Sub-9-fs pulse generation tunable in visible (550-700 nm) and near-IR (0.9-1.3 /spl mu/m) by noncollinear phase-matching and pulse-front matching

Noncollinear optical parametric amplification (NOPA) is recently attracting a great deal of attention as a novel method of ultrashort pulse generation. The noncollinear geometry can realize the group-velocity-matching between the signal and idler, which is equivalent to an achromatic phase-matching with the spectral angular dispersion of the idler, and the broadest gain bandwidth is attained. In the paper we present a novel NOPA which has led to the first tunable sub-l0 fs light source. Both concepts of a pulse-front matching (PFM) and idler angular-dispersion compensation are essential to obtain transform-limited (TL) pulses from a NOPA, and sub-9 fs pulses are generated both in the wide ranges of the visible and near-IR (NIR). Extension of this technology to a full-bandwidth operation realizes as short as a 4.7-fs pulse generation, which is the first sub-5 fs light source by other methods than the traditional continuum-compression scheme. The PFM-NOPA is superior in many aspects such as tunability, pulse energy, flexible pulse width and bandwidth, which is believed to be the most useful light source for ultrafast spectroscopy.