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Rainer Leonhardt

Publications and source records attributed to Rainer Leonhardt.

6 recordsLinked to original sources
PubMed2005

Ballistic and localized transport for the atom optics kicked rotor in the limit of a vanishing kicking period.

We present mean energy measurements for the atom optics kicked rotor as the kicking period tends to zero. A narrow resonance is observed marked by quadratic energy growth, in parallel with a complete freezing of the energy absorption away from the resonance peak. Both phenomena are explained by classical means, taking proper account of the atoms' initial momentum distribution.

Journal Article↗
PubMed2005

Deviations from early-time quasilinear behavior for the atom-optics kicked rotor near the classical limit.

We present experimental measurements of the mean energy for the atom-optics kicked rotor after just two kicks. The energy is found to deviate from the quasilinear value for small kicking periods. The observed deviation is explained by recent theoretical results which include the effect of a nonuniform initial momentum distribution, previously applied only to systems using much colder atoms than ours.

Journal Article↗
PubMed2004

Observation of robust quantum resonance peaks in an atom optics kicked rotor with amplitude noise.

The effect of pulse train noise on the quantum resonance peaks of the atom optics kicked rotor is investigated experimentally. Quantum resonance peaks in the late time mean energy of the atoms are found to be surprisingly robust against all levels of noise applied to the kicking amplitude, while even small levels of noise on the kicking period lead to their destruction. The robustness to amplitude noise of the resonance peak and of the fall-off in mean energy to either side of this peak are explained in terms of the occurrence of stable, epsilon classical dynamics [Nonlinearity 16, 1381 (2003)]] around each quantum resonance.

Journal Article↗
PubMed2004

All-optoelectronic continuous-wave terahertz systems.

We discuss the optoelectronic generation and detection of continuous-wave terahertz (THz) radiation by the mixing of visible/near-infrared laser radiation in photoconductive antennas. We review attempts to reach higher THz output-power levels by reverting from mobility-lifetime-limited photomixers to transit-time-limited p-i-n photodiodes. We then describe our implementation of a THz spectroscopy and imaging-measurement system and demonstrate its imaging performance with several examples. Possible application areas of THz imaging in the biomedical field and in surface characterization for industrial purposes are explored.

Journal Article↗
PubMed2002

All-optoelectronic continuous wave THz imaging for biomedical applications.

We present an all-optoelectronic THz imaging system for ex vivo biomedical applications based on photomixing of two continuous-wave laser beams using photoconductive antennas. The application of hyperboloidal lenses is discussed. They allow for f-numbers less than 1/2 permitting better focusing and higher spatial resolution compared to off-axis paraboloidal mirrors whose f-numbers for practical reasons must be larger than 1/2. For a specific histological sample, an analysis of image noise is discussed.

Animals↗