Laser Radiation In Plasma Research Articles

Generation of lower and higher harmonics in different plasma media with small Z

The generation of lower (third) and higher harmonics of femtosecond laser radiation in plasmas produced by laser ablation of different targets with a small atomic number Z (B, Be, Li) has been investigated. The high (10−3) efficiency of third-harmonic generation was observed in plasma produced on the boron surface. Efficient third-harmonic generation was also observed in beryllium plasma using femtosecond pulses of Ti:sapphire laser radiation (λ = 790 nm) and its second harmonic (395 nm). We could tune the higher harmonics generation spectrum by tuning the crystal converter when using 395-nm radiation to be converted. It is shown that, in plasmas formed on targets with small Z, the conversion efficiency and limiting generated harmonic order depend on the delay between the ablation pulse and the pulse to be converted.

QUANTUM THEORY OF RADIATION IN LASER PLASMA

Based on the Langevin noise approach, a full quantum theory of radiation in laser plasma is explored, where the laser intensity is limited to the range of 1010 W/cm2 to 1012 W/cm2 and the plasma is considered as a homogeneous dielectric background. By numerical calculation, the results show that the radiation is generated from the resonance of the plasma and the emitted rate of photons depends on the angular relation between the directions of radiation fields and the motion of the unbounded free electrons. In addition, the photons are more easily created under the lower collision frequency.

Development of Laser Plasma X-ray Microbeam Irradiation System and Radiation Biological Application

Laser plasma x-ray source has the features such as ultra short pulse, high brilliance, monochromaticity, and focusing ability. These features are excellent compared with conventional x-ray source. In order to apply the laser plasma x-ray source to the biomedical study and to more closely research the radiobilogical responce of the cancer cell such as radiation induced bystander effect, we have developed x-ray microbeam system using laser plasma x-ray source. The absorbed dose of laser plasma x-ray was estimated with Gafchromic EBT film and DNA double strand breaks on the cells were detected by immunofluorescence staining. When the cells were irradiated with laser plasma x-ray, the circular regions existing γ-H2AX positive cells were clearly identified. The usefulness of the laser plasma x-ray on the radiobiological study was proved in this research.

Enhancement of high-order harmonic generation using a two-color pump in plasma plumes

The results of enhanced high-order harmonic generation (HHG) in laser-produced plasmas using a two-color laser pump (98% of 800 nm and 2% of 400 nm) are presented. Even (up to the 38th order) and odd (up to the 45th order) harmonics of 800 nm radiation were generated in the case of a two-color orthogonal polarization pump of various plasmas. The comparison between HHGs using parallel and orthogonally polarized 400 and 800 nm radiations showed better conversion efficiency for the latter case. We have also used circularly polarized 800 nm pump for second-harmonic generation and HHG. We also present the results of the influence of the chirp and phase modulation of the fundamental radiation in laser plasma on the spectral properties of odd and even harmonics.

Effect of self-generated axial magnetic field and on propagation of intense laser radiation in plasmas

The present paper deals with an analytical study of a self-generated axial magnetic field (SGAMF) through the inverse Faraday effect (IFE) and its influence on the propagation of circularly polarized light wave for relativistic intensities. As a first step, the non-linear dielectric constant incorporating a magnetic field in the relativistic factor within the framework of WKB (for Wentzel, Kramers, and Brillouin) and a paraxial ray theory is formulated. It is noticed that for intensities (>1018 W cm−2), circularly polarized radiation can propagate in electron plasma whose density is greater than the critical density as well as a strong flow of relativistic electrons, axially co-moving with the pulse rise. The above generates a magnetic field up to 100 MG and strongly influences the light propagation. Two modes of propagation exist, namely, extraordinary and ordinary, and critical power for focusing is different for the two modes. The non-linear dielectric tensor, propagation equation, and the self-trapped radius are evaluated incorporating an induced magnetic field. The focusing conditions strongly depend on the power of the beam, strength of the magnetic field as well as on the density of the medium. Numerical calculations are made for a typical set of relativistic laser plasma interaction processes.

The investigation of aluminium laser plasma radiation at different air preasures

The investigation of aluminium laser plasma radiation at different air preasures

International and Asian Networks on Intense Laser Science

This paper reviews evolution of the research networks on intense laser science under international and Asian frameworks during 2000 to 2008. The OECD Global Science Forum Steering Committee on Compact, High-Intensity Short-Pulse Lasers led to the establishment of the International Union of Pure and Applied Physics (IUPAP) Working Group: International Committee on Ultrahigh Intensity Lasers (ICUIL) and the Asian Intense Laser Network (AILN) in 2004. Through various activities under AILN such as the Asian Symposium on Intense Laser Science (ASILS), the Asian Summer School on Laser Plasma Acceleration and Radiation, and the High-Order Harmonics Workshops, closer relations are being formed among the scientists and also among the young generations working in intense laser science in the Asian regions.

Generatsiya vysshikh garmonik izlucheniya moshchnykh lazerov v plazme, obrazovannoi pri vozdeistvii predympul'sa na poverkhnost' tverdotel'nykh mishenei

Generatsiya vysshikh garmonik izlucheniya moshchnykh lazerov v plazme, obrazovannoi pri vozdeistvii predympul'sa na poverkhnost' tverdotel'nykh mishenei

Generation of higher-order harmonics of chirped radiation from a titanium-sapphire laser in plasma generated by pulses of different durations

The frequency conversion of laser radiation in plasma created by pulses of different durations under conditions of the chirp variation of the radiation to be converted is investigated. It is shown that the chirp variation of the laser pulse during the generation of higher-order radiation harmonics of the femtosecond laser leads to a considerable change in the brightness, wavelength shift, and maximal order of generated harmonics. The long-and short-wavelength shifts of harmonics observed in these studies are attributed to the manifestation of a considerable concentration of free charge carriers in the plasma, as well as the self-modulation of the laser pulse. The generation of plasma by pulses whose durations vary from 160 fs to 20 ns is considered and it is shown that the generation efficiency of harmonics depends to a greater extent on the energy of the heating prepulse than on its intensity on the surface of a target to be ablated. The effect that the atomic number of the target has on the formation of optimal plasma at different delays between the heating prepulse and the femtosecond pulse to be converted is discussed.

Absorption of resonance radiation in ultracold laser plasma

Absorption of resonance radiation in ultracold laser plasma

Ultra-intense Laser Plasma Interaction Studies at RRCAT, Indore

The Laser Plasma Division at the Raja Ramanna Centre for Advanced Technology (RRCAT), Indore has been engaged in research and development activities on laser plasma interaction using 10 TW, 45 fs, Ti:sapphire laser and a variety of in-house developed diagnostic systems for ultrashort laser pulses, plasma and x-ray radiation. Our recent studies include laser wakefield electron acceleration, high order harmonic generation, resonance enhancement of single harmonics, MeV energy bremsstrahlung radiation, absorption of ultrashort laser pulses in in-situ produced metal clusters, and ultrashort pulse K-shell x-ray line emission. This paper briefly describes these studies and important results obtained.

Special features of formation of plasma torch under conditions of hybrid laser-arc welding

This paper is devoted to analytical description of processes occurring in hybrid discharge plasma under conditions of laser-arc welding with deep melting. The axially symmetric boundary layer approximation is used to solve the problem on the outflow of a jet of hot metal vapor into an atmosphere of cold protective helium gas in view of the compressibility of gas mixture and of the bulk heat release during absorption of laser radiation in plasma. In so doing, the degree of ionization of plasma is determined from the solution of kinetic problem in the approximation of constant collision frequencies for a helium-iron mixture without the assumption of local thermal equilibrium. A series of experiments in the interferometry of plasma torch under conditions of pulsed laser stimulation of metal targets are performed to confirm the obtained results.

Relativistic and ponderomotive effects on stimulated Raman scattering of intense laser radiation in plasma

The effects of relativistic nonlinearities on stimulated Raman scattering (SRS) of mildly relativistic laser radiation propagating through preionized underdense plasma is studied. The nonlinear mode coupling equations and linearized growth rates of Raman instabilities in presence of combined effects of relativistic and ponderomotive nonlinearities are derived. The temporal evolution of SRS process is then studied and analyzed using numerical techniques in presence of the two nonlinearities. It is observed that relativistic effects now taken into account significantly affect the growth rates and the nonlinear evolution of SRS process as compared to the case where they are neglected. The study shows that inclusion of relativistic nonlinearities along with the ponderomotive nonlinearities destabilizes SRS process

Compression of laser radiation in plasmas via electromagnetic cascading

A train of few-laser-cycle relativistically intense radiation spikes with a terahertz repetition rate can be organized self-consistently in plasma from two frequency detuned co-propagating laser beams of low intensity. Large frequency bandwidth for the compression of spikes is produced via laser-induced periodic modulation of the plasma refractive index. The beat-wave-driven electron plasma wave downshifted from the plasma frequency creates a moving index grating thus inducing a periodic phase modulation of the driving laser (in spectral terms, electromagnetic cascading). The group velocity dispersion compresses the chirped laser beat notes to a few-cycle duration and relativistic intensity either concurrently in the same, or sequentially in different plasmas. Particle-in-cell simulations indicate that the effect persists in a realistic three-dimensional axisymmetric geometry.

Strong temperature effect on X-ray photo-etching of polytetrafluoroethylene using a 10 Hz laser-plasma radiation source based on a gas puff target

The first results of experiments on direct photo-etching of heated PTFE using a 10 Hz X-ray source based on a laser-irradiated gas puff target are presented. X-ray radiation in the wavelength range from 6 to 20 nm was produced as a result of irradiation of a double-stream gas puff target with Nd:YAG laser pulses of energy 0.8 J and time duration 3 ns. The resulting X-ray pulses with energy of about 100–200 mJ were used to irradiate samples of PTFE to create microstructures by direct photo-etching. Strong enhancement of the photo-etching process was observed for samples heated up to 300 °C.

Self-action of laser radiation in cluster plasma

We have analytically and numerically studied the self-action dynamics of laser radiation in a plasma with ionized gas clusters. Based on the simplified model of a cluster in the form of a superposition of two charged (electron and ion) bunches, we analyze the nonlinearity mechanisms. We refine the electrodynamic cluster model by the molecular dynamics method. The polarization behavior of the plasma bunch in the main part of the laser pulse is shown to be the same as that in the simplified model. We investigate the self-action dynamics of laser radiation under conditions when the nonlinearity of the stratified medium is determined by the anharmonicity of the electron motion in the cluster, while the group velocity dispersion is determined by both the background plasma and the ionized clusters. Since the characteristic field for the electron nonlinearity depends strongly on the cluster size, the peculiarities of the self-action dynamics result from plasma bunch expansion. The spatiotemporal evolution of the wave field is shown to be accompanied by pulse self-compression near the trailing edge.

Micromachining of organic polymers by X-ray photo-etching using a 10 Hz laser-plasma radiation source

The first results of experiments on direct photo-etching of organic polymers using a 10 Hz X-ray source based on a laser-irradiated gas puff target are presented. X-ray radiation in the wavelength range from 2 to 15 nm was produced as a result of irradiation of a double-stream gas puff target with Nd:YAG laser pulses of energy 0.8 J and time duration 3 ns. The resulting X-ray pulses with energy of about 100–200 mJ were used to irradiate samples of organic polymers to create microstructures by direct photo-etching. The obtained results show that direct photo-etching using the laser-plasma X-ray source could be useful for micromachining of organic polymers.

１ｋＷ級ＣＷレーザー推進機の性能計算

Numerical analyses were performed to clarify the power conversion mechanisms in a 1kW class Continuous-Wave (CW) laser thruster. Laser plasma heating and radiation emission from the plasma, which dominate in the power conversion balance, were highlighted in the analyses. Calculation results showed that low laser power absorption and large radiation loss from the plasma cause low thruster performance. These results also showed that optimization of the nozzle shape and use of regenerative-cooling can substantially improve the thruster performance.

High resolution x-ray absorption spectroscopy using a laser plasma radiation source

In this article we present a setup of a spectrometer for near edge x-ray absorption spectroscopy at the carbon K-edge (284 eV). The spectrometer works with a laser produced plasma as x-ray source and a single x-ray optical element in grazing incidence configuration called off-axis reflection zone plate. Using different sample foils we were able to demonstrate a spectral resolution of E/ΔE≈600. The positions of specific absorption peaks are in agreement with data measured at synchrotron sources. Since the off-axis zone plate is a focusing system, the x-ray flux in the detector plane is high enough to record an absorption spectrum on a charge-coupled device detector with a single shot. In the single shot modus a spectrum can be recorded before a sample degradation takes place. This will enable time-resolved experiments using pump-probe techniques.

Self-focusing of laser radiation in cluster plasma

The self-focusing of laser radiation in plasma with ionized gaseous clusters is studied both analytically and numerically. An electrodynamic model is proposed for cluster plasma in a field of ultrashort laser pulse. The radiation self-action dynamics are studied using the equation for wave-field envelope with allowance for the electronic nonlinearity of the expanded plasma bunches and the group-velocity dispersion in a nanodispersive medium. It is shown that, for a laser power exceeding the self-focusing critical power, the wave-field self-compression occurs in a medium with dispersion of any type (normal, anomalous, or combined). Due to the strong dependence of the characteristic nonlinear field on the size of ionized cluster, the corresponding processes develop faster than in a homogeneous medium and give rise to the ultrashort pulses.