Thin-Film Beam Splitter Coating Calculator

Splitting a Beam with a Thin Metal Film

A semi-transparent silver film on glass divides incident light into reflected and transmitted beams. At 45° a thin metal layer can approach a 50/50 split, at the cost of some absorption and a difference between s- and p-polarization.

Balancing R, T and Absorption

The metal thickness sets how much light is reflected versus transmitted; thicker silver reflects more. Some energy is always absorbed, so R + T < 1. At oblique incidence the s and p components see different effective admittances, so a metallic splitter is mildly polarizing — the s beam is reflected more strongly than the p beam.

Tune the silver thickness until R and T cross near the design wavelength. Watch the absorptance A and the gap between the s and p curves grow with angle.

Interactive design tool

This page includes a live transfer-matrix calculator for this design. Adjust the parameters to recompute spectra, layer stack, and performance figures in the browser, then open the design in the full calculator.