Laser-Induced Above-Bandgap Transparency in GaAs

We report the observation of large ($\sim 40$) laser-induced above-bandgap transparency in GaAs at room temperature. The induced transparency is present only during the pulse width of the driving midinfrard laser pulses and its spectral shape is consistent with a laser-induced blue shift of the band edge. Our simulations based on the dynamic Franz-Keldysh effect reproduce the salient features of the experimental results, demonstrating in particular that the amount of the band edge shift is approximately given by the ponderomtive potential.Comment: 4 pages, 4 figure

On the role of coupling in mode selective excitation using ultrafast pulse shaping in stimulated Raman spectroscopy

The coherence of two, coupled two-level systems, representing vibrational modes in a semiclassical model, is calculated in weak and strong fields for various coupling schemes and for different relative phases between initial state amplitudes. A relative phase equal to $\pi$ projects the system into a dark state. The selective excitation of one of the two, two-level systems is studied as a function of coupling strength and initial phases.Comment: 7 pages, 4 figure

Beyond ATI: Strong Field Quantum Control

Above‐threshold ionization (ATI) is the ionization of atoms by more than the minimum number photons necessary to overcome the Coulomb binding energy. Although ATI is contrary to the predictions of minimum‐order perturbation theory, it is the dominant mode of ionization whenever the light field becomes comparable to the static fields in the atom. We have learned a great deal by studying ATI over the past several years. We now know that by controlling these high intensity optical fields, we can control atomic and molecular processes such as ionization and dissociation. We can even engineer wave‐functions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87417/2/416_1.pd

Quantum control

Tunable lasers, sources of intense narrow-band coherent radiation, enabled the parity violation experiments in atoms in the 1970’s. Ultrafast lasers are source of broadband coherent radiation. This paper reviews recent progress in experiments to control quantum dynamics in condensed phase and gas phase systems, using shaped ultrafast radiation. Many of the same techniques that have led to laser pulses in the 10-100 fsec range can also be applied to the control of quantum systems with similar dynamical time scales. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87489/2/176_1.pd