Atom driven by superstrong laser fields as a source of ultrashort-pulse XUV radiation (original) (raw)

Atoms in a superstrong laser field: towards subfemtosecond XUV sources

Laser Optics '95 and ICONO '95: Superintense Laser Fields, 1996

We present and explore an idea of creating a source of extremely short (1015 s) coherent radiation tunable in the XUV wavelength range. The underlying physical mechanism consists in nonlinear properties of rapidly ionized atoms to efficiently convert the spectra of laser radiation in the iO151O16 W/cm2 intensity range. We demonstrate that under certain conditions the nonlinear effects of high-order harmonic generation, spectrum broadening and bluesbifting can be simultaneously engaged and favorably combined. This mechanism offers an attractive possibility to enter the attosecond duration range by optimizing the process of high-order harmonic excitation at the ionizing fronts of ulirashort laser pulses.

Generalization of the Kerr effect for high intensity, ultrashort laser pulses

New Journal of Physics, 2008

We have investigated the nonlinear susceptibility of atoms induced by high intensity, ultrashort laser pulses using a numerical solution of the timedependent Schrödinger equation. We found that the instantaneous nonlinear susceptibility becomes saturated at high intensity. We also found that the saturation is closely linked to depletion of the ground state. Based on the numerical results, a simple model that generalizes the nonlinear susceptibility of atoms for high intensity, ultrashort laser pulses is proposed. We also investigated the ionization-induced dipole moment and found that the amplitude of the dipole moment induced by an ionized electron is, in general, smaller than that induced by a free-electron, and is attributable to a residual interaction between the ionized-electron and its parent ion.

Tracking propagation of ultrashort intense laser pulses in gases via probing of ionization

Physical review. E, Statistical, nonlinear, and soft matter physics, 2009

We use optical interferometry to study the propagation of femtosecond laser pulses in gases. We show the measurements of propagation in a nitrogen gas jet and we compare the results with propagation in He under the same irradiation conditions. We find that in the case of nitrogen, the detailed temporal structure of the laser pulse can be tracked and visualized by measuring the phase and the resulting electron-density map. A dramatically different behavior occurs in He gas jets, where no details of the temporal structure of the laser pulse are visible. These observations are explained in terms of the ionization dynamics of nitrogen compared to helium. These circumstances make N2 gas sensitive to variations in the electric field and, therefore, allow the laser-pulse temporal and spatial structures to be visualized in detail.

Super strong field ionization of atoms by 1019 W cm&#1092, 10 Hz laser pulses

Journal of Modern Optics, 2003

We report on the optical field ionization of rare gases (argon, krypton and xenon) by >10 19 W cm À2 laser pulses whose electric field well exceeds the Coulombic binding field in strength. Charge states as high as Ar 16 þ , Kr 19 þ , and Xe 26 þ have been observed, which correspond to He-like argon, Cl-like krypton and Ni-like xenon, respectively. The extension of the laser system to petawatt peak powers is described.

Interaction of superstrong laser fields with matter: Hypotheses, effects, and applications

Radiophysics and Quantum Electronics

A review of research results in physics of superstrong laser fields is given. It includes an analysis of the nonlinear atom response in superstrong optical fields and a discussion of the properties of a femtosecond laser-produced plasma. A description of new ezperiments on high-order harmonic generation, plasma wake field ezcitation by intense laser pulses, and ultrashort pulse self-channeling due to ionization is presented. Recent years have witnessed the formation of one of the most interesting and promising lines of research in modern physics-interactions of superstrong optical fields with matter in ultrashort time intervals. The progress in this direction is in many respects due to the creation of compact terawatt femtosecond laser complexes on the basis of new solid-state wideband active media such as Ti:Sa (sapphire with titanium ions). Such systems have considerable advantages compared, for example, with excimer-dye systems that were developed earlier for high field generation, owing to their small size, reliability, and the possibility to obtain short pulses of from 10 to 20 fsec, that is, pulses that are shorter by at least one order of magnitude than those in similar systems. It is obvious that Ti:Sa laser complexes have become an experimental basis for new trends in atomic physics, thermonuclear studies, charged particle acceleration physics, and in a variety of investigations using short-pulse sources and X-ray or ultravolet lasers. Such complexes are also a basis for extensive studies in ultrahigh time resolution spectroscopy and material science. The creation of so-called T 3 systems, or table-top terawatt laser systems, was stipulated by two important discoveries in the field of optical technologies. In 1985, the authors of [1] proposed a method of ultrashort laser pulse amplification to high energies. That method enabled one to eliminate self-focusing instability of light as the main obstacle to increasing radiated power in amplification systems. It was proposed to increase the duration of the initial femtosecond pulse from the master oscillator a few thousands of times (up to a few hundreds of picoseconds) in an optical dispersion system, amplify the resultant chirp in a wideband active medium, and then compress it to a minimum possible magnitude. At present, this method of chirp amplification is used in all terawatt laser installations. The second discovery consisted in the creation of a new class of laser crystals with an extremely wide gain line in the near IR [2]. A Ti:Sa crystal is the main representative of this class. Its active band covers a considerable part of the near IR (0.7-1.05 #m) and potentially enables one to generate laser pulses with a duration as large as 2 or 3 optical field periods. The use of a mode locking method by an induced Kerr wave and careful compensation of wave dispersion in a laser cavity have led to the creation of Ti:Sa light generators with a pulse duration of up to 10 fsec [3,4]. Such sources are considered the most promising master oscillators in chirp amplification schemes to powers of a few tens of terawatts. At present, there are about 10 terawatt femtosecond laser complexes in the world (pure Ti:Sa or with Cr:LiSAF or Nd:glass active elements in the final amplification stages), and the first multiterawatt systems

Characteristics of femtosecond laser pulses propagating in multiply ionized rare gases

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2017

A three-dimensional non-adiabatic model in combination with a rate equation model is used to characterize high-intensity (>10 16 W/cm 2) femtosecond laser pulse propagation in atomic gas medium. In these conditions the atoms in the target gas will become multiply charged ions, while the laser pulse will propagate in a medium with high electron concentration created by itself. We obtain pulse characteristics in time, frequency and space domain for two representative cases: 800 nm and 267 nm (third harmonic) multicycle pulses which are both of practical importance. We show that the spatial-temporal variation of the refractive index in the macroscopic medium is the primary reason for pulse temporal/spectral and spatial shaping during propagation.

Ultrashort Optical Pulses and Their Generation in Resonant Media (Scientific Summary)

JETP Letters, 2019

Our recent studies of methods for obtaining ultrashort light pulses and analysis of the impact of ultrashort optical pulses on classical and quantum micro-objects with the identification of the determining role of the degree of unipolarity of pulses (maximum for strictly unipolar pulses) in the efficiency of direct laser acceleration of charged particles and excitation of atoms and molecules have been reviewed. Special attention has been paid to the coherent mode locking regime in lasers, which is implemented when the laser pulse duration is less than the relaxation time of the working transition in media with resonance amplification and absorption (laser analog of the phenomenon of self-induced transparency). Experimental data on coherent mode locking in a titanium-sapphire laser with a cell with rubidium vapor at self-induced transparency in rubidium have been presented. The interaction of ultrashort pulses in resonant media has also been analyzed.

Ultrarelativistic regime in the propagation of an ultrastrong, femtosecond laser pulse in plasmas

The interaction of a multi-Petawatt, pancake-shaped laser pulse with an unmagnetized plasma is studied analytically and numerically in the regime of fully relativistic electron jitter velocities and in the context of the laser wakefield acceleration scheme. The study is applied to the specifications available at present time, or planned for the near future, of the Ti:Sa Frascati Laser for Acceleration and Multidisciplinary Experiments (FLAME) in Frascati. A set of novel nonlinear equations is derived using a three-timescale description, with an intermediate timescale associated with the nonlinear phase of the electromagnetic wave and with the spatial bending of its wave front. They describe on an equal footing both the strong and moderate laser intensity regimes, pertinent to the core and the edges of the pulse. These have fundamentally different dispersive properties since, in the core, the electrons are almost completely expelled by a very strong ponderomotive force and the electromagnetic wave packet is imbedded in a vacuum channel and has (almost) linear properties, while at the pulse edges the laser amplitude is smaller and the wave is dispersive. The new nonlinear terms in the wave equation, introduced by the nonlinear phase, describe a smooth transition to a nondispersive electromagnetic wave at very large intensities, and the simultaneous saturation of the previously known nonlocal cubic nonlinearity, without the violation of the imposed scaling laws. The temporal evolution of the laser pulse is studied by the numerical solution of the model equations in a two-dimensional geometry, with the spot diameter presently used in the selfinjection test experiment (SITE) with FLAME. The most stable initial pulse length is found to be around 1 µm, which is several times shorter than presently available. A rapid stretching of the laser pulse in the direction of propagation is observed, followed by the development of a vacuum channel and a very large electrostatic wake potential, as well as the bending of the laser wave front.

Highly non-linear ionization of atoms induced by intense high-harmonic pulses

Journal of Physics: Photonics, 2020

Intense extreme-ultraviolet (XUV) pulses enable the investigation of XUV-induced non-linear processes and are a prerequisite for the development of attosecond pump - attosecond probe experiments. While highly non-linear processes in the XUV range have been studied at free-electron lasers (FELs), high-harmonic generation (HHG) has allowed the investigation of low-order non-linear processes. Here we suggest a concept to optimize the HHG intensity, which surprisingly requires a scaling of the experimental parameters that differs substantially from optimizing the HHG pulse energy. As a result, we are able to study highly non-linear processes in the XUV range using a driving laser with a modest (≈ 10 mJ) pulse energy. We demonstrate our approach by ionizing Ar atoms up to Ar5 + , requiring the absorption of at least 10 XUV photons.