SU1265678A1 - Interference filter for total internal reflection - Google Patents

Abstract

The invention can be used in instruments for studying the characteristics of the atmosphere. The goal of the acquisition is to increase the accuracy of measurements of the intensity of radiation with a continuous spectrum by reducing the background transmittance in the long wavelength relative to the wavelength of the maximum transmittance of the spectral region. For this, the faces of two identical isosceles prisms, for which the plane of the gap is the bisector of the angle between them. made reflective. Perform an angle at the apex of prisms equal to 180 °. .-2 arcsinV2 / (n2 + 1), where (n, P2 are the refractive indices of the material of the prism of the gap filler), eliminates the dependence of the transmittance on the polarization of the radiation and preserves the radiation by natural polarization independently (Q on the size of the gap when tuning the maximum wavelength filter transmission. A ratio is given which is satisfied by the size of the gaps for S- and p-polarized radiation. 2 Il.

Description

JV Od "

The invention relates to optical filters and can be used in spectrophotometers, astronomical photometers and instruments for studying the characteristics of the atmosphere.

The aim of the invention is to improve the accuracy of measurements of the intensity of radiation with a continuous spectrum by reducing the background transmittance in the long wavelength relative to the wavelength J of the maximum transmittance region of the spectrum.

FIG. Figure 1 shows the possible constructive implementation of interference filters of total internal reflection (AIR) and the course of rays in them; in fig. 2 - the dependence of the transmittance T on the wavelength.

The filter consists of two identical prisms made of a material transparent in the working spectrum of the spectrum with a refractive index p, separated by a gap, filled with a material with a refractive index of the p. A light beam falling on the surface of the gap at an angle of 0 greater than the critical FIG. 1, due to impaired total internal reflection, is divided into reflected 1. and transmitted 2 rays, which, after reflection from reflecting x faces of prisms, merge at the second border of the gap and interfere with each other. Gap values for

 S- and p-field 1 of the radiated radiation satisfy, respectively, the following relations:

i. () d / gncoseVh sin e-i (K swe-cos Hjj

j

n 2;

j (is the length, the wavelength of the maximum transmittance of the filter. If the prisms have an angle of apex o (180 ° -arcsin (1 / n) and also provide the same optical path difference for rays 1 and 2, then the transmittances s- and p -polarized radiation is determined by the ratios

„N -cos ln-Oln sinG - (h -0sh ae + (n s; n0 OT

T (). ° 5Q - 5ih6) -i) (ns, ri Q-cose) sh3e:

(n-11%; ü © - cose) h3f H4os0 (h ih0-lf

23rdn

/ paws, / l where ae t-. D;

J

L - current wavelength. Depending on the problem being solved

the filter may have a wider spectral bandwidth (Fig. 1a) or a more narrowband (Fig. 1c) with the same value of the relative conversion index.

FIG. 2 (curve 3) shows the spectral characteristic of the filter (FIG. 1b), of which o (90 ° and. And. Μm). The presence of two maximum transmittances is related to the dependence of the transmittance on the state of polarization of the incident radiation. If the angle is at the top of the prisms satisfies the -2 arcsin N2 / () condition, then the dependence of the transmission coefficient on the radiation polarization is eliminated, resulting in a decrease in the filter bandwidth and its magnitude (Figure 2, curve 4). In this case, the output radiation saves azimuth of the output linear-cap Radiation, and also maintains natural polarization regardless of the size of the gap during the tuning of the wavelength of the maximum transmission of the filter.

The advantage of an air defense interference filter is a combination of bandpass transmission and high contrast. The use of the filter, in particular, makes it possible to attenuate the infrared radiation of the Sun 10 to 10 times outside the baseband, in addition, the shape and width of the transmission band (on a logarithmic scale of wavelengths) are preserved when it is rearranged by changing the size of the gap. „

5 of the invention formula

Total internal reflection interference filter consisting of

Claims (1)

55 The claims Total interference filter (internal reflection, consisting of two identical isosceles prisms made of a material transparent in the working region with a refractive index n, between the bases of which there is a plane-parallel gap filled with a transparent substance with a refractive index n ₂ , and n _r <n ₁₅ characterized in that, in order to increase the accuracy of • measuring the intensity of radiation with a continuous spectrum by reducing the background transmittance of the long-wavelength relative but the wavelength .λ of the maximum transmission region ^: spectrum, prism face, for which the plane of the gap is the bisector, the angle of incidence of radiation on the gap. The angle between them is made reflective, the angle at the top of the prisms is 180 ° -2 arcsin'd. where n = N 1 +1 '= η _ί / η _2, and the clearances d _s and d _p for s-. and p-polarized radiation satisfy, respectively, the relations d ₅ = c Arsh (; dp - c-At> sh _n z _ _ά n2 sirv-O-cos Qy ' Λ