Glan Laser Polarisers
Glan
Laser polarisers utilize the high bi-refringence of natural crystal calcite to
produce a linearly polarised output from a laser beam of random polarisation. They consist of two prisms of calcite separated by an
air-space and arranged so that the internally reflected beams exit through a
side port to avoid damaging the optics.
Only
laser grade calcite is used. This
material has very low scatter and high homogeneity.
For applications in the ultra-violet (from 220—350 nm) UV transmitting
Laser-UV grade calcite should be selected.
Since
lasers have axial rays and a single frequency, these Glan Laser polarisers
act very efficiently. They
produce a high degree of linear p-polarisation in the transmitted beam.
Typically
they produce an extinction ratio in excess of 1 X 10-5.
They have a transmittance of over 88% and a 6° field of view.
Glan
Laser polarisers normally supplied as square cross section prisms with an
aperture of 8, 10, 15 or 20 mm. They
are mounted in an absorbing black potting compound within a metal cell.
Cut-out escape holes in the sides of the housing permit the unwanted
reflected beam to exit without causing overheating or damage to the polariser or
mounting cell.
Single
layer MgF2 anti-reflection coatings may be applied if required. These coatings provide a reflectance of less than 2% over a
range of 400-700 nm or 650-1100 nm. They
are centered at 550 nm and 830 nm respectively.