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

We report on the generation of ultrashort tunable pulses with a cavityless traveling-wave scheme consisting of a parametric superfluorescence seed source and a parametric amplifier. We show that the traveling-wave approach, with its advantages of simplicity and direct generation of tunable energetic single pulses, can be used in the femtosecond regime, and to this end we discuss the performances that were obtained with pump pulses of almost-equal-to 1-ps and 200-fs duration at wavelengths of 0.53 and 0.6 mum, respectively. Of particular interest is the beta-barium borate-based traveling-wave parametric generator (type-II phase matching), since it offers the possibility of generating nearly transform-limited pulses that are continuously tunable within a wide spectral 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-limited beam, which could be focused, with an f/20 optics lens, to an intensity of 10(13) GW/cm2. A temperature-tuned lithium triborate-based femtosecond parametric generator, with its smaller group-velocity dispersion and absence of walk-off, can operate at a pump energy of as low as 30 muJ in a 200-fs pulse.