Abstract
We employ the finite-difference time-domain (FDTD) technique as a numerical approach to studying the effects of scatterers' sizes on near-field coherent anti-Stokes Raman scattering (CARS) microscopy under tightly focused radially and linearly polarized light excitations. The FDTD results show that in a uniform medium (water), the full width at half maximum (FWHM) (transverse resolution) of radially polarized near-field CARS (RP-CARS) radiation is approximately 7.7% narrower than that of linearly polarized near-field CARS (LP-CARS) imaging, whereas the depth of focus (DOF) of RP-CARS radiation is 6.5% longer than LP-CARS. However, with the presence of scatterers in the uniform medium, both the FHWM and DOF of near-field RP-CARS radiation become much narrower compared to those of near-field LP-CARS radiation. In addition, the signal to nonresonant background ratio of near-field RP-CARS is significantly improved when the scatterer's size is larger than a half wavelength of the pump light field. This work suggests that near-field CARS radiations are strongly influenced by the scatterers' sizes in the medium; and near-field RP-CARS microscopy is superior to the near-field LP-CARS by providing both higher transverse and axial resolutions for three-dimensional molecular imaging of fine structures in biological systems.
Highlights
Coherent anti-Stokes Raman scattering (CARS) microscopy has received much interest for imaging tissue and cells owing to its outstanding capabilities of high biochemical selectivity and sensitivity, as well as its intrinsic three-dimensional (3-D) optical sectioning ability with high spatial and spectral resolutions [1,2,3]
The radially polarized CARS (RP-CARS) microscopy has been proven to be in favor of revealing longitudinally oriented molecules [11], the near-field distributions of RP-CARS radiation compared to linearly polarized CARS (LP-CARS) have yet been investigated in details
The intensity profiles along the lateral direction [Fig. 2(c)] show that the full width at half maximum (FWHM) of RP-CARS radiation is 272 nm, which is 7.7% narrower than LP-CARS (FWHM of 293 nm). This indicates the advantage of RP-CARS microscopy for providing higher transverse resolution for molecular imaging
Summary
Coherent anti-Stokes Raman scattering (CARS) microscopy has received much interest for imaging tissue and cells owing to its outstanding capabilities of high biochemical selectivity and sensitivity, as well as its intrinsic three-dimensional (3-D) optical sectioning ability with high spatial and spectral resolutions [1,2,3]. “Heterodyne polarization coherent anti-Stokes Raman scattering microscopy,” Appl.
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