Coherent anti-Stokes Raman scattering (CARS) microscopy is a nonlinear vibrational microscopy technique that generates an anti-Stokes signal that is used to detect the presence of chemical species based on their vibrational signature. This anti-Stokes signal is generated from the interaction of pump beam, Stokes beam and probe beam in a sample. CARS microscopy involves the combination of spectroscopy and microscopy that allows noninvasive characterization and imaging of chemical species without preparation or labeling. Three-dimensional sectioning with high sensitivity and resolution can be obtained from the contrast mechanism generated from the intrinsic molecular vibrational properties of the specimen.
This work presents the building of a broadband CARS microscope set-up in the Allen laboratory. It will discuss in detail the steps that were taken for the set-up and proper alignment of the system. A femtosecond Ti:Sapphire laser is used as the laser source and is divided into arms to form the pump and the Stokes beam. A photonic crystal fiber is used to generate the broad supercontinuum of light for the Stokes beam that will interact with the narrowband pump beam to generate a CARS signal at the sample focus. For the initial generation of a CARS signal, a forward CARS signal detection set-up was explored to produce a stronger CARS signal from a sample of liquid hexadecane. After ensuring correct alignment, that is, spatial and temporal overlap of the two beams, a broad CARS signal was obtained for the CH2 symmetric stretch. After generation of a forward CARS signal, the two beams are then sent to the microscope to generate an epi-CARS signal. At present, epi-detection is being set-up and optimized for the generation of an epi-CARS signal with a good spectral resolution and sensitivity.