Free-beam spectral self-compression at supercritical peak powers.

We demonstrate free-beam spectral self-compression of ~100-GW femtosecond laser pulses due to self-phase modulation (SPM) in a transparent dielectric. While all the earlier studies of SPM-induced spectral narrowing have been performed using optical fibers, experiments and simulations presented in this Letter show that this type of spectral transformation can be implemented as a part of a full three-dimensional field-waveform dynamics and can be extended to peak powers ∼10 times higher than the critical power of self-focusing. With a properly chosen initial chirp, spectral self-compression is accompanied by pulse compression, providing spectral-temporal mode self-compression as a whole.

Highly birefringent silicate glass photonic-crystal fiber with polarization-controlled frequency-shifted output: A promising fiber light source for nonlinear Raman microspectroscopy.

A highly birefringent silicate glass photonic-crystal fiber (PCF) is employed for polarization-controlled nonlinear-optical frequency conversion of femtosecond Cr: forsterite laser pulses with a central wavelength of 1.24 mum to the 530--720-nm wavelength range through soliton dispersion-wave emission. The fiber exhibits a modal birefringence of 1.