Abstract

There has been much recent interest in generating mid-infrared (MIR) shaped pulses, useful for various applications such as extending ultrafast coherent control studies to vibrational systems of molecules of chemical and biological interests. Although high resolution pulse shaping capabilities exist for the visible and near-infrared (NIR) wavelengths [1, 2], direct phase and amplitude pulse shaping in the MIR has yet to be demonstrated. The main difficulty is the lack of appropriate materials for the usual direct methods of pulse shaping. Liquid crystal modulators absorb in the MIR; acousto-optic materials such as TeO₂ and GaP, though transparent, have very low diffraction efficiency. One solution is to shape pulses in the visible or near-infrared wavelengths and transfer the shape to a pulse of another wavelength by a nonlinear optical process. There have been some recent successes in this approach[3]. However, in all these cases the shaped pulses are the result of nonlinear optical process between two pulses with similar bandwidth, and the resolution of the final pulse shape may be limited as it is a non-trivial convolution between the two input pulses. On the other hand, an OPA process pumped by a narrower spectral bandwidth pulse can effect a high fidelity transfer of a broadband pulse shape to another pulse of a different wavelength. We demonstrate this principle by generating complex high resolution shaped pulses with considerable pulse energy at NIR by a β-barium borate (BBO) based noncollinear optical parametric amplification (NOPA)[4] of visible shaped pulses [5]. We also demonstrate, for the first time to our knowledge, that with similar principles, a potassium niobate (KNB) based NOPA can amplify NIR shaped pulses with high fidelity and thereby obtaining MIR (3−4 µm) shaped pulses.

© 2002 Optical Society of America