SU773558A1 - Controllable light filter for optical system with objective lens - Google Patents

Description

The invention relates to optical instrumentation and can be used in astronomical instruments for observing objects with sharply different luminosities and in various systems of space navigation and orientation. Known polarization controlled light filters are known in which the degree of attenuation of the incident light flux is adjusted by rotating one polarization element relative to another 1. The disadvantage of such a device is the same degree of attenuation of the incident flux throughout the field of view of the device in which This filter is inserted. Closest to the invention is a controlled light filter consisting of two polarizers, a light-modulating medium between them and transparent electrodes 2. The disadvantage of this filter is the impossibility of observing simultaneously objects through it with sharply differing luminosity. The purpose of the invention is the realization of the possibility of simultaneous observation of objects with sharply differing luminosities. This goal is achieved by the fact that a transparent photocathode is introduced into the controlled optical filter for the optical system with a lens, and the light-modulating medium, polarizer and photocathode are arranged in series between the transparent electrodes. FIG. Figure 1 shows the structural scheme of the proposed controlled light filter; in fig. 2 characteristic of the light transmission device. The controlled filter contains a polarizer 1, a transparent electrode 2, a light-modulating medium 3, a polarizer 4, a transparent photocathode 5, a transparent electrode 6, a potentiometer 7. Polarizers 1 and 4 are parallel to the polarization planes. Between polarizers, a light-modulating medium 3 is placed, on one surface of which a transparent electrode 2 is applied, is applied to it

positive potential through potentiometer 7. A transparent photocathode 5 is in contact with polarizer 4, to which a negative potential is applied.

The transparent electrode b, to which a positive potential is applied, is at a distance from the photocathode 5 and serves to draw back electrons emitted from the surface of the photocathode. An electro-optical crystal can be used as a light-modulating medium, for example, Oa ,, Bi, 5i, etc.

The device works as follows.

Rays of light from the object of observation pass through the polarizer 1, the transparent electrode 2, the light-modulating medium 3, the polarizer 4 and fall onto the transparent photocathode 5. For greater efficiency of use of the light filter, it is installed in the optical system behind the lens that forms the image of the object of observation transparent photocathode. Electrons are emitted from each point of the photocathode under the action of the energy of the light rays due to an external photoelectric effect. The density of the flux of electrons emerging from a given point of the photocathode corresponds to the density of the rays passing through this point of the photocathode. As a result, an electronic image is formed above the surface of the photocathode - a copy of the object of observation. Under the action of an electric field, electrons emitted from the surface of the photocathode are transferred to the transparent electrode b, and the light rays, the photocathode, and the transparent electrode pass, ultimately being fed into the eye of the observer or onto a photographic plate.

In the absence of electron emission from the photocathode 5, the transparency of the light filter is maximal and uniform over the entire field of view. If there is emission at the photocathode between the transparent electrode 2 and the photocathode 5, an additional electric field arises, the strength of which depends on the number of emitted electrons. The arising electric field leads to a phase shift between ordinary and extraordinary rays of light propagating in an electro-optical crystal. A phase shift causes a change in the plane of polarization of the beam emerging from the crystal, and as a result, weakens the intensity of the light beam at the polarizer 4 output , While in the field of view of the optical system with a lens there are no objects with high brightness (sun, etc.).

; The emission of photolengths from the photocathode is relatively small, and the intensity of the electric field is also low. The attenuation of the light flux by the light filter in this case is insignificant due to the nonlinear nature of the light-transmitting characteristic. FIG. Figure 2 shows the light transmission characteristic of a controlled light filter, where, 3o the intensity of the luminous flux at the input surface of the light-modulating medium, 3 - the intensity of the luminous flux at the exit of polarizer 4, E is the intensity of the electric field between the electrode 2 and the photocathode 5.

5 The occurrence of an object with a high luminosity at some point in the field of view of the instrument leads to an increase in the emission of electrons from the conjugate point of the photocathode, which leads to

0 a sharp increase in the intensity of the electric field inside the light-modulating medium and, consequently, a sharp decrease in the transmission of light at this point. Since time is

Since the response of the light-modulating medium is about c, it is practically impossible to blind the observer.

Potentiometer 7 is used to set the initial intensity of the electric field and control the degree of attenuation of the radiation intensity from bright objects.

The use of a controlled light filter of the indicated construction in

Optical systems with a lens allow for simultaneous observation of objects with sharply different luminosities, automatically excluding the possibility of blinding the observer.

Claims (2)

1. US patent number 2423321, kl.350159, published. 1947. 2. Authors certificate of the USSR W 176489, cl. G 02 B 5/30, 1963 (prototype). 2 J “5