I. B. Földes

Absolute measurement of velocity distribution of neutrals in sodium laser blow-off beam

Abstract Absolute density measurements of Na blow-off atomic beam were carried out with time of flight laser induced fluorescence. The preferentially used 1 μm Na layer was in situ evaporated on a glass plate. The velocity distribution of the blow-off neutrals was investigated as a function of the Nd laser fluence. The measurements showed that the blow-off beam contains two atomic packets with different propagation velocities in the laser range of 10–20 J/cm 2 and one atomic packet elsewhere. The faster packet has a maximum total number of atoms at 3 J/cm 2 and its velocity can be well fitted with a power function of the irradiance with v ∼ I 0.29 .

High-intensity narrow light pulse produced by self-focusing in laser spark

The shape of the laser light pulse transmitted through the spark produced in air by the same light pulse is investigated. A single‐mode and single‐frequency ruby laser is used. A narrow spike, overriding the amplitude of the original light pulse, is observed in the transmitted light. The spike is explained as the result of self‐focusing taking place in the plasma. The amplitude and the time of the appearance of the spike, i.e., of the self‐focused pulse, is investigated independently of the different experimental parameters. The light scattered by the spark is also observed; furthermore, clear experimental evidence of the self‐focusing taking place during the cascade ionization process is presented.

Investigation of laser blow-off atomic beams by electron impact excitation

Electron impact excitation in the edge region of the MT‐1 tokamak was used to measure the velocity distribution of a sodium laser blow‐off beam in a single shot. The different dependencies of the propagation velocity of the blow‐off neutral beam on the laser fluence at different sodium layer thicknesses reveal different regimes of the blow‐off process. In the case of thick targets laser ablation is the main accelerating mechanism giving a v∼I1/3 dependence. Thin targets, however, burn through during the laser pulse, and simple thermal heating process results in v∼I1/2 in good agreement with the experiments.

Self-focusing of laser beam crossing a laser plasma

Abstract A crossed beam experiment was performed to clarify the mechanism of self-focusing in a laser produced spark. The plasma was created by one beam and self-focusing was observed in the weak probe beam which crossed the plasma. Experimental results show that the cause of self-focusing is the nonuniform heating mechanism.

Light pulse narrowing and power density increase in a laser-produced spark

Abstract The gaussian shape of a light pulse is distorted in a laser spark. A narrowing pulse appears with an amplitude enlarged by an order of magnitude due to self-focusing.

Next Generation Driver for Attosecond and Laser-plasma Physics

The observation and manipulation of electron dynamics in matter call for attosecond light pulses, routinely available from high-order harmonic generation driven by few-femtosecond lasers. However, the energy limitation of these lasers supports only weak sources and correspondingly linear attosecond studies. Here we report on an optical parametric synthesizer designed for nonlinear attosecond optics and relativistic laser-plasma physics. This synthesizer uniquely combines ultra-relativistic focused intensities of about 1020 W/cm2 with a pulse duration of sub-two carrier-wave cycles. The coherent combination of two sequentially amplified and complementary spectral ranges yields sub-5-fs pulses with multi-TW peak power. The application of this source allows the generation of a broad spectral continuum at 100-eV photon energy in gases as well as high-order harmonics in relativistic plasmas. Unprecedented spatio-temporal confinement of light now permits the investigation of electric-field-driven electron phenomena in the relativistic regime and ultimately the rise of next-generation intense isolated attosecond sources.

Pre-excitation studies for rubidium-plasma generation

The key element in the Proton-Driven-Plasma-Wake-Field-Accelerator (PWFA) project is the generation of highly uniform plasma from Rubidium vapor. A scientifically straightforward, yet highly challenging way to achieve full ionization is to use high power laser which can assure the barrier suppression ionization (BSI) along the 10 m long active region. The Wigner-team in Budapest is investigating an alternative way of uniform plasma generation. The proposed Resonance Enhanced Multi-Photon Ionization (REMPI) scheme can be probably realized by much less laser power. In the following we plan to investigate the resonant pre-excitations of the Rb atoms, both theoretically and experimentally. In the following our theoretical framework is presented together with the status report about the preparatory work of the planned experiment.

Relativistic self-focusing of fs-laser pulses and their heating effect on the preformed plasma

Experiments in the context of fast ignition were carried out by focusing a 6-TW laser beam into a preformed plasma. An electron population with a quasi-temperature of 2 MeV was generated. The 2/spl omega/ self-emission image reveals a self-focused plasma channel formation, whereas X-ray pinhole photography shows a postheating of the preformed plasma.

Analysis of tokamak collector probes by resonance ionization spectroscopy

Abstract Resonance ionization spectroscopy has been applied to analyze tokamak collector probes. The edge plasma of the MT-1 tokamak was investigated using nonintrinsic sodium impurities injected by the laser blow-off technique. Silicon single crystal deposition probes were analyzed by laser atomization, followed by the resonance ionization method. The unique sensitivity of the selective photoionization made it possible to determine the radial distribution of impurities on a probe exposed to a single tokamak discharge.

Light scattering and self-focusing in laser produced sparks

Abstract The spectral and temporal behaviour of back-and forward-scattered laser light on laser produced spark are investigated. Short backscattered pulses from the plasma fronts appears just after the breakdown. Self-focusing caused by nonlinear heating begins when the plasma filament is already formed.