Application of spectral phase shaping to high resolution CARS spectroscopy

By spectral phase shaping of both the pump and probe pulses in coherent anti-Stokes Raman scattering (CARS) spectroscopy we demonstrate the extraction of the frequencies, bandwidths and relative cross sections of vibrational lines. We employ a tunable broadband Ti:Sapphire laser synchronized to a ps-Nd:YVO mode locked laser. A high resolution spectral phase shaper allows for spectroscopy with a precision better than 1 cm-1 in the high frequency region around 3000 cm-1. We also demonstrate how new spectral phase shaping strategies can amplify the resonant features of isolated vibrations to such an extent that spectroscopy and microscopy can be done at high resolution, on the integrated spectral response without the need for a spectrograph

Femtosecond spectral phase shaping for CARS spectroscopy and imaging

Coherent Anti-Stokes Raman Scattering (CARS) is a third-order non-linear optical process that provides label-free, chemically selective microscopy by probing the internal vibrational structure of molecules. Due to the resonant enhancement of the CARS process, faster imaging is possible compared to Raman microscopy. CARS is unaffected by background fluorescence, but the inherent non-resonant background signal can overwhelm the resonant signal. We demonstrate how simple phase shapes on the pump (and probe) beam reduce the background signal and enhance the resonant signal. We demonstrate chemically selective microscopy using these shaped pulses on plastic beads

Tailoring pulses for coherent raman microscopy

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

Spectral phase shaping for high resolution CARS spectroscopy around 3000 cm-1

By spectral phase shaping of both the pump and probe pulses in coherent anti-Stokes Raman scattering (CARS) spectroscopy we demonstrate the extraction of the frequencies of vibrational lines using an unamplified oscillator. Furthermore we demonstrate chemically selective broadband CARS microscopy on a mixed sample of 4 μm diameter polystyrene (PS) and poly(methyl methacrylate) (PMMA) beads. The CARS signal from either the PS or the PMMA beads is shown to be enhanced or suppressed, depending on the phase profile applied to the broadband spectrum. Using a combination of negative and positive (sloped) π-phase steps in the pump and probe spectrum the purely non-resonant background signal is remove

Phase aspects of (broadband) stimulated Raman scattering

The phase of the molecular response can be exploited to improve selectivity without sacrificing speed in both narrowband and broadband coherent anti-Stokes Raman scattering (CARS) microscopy, both of which will be considered in this review of the work that was performed in our grou