Non-uniform spatial response of the LCoS spatial light modulator

•Phase shift spatial non-uniformity depends on the average induced phase shift.•The two beams method used to calibrate the SLM could be affected by non-uniformity.•SLM used as phase shifters could introduce non constant wave front aberrations.•It is possible to mitigate the undesirable effects of the phase shift no-uniformity.

Liquid crystal on silicon (LCoS) spatial light modulators have been considered for a wide variety of scientific applications, due to their phase modulation capability and high spatial resolution. Nevertheless, their intrinsic characteristics, like the extensively studied depolarization and phase shift fluctuations, can make their behavior significantly distant from the ideal and somewhat unpredictable. Here, we present the characterization of a different source of uncertainty: the non-uniform spatial response of the LCoS, which is fundamentally different to the static aberrations of the panel. We measured local deviations of ±22% from the expected phase shift, resulting in non-negligible effects for phase modulation measurements, phase shifting interferometry, wavefront correction, and speckle interferometry.