Baorui Yang

Highly efficient synchronous amplification of a picosecond dye laser at a kHz repetition rate

A short pulse, high energy, high repetition rate dye amplifier with superior conversion efficiency is reported. The dye amplifier is composed of three single-pass dye cells, longitudinally pumped by a frequency doubled 1 kHz Nd: YLF regenerative amplifier. The dye amplifier yields 3.5 ps, 150 μJ pulses at 595 nm, corresponding to a 12% conversion efficiency. The ASE is 1% or less, and the transverse mode quality is near-Gaussian.

Strong-field dissociation dynamics

We examine the strong-field dissociation behavior of diatomic molecules under two distinctive physical scenarios. In the first scenario, we discuss the dissociation of the isolated hydrogen and deuterium molecular ions. The dynamics of above-threshold dissociation (ATD) are investigated over a wide range of green and infrared intensities and compared to a dressed- state model. The second situation arises when strong-field neutral dissociation is followed by ionization of the atomic fragments. The study results in a direct measure of the atomic fragments ac-Stark shift by observing the intensity-dependent shifts in the electron or nuclear fragment kinetic energy.

Intense Field Dynamics of Diatomic Molecules

Over the last decade studies examining the behavior of isolated atoms in intense radiation fields has resulted in a cumulative literature rich in new phenomena1, unresolved issues, and exciting new predictions2 for future studies. Very recently, similar investigations have begun to examine the general behavior of molecules in intense fields, especially in the studies of photodissociation dynamics. The additional challenge associated with studying molecules in strong fields result from the difficulty of sorting out the general behavior of field-induced effects from the details or specifics of the molecular structure. Previous studies on atoms3 clearly demonstrate the importance of the atomic structure in describing the “non-resonant” ionization dynamics. Consequently, it is not surprising to expect enhanced structural effects in molecules due to the many internal degrees of freedom as compared to atoms. In addition, molecular strong-field studies raise some interesting and unique questions concerning the role and interplay of ionization and dissociation. Furthermore, the time-scales associated with the molecular nuclear motion, i.e. vibrations, are comparable to the duration of current ultra-short laser pulses, thus presenting the ability to freeze-out certain degrees of freedom. The attraction for such molecular studies derives its fundamental interest from the ability to control chemical dynamics by external variation of a laser field. The traditional chemical physics approach of using the laser frequency as the only external field parameter for achieving state-selective chemistry has met with little success. However, recent efforts, such as those represented in this book, have focussed on studying all aspects of the laser field for achieving control. Although premature in realization, an understanding of the influence of intensity, coherence, and pulse duration and shaping in concert with frequency may ultimately lead to our ability or inability to control chemical dynamics.