CC-POL Implementation Focal Plane Mask & Calibration
Placed upstream of Wollaston prism in collimated beam
Constructed from any opaque material
Should have knife edges to eliminate scattering
Slot size, duty ratio, etc. to be decided after final Wollaston specification
Requirements
- mechanism to insert/retract (rotate?) into beam
- on axis centering ɘ.1mm
- Wire grid polariser placed infront of HWPs
- most readily located in front cryostat window
- Should be quick to insert into optical beam via computer control
- Zero & non-zero polarisation standards observed as part of observing preparation
- Efficiency and PA correction invariant, primarily used for instrument QC and functionality tests