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.
Flat enough? Sure
Useful? Not really, they are optimized for a whole different wavelength. If I look in my CO2 laser machines mirrors everything looks grey/washed out. They are highly reflective for waves in the 10060nm range, but aren’t as reflective in other parts of the em spectrum.
Do you have the silver or the golden ones?
The silver ones, I believe they are some form of silver coated silicon. But they are highly specialized with several coatings that improve the performance and longevity in different ways. They also come with very clear instructions to clean them as little as possible, as that can ruin the coatings. So I try to optimize my dust extraction when cutting anything that puts sticky stuff in the air.
Silver should have good reflection over most of the spectrum, guess its the coatings making things strange then :/
I know enough about these kinds of optics to be firmly in the valley of despair on the dunning kruger graph. It’s super complicated and well beyond my understanding.
