Enhanced χ^(3) interactions of unamplified femtosecond Cr:forsterite laser pulses in photonic-crystal fibers

Enhancement of nonlinear optical interactions in the core of a photonic-crystal fiber allows several ${\chi }^{(3)}$ processes to be simultaneously observed in the field of unamplified 30-fs pulses of a Cr:forsterite laser. Subnanojoule fundamental-radiation pulses of this laser experience spectral broadening arising from self-phase modulation and generate the third harmonic at 410–420 nm. Third-harmonic pulses also appear spectrally broadened at the output of the fiber as a result of the cross-phase-modulation effect. This catalog of enhanced ${\chi }^{(3)}$ processes observed in photonic-crystal fibers opens the way for using such fibers for frequency conversion of low-energy femtosecond pulses with simultaneous chirp control and subsequent pulse compression.