Partially reflecting mirror film for CO2 laser

Abstract

The invention belongs to the field of optical films, and particularly relates to a partial reflector film for a CO2 laser. When light obliquely enters a common thin film deposited on a flat substrate, separation between P-and S-polarization components is inevitably generated, which is a polarization effect; when a conventional short-wave-pass or long-wave-pass cut-off filter is used in an inclined mode, P-and S-are seriously separated at the required wave band due to the polarization effect, and therefore the using effect is seriously affected. According to the design scheme of the depolarization beam-splitting film, the polarization spectrum separation amount at the required wave band can be effectively eliminated at any incident angle, and particularly, the depolarization of a part of reflecting film is realized; the reflection and transmissivity of the required wave band can be conveniently adjusted; the film system design is simple and can be completed by means of any conventional film design software; the film is suitable for all dielectric film materials in the current optical film industry; the method has the characteristics of strong pertinence, wide application range, high quality and low manufacturing difficulty.

Description

Technical Field

[0001] The invention belongs to the field of optical films, and in particular relates to a partial reflector film for a CO2 laser. Background Art

[0003] Carbon dioxide (CO2) laser was invented by C.Kumar N.Patel at Bell Labs in 1964. It is also called glass laser tube. It is a laser product with high continuous output power. It is widely used in textile, medical, material processing, industrial manufacturing and other fields, especially in packaging coding, non-metallic material cutting, medical beauty and other industries. It is a hot topic in current research. In the process of CO2 laser research, because of the different polarization states of 10.6um polarized light at different angles, the polarization effect caused by oblique incidence of the film must be eliminated as much as possible in the optical path.

[0004] The initial structure of conventional short-wave pass or long-wave pass cut-off filters is G(0.5LH0.5L) p A and G (0.5HL0.5H) p A. Here G and A represent the flat substrate and air, respectively, H and L represent the quarter optical thickness of the high and low refractive index materials, respectively, and p is the number of periods. Cut-off filters based on this initial structure have been widely used so far. However, at large angles of oblique incidence, the P- and S-polarization separation at the transition band is very serious, so it cannot meet the increasing angle requirements, and a new thin film design method is urgently needed.

[0005] The multi-cavity narrow-band thin-film filter film system design method has many advantages such as low insertion loss, temperature insensitivity and high rectangularity, so it has been widely used in the field of infrared gas detection. However, when the thin-film filter is under oblique incidence, the reduction of the equivalent optical thickness of its spacer layer will cause the central wavelength of its transmission to drift toward the short-wave direction. At the same time, there is a significant separation between the central wavelength of its P-polarized light and the central wavelength of the S-polarized light, which leads to serious polarization-related loss of the average light and limits the oblique incidence angle of the filter. The polarization effect mentioned above refers to the separation between the P- and S-polarized components that usually occurs when light is obliquely incident on the film. Therefore, when designing a short-wave pass or long-wave pass cutoff filter with 45° incidence, it is required that the film can separate two similar wavelengths, so that one wavelength is highly reflected and the other wavelength is highly transmitted, and the polarization spectrum separation of the transition band P- and S-polarized light at 50%-60% transmittance is required to be as small as possible.

[0006] The multi-cavity narrow-band thin film filter film system design method solves part of the polarization effect, but the defects of this method are also significant. First, due to the high order of the spacer layer, the overall thickness of the film is very thick, which is not conducive to practical preparation. Secondly, the width of the transmission band and the cutoff band is still not wide enough, and may no longer be applicable in some cases. Finally, when the H and L refractive indices do not match, there may be a situation where the P- and S-polarization separation in the transition band cannot be eliminated and mass production cannot be achieved. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a new depolarization design of a partial reflector film for a CO2 laser in view of the shortcomings of the background technology.

[0008] The present invention adopts the following technical solutions to solve the above technical problems:

[0009] A partial reflector film for a CO2 laser comprises a film, wherein the initial structure of the film is: G(aMbHcL)^P dL A; wherein G and A represent a flat substrate and air respectively, H, M and L represent a quarter of the optical thickness of high, medium and low refractive index materials respectively, and P is the number of periods; a, b, c and d are coefficients in front of different high, medium and low materials respectively.

[0010] As a further preferred embodiment of a partial reflector film for a CO2 laser of the present invention, the basic periodic structure of the film is: (aMbHcL)^P dL; by adjusting the relative proportions of a, b, c, and d, the polarization spectrum separation of P- and S- at the required band during oblique incidence is adjusted until complete depolarization is achieved.

[0011] As a further preferred embodiment of the partial reflector film for CO2 laser of the present invention, the material in the basic periodic structure of the film is an asymmetric structure. The width of the transmission band and the cutoff band can be adjusted by adjusting the proportion of the corresponding materials of a, b, c, and d.

[0012] As a further preferred embodiment of the partial reflector film for CO2 laser of the present invention, the basic periodic structure of the film comprises three types of film dielectric materials with high, medium and low refractive indexes.

[0013] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0014] 1. For a flat substrate, the present invention can effectively eliminate the problem that the polarization spectrum separation between P- and S- at 50%-60% of the wavelength band is small at any incident angle;

[0015] 2. The present invention can conveniently adjust the size of the P light and S light offset through the coefficients in the basic periodic structure;

[0016] 3. The present invention can conveniently adjust the width of the transmission band and the cutoff band by adjusting the number of membrane layers in the basic periodic structure;

[0017] 4. The method of the present invention is simple and easy to implement. It can be completed by using a computer and any conventional thin film design software;

[0018] 5. The method of the present invention is highly targeted, has a wide range of applications and high quality; this method is applicable to all dielectric thin film materials in the current optical thin film industry; the designed film system does not contain an extremely thick layer, and the total thickness of the film layer is relatively thin, which is conducive to precise preparation and is conducive to significantly improving the product yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 This is a schematic diagram of the spectrum curve of the initial structure G(1.0M0.6H.2L)^2 0.8LA at 45° incidence in the present invention;

[0021] Figure 2 This is a schematic diagram of the spectrum curve of the initial structure G(1.0M0.6H.2L)^3 0.8LA at 45° incidence in the present invention;

[0022] Figure 3 This is the actual spectral curve of the initial structure G(1.0M0.6H.2L)^6 0.8LA at 45° incidence in the present invention. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings:

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The present invention is described in detail below based on the drawings and preferred embodiments, and the purpose and effect of the present invention will become clearer. It should be understood that the specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0025] A partial reflector film for a CO2 laser comprises a film, wherein the initial structure of the film is: G(aMbHcL)^P dL A; wherein G and A represent a flat substrate and air respectively, H, M and L represent a quarter of the optical thickness of high, medium and low refractive index materials respectively, and P is the number of periods; a, b, c and d are coefficients in front of different high, medium and low materials respectively.

[0026] The basic periodic structure of the film is: (aMbHcL)^P dL; by adjusting the relative proportions of a, b, c, and d, the polarization spectrum separation of P- and S- at the required band during oblique incidence is adjusted until complete depolarization is achieved.

[0027] The materials in the basic periodic structure of the film are asymmetric structures. The widths of the transmission band and the cutoff band can be adjusted by adjusting the proportions of the corresponding materials of a, b, c, and d.

[0028] The basic periodic structure of the film includes three types of film dielectric materials with high, medium and low refractive indexes.

[0029] Embodiment 1:

[0030] For CO2 lasers, it is necessary to separate the 10600nm wavelength at 45° incidence so that the reflectivity of 10600nm is 98%, and at the same time, the polarization spectrum separation of P- and S- at 9600-10600nm is required to be less than 1%.

[0031] The membrane system design can be obtained by the following methods:

[0032] L represents YbF3 with a refractive index of 1.33, H represents Ge with a refractive index of 4.4, and M represents ZnS with a refractive index of 2.19. These are the most common dielectric thin film materials in industry. The substrate G is a ZnSe substrate, and the incident medium A is air. The absorption of the film and substrate is not considered here.

[0033] Given the initial structure: G(aMbHcL)^P dLA, temporarily take a=1, b=0.6, c=0.2, d=0.8. , p=2, reference wavelength is 10600nm, and we get Figure 1 It can be found that the polarization spectrum separation of P- and S- in the transition band at 9600-10600nm is already small. Therefore, the parameters are further adjusted to: a = 1, b = 0.6, c = 0.2, d = 0.8, p = 3, and the reference wavelength is 10600nm, and the following is obtained: Figure 3 The spectrum shown. It can be found that the polarization spectrum separation of P- and S- at 9600-10600nm is 0.02%. At the same time, the reflectivity near 10600nm also meets the requirement of 98% + / - 2%. The horizontal axis in the figure is wavelength, and the vertical axis is reflectivity.

[0034] So far, it can be considered that the appropriate initial structure of the film has been found: G(M0.6H0.2L)^1 0.8LA.

[0035] Based on this, the ideal depolarized long-wave pass can be obtained using any thin film design software. Figure 3 The design with G(M0.6H0.2L)^60.8LA does not require optimization results. It can be found that at 9600-10600nm, the reflectivity is greater than 97%, and the polarization spectrum separation of P- and S- at 9600-10600nm is 0.02%. It fully meets the use requirements.

[0036] like Figure 1 As shown, at 45° incidence, the spectral curve of the initial structure G(1.0M0.6H.2L)^2 0.8LA (L represents YBF3, with a refractive index of 1.33, H is Ge, with a refractive index of 4.4, M is ZnS, with a refractive index of 2.19, the substrate G is ZNSe, the incident medium A is air, and the reference wavelength is 10600nm).

[0037] like Figure 2 As shown, at 45° incidence, the spectral curve of the initial structure G(1.0M0.6H.2L)^3 0.8LA (L represents YBF3, with a refractive index of 1.33, H is Ge, with a refractive index of 4.4, M is ZnS, with a refractive index of 2.19, the substrate G is ZNSe, the incident medium A is air, and the reference wavelength is 10600nm).

[0038] like Figure 3 As shown, at 45° incidence, the actual spectral curve of the initial structure G(1.0M0.6H.2L)^6 0.8LA (L represents YBF3, with a refractive index of 1.33, H is Ge, with a refractive index of 4.4, M is ZnS, with a refractive index of 2.19, the substrate G is ZNSe, the incident medium A is air, and the reference wavelength is 10400nm).

[0039] Those skilled in the art can understand that the above are only preferred examples of the invention and are not intended to limit the invention. Although the invention is described in detail with reference to the above examples, those skilled in the art can still modify the technical solutions recorded in the above examples or replace some of the technical features with equivalents. Any modification, equivalent replacement, etc. made within the spirit and principle of the invention should be included in the protection scope of the invention. All technical features in this embodiment can be freely combined according to actual needs.

[0040] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A partial reflector film for a CO2 laser, characterized in that: It comprises a thin film, wherein the initial structure of the thin film is: G(aMbHcL)^P dL A; wherein G and A represent a flat substrate and air respectively, H, M and L represent one quarter of the optical thickness of high, medium and low refractive index materials respectively, P is the number of periods; a, b, c and d are the coefficients in front of different high, medium and low materials respectively.

2. A partial reflector film for a CO2 laser according to claim 1, characterized in that: The basic periodic structure of the film is: (aMbHcL)^P dL; by adjusting the relative proportions of a, b, c, and d, the polarization spectrum separation of P- and S- at the required band during oblique incidence is adjusted until complete depolarization is achieved.

3. A partial reflector film for a CO2 laser according to claim 2, characterized in that: The materials in the basic periodic structure of the film are asymmetric structures. The widths of the transmission band and the cutoff band can be adjusted by adjusting the proportions of the corresponding materials of a, b, c, and d.

4. The partial reflector film for CO2 laser according to claim 1, characterized in that: The basic periodic structure of the film includes three types of film dielectric materials with high, medium and low refractive indexes.

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