to obtain the deviation ratio P of the overall relative intensity, and the output voltage value of the light source is adjusted by using the deviation ratio P to control the output of the relative light intensity.

[0098] Taking the case of a zinc lamp as the light source and four ultraviolet filters as an example (as shown in Figure 6 and Figure 7 ), the working principle of the light filtering device of the embodiment of the present application is as follows:

[0099] The ultraviolet light is collimated by the collimating lens 5 and incident on the first film layer of the first ultraviolet filter 6 at a specific angle (R 总 =R 单The light beam, after passing through the first filter, is then incident on the second ultraviolet filter 6 at the same angle. At this point, the outgoing light has undergone two filters, and the overall reflectivity of the outgoing reflected light decreases by the square of the difference (R). 总 =R 单 2 This results in a reduction and convergence of the spectral intensity I and the full width at half maximum (FWHM) after two filtering processes. The emitted reflected light is incident on the third ultraviolet filter 6 at the same angle. After the third filtering, the overall reflectance of the emitted reflected light decreases cubically (R0). 总 =R 单 3 This causes the spectral intensity I and full width at half maximum (FWHM) after the third filtering to decrease and converge again. The outgoing reflected light is incident on the fourth ultraviolet filter 6. After the fourth filtering, the overall reflectance of the outgoing reflected light decreases by the fourth power (R). 总 =R 单 4 This causes the spectral line intensity and full width at half maximum (FWHM) to decrease and converge again. Throughout the filtering process, the photodetector behind each ultraviolet filter detects the change in light intensity of the wavelength band with the highest transmittance for its corresponding filter, and compares it with the reference light intensity after filtering at each stage for real-time correction.

[0100] The filtering method of this invention is applied to the filtering device of this invention. The method includes...

[0101] The light beam emitted by the light source is collimated by the collimating transparent material to obtain collimated light;

[0102] Collimated light is reflected and filtered by each ultraviolet filter at the same incident angle to obtain a light beam with a convergent spectral range.

[0103] In some embodiments, the filtering method of the present invention further includes: each photodetector 7 synchronously detects the transmitted light intensity of its corresponding ultraviolet filter, and corrects the reference light intensity of the ultraviolet filter.

[0104] The specific process of the filtering method in this embodiment of the invention is similar to the working principle of the filtering device in this embodiment of the invention, and will not be repeated here.

[0105] The filtering method of this invention can be used to detect sulfur dioxide gas concentration and reduce the detection limit of trace SO2 gas concentration by ultraviolet fluorescence. In the filtering process of reducing the detection limit of trace SO2 gas concentration by ultraviolet fluorescence, a zinc lamp or a scintillation xenon lamp is used as the light source, the incident angle of the beam is 22.5-45°, and the number of ultraviolet filters is 4. The spectral range of the light source after being filtered by all ultraviolet filters converges to 200-230nm.

[0106] The ultraviolet filter and the preparation method thereof will be described below in combination with preferred embodiments of the present application.

[0107] Example 1 ultraviolet filter

[0108] The ultraviolet filter of the embodiment of the present application comprises a substrate 1, a first film layer 2 and a second film layer 3; the substrate 1 has a first surface 101 and a second surface 102 arranged oppositely; the first film layer 2 is arranged on the first surface 101, and the first film layer 2 is formed by alternately arranging a plurality of first high refractive index material layers 201 and a plurality of first low refractive index material layers 202, the side of the first film layer 2 close to the first surface 101 and the side of the first film layer 2 away from the first surface 101 are both the first high refractive index material layers 201; the second film layer 3 is arranged on the second surface 102, and the second film layer 3 is formed by alternately arranging a plurality of second high refractive index material layers 301 and a plurality of second low refractive index material layers 302, the side of the second film layer 3 close to the second surface 102 is the second low refractive index material layer 302, and the side of the second film layer 3 away from the second surface 102 is the second high refractive index material layer 301.

[0109] The first surface 101 is the upper surface of the substrate, and the second surface 102 is the lower surface of the substrate. The material of the substrate 1 is ultraviolet fused silica (F_silica); the materials of the first high refractive index material layer 201 and the second high refractive index material layer 301 are both hafnium dioxide; the materials of the first low refractive index material layer 202 and the second low refractive index material layer 302 are both aluminum fluoride. The first film layer is a 29-layer film with a total thickness of 1.14 μm; the second film layer is a 28-layer film with a total thickness of 1 μm. The specific structure of the first film layer and the second film layer is shown in Table 1, wherein the film layer 1 is the outermost layer on the side away from the surface of the substrate.

[0110] Table 1 structure of the first film layer and the second film layer of the ultraviolet filter of Example 1

[0111]

[0112]

[0113] Example 2 preparation method of the ultraviolet filter in Example 1

[0114] The quartz substrate is put into a mixed solution of alcohol and ether in a volume ratio of 1:1 for ultrasonic cleaning for 10 minutes, and then cleaned with deionized water for 10 minutes. Then the cleaned quartz substrate is dried by blowing Ar gas, and then treated again with high-energy ions from a Hall ion source. Then the HfO2 and AlF3 films are pre-melted (HfO2 has a melting point of 2750°C, and AlF3 has a melting point of 1300°C). The pre-melting method of HfO2 is as follows: the electron gun beam current is increased from 0 mA to 180 mA, and the surface of the HfO2 film is repeatedly pre-melted by increasing the beam current by 30 mA each time until the HfO2 film particles are completely melted and the surface of the HfO2 film is completely flat. The pre-melting method of AlF3 is as follows: the electron gun beam current is slowly increased by 15 mA, and the electron gun scanning radius is increased to 15 mm to cover the entire spot to repeatedly pre-melt the surface of the AlF3 film. Then the pre-melted HfO2 is sintered in a muffle furnace at 1900°C for 240 minutes, and the pre-melted AlF3 is sintered in a muffle furnace at 1250°C for 300 minutes to remove the gas and impurities adsorbed between the two films and on the surface. Finally, the vacuum evaporation parameters are set, including a vacuum degree of 1×10-3 Pa, an evaporation rate of HfO2 of 2 nm / s and an evaporation rate of AlF3 of 0.8 nm / s, a quartz substrate baking temperature of 290°C, and a baking time of 30 minutes. Finally, the first film layer and the second film layer are evaporated to obtain the ultraviolet filter of Example 1.

[0115] The filtering effect of the ultraviolet filter of Example 1 prepared in this embodiment is detected, and the detection results are shown in Figure 4 From Figure 4 it can be seen that the 200-230 nm band is a high reflection interval, the 235 nm-290 nm band is a transition interval of transmission-reflection, and the 290 nm-700 nm band is a high transmission interval.

[0116] Example 3 contains a filtering device of the ultraviolet filter of Example 1 and a filtering method for reducing the detection limit of the concentration of trace sulfur dioxide gas in ultraviolet fluorescent marks

[0117] As shown in Figure 7 , it includes a light source 4, a collimating lens 5, and four ultraviolet filters 6 of Example 1 arranged in sequence, and there is a gap between the light source 4, the collimating lens 5, and the four ultraviolet filters 6. Each ultraviolet filter 6 is provided with a photodetector 7 behind it, and the photodetector 7 is arranged perpendicular to the transmission direction of the light beam.

[0118] The light source 4 is a zinc lamp, and the light beams emitted by the light source 4 are incident on the first piece of ultraviolet filter, the second piece of ultraviolet filter, the third piece of ultraviolet filter and the fourth piece of ultraviolet filter in sequence at a relative angle of 45° with respect to the ultraviolet filter, and the first film layer 2 of each piece of ultraviolet filter is the incident surface of the light beams.

[0119] The light source 4 is a zinc lamp, and the light beams emitted by the light source 4 are incident on the first piece of ultraviolet filter, the second piece of ultraviolet filter, the third piece of ultraviolet filter and the fourth piece of ultraviolet filter in sequence at a relative angle of 45° with respect to the ultraviolet filter, and the first film layer 2 of each piece of ultraviolet filter is the incident surface of the light beams.

[0120] The light source 4 is a zinc lamp, and the light beams emitted by the light source 4 are incident on the first piece of ultraviolet filter, the second piece of ultraviolet filter, the third piece of ultraviolet filter and the fourth piece of ultraviolet filter in sequence at a relative angle of 45° with respect to the ultraviolet filter, and the first film layer 2 of each piece of ultraviolet filter is the incident surface of the light beams.

[0121] The light source 4 is a zinc lamp, and the light beams emitted by the light source 4 are incident on the first piece of ultraviolet filter, the second piece of ultraviolet filter, the third piece of ultraviolet filter and the fourth piece of ultraviolet filter in sequence at a relative angle of 45° with respect to the ultraviolet filter, and the first film layer 2 of each piece of ultraviolet filter is the incident surface of the light beams. 总 单 总 单 2 总 单 3 总 单 4 ​​​​​​​), so that the spectral line intensity and full width at half maximum are reduced and converged again. After 4 times of filtering, the spectral range of the ultraviolet light converges to 200nm-230nm, and the light intensity after 230nm is less than 1%, and finally a high-intensity, narrow-band ultraviolet light covering the whole SO2 molecule strong absorption cross section is formed, which is suitable for SO2 gas detection needs, while suppressing the noise band after 230nm, as shown in Figure 10 The whole filtering process, the photodetector behind each ultraviolet filter detects the light intensity variation of the waveband with the highest transmittance of the corresponding filter, and compares it with the reference light intensity after each stage of filtering to make real-time correction, reduce background signal interference, and reduce the SO2 detection limit. Specifically, the first photodetector measures the spectral intensity of the 400nm-700nm segment after one filtering as I T1 , the second photodetector measures the spectral intensity of the 230nm-290nm segment after two filtering as I T2 , the third photodetector measures the spectral intensity of the 230nm-290nm segment after three filtering as I T3 , and the fourth photodetector measures the spectral intensity of the 200nm-230nm segment after four filtering as I T4 , and the relative intensity I T1 -I T4 is compared with the standard light intensity in real time to obtain the deviation ratio P of the overall relative intensity. The output voltage value of the light source is adjusted using this deviation ratio P to control the output of the relative light intensity.

[0122] After 800s of testing and Allen variance calculation, the filtering device and filtering method of the present embodiment can reduce the lower limit of SO2 gas detection to 85ppt, as shown in Figure 11 .

[0123] Comparing the multiple reflection filtering effect of the filtering device and filtering method of the present embodiment with the traditional transmission interference filtering effect, the results are shown in Figure 9 From Figure 9 it can be seen that after 4 times of reflection filtering of the ultraviolet light by the filtering device and filtering method of the present embodiment, the spectral intensity of the central wavelength in the 200nm-230nm waveband is more than 50%, and the spectral intensity after the 230nm waveband is not more than 1%, while the spectral intensity of the central wavelength after transmission filtering is not more than 20%, and the spectral intensity after the 230nm waveband is more than 5%, as shown in Figure 9 It can be seen that the multiple reflection filtering effect of the filtering device and filtering method of the present embodiment is obviously better than the traditional transmission interference filtering effect.

[0124] Embodiment 4: Filtering device containing ultraviolet filter of embodiment 1 and filtering method for reducing the detection limit of trace sulfur dioxide gas concentration of ultraviolet fluorescence

[0125] This embodiment is basically the same as embodiment 3, except that:

[0126] As shown in the figure, in the light filtering device: Figure 6

[0127] The first piece of ultraviolet filter is arranged at 67.5° with the central axis of the collimating lens 5; the second piece of ultraviolet filter is arranged below and parallel to the first piece of ultraviolet filter; the third piece of ultraviolet filter is arranged at -67.5° with the central axis of the collimating lens 5; the fourth piece of ultraviolet filter is arranged to the right of the first piece of ultraviolet filter, and the fourth piece of ultraviolet filter is arranged between the first piece of ultraviolet filter and the third piece of ultraviolet filter.

[0128] The light beam emitted by the light source 4 is incident on the first piece of ultraviolet filter, the second piece of ultraviolet filter, the third piece of ultraviolet filter and the fourth piece of ultraviolet filter in turn at a relative angle of 22.5° corresponding to the ultraviolet filter.

[0129] In the light filtering method for reducing the detection limit of trace sulfur dioxide gas concentration by ultraviolet fluorescence, the light filtering device of this embodiment is used:

[0130] After the ultraviolet light is collimated by the collimating lens 5, it is incident on the first piece of ultraviolet filter, the second piece of ultraviolet filter, the third piece of ultraviolet filter and the fourth piece of ultraviolet filter in turn at a relative angle of 22.5° corresponding to the ultraviolet filter.

[0131] The light filtering effect of the light filtering device and the light filtering method of this embodiment is basically the same as that in embodiment 3, and will not be described here.

[0132] In summary, the present application uses a double-sided split vacuum evaporation method to divide the reflection band into two, and prepares an ultraviolet filter with a first film layer and a second film layer. By using specific angle (22.5°-45°) of ultraviolet light irradiation on the first film layer and the second film layer of the ultraviolet filter with high reflectivity characteristics, and combining multiple light filtering, the spectral range of ultraviolet light is overall covered in the 200-230nm waveband absorption cross section of SO2 molecules, while the noise waveband after 230nm is suppressed. The light emitting efficiency of the light source is detected in real time by the transmitted light intensity after each light filtering, and the light source voltage fluctuation is corrected in time, the background signal interference is reduced, the SO2 detection limit is reduced, and through long-term testing and calculation of Allen variance, the detection lower limit of SO2 gas can be reduced to 85ppt.

[0133] ​In the description of the present application, it is to be understood that the orientations or positional relationships indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like are based on the orientations or positional relationships shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the devices or elements indicated thereby must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0134] In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated thereby. Therefore, the features defined with "first", "second", etc. can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise explicitly specified and limited.

[0135] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting", "fixing" and the like should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected or in communication with each other; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication or interaction relationship of two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0136] In the present application, unless otherwise explicitly specified and limited, the first feature "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature "above", "over" and "on" the second feature can be that the first feature is directly above or obliquely above the second feature, or it can only mean that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "under" and "under" the second feature can be that the first feature is directly below or obliquely below the second feature, or it can only mean that the horizontal height of the first feature is less than that of the second feature.

[0137] In this disclosure, the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" mean that a particular feature, structure, material, or characteristic is included in at least one embodiment or example of the present disclosure. The illustrative appearances of the above-mentioned terms in various places in the specification are not necessarily referred to the same embodiment or example. Moreover, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples. Furthermore, the terminology "comprising" is used in the disclosure as comprising but not limited to, that is, it is open-ended and does not exclude the presence of additional features, structures, materials, or characteristics.

[0138] Although the embodiments of the present disclosure have been shown and described above, it should be understood by those having ordinary skill in the art that the above-mentioned embodiments are exemplary and should not be construed as limiting the present disclosure, and those skilled in the art can make changes, modifications, replacements, and variations to the above-mentioned embodiments within the scope of the present disclosure.

Claims

1. An ultraviolet filter, characterized in that, include A substrate having a first surface and a second surface disposed opposite to each other; A first film layer is disposed on the first surface. The first film layer is composed of alternating layers of first high refractive index material and layers of first low refractive index material. Both the side of the first film layer near the first surface and the side away from the first surface are layers of first high refractive index material. The second film layer is disposed on the second surface. The second film layer is composed of a plurality of second high refractive index material layers and a plurality of second low refractive index material layers alternately disposed. The side of the second film layer closer to the second surface is the second low refractive index material layer, and the side of the second film layer away from the second surface is the second high refractive index material layer. The first film layer comprises 19-39 layers of a first high-refractive-index material layer and a first low-refractive-index material layer; the second film layer comprises 18-38 layers of a second high-refractive-index material layer and a second low-refractive-index material layer; the first film layer is used to achieve high reflectivity of 200-230nm and high transmittance of 230-700nm, and the second film layer is used to achieve high reflectivity of 220-290nm and high transmittance of 290-700nm; Both the first low-refractive-index material layer and the second low-refractive-index material layer are made of aluminum fluoride or magnesium fluoride.

2. The ultraviolet filter according to claim 1, characterized in that, The unit thickness of the first high refractive index material layer is 27-33 nm, and the thickness of the first high refractive index material layer is between 20-43.9 nm; The unit thickness of the first low-refractive-index material layer is 35-41 nm, and the thickness of the first low-refractive-index material layer is between 32.66-53.78 nm; The unit thickness of the second high refractive index material layer is 27-33 nm, and the thickness of the second high refractive index material layer is between 22.91-43.09 nm; The unit thickness of the second low-refractive-index material layer is 35-41 nm, and the thickness of the second low-refractive-index material layer is between 30.63-84.54 nm.

3. The ultraviolet filter according to claim 1, characterized in that, The substrate is made of ultraviolet fused silica or calcium fluoride; the first high refractive index material layer and the second high refractive index material layer are both made of hafnium dioxide or aluminum oxide.

4. A method for preparing an ultraviolet filter as described in any one of claims 1 to 3, characterized in that, include The substrate is preprocessed; The first high refractive index material layer, the first low refractive index material layer, the second high refractive index material layer, and the second low refractive index material layer are pre-melted and sintered sequentially. The first film layer and the second film layer are formed on the first and second surfaces of the pretreated substrate by vacuum evaporation.

5. The method for preparing an ultraviolet filter according to claim 4, characterized in that, The pretreatment method is as follows: the substrate is ultrasonically cleaned, then purged and dried with inert gas, and then treated with high-energy ions from an ion source.

6. The method for preparing an ultraviolet filter according to claim 4, characterized in that, The method for pre-melting the first high refractive index material layer and the second high refractive index material layer is as follows: an electron gun is used to pre-melt the material under a current of 0.1-180mA, and the current is increased by 30mA every time starting from 0.1mA to repeatedly pre-melt the surface of the first high refractive index material layer or the second high refractive index material layer until all the particles of the first high refractive index material layer or the second high refractive index material layer are melted solid and the surface of the first high refractive index material layer or the second high refractive index material layer is completely melted flat.

7. The method for preparing an ultraviolet filter according to claim 4, characterized in that, The method for pre-melting the first low-refractive-index material layer and the second low-refractive-index material layer is as follows: repeated pre-melting is performed using an electron gun under conditions of current 0.1-15mA and scanning radius 10-20mm.

8. The method for preparing an ultraviolet filter according to claim 4, characterized in that, The vacuum evaporation process conditions for the first and second high-refractive-index material layers are as follows: vacuum degree (0.5 × 10⁻⁶). -3 )-(2×10 -3 Pa, evaporation rate 1-3 nm / s, baking temperature 270-310℃, baking time 30-60 min.

9. The method for preparing an ultraviolet filter according to claim 4, characterized in that, The vacuum evaporation process conditions for the first and second low-refractive-index material layers are as follows: vacuum degree (0.5 × 10⁻⁶). -3 )-(2×10 -3 Pa, evaporation rate 0.3-1.3 nm / s, baking temperature 270-310℃, baking time 30-60 min.

10. A filtering device, characterized in that, It includes a light source, a collimating lens, and at least two ultraviolet filters as described in any one of claims 1 to 3, wherein the light beam emitted by the light source is incident on each ultraviolet filter at the same angle in sequence.

11. The filtering device according to claim 10, characterized in that, The first film layer of the ultraviolet filter is the incident surface of the light beam.

12. The filtering device according to claim 10, characterized in that, The incident angle of the light beam is 22.5-45°; the number of ultraviolet filters is 4.

13. The filtering device according to any one of claims 10 to 12, characterized in that, Each of the ultraviolet filters is backed by a photodetector, which is positioned perpendicular to the transmission direction of the light beam.

14. A filtering method, applied to the filtering apparatus as described in any one of claims 10 to 13, characterized in that, include The light beam emitted by the light source is collimated by the collimating lens to obtain collimated light; The collimated light passes through each of the ultraviolet filters at the same incident angle for reflection and filtering, thereby obtaining a light source beam with a convergent spectral range.

15. The filtering method according to claim 14, characterized in that, Also includes: When each of the ultraviolet filters is equipped with a photodetector, each photodetector synchronously detects the transmitted light intensity of its corresponding ultraviolet filter and corrects the reference light intensity of that ultraviolet filter.

16. The application of the filtering method as described in claim 14 or 15 in the detection of sulfur dioxide gas concentration, characterized in that, include The light source is a zinc lamp or a flashing xenon lamp; The incident angle of the beam is 22.5-45°; The number of ultraviolet filters is 4; The spectral range of the light source converges to 200-230 nm after being filtered by all ultraviolet filters.

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