Tailoring pulses for coherent Raman microscopy

Abstract

This thesis describes improvements of chemical selectivity and contrast in coherent Raman scattering (CRS) spectroscopy and microscopy. Stimulated Raman Scattering (SRS) and Coherent Anti-Stokes Raman Scattering (CARS) provide chemical information of a sample bsed on the vibrational resonances in molecules. These resonances occur at characteristic frequencies related to the mass of the atoms and the strength of the bonds between the atoms. From the presence of these resonances the presence of compounds of interest can be inferred. In conventional narrowband CRS, the contrast is based on a narrow frequency range, covering only a single vibrational resonance. In samples with many compounds, vibrational resonances can overlap significantly and contrast based on a single resonance may not be sufficient to separate different compounds. Furthermore, CARS suffers from a non-resonant background that is generated even in the absence of vibrational resonances. This non-resonant background can overwhelm the resonant CARS signal. The CRS techniques described in this thesis excite multiple vibrational resonances simultaneously. Spectral phase shaping of the excitation light is used to influence the interferences between the different resonances and excitation pathways. In this way selective and background-free images are obtained.