Group-velocity-matched cascaded X(2)-processes in two-dimensional QPM gratings

The simultaneously group velocity (GV) matched second harmonic generation (SHG) and third harmonic generation (THG) of femtosecond pulse in a single 2D quasi-phase-matching (QPM) device have been demonstrated. The conversion efficiencies of 27% for SHG and 7% for THG with the pulse duration of -100 fs was achieved. The demonstration has proved that 2D QPM devices are of significant importance for compact and powerful ultrafast coherent sources. It was believed that the same concept is promising for other multistep chi(2) cascading applications of ultrashort pulses.