4-inch Ultra Flat

I was honestly a little nervous about the 4% reflectivity spec, but it's dead on. The lambda/50 PVr flatness is perfect for my interferometry setup, and it's been rock solid at both wavelengths.

The dual coatings at 633 nm and 1.064 µm make this a workhorse for my lab setup—I can switch between wavelengths without swapping optics. Reflectivity measures right at that 4% spec during testing. Solid build for the price.

The lambda/50 PVr figure is no joke — I checked it against my reference flat and the fringe pattern was dead straight across the whole 4-inch aperture. The dual 633 nm and 1.064 μm coatings saved me from swapping optics between my HeNe and Nd:YAG setups.