Digital holomicroscopy for nanometer depth resolution

We report a technique which provides the details of three dimensional phase profile of a transparent microscopic sample. The depth resolution achievable is of the order of nanometers. The physical dimensions of the sample are obtained from the numerically reconstructed phase of the object wave. The method involves digital holographic recording of interferograms produced by superposition of the object wave and the coherent reference wave. We sequentially record four different holograms by altering the phase differences between the object wave and the reference wave. To introduce different phase differences between the two interfering beams, we have made use of polarization phase shifting. Therefore, the configuration used is simple and provides accuracy as the phase is introduced by simply rotating a linear polarizer. Experimental results for a microhole etched on glass are presented.