Absolutely. I guess it involves very thick volume Bragg gratings, recorded into PTR glass (photo-thermo-refractive glass). Since PTR glass is probably out of reach for most of us, I wonder to what extend alternative recording materials might be used. Of course most of these materials cannot rival glass when it comes to heat resistance/ coefficient of expansion etc. With high power lasers this certainly becomes a limiting factor. But what about lower powered lasers? I wonder if less restrictive recording materials might become an option - maybe something alike Denisyuk/Ganzherli did a while ago with processing-free dichromated glycerol gelatin layers.There might be other candidates for such a task as well.
Furthermore, would stacked layers be an option? What happens if we stacked 10 pieces of Covestro film between two glass plates? How good would they perform optically - big question mark since there would be several pieces of PET or TAC film present in that structure.
Probably so. I would go for just one diode. Would it not be nice turning a cheap laser diode into a precious long coherence length laser?