20,423 research outputs found
Separation of Target Structure and Medium Propagation Effects in High-Harmonic Generation
We calculate high-harmonic generation (HHG) by intense infrared lasers in
atoms and molecules with the inclusion of macroscopic propagation of the
harmonics in the gas medium. We show that the observed experimental spectra can
be accurately reproduced theoretically despite that HHG spectra are sensitive
to the experimental conditions. We further demonstrate that the simulated (or
experimental) HHG spectra can be factored out as a product of a \macroscopic
wave packet" and the photo-recombination transition dipole moment where the
former depends on the laser properties and the experimental conditions, while
the latter is the property of the target only. The factorization makes it
possible to extract target structure from experimental HHG spectra, and for
ultrafast dynamic imaging of transient molecules
Attochirp-free High-order Harmonic Generation
A method is proposed for arbitrarily engineering the high-order harmonic
generation phase achieved by shaping a laser pulse and employing xuv light or x
rays for ionization. This renders the production of bandwidth-limited
attosecond pulses possible while avoiding the use of filters for chirp
compensation. By adding the first 8 Fourier components to a sinusoidal field of
W/cm, the bandwidth-limited emission of 8 as is shown to be
possible from a Li gas. The scheme is extendable to the zs-scale
Attosecond pulse shaping using partial phase matching
Peer ReviewedPostprint (published version
High-order harmonic generation driven by chirped laser pulses induced by linear and non linear phenomena
We present a theoretical study of high-order harmonic generation (HHG) driven
by ultrashort optical pulses with different kind of chirps. The goal of the
present work is perform a detailed study to clarify the relevant parameters in
the chirped pulses to achieve a noticeable cut-off extensions in HHG. These
chirped pulses are generated using both linear and nonlinear dispersive
media.The description of the origin of the physical mechanisms responsible of
this extension is, however, not usually reported with enough detail in the
literature. The study of the behaviour of the harmonic cut-off with these kind
of pulses is carried out in the classical context, by the integration of the
Newton-Lorentz equation complemented with the quantum approach, based on the
integration of the time dependent Schr\"odinger equation in full dimensions
(TDSE-3D), we are able to understand the underlying physics.Comment: 13 pages, 8 figure
Continuous spectra in high-harmonic generation driven by multicycle laser pulses
We present observations of the emission of XUV continua in the 20-37 eV
region by high harmonic generation (HHG) with - pulses
focused onto a Kr gas jet. The underlying mechanism relies on coherent control
of the relative delays and phases between individually generated attosecond
pulse, achievable by adjusting the chirp of the driving pulses and the
interaction geometry. Under adequate negative chirp and phase matching
conditions, the resulting interpulse interference yields a continuum XUV
spectrum, which is due to both microscopic and macroscopic (propagation)
contributions. This technique opens the route for modifying the phase of
individual attosecond pulses and for the coherent synthesis of XUV continua
from multicycle driving laser pulses without the need of an isolated attosecond
burst.Comment: 14 pages, 5 figures. Submitted to Physical Review
Chemical applications of escience to interfacial spectroscopy
This report is a summary of works carried out by the author between October 2003 and September 2004, in the first year of his PhD studie
Self-heterodyned detection of dressed state coherences in helium by noncollinear extreme ultraviolet wave mixing with attosecond pulses
Noncollinear wave-mixing spectroscopies with attosecond extreme ultraviolet (XUV) pulses provide unprecedented insight into electronic dynamics. In infrared and visible regimes, heterodyne detection techniques utilize a reference field to amplify wave-mixing signals while simultaneously allowing for phase-sensitive measurements. Here, we implement a self-heterodyned detection scheme in noncollinear wave-mixing measurements with a short attosecond XUV pulse train and two few-cycle near infrared (NIR) pulses. The initial spatiotemporally overlapped XUV and NIR pulses generate a coherence of both odd (1snp) and even (1sns and 1snd) parity states within gaseous helium. A variably delayed noncollinear NIR pulse generates angularly-dependent four-wave mixing signals that report on the evolution of this coherence. The diffuse angular structure of the XUV harmonics underlying these emission signals is used as a reference field for heterodyne detection, leading to cycle oscillations in the transient wave-mixing spectra. With this detection scheme, wave-mixing signals emitting from at least eight distinct light-induced, or dressed, states can be observed, in contrast to only one light induced state identified in a similar homodyne wave-mixing measurement. In conjunction with the self-heterodyned detection scheme, the noncollinear geometry permits the conclusive identification and angular separation of distinct wave-mixing pathways, reducing the complexity of transient spectra. These results demonstrate that the application of heterodyne detection schemes can provide signal amplification and phase-sensitivity, while maintaining the versatility and selectivity of noncollinear attosecond XUV wave-mixing spectroscopies. These techniques will be important tools in the study of ultrafast dynamics within complex chemical systems in the XUV regime
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