Thankx RA, the reason is to be able to use a laser pointer on a glass HUD simulator to direct the pilots' eyes to where an instructor wants his focus. A monocular IR lense picks up the reflection more because it's magnified and within the refractive index of the HUD glass. Some coatings...
I appreciate that informed response, you'reobviously an expert in lasers. However; I actually need to use a beam splitter, polarizer or coating to prevent laser from reflecting back to the emmiter.