Podcasts about attosecond

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Listen to Future Now Wireless   It’s not often that a level-headed engineer would take on conspiracy theory ideas like Maui’s fires were due to directed energy weapons from orbit.  And hey, we are lucky to have an investigation of this concept, and I think you will find his conclusions to be satisfying.  Also of interest in the energy department are the advancements happening in the world of wireless energy. Not simply in terms of charging your car, but also providing Gigawatts of power from space!  And we take a closer look at the wireless emergency alert system, with an experiment we did with iPhones and Androids.  Also this week, the Nobel prize for physics went to scientists who are slicing time into attoseconds, a billionth of a billionth of a second, so that we may have clearer views of what is happening on the molecular and atomic realms of universe.  And we look at the new evidence suggesting widespread creation of fairy circles on the planet.  Bobby shares more info on his infra-red healing experiments and we explore the finding of fresh carbon molecules on the surface of Europa. What could this mean?  Enjoy! The Las Vegas Sphere illuminated at night      

We also chat about that embarrassing leak of the chemistry winners in this podcast

We do a Nobel Prize recap as we look at this year's winners and the research that got them there. Plus BlackBerry announced on Wednesday it would separate its Internet of Things and cybersecurity business units. And we analyze recent comments by X CEO Linda Yaccarino about brands returning to the platform. Starring Sarah Lane, Robb Dunewood, Roger Chang, Joe. To read the show notes in a separate page click here! Support the show on Patreon by becoming a supporter!

We do a Nobel Prize recap as we look at this year's winners and the research that got them there. Plus BlackBerry announced on Wednesday it would separate its Internet of Things and cybersecurity business units. And we analyze recent comments by X CEO Linda Yaccarino about brands returning to the platform.Starring Sarah Lane, Robb Dunewood, Dr. Niki Ackermans, Roger Chang, Joe.Link to the Show Notes. Become a member at https://plus.acast.com/s/dtns. Hosted on Acast. See acast.com/privacy for more information.

In dieser Folge dreht sich alles um den Tunneleffekt. Was ist das überhaupt? Wie funktioniert er und wie ist der aktuelle Stand der Forschung? Welche interessanten Durchbrüche wurden in den letzten zwei Jahrzehnten erzielt? Das und ob eigentlich auch Menschen Dinge durchtunneln könnten, erfährst Du in Folge 13 von "Darf's ein bisschen Chemie sein?". Möchtest Du mehr über Quantenobjekte erfahren, die sich gegenseitig mit einer Räuberleiter helfen, Barrieren zu durchtunneln? Dann schau doch mal bei Patreon vorbei und höre in die neue Bonusfolge zum Podcast rein. Den Zusatzbeitrag zur Folge findest du wie immer bei Instagram, eine Möglichkeit zur Unterstützung und weiteres, exklusives Material bei Patreon."Darf's ein bisschen Chemie sein?" ist eine Produktion von Zimt & Pfeffer Studio.Recherche und Skript: Anne MayerTon und Schnitt: Fabian Schneider Instagram @darfs_ein_bisschen_chemie_seinFacebook @darfseinbisschenchemiesein Für weitere Zusatzmaterialen, Bonus-Folgen und die Unterstützung meiner Arbeit, kannst Du auch gerne mal bei meinem Patreon-Account vorbeischauen. Impressum und Anmerkungen unter www.greenmaya.de - Mails an green_maya@web.de  Quellenangaben: Links, letzter Aufruf (22.06.2023) https://www.studysmarter.de/schule/physik/quantenmechanik/tunneleffekt/ https://de.wikipedia.org/wiki/Quant https://www.ds.mpg.de/203044/07 https://de.wikipedia.org/wiki/Radioaktivit%C3%A4t https://www.weltderphysik.de/gebiet/teilchen/quanteneffekte/tunnelblick/#:~:text=Ohne%20Tunneleffekt%20g%C3%A4be%20es%20keine,dessen%20Zeitverlauf%20in%20Echtzeit%20beobachten https://www.mpq.mpg.de/4857719/10_05_17#:~:text=In%202001%2C%20Ferenc%20Krausz%20and,the%20emission%20of%20an%20electron https://www.mpg.de/11414673/quantenmechanisch-tunneleffekt-zeit https://www.weltderphysik.de/gebiet/teilchen/nachrichten/2014/quantengrinsekatze/quantenteilchen-tunneln-mehrfach/ https://de.wikipedia.org/wiki/Potentielle_Energie Paper: Uiberacker, Matthias, et al. "Attosecond real-time observation of electron tunnelling in atoms." Nature 446.7136 (2007): 627-632. Camus, Nicolas, et al. "Experimental evidence for quantum tunneling time." Physical review letters 119.2 (2017): 023201.

The work presented in this thesis was aimed at developing a high-repetition rate source of coherent radiation in the extreme ultra-violet (XUV) spectral region, envisaging applications in attosecond physics or precision metrology in the XUV. Due to the lack of laser oscillators operating in the XUV, the method of choice was the frequency upconversion of a near-infrared laser via the nonlinear process of high-order harmonic generation. Obtaining sufficient XUV photon flux per pulse at repetition rates of several tens of MHz, despite the inherently low conversion efficiency, requires a powerful driving source. To date, passive enhancement of ultrashort pulses in an external resonator has been the most successful strategy in meeting this demand. In this thesis four main achievements towards extending this technique and understanding its limitations are presented. A first experiment was dedicated to obtaining shorter intracavity pulses without compromising the high average power available from Yb-based laser technology. To this end, we spectrally broadened and temporally compressed the pulses prior to the enhancement in a broadband resonator. Aside from being a prerequisite for time-domain applications, shorter intracavity pulses led to improved conditions for the harmonic generation process. Furthermore, we addressed the task of extracting the intracavity generated XUV light. We established two methods for geometrical XUV output coupling, one employing the fundamental mode of the cavity, and the other a tailored transverse mode, which offers additional degrees of freedom to shape the harmonic emission. Both techniques are particularly suited for the intracavity generation of attosecond pulses, because they afford an unparalleled flexibility for the resonator design, and exhibit a broadband output coupling efficiency approaching unity for short-wavelength radiation. This enabled a significant improvement of the crucial parameters, photon flux and photon energy. In a combined experimental and theoretical study, we investigated the ionization-related intensity limitations observed in state-of-the-art enhancement cavities. The quantitative modeling of the nonlinear interaction allows for an estimation of the achievable intracavity parameters and for a global optimization of the XUV photon flux. Based on this model, we proposed a strategy to mitigate this limitation by using the nonlinearity in combination with customized cavity optics for a further spectral broadening and temporal compression of the pulse in the resonator. More importantly, this work establishes enhancement cavities as a tool to investigate nonlinear light-matter interactions with the increased sensitivity provided by the resonator. The last study was dedicated to the technological challenge of building a resonator in which the electric field of the circulating pulse is reproduced at each round-trip. This is an essential prerequisite to generate identical XUV emission with each driving pulse. By tailoring the spectral phase of the cavity mirrors we succeeded in enhancing pulses of less than 30 fs (less than nine cycles of the driving field) to a few kilowatts of average power with zero pulse-to-pulse carrier-to-envelope phase slip. At similar pulse durations, the generation of isolated attosecond pulses has already been demonstrated in single-pass geometries. In conclusion, the results presented in this thesis are milestones on the way to a powerful, compact and coherent source of ultrashort XUV radiation. The unique property of the source, that is, its high repetition rate lays the foundation for advancing attosecond physics and precision spectroscopy in the XUV region

Thu, 3 Dec 2015 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/19001/ https://edoc.ub.uni-muenchen.de/19001/1/Guggenmos_Alexander.pdf Guggenmos, Alexander ddc:530, ddc:500, Fakultät für Ph

Attosecond pulses are ultrashort radiation bursts produced via high harmonic generation (HHG) during a highly nonlinear excitation process driven by a near infrared (NIR) laser pulse. Attosecond pulses can be used to probe the electron dynamics in ultrafast processes via the attosecond streaking technique, with a resolution on the attosecond time scale. In this thesis it is shown that both the generation of attosecond (AS) pulses and the probing of ultrafast processes by means of AS pulses, can be extended to cases in which the respective driving and streaking fields are produced by surface plasmons excited on nanostructures at NIR wavelengths. Surface plasmons are optical modes generated by collective oscillations of the surface electrons in resonance with an external source. In the first part of this thesis, the idea of high harmonic generation (HHG) in the enhanced field of a surface plasmon is analyzed in detail by means of numerical simulations. A NIR pulse is coupled into a surface plasmon propagating in a hollow core tapered waveguide filled with noble gas. The plasmon field intensity increases for decreasing waveguide radius, such that at the apex the field enhancement is sufficient for producing high harmonic radiation. It is shown that with this setup it is possible to generate isolated AS pulses with outstanding spatial and temporal structure, but with an intensity of orders of magnitude smaller than in standard gas harmonic arrangements. In the second part, an experimental technique for the imaging of surface plasmonic excitations on nanostructured surfaces is proposed, where AS pulses are used to probe the surface field by means of photoionization. The concept constitutes an extension of the attosecond streak camera to ``Attosecond Photoscopy'', which allows space- and time-resolved imaging of the plasmon dynamics during the excitation process. It is numerically demonstrated that the relevant parameters of the plasmonic resonance buildup phase can be determined with subfemtosecond precision. Finally, the method used for the numerical solution of the Maxwell's equations is discussed, with particular attention to the problem of absorbing boundary conditions. New insights into the mathematical formulation of the absorbing boundary conditions for Maxwell's equations are provided.

The continuous development and improvement of laser sources has steadily increased the number of applications and pushed the limit of high precision measurements in various fields. The goal of the work presented in this thesis is to improve the spectrally broadened Ti:sapphire laser system used for isolated extreme ultraviolet (XUV) pulse generation, which has, in the last decade, allowed the study of electron dynamics on a sub-femtosecond (1 fs = 10^-15 s) level and delivered new insights into ultrafast dynamics of electrons in atoms, molecules and solids. By adding a second stage amplifier to the commonly used one-stage chirped pulse amplification laser system the compressed output power of a sub-5 fs laser system has been tripled to 1.5 mJ. A crucial part for achieving this result is the comparison of two different efficient compressor setups in order to optimize the compression. With these higher pulse energies, it is possible to increase the generated photon ux in an isolated attosecond (10^-18 s) pulse and to push the XUV photon energy higher. Run at 4 kHz repetition rate, integrative measurements with sub-2 cycle laser pulses can be conducted much faster than with most laser sources in this energy range. The resulting pulses are used for high-harmonic generation (HHG) and characterized via attosecond streaking, demonstrating excellent stability and quality of the whole laser system. First experiments with these pulses were conducted by probing the temporal behavior of the photo-emission of the giant resonance of 4d electrons in xenon with broadband XUV-pulses at 100 eV and inducing and measuring the nonlinear propagation in fused silica at high intensities via its effect on the waveform of the ultra-short visible-near-infrared pulse measured by means of attosecond streaking. The higher pulse energy of the driving laser field will also prove to be very useful as soon as nonlinear effects besides HHG contribute to the pump and probe setup e.g. an ultrashort UV-pulse is used to pump electron dynamics which are subsequently probed with high temporal resolution by the XUV-pulse.

When the optical pulses emitted by a laser become so short in time that they encompass only a few cycles of the carrier wave, the phase between carrier and envelope becomes a crucial parameter. The ability to control this carrier-envelope phase (CEP) is elemental to experiments probing the fastest processes in the microcosm, occurring on the time-scale of attoseconds. More than a decade into the attosecond era, the limitations of the established CEP stabilisation technique have begun to curtail experimental progress. First, increasingly complex experiments require many hours of uninterrupted operation at the same waveform. Second, the pulses used in experiments are approaching the single-cycle boundary, calling for ever-decreasing CEP noise. With the conventional stabilisation technique, already these two requirements cannot be fulfilled simultaneously. Ultimately, the low efficiency of the underlying nonlinear processes can only be compensated by driver lasers at a higher repetition rate than available at present. In order to advance attosecond pulse generation, novel approaches to CEP control thus face a threefold challenge that outlines this thesis: To simultaneously provide low CEP noise and long-term operation to present-day few-cycle lasers and amplifiers, and to investigate CEP control capability in high average power sources that are currently under development. This thesis describes the adaptation of cavity-external CEP stabilisation for use with few-cycle pulses. The intrinsic limitations of the conventional feed-back technique are lifted. A laser oscillator is demonstrated to maintain record-low CEP noise for tens of hours of operation free from phase discontinuities. In addition, a modification of the technique is presented that further enhances the applicability to amplified systems. Two routes are investigated to achieve CEP control in system architectures that represent potential megahertz repetition rate driver sources. In combination with temporal pulse compression, a thin-disk laser is shown to yield few-cycle pulses. Experiments are presented that provide the groundwork towards the first CEP-stabilised thin-disk oscillator. The second approach targets the seed oscillator of a fibre chirped-pulse amplifier. The CEP noise properties of different amplification regimes are examined. Intensity enhancement of the output pulses in a passive resonator is shown to benefit greatly even from a coarse lock of the CEP slip rate. For few-cycle pulse energy to reach the millijoule level and above, amplification and temporal compression will remain indispensable in the foreseeable future. Maintaining CEP stability across such stages is crucial, irrespective of the technology employed. Cavity-external CEP control is demonstrated to enable more than 24 hours of constant-CEP operation in chirped-pulse amplifiers. Furthermore, a novel actuator is introduced that, in conjunction with a fast means of measuring the CEP, is able to provide phase correction of the amplified waveform up to several kilohertz bandwidth. The result is a train of millijoule-level pulses with residual CEP noise comparable to that of state-of-the-art nanojoule oscillators. Eventually, an experiment is presented to examine the influence of different types of hollow-core fibre-based temporal compression on the CEP. The findings shed new light on the origin of adverse effects introduced by this technique, and point out ways towards effective compensation.

Many physical and chemical processes which define our daily life take place on atomic scales in space and time. Time-resolved electron diffraction is an excellent tool for investigation of atomic-scale structural dynamics (4D imaging) due to the short de Broglie wavelength of fast electrons. This requires electron pulses with durations on the order of femtoseconds or below. Challenges arise from Coulomb repulsion and dispersion of non-relativistic electron wave packets in vacuum, which currently limits the temporal resolution of diffraction experiments to some hundreds of femtoseconds. In order to eventually advance the temporal resolution of electron diffraction into the few-femtosecond range or below, four new concepts are investigated and combined in this work: First, Coulomb repulsion is avoided by using only a single electron per pulse, which does not repel itself but interferes with itself when being diffracted from atoms. Secondly, dispersion control for electron pulses is implemented with time-dependent electric fields at microwave frequencies, compressing the duration of single-electron pulses at the expense of simultaneous energy broadening. Thirdly, a microwave signal used for electron pulse compression is derived from an ultrashort laser pulse train. Optical enhancement allows a temporal synchronization between the microwave field and the laser pulses with a precision below one femtosecond. Fourthly, a cross-correlation between laser and electron pulses is measured in this work with the purpose of determining the possible temporal resolution of diffraction experiments employing compressed single-electron pulses. This novel characterization method uses the principles of a streak camera with optical fields and potentially offers attosecond temporal resolution. These four concepts show a clear path towards improving the temporal resolution of electron diffraction into the few-femtosecond domain or below, which opens the possibility of observing electron densities in motion. In this work, a compressed electron pulse's duration of 28±5 fs full width at half maximum (12±2 fs standard deviation) at a de Broglie wavelength of 0.08 Å is achieved. Currently, this constitutes the shortest electron pulses suitable for diffraction, about sixfold shorter than in previous work. Ultrafast electron diffraction now meets the requirements for investigating the fastest primary processes in molecules and solids with atomic resolution in space and time.

Fri, 4 Oct 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16245/ https://edoc.ub.uni-muenchen.de/16245/1/Krueger_Michael.pdf Krüger, Michael ddc:530, ddc:500, Fakultät für Physik

This work focuses on the interaction of few-cycle laser pulses with nanosystems. Special emphasis is placed on the spatio-temporal evolution of the induced near-fields. Measurements on carrier-envelope-phase (CEP) controlled photoemission from isolated SiO2 nanospheres are taken by single-shot velocity map imaging (VMI) combined with CEP tagging. The obtained photoelectron spectra show a pronounced dependence on the CEP and extend to unexpectedly high energies. Comparison with numerical simulations identify the additional Coulomb forces of the liberated electron cloud as an effective additional acceleration mechanism for distinct trajectories. For larger spheres, an asymmetry in the field distribution is classically predicted. This asymmetry is also observed in the photoelectron momentum distributions. The mapping between position and momentum space in the VMI approach are investigated by analyzing the correlation of the photoelectron's birth and detection position. In a second set of experiments, photoemission at intensities exceeding 10^14 W/cm^2 from isolated nanospheres of different composition (SiO2, ZrO2, TiO2, Si, Au) is examined by stereo time-of-flight spectroscopy. It is found that the measured cutoff energies scale non-linearly with laser intensity depending on the material properties of the nanosystem. A trend towards a unified behavior for high intensities is observed indicating a drastic change in optical properties within the duration of the few-cycle laser pulse. The charge carrier generation mechanisms that could lead to such a transient effect are discussed. For a better understanding of the interaction of few-cycle fields with nanosystems, a direct access to the temporal evolution of (plasmonic) near-fields is highly desirable. The efforts on the realization of nanoplasmonic attosecond streaking spectroscopy are presented. Numerical simulations are used to identify the influence of the inhomogeneous near-field distributions on the streaking process. First experimental results obtained from Au nanotips show clear streaking features of sub-micron localized near-fields. The near-field oscillations are found to be phase offset as compared to reference measurements. The exact origin of the streaking features of the Au tip and possible improvements of the experimental approach are discussed.

Thu, 14 Mar 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16123/ https://edoc.ub.uni-muenchen.de/16123/1/Hassan_Mohammed.pdf Hassan, Mohammed ddc:530, ddc:500, Fakultät für Physik

Attosecond (as) physics has become a wide spreaded and still growing research field over the last decades. It allows for probing and controlling core- and outer shell electron dynamics with never before achieved temporal precision. High harmonic generation in gases in combination with advanced extreme ultraviolet (XUV ) optical components enable the generation of isolated attosecond pulses as required for absolute time measurements. But until recently, single attosecond pulse generation has been restricted to the energy range below 100 eV due to the availability of sources and attosecond optics. Multilayer mirrors are the up to date widest tunable optical components in the XUV and key components in attosecond physics from the outset. In this thesis, the design, fabrication and measurement of periodic and aperiodic XUV multilayer mirrors and their application in the generation and shaping of isolated attosecond pulses is presented. Two- and three material coatings based on a combination of molybdenum, silicon, boron carbide, lanthanum and scandium covering the complete spectral range between 30 and 200 eV are developed and characterized. Excellent agreement between reflectivity simulations and experiments is based on the highly stable ion beam sputter deposition technique. It allows for atomically smooth deposition and the realization of aperiodic multilayer structures with high precision and reproducibility. XUV reflectivity simulation of lanthanum containing multilayer coatings are based on an improved measured set of optical constants, introduced in this thesis. This work enabled the generation of the shortest ever measured isolated light pulses so far, the creation of the first isolated attosecond pulses above 100 eV , the first demonstration of absolute control of the “attochirp” by means of multilayer mirrors and the formation of spectrally cleaned attosecond pulses, in a spectral region which lacks appropriate filter materials, for a never before achieved combination of spectral and temporal resolution at 125 eV . Here presented concepts are in principle not restricted to specific energies or experimental set-ups and may be extended in the near future to enter completely new regimes of ultrashort physics.

Wed, 20 Jul 2011 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/14012/ https://edoc.ub.uni-muenchen.de/14012/1/Wirth_Adrian.pdf Wirth, Adrian ddc:530, ddc:500, Fakultät für Physik

Thu, 31 Mar 2011 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/13057/ https://edoc.ub.uni-muenchen.de/13057/1/Magerl_Elisabeth.pdf Magerl, Elisabeth ddc:530, ddc:500, Fakultät für Physik

Since the original prediction and demonstration of attosecond pulses, attosecond physics has entrenched itself in the ultrafast sciences, and promises to advance a wide range of scientific disciplines. It has the potential to provide key developments and insights in several research areas, such as atomic physics, quantum chemistry, biology and medicine. At present, engaging in this novel field of research is rather prohibitive, due to the high costs of cutting-edge technology and a steep learning curve. After all, playing with attosecond pulses is tantamount to playing with the shortest events ever made by man! Nonetheless, these are just typical growing pains of a new and exciting research area, and will eventually subside to make attosecond science accessible to a broad research community. In the meanwhile, as this promising field is taking its baby steps, it is the responsibility of those working at the cutting edge to propose novel experiments, and develop the tools and models that will be used in the future, as the field matures. Attosecond science comprises two frontiers: (i) the generation and characterization of increasingly intense, energetic, short and isolated attosecond pulses; and (ii) the design of experiments to probe physical systems on the attosecond time scale, the holy grail being the attosecond pump-attosecond probe time-resolved spectroscopic measurement. The second frontier offers a deeper understanding of the temporal behavior of the microcosm, but relies on advancements made in the first one. At present, both of these frontiers heavily rely on the attosecond streaking technique, which consists in energy-resolving photoelectrons ejected by an attosecond extreme ultraviolet pulse, in the presence of a phase-stabilized and temporally synchronized near-infrared field. Although it was originally devised as a means to characterize attosecond pulses, this measurement technique has even produced new discoveries in atomic and solid-state physics, due to pioneering experiments by M. Drescher, A. Cavalieri, G. Sansone, M. Schultze, and others, and has inspired novel theories of laser-dressed photoionization by V. S. Yakovlev, A. Scrinzi, O. Smirnova, M. Y. Ivanov and others. In the first part of this thesis, I focus on new methods I developed for the analysis of attosecond streaking measurements. One of these methods, based on a formalism I devised based on electron trajectories in a laser field, can directly recover the chirp of an attosecond pulse from a set of streaked photoelectron spectra. Next, I describe a robust optimization algorithm, based on a formalism due to M. Kitzler et al., that can completely recover the temporal profile of an attosecond pulse with an arbitrary shape. This optimization algorithm was used to characterize the field of 80 as pulses, the shortest on record, and to uncover a delay of 20 as between the photoemissions from the 2s and 2p sub-shells of neon; both experiments were performed here at the Max Planck Institut fuer Quantenoptik in 2008 and 2010, respectively. Moreover, during the course of this work, it was established by V. S. Yakovlev et al. that the attosecond streaking technique generally measures a quantity that is related to the photoelectron wave packet, not the attosecond light pulse. Only when the energy-resolved dipole response, given by the bound-free transition matrix elements, is nearly constant can we take the electron wave packet as a replica of the attosecond pulse. In light of this finding, I show that the attosecond streaking technique provides a means to measure and even time-resolve the energy-dependent phase of transition dipole matrix elements. Finally, I consider the laser-dressed scattering of an attosecond photoelectron wave packet. I show that the scattering of a photoelectron, emitted by an attosecond pulse from a localized state in a spatially extended system, can be influenced by a near-infrared laser field. Measuring the photoelectron spectrum reveals an interference pattern which is affected by the intensity of the near-infrared field. To describe these effects, I introduce a model based on classical trajectories that quantitatively predicts laser-dressed photoelectron spectra for such a spatially-extended system.

Thu, 29 Jul 2010 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/11913/ https://edoc.ub.uni-muenchen.de/11913/1/Fiess_Markus.pdf Fieß, Markus ddc:530, ddc:500, Fakultät für Physik

Our desire to observe electron dynamics in atoms and molecules on their natural timescale with the tools of attosecond physics demands ever shorter laser pulse durations. The reliance of this young eld on laser pulses is understandable: both the generation and the characterization of attosecond pulses, as well as time-resolved measurements directly use the electrical field that lasts only for a few oscillations of the wave. This also means that exerting control over the evolution of the waveform on a sub-cycle scale can modify the characteristics of attosecond pulses and possibly in a favorable way. In this thesis we introduce a laser system that provides near single-cycle laser pulses and generate through their interaction with gases coherent XUV radiation. Our measurements indicate that the thus produced XUV spectrum supports the potential compressibility to an isolated attosecond pulse of a sub-100 as duration. Considering our already broadband fundamental laser spectrum, we demonstrate moreover a technique to further enhance our spectral intensity in the blue. By frequency-doubling a part of the original spectrum, and controlling the time-delay between the two harmonic laser pulses we show that we can induce a change in the waveform on an attosecond time-scale, suppress or increase some half-cycles or change the effective wavelength of the laser light. Our method's influence on the generation of XUV light is tested via spectral characterization, and we found that broad tunability of the central XUV-energy is possible by a change of the time-delay between the fundamental and the second-harmonic laser pulses. Our results furthermore give strong evidence that waveform-dependent interference of two quantum-paths was observed, which effect comes from two electron-trajectories that are inside one half-cycle of the laser field. It is also of utmost importance to know the level of control over the waveform. To characterize the waveform, we demonstrate here the first single-shot measurement of the carrier-envelope phase (CEP) of a lightpulse. We measured with no phase-ambiguity the CEP of high repetition-rate (3 kHz) non-phase-stabilized and phase-stabilized laser pulses consecutively with an unprecedented measurement precision. Our method uniquely requires no prior phase-stabilization. It opens the door to CEP-tagging with non-phase-stabilized pulses using emerging few-cycle laser systems with relativistic peak intensities.

For Munich physicist Ferenc Krausz, one second lasts half an eternity. For him, the measure of all things is the attosecond; a number with 17 zeros after the decimal point. Professor Krausz is the founder of attosecond physics, which explores the world of electrons. He is professor at the LMU Department of Physics and director of the Max Planck Institute for Quantum Optics.

Dr. Schafer is a theoretical AMO physicist who specializes in strong field physics. The name "strong field physics'' refers to the interaction of intense, ultrafast laser pulses with atomic and molecular systems. Strong field physics takes place in the interesting regime where the electron-ion and electron-laser interactions are of competing strengths. This gives rise to a host of time-dependent and highly non- linear phenomenon such as above threshold ionization, high harmonic generation, sequential and non-sequential multiple ionization of atoms and molecules, and x-ray production from clusters, which are characterized both by rapid ionization and the coherent interaction of the ionizing electron with the parent atomic or molecular ion. His current research centers on the theory of intense laser-matter interactions with an emphasis on the generation and application of attosecond pulses. An attosecond is 1/1000 of a femtosecond, and attosecond sources are the shortest light pulses ever made. Since attosecond pulses were first measured in 2001, the growth of "attoscience" has been exponential, spurred by the potential these pulses have for imaging and controlling electron motion. Our research group, consisting of myself and Mette Gaarde, has the unique capability to investigate all phases of the attosecond pulse generation process, from the microscopic single atom interaction to the macroscopic propagation and phase matching of the emitted radiation. The research is interdisciplinary, combining atomic and optical physics, and centered around high performance computing for non-perturbative solutions of both the time- dependent Schroedinger equation and the Maxwell wave equation. The research is highly relevant to experiment and we have active collaborations with several of the leading experimental groups pursuing attosecond science. We are involved in all phases of the experimental work, both as interpreters of results and as partners in designing new experiments. Lecture presented Dec. 15, 2008.

Mon, 30 Jun 2008 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/9509/ https://edoc.ub.uni-muenchen.de/9509/1/Schultze_Martin.pdf Schultze, Martin ddc:530, ddc:500, Fakultät f

Attosecond physics has become one of the most thriving field of science over the last decade. Although high-order harmonic generation from gaseous media is widely used as the source of attosecond pulses, a demand for more intense coherent extreme ultraviolet (XUV) and soft x-ray (SXR) radiation sources is growing. The process of high-order harmonic generation from plasma surfaces has attracted a strong interest as a promising candidate to meet this demand. Despite many theoretical predictions of the possibilities to generate intense attosecond pulses, experimental verifications are yet to come. The main theme of this thesis is to characterize the temporal structure of the harmonics generated from plasma surfaces. To achieve this goal, several preparatory experiments are made first. The contrast of the laser pulse is one of the most critical parameters for the harmonic generation process and its improvement is demonstrated by using a plasma mirror. The properties of the generated harmonics are studied thoroughly to find the optimal condition for temporal characterization. These experiments provide the groundwork for the autocorrelation measurements of the pulse train. To characterize the temporal structure of the generated harmonics, the technique of the volume autocorrelation using two-photon ionization of helium is applied. The measured autocorrelation traces reveal attosecond structures within the XUV radiation generated from the plasma surfaces for the first time. The observation of attosecond structures prove the potential of this harmonic generation process as a source of attosecond pulses. The process holds a promise to generate attosecond pulses with unprecedented intensities, which will open up a new regime of attosecond physics.

The most direct way to probe the strength of an electric field, is to measure the force that exerts to a charged particle. For a time varying field, charge placement within an interval substantially shorter than the characteristic period of variation of the field is essential for sampling its temporal evolution. Employing such a scheme to track the field variation of light waves that changes its direction 1015 times per second, charge release shall be confined within a fraction of a femtosecond. In this thesis, the complete characterization of a light pulse is demonstrated experimentally for the first time by probing its field variation using a 250 attosecond electron burst. Such an ultrafast charge probe, can be generated by the impulsive ionization of atoms, using an XUV attosecond pulse precisely synchronized with the light waveform to be characterized. The technique allows access to the instantaneous value of the electric field of IR, visible, or UV light and thereby opens the door for the synthesis of controlled, extremely broadband and arbitrarily shaped light waveforms. The above experiments, are presented along with critical pertinent developments on the generation of few-cycle phase-controlled light waveforms and their subsequent exploitation, for the generation of isolated XUV attosecond pulses. Precisely characterized and controlled light fields and XUV attosecond pulses employed in combination, hold the promise for probe and control of elementary processes evolving on an attosecond time scale.