Quote Originally Posted by Hologram View Post
It's not an issue either if a thick (holographic) grating is used that largely suppresses higher diffraction orders.
Are you sure? diffraction orders are part of the nature of diffration gratings. It's the overlap between the 1st order and 2nd order that comes into play when trying to record a wide range of wavelengths. If you are trying to measure upto 900 nm in the IR with a 1st order diffraction, the second order diffractio for 900 nm will start to overlap at 900/2= 450 nm, which is where you are trying to record blue wavelengths.

We don't even have to worry about 3rd and 4th order diffrations, as they will overlap starting at 300 nm and 225 nm respectively.