Spectrally-Compressed Fiber Laser Source for Supercontinuum-Based Broadband-CARS Spectroscopy

摘要

Supercontinuum (SC)-based broadband coherent anti-stokes Raman scattering (BCARS) spectroscopy can identify a large spectral band of complex samples simultaneously, which has been widely employed in analytical biochemistry. On the excitation laser source, there is usually a tradeoff between spectral bandwidth and resolution in BCARS. Specifically, femtosecond lasers are preferred for SC generation (as stokes), while narrowband picosecond pulses (as pump) are more suitable for obtaining high spectral resolution. Here, we report a fiber laser source for SC-based BCARS spectroscopy based on a spectrally compressed broadband seed, which ensures broadband and high resolution simultaneously. The spectral compression is achieved by self-phase modulation suffered by negative-chirp pulses in optical fibers, the power efficiency of which is much higher than that of conventional spectral filtering. High-power narrowband picosecond pump pulses, with pulse energy of 16.7 nJ and linewidth of 5.8 cm-1, are obtained for BCARS, by spectral compression in a cascaded fiber amplifier with compression ratio of 16. Combining with SC pulses as stokes beam, we obtain BCARS spectra in 700-1900 cm-1 spectral range simultaneously. Moreover, the influences of spectrally-compressed pump on BCARS signal are investigated.