239 research outputs found
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 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
Laser-Induced Above-Bandgap Transparency in GaAs
We report the observation of large () 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
Coherence measurements on Rydberg wave packets kicked by a half-cycle pulse
A kick from a unipolar half-cycle pulse (HCP) can redistribute population and
shift the relative phase between states in a radial Rydberg wave packet. We
have measured the quantum coherence properties following the kick, and show
that selected coherences can be destroyed by applying an HCP at specific times.
Quantum mechanical simulations show that this is due to redistribution of the
angular momentum in the presence of noise. These results have implications for
the storage and retrieval of quantum information in the wave packet.Comment: 4 pages, 4 figures (5 figure files
Probing the evolution of Stark wave packets by a weak half cycle pulse
We probe the dynamic evolution of a Stark wave packet in cesium using weak
half-cycle pulses (HCP's). The state-selective field ionization(SSFI) spectra
taken as a function of HCP delay reveal wave packet dynamics such as Kepler
beats, Stark revivals and fractional revivals. A quantum-mechanical simulation
explains the results as multi-mode interference induced by the HCP.Comment: 4 pages, incl. 3 figures, submitted to PR
Attosecond Control of Ionization Dynamics
Attosecond pulses can be used to initiate and control electron dynamics on a
sub-femtosecond time scale. The first step in this process occurs when an atom
absorbs an ultraviolet photon leading to the formation of an attosecond
electron wave packet (EWP). Until now, attosecond pulses have been used to
create free EWPs in the continuum, where they quickly disperse. In this paper
we use a train of attosecond pulses, synchronized to an infrared (IR) laser
field, to create a series of EWPs that are below the ionization threshold in
helium. We show that the ionization probability then becomes a function of the
delay between the IR and attosecond fields. Calculations that reproduce the
experimental results demonstrate that this ionization control results from
interference between transiently bound EWPs created by different pulses in the
train. In this way, we are able to observe, for the first time, wave packet
interference in a strongly driven atomic system.Comment: 8 pages, 4 figure
Information hiding and retrieval in Rydberg wave packets using half-cycle pulses
We demonstrate an information hiding and retrieval scheme with the relative
phases between states in a Rydberg wave packet acting as the bits of a data
register. We use a terahertz half-cycle pulse (HCP) to transfer phase-encoded
information from an optically accessible angular momentum manifold to another
manifold which is not directly accessed by our laser pulses, effectively hiding
the information from our optical interferometric measurement techniques. A
subsequent HCP acting on these wave packets reintroduces the information back
into the optically accessible data register manifold which can then be `read'
out.Comment: 4 pages, 4 figure
Optimal molecular alignment and orientation through rotational ladder climbing
We study the control by electromagnetic fields of molecular alignment and
orientation, in a linear, rigid rotor model. With the help of a monotonically
convergent algorithm, we find that the optimal field is in the microwave part
of the spectrum and acts by resonantly exciting the rotation of the molecule
progressively from the ground state, i.e., by rotational ladder climbing. This
mechanism is present not only when maximizing orientation or alignment, but
also when using prescribed target states that simultaneously optimize the
efficiency of orientation/alignment and its duration. The extension of the
optimization method to consider a finite rotational temperature is also
presented.Comment: 14 pages, 12 figure
- …