Abstract

Interest in the uses of controlled radiation fields to alter molecular states or drive chemical reactions–originally called “laser selective chemistry,” but now commonly called “quantum molecular control”¹–has resurged in the last few years, largely because the technology for controlling optical fields has improved dramatically. Programmable pulse shaping has been demonstrated with temporal resolution of ≈30 fs and peak powers limited only by the amplifying lasers, and a tremendous range of applications can be readily envisioned. Nonetheless, pulse shaping has not become widely applied in the ultrafast optical community, for two basic reasons. Robustness is a fundamental issue–it is relatively easy to calculate waveforms which can break strong bonds or alter reaction dynamics, but in many cases, laboratory inhomogeneities or lack of knowledge of the exact Hamiltonian make practical implementation impossible. In addition, none of the demonstrated techniques for controllable fs pulse shaping is truly “easy.” Arbitrary ps pulse shape generation was first demonstrated in 1985², but each new waveform required a new fabricated amplitude mask. Our electro-optic approach³ was the first method which gave programmable pulse shapes, but in 1986 we used traveling wave EO modulators and microwave waveform generators which are past the commercial state-of-the-art even today. More recently, liquid crystal modulators (LCMs)⁴. or holographic patterns⁵ have been used to tailor the optical waveform. Tremendous improvements have been demonstrated, particularly in the LCM-based approach; however, alignment, pixel isolation and calibration, and gaps between pixels become limiting factors when the desired waveform requires substantial frequency modulation.

© 1994 Optical Society of America