Synthetic aperture laser optical feedback imaging using a translational scanning with galvanometric mirrors

Abstract

In this paper we present an experimental setup based on Laser Optical Feedback Imaging (LOFI) and on Synthetic Aperture (SA) with translational scanning by galvanometric mirrors for the purpose of making deep and resolved images through scattering media. We provide real 2D optical synthetic-aperture image of a fixed scattering target with a moving aperture and an isotropic resolution. We demonstrate theoretically and experimentally that we can keep microscope resolution beyond the working distance. A photometric balance is made and we show that the number of photons participating in the final image decreases with the square of the reconstruction distance. This degradation is partially compensated by the high sensitivity of LOFI.

Deep and optically resolved imaging through scattering media by space-reversed propagation

“…That results in a capacity of making an image through an increased optical density of ~3.5 (~8 transport mean free paths) at the shot noise limit. To conclude we have demonstrated the possibility to combine Acoustic Photon Tagging [9] with Synthetic Aperture [10]. Indeed possibility to get both resolved and shot noise limited (see Fig.…”

“…This is the optical analogous to what was done with acoustic waves by Fink et al [12]. This technique is called SA operation and one finally get the following filtered signal [10]:…”

“…However the accessible depth is quickly limited by the small number of remaining ballistic photons and by the working distance of the objective. In this paper, we present a new sensitive imaging technique belonging to the second family, which combines Laser Optical Feedback Imaging (LOFI, based on the ballistic photons detection) [8], Acoustic Photon Tagging (APT) [9] and Synthetic Aperture (SA) [10]. We demonstrate a shot noise limited [11] microscopy technique with an optical resolution enabling images beyond the working distance of the microsope objective, while the laser power is kept low for imaging biological media without damage.…”

“…SA is a technique that can be used to make resolved images beyond the working distance of the objective, which is useful for making images deep in the medium. When a punctual target located at a distance L from the image plane of the objective is scanned, one obtains the point spread function [10]:…”

“…Therefore the signal loss is proportional to L 2 . LOFI is a confocal microscope used beyond the confocal zone [10] and can then quickly be limited by the background. More precisely, it was shown in [13] that the main limitations are parasitic reflections (see background on Fig.…”