Chapter 4 - Hyperspectral SRS imaging via spectral focusing

Abstract

Stimulated Raman scattering (SRS) microscopy typically requires picosecond lasers to achieve a delicate balance between excitation efficiency and spectral resolution. Femtosecond lasers can also be used for SRS microscopy, provided that proper pulse shaping is implemented to narrow the excitation bandwidth. This is often achieved with spectral focusing, a technique that stretches out both the pump and Stokes lasers in time to a few picoseconds for narrowband Raman excitation. Compared to traditional SRS, spectral focusing SRS has the benefit of changing the Raman excitation through a mechanical delay, which is much faster and more robust compared to tuning laser wavelength. As a result, it has seen growing popularity for various SRS applications. In this chapter, we will provide a theoretical description of the spectral focusing-based SRS excitation process. Different methods for implementing spectral focusing and approaches in improving spectral resolution and spectral coverage will be discussed. Lastly, we will discuss a few recent technical advances in adopting the spectral focusing approach for dual-band SRS and frequency-modulation SRS imaging.