A method for preparing high-performance narrow-band filter film with oblique incidence

Abstract

The present invention relates to a method for preparing an oblique-incidence high-performance narrow-band filter film, comprising the following steps: step 1: prepare obliquely deposited single-layer films of high and low refractive index materials respectively; step 2: test the transmittance and reflectance curves of the single-layer films of high and low refractive index materials respectively, and obtain the thickness and refractive index parameters of the single-layer films of high and low refractive index materials by fitting according to the transmittance and reflectance respectively; step 3: design and determine the film system structure of the five-cavity narrow-band filter film at the working angle according to the thickness and refractive index parameters of the single-layer films of high and low refractive index materials; step 4: prepare an oblique-incidence high-performance narrow-band filter film according to the film system structure of the five-cavity narrow-band filter film, and test the transmission spectrum of the oblique-incidence high-performance narrow-band filter film. Compared with the prior art, the present invention can solve the problem that the optical properties of the narrow-band filter film will change significantly when the incident angle is greater than 25° in the prior art, and the film has high transmittance.

Description

Technical Field

[0001] The invention relates to the technical field of film thickness control, and in particular to a method for preparing an oblique-incidence high-performance narrow-band filter film. Background Art

[0002] Narrowband filter films are widely used in various fields such as optics, astrophysics, lasers, and communications. Their high spectral efficiency, high steepness, and narrow bandwidth characteristics are ideal conditions for various precision optical system applications. For example, narrowband filter groups are used to couple different high-power laser beams to increase the total power output of the laser.

[0003] Fabry-Perot interference film is a simple and commonly used narrowband filter film. This type of film has a fatal disadvantage, that is, they are only suitable for collimated light with vertical incidence or small angle incidence. However, when the incident angle increases, the filter characteristics will deteriorate significantly. The reason is that when the incident light is oblique, the effective refractive index of the high and low refractive index film layers is different, so the central wavelengths of the two polarization components no longer coincide, the S polarized light and P polarized light characteristics are separated, and the passband of the narrowband filter collapses. However, the actual situation requires narrowband filters to serve under oblique incidence conditions, which seriously limits the practical application of narrowband filter films.

[0004] In view of the problem of the application of filter films under large-angle incidence conditions, people have conducted a lot of research on depolarizing filter films. Cai et al. proposed a simple design method for depolarizing filter films based on dielectric-metal-dielectric film stacks. However, due to the high absorption and low damage threshold of metal materials, their application in high-power laser systems is limited. Baumeister used standing wave ratio technology to match the reflection band and designed a 45° depolarizing bandpass filter. However, this method uses up to 7 materials, which brings difficulties to the preparation. Thelen discovered another new method based on detuned FP cavity. However, this kind of filter film usually requires an irregular film structure to achieve high transmittance, but the manufacturing process is complicated and cumbersome. At the same time, due to the low tolerance and high sensitivity of the film structure, the passband efficiency will be reduced due to the monitoring error and error accumulation effect, which is not conducive to the efficient preparation of the film. So far, no coating technology has been proposed that can efficiently and stably prepare narrow-band filter films with high spectral performance under oblique incidence. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a high-performance narrow-band filter film with oblique incidence in order to overcome the defects of the above-mentioned prior art. The present invention can solve the problem in the prior art that the optical properties of the narrow-band filter film will change significantly when the incident angle is greater than 25°, and the film has a high transmittance.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] The present invention provides a method for preparing an oblique-incidence high-performance narrow-band filter film, comprising the following steps:

[0008] Step 1: Prepare obliquely deposited single-layer films of high and low refractive index materials respectively;

[0009] Step 2: testing the transmittance and reflectance curves of the single-layer films of the high and low refractive index materials prepared in step 1 respectively, and fitting the thickness and refractive index parameters of the single-layer films of the high and low refractive index materials respectively according to the transmittance and reflectance;

[0010] Step 3: Based on the thickness and refractive index parameters of the single-layer films of the high and low refractive index materials obtained in step 2, design and determine the film system structure of the five-cavity narrow-band filter film at the working angle;

[0011] Step 4: According to the film system structure of the five-cavity narrow-band filter film determined in step 3, prepare an oblique-incidence high-performance narrow-band filter film, and test the transmission spectrum of the prepared oblique-incidence high-performance narrow-band filter film.

[0012] Preferably, the step 3 is specifically:

[0013] According to the thickness and refractive index parameters of the single-layer films of the high and low refractive index materials obtained in step 2, the initial film system structure of the five-cavity narrow-band filter film is designed, and then according to the relationship between the physical thickness and optical thickness of the film, the initial film system structure of the five-cavity narrow-band filter film is optimized, and the film system structure of the five-cavity narrow-band filter film is determined as follows:

[0014] Sub|(1.02H 1.04L)^4 1.021H 4.17L(1.02H 1.04L)^10 1.2H 2.09L(1.02H1.04L)^10 1.02H 12.52L(1.02H 1.04L)^10 1.2H 2.09L(1.02H 1.04L)^10 1.02H4.17L(1.02H 1.04L)^4 1.39H 1.37L|Air;

[0015] Among them, H is a high refractive index material, and L is a low refractive index material.

[0016] Preferably, the formula describing the relationship between the physical thickness and optical thickness of the film is as follows:

[0017]

[0018] Where Q is the unit thickness of QWOT, λ0 is the control wavelength, θ m is the working angle, n(λ0) is the refractive index of the material at the control wavelength, n mTo match the refractive index of the medium, d is the physical thickness.

[0019] Preferably, in step 3, the five-cavity narrow-band filter film is composed of alternating dielectric layers of high-refractive index and low-refractive index materials, and the cavity layer of the five-cavity narrow-band filter film is made of low-refractive index material.

[0020] Preferably, the tilting tool is used to monitor the tilting deposition process of the single-layer films of high and low refractive index materials and the oblique-incidence high-performance narrow-band filter film.

[0021] Preferably, the tilting tooling includes a light source, a monitoring film, a detector and a light-controlled computer. The light beam is emitted by the light source, irradiated to the back of the monitoring film through the second reflector, and then transmitted to the detector through the first reflector, and then transmitted to the light-controlled computer by the detector. The tilting angle of the monitoring film is consistent with the working angle of the five-cavity narrow-band filter film.

[0022] Preferably, in step 1, single-layer films of high and low refractive index materials are prepared respectively by dual ion beam sputtering deposition method.

[0023] Preferably, in step 2, a spectrometer is used to test the spectrum of the single-layer film at 450 nm to 1200 nm, and the thickness and refractive index parameters of the single-layer films of high and low refractive index materials are respectively obtained by fitting using the envelope method.

[0024] Preferably, the oblique-incidence high-performance narrow-band filter film is prepared by a dual ion beam sputtering deposition method.

[0025] Preferably, the film thickness of the oblique-incident high-performance narrow-band filter film during the deposition process is monitored and controlled by a mixed monitoring strategy of inclined direct single-wavelength monitoring and time monitoring.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention provides a method for preparing a high-performance narrow-band filter film for oblique incidence. The method designs an initial film system structure of a five-cavity narrow-band filter film by obtaining the thickness and refractive index parameters of a single-layer film of a high-refractive index material and a low-refractive index material. The film system structure is then optimized according to a formula describing the relationship between the physical thickness and the optical thickness of the film. When the incident angle of the film designed and prepared by the present invention is greater than 25°, the effective refractive indexes of the high and low refractive index layers are the same, so that the central wavelengths of the two polarization components coincide, thereby suppressing the passband collapse. This solves the problem in the prior art that the optical properties of the narrow-band filter film will change significantly when the incident angle is greater than 25°.

[0028] (2) The present invention provides a method for preparing an oblique-incidence high-performance narrow-band filter film. By designing an inclined tool, the oblique monitoring of the narrow-band filter film is achieved. Combined with the structural characteristics of the narrow-band filter film, the influence of thickness error and error accumulation on the spectrum is minimized.

[0029] (3) The present invention provides a method for preparing an oblique-incidence high-performance narrow-band filter film, which prepares a single-layer film by adopting a dual ion beam sputtering deposition method, thereby ensuring that there is almost no difference in the refractive index of the single-layer film deposited obliquely and normally.

[0030] (4) The method for preparing an oblique-incidence high-performance narrow-band filter film provided by the present invention can effectively prepare an oblique-incidence narrow-band filter film, which is of great significance for the preparation of high-performance narrow-band filter films. The present invention is universal for narrow-band filter films with different working wavelengths and different working angles. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A flow chart of a method for preparing an oblique-incidence high-performance narrow-band filter film provided in this embodiment;

[0032] Figure 2 This is a schematic diagram of tilt direct single wavelength monitoring;

[0033] Figure 3 Transmission spectra of Ta2O5 monolayer films deposited normally and tilted;

[0034] Figure 4 The theoretical transmission spectrum of the initially designed 1064nm narrow filter film;

[0035] Figure 5 The theoretical transmission spectrum of the optimized 1064nm narrow-band filter film for 25° incidence.

[0036] Figure 6 This is the film thickness diagram of the optimized 1064nm narrow-band filter film;

[0037] Figure 7 It is the tilt direct single wavelength monitoring curve;

[0038] Figure 8 This is the test spectrum of the prepared narrow-band filter film sample.

[0039] Fig. 9 Schematic diagram of the 1064nm narrow-band filter film structure. DETAILED DESCRIPTION

[0040] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0041] refer to Figure 1 As shown, the present invention provides a method for preparing an oblique-incidence high-performance narrow-band filter film, comprising the following steps:

[0042] Step 1: Prepare obliquely deposited single-layer films of high and low refractive index materials respectively;

[0043] As an optional embodiment, single-layer films of high and low refractive index materials are prepared respectively by a dual ion beam sputtering deposition method; preparing a single-layer film by a dual ion beam sputtering deposition method can ensure that there is almost no difference in the refractive index of the single-layer film deposited by oblique deposition and that by normal deposition, but there is still a difference in thickness.

[0044] As an optional implementation, the single-layer film of the high-refractive-index material is a Ta2O5 single-layer film, and the single-layer film of the low-refractive-index material is a SiO2 single-layer film.

[0045] Step 2: testing the transmittance and reflectance curves of the single-layer films of the high and low refractive index materials prepared in step 1 respectively, and fitting the thickness and refractive index parameters of the single-layer films of the high and low refractive index materials respectively according to the transmittance and reflectance;

[0046] As an optional implementation, a spectrometer is used to test the spectrum of a single-layer film at 450nm to 1200nm, and the thickness and refractive index parameters of the single-layer films of high and low refractive index materials are respectively obtained by fitting using an envelope method;

[0047] Step 3: Based on the thickness and refractive index parameters of the single-layer films of the high and low refractive index materials obtained in step 2, design and determine the film system structure of the five-cavity narrow-band filter film;

[0048] As an optional implementation, a five-cavity narrow-band filter film structure is designed through OptiLayer's WDM module;

[0049] Specifically, according to the thickness and refractive index parameters of the single-layer films of the high and low refractive index materials obtained in step 2, the initial film system structure of the five-cavity narrow-band filter film is designed as follows:

[0050] Sub|(HL)^4H 4L(HL)^10H 2L(HL)^10H 12L(HL)^10H L(HL)^10H L(HL)^41.358H 1.317L|Air

[0051] According to the relationship between the physical thickness and optical thickness of the film, the film structure of the five-cavity narrow-band filter film is optimized and confirmed as follows:

[0052] Sub|(1.02H 1.04L)^4 1.021H 4.17L(1.02H 1.04L)^10 1.2H 2.09L(1.02H1.04L)^10 1.02H 12.52L(1.02H 1.04L)^10 1.2H 2.09L(1.02H 1.04L)^10 1.02H4.17L(1.02H 1.04L)^4 1.39H 1.37L|Air,

[0053] Among them, H represents high refractive index material, L represents low refractive index material, and the operating wavelength is 1064nm.

[0054] Specifically, the formula describing the relationship between the physical thickness and optical thickness of a film is as follows:

[0055]

[0056] Where Q is the unit thickness of QWOT, λ0 is the control wavelength, θ m is the matching angle, n(λ0) is the refractive index of the material at the control wavelength, and n m To match the refractive index of the medium, d is the physical thickness.

[0057] Since the theoretical spectrum of this film system has a good passband waveform at 0° incidence, but when the incident angle is greater than 25°, the passband will collapse severely. Figure 4 As shown. The reason is that the effective refractive index of the high and low refractive index film layers is different under large angle incidence, so that the central wavelengths of the two polarization components no longer overlap. Therefore, the present invention optimizes the film system structure by describing the relationship between the physical thickness and optical thickness of the film, and then can obtain that when the incident angle is greater than 25°, the effective refractive index of the high and low refractive index layers is the same, so that the central wavelengths of the two polarization components overlap, thereby suppressing the passband collapse.

[0058] As an optional implementation, the five-cavity narrow-band filter film is composed of alternating high- and low-refractive index dielectric layers, wherein the cavity layer is made of low-refractive index material to improve the damage resistance of the film in a high-intensity laser system;

[0059] Step 4: According to the film system structure of the five-cavity narrow-band filter film determined in step 3, prepare an oblique-incidence high-performance narrow-band filter film, and test the transmission spectrum of the prepared oblique-incidence high-performance narrow-band filter film.

[0060] As an optional implementation, the oblique-incidence high-performance narrow-band filter film is prepared by a dual ion beam sputtering deposition method.

[0061] As an optional implementation, the film thickness of the oblique-incident high-performance narrow-band filter film during the deposition process is monitored and controlled by a mixed monitoring strategy of inclined direct single-wavelength monitoring and time monitoring.

[0062] As an optional embodiment, the tilting tool is used to monitor the tilting deposition process of single-layer films of high and low refractive index materials and oblique-incidence high-performance narrow-band filter films.

[0063] Specifically, the tilting tooling includes a light source, a monitoring film, a detector and a light-controlled computer. The light beam is emitted by the light source, irradiated to the back of the monitoring film through the second reflector M2, and then transmitted to the detector through the first reflector M1, and then transmitted to the light-controlled computer by the detector. The tilting angle of the monitoring film is consistent with the working angle of the five-cavity narrow-band filter film.

[0064] Any combination of the above preferred implementation modes can result in a better implementation mode. The following specifically describes an optimal implementation mode obtained by combining all the implementation modes.

[0065] JGS1 is used as the substrate, which is double-sided polished and has a specification of Φ50*3mm.

[0066] The coating materials are high refractive index material Ta2O5 and low refractive index material SiO2.

[0067] Step 0: Design a tilting fixture whose tilting angle is consistent with the working angle of the five-cavity narrow-band filter film.

[0068] refer to Figure 2 As shown, the tooling includes a light source, a monitoring film, a detector and a light-controlled computer. The light beam is emitted by the light source, irradiated to the back of the monitoring film through the second reflector M2, and then transmitted to the detector through the first reflector M1, and then transmitted to the light-controlled computer by the detector. In this embodiment, the inclination angle of the monitoring film is 25°.

[0069] Step 1: Prepare obliquely grown Ta2O5 monolayer and SiO2 monolayer films;

[0070] Before starting to prepare oblique-incidence narrow-band filter films, it is necessary to obtain accurate refractive index parameters of high and low refractive index materials. In this experiment, the dual ion beam sputtering deposition method was used to prepare Ta2O5 and SiO2 single-layer films with a central wavelength of 1064nm and an optical thickness of 4QW.

[0071] Step 2: testing the transmittance and reflectance curves of the Ta2O5 single-layer film and the SiO2 single-layer film prepared in step 1 respectively, and fitting to obtain the thickness and refractive index parameters of the Ta2O5 single-layer film and the SiO2 single-layer film;

[0072] The spectrometer was used to test the single-layer film spectrum at 450nm to 1200nm, and the obliquely deposited Ta2O5 single-layer film was tested. Figure 3 As shown in the figure, the thickness and refractive index parameters of the Ta2O5 monolayer film under the two deposition methods were obtained by envelope method fitting. The physical thickness of the Ta2O5 monolayer film deposited normally is 504.4nm, and the physical thickness of the Ta2O5 monolayer film deposited obliquely is 453.9nm. There is almost no difference in the refractive index of the Ta2O5 film deposited obliquely and normally. At 1064nm, n H =2.111.

[0073] The same method was used to obtain the refractive index parameters of SiO2 oblique deposition. Similarly, there was almost no difference between the refractive index of SiO2 deposited by oblique deposition and that of SiO2 deposited by normal deposition. L =1.478.

[0074] Step 3: Based on the thickness and refractive index parameters of the single-layer films of high and low refractive index materials obtained in step 2, design and determine the film structure of a five-cavity narrow-band filter film with a working angle of 25°. The five-cavity narrow-band filter film is composed of alternating Ta2O5 / SiO2 dielectric layers, in which the cavity layer is made of SiO2 material.

[0075] The design of the narrowband filter film is realized through the WDM module of the commercial software OptiLayer.

[0076] The initial design structure is Sub|(HL)^4H 4L(HL)^10H 2L(HL)^10H 12L(HL)^10H L(HL)^10H L(HL)^4 1.358H 1.317L|Air.

[0077] Although the theoretical spectrum of this film system has a good passband waveform at 0° incidence, the passband will collapse seriously when the incident angle increases to 25°. Figure 4 The reason is that the effective refractive index of the high and low refractive index films is different under large angle incidence, so that the central wavelengths of the two polarization components no longer overlap.

[0078] Therefore, the present invention relates a special physical thickness to the optical thickness. This relationship is determined by the refractive index of the material, the matching angle refractive index, and the matching angle. The matching angle mentioned here is the working angle, and the expression is as follows:

[0079]

[0080] Here Q is the unit thickness of QWOT, λ0 is the control wavelength, θ m is the matching angle (working angle), n(λ0) is the refractive index of the material at the control wavelength, and nm To match the refractive index of the medium, d is the physical thickness.

[0081] According to this method, the effective refractive index of the high and low refractive index layers can be the same at 25° incidence, so that the central wavelengths of the two polarization components coincide, thereby suppressing the passband collapse, such as Figure 5 shown.

[0082] The final confirmed film structure is Sub|(1.02H 1.04L)^4 1.021H 4.17L(1.02H 1.04L)^101.2H 2.09L(1.02H 1.04L)^10 1.02H 12.52L(1.02H 1.04L)^10 1.2H 2.09L(1.02H1.04L)^10 1.02H 4.17L(1.02H 1.04L)^4 1.39H 1.37L|Air, where H represents high refractive index material and L represents low refractive index material. The operating wavelength is 1064nm. The structure of the narrowband filter film is as follows: Figure 6 shown.

[0083] Step 4: According to the film system structure of the five-cavity narrow-band filter film determined in step 3, prepare an oblique-incidence high-performance narrow-band filter film, and test the transmission spectrum of the prepared oblique-incidence high-performance narrow-band filter film.

[0084] The narrow-band filter film was prepared by dual ion beam sputtering deposition method. The targets were Ta target and SiO2 target. The sputtering deposition rates were and The vacuum degree in the chamber at the beginning of coating is 2×10 -4 torr, and the baking substrate temperature is constant at 150°C. During the deposition process, a mixed monitoring strategy of tilted direct single wavelength monitoring and time monitoring is used to control the film thickness. The monitoring wavelength and fitting wavelength of the tilted direct single wavelength monitoring are 1064nm, and the stop judgment method is the extreme point monitoring strategy. The monitoring curve of the tilted single wavelength monitoring is as follows: Figure 7 The time monitoring strategy is applied to the spacer layer and the admittance matching layer in the film structure. The number of layers involved is 20, 44, 64, 88, 107, and 108. The time monitoring parameters are obtained from the average deposition rate of the first 6 layers deposited to the spacer layer.

[0085] The transmission spectrum of the prepared narrow-band filter film was tested using Agilent's Cary7000 at a test angle of 25°. The test results are shown in the figure below. Figure 8 As shown, the transmittance at a wavelength of 1064 nm is 98% and the bandwidth is about 3 nm.

[0086] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for preparing an oblique-incidence high-performance narrow-band filter film, characterized in that: The following steps are involved: Step 1: Prepare obliquely deposited single-layer films of high and low refractive index materials respectively; Step 2: testing the transmittance and reflectance curves of the single-layer films of the high and low refractive index materials prepared in step 1 respectively, and fitting the thickness and refractive index parameters of the single-layer films of the high and low refractive index materials respectively according to the transmittance and reflectance; Step 3: Based on the thickness and refractive index parameters of the single-layer films of the high and low refractive index materials obtained in step 2, design and determine the film system structure of the five-cavity narrow-band filter film at the working angle; Step 4: According to the film system structure of the five-cavity narrow-band filter film determined in step 3, prepare an oblique-incidence high-performance narrow-band filter film, and test the transmission spectrum of the prepared oblique-incidence high-performance narrow-band filter film; The step 3 is specifically as follows: According to the thickness and refractive index parameters of the single-layer films of the high and low refractive index materials obtained in step 2, the initial film system structure of the five-cavity narrow-band filter film is designed, and then according to the relationship between the physical thickness and optical thickness of the film, the initial film system structure of the five-cavity narrow-band filter film is optimized, and the film system structure of the five-cavity narrow-band filter film is determined as follows: Sub|(1.02H 1.04L)^4 1.021H 4.17L(1.02H 1.04L)^10 1.2H 2.09L(1.02H1.04L)^10 1.02H 12.52L(1.02H 1.04L)^10 1.2H 2.09L(1.02H 1.04L)^10 1.02H 4.17L(1.02H1.04L)^4 1.39H 1.37L|Air; Among them, H is a high refractive index material, and L is a low refractive index material; The formula that describes the relationship between the physical thickness and optical thickness of a film is as follows: Where Q is the unit thickness of QWOT, λ0 is the control wavelength, θ m is the working angle, n(λ0) is the refractive index of the material at the control wavelength, n m To match the medium refractive index, d is the physical thickness; In step 3, the five-cavity narrow-band filter film is composed of alternating dielectric layers of high-refractive index and low-refractive index materials, and the cavity layer of the five-cavity narrow-band filter film is made of low-refractive index material.

2. The method for preparing an oblique-incidence high-performance narrow-band filter film according to claim 1, characterized in that: The tilt tool is used to monitor the tilt deposition process of single layers of high and low refractive index materials as well as high-performance narrow-band filter films at oblique incidence.

3. The method for preparing an oblique-incidence high-performance narrow-band filter film according to claim 2, characterized in that: The tilting tooling includes a light source, a monitoring film, a detector and a light-controlled computer. The light beam is emitted by the light source, irradiated to the back of the monitoring film through the second reflector, and then transmitted to the detector through the first reflector, and then transmitted to the light-controlled computer by the detector. The tilting angle of the monitoring film is consistent with the working angle of the five-cavity narrow-band filter film.

4. The method for preparing an oblique-incidence high-performance narrow-band filter film according to claim 1, characterized in that: In the step 1, single-layer films of high and low refractive index materials are prepared respectively by a dual ion beam sputtering deposition method.

5. The method for preparing an oblique-incidence high-performance narrow-band filter film according to claim 1, characterized in that: In the step 2, a spectrometer is used to test the spectrum of the single-layer film at 450 nm to 1200 nm, and the thickness and refractive index parameters of the single-layer films of high and low refractive index materials are respectively obtained by fitting using the envelope method.

6. The method for preparing an oblique-incidence high-performance narrow-band filter film according to claim 1, characterized in that: Oblique-incidence high-performance narrow-band filter films were prepared by dual ion beam sputtering deposition method.

7. The method for preparing an oblique-incidence high-performance narrow-band filter film according to claim 1, characterized in that: The film thickness of the oblique-incidence high-performance narrow-band filter film during the deposition process is monitored and controlled by a mixed monitoring strategy of inclined direct single-wavelength monitoring and time monitoring.

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