Maybe some of you have a FTIR spectrometer that could work in Far-IR region. I'm
wondering whether you could send me a photo showing the mylar beamsplitter.

  I am trying to make one for my spectrometer but I have never seen a real one
in the first place so I'm not sure where mine went wrong. I used a stretched
sheet of 25um, 50um and 75um thickness Mylar for our beamsplitter but our
Michelson interferometer couldn't get any interferogram.

  So if you could show me a real one that'll be great! Also, any advice is
warmly welcome.