Doubling the field of view in off-axis low-coherence interferometric imaging

Abstract

We present a new interferometric and holographic approach, named interferometry with doubled imaging area (IDIA), with which it is possible to double the camera field of view while performing off-axis interferometric imaging, without changing the imaging parameters, such as the magnification and the resolution. This technique enables quantitative amplitude and phase imaging of wider samples without reducing the acquisition frame rate due to scanning. The method is implemented using a compact interferometric module that connects to a regular digital camera, and is useful in a wide range of applications in which neither the field of view nor the acquisition rate can be compromised. Specifically, the IDIA principle allows doubling the off-axis interferometric field of view, which might be narrower than the camera field of view due to low-coherence illumination. We demonstrate the proposed technique for scan-free quantitative optical thickness imaging of microscopic biological samples, including live neurons and a human sperm cell in rapid motion under high magnification. In addition, we used the IDIA principle to perform non-destructive profilometry during a rapid lithography process of transparent structures. Researchers in Israel have developed a method for doubling the field of view in single-exposure depth-resolved holographic imaging. Pinhas Girshovitz and Natan Shaked from Tel Aviv University based their technique on digital interferometric microscopy, which uses interference effects to extract quantitative information on the thickness or height profile of the imaged object. Such information is useful, for example, in imaging of biological samples without labeling, or for optically profiling elements for non-destructive testing with sub-nanometer accuracy. Unfortunately, to enable capturing the entire quantitative image in a single exposure, a reduction in the field of view occurs. Girshovitz and Shaked proposed a way to optically compress more information into the same camera frame without loss in the imaging details or the magnification. A compact and portable interferometric module, positioned only in the output of the imaging system, splits the image beam into two components that are then superimposed at different angles on the imaging camera. This multiplexing approach increases the information in the image and doubles the field of view over previous techniques. Therefore, they were able to image wider samples or acquire the samples in faster frame rates. The main experimental demonstrations include fast high-magnification quantitative imaging of a swimming sperm cell, and non-destructive profiling of a thin element during rapid lithography process.