it’s called dielectric mirror, this type of mirror can be made to be extremely effective over narrow range of wavelengths and it’s used in lasers for this reason. this is also the only way to manipulate extreme UV (13nm tin source, used in EUV semiconductor manufacturing)
similar effect is responsible for blue color of some butterflies and feathers that don’t contain blue pigment
it’s called dielectric mirror, this type of mirror can be made to be extremely effective over narrow range of wavelengths and it’s used in lasers for this reason. this is also the only way to manipulate extreme UV (13nm tin source, used in EUV semiconductor manufacturing)
similar effect is responsible for blue color of some butterflies and feathers that don’t contain blue pigment