Bioimaging by Fourier-transform coherent anti-Stokes Raman scattering microscopy

Abstract

Coherent anti-Stokes Raman scattering (CARS) is a nonlinear Raman process in which pulsed light of at least two frequencies is mixed within a sample. By overlapping pump light at a frequency of ω p and Stokes light at ω s temporally and spatially, CARS light at a frequency of 2ω p -ω s is produced. When the frequency difference (ω p -ω s ) can be tuned to specific vibrational resonances within a sample, CARS microscopy provides intrinsic vibrational contrast [1]. However, in the case of the use of ultrabroadband pulses as an excitation light source, the resonant CARS signal is accompanied by significant nonresonant CARS signals from the electronic contribution. Fourier-transform CARS (FT-CARS) spectroscopy provides the suppression of the nonresonant CARS signals and the measurement of broadband CARS spectra with high spectral resolution at a time [2]. In this paper, we demonstrate that FT-CARS microscopy employing 5-fs ultrabroadband pulses can be applied to imaging of unstained HeLa cells.