Coherent Anti-Stokes Raman Scattering Microscopy for Biomedical Applications

Book excerpt: Coherent anti-Stokes Raman scattering (CARS) microscopy is considered as a powerful tool for non-invasive chemical imaging of biological samples. CARS microscopy provides an endogenous contrast mechanism that it is sensitive to molecular vibrations. CARS microscopy is recognized as a great imaging system, especially in vivo experiments since it eliminates the need for the contrast agents. In this thesis, CARS microscopy/spectroscopy is built from scratch by employing a single (Ti-Sapphire) laser source generating 65 femtosecond laser pulses centered at 800 nm wavelength. Two closely lying zero dispersion photonic crystal fiber (PCF) is used to generate the supercontinuum for the Stokes beam to generate CARS at 2885 cm-1 to match lipids rich vibrational frequency. XY galvanometers are used for laser raster scanning across the sample. The initial generation of CARS signal was in the forward direction. After guaranteeing a strong CARS signal, images for chemical and biological samples were taken. To achieve a multimodal imaging technique, CARS microscopy imaging system is combined with two- photon excitation fluorescent (TPEF) and second harmonic generation (SHG) imaging techniques, where various information was extracted from the imaged samples. Images with our CARS microscopy show a good resolution and sensitivity. The second part of my work is to reduce the footprint for this setup to make it more suitable for use in clinical applications. For that reason, I integrated a homebuilt endoscope and all fiber femtosecond laser source together to get a fiber based imaging system. Proof of principal for the integrated system is achieved by obtaining a reasonable agreement in accuracy and resolution to those obtained by the endoscope driven by Ti-sapphire laser.