Fourier transform light scattering of inhomogeneous and dynamic structures

Abstract

Fourier transform light scattering (FTLS) is a novel experimental approach that combines optical microscopy, holography, and light scattering for studying inhomogeneous and dynamic media. In FTLS the optical phase and amplitude of a coherent image field are quantified and propagated numerically to the scattering plane. Because it detects all the scattered angles (spatial frequencies) simultaneously in each point of the image, FTLS can be regarded as the spatial equivalent of Fourier transform infrared spectroscopy, where all the temporal frequencies are detected at each moment in time.

FIG: 1.

FTLS reconstruction procedure of angular scattering from 3 Δm beads. (a) Amplitude image. (b) Reconstructed phase image. (c) Scattering wave vector map. (d) Retrieved angular scattering and comparison with Mie calculation.

FIG: 2

(a) Angular scattering signals associated with 1, 3, 6, and 11 particles, as indicated. The solid line indicates the Mie calculation and the dash line the background signal, measured as described in text. (b) Power spectrum of scattering intensity fluctuations associated with 3 μm particles in water. The solid line indicates the fit with a Lorentzian function. (c) Measured spectral bandwidth vs expected bandwidth for different particles and liquids, as indicated.

FIG: 3.

(a) Spatially resolved phase distribution of red blood cells. The color bar indicates phase shift in radians. (b) Scattering phase function associated with the cells in (a). The FDTD simulation by Karlsson et al. is shown for comparison (the x axis of the simulation curve was multiplied by a factor of 532/633, to account for the difference in the calculation wavelength, 633 nm, and that in our experiments, 532 nm). (c) Gigapixel quantitative phase image of a rat mammary tumor tissue slice. Color bar indicates phase shift in radians. (d) Angular scattering from the tissue in (c). The inset shows the 2D scattering map, where the average over each ring corresponds to a point in the angular scattering curve. The dashed lines indicate power laws of different exponents, as indicated.

FIG: 4.

Dynamics FTLS of red blood cells: log-log power spectra at 5 and 15 degrees with the respective power law fits, as indicated. The inset shows one RBC phase image from the time sequence.