Intra- and extra-cavity spectral broadening and continuum generation at 1.5 μm using compact low-energy femtosecond Cr:YAG laser
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- Sorokin, E., Kalashnikov, V., Naumov, S. et al. Appl Phys B (2003) 77: 197. doi:10.1007/s00340-003-1198-3
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Spectral broadening mechanisms at 1.5 μm in a Kerr-lens mode-locked Cr4+:YAG laser and in a tapered silica fiber have been analyzed. It is shown theoretically and experimentally that both approaches allow generation of coherent smooth spectra with up to 400-nm bandwidth, as required for optical coherence tomography and other applications. The necessary power levels of 200 pJ are accessible to the directly diode-pumped femtosecond Cr4+:YAG lasers. The spectral broadening in the tapered silica fiber at 1.5 μm is different from that at 800 nm, because of the compensation of the Raman shift by the third-order dispersion at 1.5 μm. The existence of the optimum taper-waist length is predicted and explained.