RU1781694C - Practice device for optics - Google Patents

Abstract

SUMMARY OF THE INVENTION: the device comprises a light source collecting a lens, a polarization part consisting of a polaroid-polarizer, a thick plane-parallel plate cut from a uniaxial crystal parallel to the optical axis of the polaroid-analyzer, and an observation screen. New in the device is that it has a second crystalline plate identical to the first, located after the first, turning the second plate 90 ° in its plane in its plane. and the transition to a compensation arrangement allows one to achieve a high degree of temporal coherence of overlapping beams without monochromatization of the primary light beam and a high degree of spatial coherence without limiting the size of the illuminating source and without the use of focusing optics. The device allows one to obtain a high contrast, long, bright and colorful interference pattern at any distance from the observation screen and to give a clear interpretation of the nature of the phenomenon, based on symmetry considerations of the crystal optical system. 1 ill.

Description

The invention relates to training materials in physics and is intended to obtain and demonstrate a long and bright picture of interference in polarized beams of non-monochromatic (white) light from a crystal-optical system cut out parallel to the optical axis.

A training device is known for demonstrating isochromatic stripes from a thick (several mm thick) crystalline plate cut parallel to the optical axis, adopted as a prototype. This device includes a monochromatic light source, a capacitor and a focusing lens, a polarizer, a thick crystalline plate cut parallel to the optical axis from a single crystal (e.g., Iceland spar), an analyzer, a projection lens system and an observation screen. An advantage of the prototype is the possibility of obtaining an extended interference pattern in the form of a family of isochromatic bands of a hyperbolic shape. However, we can note the following significant disadvantages of the prototype. The lighting source has very stringent requirements in terms of its monochromaticity, due to the need to achieve a high degree of temporal coherence of overlapping beams having a relatively large path difference. For this reason, a gas discharge lamp (e.g., sodium or mercury) is used as the light source in the prototype, emitting individual spectral lines, on one of which the pattern is observed, and the rest are eliminated by a suitable filter. This circumstance significantly reduces the speed of the device and makes little VJ

00

Ј

Јь

its effective use in a large room. The relatively large transverse displacement of the ordinary and extraordinary beams in the case of a thick plate leads to the fact that in order to achieve a sufficiently high degree of spatial coherence of the overlapping beams, it is necessary either to sharply reduce the transverse dimensions of the illuminating source, which reduces the bistetia and complicates the illumination of the device by introducing a diaphragm and additional optics , or it is necessary to observe the picture in the focal plane of the auxiliary lens or display to place this plane on the observation screen, which requires the introduction of additional projection optics into the device, cluttering the device and making it less free. A significant drawback of the prototype in the didactic plane is associated with difficulties in explaining the observed course of the stripes of the picture, its geometry, and therefore the nature of the phenomenon without involving rather cumbersome calculations.

All these shortcomings have been completely eliminated in the training instrument on optics proposed below. The device called ef ffoTTy Pftb to observe a high contrast extended and bright interference pattern in white light without monochromatization of the light beam, without reducing the size of the illuminating source and without the use of projection optics. Thus, the optics training device is distinguished by high luminosity combined with simplicity of design. At the same time, the transition from observation of high-order isochromats to observation of the very first-order isochromats (KO, 1, 2, 3 ...) carried out in an optical training device allows us to give a simple and clear interpretation of the phenomenon and geometry of the picture based on symmetry considerations, which determines the didactic advantages of the educational instrument in optics.

The aim of the invention is to increase the clarity by increasing the temporal coherence of overlapping beams without monochromatizing the primary light beam.

A significant structural difference between the educational instrument in optics and the prototype is that instead of one crystalline plate, sawn parallel to the optical axis, it uses two plates, identical in size and geometry, fixed in the frame so that each of the plates can be rotated in its own plane clockwise or counterclockwise to the desired angle.

The conditions for splitting the primary light beam in such a system are essential

are cast depending on the relative orientation of the optical axes of the plates. With a parallel orientation, which can be called uncompensated, the system is completely equivalent to one single plate of double thickness. When one of the plates rotates 90 ° in its plane (it is understood that the initial arrangement of the plates is diagonal and the angle between the direction of the polarizer

5 and the direction of the optical axis of the plates) and the transition to a compensation arrangement in which the optical axes of the plates are oriented mutually perpendicularly, the splitting conditions radically change.

The reduction of the path difference and the formation of a system of bands of the very first orders of interference (K 0,1,2,3, ...) ensures the achievement of a high degree of temporary

5 coherences of overlapping beams in non-monochromatic and even in white light. The possibility of carrying out the experiment in white light allows, firstly, to simplify the device by using as

0 light source of a cheap small-sized projection lamp incandescent instead of a bulky low-power gas-discharge source of a line spectrum. Secondly, observing a picture in white

5 in the light provides the ability to isolate and establish the course of the zero band due to its achromaticity. With a parallel orientation of the polarizer and analyzer and a diagonal arrangement of the crystal plates, the zero band appears unpainted (white), and when the analyzer (or the polarizer) is rotated 90 °, it becomes velvet black. Having in the field of view, as a reference point, a zero band that is distinguished in appearance, it is possible to directly determine the interference order (number K) of any band directly. Thirdly, the observation of a bright and colorful picture in white light significantly increases the emotionality of the demonstration. A decrease in the transverse displacement of the rays arising from birefringence in a crystal-optical system makes it possible

5 achieving a high degree of spatial coherence of overlapping beams with the complete elimination of focusing optics at the output of the device, which leads to a significant simplification of the design of the device. In this case, the interference pattern is localized in the entire surrounding space and the contrast system isochromat is formed at any distance from the observation screen, which increases, so to speak, the degree of freedom of the device. The formation of a pattern with a zero band extending across the entire field of vision greatly simplifies the nature of the phenomenon.

The drawing shows the device.

The device contains a illuminator consisting of a low-power incandescent lamp and a projecting condenser, a polarization unit consisting of a polaroid polarizer, two crystalline plates and a polaroid analyzer, and an observation screen, a Illuminator, and a polarization system are fixed on a common base. The details of the polarization system are fixed in a frame that looks like a hollow half-cylinder with grooves in which a light filter (orange or light red glass), a polaroid polarizer, two crystalline plates and a polaroid analyzer are openly attached to round mandrels. The details of the polarization system have indications of corresponding directions: crystalline plates — indications of the direction of the optical axis, and polaroid — indications of transmission directions. The drawing shows a General view of the educational instrument in optics. Here 1 is the base plate on which the illuminator and the polarization system are mounted; 2 - retractable lighter cartridge with lamp 8 V, 20 W; 3 - illuminator casing; 4 - lens; 5 - light filter (orange or light red glass); 6 - floor roid-polarizer; 7 - the first crystalline plate; 8 - second crystalline plate; 9 - gender analyzer; 10 is a frame for parts of a polarization system.

The experiment is carried out as follows.

The pointers of polaroids are oriented vertically, and the pointers of both crystalline plates rotate on the same side by 45 ° B. In this non-compensatory arrangement, a system of two parallel-oriented plates is equivalent to one solid plate of double thickness. Our device uses identical plane-parallel plates of Icelandic spar, cut parallel to the optical axis. The plates were worked out for plane parallelism up to 2 microns.

When the device is illuminated with non-monochromatic (white) light, an interference pattern does not form. In the course of the experiment, they demonstrate that with parallel ori-. 5 of the plate orientation, the overlapping region of the light beams has uniform illumination. The absence of an interference pattern on the observation screen is due to the lack of temporal and spatial coherence of overlapping beams. Then the pointer of one of the crystalline plates is rotated 90 ° in its plane to its symmetrical orientation at an angle of -45 ° to the direction of the polarizer 5, i.e. transition to the compensating arrangement .. In this case, the difference in the path and displacement of the rays arising from birefringence in the crystal-optical system sharply decreases and increases

0 degree of temporal and spatial coherence of overlapping beams, which leads to the appearance in white light of a contrast interference pattern in the form of a bright and colorful isochromatic system

5 hyperbolic shape with a central achromatic white zero cross. When the analyzer is rotated 90 °, the system of bands is shifted by half a strip, the pattern is reversed and the white zero cross turns into velvet black, and the color of the isochromat changes to an additional one. The experience is highly emotional and very arrogant. With the introduction of filter 5, the picture is observed in

5 orange or red light. The device is simple in design, reliable in use and trouble-free. The device can be successfully used in teaching a course of physics (optics) in technical universities,

0 pedagogical institutes and universities.

Claims (1)

SUMMARY OF THE INVENTION An optics training device consisting of a light source collecting lenses, 5 a thick plane-parallel birefringent plate made of a uniaxial crystal parallel to the optical axis, two polarity and an observation screen, characterized in that, for the purpose of In order to increase the clarity by increasing the degree of temporal coherence of the overlapping beams without monochromatizing the primary light beam, it has an additional crystal plate, 5 identical to the first and located after it with the possibility of rotation in its plane.