Efficient femtosecond optical parametric generation in group-velocity-matched MgO:PPLN at 10†MHz.

We report on efficient single-pass optical parametric generation (OPG) of broadband femtosecond pulses in the mid-infrared at 10 MHz by exploiting group-velocity-matched interaction in a 42-mm-long MgO:PPLN crystal. Using a microchip-started femtosecond amplified Mamyshev oscillator at 1064 nm as the pump, the OPG source can provide tunable femtosecond pulses across 1516-1566 nm in the signal and 3318-3568 nm in the idler, with slope efficiencies of ∼93% and ∼41%, respectively. For 650 mW of average input pump power, signal powers of up to 283 mW at 1524 nm are generated, with more than 200 mW over the entire tuning range. Idler average powers of up to 104 mW at 3450 nm, with more than 80 mW across the full range, are also obtained. For input pump pulses of ∼182 fs, the generated signal pulses have a duration of ∼460 fs at 1516 nm. The idler pulses have a typical bandwidth of ≥100 nm over the entire tuning range, and as wide as 181 nm at 3457 nm. The OPG source exhibits excellent passive power stability, better than 0.5% rms in the signal and 0.6% rms in the idler, over 1 h, both in Gaussian TEM00 spatial profile with M2 < 1.5.

50-mJ macro-pulses at 1064 nm from a diode-pumped picosecond laser system.

Pulse-picking from a 100-mW cw mode-locked seeder, a hybrid master-oscillator power-amplifier (MOPA) system, based on Nd:YVO4 and Nd:YAG amplifier modules, has been developed, delivering single-pulses of 8.6 ps at 455-MHz repetition-rate, bunched into ~1-µs trains of 50 mJ ("macro-pulses"). The output beam is linearly polarized and nearly diffraction limited up to the maximum macro-pulse repetition-rate of 50 Hz. The single-pulse peak power and the macro-pulse duration and energy are quite suitable for high-energy nonlinear optical applications such as low-threshold synchronously-pumped parametric converters in the mid infrared. The impact on the overall efficiency of saturation distortion of the macro-pulse envelope as well as of amplified spontaneous emission (ASE) is considered. The managing of the envelope distortion compensation and of the ASE suppression by means of fast saturable absorbers is reported.