Experimental and theoretical limits of random phase transducers

A simple incoherent processing theory is developed for random-phase transducers. To control the spatial coherence, a moving random-phase screen (RPS) is located across the beam of a coherent transducer. Envelope detection and spectral analysis are then processed for each position of the random-phase screen and the averaging of these data performed on a set of RPS locations. The proposed theoretical model allows the prediction of the signal-to-noise ratio (SNR) and of the beam profile in monochromatic mode. This model gives the optimal choice for the random phase screen statistics. It shows that there is a simple relation between the SNR improvement and the number of speckle grains intercepted by the phase screen. Experimental results are presented on the decorrelation efficiency, the defocusing effect the effect of envelope averaging, and spectral averaging.<>