A Common-Mode Digital Holographic Microscope

NASA’s Jet Propulsion Laboratory, Pasadena, California

Digital holography is a fast-growing field in optics, recently spurred by the advent of large-format digital cameras and high-speed computers. This method provides a time-series of volumetric information about a sample, but the instrument itself has no moving parts. It does not compromise performance such as image quality and spatial resolution. However, these systems are typically implemented as optical interferometers with two separate beam paths: one is the reference beam and the other is the science beam. Interferometers are sensitive instruments that are subject to misalignment, and they will have significantly reduced performance in the presence of mechanical vibrations.

The optics between the science and reference arms propagate along adjacent beam paths through most of the same optical elements.

This novel design is an optical system where many of the optics for the science and reference arms are common. This simply means the beams propagate along adjacent paths through many of the same optical elements. The result is a system that is simple, compact, and insensitive to mechanical misalignment and vibration. This system is also enclosed, which mitigates against both dust and dirt, as well as stray light.

This design consists of a single-mode fiber collimated light source to provide illumination for both the science and reference arms, a pair of small microscope objectives located side-by-side, a relay lens centered between the two objectives, and a focal plane sensor where the optical intensity of the interfered beams is measured.

Compared to a canonical, Mach-Zehnder interferometer, this design removes two beamsplitters, thus saving light; the beam paths propagate along adjacent paths (making the system insensitive to opto-mechanical disturbances); the system is lightweight, compact, enclosed, and robust for field deployment; it uses fewer components and is easy to assemble; and it is intrinsically coherent, which means for most optical sources the science and reference beams will combine interferometrically.

This work was done by J. Kent Wallace, Kurt M. Liewer, Christian A. Lindensmith, Eugene Serabyn, Stephanie Rider, and Emilio Graff of Caltech for NASA’s Jet Propulsion Laboratory. NASA is seeking partners to further develop this technology through joint cooperative research and development. For more information about this technology and to explore opportunities, please contact Dan Broderick at This email address is being protected from spambots. You need JavaScript enabled to view it.. NPO-49636