Podcasts about xuv

Bienvenue au Palmarès musical! Laura Schembri reçoit Sarah Vanderzon, une autrice-compositrice-interprète dont l'univers mélange folk et country. Écoutez l'émission pour entendre en primeur une performance live de sa chanson Cowboy's A Coward.  Liste de chansons jouées: Photoromance - Béli - XUV  Y sont ou - Larynx - Ma troisième émergence  Evangeline - Sarah Vanderzon - Single  I don't know myself at all - Sarah Vanderzon - Single  Passion Poire - Passion Poire - La Pression des poires 

Deux jours avant la sortie de son album XUV, BéLi vient rendre visite à Estelle pour parler de coquerelles, de douter souvent et de tremper ses chips dans le ketchup. Son lancement d'album aura lieu le 15 novembre au Café Cléopâtre dams le cadre du festival Coup de coeur francophone. Liste des chansons diffusées: BéLi - Totally Psych ft. Rose Yink - XUVWe Hate You Please Die - Adrenaline - Chamber SongsCoeur à l'index - Tomber de haut - Adieu minette

Removal of Hot Saturns in Mass-Radius Plane by Runaway Mass Loss by Daniel P. Thorngren et al. on Wednesday 23 November The hot Saturn population exhibits a boundary in mass-radius space, such that no planets are observed at a density less than $sim$0.1 g cm$^{-3}$. Yet, planet interior structure models can readily construct such objects as the natural result of radius inflation. Here, we investigate the role XUV-driven mass-loss plays in sculpting the density boundary by constructing interior structure models that include radius inflation, photoevaporative mass loss and a simple prescription of Roche lobe overflow. We demonstrate that planets puffier than $sim$0.1 g cm$^{-3}$ experience a runaway mass loss caused by adiabatic radius expansion as the gas layer is stripped away, providing a good explanation of the observed edge in mass-radius space. The process is also visible in the radius-period and mass-period spaces, though smaller, high-bulk-metallicity planets can still survive at short periods, preserving a partial record of the population distribution at formation. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.11770v1

Removal of Hot Saturns in Mass-Radius Plane by Runaway Mass Loss by Daniel P. Thorngren et al. on Wednesday 23 November The hot Saturn population exhibits a boundary in mass-radius space, such that no planets are observed at a density less than $sim$0.1 g cm$^{-3}$. Yet, planet interior structure models can readily construct such objects as the natural result of radius inflation. Here, we investigate the role XUV-driven mass-loss plays in sculpting the density boundary by constructing interior structure models that include radius inflation, photoevaporative mass loss and a simple prescription of Roche lobe overflow. We demonstrate that planets puffier than $sim$0.1 g cm$^{-3}$ experience a runaway mass loss caused by adiabatic radius expansion as the gas layer is stripped away, providing a good explanation of the observed edge in mass-radius space. The process is also visible in the radius-period and mass-period spaces, though smaller, high-bulk-metallicity planets can still survive at short periods, preserving a partial record of the population distribution at formation. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.11770v1

Removal of Hot Saturns in Mass-Radius Plane by Runaway Mass Loss by Daniel P. Thorngren et al. on Tuesday 22 November The hot Saturn population exhibits a boundary in mass-radius space, such that no planets are observed at a density less than $sim$0.1 g cm$^{-3}$. Yet, planet interior structure models can readily construct such objects as the natural result of radius inflation. Here, we investigate the role XUV-driven mass-loss plays in sculpting the density boundary by constructing interior structure models that include radius inflation, photoevaporative mass loss and a simple prescription of Roche lobe overflow. We demonstrate that planets puffier than $sim$0.1 g cm$^{-3}$ experience a runaway mass loss caused by adiabatic radius expansion as the gas layer is stripped away, providing a good explanation of the observed edge in mass-radius space. The process is also visible in the radius-period and mass-period spaces, though smaller, high-bulk-metallicity planets can still survive at short periods, preserving a partial record of the population distribution at formation. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.11770v1

Removal of Hot Saturns in Mass-Radius Plane by Runaway Mass Loss by Daniel P. Thorngren et al. on Tuesday 22 November The hot Saturn population exhibits a boundary in mass-radius space, such that no planets are observed at a density less than $sim$0.1 g cm$^{-3}$. Yet, planet interior structure models can readily construct such objects as the natural result of radius inflation. Here, we investigate the role XUV-driven mass-loss plays in sculpting the density boundary by constructing interior structure models that include radius inflation, photoevaporative mass loss and a simple prescription of Roche lobe overflow. We demonstrate that planets puffier than $sim$0.1 g cm$^{-3}$ experience a runaway mass loss caused by adiabatic radius expansion as the gas layer is stripped away, providing a good explanation of the observed edge in mass-radius space. The process is also visible in the radius-period and mass-period spaces, though smaller, high-bulk-metallicity planets can still survive at short periods, preserving a partial record of the population distribution at formation. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.11770v1

First Detection of the Molecular Cloud Population in the Extended Ultraviolet XUV Disk of M83 by Jin Koda et al. on Monday 26 September We report a CO(3-2) detection of 23 molecular clouds in the extended ultraviolet (XUV) disk of the spiral galaxy M83 with ALMA. The observed 1kpc^2 region is at about 1.24 times the optical radius (R25) of the disk, where CO(2-1) was previously not detected. The detection and non-detection, as well as the level of star formation (SF) activity in the region, can be explained consistently if the clouds have the mass distribution common among Galactic clouds, such as Orion A -- with star-forming dense clumps embedded in thick layers of bulk molecular gas, but in a low-metallicity regime where their outer layers are CO-deficient and CO-dark. The cloud and clump masses, estimated from CO(3-2), range from 8.2x10^2 to 2.3x10^4 Msun and from 2.7x10^2 to 7.5x10^3 Msun, respectively. The most massive clouds appear similar to Orion A in star formation activity as well as in mass, as expected if the cloud mass structure is universal. The overall low SF activity in the XUV disk could be due to the relative shortage of gas in the molecular phase. The clouds are distributed like chains up to 600 pc (or longer) in length, suggesting that the trigger of cloud formation is on large scales. The universal cloud mass structure also justifies the use of high-J CO transitions to trace the total gas mass of clouds, or galaxies, even in the high-z universe. This study is the first demonstration that CO(3-2) is an efficient tracer of molecular clouds even in low-metallicity environments. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2208.11738v2

Is the automotive industry product-driven? Or do brands have a part to play? Why are specific models more successful than most others? Discover answers to all these questions in the ninth episode of Speakeasy..In this episode, our CEO & CSO Leo Burnett, South Asia - Dheeraj Sinha, delves deep with Rajesh Jejuriker, Executive Director, Mahindra & Mahindra Ltd. to discuss the thinking behind the newly launched Mahindra SUVs, what the future holds for Mahindra in the automotive space, what makes for success in this space today and much more. Tune in now!Find Rajesh on the Internet:LinkedIn | Twitter Find Dheeraj Sinha on Social Media:Facebook | Twitter | Instagram | LinkedIn Check out our website: (https://speakeasywithdheerajsinha.in/) Follow Speakeasy on Social Media:Facebook | Twitter | Instagram | LinkedIn Find Leo Burnett on Social Media:Facebook | Twitter | Instagram | LinkedIn

In this episode we are going to learn about, driver awareness system. which will be seen in XUV 700 laughing this week.This system will help reduce accident that is happening on road due to lack of awareness of driver. Any question/query feel free to contact at :-ojhashubham11@gmail.com --- Send in a voice message: https://anchor.fm/shubham-ojha/message

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

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.

High harmonic generation on solid and gaseous targets has been proven to be a powerful platform for the generation of attosecond pulses. Here we demonstrate a novel technique for the XUV generation on a smooth liquid surface target in vacuum, which circumvents the problem of low repetition rate and limited shot numbers associated with solid targets, while it maintains some of its merits. We employed atomically smooth, continuous liquid jets of water, aqueous salt solutions and ethanol that allow uninterrupted high harmonic generation due to the coherent wake emission mechanism for over 8 h. It has been found that the mechanism of plasma generation is very similar to that for smooth solid target surfaces. The vapor pressure around the liquid target in our setup has been found to be very low such that the presence of the gas phase around the liquid jet could be neglected.

Abstract: Attosecond XUV spectroscopy is a powerful new technique for real-time probing of electronic processes in atoms, molecules and materials. Sandhu began by outlining the basic concepts of attosecond science along with some background information on its development and progress. Physicists have applied attosecond pulse trains to problem the electronic states of atoms subjected to strong laser fields. Sandhu described the measurements which reveal quantum interferences in photoionization pathways, and have implications for the attosecond control of light-matter interaction. Next, he discussed ultrafast dynamics in molecules, which are more complex due to the coupling between electronic and nuclear degrees of freedom. He described how physicists utilized attosecond XUV pulses to measure the predisssociation and auto ionization rates in super excited molecules. Measurements addressed two long-standing questions on the relaxation dynamics of super excited oxygen, which could not be resolved in conventional synchrotron studies. In the last part of the talk, he introduced the latest efforts on the use of ultrafast techniques to understand the electron and phono dynamics in carbon nano materials and their molecular fragments. Presented August 31, 2012.

The goal of this thesis is to develop a compact high-power solid-state oscillator capable of superseding existing ultrafast technology based on low-power Ti:sapphire oscillators. Different applications such as extra- or intra-cavity XUV generation, seeding of high-energy low-repetition-rate amplifier systems and femtosecond enhancement cavities can be dramatically influenced by the availability of such a reliable, compact femtosecond source. We applied, for the first time, Kerr-lens mode-locking to a thin-disk Yb:YAG oscillator, resulting in an unprecedented combination of an average power 45 W and pulse duration of 250 fs directly available from the oscillator with repetition rate of 40 MHz and a footprint of only 1*0.4 m^2. Even shorter emission-bandwidth-limited 200-fs pulses have been generated with the reduced output coupler transmission of 5.5% at an average power of 17 W. Moreover, the oscillator was operating not only in the negative dispersion regime common to solid-state oscillators but also in the positive dispersion regime, resulting in a spectrum spanning a range of 20 nm, which is the broadest hitherto reported for Yb:YAG material in high-power operation. First attempts towards CE phase-stabilized high-power pulses from such an oscillator are also described. State-of-the-art XUV generation driven by high-power NIR femtosecond systems requires methods of separating generated XUV from NIR radiation. Such a method has been proposed and realized. It constitutes a glass substrate having a low-loss anti-reflection coating for NIR wavelengths at grazing incidence of >70° and serving simultaneously as a high reflector for radiation in the range of 1-100 nm with reflectivity >60%. The device can be used for both extra- and intra-cavity XUV generation.

In the work for this thesis, a split-mirror-setup was designed and build, which was used to split the XUV laser-pulse of FELs (Free Electron Laser) into two identical pulses from which one can be delayed. With this setup the laser pulses of FLASH, Hamburg and SCSS, Harima(Japan) where characterized temporally, to determine the temporal pulse-structure for subsequent experiments. The intermolecular dynamics of the homonuclear diatomic molecules nitrogen and oxygen were examined and the experimental results were reproduced by classical simulations. In the measurement with oxygen for an energy band of the coincident singly charged ions, an ionization probability was found that depends on the delay between the two XUV-pulses. This can most probably be explained by the autoionization of an excited singly charged molecular state. Subsequently the investigation of the two photon double ionization (TPDI) of deuterium is presented. In the single pulse experiments simulations within the Born-Oppenheimer approximation made it possible to distinguish between the direct and sequential TPDI. In the pump-probe experiments light was shed onto the dynamics of the TPDI. In addition, experiments with strong few-cycle near-infrared (NIR) pulses are presented that examined the carrier envelope phase (CEP) dependence of the non-sequential double ionization of argon. Implementing single-shot CEP-tagging in conjunction with coincidence spectroscopy allowed to achieve unprecedented accuracy in measuring correlated electron dynamics.

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.

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.

The generation of coherent high-order harmonics from the interaction of ultra-intense femtosecond laser pulses with solid density plasmas holds the promise for table-top sources of intense extreme ultraviolet (XUV) and soft x-ray (SXR) radiation. Furthermore, they give rise to the prospect of combining the attosecond pulse duration of conventional gas-harmonic sources with the photon flux currently only available from large-scale free-electron laser or synchrotron facilities. In this thesis a series of experiments studying various aspects of harmonic generation from such a plasma source are presented and the emitted XUV-radiation is characterized spectrally, spatially and temporally. The measurements probe the dynamics of the plasma surface on a sub-laser-cycle time scale and help to increase our understanding of the harmonic generation process. It is shown that, at moderate intensities and laser contrast, the emitted harmonics are indeed phase-locked but chirped and emitted as a train of XUV-bursts of attosecond duration. Measurements with very high contrast relativistically intense driving pulses reveal the generation of harmonics up to the relativistic cutoff in a diffraction-limited beam with constant divergence observed for all wavelength. This implies that the harmonics are generated on a curved surface and travel through a focus after the target possibly opening a route towards extreme intensities in the process. In addition it is found that a target roughness on the scale of the wavelength of the highest generated harmonic does not adversely affect the harmonic beam quality implying that the generation of diffraction-limited keV-harmonic beams should be possible. In a third set of experiments the first demonstration of harmonic generation from solid targets using an 8 fs driving laser opens a route towards the generation of ultra-intense single-as pulses and gives conclusive evidence for the unequal spacing of the harmonic emission. Based on these results the development of ultra-intense sources of single as-pulses from the interaction of intense laser pulses with solid surfaces could advance at a fast pace making XUV-pump XUV-probe type investigations of nonlinear processes with attosecond time resolution feasible in the near future.

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 investigation of laser-matter interactions calls for ever shorter pulses as new effects can thus be explored. With laser pulses consisting of only a few cycles of the electric field, the phase of these electric field oscillations becomes important for many applications. In this thesis ultrafast laser sources are presented that provide few-cycle laser pulses with controlled evolution of the electric field waveform. Firstly, a technique for phasestabilizing ultra-broadband oscillators is discussed. With a simple setup it improves the reproducibility of the phase by an order of magnitude compared to previously existing methods. In a further step, such a phase-stabilized oscillator was integrated into a chirped-pulse amplifier. The preservation of phase-stability during amplification is ensured by secondary phase detection. The phase-stabilized intense laser pulses from this system were employed in a series of experiments that studied strong-field phenomena in a time-resolved manner. For instance, the laser-induced tunneling of electrons from atoms was studied on a sub-femtosecond timescale. Additional evidence for the reproducibility of the electric field waveform of the laser pulses is presented here: individual signatures of the electric field half-cycles were found in photoelectron spectra from above-threshold ionization. Frequency conversion of intense laser pulses by high-order harmonic generation is a common way of producing coherent light in the extreme ultraviolet (XUV) spectral region. Many attempts have been made to increase the low efficiency of this nonlinear process, e.g. by quasi phase-matching. Here, high-harmonic generation from solid surfaces under grazing incidence instead from a gas target is studied as higher efficiencies are expected in this configuration. Another approach to increasing the efficiency of high-harmonic generation is the placing of the gas target in an enhancement resonator. Additionally, the production of XUV photons happens at the full repetition rate of the seeding laser, i.e. in the region of several tens to hundreds of megahertz. This high repetition rate enables the use of the XUV light for high-precision optical frequency metrology with the frequency comb technique. With such an arrangement, harmonics up to 15th order were produced. A build-up cavity that stacks femtosecond laser pulses in a coherent manner to produce intra-cavity pulse energies of more than ten microjoules at a repetition rate of ten megahertz is presented here. With this high average power measuring hitherto uninvestigated optical transition frequencies in the XUV, such as the 1S-2S transition in singly charged helium ions may become a reality.

In the course of this work, a system was designed and developed to nonlinearily convert a femtosecond frequency comb laser into the extreme ultraviolet (XUV) spectral range (120-30 nm). The optical frequency comb, for which the nobel prize 2005 was awarded to John Hall and Theodor W. Hänsch, has become an indispensable tool for high precision spectroscopy. With the aid of a mode locked femtosecond laser it is possible to directly and phase coherently link the radio frequency domain and the frequency range of visible light. Today's most accurate time standard, the cesium atomic clock operates in the former and therefore it became possible for the first time to compare arbitrary optical frequencies with our primary time standard and measure them with 15 digits of accuracy. Among other things, this method allowed one of the most accurate test of quantum electrodynamics (QED) today in the course of the determination of the 1S-2S transition frequency of atomic hydrogen that is carried out in one of our labs. But also experiments in the field of ultrafast physics rely on the frequency comb technique to generate precisely controlled optical waveforms. An especially intriguing possibility is to exploit the unique combination of high peak power in the megawatt range and the high spectral quality (on the order of 10^14) of single comb modes of a femtosecond frequency comb. To this end, in the method presented in this thesis, the femtosecond pulse train is coupled to an optical resonator of high finesse. With this trick, the field strength inside the resonator exceeds the driving lasers field by almost an order of magnitude. Enough to efficiently drive a nonlinear process of high order inside a medium of xenon atoms. As a result harmonics of the driving frequency comb up to 15nth order are generated. The obtained field contains photons with energies exceeding 20~eV, a spectral region which is not or only hard to access by conventional continuous laser source. Therefore the presented XUV frequency comb source brings direct frequency measurements at such high photon energies into the realm of possibility for the first time. In particular, an improved version of the demonstrated source will be used to take the next step in an experiment with a long tradition in our group, the 1S-2S spectroscopy of atomic hydrogen. The generated frequency comb in the vicinity of 60~nm wave length will be used to probe the 1S-2S transition in singly charged helium, a hydrogen like system with larger nuclear charge. From such a measurement it can be expected that, compared to hydrogen, relativistic corrections from the QED theory become more important as the system has higher energies in general. For this reason this could lead to a test of QED with increased sensitivity. Other applications of such a compact and relatively simple coherent source of XUV radiation could be high resolution spectroscopy, XUV holography, but could also lie in the research area of ultrafast 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.