Taking advantage of the tunable dispersion and high nonlinearity of photonic crystal fibers (PCFs), the supercontinuum generated in PCFs can be used as a tunable source that is synchronized with the ultrafast pump source. This special property makes PCFs ideally suited for nonlinear optical imaging, such as two-photon excitation fluorescence (TPEF) and coherent anti-Stokes Raman scattering (CARS) microscopy or spectroscopy....[ Read more ]

Taking advantage of the tunable dispersion and high nonlinearity of photonic crystal fibers (PCFs), the supercontinuum generated in PCFs can be used as a tunable source that is synchronized with the ultrafast pump source. This special property makes PCFs ideally suited for nonlinear optical imaging, such as two-photon excitation fluorescence (TPEF) and coherent anti-Stokes Raman scattering (CARS) microscopy or spectroscopy.

Accordingly, we instrumented a TPEF microscopy system based on the PCF and an ultrafast pump laser. When the PCF was excited at 810 nm with the average power of 70 mW, the supercontinuum emission is peaked around 700 nm. Using the spectral component from the PCF as the excitation source, the two-photon emission spectra of NADH were excited and the TPEF images of SiHa cells were successfully generated. Combining the fundamental laser pulses as the excitation source for the fluorophore FAD, we demonstrated the feasibility to use a PCF and pumping source for two-color TPEF microscopy.

A CARS spectroscopy system was also developed based on PCF. The setup utilized a PCF to generate a frequency-shifted beam in the range 720-745 nm that was used as the pump source in the CARS process. Combined with the fundamental 800 nm beam from the pump laser, the CARS signals from liquid toluene were excited. By tuning the time delay between the pump and Stokes pulses, anti-Stokes spectra of toluene corresponding to different Raman resonances were observed. The results show that a PCFs-based excitation configuration significantly simplified the CARS spectroscopy system. Further study will be focused to evaluate the potential of a PCF as a light source in CARS microscopy of cells and tissues.