Tunable light source for coherent anti-Stokes Raman scattering microspectroscopy based on the soliton self-frequency shift.
ABSTRACT We present a photonic crystal fiber (PCF)-based light source for generating tunable excitation pulses (pump and Stokes) that are applicable to coherent anti-Stokes Raman scattering (CARS) microspectroscopy. The laser employed is an unamplified Ti:sapphire femtosecond laser oscillator. The CARS pump pulse is generated by spectral compression of a laser pulse in a PCF. The Stokes pulse is generated by redshifting a laser pulse in a PCF through the soliton self-frequency shift. This setup allows for probing up to 4000 cm(-1) with a spectral resolution of approximately 25 cm(-1). We characterize the stability and robustness of CARS microspectroscopy employing this light source.
Article: Photonic Crystal Fiber Based Time-Resolved Coherent Anti-Stokes Raman Scattering Spectroscopy[show abstract] [hide abstract]
ABSTRACT: We demonstrate a novel technique for three-color time-resolved coherent anti-Stokes Raman scattering using a Ti:Sapphire oscillator and four-wave mixing in a photonic crystal fiber. We measure vibrational coherence decays in calcite and several molecules. Femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) measurements provide chemical information by recording the molecular vibrational dynamics in the time domain. In a fs-CARS experiment, the molecules are excited to one or more Raman-active vibrational modes by two coherent laser pulses, namely pump and Stokes pulses. The created vibrational coherence due to the Raman excitation is subsequently probed by a delayed third pulse, and generates a CARS signal, which is resonantly enhanced when the difference frequency between the pump and Stokes pulses matches with the frequency of a Raman transition, providing chemical information of the sample. Complicated and costly laser systems such as two optical parametric amplifiers with a Ti:Sapphire regenerative amplifier system are usually used to generate different wavelengths. Recently however, there is an emerging interest in multi-wavelength pulses generation through the nonlinear interaction between Ti:Sapphire oscillator and a photonic crystal fiber (PCF), taking advantage of the continuum and/or soliton generation in PCF.[1-4] Fig. 1a. Experimental setup (left) and b. The pump, Stokes, and probe beam spectra as generated in the PCF. The inset shows the cross-correlation between the generated Stokes and probe, with a temporal resolution of 200fs.