T/R Mirror Design

Created April 24, 2004

Last updated April 24, 2004

The T/R mirror is (most likely) a 6-inch diameter, 1-inch thick piece of glass whose surfaces are of moderate optical quality and largely transparent. Most of the surface will be anti-reflection (AR) coated for 532 nm, except for small mirrore patches (multi-layer dielectric interference coatings) to handle reflection of the high-power laser beam. But more than just this, the T/R mirror is to properly attenuate the return pulse from the internal corner-cubes. It turns out that this task requires reflective coatings on the front and back surfaces, for a roughly 10^-10 attenuation. The coating design must be tuned to put us in the approximate range of attenuation desired. We may even want several attenuations to choose from. In addition to coating details, the mechanical aspects of the mirror (coupling to shaft, perpendicularity) must be addressed.

Requirements for the mirror:

• Rotate at 20 Hz with less than 0.25 milliradian of wobble
• Be free of internal bubbles
• Have 1/8 wavelength flatness on both sides
• Be AR coated on both sides
• Provide proper level of attenuation for internal corner-cube return when both dielectric patches are passed through
• Provide proper level of attenuation for imaging return using CCD when only the front patch is used

Determination of the "proper levels" of attenuation must be carried out before the design can be complete.

APOLLO To Do Task List.