A new method for three-dimensional tracking using a liquid crystal on silicon (LCoS)

“Imaging of samples by different microscopy techniques has produced a relevant impact in the development of new diagnosis techniques in biology, medicine, and material science. In many biological applications, where the sample changes or moves during the observation, a dynamical focusing of the microscope is needed. To this end it is necessary to localize the sample previously to the refocusing process. We introduce here an optical system that can perform three-dimensional (3D) tracking without mechanical displacements. The system is based on the use of a high resolution liquid crystal on silicon (LCoS) device working as a phase mostly wavefront modulator. The additional advantage of this system is performing the motion of the spot at video rate. By using elliptical polarization we have experimentally found a configuration where the phase modulation is 2π and the intensity modulation has a variation less than 25%. For this configuration we show how the spot can be moved through the focus plane by means of linear phases, or displaced out of this plane by using a quadratic phase.”