WIYN / Bench Upgrade: VPH 3300 l/mm gratings
For CSL/WP4200 we have finalized the substrate size and thickness. The size is 500 x 230mm with a 480 x 210mm clear aperture. To place a severe specification on the final wavefront (lambda/4) requires an appropriate glass thickness and flatness (lambda/10). The rule of thumb used by polishers is that the thickness should be at least equal to a tenth of the maximal inplane dimension (diagonal or diameter). For a 500 x 230 mm grating the thickness should then be 55mm. However, we are informed by CSL that their coating machine can admit substrates with a maximum of 33mm thickness. Reducing the thickness may reduce the blank stiffness and thus increase the final wavefront error. Charles Harmer's analysis is that a thickness of 30 mm is acceptable. The final substrates (2) purchased from Zygo have dimensions of 500 x 230 x 30 mm, and have been delivered on Jul 06 2004.
|RCWA predicted efficiency of 3300 l/mm VPH grating with unknown parameters (Barden)|
| RCWA predicted efficiency of 3300 l/mm VPH grating WP3200
parameters from CSL (Bershady):
|Configuration for high-density grating (large angle). Rectangular housing (inner and outer) fasten to existing, encoded, grating turret (#1), currently used for reflection gratings.|
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