Near-field effects on coherent anti-Stokes Raman scattering microscopy imaging

Area of Science:

• Nanophotonics
• Optical Microscopy
• Computational Physics

Background:

• Coherent anti-Stokes Raman Scattering (CARS) microscopy is a powerful label-free imaging technique.
• Near-field optical effects can significantly alter light-matter interactions at the nanoscale.
• Understanding these effects is crucial for advancing CARS microscopy applications, especially with nanoparticles.

Purpose of the Study:

• To investigate the impact of near-field effects on CARS microscopy signals from nanoparticles.
• To quantify changes in nonlinear polarization and scattering patterns with varying nanoparticle sizes.
• To explore the role of polarization properties in CARS imaging of nanoscale structures.

Main Methods:

• Utilized the finite-difference time-domain (FDTD) numerical method.
• Calculated induced nonlinear polarization, scattering patterns, and polarization properties.
• Analyzed CARS signals for spherical nanoparticles of different diameters.

Main Results:

• Near-field effects enhance nonlinear polarization by 1.5-fold at the water-particle interface.
• Enhancement increases with decreasing nanoparticle diameter, dominating scattering below half excitation wavelength.
• Perpendicular polarization component of CARS signals is confined to the interface and contributes ~20% to backward scattering.

Conclusions:

• Near-field effects are critical in CARS imaging of nanoparticles.
• Exploiting the perpendicular polarization component enhances CARS image contrast.
• This approach is valuable for high-resolution imaging of bio-materials at the nanoscale.