Single-shot common-path off-axis dual-wavelength digital holographic microscopy

Abstract

A single-shot common-path off-axis self-interference dual-wavelength digital holographic microscopic (DHM) system based on a cube beam splitter is demonstrated to expand the phase range in a stepped microstructure and for simultaneous measurement of the refractive index and physical thickness of a specimen. In the system, two laser beams with wavelengths of 532 nm and 632.8 nm are used. These laser beams are combined to transilluminate the object under study, then the object beam is divided into two beams by using a beam splitter oriented in such a way that both the beams propagate in almost the same direction, with an appropriate lateral separation between them. One of the object beams is spatially filtered at its Fourier plane, using a pinhole to generate a reference spherical beam free from the object information. The reference beam interferes with the object beam to form a digital hologram at the faceplate of the image sensor. The phase information is extracted from a single recorded digital hologram using the phase aberration compensation method that is based on principal component analysis (PCA). Owing to the common-path configuration, the system shows high temporal phase stability and it is less vibration-sensitive compared to counterparts such as a Mach-Zehnder type DHM. The performance of the dual-wavelength DHM system is verified in two different application fields by conducting the experiments using microsphere beads and living plant cells.