Theory of coherent anti‐Stokes Raman scattering for mesoscopic particle with complex molecules: angular‐dependent spectrum

Abstract

We present a microscopic theory of nonlinear scattering of mesoscopic particle that may be composed of complex molecules. We predict that the spectrum of the scattered field depends on the angle of observation. Transform theory is used to compute the third-order susceptibility for coherent anti-Stokes Raman scattering (CARS) of molecules with known absorption spectrum and vibrational modes. By incorporating the theory into an integral scattering formula, we develop a rigorous theory which leads to powerful numerical experimentation of nonlinear optical process in mesoscopic systems composed of complex molecules and driven by laser pulses with arbitrary shape and spectral content. We obtain an expression for spectral dependent CARS field which includes multiple internal reflection and refraction of the incident fields via Mie theory. The theory is used to study the variations of the CARS spectra and intensity on laser parameters and direction of detection. High-resolution spectra computed for hybrid CARS scheme shows that the relative intensities of the characteristic peaks in the CARS spectrum depend on the direction of detection. This effect can be explained by the interference between the linear response (absorption and dispersion) and the four-wave mixing process in the mesoscopic medium. The theory is useful for nonlinear spectroscopy, microscopy and nanophotonics involving small particles.

Rapid identification of heterogeneous mixture components with hyperspectral coherent anti‐Stokes Raman scattering imaging

“…We have observed that the His crystals are highly scattering and display birefringence by transmitting light through crossed polarizers. We believe that the peak shift may be an interference because of the orientation of the crystal and optical fields or as a result of material anisotropy, though a detailed study is beyond the scope of this manuscript.…”

Quantum spectra of Raman photon pairs from a mesoscopic particle

“…The imaginary part would be responsible for the damping (or amplification) of the fields inside the particle, as well as the directional dependence [22] of the spectra.…”