Polarization opticsreview

Linearly birefringent uniaxial crystalline materials are characterised by having a unique axis ofsymmetry, called the optic axis, which imposes constraints upon the propagation of light beamswithin the crystal. Two modes are permitted, either as an ordinary beam polarized in a planenormal to the optic axis, or as an extraordinary beam polarized in a plane containing the opticaxis. Each of the beams has an associated refractive index, such that both the electric field(wave normal) velocities and the beam (ray) angles of refraction are different. It is this latterproperty that enables suitably cut and oriented prisms of birefringent materials to act aspolarizers and polarizing beam splitters.

We have perfected a number of proprietary processes for cutting, grinding and polishing perfectoptical surfaces on calcite prisms, routinely achieving flatnesses down to lambda/8 over severalcm with 10/5 scratch dig. These skills are evident in the high quality of the finished components,and enable our polarizers to be used with very high peak power lasers.

Linearly polarized light

Choosing the right polarization optic for your application can be a bewildering task, as we offer a wide range for many different uses.

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By polarized light we mean optical radiation with its electric field oscillating in a specific regularmode. Any generally polarized electric field can be resolved into two orthogonally polarizedcomponents. If the light is plane polarized then the electric field oscillates in a single plane – theplane of polarization, and the two components are in phase. If it is elliptically polarized, the twocomponents have a constant phase difference, and the tip of the electric field vector follows athree dimensional ellipse as the beam propagates.Circularly polarized light is a special case of elliptically polarized light in which the twocomponents have a 90° phase difference and the electric field vector describes a circular crosssection spiral. When viewed looking towards the source, a right circularly polarized beam has alight vector that describes a clockwise circle, while left circularly polarized light describes ananti-clockwise circle.

Polarizationexamples

We hope this short tutorial has been of use to you. If you require further information on the birefringent materials available or on component possibilities, please contact us.

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s-polarization vs ppolarization

If a plane polarized beam propagates down the optic axis of a material exhibiting circularbirefringence it is resolved into two collinear circularly polarized beams, each propagating with aslightly different velocity. When these two components emerge from the material, theyrecombine into a plane polarized beam whose plane of polarization is rotated from that of theincident beam. This effect of producing a progressive rotation of the plane of polarization withpath length is called optical activity, and is used to produce optical rotators.

We use various materials out of a fairly wide range of birefringent crystals for the production ofour polarizing components – calcite, crystal quartz, magnesium fluoride (MgF2), YVO4 and -BBO.

Single crystal magnesium fluoride is another extremely useful material for the production ofpolarizers due to its very wide spectral transmission, extending from 120nm in the vacuumultraviolet to beyond 7.0um in the infra red. Because suitable index matching cements do nottransmit below 220nm, magnesium fluoride polarizers are manufactured by optically contactingthe two prisms.Thin plates can be manufactured from this material for use in achromatic retardation plates. Inthese optical components the spectral dispersion of the magnesium fluoride is used tocompensate that of quartz, producing a near uniform retardation over a defined spectral band.

Circularpolarization

Surface figure: λ/20Angle: 0,5 arcsecRadius: 0,01%Focal length: 0,03%-0,3%Centration: +/-0,2µm or +/-2 arcsecWavelength: +/-0,3nm (190-1100nm)

Yttrium orthovanadate is useful due to its extended wavelength range. We provide polarizersfunctional to 4000nm (4µm) wavelength. Magnesium Fluoride is also a good candidate, but theseparation angle using YVO4 for Wollaston and Rochon polarizers is much higher.

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Polarizationof electromagnetic waves pdf

We take quality control very seriously: we rely on accurate, widely recognized measurement systems for testing our optics. The following table indicates the accuracy of measurement for the most relevant parameters.

Linearpolarization

Calcite is a widely preferred choice of material, owing to its very high birefringence, widespectral transmission and the availability of reasonably sized crystals. Unfortunately, calcitecannot be manufactured synthetically. Only natural crystals exist which limits the maximum size with good optical quality. It has the advantage of being non-hygroscopic, so that protection from the atmosphere is notnecessary, though it is a fairly soft crystal and is easily scratched.

Quartz is an extremely useful birefringent material and is available as either natural crystals oras synthetic boules. Natural crystals occur as rough lumps that require orientation to determinethe optic axis before processing, while synthetic crystals have reference surfaces aligned tocrystallographic axes. When deciding which sort of quartz should be used for a component, twoparameters that differ significantly between the two types should be considered: size andspectral transmission.In general, components from synthetic quartz are limited to a maximum size in the direction ofthe optic axis of around 70mm, while natural quartz boules are available large enough to yieldworking apertures up to 100mm. The other significant discriminant between natural andsynthetic quartz is the low wavelength cut-off. Natural quartz has a useful transmission (app.80%) from 220nm, while synthetic quartz transmits similarly from 190nm. Both transmit out toabout 2.6µm.Quartz is very hard (Mohs scale 7) and is very strong. It thus lends itself to the fabrication ofvery thin low order retardation plates. Unlike calcite or magnesium fluoride, quartz exhibitscircular birefringence, and there is no unique direction (optic axis) down which ordinary andextraordinary beams propagate under one refractive index with the same velocity. Instead, theoptic axis is the direction for which the two indices are closest: a beam propagates down it astwo circularly polarized beams of opposite hand edness (chirality). This produces progressiveoptical rotation of an incident plane polarized beam; which effect is put to good use in rotators.

Ellipticalpolarization

Feel free to contact us for assistance. Our experienced staff is only too pleased to help you with the decision process.

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Active Area: 13mm^2 (3.6 x 3.6mm) Rise Time: 10ns @20V NEP: 1.2 x 10^(-14) W/Hz^(1/2) @ 900nm, 20V Dark Current: 20nA @ 20V Junction capacitance: 40pF @ 10V

The high Temperature form of BBO (-BaB2O4) is a negative uniaxial crystal. It has a largebirefringence over the broad transparency range from 190 nm to 3500 nm. Due to its unique UVtransparency, good mechanical properties and high damage threshold, -BBO is an excellentcrystal to replace Calcite, TiO2, and LiNbO3, etc. in Glan-Taylor and Glan-Thompson Polarisersas well as walk-off beam splitters, especially for high power and UV polarizers. Since the crystalis centrosymmetric, it cannot be used for non-linear optical applications.