Achromatic combinations of birefringent plates. Part I. An achromatic circular polarizer

Abstract

Circularly polarised light is obtained by superposing two half-wave plates and one quarter-wave plate, all of the same material, such that the fast vibration-directions of the successive plates make specific angles θ₁, θ₂, θ₃ with the azimuth of the linear vibration incident on the first plate. The required range of achromatism determines the optimum values of the angles. Thus, using mica retardation plates prepared for Na 5890, the range from 4000 Å to 7800 Å is covered with θ₁ = 6° 52', θ₂ = 34° 32' θ₃ = 100° 20'; while the range 4400 Å to 7400 Å can be covered with superior achromatism by taking θ₁ = 6° 30', θ₂ = 34° 34', θ₃ = 101° 8'.