Spatial shaping of femtosecond beam for controlling attosecond pulse (original) (raw)
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Generation of isolated attosecond pulses by spatial shaping of a femtosecond laser beam
New Journal of Physics, 2008
We present a new method for generating isolated attosecond pulses via high-order harmonic generation in gases. It relies on using collective effects to achieve transient phase-matching which provides both a high efficiency and a strong temporal confinement under specific conditions. By controlling the spatial shape of the fundamental beam and the geometry of the laser-gas interaction, this transient phase matching leads to the generation of isolated broadband attosecond pulses with long driving pulses (10-20 fs) even without controlling their carrier envelope phase. Such laser pulses are becoming available at high energy levels and our approach offers a route to increase the energy of isolated attosecond pulses by orders of magnitude as compared to existing sources.
Propagation-assisted generation of intense few-femtosecond high-harmonic pulses
Journal of Physics: Photonics, 2020
The ongoing development of intense high-harmonic generation (HHG) sources has recently enabled highly non-linear ionization of atoms by the absorption of at least 10 extreme-ultraviolet (XUV) photons within a single atom (Senfftleben et al, arXiv:1911.01375). Here we investigate how the generation of these very intense HHG pulses in our 18-m-long beamline is aided by the reshaping of the fundamental, few-cycle, near-infrared (NIR) driving laser within a 30-cm-long HHG Xe medium. Using an incident NIR intensity that is higher than what is required for phase-matched HHG, signatures of reshaping are found by measuring the NIR blueshift and the fluorescence from the HHG medium along the propagation axis. These results are well reproduced by numerical calculations that show temporal compression of the NIR pulses in the HHG medium. The simulations predict that after refocusing an XUV beam waist radius of 320 nm and a clean attosecond pulse train can be obtained in the focal plane, with an...
Coherent control of high-order harmonics generated with intense femtosecond laser pulses
The European Physical Journal D - Atomic, Molecular and Optical Physics, 2003
High-order harmonics were coherently controlled using chirped femtosecond laser pulses for the production of sharp and strong harmonics. As the laser intensity was increased above the saturation intensity for optical-field ionization, the laser chirp needed to suppress harmonic chirp in the plateau region changed from positive to negative. We showed that the modification of a laser chirp condition in a rapidly ionizing medium should be included for the proper coherent control of high-order harmonics, necessitating the integral treatment of the interaction between atoms and a driving laser pulse.
Control of high harmonic generation processes using chirped and self-guided femtosecond laser pulses
2007
High-order harmonic generation in a long gas jet is controlled in the space and time domains using chirped and self-guided femtosecond laser pulses. Since high-order harmonic generation is intrinsically connected to the ionization process of harmonic generation medium, ionization effects on high-order harmonic generation should be properly understood and taken into account. Here, we present a method to control high-order harmonic generation process by controlling the propagation mode of intense femtosecond laser pulses through the ionizing medium. Experimental results and theoretical analysis show that self-guided and chirped laser pulses can optimize high-order harmonics for achieving high brightness, low beam divergence, and narrow spectral bandwidth.
Generation of high-order spatially coherent harmonics from solid targets by femtosecond laser pulses
Physical Review A, 2000
This paper discusses the generation of high-order optical harmonics from solid targets using laser pulses of 35 and 120 femtoseconds. Harmonics up to the 35th order were observed. High conversion efficiency has been achieved, e.g., 10 Ϫ6 to the 10th harmonic. It is demonstrated that the harmonic emission is highly directional and that the harmonic efficiency decreases rapidly with increasing plasma scale length.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2006
Bright harmonic generation in a long Ne gas jet achieved using self-guided and chirped femtosecond laser pulses has been analysed. Three-dimensional modelling was performed to look into the details of laser pulse propagation, harmonic generation and attosecond pulse characteristics. The theoretical analysis and the comparison to the experimental results showed emitted harmonics form a bright attosecond pulse train with good synchronization in time. In the space domain the synchronization is especially good in the self-guided region.
Spatio-spectral structures in high-order harmonic beams generated with Terawatt 10-fs pulses
Nature communications, 2014
A large international effort is nowadays devoted to increase the energy of the extreme ultraviolet pulses by using high-peak power ultrashort fundamental pulses (Terawatt level). Using such fundamental pulses brings specific constraints that need to be addressed. Here we study high-order harmonic generation in gases with 10 fs pulses at Terawatt peak power and demonstrate that extreme ultraviolet beams can be highly structured and complex in various conditions. We use a single-shot spatially resolved spectral detection and demonstrate direct observation of the spatio-temporal coupling occurring in the generating medium. Clear and reproducible complex spatio-spectral structures are observed in the far field. Similar structures are reproduced with simulations and we show that they are intimately associated to the high nonlinearity of high-order harmonic generation. Those findings are of prime importance for the generation of high-energy attosecond pulses and reveal important issues fo...
Coherent Control of High-Order Harmonics with Chirped Femtosecond Laser Pulses
Physical Review Letters, 2001
High-order harmonics were coherently controlled using chirped femtosecond laser pulses for the production of sharp and strong harmonics. As the laser intensity was increased above the saturation intensity for optical-field ionization, the laser chirp needed to suppress harmonic chirp in the plateau region changed from positive to negative. We showed that the modification of a laser chirp condition in a rapidly ionizing medium should be included for the proper coherent control of high-order harmonics, necessitating the integral treatment of the interaction between atoms and a driving laser pulse.