Pairs of Brewster Plates can be used to attenuate a linearly polarised CO₂ laser beam. This is possible because the S and P reflectances are near 100% and 0% respectively. the Brewster plate acts like a polarising beamsplitter.
The difference in reflectance also allows two perpendicular (linearly) polarised beams to be combined into a single beam. The C-BC2 is an assembly which allows you to do this. It is part of the CO₂mpact range.
Due to the difficulty in producing the enhanced Brewster coating, the unit is only currently available for 10.6 Microns.
|Optics:||Matched pair of ZnSe Enhanced Brewter plates(EZBW532MP), two Silicon mirrors (11SIS-00) coated Supermax|
|Input apertures:||100mm spacing with M29 x 1 female therad to accept thread inserts(C-TI) or coupling rings (C-CR).|
|Note:|| Three C-TI will be supplied with the unit.|
|Output Aperture:||Straight through from one input.Also with M29 x 1 female thread.|
Referring to the photo, the two input apertures are shown in in the lower side panel. A horizontally (left-right in the photo) polarised beam is sent centrally through the left aperture and is incident on the two Brewster plates in the P polarisation where it is transmitted through both plates and exits through the upper plate aperture. About 97% of the beam will be transmitted. The rest in reflected into a pair of beam dumps.
Brewster plates work best with some wedge between their surfaces and the reason for using a pair of matches plates is to cancel out the angular beam deviation that would otherwise result from a single plate. There would also be some lateral beam displacement with a single plate, but this is eliminated by the ‘V’ configuration.
The second beam is polarised vertically (up-down in the photo) and is sent into the right aperture. It is reflected off the two mirrors and then onto the second Brewster plate. The two mirrors can be orientated to align the beam to the other. the adjustments will be iterative . With the angle of incidence on the Brewster plate set correctly, the second beam will be strongly reflected (98%) out of the exit aperture. A small amount of power will be transmitted by the plate and enter a beam dump behind.
Should the user accidentally send the wrong polarisation into each aperture, most of the power will be dumped into the beam dumps with little power exiting the unit. In the current version the beam dumps are not water-cooled.
Click on the technical drawing below for further details.