V. A. Gasilov

Energy Increase in Multi-MeV Ion Acceleration in the Interaction of a Short Pulse Laser with a Cluster-Gas Target

We demonstrate generation of 10-20 MeV/u ions with a compact 4 TW laser using a gas target mixed with submicron clusters, corresponding to tenfold increase in the ion energies compared to previous experiments with solid targets. It is inferred that the high energy ions are generated due to formation of a strong dipole vortex structure. The demonstrated method has a potential to construct compact and high repetition rate ion sources for hadron therapy and other applications.

Gas-cluster targets for femtosecond laser interaction: Modeling and optimization

A novel mathematical model for the investigations of a cluster formation process in a gas jet is presented, which enables us to obtain the detailed description of the spatial and temporal distributions of all cluster target parameters. In this model, a cluster target is considered as a two-phase medium, consisting of the continuous gas phase and the discrete condensed phase (clusters). The detailed nozzle geometry is also taken into account in this model. In order to confirm the advantage of the present model over a conventional model, a considerable amount of numerical computations has been carried out and the results are compared with the data obtained from Hagena’s theory [Rev. Sci. Instrum. 63, 2374 (1992)]. Based on the developed modeling, a three-staged nozzle, which cannot be modeled using the conventional model, is designed for the purpose of producing a sufficient amount of micron-sized clusters. The generation of unprecedented amount of keV x rays from the laser-cluster interaction experiments w...

Generation of X rays and energetic ions from superintense laser irradiation of micron-sized Ar clusters

AbstractHigh-resolutionK-shell spectra of a plasma created by superintense laser irradiation of micron-sized Ar clusters havebeen measured with an intensity above 10 19 W0cm 2 and a pulse duration of 30 fs. The total photon flux of 2310 8 photons0pulse was achieved for He a1 resonant line of Ar ~l 5 3.9491 A, 3.14 keV !. In parallel with X-raymeasurements,energydistributionsofemittedionshavebeenmeasured.Themultiplychargedionswithkineticenergiesup to 800 keV were observed. It is found that hot electrons produced by high contrast laser pulses allow the isochoricheating of clusters and shift the ion balance toward the higher charge states, which enhances both the X-ray line yield ofthe He-like argon ion and the ion kinetic energy.Keywords: Cluster; High power laser; Isochoric heating; Multiply charged ion; X ray 1. INTRODUCTIONRecent development of ultrashort, high peak-power lasersystems, based on the chirped pulse amplification ~CPA!technique, opens up a new regime of laser–matter inter-action ~Perry & Mourou, 1994!. Nowadays a focusing ofsuch laser pulses produces laser peak intensities well above10

X-ray Study of Microdroplet Plasma Formation under the Action of Superintense Laser Radiation

We have measured the X-ray emission spectra of a plasma generated by laser radiation with an intensity above 1019W/cm2 and a pulse duration of 30 fs acting upon an argon jet target with a large abundance of micron-sized clusters. The time variation of the X-ray yield from ions of various multiplicities, calculated within the framework of a nonstationary kinetic model, shows a good qualitative agreement with the experimental time-integrated spectrum.

On the Generation of Large Clusters in Forming Gas-Jet Targets for Lasers

The problem of increasing the mean size of clusters in gas-jet targets is tackled. Based on a mathematical model of clustering, the dependence of the cluster mean size on the nozzle length and rate of expansion is derived. The nozzle shape providing micrometer-size clusters is found. The parameters of gas-jet targets produced with this nozzle are studied in detail.

Submicron ionography of nanostructures using a femtosecond-laser-driven-cluster-based source

An intense isotropic source of multicharged carbon and oxygen ions with energy above 300 keV and particle number >108 per shot was obtained by femtosecond Ti:Sa laser irradiation of submicron clusters. The source was employed for high-contrast contact ionography images with 600 nm spatial resolution. A variation in object thickness of 100 nm was well resolved for both Zr and polymer foils.

X-ray spectroscopy diagnostic of a plasma produced by femtosecond laser pulses irradiating a cluster target

The parameters of a plasma produced upon the interaction of ultrashort laser pulses with cluster targets are measured by the methods of X-ray spectroscopy. The dependence of the plasma parameters on the initial properties of a cluster target (the design of a supersonic nozzle, the average size of clusters, the spatial inhomogeneity) and the laser pulse properties (its duration and contrast) is studied. The plasma diagnostics is performed using the model of formation of emission spectra, which was proposed earlier and includes a number of fitting parameters, which provide good agreement with experimental spectra. The systematic experimental studies performed by us showed that our model of cluster heating by ultrashort pulses is indeed a physical model, and the fitting parameters represent the average values of plasma parameters in the corresponding space-time regions.

Characterization of submicron-sized CO2 clusters formed with a supersonic expansion of a mixed-gas using a three-staged nozzle

The size of CO2 clusters, produced in a supersonic expansion of a mixed-gas of CO2/He or CO2/H2 through a three-staged conical nozzle designed based on the Boldarevs model, has been evaluated by measuring the angular distribution of light scattered from the clusters. The data are analyzed utilizing the Mie scattering theory, and the sizes of CO2 clusters are estimated as 0.22 μm and 0.25 μm for the cases of CO2/He and CO2/H2 gas mixtures, respectively. The results confirm that the Boldarevs model is reliable enough for the production of micron-sized clusters.

Modeling Cluster Jets as Targets for High-Power Ultrashort Laser Pulses

A hydrodynamic model is formulated that describes the formation of clusters in atomic gas jets expanding into vacuum, which are used as laser plasma targets. Detailed model calculations performed for an argon gas jet describe spatial distributions of the density of gas and cluster phases formed in the Laval nozzle at room temperature in a broad range of entrance gas pressures. The cluster density distribution is significantly inhomogeneous. The cluster distribution features revealed by the model calculations were qualitatively confirmed by the X-ray spectroscopic measurements of the spatial distribution of emission from the plasma created in the jet tar-gets by high-power ultrashort laser pulses.

On the Interaction of Femtosecond Laser Pulses with Cluster Targets

The heating of clusters by femtosecond laser pulses is studied theoretically and experimentally. Both the formation of a cluster target and the results of experimental studies of the cluster plasma by the methods of X-ray emission spectroscopy are considered. A numerical model of cluster formation in a supersonic gas jet is proposed. It is shown that detailed studies of two-phase gas-dynamic processes in a nozzle forming the jet give the spatial distributions of all parameters required for the correct calculation of the cluster heating by short laser pulses. Calculations of nozzles of different configurations show that in a number of cases an almost homogeneous cluster target can be formed, whereas in other cases the distributions of parameters prove to be not only inhomogeneous but also even nonmonotonic. A simple physical model of the plasma production by a femtosecond laser pulse and a picosecond prepulse is proposed. It is shown that a comparison of X-ray spectra with detailed calculations of the ion kinetics makes it possible to determine the main parameters of the plasma being produced.