An optical system for laser eye protection application is presented. The optical device includes a first lens having a positive power of magnification a second lens having a negative power of magnification and a flat interference based reflector(s) between the two lenses. Incoming light rays are redirected by the lenses so that they pass through the interference filter at normal incidence. 1.
Jon D. Masso,
"Collimating lens system for laser eye protection", Proc. SPIE 1207, Laser Safety, Eyesafe Laser Systems, and Laser Eye Protection, (1 July 1990); doi: 10.1117/12.17841; https://doi.org/10.1117/12.17841