Abstract
Femtosecond Optical Parametric Amplifiers (OPAs) pumped by the fundamental frequency (FF) or the second harmonic (SH) of Ti:sapphire not only provide broad frequency tunability but also enable to dramatically shorten the pulsewidths because of their broad gain bandwidths [1]. The phase-matching bandwidth in an OPA becomes large when the group velocities of signal and idler are matched; this can be obtained in the Non-collinear OPA (NOPA) by making the signal group velocity equal to the projection of the group velocity of the idler along the signal direction. The well- known SH-pumped visible NOPA based on β-barium borate (BBO) [2] generates pulses down to 4 fs and is a workhorse of time-resolved spectroscopy. However in the near-IR, for both SH and FF pumps, the group velocity of the idler in BBO is smaller than that of the signal; therefore the NOPA concept does not work with BBO. In this paper we show that for periodically poled stoichiometric lithium tantalate (PPSLT) and several other crystals (LiIO3, KNbO3, LiNbO3) the group velocity of the idler in a FF-pumped OPA is higher than that of the signal, allowing for ultrabroadband non-collinear amplification in the near-IR. We present a near-IR NOPA based on PPSLT pumped at 785 nm by an amplified Ti:sapphire laser. The NOPA generates ultrabroad spectra spanning from 1.1 to 1.7 μm; preliminary pulse compression experiments on a limited spectral portion produced nearly transform-limited 16-fs pulses.
© 2007 IEEE
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