Application of second-harmonic generation to retardation measurements

The efficiency of second-harmonic generation from thin films by use of two input beams at the fundamental frequency depends sensitively on the polarization states of the fundamental beams. This dependence allows precise measurement of the retardation induced by optical elements. We present a theoretical analysis of the technique and discuss its advantages and limitations with regard to retardation measurements. We demonstrate our technique by measuring the retardation of a commercial half-wave plate to a precision and repeatability of better than λ/104. The technique is remarkably insensitive to misalignments of the optical components and of the fundamental beams for the retardation range investigated (δ=180±10°). The extension of the technique to measure low values of retardation (δ~0°) is straightforward.