Csaba Tóth

A 50-EW/cm 2 Ti:sapphire laser system for studying relativistic light-matter interactions

A 10-Hz repetition rate, 60-TW peak power, Ti:sapphire laser system was developed for use in experiments where relativistic effects dominate the physics. The temporal, spectral, energy and spatial characteristics of the laser pulses were measured in single shot format. The pulse duration ranged from 22 fs to 25 fs and the pulse energy averaged 1.3 J. Atomic photoionization measurements quantified the peak intensity of the laser pulse in situ. The measurements indicated an intensity of at least 510 19 W/cm 2 was produced.

Above-threshold multiphoton photoelectric effect of a gold surface

Abstract. A discrete structure consisting of peaks separated by hv pho-ton energy was found experimentally in the photoelectron energy spec- trum, when illuminating a gold target surface by relatively long light pulses (approximately nanoseconds) and using moderate (approximately1 20 MW/cm2) intensity of Nd:glass lasers (X = 1 .06 pm). This structurecan be considered as the above-threshold photoeffect (ATP) of metalsurfaces. Its occurrence at surprisingly low laser intensities [which arefour orders of magnitude less than the typical intensity range of the anal-ogous above-threshold ionization (ATI) of atoms] was observed whenthe space charge was considerably eliminated. Subject terms: laser pulses; metal surfaces; multiphoton photoeffect of metals;highly energetic photoelectrons; above-threshold photoeffect.Optical Engineering 32(10), 2476—2480 (October 1993). Tocheck this supposition we clearly demonstrated in ourrecent 2, 1 3 that photoelectron energies above E0up to approximately 600 eV from a polycrystalline gold sur-face, where the photoelectrons are induced by Nd:glass laserpulses (8 p5, 25 GW/cm2). There, however, because of theultrashort duration and the extreme electron density, inter-electronic Coulombic forces occurred, causing space-chargeeffects, which might play an important role. The fast electronswere created mainly by the Coulombic explosion, thereforeeven if ATP peaks existed, Coulombic forces and the laserfluctuation might have hidden them, as was shown in Refs.14

Femtosecond X-Ray Diffraction

By combining traditional x-ray ntechniques for structural determination nwith the time resolution of nultrafast laser spectroscopy, researchers nare beginning to measure atomic nrearrangements directly.

Ultrafast movies of atomic motion with femtosecond laser-based x-rays

Using ultrafast x-ray diffraction from a laser-plasma x-ray source, we have observed coherent photon generation and propagation in bulk(111)-GaAs, (111)-Ge, and thin(111)-Ge- on-Si films. At higher optical pump fluences, ultrafast melting of Ge films is observed.

Pulse Characterization Techniques for sub-30 Femtosecond Terawatt Lasers

Single-shot characterization of spectral phase, pulse duration, and spectrum of femtosecond, terawatt pulses is described, using a specially designed, low-dispersion polarization-gate frequency-resolved optical gating arrangement.

Characterization of a broadband multi-keV laser plasma x-ray source for femtosecond time-resolved EXAFS

Recent advances in femtosecond laser plasma x-rays sources have resulted in several experiments to explore the dynamics of physical and chemical processes on the femtosecond time scale. We present our most recent progresses on the development of an intense broadband x-ray source in the multi-keV range, for application to time-resolved EXAFFS experiments. Experiments have been realized with two different CPA laser systems having different pulse durations and characteristics. X-ray emissions in the 5KeV range generated form solid targets with the INRS Nd:Glass laser and the UCSD Ti:Sapphire laser have been characterized through high resolution and time resolved x-ray spectroscopy. The application of this source to time resolved EXAFS measurements with a sub-picosecond time resolution will also be discussed.

Ionization of Argon n=2 (Ar+9 to Ar+16) by a “relativistic” laser field

The high field photoionization cross sections for the (n=2) shell of argon were measured with pulsed 800 nm radiation (27±5u200afs duration) at an intensity of 1.5×1019u200aW/cm2±1×1019u200aW/cm2. The pondermotive energy for an electron at these field intensities is approximately 1 MeV. The best agreement with a calculated AC tunneling model was at an intensity of 0.6×1019u200aW/cm2. The difference between experimental and calculated relative charge state yields is less than an order of magnitude for Ar+9 to Ar+14 and Ar+16.

Coster-Kronig mediated inner-shell X-ray lasers pumped by 20 fs, 100-TW-class lasers

Summary form only given. The development of keV X-ray lasers based on inner-shell atomic transitions requires extremely fast energy deposition on a target in order to effectively compete with the inherently fast (0.1-20 fs) atomic decay processes. The duration of ultrahigh peak power laser systems is now reaching this timescale. In principle, these systems can be used to produce sufficient duration and energy X-rays or electrons for pumping inner-shell transitions. In this paper X-ray laser schemes in which the Coster-Kronig Auger-process is the dominant lower level decay mechanism are described. Such systems have inherently short lower level lifetimes and under certain conditions can be inverted both with excitation by energetic electrons as well as X-rays. They are therefore relatively immune to secondary electron ionization and thus have dramatically reduced threshold conditions and simpler geometric considerations than previously proposed inner-shell laser schemes.

Coster-Kronig mediated inner-shell x-ray lasers pumped by 20-fs 100-TW-class lasers

The development of keV X-ray lasers based on inner-shell atomic transitions requires extremely fast energy deposition on a target in order to effectively compete with the inherently fast (0.1 - 20 fs) atomic decay processes. The duration of ultrahigh peak power laser systems is now reaching this timescale. In principle, these systems can be used to produce sufficient duration and energy X-rays or electrons for pumping inner-shell transitions. In this paper X-ray laser schemes are described in which the Coster-Kronig Auger-process is the dominant lower level decay mechanism. Such systems have inherently short lower level lifetimes and it is shown that under certain conditions they can be inverted with excitation by energetic electrons as well as X-rays. They are therefore relatively immune to secondary electron ionization.

Low-dispersion polarization gate frequency-resolved optical gating for measuring high-power <30-fs pulses

SHG FROG has an ambiguity in the direction of time and restrictions on the thickness of the nonlinear crystal due to phase matching for the large bandwidths needed to support such short pulses. In large amplified systems, a polarisation gate (PG) FROG would be much more desirable. The shot-to-shot stability of these systems makes single shot measurements necessary, which puts a premium on having a nonlinear medium with high optical quality.