Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 01/05

This thesis investigates quantum transport in the energy space of two paradigm

systems of quantum chaos theory. These are highly excited hydrogen atoms

subject to a microwave field, and kicked atoms which mimic

the delta-kicked rotor model. Both of these systems show a complex

dynamical evolution arising from the interaction with an external

time-periodic driving force. In particular two quantum phenomena,

which have no counterpart on the classical level, are studied:

the suppression of classical diffusion, known as

dynamical localisation, and quantum resonances as a regime of enhanced

transport for the delta-kicked rotor.

The first part of the thesis provides new

support for the quantitative analogy between energy transport

in strongly driven highly excited atoms and particle transport

in Anderson-localised solids. A comprehensive numerical analysis of the

atomic ionisation rates shows that they obey a universal power-law

distribution, in agreement with Anderson localisation theory.

This is demonstrated for a one-dimensional model as well as

for the real three-dimensional atom. We also discuss the

implications of the universal decay-rate distributions for the

asymptotic time-decay of the survival probability of the atoms.

The second part of the thesis clarifies the effect of

decoherence, induced by spontaneous emission, on the quantum resonances

which have been observed in a recent experiment with delta-kicked atoms.

Scaling laws are derived, based on a quasi-classical approximation of the

quantum evolution. These laws describe

the shape of the resonance peaks in the mean energy of

an experimental ensemble of kicked atoms. Our analytical results

match perfectly numerical computations and explain the initially

surprising experimental observations.

Furthermore, they open the door to the study of the competing

effects of decoherence and chaos on the stability of the time evolution

of kicked atoms.

This stability may be characterised by the overlap of two identical initial

states which are subject to different time evolutions. This overlap, called

fidelity, is investigated in an experimentally accessible situation.

Der 3P0 - 1S0 Übergang (Uhrenübergang) des einfach ionisierten Indiums (lambda = 236,5 nm) gilt als einer der aussichtsreichsten Kandidaten für ein neues Frequenznormal im optischen Bereich mit einer relativen Genauigkeit von 10^-18.

Als kurzzeitstabilen Oszillator benötigt man hierfür einen Laser mit einer Linienbreite, die kleiner als die natürliche Linienbreite des Uhrenübergangs ist (0,8 Hz). Die Koinzidenz der vierfachen Frequenz des Nd:YAG Laserüberganges bei 946 nm mit dem Indiumübergang bietet die Möglichkeit einen diodengepumpten monolithischen Ringlaser aus Nd:YAG (MISER) hierfür zu verwenden, was die Möglichkeit eröffnet mit einem sehr kompakten Aufbau in neue Bereiche der Frequenzstabilität vorzudringen. Der MISER wird hierfür auf einen hochstabilen Referenzresonator mittels der Pound-Drever-Hall Stabilisierungstechnik stabilisiert. Als Resonatoren werden verschiedene Materialien (Zerodur und ULE), wie auch verschiedene geometrische Abmessungen verwendet, die jeweils in einer Vakuumkammer innerhalb einer temperaturstabilisierten Umgebung gelagert sind. Das Hauptproblem bei der Verbesserung der absoluten Frequenzstabilität des Uhrenlasers besteht darin, dass der Referenzresonator, eine sehr gute Isolierung gegenüber äußeren Einflüssen wie seismischen Vibrationen und Temperaturfluktuationen erhalten muß. Auf dem Weg zur sub-Hertz Stabilität des Lasers werden hierfür verschiedene Methoden untersucht. Für die Isolierung der seismischen Vibrationen stellt sich ein aktiv vibrationsisolierendes System (AVI) als besonders effektiv heraus, dessen Leistungsfähigkeit ausgiebig untersucht wird. Mit Hilfe einer neuen Art der zweifachen Frequenzstabilisierung eines Lasers auf einen Referenzresonator werden schließlich Rekordwerte hinsichtlich der Qualität der Anbindung des Lasers an die Referenzfrequenz eines Resonators von <10^-16 erreicht. Um die absolute Frequenzstabilität des MISERs zu überprüfen wird ein zweiter unabhängiger Referenzresonator benötigt, der auf einem zweiten unabhängigen AVI-System aufgebaut wird. Um zu zeigen, dass die Verwendung von zwei unabhängig voneinander stabilisierten Laserstrahlen des MISERs bei Schwebungssignalmessungen denselben Informationsgehalt liefern, wie zwei unabhängige Laser, werden entsprechende vergleichende Messungen durchgeführt. Durch den Aufbau der beiden Lasersysteme in zwei verschiedenen Labors des Instituts, die durch eine 100 m lange optische Faser verbunden sind, wird die größtmögliche Unabhängigkeit von einer gemeinsamen, beispielsweise seismischen Anregung gewährleistet. Der frequenzverbreiternde Einfluss der optischen Faser wird durch eine aktive Frequenzstabilisierung auf mHz-Niveau gedrückt. Weitere begrenzende Einflüsse auf die Frequenzstabilität wie Laserintensitätsschwankungen werden durch eine effektive Leistungsstabilisierung ebenfalls stark unterdrückt. Aufgrund dieser Maßnahmen werden für die Absolutfrequenzstabilität des MISERs schließlich die geforderten sub-Hertz Werte erreicht.

Insgesamt ist durch die im Rahmen dieser Arbeit erzielten Ergebnisse hinsichtlich der Frequenzstabilität des Uhrenlasers für das Indiumfrequenznormal die Grundlage für die zukünftige Realisierung der SI-Sekunde über ein einzelnes In+ Ion geschaffen worden.

Young stars close to the sun (within 100 pc) yield

an interesting sample in many respects: They are relatively bright and

because of their close distance we can resolve the surroundings of

these stars by using adaptive optics on 8 to 10 m class telescopes

(e.g. VLT or Keck). In the K-band the achievable angular resolution is

about 50 mas which corresponds to 5 AU at a star closer than

100 pc; 5 AU is about the distance between the Sun and Jupiter. This

possibility can be used to study surrounding material such as disks

made up of gas and dust as well as stellar and substellar companions.

A sample consisting of young stars in the solar vicinity and in an

evolutionary stage between the classical T Tauri phase with a disk and

the zero-age main sequence can be provided by the catalog of flare

stars and related objects compiled by Gershberg et al. (1999) because young

stars are often variable and exhibit large eruptions (flares). In a

first step we need to verify that these stars are indeed young and did

not come to lie above the main sequence in a Hertzsprung-Russell

diagram because they are old or unresolved binaries or multiples.

Therefore, we have taken spectra of 223 stars lying above the main

sequence (of the 463 stars of the sample). The distances to these

stars were measured (in most cases by Hipparcos) and they are located

at a few to 100 pc. The goal was to detect lithium absorption at

6708 A which all young stars have in common. In addition to the

detection of lithium, we want to identify other age indicators such as

filling in or emission of the Halpha -, the magnesium Ib- and the

calcium lines. The G- and K-type stars of the northern hemisphere were

also observed with high resolution, and high signal-to-noise ratio

spectroscopy to study these objects with methods of spectral synthesis

analysis to determine the surface gravity, the chemical composition,

and the temperature. The age determination of these 223 stars lead to

a value between 10 Myr and the zero-age main sequence, they are

indeed nearby and 17 stars are clearly pre-main sequence. In the

course of this work, we discovered the closest pre-main sequence star

(HIP 108405 A, 10+-10 Myrs at a distance of 16.1pc). The star is

younger than GJ 182 (27 pc, 20+-10 Myrs) which held the record up

to now. A planet with a mass of 5 MJup in orbit of a (for

this sample) typical M-star, would have an apparent magnitude in the

K-band of 14.5 to 17.5 mag at a distance of 16 pc. This would lead

to a magnitude difference DeltaK of 8 to 11 mag between the star

and the companion, which could be detected with 8 to 10 m class

telescopes at a separation of 1" or a projected separation of 16 AU.

All newly discovered young flare stars were imaged using NAOS/CONICA

to search for distant companions. Depending on the space motion of the

stars, they have to be reobserved in one or more years to distinguish

comoving companions from stagnant background stars.

In this work we have measured radial velocity variations of young

stars for the first time using the échelle spectrograph of the

Thüringer Landessternwarte. In these measurements one can see the

problems of such an investigation, such as variability caused by

activity and stellar spots. But one can also see that it is in

principle possible to detect planets around active young stars. To

verify the results and to measure longer rotation periods, we have to

observe these stars for another season.

Grundlegend für die Entwicklung molekularer Werkzeuge ist es, Kontrolle über das Verhalten einzelner Moleküle zu erlangen. Ein Beispiel dafür ist das gezieltes An- und Abkoppeln ein-zelner Moleküle an Oberflächen, das eine Basis für eine Vielzahl von Anwendungen bietet. Im Rahmen dieser Arbeit wurde unter Verwendung der AFM- Einzelmolekülkraftspektroskopie untersucht, wie und unter welchen Umständen einzelne Polyelektrolytmoleküle an funkti-onalisierte oder unfunktionalisierte Oberflächen binden und es wurden Ansätze entwickelt, wie dieses Bindungsverhalten beeinflusst werden kann:

∑ Abhängig von den experimentellen Rahmenbedingungen und der Dissoziationskonstante der untersuchten Bindungen, kann die angelegte Kraftrate einen Einfluß auf die gemessene Abrisskraft haben. Ist dies der Fall, muss eine differenzierte Analyse der gemessenen Daten erfolgen. Im Rahmen dieser Arbeit wurden neue Ansätze entwickelt, die eine effiziente und aussagekräftige Datenanalyse über das gesamte Spektrum an messbaren Wechselwirkungen ermöglichen.

∑ Aufgrund ihrer vielfältigen Anwendungsmöglichkeit ist die Polyelektrolytadsorption an feste Substrate im Blickpunkt des Interesses, sowohl im akademischen als auch im industriellen Bereich. Bei der Adsorption von Polyelektrolytmolekülen an Oberflächen sind viele verschiedene Arten von nichtkovalenten Wechselwirkungen beteiligt. Auf der Basis von kraftspektroskopischen Untersuchungen auf unterschiedlichen Substraten wurden erstmals Ansätze entwickelt, die es erlauben, verschiedenste Arten von Wechselwirkungen zu identifizieren und zu charakterisieren.

∑ Extern angelegte elektrische Felder bieten eine Möglichkeit, direkt auf einzelne geladene Moleküle Einfluss zu nehmen. Um dieses Konzept zu realisieren, wurde ein ent-sprechender Aufbau entwickelt, der eine Kombination von Elektrochemie und Kraft-spektroskopie ermöglicht. Es konnte gezeigt werden, dass die Bindungsstärke von Polyelektrolyten an leitfähige Substrate über anziehende Potenziale verstärkt und über abstoßende Potenziale erniedrigt werden kann. Beim Anschalten anziehender Potenziale konnten individuelle Polyelektrolytmoleküle auch über größere Entfernungen ein-gefangen werden. Mittels an- und abstoßender Spannungspulse konnte erstmals gezeigt werden, dass einzelne Polyelektrolytmoleküle wiederholt an- und abgekoppelt werden können.

Within the theory of ion channeling in single crystals the so-called rule of reversibility claims equal probabilities for de- and rechanneling. However, the experimental study of this work shows a strong violation of this rule. Specially developed computer simulations provide the explanation of this unexpected behavior in terms of a hysteresis of the mean ion charge state during the ion's motion along lattice directions. This sheds new light on the process of charge exchange of heavy ions in solids.

Trace gas measurements of NO, NOy, CO and O3 performed on board the DLR aircraft Falcon are used to examine the interhemispheric differences for midlatitudes during local autumn. The measurements were part of the INCA campaign (Interhemispheric differences in cirrus properties due to anthropogenic emissions). Major deployment sites were Punta Arenas, Chile (53°S) and

Prestwick, Scotland (55°N). In addition, the meridional distribution of trace gases measured during the transfer flights between Germany and Chile were analysed for latitudes between 60°N and 60°S.

Median mixing ratios of NO, NOy, CO and O3 in the upper troposphere in the investigation area near Prestwick exceed the observed concentrations in Punta Arenas by factors of 4.5, 3, 1.5 and 1.2, respectively, due to the influence of convective vertical transport of polluted boundary layer air and aircraft emissions. The INCA measurements at northern midlatitudes agree well with the

data of previous campaigns such as NOXAR and POLINAT 2.

Based on selected case studies net ozone production was calculated

from O3, NO, CO and H2O measurements. For these estimates the chemical reactions with hydrocarbons were neglected and model results were used for the ozone photolysis frequency and the OH concentrations. The results for Punta Arenas show net ozone production for the upper troposphere, but net ozone destruction

for the middle troposphere due to the very low NO levels observed there. For northern midlatitudes a significant net ozone production was calculated for the middle and upper troposphere caused by the higher concentration levels of ozone precursors in the region of the North Atlantic flight corridor.

The meridional trace gas distributions in the upper troposphere show strongly enhanced CO and NOy concentrations over tropical South America. These air masses encountered deep convection over the Amazon basin and are distributed over a large area due to an upper level anticyclonic flow over South America, which is typical for the wet season. Long-distance transport of CO emissions from

West African biomass burning sites partly contributes to the high CO concentrations over the tropics.

Comparisons of the INCA measurements for the Southern midlatitudes with the chemical transport model MOZART show that CO and NOy concentrations over Punta Arenas are overestimated by the model. Probably the assumptions for the local surface emissions and the long-distance transport of biomass burning emissions are too high. In addition the tropopause height simulated by the model is too

low. Except for the tropopause region the model simulates ozone and nitrogen oxides in good agreement with the observations. The net chemical ozone production calculated by the model agrees well with the estimates based on the measurements.

For comparison with the INCA data for the northern midlatitudes model simulations of MOZART and NILU were used. The measured CO profile over Prestwick was well represented by the regional NILU simulation. In contrast, the MOZART model sometimes showed more than twice the amount of CO observed. This can be caused by

the rough resolution of the model and the assumption of too high surface emissions in Europe. The observed trace gas distributions of NO, NOy and O3 are well reproduced by the model. For the upper troposphere the net ozone productions calculated by the models agree well with the results of this study calculated directly from the observations. Only in the middle troposphere lower net ozone production rates than simulated by the CTM were calculated from the observations due to the neglection of the hydrocarbon chemistry.

This doctoral thesis presents new approaches for the characterisation of ultrafast energy flow in complex systems, based on concepts of coherent control. By initiating a photoreaction with femtosecond pulses whose temporal phase and amplitude are shaped in such a manner that specific molecular vibrations and states are addressed, the energy flow can be steered at will. The comparison between the ensuing energy flow patterns following shaped and unshaped excitation pulses constitutes a differential measurement of the function of the controlled vibrations and states within the photoreaction.

Coherent control as a spectroscopic tool is first applied to biological systems, specifically the light harvesting complex LH2 from the photosynthetic purple bacterium Rhodopseudomonas acidophila, and the isolated carotenoid donor of the same complex. The pump-probe method using shaped excitation pulses is shown to be successful for the first time in controlling the natural function of a biological system, namely the flow of excitation energy in the complex network of states in LH2. By means of a closed-loop optimisation of parametrised excitations, a bending mode in the carotenoid donor can be identified as being responsible for steering the energy flow. This bu vibrational mode couples the carotenoid S2-S1 states; its frequency is determined to be 160±25cm-1. Furthermore the deactivation of the carotenoid S2 state in LH2 and in solution is studied with pump-probe and pump-deplete-probe spectroscopy. Here it is shown that there exists an alternative singlet state S*T (1Bu-) involved in the deactivation process, though only in LH2. Its function as a precursor of ultrafast triplet population and as a donor for photosynthetic energy transfer is characterised with a novel evolutionary target analysis of conventional pump-probe spectra.

Secondly, coherent control as a measurement technique is applied to another extremely complex system, in this case a material dominated by non-linear interactions with instantaneous dynamics: Propagation of femtosecond pulses in optical fibres that are only a few micrometers in diameter to generate a supercontinuum of optical frequencies. Here shaped pump pulses succeed in resolving for the first time the sequential steps leading to the enormous spectral broadening. Open-loop variations of precompression allows the evolution and fission of optical solitons to be followed, while closed-loop optimisations render observable the coupling of solitons with phase-matched visible frequencies.

On atoms, finally, open-loop control of interfering pathways from the ground to the excited state by application of strongly modulated spectra seeks to establish a direct link between coherent control experiments and theory. The novel phenomenon of a Fresnel zone plate in the time domain is first developed in theory and then successfully realised in experiment.

The fully automated in-situ measuring system SIOUX (StratospherIc Observation Unit for nitrogen oXides) has been developed and established under flight conditions. SIOUX is a two channel measuring device designed for the high-altitude research aircraft M55-Geophysica to record reactive nitrogen oxides in the upper troposphere and the lower stratosphere. Channel A detects nitric oxide (NO) and channel B the total reactive nitrogen (NOy), which is reduced to NO on the surface of a heated gold-converter in conjunction with carbon monoxide (CO) as reducing agent. The technique used for the measurement of NO is chemiluminescence. The detection limit of channel A is 6 pmol/mol and of channel B 10 pmol/mol for an integration time of 1 s. The main components of SIOUX are the sample inlet, the detector incorporating the reaction chambers, photomultipliers and ozone generators, the converter, a pumping system, a calibration/operation gas system and the data recording unit. Except for the sample inlet all components are housed in a pressurised aluminium container. This has a length of 1.1 m, a diameter of 0.6 m and a total mass of 250 kg; the maximum power consumption of SIOUX is 1300 W. For aeronautical compliance four test procedures were required to guarantee the flight compatibility of the mechanics and electronics of the device: shock/vibration/EMC (ElectroMagnetic Compatibility)/pressure test. In October 2001 SIOUX was implemented for the first time aboard the M55-Geophysica during a test campaign in Russia. There, the measuring system was monitored under flight conditions and its operation was established for stratospheric conditions. Mixing ratios for NO and NOy were registered up to an altitude of 20 km. In July 2002 SIOUX was used aboard the M55-Geophysica for validation the ENVISAT instrument MIPAS-E in Italy. A comparison was made for the first time between MIPAS-E measurements of nitric acid (HNO3) and SIOUX measurements of NOy-NOx (≈ HNO3 in the altitude range 17 - 20 km). A mean deviation of 20% ± 6% between the MIPAS-E and the SIOUX data was registered.