Highly longitudinally polarized coherent anti-Stokes Raman scattering microscopy with improved spatial resolution

Jian Lin,Shishen Wei,Songlin Zhuang

doi:10.1063/1.5045235

Abstract

We proposed a method to enhance the longitudinally polarized component and improve the spatial resolution of radially polarized coherent anti-Stokes Raman scattering (CARS) microscopy by phase modulation. A specially designed phase pattern is applied onto the pump beam to suppress the radially polarized field component at the focal region. With this modulation, the calculated intensity ratio between the longitudinally and radially polarized CARS field is increased from 2.57 to 14.7, and the simulation of CARS imaging on a 120 nm polystyrene bead shows more than 3-fold spatial resolution improvement for both forward and backward detection. It is expected that this method could also be applied to other nonlinear optical imaging modalities for enhancing the longitudinally polarized component.

Highlights

Coherent anti-Stokes Raman scattering (CARS) microscopy keeps attracting people’s attention in imaging tissues and cells owing to its outstanding capabilities of high biochemical selectivity and sensitivity, as well as its intrinsic three-dimensional optical sectioning ability with high spatial and spectral resolutions.[1,2,3,4,5,6,7,8] CARS is a third-order nonlinear optical process, where temporally and spatially overlapped pump and Stokes beams are focused onto the sample to generate CARS signal
To enhance CARS image contrast on longitudinally orientated molecules, tightly focused radially polarized laser beams have been used,[15] since they have a very strong longitudinal field component and a tight focal spot size at the focal point by using a high numerical aperture (NA) objective;[16] besides the strong longitudinal component, the radially polarized component exists at focus
The longitudinal component in radially polarized CARS microscopy enhances the image contrast of longitudinally orientated molecules and slightly improves spatial resolution, which was demonstrated by CARS imaging in the high-wavenumber region,[14] where the pump and Stokes beams have a large difference in wavelengths

Summary

Introduction

Coherent anti-Stokes Raman scattering (CARS) microscopy keeps attracting people’s attention in imaging tissues and cells owing to its outstanding capabilities of high biochemical selectivity and sensitivity, as well as its intrinsic three-dimensional optical sectioning ability with high spatial and spectral resolutions.[1,2,3,4,5,6,7,8] CARS is a third-order nonlinear optical process, where temporally and spatially overlapped pump and Stokes beams are focused onto the sample to generate CARS signal. The longitudinal component in radially polarized CARS microscopy enhances the image contrast of longitudinally orientated molecules and slightly improves spatial resolution, which was demonstrated by CARS imaging in the high-wavenumber region,[14] where the pump and Stokes beams have a large difference in wavelengths.

Results

Conclusion