We investigate the effects of a piece of zero-dispersion fiber(ZDF) on the pulse dynamics of a passively mode-locked fiber laser operating in the stretched-pulse regime.Numerical simulation suggests that the proper location and length of ZDF facilitate spectrum broadening and pulse shortening in fiber lasers while maintaining constant net cavity dispersion.A nonlinear polarization evolution mode-locked Er-doped fiber laser with a dispersion map is built based on the simulation.Larger optical spectrum broadening is obtained by inserting a longer ZDF after the active fiber during single-pulse operation,which well agrees with the simulation.
We present a review of the development of a compact and high-power broadband terahertz (THz) source optically excited by a femtosecond photonic crystal fiber (PCF) amplifier.The large mode area of the PCF and the stretcher-free configuration make the pump source compact and very efficient.Broadband THz pulses of 150 μW extending from 0.1 to 3.5 THz are generated from a 3-mm-thick GaP crystal through optical rectification of 12-W pump pulses with duration of 66 fs and a repetition rate of 52 MHz.A strong saturation effect is observed,which is attributed to pump pulse absorption;a Z-scan measurement shows that three-photon absorption dominates the nonlinear absorption when the crystal is pumped by femtosecond pulses at 1 040 nm.A further scale-up of the THz source power is expected to find important applications in THz nonlinear optics and nonlinear THz spectroscopy.
