13 research outputs found
Generation of high-order harmonics with tunable photon energy and spectral width using double pulses
This work theoretically investigates high-order harmonic generation in rare
gas atoms driven by two temporally delayed ultrashort laser pulses. Apart from
their temporal delay, the two pulses are identical. Using a single-atom model
of the laser-matter interaction it is shown that the photon energy of the
generated harmonics is controllable within the range of one eV -- a bandwidth
comparable to the photon energy of the fundamental field -- by varying the time
delay between the generating laser pulses. It is also demonstrated that
high-order harmonics generated by double pulses have advantageous
characteristics, which mimick certain properties of an extreme ultraviolet
(XUV) monochromator. With the proposed method, a simpler setup at a much lower
cost and comparatively higher spectral yield can be implemented in contrast to
other approaches.Comment: 7 pages, 6 figures, after peer-review, corrected typo in author lis
Generation of high-order harmonics with tunable photon energy and spectral width using double pulses
This work theoretically investigates high-order harmonic generation in rare-gas atoms driven by two temporally delayed ultrashort laser pulses. Apart from their temporal delay, the two pulses are identical. Using a single-atom model of the laser-matter interaction it is shown that the photon energy of the generated harmonics is controllable within the range of one eV-a bandwidth comparable to the photon energy of the fundamental field-by varying the time delay between the generating laser pulses. It is also demonstrated that high-order harmonics generated by double pulses have advantageous characteristics, which mimick certain properties of an extreme ultraviolet monochromator. With the proposed method, a simpler setup at a much lower cost and comparatively higher spectral yield can be implemented in contrast to other approaches
All-Optical Experimental Control of High-Harmonic Photon Energy
We generate high-order harmonics in gaseous medium with tunable photon energy
using time domain interferometry of double pulses in a non-collinear generation
geometry. The method is based on the fact that the generated harmonics inherit
certain spectral properties of the driving laser. The two temporally delayed
ultrashort laser pulses, identical in all parameters, are produced by a
custom-made split-and-delay unit utilizing wave front splitting without a
significant energy loss. The arrangement is easy to implement in any attosecond
pulse generation beamline, and is suitable for the production of an extreme
ultraviolet source with simply and quickly variable central photon energy,
useful for a broad range of applications.Comment: 6 pages, 5 figures, after peer-revie
Spectrally tunable ultrashort monochromatized extreme ultraviolet pulses at 100 kHz
We present the experimental realization of spectrally tunable, ultrashort,
quasimonochromatic extreme ultraviolet (XUV) pulses generated at 100 kHz
repetition rate in a user-oriented gas high harmonic generation (GHHG) beamline
of the Extreme Light Infrastructure - Attosecond Light Pulse Source (ELI ALPS)
facility. Versatile spectral and temporal shaping of the XUV pulses are
accomplished with a double-grating, time-delay compensated monochromator
accommodating the two composing stages in a novel, asymmetrical geometry. This
configuration supports the achievement of high monochromatic XUV flux
(2.8e10+/-0.9e10 photons/s) combined with ultrashort pulse duration (4.0+/-0.2
fs using 12.1+/-0.6 fs driving pulses) and small spot size (sub-100 um).
Focusability, spectral bandwidth, and overall photon flux of the produced
radiation were investigated covering a wide range of instrumental
configurations. Moreover, complete temporal (intensity and phase)
characterization of the few-femtosecond monochromatic XUV pulses - a goal that
is difficult to achieve by conventional reconstruction techniques - has been
realized using ptychographic algorithm on experimentally recorded XUV-IR
pump-probe traces. The presented results contribute to in-situ, time-resolved
experiments accessing direct information on the electronic structure dynamics
of novel target materials.Comment: 20 pages, 8 figure
A detailed investigation of single-photon laser enabled Auger decay in neon
Single-photon laser enabled Auger decay (spLEAD) is an electronic de-excitation process which was recently predicted and observed in Ne. We have investigated it using bichromatic phase-locked free electron laser radiation and extensive angle-resolved photoelectron measurements, supported by a detailed theoretical model. We first used separately the fundamental wavelength resonant with the Ne+ 2s?2p transition, 46.17 nm, and its second harmonic, 23.08 nm, then their phase-locked bichromatic combination. In the latter case the phase difference between the two wavelengths was scanned, and interference effects were observed, confirming that the spLEAD process was occurring. The detailed theoretical model we developed qualitatively predicts all observations: branching ratios between the final Auger states, their amplitudes of oscillation as a function of phase, the phase lag between the oscillations of different final states, and partial cancellation of the oscillations under certain conditions
Characterization of ultrashort double pulses and their application in attosecond physics
Temporal double pulses, produced in femtosecond laser laboratories, sometimes positively, sometimes negatively affect the outcome of an experiment. In my research I have improved an already existing femtosecond laser pulse characterization technique, called SRSI to be able to reconstruct femtosecond double-pulse structures. In addition, I have investigated the impact of the double pulses on the spectral characteristics of high-order harmonics, generated in gaseous material, by changing the delay between the constituting pulses of the double-pulse structure
Double-pulse characterization by self-referenced spectral interferometry
The reconstruction of ultrashort optical pulses with a complex intensity substructure is demonstrated using the Self-Referenced Spectral Interferometry (SRSI) pulse characterization technique with a modified phase retrieval algorithm. A correction spectral phase term is extracted by the manipulation of the temporal interferogram, allowing the treatment of scenarios with complicated pulse shapes, where the original algorithm fails. The improved SRSI algorithm is verified through the application on two temporally well-separated pulses having the same polarization direction and spectral shape, generated by duplicating 37 fs-long amplified pulses of a Ti:Sa based laser system. The spectral phase of highly chirped double pulses with equal or different amplitude ratios is numerically retrieved. The collinear and achromatic experimental arrangement results in a compact and easy-to-align system. Published under license by AIP Publishing
Detailed study of quantum path interferences in high harmonic generation driven by chirped laser pulses
We investigate the electron quantum path interference (QPI) effects during high harmonic generation in atomic gas medium driven by ultrashort chirped laser pulses. To achieve that, we identify and vary the different experimentally relevant control parameters of such a driving laser pulse influencing the high harmonic spectra. Specifically, the impact of the pulse duration (from the few-cycle to the multi-cycle domain), peak intensity and instantaneous frequency is studied in a self-consistent manner. Simulations involving macroscopic propagation effects are also considered. The study aims to reveal the microscopic background behind a variety of interference patterns capturing important information both about the fundamental laser field and the generation process itself. The results provide guidance towards experiments with chirp control as a tool to unravel, explain and utilize the rich and complex interplay between QPIs including the tuning of the periodicity of the intensity dependent oscillation of the harmonic signal, and the curvature of spectrally resolved Maker fringes