Portable advanced off-axis camera for quantitative phase microscopy
We propose and experimentally demonstrate a device in which common-path interferometry combined with off-axis holographic geometry is used to realize a digital holographic camera which can be attached to the camera port of a conventional transmission microscope for complex wavefront analysis. A thick transmission volume grating recorded holographically into thick photosensitive glass splits the beam containing the sample information in two beams. The untouched transmitted beam creates the sample arm of the interferometer. The Bragg diffracted order of the grating is spectrally and spatially filtered by diffraction to generate a clean reference beam. Double passing the diffracted order through the grating using a retroreflector device provides filtering in two dimensions. The spatial filtering done by the grating which works based on high angular selectivity of thick volume gratings, reduces the alignment spatial sensitivity which is an advantage over the conventional spatial filtering done by pinholes. Besides, using a second thick grating, we introduce a desired coherence plane tilt in the reference beam which is sufficient to create high-visibility interference over the entire field of view. The full-field off-axis interferograms are created from which the amplitude and phase can be reconstructed. The advantage of the proposed camera is the insensitivity to the alignment, thus can be the basis for a standalone camera mountable on a standard optical microscope.