Interference mirror

 

(57) Abstract:

Usage: to create was highly reflective mirrors with guaranteed low value of the transmittance, mainly for IR laser technology. The essence of the invention: interference in the mirror that includes an optically polished substrate and a deposited metal reflective coating, was highly reflective layer of metal has a thickness of from 0.03 to 0.06 μm, and the substrate and adhesively pestiviruses layers made of optically transparent material. This was highly reflective layer of metal may be made of silver or gold, or copper, or aluminum. 1 C.p. f-crystals, 1 Il.

The invention relates to an optical instrument, in particular to the technology of optical coatings, and can be used for manufacturing was highly reflective mirrors with guaranteed low value of transmittance for measuring systems, mainly in the infrared laser technology.

Interference coatings have found wide application in optical instrumentation, including laser technology, in particular in technological lasers. In the system of measuring the radiation power of technological lasers frequent the rate of transmission. In this case the output power of laser radiation are judged by a small part of the output via the "back" of the resonator mirror and measured by the light receiver.

Typical requirements for such cavity mirrors are high reflectivity, at least 99% due to the minimal loss in the resonator, and the guaranteed value of the transmittance of 0.5% due to the necessity of the withdrawal of a certain small part of the radiation from the resonator. In the latter case, the mirror acts as a reliever powerful radiation to the radiation detector. A necessary requirement for such mirrors are minimal loss to scattering and absorption.

Traditionally, such mirrors are optically polished substrate is transparent at the operating wavelength of the material, which is applied to multilayer interference mirror coating of the form P(HB)pwhere P - substrate, N and alternating, usually a quarter-wave interference layers having low and high refractive indices, respectively, p is the number of pairs of interference layers. So, for example, infrared rear resonator mirror on a substrate of germolene of 1.35 and 2.4, respectively, which is typical for optical companies in the USA. In another case, the interference mirror coating consists of 10 to 12 layers of zinc selenide and germanium having a refractive index of 4.0.

The main disadvantages of such conventional solutions of mirrors, especially for the infrared radiation, are relatively high complexity due to the large number of layers and increased losses on the scattering and absorption, which in the last analogue can reach 1%

Known technical solution (prototype) was highly reflective mirrors, mainly for the infrared radiation, in which an optically polished substrate deposited reflective coating type P AND1Me A2(HB)pwhere the substrate is made of metal, AND1and a2adhesively pestiviruses layers of chromium and ZnSe, respectively, Me - reflective layer of silver of a thickness of 0.1 to 0.15 μm, N and quarter-wave interference layers of ThF4and ZnSe, respectively, in the amount of from two to three pairs. These mirrors achieve a high reflectance factor up to 99.5 99.8%, including at a wavelength of 10.6 μm, which is necessary for technological CO2-lasers.

The main disadvantage of the prototype in relation to "rear which I receive a guaranteed small values of transmittance at high value of the reflection coefficient, not less than 99,0%

This goal is achieved by the fact that in the known structure of metal-dielectric mirror substrate and adhesively pestiviruses layers made of optically transparent at the operating wavelength of the material, and the layer was highly reflective metal such as silver, gold, copper, aluminum, and has a thickness of from 0.03 to 0.06 μm.

The proposed solution has the following essential features of novelty. The first sign of a substrate and adhesively pestiviruses layers made of optically transparent material. This is due to the need to obtain a guaranteed transmittance. The choice of substrate material in accordance with this requirement is, for example, by reference. Adhesively pestiviruses layers with a thickness of 0.05 to 0.2 μm apart from the main purpose of improving the adhesion of the metal layer with the substrate and amplifying the interference layers act as diffusion barrier for stabilizing the structure of the metal layer and the preservation of its optical and physical characteristics. To assess the correctness of the choice of material adhesively passivating layers is convenient to use a valid value of absorption at the operating wavelength is not more than the IRS silicon (SiO2), we obtain RF-cathode technology in a single technological process was highly reflective layer of metal.

The second sign was highly reflective layer of metal has a thickness of from 0.03 to 0.06 μm. In relation to this type of mirror it is reasonable to believe was highly reflective of those metals which, when the layer thickness of not less than 0.1 μm are at the working wavelength reflectance not less than 99% for example, silver in the area longer to 0.75 μm gold longer than 1.5 μm, the copper is longer than 10 μm and aluminum long to 20.0 μm. It is widely known application of these materials as a broadband mirror coatings, in this case, the layer thickness is not less than 0.1 μm, and the transmittance is equal to zero. It is also known to use layers was highly reflective of the metals in the composition of the metal-dielectric filters, where the thickness of the layer is chosen from a transmittance of a few percent. It is also known to use layers of aluminum as the output mirror coatings for excimer laser at a wavelength of 172,5 nm. The thickness of the aluminum layer was 0,021 mm, which ensured that the reflection coefficient of 73% and a transmittance of 3.0% As you can see, the last example does not implement the in, for example of copper obtained cathode magnetron technology, when the transmittance (0,1 -0,2)% had a sufficiently high reflection coefficient (98,0 98,8)% at a wavelength of 10.6 μm, which corresponded to a layer thickness of from 0.04 to 0.03 μm, respectively. In the patent and scientific literature, the use of partially transparent layers was highly reflective metals in the composition was highly reflective mirrors with a guaranteed low value of the transmittance was not found.

In the drawing conditionally in cross section showing the proposed design was highly reflective mirrors, where: 1 substrate of optically transparent material, 3 partially transparent layer was highly reflective metal, which on both sides framed adhesively pestiviruses layers 2 and 4, over the last applied amplifying the reflection of the interference layers 5. The radiation is directed to the mirror side of the interference layers, not less than 99,0% of the energy is reflected and not less than 0.05% passes through the mirror and is supplied to the radiation receiver.

The proposed mirror is implemented as follows.

On the basis of the operating wavelength, choose a substrate material, such as germanium for a wavelength of 10.6 microns, or optical is 11141-84 and in accordance with the requirement of drawing the shape of the surface. Then the method of cathode sputtering in a single technological cycle is applied consistently adhesively passivating layer is then partially transparent layer was highly reflective metal such as silver, and then adhesively passivating layer, for example silicon dioxide with a thickness of 0.05 to 0.2 μm. The thickness of the partially transparent layer was highly reflective metal is selected in the range from 0.03 to 0.06 μm on the magnitude of the reflection coefficient, which must be not less than 98% and a transmittance of not less than 0.1% together with the substrate and pestiviruses layers. Thus the criterion for the correctness of the choice of material and thickness of the adhesion-passivating layers is valid absorption of not more than 0.1% Next any vacuum applied technology enhances the reflection of the interference layers General view (HB)pwhere N and - interference, basically a quarter-wave at the operating wavelength layers with low and high values of refractive index, n the number of pairs of such layers (at least one). It should be noted that the total optical thickness of the adhesion-pestiviruses layer AND2and the nearest layer with low refractive index must be equal to a quarter of the working wavelength. 2 and with the high value of the refractive index of refractory oxides of zirconium, hafnium, titanium and other operating wavelength of 10.6 microns as amplifying the interference layers are materials ThF4and ZnSe (based on the experience of firms in the U.S.) or ZnSe and Ge, or in our experience materials ZnSe and telluride Germany (GeTe) with a refractive index n of 3.7. The principle of selecting the number of pairs of interference layers such that, when the minimum number to obtain a reflectivity of more than 99% [7] In particular, for materials ZnSe and GeTe enough one pair of quarter-wave interference layers to get10,699,0 and10,60,05%.

The proposed solution is illustrated by the following example. We have made was highly reflective resonator "rear" mirror with a guaranteed low value of transmittance for technological CO2laser type t is 1.5. produced in SIC t RAS. Conventionally, the design of such mirrors can be written as: P SiO2CuSiO2ZnSeGeTe, where P is the substrate of Germany, Cu partially transparent layer of copper with a thickness of 0.03 to 0.04 μm, the applied cathodic magnetron technology, and the exact thickness of this layer was determined by optical characteristics10,698% and10,6of 99.3-99.5% and10,6= 0,05-0,1%. Such mirrors are successfully used in the composition of the resonators of technological lasers type TL-1.5, if the power density of up to 1.0 kW/cm2when the output of the laser power up to 1.5 kW, ensuring the functioning of the integrated system for measuring average power is the same.

Thus, in comparison with analogues reduced the complexity of manufacturing mirrors by reducing the number of layers and significantly reduced losses by scattering (more than an order of magnitude). Compared with the prototype at a high value of the reflection coefficient obtained guaranteed transmittance satisfying the requirements of an embedded system average power measurement radiation technology CO2laser type t is 1.5.

1. Interference mirror comprising an optically polished substrate and a deposited mirror coating

Pamea(HB)n,

where n substrate;

IU was highly reflective layer of metal;

A1 and A2 adhesively pestiviruses layers with a thickness of 0.05 to 0.2 microns;

N and amplifying the reflection of alternating layers of low and high rates which has a thickness of from 0.03 to 0.06 μm, and the substrate and adhesively pestiviruses layers made of optically transparent material.

2. Mirror under item 1, characterized in that the layer was highly reflective metal made of silver, or gold, or copper, or aluminum.

 

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