Hi Andrew,
If you are working in the first order there is no overlap at the UV end so no need to use an IR cut to get the UV part of the spectrum. The response of the Star Analyser rolls off quite rapidly at the UV end though. Note that the zero order has a rather odd spectral content. (Effectively the inverse of the grating response, so predominantly contains the blue and red ends with the central wavelengths missing.) An IR cut filter before the grating might therefore be useful to enhance the sensitivity of the zero order to changes specifically in the blue without affecting the spectrum as the IR part of the 1st order spectrum would be invalid in any case without an order filter to cut the overlapping 2nd order blue end. I’ll see if I can dig out the raw spectra for you to play with
Cheers
Robin