Widely tunable soliton frequency shifting of few-cycle laser pulses

Abstract

Photonic-crystal fibers are employed to demonstrate widely tunable frequency down-conversion of unamplified $6\text{\ensuremath{-}}\mathrm{fs}$ Ti:sapphire laser pulses through the soliton self-frequency shift induced by the Raman effect. Wavelength shifts as large as $500\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ are achieved for input few-cycle pulses with broadband spectra centered at approximately $820\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The central wavelength of the redshifted output of a photonic-crystal fiber is smoothly tuned from the low-frequency edge in the spectrum of the $6\text{\ensuremath{-}}\mathrm{fs}$ Ti:sapphire laser pulse up to $1.35\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ by varying the input energy in the fundamental mode of the fiber.