Measurement of the sensitivity of heterodyne detection to aberrations using a programmable liquid-crystal modulator

Heterodyne detection is known to be highly sensitive to wavefront distortio ns. However, quantitative measurements of the effects of aberrations are no t easy to obtain. We propose to use a liquid-crystal spatial light modulato r as a programmable wavefront aberrator. This allows us to simulate experim entally a coherent detection system at lambda = 632.8 nm. Two frequency-shi fted plane waves (backscattered signal and local oscillator) are generated. The programmable liquid-crystal wavefront aberrator is used to computer-co ntrol the phase of the backscattered signal, and the heterodyne efficiency is measured. We present experimental measurements of the field-of-view, the effect of defocus and the sensitivity to atmospheric perturbations. In all three cases, the experimental data are compared to the theoretical predict ions. (C) 1999 Elsevier Science B.V. All rights reserved.