Superresolution effect on a microstep phase image in a laser heterodyne microscope

The possibility of achieving superresolution on a microstep phase image in a laser scanning differential heterodyne microscope is studied both heoretically and experimentally. The superresolution is estimated as the width ratio for the amplitude and phase components of the microscope response measured at half the height of the corresponding parts of the response. It is shown theoretically that superresolution greatly exceeding unity can be achieved for an object in the form of a phase microstep introducing a phase shift equal to π. Superresolution of ~2 is experimentally obtained for certified test micro-objects. A possibility of tuning a test sample into the superresolution regime by shifting a point photodetector in the microscope's Fourier plane is demonstrated.