Search

Second-harmonic generation (SHG) microscopy provides label-free imaging of biological tissues with unique contrast mechanisms, but its resolution is limited by the diffraction limit. Here, we present the first experimental demonstration of super-resolution quantitative phase imaging of the SHG field based on synthetic aperture Fourier holographic microscopy. We discuss the mathematical model of synthetic-aperture imaging of SHG fields, as well as the computational adaptive optics technique for correcting sample-induced aberration. We demonstrate proof-of-concept experiments where SHG targets are embedded within a thick scattering medium to validate the performance of the proposed imaging technique. It is shown to be able to overcome the conventional Abbe diffraction limit even in the complex aberrations and strong multiple scattering. We also demonstrate SHG-based super-resolution deep-tissue phase imaging of ex-vivo zebrafish muscle tissue.

Multiple light scattering hampers imaging objects in complex scattering media. Approaches used in real practices mainly aim to filter out multiple scattering obscuring the ballistic waves that travel straight through the scattering medium. Here, we propose a method that makes the deterministic use of multiple scattering for microscopic imaging of an object embedded deep within scattering media. The proposed method finds a stack of multiple complex phase plates that generate similar light trajectories as the original scattering medium. By implementing the inverse scattering using the identified phase plates, our method rectifies multiple scattering and amplifies ballistic waves by almost 600 times, which leads to a substantial increase in imaging depth. Our study marks an important milestone in solving the longstanding high-order inverse scattering problems.

Supplementary Information

Optical diffraction tomography (ODT) has emerged as a powerful label-free three-dimensional (3D) bioimaging techniques for observing living cells and thin tissue layers. We report a new reflection-mode ODT (rODT) method for imaging thick biological specimens with 500 nm lateral resolution and 1 {\mu}m axial resolution. In rODT, multiple scattering background is rejected through spatio-temporal gating provided by dynamic speckle-field interferometry, while depth-resolved refractive index maps are reconstructed by developing a comprehensive inverse scattering model that also considers specimen-induced aberration. Benefiting from the high-resolution and full-field quantitative imaging capabilities of rODT, we succeeded in imaging red blood cells and quantifying their membrane fluctuations behind a turbid sample with a thickness of 2.8 scattering mean-free-paths. We further realized volumetric imaging of cornea inside an ex vivo rat eye and quantified its optical properties, including mapping the topography of Dua's and Descemet's membrane surfaces on the nanometer scale.

supplemental document

This document provides supplementary information to "Reflection phase microscopy using spatio-temporal coherence of light".

Thick biological tissues give rise to not only the scattering of incoming light waves, but also aberrations of the remaining unscattered waves. Due to the inability of existing optical imaging methodologies to overcome both of these problems simultaneously, imaging depth at the sub- micron spatial resolution has remained extremely shallow. Here we present an experimental approach for identifying and eliminating aberrations even in the presence of strong multiple light scattering. For time-gated complex-field maps of reflected waves taken over various illumination channels, we identify two sets of aberration correction maps, one for the illumination path and one for the reflection path, that can preferentially accumulate the unscattered signal waves over the multiple-scattered waves. By performing closed-loop optimization for forward and phase- conjugation processes, we demonstrated a spatial resolution of 600 nm up to the unprecedented imaging depth of 7 scattering mean free paths.

We present a study on characteristics of a magneto-optical trap (MOT) as an optical lattice. Fluorescence spectra of atoms trapped in a MOT with a passively phase-stabilized beam configuration have been measured by means of the photon-counting heterodyne spectroscopy. We observe a narrow Rayleigh peak and well-resolved Raman sidebands in the fluorescence spectra which clearly show that the MOT itself behaves as a three-dimensional optical lattice. Optical-lattice-like properties of the phase-stabilized MOT such as vibrational frequencies and lineshapes of Rayleigh peak and Raman sidebands are investigated systematically for various trap conditions., Comment: 8 pages, 8 figures

Analytical solution for the stationary density matrix is derived, by using the Morris-Shore transformation, for an open Jaynes-Cummings system of a two-level atom with Zeeman sublevel degeneracy coupled to an arbitrary-polarized cavity mode. In the limit of weak excitation with the number of quantum in the system not exceeding one, we have obtained the stationary solution of the master equation up to the first order of the driving field intensity. We have also derived the analytic expressions for the excitation spectra of atomic spontaneous emission and cavity transmission. Our results show that the system can be regarded as a non-degenerate two-level system with a single effective coupling constant which depends only on the elliptic angle of the driving field as long as the atom-cavity coupling is not too strong. A precise condition for this approximation is derived. This work provides a theoretical ground for experimentally realizing a Jaynes-Cummings system with a coupling constant continuously varied for various cavity quantum electrodynamics studies., Comment: 9 pages, 4 figures, 1 table

Stochastic properties of loading and loss mechanism in a few atom trap are analyzed. An approximate formula is derived for the atom-number correlation function for the trapped atoms in the limit of reasonably small two-atom loss rate. Validity of the approximate formula is confirmed by numerical simulations., 5 pages, 3 figures