Position and Intensity Modulations in Holographic Optical Traps Created by a Liquid Crystal Spatial Light Modulator

“The addressing of the liquid crystals in spatial light modulators gives rise to temporal modulation of the phase pattern. Here we investigate the effect of this on the intensity and position of holographic optical traps. We use high-speed camera imaging of the laser spots back-reflected off the sample cover slip to determine the integrated pixel intensity and track the position of a laser spot. Using this method we find that the intensity modulation is 12% for three different trap configurations. We also find that for a single trap steered by 5 mrad (14.3 µm in the focal plane), the angular modulation is 0.35 µrad (1 nm), and that this modulation increases for increasing number of traps. These modulations need to be taken into account when using holographic optical traps for quantitative force measurements.”