Recent advances in coherent anti-Stokes Raman scattering spectroscopy: Fundamental developments and applications in reacting flows

We present a systematic characterization of coherent anti-Stokes Raman scattering (CARS) microscopy. CARS signal generation in a heterogeneous sample under a tight-focusing condition is formulated by the Green’s function method. The CARS radiation pattern and the forward- and backward-detected CARS signals from a three-dimensional Raman scatterer are calculated. The coherent nature of CARS image formation and its consequences for image contrast and spatial resolution are investigated. Experimental implementations of CARS microscopy with collinearly copropagating and counterpropagating excitation beams, forward and backward data collection, and polarization-sensitive detection are described. Finally, CARS images of unstained live cells with forward detection, epidetection, and polarization-sensitive detection are presented and compared.

Theoretical and experimental characterization of coherent anti-Stokes Raman scattering microscopy

For noninvasive characterization of chemical species or biological components within a complex heterogeneous system, their intrinsic molecular vibrational properties can be used in contrast mechanisms in optical microscopy. A series of recent advances have made coherent anti-Stokes Raman scattering (CARS) microscopy a powerful technique that allows vibrational imaging with high sensitivity, high spectral resolution and three-dimensional sectioning capability. In this review, we discuss theoretical and experimental aspects of CARS microscopy in a collinear excitation beam geometry. Particular attention is given to the underlying physical principles behind the new features of CARS signal generation under tight focusing conditions. We provide a brief overview of the instrumentation of CARS microscopy and its experimental characterization by means of imaging of model systems and live unstained cells. CARS microscopy offers the possibility of spatially resolved vibrational spectroscopy, providing chemical and physical structure information of molecular specimens on the sub-micrometre length scale. We review multiplex CARS microspectroscopy allowing fast acquisition of frequency-resolved CARS spectra, time-resolved CARS microspectroscopy recording ultrafast Raman free induction decays and CARS correlation spectroscopy probing dynamical processes with chemical selectivity.

https://iopscience.iop.org/article/10.1088/0022-3727/38/5/R01/pdf

Vibrational imaging and microspectroscopies based on coherent anti-Stokes Raman scattering microscopy

High intensity Raman interactions

Combustion diagnostics by laser Raman and fluorescence techniques

Background signals which appear in Coherent anti‐Stokes Raman spectroscopy and in the Raman‐induced Kerr effect can be eliminated using polarization technqiues based upon four‐wave mixing. Specific polarization conditions will suppress all signals with the exception of those arising from Raman modes. The interference between resonant and background contributions is eliminated, and undistorted line shapes are obtained.

M. D. Levenson

Papers

Background suppression in coherent Raman spectroscopy