Beam Frequency Disks

This idea came to me not too long ago. These disks on a motor will spin, and through one of the holes you can put your beam (laser, photons, etc pretty much any beam or whatever so long as the beam doesn't penetrate the plastic xD). So as the disk is spinning, its chopping your beam and giving you a frequency. Also, if you use aluminum foil to cover the plastic and not the holes you can prob play with other radiations lol. I think you can also use these disks as little "observing windows" that p