Exploring the potential of tailored spectral focusing

Abstract

We introduce an advanced and flexible spectral focusing coherent anti-Stokes Raman scattering (CARS) microspectroscopy scheme based on the independent control of pump, Stokes, and probe frequencies offered by a pulse shaper. Adjusting the instantaneous bandwidth of 10 fs pulses in the focus of a microscope to different Raman linewidths assures high spectral resolution and signal intensities from the CH-bond to the fingerprint region. Experimental results are confirmed by simulations based on the CARS signal generation process. By delaying the probe, increased signal intensity and minimized nonresonant background are achieved while enabling time-dependent measurements. Contrast based on the difference of decoherence times is established and used to distinguish initially overlapping CH resonances of sunflower oil. Because of the transform-limited nature of the tailored probe, enhanced instantaneous nonlinear signals enable simultaneous multimodal imaging and molecule-specific CARS contrast as demonstrated on human skin tissue.