DE2933858A1 - POLARIZER - Google Patents

Description

The invention relates to a polarizer based on a optically anisotropic ion crystal. More particularly, the invention relates to polarizers, their active ingredient is a birefringent crystal from aer groups, for example mercury halides, Icelandic lime spar (Calcite) and sodium nitrate.

The range of application and the total value of a polarizer depend on the range of optical transmittance and the Value of the critical angle and the cleavage angle. It is therefore advantageous for the manufacture of polarizers Single crystals with the highest possible value for the optical Birefringence, i.e. the difference between the refractive index of an ordinary ray η and an extraordinary ray To use beam η, the following properties are particularly advantageous at the same time: a positive one Character of birefringence, the smallest possible critical angle of total reflection and the largest possible splitting angle of the ordinary and extraordinary ray.

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2935858

When investigating whether certain birefringent crystals are suitable for the production of polarizers, will for the reasons mentioned above, above all the range of the spectral range of the optical transmission, the size and the character of optical birefringence, the critical angle of total reflection and the angle of splitting of the ordinary and extraordinary ray tested. The range of optical permeability should be as broad as possible and as far as possible into the infrared spectrum.

Currently used types of polarizer, the effective component of which are birefringent single crystals, have hitherto been built predominantly in the form of individual or permanently connected and at least two-part optical systems. So is z. B. a Nicol prism is known, which consists of a birefringent single crystal of Icelandic limestone (calcium carbonate calcite) or quartz, which is divided along a diagonal section and cemented with Canada balsam; a Glan-Thompson prism is also known, which consists of sodium nitrate. A double nicol is also known, which is formed from a nicol prism divided by a vertical longitudinal section by obliquely grinding the surfaces thus created and connecting the two halves. Finally, a polarizer according to Lippich is known, which consists of two parts consisting of a calcite prism and an auxiliary semi-prism and a number of other constructions which differ from one another in terms of their crystallographic orientation. The refractive index for the extraordinary ray η is highly dependent on the crystallographic orientation, while the refractive index for the ordinary ray n _{Q is} isotropic, which results in an unfavorable dependence of the polarizers, which are made up of Icelandic calcite and sodium nitrate, on the given structure of the single crystal used results. In the following table I

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are the main physical values for single crystals Icelandic lime (calcite) and sodium nitrate indicated, which show that the mentioned single crystals are suitable for one use are very suitable in the ultraviolet region of the spectrum.

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TABLE I.
Physical properties of some birefringent single crystals

Type of single crystal

characteristic

Icelandic lime sodium nitrate "

Mercury compounds

bromide

iodide

• fc-O

Range of optical transmittance in micrometers

Optical birefringence for 0.589 microns

Character of the optical
Birefringence

Critical angle of the total
Reflection for 0.589 microns

neat beam
extraordinary beam splitting angle for
0.589 microns

0.25-2.3

0.172

negative

37.1 ° 42.3 °

6.26 ^C 0.28-3.5 0.38-20

0.251

negative

39.1 ° 4-8.5 °

9.82 ^C 0.681

positive

30.5 ^g
22.1 °

16.75 ^C

0.42 - 30 0.53 - 46

0.894-

positive

27.9 °
19.3 °

19 _t 63 ⁽

1.64-0

positive

23.9 °
14.1 °

28.04 ^c

CO CO

CO CO

tn OO

2933S58

In technical practice, the need for a shown new type of polarizers that would be suitable for use in the infrared spectral range, with them Should have similar properties as polarizers with single crystals of Icelandic lime spar (calcite) and sodium nitrate. In CS-PS 147 476 and GB-PS 1 310 432 the production of mercury (halides in one described closed system, the conditions for the production of polarizers, compensators and others optical devices that rely on the use of birefringence, a high refractive index and a based on large optical dispersion. It is also a prism-polar is at or known with mercury chloride, which consists of two parts that are created by the adhesion of polished surfaces or are connected to one another by cement using a suitable binding agent.

The mentioned single crystals of mercury halides have the advantage of a favorable high optical density. Her Critical angles have extremely low values, so that the thickness of polarizers of a generally known type can be very small, as can be seen in Table II below.

TABLE II

Two-part Glan-Thompson polarizing prism made of mercury (I) halides

Chemical To- Work area Ratio of the length and width composition in the polarizer

of the encroachment
stalles Micometers without always
sion Immersion
η = 1.54 Immersion
η = 1.487 mercury
chloride 0.38 - 0.4888 0.933 0.839 Mercury-
bromide 0.42 - 0.445 0.781 0.754 Mercury-
Oodid 0.53 - 0.384 0.649 0.625 - 20th - 30 - 4-5

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Polarizers with single crystals of mercury halides have the advantage over currently known polarizers a smaller thickness; However, because of their high refractive index values, their disadvantage is a smaller viewing angle and relatively high reflection losses. This can be improved by applying immersion, whereby the viewing angle is increased and the reflection losses are reduced, which is approximately double Bringing extension of the polarizer with it, the reflection losses still remain relatively high, as can be seen from Table III below.

TABLE III

Loss of light at a wavelength of 0.6328 micrometers when incident perpendicularly on a Glan-Thompson polarizer

Percentage of the light that penetrates through the polar nature of a single crystal

^sators Mercury (I) - Mercury ^) - Mercury (I) -

Chloride bromide, iodide

without immersion 39 »3 32.7 23.6

Immersion

η = 1.487 64.8 58.0 43.1

The relatively high losses caused by reflection are a common characteristic of all currently known two-part polarizers, including the one with crystals of calcite and sodium nitrate. A disadvantage of the two-part Polarizers are also demanding and expensive to manufacture. An advantage of polarizers with single crystals from mercury (I halides is beyond their permeability far into the infrared range of the spectrum also the fact that they are optically positive, and therefore lower demands to the quality of the crystals used than for example

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the visually negative Icelandic lime (calcite) and sodium nitrate. (See Table I).

The disadvantages mentioned could only be complete or at least can essentially be remedied by the present invention, according to which a polarizer on the base an anisotropic ion crystal, for example from a mercury (I) halide such as calomel, Icelandic lime spar or sodium nitrate is characterized in that its active component is a monolithic single crystal, whose shape is determined by the general equations:

+ m tg e ₂ Ί ^Λ %% (Ό

BC - _τ ^ ~ ^{+ Λ%%} (2)

S = arc tg —— + 5 ° ^ (3)

in which

3Π3 the projection of the entry surface of the single crystal

ÜE * the projection of the entire exit surface of the single crystal, thus the sum of the projection of the exit area US of the ordinary ray η and the projection of the exit surface DE of the extraordinary ray η

ΕΤΙ the length of the single crystal

£ x] is the angle formed by the main crystallographic axis the longitudinal axis of the single crystal,

E 2 is the angle enclosed by the surfaces of the projections ΆΈ and ΆΤ), and

S is the angle enclosed by the main crystallographic axis C and the longitudinal axis of the single crystal.

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An embodiment is preferred in which the angles E λ and £ ο .leder per se have a size within the limits of 10 to 40 and the angle S is within the limits of 10 to 86 °. The inclined side wall of the single crystal, which is caused by the projection ÄT? is shown, can be cut off in the direction towards the lower exit surface represented by the projection UE by a plane which forms an angle of 90 ° + 15 % with the surface of the side wall, or the single crystal can be cut off parallel to the longitudinal axis, with the total width of the polarizer represented by the projection CS "of the exit surface is determined by the general equation:

CG "= ΧΉ + 0.5 BT? · Tg E ₂ ± 5 % ( ² O

A plate can be attached to the entrance or exit surface of the polarizer or to both surfaces by means of immersion made of glass and / or single crystal, which is provided with a reflection-reducing surface. It should the plate mentioned to be impermeable to electromagnetic radiation and that for a single crystal of mercury chloride in the spectral range below 0.38 micrometers, for mercury bromide in the spectral range below 0.42 micrometers and for mercury odide in the spectral range below 0.55 micrometers, however, it should be transparent in the visible and infrared regions of the spectrum.

The invention is based on the knowledge that monolithic crystals z. B. on the basis of halides of the monovalent Mercury, Icelandic lime spar (calcite) and sodium nitrate are more suitable than two-part single crystals, which divided according to a diagonal cut and then cemented or glued, being in the whole area of permeability have advantageous parameters.

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Looking at the values in Table I, it is evident that that polarizers with single crystals are best for working in the ultraviolet range of the spectrum Icelandic lime (calcite) and sodium nitrate are suitable, but for work in the infrared range of the polarizers spectrum with single crystals of halides of monovalent mercury are most suitable. A major advantage of the polarizer according to the invention is the formation of its effective component in the form of a monolithic single crystal, since it is much easier to manufacture than polarizers based on single crystals, which are made by split a diagonal cross-section and then connected. Also, with monolithic polarizers, there are losses much lower than with two-part polarizers due to reflection. To further reduce losses through reflection the monolithic polarizer can be provided with a reflection-reducing layer on the entry and / or exit surface be provided, which is either applied directly to the surface of the monolithic single crystal or to a glass plate and / or a single crystal plate with suitable absorption characteristics that attach to the stated surfaces of the monolithic single crystal is connected. The advantages of this arrangement in the event that the single crystals consist of mercury halides can be seen from the data in Table IV below.

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TABLE IV

Loss of light due to reflection in the case of a monolithic single crystal based on a mercury halide.

Type of polarizer

% of the transmitted light with a wavelength of 0.6528 micrometers

Mercury- mercury- mercury chloride bromide iodide

Monolithic polarizer without reflection-reducing arrangement 80.1

Monolithic polarizer with a glass plate with anti-reflective Layer at the entry and exit surfaces 96.1

75.9

95.6

64.8

88.9

An investigation of the percentage loss of the beam that hits the entrance surface of a polarizer based on a Glan-Thompson prism made of a mercury halide is noticeable leads to the following results:

a) - a two-part polarizer made with a single crystal

Mercury halides with air gap: the reflection losses for a single crystal are 61 # from mercury chloride, 67 % from mercury bromide and 76 # from mercury iodide, each calculated on the total amount of incident light.

b) - a two-part polarizer with a single crystal

a mercury halide with immersion η = 1.487:

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the reflection losses for a single crystal of mercury chloride 35 # »from mercury bromide are 42 %
and of mercury iodide 57 #, each calculated on the total amount of incident light.

c) - monolithic polarizer with a single crystal

a mercury halide according to the present invention without a reflection-reducing layer: the reflection losses are 20% for a single crystal of mercury chloride, 24% of mercury bromide and 35% of mercury iodide, each calculated on the total amount of incident light.

d) - monolithic polarizer with a single crystal

Mercury halide according to the present invention, where glass plates provided with a reflection-reducing layer are connected to the entry and exit surfaces by means of immersion with η = 1.487 »: the reflection losses are: for a single crystal of mercury chloride 4%, of mercury bromide 6 % and of mercury iodide 11 #, each calculated on the total amount of incident light.

The drawing shows two exemplary embodiments of a polarizer based on an optically anisotropic monolithic Single crystal of mercury (I) chloride (calomel) shown.

Fig. 1 shows a section through a monolithic polarizer, the line segment ΈΒ the projection of the entrance surface of the light beam, the line segment CD the projection of the exit _{surface of the ordinary ray n Q} , the line segment ϋΈ the projection of the exit surface of the extraordinary ray η and the line segment I. ¹ G "

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represents a projection of the narrowing of the polarizer for working with a beam. The one in the projection The area represented by the line segment DTT can optionally can be provided with a black coating, and in the same way can also be projected through Line sections üF, Ä "F and B" ü formed areas shown will. The line segment DU shows a projection a possible cutting off of the polarizer on a surface to which the extraordinary ray η is perpendicular and along which a single crystal of mercury (I) chloride is cut in the event that the internal depolarization of the reflected extraordinary ray with the refractive index η is to be reduced.

The line segment DJ * shows a projection of the cut off part of the polarizer onto the surface from which the extraordinary ray η exits at the so-called Brewster angle without losses. £ ^ is the angle which the surfaces of the projections BÜ and! BD enclose, £ p is the angle that the surfaces of the projections A "ü and ÄT) lock in. The angle J ^ is the angle of the crystallographic Orientation of the polarization principle, which is an angle formed by the longitudinal axis of the prism or a normal on its entry surface with the direction of the crystallographic axis C of the monolithic single crystal, from which the polarizing prism is made. Advantages of this solution can be seen from the following exemplary embodiments, which explain the essence of the Emndung in more detail, without limiting it in any way.

example 1

A monolithic polarizer is made with a single crystal of mercury (I) chloride according to Fig. 1 in a form, whose projection is given by the reference symbol ABCE

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where the angle £ ^ 14 °, the angle £ ₂ 21 °, the distance TE 10 mm, the distance B "ü 39 mm and the angle S 54 °.

Example 2

A monolithic polarizer is produced with a single crystal of mercury (I) bromide according to FIG. 1 in a form, the projection of which is given by the reference symbol ABODE, the angle S * 16 °, the angle S ~ 22 °, the distance AB 15 mm, the distance BTJ 52.5 mm and the angle «? 55 °.

Example 3

A monolithic polarizer is produced with a single crystal of mercury (I) iodide according to FIG. 1 in a form, the projection of which is given by the reference symbol ABCDJ, the angle S ^ 20 °, the angle £ ^ 27 °, the distance 15 10 mm, the distance BTT is 28 mm and the angle S is 58 °.

Example 4

A monolithic polarizer is made with a single crystal of mercury (I) chloride according to FIG. 1 in a form whose projection is given by the reference symbol ABCE and which is parallel to the longitudinal axis by a section FT? is cut at a total length of the polarizer 17 »5.

Example 5

A monolithic polarizer is made with a single crystal of calcium carbonate (calcite), the angle £ _Λ 5.5 °, £ 2 10.7 °, the distance SB 10 mm, the distance 98.8 mm and the angle? -41 °.

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Example 6

A monolithic polarizer is produced with a single crystal of sodium nitrate according to FIG. 1 with a shape whose projection is determined by the reference symbol ABCE, where the angle £ ^ 9.5 °, the angle £ ₂ 1 ° »9 °, the distance from "10 mm, the distance BÖ 59» 1 mm and the angle -40 °.

Example 7

A monolithic polarizer is made with a single crystal of mercury (I) chloride according to the method as in Example 1, but with the difference that a glass plate 2 provided with a reflection-reducing layer is connected to the entry surface with a projection TE of the single crystal 1 by means of immersion and a glass plate 5 provided with a reflection-reducing layer 4 is connected to the exit surface with a projection UE of the single crystal 1 by means of immersion.

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Claims (5)

Claims Λ .. Polarizer based on an optically anisotropic ion crystal, for example from a mercury halide such as calomel, Icelandic lime (calcite) or sodium nitrate, characterized in that the active component of the polarizer is a monolithic single crystal, which is characterized by the following equations: CE = AB + BC - tg / T ₀ + 2 ° % O) Ic = η = arc tg ~ +10 - +10 - in which SB "is the projection of the entry surface of the single crystal UE is the projection of the total exit area of the single crystal, the sum of the projection of the exit area ÜB of the ordinary ray n _Q and the projection of the exit area DE of the extraordinary ray η, B "ü the length of the single crystal £ ^ the angle enclosed by the surfaces with projections Ήϋ and Έ5 , E2 ^ ^θη angle enclosed by the surfaces with projections ΆΈ and ΆΤ5, 233- (S 959O-DfWa 030014/0617 andJ ³ denotes the angle which the main crystallographic axis C forms with the longitudinal axis of the single crystal. 2. Polarizer according to claim 1, characterized in that the inclined side wall of the single crystal represented by the projection ΆΈ is cut in the direction of the lower exit surface determined by the projection ΈΕ along a plane which forms an angle 90 - 15 # with the side wall. 3. Polarizer according to claim 1, characterized in that the single crystal is cut parallel to the longitudinal axis and the total width of the polarizer, which is represented by the projection ÜG "of the exit surface, by the general equation is given: ÜG "= Ib + 0.5 Bc 'tg E ₂ ± 5 #. 4, polarizer according to claim 1, characterized in that on the exit surface with the projection TE and / or on the exit surface with the projection ^ G "or ÜE of the single crystal (1) by means of immersion a plate (2, 3) made of glass and / or single crystal is connected, which is provided with a reflection-reducing layer (4-, 5). 5. Polarizer according to one of claims 1 to 4, characterized in that the angles £ ^ and £ o each have a size in the limits of 10 to 40 ° and the angle J ¹ in the limits of 10 to 86 ° lies. 0 3 C '' ⁿ ο 1 7