TRAVELING-WAVE PARAMETRIC GENERATION OF WIDELY TUNABLE, HIGHLY COHERENT FEMTOSECOND LIGHT-PULSES

We report on the generation of ultrashort tunable pulses with a cavity less traveling-wave scheme consisting of a parametric superfluorescenc e seed source and a parametric amplifier. We show that the traveling-w ave approach, with its advantages of simplicity and direct generation of tunable energetic single pulses, can be used in the femtosecond reg ime, and to this end we discuss the performances that were obtained wi th pump pulses of almost-equal-to 1-ps and 200-fs duration at waveleng ths of 0.53 and 0.6 mum, respectively. Of particular interest is the b eta-barium borate-based traveling-wave parametric generator (type-II p hase matching), since it offers the possibility of generating nearly t ransform-limited pulses that are continuously tunable within a wide sp ectral range to as high as 3 mum in the IR. With a diffraction-limited pump at 0.53 mum we obtained tunable pulses in a 1.2 X diffraction-li mited beam, which could be focused, with an f/20 optics lens, to an in tensity of 10(13) GW/cm2. A temperature-tuned lithium triborate-based femtosecond parametric generator, with its smaller group-velocity disp ersion and absence of walk-off, can operate at a pump energy of as low as 30 muJ in a 200-fs pulse.