The vast majority of quantitative phase imaging techniques face the same major issue of phase unambiguity. The phase of light is 2π-periodic, and as such can only be extracted in a small range of typically 0.4 µm to 0.7µm in the visible range. As most of the samples in biology and metrology are much higher, phase data is wrapped within this small range. One of the more reliant solutions of phase unambiguity is phase unwrapping, where the it is unwrapped based on the surrounding data. Unwrapping, however, works best on continuous phase changes and fails when abrupt phase jumps appear, e.g steps greater than the unambiguous range. An alternative method to overcome the unambiguous phase problem is multiplexing two wavelengths to capture the same phase image. Processing together the two phase images captured by different wavelengths can produce a new image, corresponding to a phase image with a synthetic wavelength that larger than each of the original wavelengths. This effectively enlarges the unambiguous range, making costly unwrapping algorithms redundant.
We present a new dual-wavelength interferometry setup that can capture and multiplex two different phase images in an external module, portable to existing microscopy systems. The module is based on a self-interference multiplexing technique. As such, it is very flexible and can work with either transmission or reflection based microscopes. It can be used for either enlarging the unambiguous range or other dual-wavelength phase imaging applications.
Nir A. Turko and Natan T. Shaked, "Phase unwrapping using a portable two wavelength multiplexing module (Conference Presentation)," Proc. SPIE 10074, Quantitative Phase Imaging III, 100740M (Presented at SPIE BiOS: January 30, 2017; Published: 24 April 2017); https://doi.org/10.1117/12.2256087.5380600129001.
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