84 research outputs found
Detection of HF and VHF Fields through Floquet Sideband Gaps by `Rabi Matching' Dressed Rydberg Atoms
Radio frequencies in the HF and VHF (3 MHz to 300 MHz) bands are challenging
for Rydberg atom-based detection schemes, as resonant detection requires
exciting the atoms to extremely high energy states. We demonstrate a method for
detecting and measuring radio frequency (RF) carriers in the HF and VHF bands
via a controlled Autler-Townes line splitting. Using a resonant, high-frequency
(GHz) RF field, the absorption signal from Townes-Merrit sidebands created by a
low frequency, non-resonant RF field can be enhanced. Notably, this technique
uses a measurement of the optical frequency separation of an avoided crossing
to determine the amplitude of a non-resonant, low frequency RF field. This
technique also provides frequency-selective measurements of low frequency RF
electric fields. To show this, we demonstrate amplitude modulated signal
transduction on a low frequency VHF carrier. We further demonstrate reception
of multiple tones simultaneously, creating a Rydberg `spectrum analyzer' over
the VHF range.Comment: Data for figures can be found at:
https://datapub.nist.gov/od/id/mds2-285
Theory of dressed states in quantum optics
The dual Dyson series [M.Frasca, Phys. Rev. A {\bf 58}, 3439 (1998)], is used
to develop a general perturbative method for the study of atom-field
interaction in quantum optics. In fact, both Dyson series and its dual, through
renormalization group methods to remove secular terms from the perturbation
series, give the opportunity of a full study of the solution of the
Schr\"{o}dinger equation in different ranges of the parameters of the given
hamiltonian. In view of recent experiments with strong laser fields, this
approach seems well-suited to give a clarification and an improvement of the
applications of the dressed states as currently done through the eigenstates of
the atom-field interaction, showing that these are just the leading order of
the dual Dyson series when the Hamiltonian is expressed in the interaction
picture. In order to exploit the method at the best, a study is accomplished of
the well-known Jaynes-Cummings model in the rotating wave approximation, whose
exact solution is known, comparing the perturbative solutions obtained by the
Dyson series and its dual with the same approximations obtained by Taylor
expanding the exact solution. Finally, a full perturbative study of high-order
harmonic generation is given obtaining, through analytical expressions, a clear
account of the power spectrum using a two-level model, even if the method can
be successfully applied to a more general model that can account for ionization
too. The analysis shows that to account for the power spectrum it is needed to
go to first order in the perturbative analysis. The spectrum obtained gives a
way to measure experimentally the shift of the energy levels of the atom
interacting with the laser field by looking at the shifting of hyper-Raman
lines.Comment: Revtex, 17 page
Localization of shadow poles by complex scaling
Through numerical examples we show that the complex scaling method is suited
to explore the pole structure in multichannel scattering problems. All poles
lying on the multisheeted Riemann energy surface, including shadow poles, can
be revealed and the Riemann sheets on which they reside can be identified.Comment: 6 pages, Latex with Revtex, 3 figures (not included) available on
reques
Adiabatic Theory of Electron Detachment from Negative Ions in Two-Color Laser Field
Negative ion detachment in bichromatic laser field is considered within the
adiabatic theory. The latter represents a recent modification of the famous
Keldysh model for multiphoton ionization which makes it quantitatively
reliable. We calculate angular differential detachment rates, partial rates for
particular ATD (Above Threshold Detachment) channels and total detachment rates
for the Hydrogen ion in a bichromatic field with 1:3 frequency ratio and
various phase differences. Reliability of the present, extremely simple
approach is testified by comparison with much more elaborate earlier
calculations.Comment: 22 pages, 6 Postscript figure
Ionization Probabilities through ultra-intense Fields in the extreme Limit
We continue our investigation concerning the question of whether atomic bound
states begin to stabilize in the ultra-intense field limit. The pulses
considered are essentially arbitrary, but we distinguish between three
situations. First the total classical momentum transfer is non-vanishing,
second not both the total classical momentum transfer and the total classical
displacement are vanishing together with the requirement that the potential has
a finite number of bound states and third both the total classical momentum
transfer and the total classical displacement are vanishing. For the first two
cases we rigorously prove, that the ionization probability tends to one when
the amplitude of the pulse tends to infinity and the pulse shape remains fixed.
In the third case the limit is strictly smaller than one. This case is also
related to the high frequency limit considered by Gavrila et al.Comment: 16 pages LateX, 2 figure
Multiphoton Ionization as Time-Dependent Tunneling
A new semiclassical approach to ionization by an oscillating field is
presented. For a delta-function atom, an asymptotic analysis is performed with
respect to a quantity h, defined as the ratio of photon energy to ponderomotive
energy. This h appears formally equivalent to Planck's constant in a suitably
transformed Schroedinger equation and allows semiclassical methods to be
applicable. Systematically, a picture of tunneling wave packets in complex time
is developped, which by interference account for the typical ponderomotive
features of ionization curves. These analytical results are then compared to
numerical simulations and are shown to be in good agreement.Comment: 36 pages (also printable half size), uuencoded compressed tarred
Latex file with 9 Postscript figures included automaticall
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