They seam to have a flatness of λ/2 - λ/4 and are quite cheap, 10 bucks for a 25mm diameter one (that 1/5 the price of a normal 25mm secondary elliptical mirror)
They seam to have a flatness of λ/2 - λ/4 and are quite cheap, 10 bucks for a 25mm diameter one (that 1/5 the price of a normal 25mm secondary elliptical mirror)
Are you sure flatness is measured the same way as you’re used to? For a resonant cavity I’d expect total surface shape is not as important as it would be for something image-forming.
I mean, it could be. You can lapp something flat pretty easily. I’d consider it, though.