Effect of scattering on coherent anti-Stokes Raman scattering (CARS) signals

Abstract

Abstract:We develop a computational framework to examine the factors responsible for scattering-induced distortions of coherent anti-Stokes Raman scattering (CARS) signals in turbid samples. We apply the Huygens-Fresnel Wave-based Electric Field Superposition (HF-WEFS) method combined with the radiating dipole approximation to compute the effects of scatteringinduced distortions of focal excitation fields on the far-field CARS signal. We analyze the effect of spherical scatterers, placed in the vicinity of the focal volume, on the CARS signal emitted by different objects (2µm diameter solid sphere, 2µm diameter myelin cylinder and 2µm diameter myelin tube). We find that distortions in the CARS signals arise not only from attenuation of the focal field but also from scattering-induced changes in the spatial phase that modifies the angular distribution of the CARS emission. Our simulations further show that CARS signal attenuation can be minimized by using a high numerical aperture condenser. Moreover, unlike the CARS intensity image, CARS images formed by taking the ratio of CARS signals obtained using xand y-polarized input fields is relatively insensitive to the effects of spherical scatterers. Our computational framework provide a mechanistic approach to characterizing scattering-induced distortions in coherent imaging of turbid media and may inspire bottom-up approaches for adaptive optical methods for image correction.

Coherent Anti-Stokes Raman Scattering Through Thick Biological Tissues by Single-Wavefront Shaping

“…In CARS, the requirement to coherently manipulate two incident beams makes the situation more complex, and CARS generation behind a scattering medium a still unresolved challenge [2]. First, the presence of a few scatterers is already expected to strongly degrade the CARS signal due to a rapid modification of the nonlinear spatio-temporal coherent build-up [13].…”