Antireflection Coatings for Silicon in the 2.5-50-microm Region

It has been found that vacuum-deposited films of CsI, AgCl, TlBr, and TlCl are useful as antireflection coatings for silicon over a broad spectral range in the infrared. Measurements performed on a plane-parallel silicon plate coated with various thicknesses of the above materials yield transmittance values ranging from 99% at lambda = 2.9 microm to 88% at lambda = 27 microm. Experimental details of the coating process and properties of the coatings are discussed.