SU1755237A1 - Polarizing prism - Google Patents

Abstract

Using, obtaining two polarized beams of light in one plane, divorced at an angle of 90 ° among themselves, with a degree of polarization close to 100%. SUMMARY OF THE INVENTION: A polarization prism consists of two prism (oblique and rectangular) made of a uniaxial birefringent crystal so that the optical axes of prism crystals are parallel to the input face and perpendicular to the non-working side face. 1 Il.

Description

The invention relates to optics, mainly to devices for the polarization of light, and can be used in spectrophotometric, polarization and interference-polarization devices. A specific area of application of polarizers when it is necessary to have two polarized light beams in one plane is interferometry and its various applications (non-destructive testing of transparent and opaque objects, plasma diagnostics, measurement of the refractive index of the medium, etc.).

Birefringent polarization devices based on crystals are known, producing one or two significantly divorced in beam angles at the output, oscillations of which occur in a plane, called polarizers. Such devices include Arens, Nikol, Wollaston, Rochon, Senarmon, Cotton, Osipov-King West prisms.

For example, the Wollaston prism, which is a two piece Icelandic

spar, connected by a layer of Canadian balsam so that their optical axes are perpendicular. The Wollaston prism gives two orthogonally polarized beams. It decomposes the incident light into two polarized components and skips both, deflected in different directions. The total angle of decomposition of the rays p depends on the angle at the tip of the wedge 0 and varies slightly with the wavelength. For the Wollaston prism, as for all the listed birefringent polarization prisms, it is characteristic that the rays at the exit make an angle of 90 ° between each other.

The known Glas-on-Foucault polarization prism consists of two rectangular prisms cut from calcite in such a way that their optical axes are parallel to the input and perpendicular to the top face. In this case, an extraordinary ray exits the prism, does not change direction compared to the incident one. An extraordinary ray (e-ray) suffers large losses of intensity when reflected from the crystal-gap boundaries (Iceland spar - air), so

cl

with

Xi

cl

SP

Yu

W

Xj

that the magnitude of the greatest principal transmittance k1 is only about 0.50. The disadvantages of the Glan-Foucault prism also include the fact that the ordinary beam (o-beam) leaves the prism at an angle of & 90 ° to the incident one, which makes it difficult to use it without additional quotation procedures, and that part of the e-beam extends in the same direction, resulting in depolarization of the outgoing light beam.

The forester polarization prism is known. which is designed to produce two linearly polarized rays in mutually perpendicular planes, divorced by 90 °, the Foster Prism, according to a number of features (making one of its prisms, oblique, diluting outgoing rays by 90 °) is close dual beam prism. Although it still performs the solution of another task (not entirely successfully) - obtaining two linearly polarized rays in mutually perpendicular planes divorced at an angle of 90 °, can be taken as a prototype.

Foster prism has a number of significant flaws. It cannot produce at the output two linearly polarized beams in mutually perpendicular planes with a high degree of polarization. Reflection from the silvered edge of the Foster prism does not improve the degree of polarization at the exit of the prism of the so-called ordinary beam, which has an extraordinary beam (e-beam) component, which is due to multiple e-beam reflections at the crystal air (glue) edges. the gap between the two folded prisms. Although the second beam comes out at an angle of 90 ° to. the incident beam on the entrance face (and the e-beam, which passed the gap without reflection), but it is significantly depolarized. The state of its polarization corresponds to the general case of an ordered structure of polarized light — elliptical polarization, since at the exit of the Foster prism two waves with different velocities and different amplitudes of electric vector oscillations propagate in one direction. perpendicular directions.

The aim of the invention is to obtain at the output of a polarization prism two linearly polarized in parallel planes of light beams, divorced at an angle of 90 ° without changing the direction of the extraordinary beam.

The goal is achieved by the fact that in a polarized prism spreading polarized beams by an angle of 90 °

from two separated by optical medium with a refractive index of the n layer and prisms cut from the birefringent material, the second of which is made rectangular along the radiation path, and the angle between the input face of the first prism and its face adjacent to the hypotenuse face of the rectangular prism of condition

arcsin arcsin

PePo

where Paws are the refractive indices of the extraordinary and ordinary rays in the prism material, respectively, the angle between the faces of the first prism opposite to its entrance face is 45 °, the angle of the rectangular prism adjacent to the angle of 45 ° of the first prism is a, and the optical axes the components of the prisms are parallel to the entrance and perpendicular to the lateral non-working faces of the polarization prism, the parameters Po and o; connected by the ratio n0 ctg (cr -45 °)

The drawing shows the proposed polarization prism.

It consists of an oblique prism 1 and a rectangular prism 2, folded by faces KM and K M and separated by a gasket 3 to form a gap filled with medium 4 with the refracting index Pslo. Instead of gasket 3, a prism can be glued together to fulfill the condition.

arcsin arcsin pslo

Pe

By

where Pslo - is the index of refraction of glue. The optical axes of the material of the prism components are parallel to the input face DK and perpendicular to the non-working face parallel to the plane of the drawing. The polarization of the prism has two mutually perpendicular output faces: the face for the ordinary ray (o-ray) KN and the face MN for the extraordinary ray (e-beam). An oblique prism can be made quadrangular or triangular (dashed image), but this is not essential for the task. Making a quadrilateral prism saves costly material.

The device works as follows.

A parallel beam of natural light rays (a-beam) falls on the entrance face D of an oblique prism and, entering the prism, turns into two linearly polarized beams running in the same direction. On the verge of KM, there is a phenomenon of total internal reflection for ordinary

the beam, since for this beam the optical medium in the gap is a less dense medium. In this part of the e-beam passes through the gap only slightly shifted parallel to the incident and leaves the prism 2. Another part of the e-beam when reflected from the crystal-gap boundaries propagates in the direction of the ordinary beam (o-beam). This is explained as follows.

With a single reflection of light, the complex amplitude R of the reflected wave is associated with the amplitude of the incident wave by the relation R g e, and the amplitude of the transmitted wave D is the ratio D d Ј. The values of r and d are the Fresnel coefficients. They depend on the polarization of light and are determined by the Fresnel formulas for the s- and p- components of the incident wave (in our case, o and e-rays). The extraordinary beam with the amplitude of the electric vector, reflected at point A in the direction of propagation of the O-beam, which experienced total internal reflection at point A, has the same frequency of oscillations of the electric vector; the plane of oscillations of the O-beam and the reflected part of the e-beam are mutually perpendicular. In addition, the light inside the dielectric layer (the gap between the folded prisms) experiences multiple reflections on its

.. 2trcso frontiers. If o j ± bLH s

T

difference

phase, corresponding to the double passage of light through the layer I (ie, from one of its borders K M to another KM and back), then taking into account multiple reflections for the complex amplitude of the reflected wave, you can write

-j P + didi1 r2 e + didi1 r1 G22 40

(5 + did11 (nW + ..., whence

R n + rz.e M Ј l + ncse- O

rflet - Frenel coefficients on the verge KM and KM1 for the e-ray. Physically, the expression () means that the amplitude of the reflected part of the e-beam can be significant (larger than P p E) due to multiple reflections at the edges of the gap between the prisms.

The arrangement of the side face of the oblique prism VM at an angle of 45 ° to the face KM and the fulfillment of the condition n0 - ctg (a - 45 °) leads to the fact that the angle of incidence of the light beam on it is equal to the Brewster angle and in this case in the direction perpendicular

0

five

0

five

0

the incident beam of light at the entrance to the prism reflects only a wave in which the electric vector E oscillates perpendicular to the plane of incidence (R 0, RI 0) and at the output we have a 100% polarized wave in the plane of polarization of the extraordinary ray diluted by the angle p 90 With respect to the extraordinary ray at the exit. In the place of the fall of the ordinary ray onto the face B. The refracted wave (at an angle of 90 degrees to the reflected wave, i.e. in the direction of the incident ray at the input of the prism) is not used in this device.

Elimination of the deficiencies of the Phoster prism, achieved in the proposed device, makes it possible to use it as a beam divider with a dilution angle of linearly polarized rays of 90 °, which expands the possibilities of using the polarizer in the practice of polarization measurements, simplifies quotation procedures and saves costly crystalline materials, since no additional polarizers are required in circuits where two beams of linearly polarized light are needed.

The image is as follows.

If the light diameter of the incident beam is a, then:

five

0

five

a-MN CN.

M v

sin (a + 45 °) a

- (12)

0

W cos KN atg a, (4)

Dk

(3)

DM1

cos a + cos a sin a a tg "

(five)

five

sin (a + 45 °) 0 + 45 °,

p & P arctg,

(6)

(7) (8) (9)

B D a (tga- 1) sln ",

When used as a birefringent material of calcite crystals:

on (at I - 5983 A) 1,6584; and 76.089 ° and rBr 31.089 °. When a is 5.0 mm; In M 5.8 mm; KM 20.80 mm; KN 20.19 mm; DK 17.17 mm; DM 23.57 mm; D In - 14,74 mm.

Performing a polarization prism according to the above relations allowed to obtain a qualitatively new technical effect, namely: at the exit of the prism there are two mutually perpendicular light beams linearly polarized in parallel planes, the degree of polarization of the beams is close to 100%; The device simplifies the alignment procedure and its use reduces the cost of producing polarizers when creating optical instruments and schemes where linearly polarized light beams are needed (interferometers, spectrophotometers, polarimeters).

Claims (1)

Claims of the invention A polarizing prism, spreading polarized beams at an angle of 90 °, consists of two optics separated by an optical medium with a refractive index and cut out of a birefringent material prisms, the second of which are radial, the input face of the first prism and its face adjacent to the hypotenuse edge of the rectangular prism is chosen from the condition arcsin ps / ne a arcsin nc / n0 where ne and Po are the refractive indices of the unusual and ordinary rays in the prism material, respectively, the angle between the faces of the first prism opposite to its input face is 45 °, the angle of the rectangular prism adjacent to the 45 ° angle of the first prism is equal to a, and the optical axes of the component prisms are parallel to the input and perpendicular to the lateral non-working facets of the polarization prism, characterized in that forming at the exit of beams linearly polarized in parallel planar-tTax, the parameters n0 and a are related by n0 cu ("-45 °) . e- / 7 ##