Self-focusing effect in Au-target induced by high power pulsed laser at PALS

AbstractSelf-focusing effects, induced by ASTERIX pulsed laser at PALS Laboratory of Prague, have been investigated. Laser was employed at the third harmonics (438 nm) and intensities of the order of 1016 W/cm2. Pure Au was used as thin target and irradiated with 30° incidence angle. An ion energy analyzer was employed to detect the energy-to-mass ratio of emitted ions from plasma. Measurements were performed by changing the focal point position with a high spatial resolution step-motor. Results demonstrated that non linear processes, due to self-focusing effects, occurs when the laser beam is focused at about 200 µm in front of the target surface. In such conditions, a new ion group, having high charge state and kinetic energy, is produced because of the increment in temperature of the laser-generated plasma

Experimental studies of generation of ~100 MeV Au-ions from the laser-produced plasma

AbstractUsing the PALS iodine laser system, Au ions with the charge state up to 58+ and with the kinetic energy as high as ~300 MeV were generated. The production of these ions was tested in dependence on the laser frequency (1ω, 3ω), on the irradiation/detection angles (0°, 30°), on the focus position with regard to the target surface, and on the target thickness (500 µm, 200 µm, 80 µm). A larger amount of the fastest ions was produced with 1ω than with 3ω, the most of the fast ions were recorded in the direction ~10°from the target normal, the optimum focus position is in front of the target and should be set on with a precision of 50 µm. The forward emission is weaker than the backward one for both of the thinner targets (which burn through) at our experimental conditions

Semiconductor Detectors for Observation of Multi-MeV Protons and Ions Produced by Lasers

The application of time-of-flight Faraday cups and SiC detectors for the measurement of currents of fast ions emitted by laser-produced plasmas is reported. Presented analysis of signals of ion detectors reflects the design and construction of the detector used. A similarity relation between output signals of ion collectors and semiconductor detectors is established. Optimization of the diagnostic system is discussed with respect to the emission time of electromagnetic pulses interfering with signals induced by the fastest ions accelerated up to velocities of 107 m/s. The experimental campaign on laser-driven ion acceleration was performed at the PALS facility in Prague

Angular distributions of ions emitted from laser plasma produced at various irradiation angles and laser intensities

AbstractAngular distributions of currents and velocities (energies) of ions produced at various target irradiation angles and laser intensities ranged from 1010 W/cm2 to 1017 W/cm2 were analyzed. It was confirmed that for low laser intensities the ion current distributions are always peaked along the target normal. However, at laser intensities comparable to or higher than 1014 W/cm2, the preferred direction of ion emission strongly depends on the irradiation geometry (laser focus setting, the irradiation angle), and can be off the target normal. This is very likely caused by the non-linear interaction of the laser beam with produced plasma, in particular, by the action of ponderomotive forces and the laser beam self-focusing

Factors influencing parameters of laser ion sources

Various applications demand various kinds of ions. Charge state, energy and the amount of laser produced ions depend, primary, on the wavelength, the energy, the pulse duration, and the focusing ability of the laser used. Angle of the target irradiation, angle of the ion extraction (recording), and mainly the focus setting may significantly influence especially the portion of ions with the highest charge states. The participation of non-linear processes on the generation of ions with extremely high parameters is demonstrated. The observed effects support the idea of a longitudinal structure of the self-focused laser beam with a space period of ∼200 µm

The influence of an intense laser beam interaction with preformed plasma on the characteristics of emitted ion streams

AbstractIntense laser-beam interactions with preformed plasma, preceding the laser-target interactions, significantly influence both the ion and X-ray generation. It is due to the laser pulse (its total length, the shape of the front edge, its background, the contrast, the radial homogeneity) as well as plasma (density, temperature) properties. Generation of the super fast (FF) ion groups is connected with a presence of non-linear processes. Saturated maximum of the charge states (independently on the laser intensity) is ascribed to the constant limit radius of the self-focused laser beam. Its longitudinal structure is considered as a possible explanation for the course of some experimental dependencies obtained

DIAMOND DETECTORS FOR CHARACTERIZATION OF LASER-GENERATED PLASMA

Abstract -CVD mono-crystalline diamond films were employed as detectors of the Introduction -Laser-generated plasma is characterized by high temperature and density