Showing papers by "Herbert Walther published in 1989"

Chaos and order of laser-cooled ions in a Paul trap.

Abstract: We present recent experimental and theoretical results on the behavior of two-, three-, and four-ion crystals close to the Mathieu instability. In particular, we show that the crystals are stable until the Mathieu instability is reached, i.e., for the parameter space investigated, there is no ``melting'' of the crystals. Laser and rf heating are studied in detail. A simple model of chaotic rf heating as well as a classification of the ion dynamics into four characteristic regimes are presented.

Preparation of a pure number state and measurement of the photon statistics in a high-Q micromaser.

Abstract: Two schemes to prepare pure number states in a high-Q micromaser with Rydberg atoms are proposed. In the first experiment the atoms are probed after the interaction with the cavity field and the number state is obtained via state reduction. In the second experiment the interaction time of ionic Rydberg atoms with the maser field can be controlled via an electric accelerating field. The velocity of the ions is adjusted in such a way that every ion emits a photon and the total number of photons is exactly known via the total number of passing ions. It is also shown how the photon statistics in the micromaser in general can be probed via the outgoing atoms.

Microwave excitation of Rydberg atoms in the presence of noise.

Abstract: We study theoretically and experimentally the effect of noise on Rydberg atoms passing through a strong coherent microwave field. We derive a master equation containing the coherent field exactly. Its solution reveals the presence of four universal dynamical regimes: (i) an initial classical regime, (ii) a subsequent coherent localized regime, (iii) a transition, induced by the noise, in which coherence and localization are destroyed, and (iv) the final regime, where equidistribution over the quasienergy states is reached.

Proposal for a Joint German-British Interferometric Gravitational Wave Detector

Abstract: For many years there has been steady progress towards the detection of gravitational radiation. It has now become clear that the next major step should be the construction of a number of long-baseline detectors around the world. An array of detectors of this type is expected to allow the observation of gravitational waves from a range of astrophysical sources, leading to improved insight in many areas including stellar collapse, binary coalescence and the expansion of the Universe. We propose that one of these detectors be built by a collaboration formed around the gravitational wave groups in Britain and Germany. In this document we present our case for this collaborative venture and outline the design philosophy of our proposed instrument - an interferometric detector with arms of length close to 3km. Two detectors of the same general type are planned for the USA (LIGO project), one is planned for Italy (Italian/French VIRGO project) and another is proposed for Australia (AIGO project). It is expected that all the long baseline detectors to be built will operate as part of a coordinated worldwide network.

The ν1 Vibration of H3+ and Autoionizing Rydberg States of H3

Abstract: The first direct spectroscopic determination of the frequency of the ν1 vibration of H3+ is reported: ω1 = (3178.29 ± 0.1) cm−1. This value was derived from the limits of Rydberg series of H3. Rydberg states of H3 were prepared by using laser excitation of a fast molecular beam and detected by means of H3+ ions formed by autoionization. Vibrational frequencies of H3 were accurately determined for the first time. Perturbations in the Rydberg series and Fano profiles were observed.

Lidar setup for daytime and nighttime probing of stratospheric ozone and measurements in polar and equatorial regions

Abstract: Measurements of atmospheric ozone at altitudes from 5 to 50 km using the lidar (DIAL) differential absorption technique are described. A XeCl excimer laser with a repetition rate of up to 50 Hz and a wavelength of 308 nm was used for the measurements. The reference line was produced by the stimulated Raman effect in a hydrogen gas cell, leading to a wavelength of 353 nm. The time-resolved measurement of the backscattered light allows one to evaluate the ozone concentration as a function of the altitude. Exceptionally good agreement between the lidar data and those measured with chemical balloonsondes was obtained. A narrow-band laser and a receiving system, including a set of three Fabry-Perot filters, also allow daytime measurements. Thus investigations in polar regions are possible even in summer periods. Measurements performed in arctic and equatorial regions with the lidar system installed on board the research vessel Polarstern are reported.

Survival, relaxation, and excitation of vibrational energy during the scattering of NO molecules from a graphite surface

Abstract: The rotational, angular, and translational scattering behavior of NO molecules prepared in a single ro‐vibrational state before their interaction with a cleaved graphite surface was determined (v=1→v=1 process). Moreover, the deactivation probability of the vibrational energy into the rotational and translational motion of the molecule could be evaluated (v=1→v=0 process). Finally, it was possible to investigate the scattering behavior of NO molecules that experienced vibrational excitation during their surface encounter (v=0→v=1 process).

Spectroscopy of triatomic hydrogen

Abstract: The visible emission spectra of H3, D2H, H2D and D3 were studied. Triatomic hydrogen molecules were produced by neutralization of fast ion beams in alkali vapors. In addition to the well-known 0-0 bands, weak vibrational bands of the electronic 3p2A″2 → 2s2A′1 transition of D3 and D2H were observed and analyzed. From the decay of the emission along the molecular beam lifetimes of excited states were obtained. For all observed states, 3p2A″2, 3s2A′1 and 3d, lifetimes strongly depend on the isotopic mixture. Many lifetimes measured were considerably shorter than ab initio predictions of the radiative lifetimes. Thus radiationless decay is important for all these excited states. Predissociation of the 3p2A″2 state increases with the rotational quantum number. Possible decay channels are discussed.

Spectroscopy of triatomic hydrogen. II: Bands near 4500 and 7100 Å

Abstract: The strongest emission band of triatomic hydrogen near 7100 A was observed after neutralization of mass-selected ion beams of H 3 + , H 2 D + , D 2 H + and D 3 + . For D 3 improved molecular constants were determined by inclusion of higher rotational lines. Lifetimes of the upper states of the 7100 A band were measured. They strongly decrease for the lighter isotopomers because of predissociation. New emission bands of D 3 observed between 4200 A and 4600 A are assigned to transitions between n=4 and n=2 states

High Rydberg states of helium hydride

Abstract: High-lying Rydberg states (11\ensuremath{\le}n\ensuremath{\le}34) of helium hydride have been observed. They were produced by laser excitation of a fast molecular beam and detected by field ionization. Ionization potentials, quantum defects, and the binding energy of ${\mathrm{HeH}}^{+}$ were determined. Pure rotational autoionization leads to break offs of the series. From missing lines it is concluded that B $^{2}\mathcal{'}$) state decays by predissociation.

Order and chaos with frozen ions

Abstract: A single ion at rest, unperturbed by its environment and forced into such a state for hours – once only a physicist's dream – has now been achieved by the combination of electromagnetic traps and laser technology. The Penning trap and the dynamical Paul trap developed in the 1930s and the late 1950s respectively, provide the experimenter with a unique tool to isolate a single ion from its surroundings. Tunable lasers can then be used to force the ion to fluoresce; simultaneously, as will be described, it is cooled to milli- or even micro-Kelvin temperatures. An ion driven into saturation by a sufficiently high laser intensity so that it spends half of the time in the excited state and half in the ground state, scatters roughly 108 photons per second. This leads to a high detection probability and at the same time to a reduction of the ion's kinetic energy via photon recoil.

Localization properties of rydberg atoms in the presence of noisy microwave fields

Abstract: We present experimental and theoretical results on highly excited Rb-Rydberg atoms passing through a wave guide. The wave guide field consists of a coherent micro wave field and a controlled component of technically generated colored noise. The presence of the noise field influences the localization properties of the Rydberg atoms and we show that the dynamics of Rydberg atoms subjected to a mixture of coherent and noisy fields can be classified into four dynamical regimes: (i) an initial classical diffusive regime, in which the initially prepared pure Rydberg state quickly broadens, (ii) a subsequent coherent localized regime, (iii) a transition, induced by the noise, in which coherence and localization are destroyed, and (iv), relaxation to equilibrium. The existence of the four dynamical regimes could be demonstrated in a clean atomic beam experiment in which excitation-, interaction- and analyzing regions are well separated from each other. The microwave interaction time is controlled by irradiating the Rydberg atoms with electronically shaped microwave pulses.