Reflective Optical Chopper Used in NIST High-Power Laser Measurements

For the past ten years, NIST has used high-reflectivity, optical choppers as beamsplitters and attenuators when calibrating the absolute responsivity and response linearity of detectors used with high-power CW lasers. The chopper-based technique has several advantages over the use of wedge-shaped transparent materials (usually crystals) often used as beam splitters in this type of measurement system. We describe the design, operation and calibration of these choppers. A comparison between choppers and transparent wedge beampslitters is also discussed.