Heating of deuterium clusters by a superatomic ultra-short laser pulse

The mechanisms of heating of the electronic component of large deuterium clusters by a super-atomic ultra-short laser pulse field are considered. During pulse rise, the so-called “vacuum heating” plays the determining role. Electrons escaping from a cluster into the vacuum with a low energy return back in a time equal to the period of the laser under laser field action. The returning electrons have a higher energy (on the order of the vibrational energy in the laser radiation field), which causes cluster heating. As the laser field increases, the electronic temperature largely grows at the expense of decreasing the Coulomb potential energy of electron repulsion because of a decrease in the number of electrons. The dynamics of above-barrier cluster ionization at the leading edge of a superatomic laser pulse is calculated. The results are discussed in the light of recent experiments aimed at creating desktop sources of monoenergetic neutrons formed as a result of the fusion of deuterium nuclei in a cluster plasma.     

Effect of radiation on compressibility of hot dense sodium and iron plasma using improved screened hydrogenic model with l splitting

High pressure investigations of matter involve the study of strong shock wave dynamics within the materials which gives rise to many thermal effects leading to dissociation of molecules, ionization of atoms, and radiation emission, etc.The response of materials experiencing a strong shock can be determined by its shock Hugoniot calculations which are frequently applied in numerical and experimental studies in inertial confinement fusion, laboratory astrophysical plasma,etc. These studies involve high energy density plasmas in which the radiation plays an important role in determining the energy deposition and maximum compressibility achieved by the shock within material. In this study, we present an investigation for the effect of radiation pressure on the maximum compressibility of the material using shock Hugoniot calculations. In shock Hugoniot calculations, an equation of state(EOS) is developed in which electronic contributions for EOS calculations are taken from an improved screened hydrogenic model with-l splitting(I-SHML) [High Energy Density Physics(2018) 26 48] under local thermodynamic equilibrium(LTE) conditions. The thermal ionic part calculations are adopted from the state of the art Cowan model while the cold ionic contributions are adopted from the scaled binding energy model. The Shock Hugoniot calculations are carried out for sodium and iron plasmas and our calculated results show excellent agreement with published results obtained by using either sophisticated self-consistent models or the first principle study.     

神光Ⅲ原型黑腔物理实验研究

总结了在神光Ⅲ原型激光装置上开展的一系列黑腔物理实验研究,从多个方面研究了黑腔内部等离子体状态和辐射场特性。用真空黑腔能量学研究获得了散射光、辐射温度和不同能段辐射流份额的定标规律,从能量学角度梳理和分析了整个激光黑腔相互作用过程。通过对黑腔中充入低密度低Z气体抑制了腔壁等离子体运动,明显减少了可能造成靶丸预热的金M带辐射流(1.6~4.4keV)份额。针对黑腔内部不同区域等离子体,研究了光斑区等离子体的运动,分析了其与电子热传导限流因子的关系;研究了冕区等离子体的运动,分析了不同充气等离子体条件对其的影响;在同一发次实验中同时测量了光斑区与再发射区的辐射流比值。     

Exploring interatomic Coulombic decay by free electron lasers

To exploit the high intensity of laser radiation, we propose to select frequencies at which single-photon absorption is of too low energy and two or more photons are needed to produce states of an atom that can undergo interatomic Coulombic decay (ICD) with its neighbors. For Ne(2) it is explicitly demonstrated that the proposed multiphoton absorption scheme is much more efficient than schemes used until now, which rely on single-photon absorption. Extensive calculations on Ne(2) show how the low-energy ICD electrons and Ne(+) pairs are produced for different laser intensities and pulse durations. At higher intensities the production of Ne(+) pairs by successive ionization of the two atoms becomes competitive and the respective emitted electrons interfere with the ICD electrons. It is also shown that a measurement after a time delay can be used to determine the contribution of ICD even at high laser intensity.     

Zur Theorie der nichtstationären Resonanzfluoreszenz an bewegten Molekülen. II. Untersuchungen zur hochauflösenden Resonanzfluoreszenzspektroskopie

Non-stationary Theory of Resonance Fluorescence for Moving Molecules. II. Highly Resolved Fluorescence Spectroscopy With respect to tke Doppler-effect a formula for the spectral energy density of fluorescence radiation of gases (vapours) generated by resonance scattering of short laser pulses is derived. The spectral energy density consists of a coherent and an incoherent part which differs in a characteristic way. The coherent fluorescence radiation reproduces the spectrum of the laser light. Informations about the homogeneous line widths are obtained only from the incoherent spectra. The results of numerical calculations of highly resolved spectra in forward and backward directions under different conditions are discussed.     

Brightness-Spectrum Characteristics of the Surface Laser Plasma of Polymeric Targets in the VUV Spectral Region

The brightness-spectrum and energy parameters in the VUV range of the spectrum (h 9–70 eV) of the surface laser plasma of polymeric targets in vacuum are determined experimentally. Using the experimental technology of double open and closed ionization chambers (as radiation detectors) requiring no absolute energy calibration in a wide range of regulation parameters of the effect of standard laser frequencies, we obtained new data on multifactor radiative gasdynamic processes of effect which are needed to determine emission and mass-output characteristics of the targets irradiated under vacuum.     

Energy of a shock wave generated in different metals under irradiation by a high-power laser pulse

The energies of a shock wave generated in different metals under irradiation by a high-power laser beam were determined experimentally. The experiments were performed with the use of targets prepared from a number of metals, such as aluminum, copper, silver and lead (which belong to different periods of the periodic table) under irradiation by pulses of the first and third harmonics of the PALS iodine laser at a radiation intensity of approximately 10¹⁴ W/cm². It was found that, for heavy metals, like for light solid materials, the fraction of laser radiation energy converted into the energy of a shock wave under irradiation by a laser pulse of the third harmonic considerably (by a factor of 2–3) exceeds the fraction of laser radiation energy converted under irradiation by a laser pulse of the first harmonic. The influence of radiation processes on the efficiency of conversion of the laser energy into the energy of the shock wave was analyzed.     

Radiative corrections in laser-dressed atoms: formalism and applications

The dressing of atomic states in a strong laser field modifies the structure of the incoherently scattered fraction of the laser intensity, which is described to a good approximation by the Mollow spectrum. The incoherent spectrum is generated by the fluctuations of the atomic dipole moment about its expectation value, and the positions of the peaks are approximately given by the energy differences between the dressed atomic energy levels. In this paper, we investigate radiative corrections received by the dressed states. Our calculations are motivated by the quest to understand in detail the interplay of a bound electron dressed by the highly populated laser mode and its interaction with the vacuum modes. Alternatively, this may be seen as an electron experiencing modified stimulated and spontaneous radiative corrections in a vacuum tailored by the laser field. We obtain dressed self-energy shifts that depend on the Rabi flopping frequency (and in turn on the laser intensity) and on the detuning of the laser field relative to the atomic resonance frequency. We find that the dressed radiative corrections differ in a nontrivial manner from the radiative shifts of the ‘bare’ atomic states.     

超强激光与固体靶作用驱动量子电动力学级联和稠密正电子产生的研究进展

极端超短超强激光脉冲的诞生将光与物质的相互作用推进到由辐射阻尼效应和量子电动力学（QED）效应占主导的高度非线性物理范畴。强场QED效应蕴含了丰富的物理过程包括辐射阻尼、高能伽马辐射、正负电子对产生、QED级联、真空极化等,是高能量密度物理和强场物理研究领域的前沿热点。QED级联是解释致密天体辐射和伽马射线暴形成的重要物理机制,其产生的稠密正电子源在高能物理、材料无损探测、癌症诊断等领域亦有重要的应用前景。介绍了QED级联过程及其理论模型,讨论了固体靶中的QED级联发展及其诱导的非线性物理效应,并回顾了固体靶中稠密正电子产生的主要研究成果。     

Vacuum energy in the presence of dielectric and conducting surfaces

The polarization of the electromagnetic vacuum is examined in the neighborhood of dielectric and conducting surfaces and the energy associated with this polarization is shown to depend on a cutoff related to the microstructure of the boundary. The appearance of the cutoff permits the vacuum energy to be expressed in terms of a surface tension and certain higher shape tensions. For the case of a dielectric boundary the surface tension reproduces the Schmitt-Lucas formula which accounts reasonably for the observed surface tensions of many materials. The curvature tension is also calculated and it seems the effect of this energy may well be accessible to experimental verification. For the case of perfectly conducting surfaces the first four shape tensions are calculated. It is shown that previous calculations of the vacuum energy due to perfectly conducting surfaces are in error and these errors are corrected.     

Control of parameters of micropinches formed in current-carrying plasma jet

The temporal evolution and spatial pattern of X-ray emission from a laser-induced vacuum discharge of moderate power has been investigated. It was found that micropinches in the initial stage of the cathode jet expansion into the vacuum ambient were formed. They generated a soft X-ray radiation and beams of accelerated electrons; therewith these phenomena occurred just when both amplitude of the discharge current and energy of the initiating laser pulse lied in the specified ranges of values. Parameters of the micropinch, namely, its position within the interelectrode gap and also, intensity of the X-ray radiation and beams of the accelerated electrons emitted from the micropinch are variable over a wide range of values through changes of energy of the laser pulse and/or amplitude of the discharge current.     

Influence of angles of incidence of laser radiation on the generation of fast ions

It was established experimentally that the number and energy of fast ions in laser plasma increased with increasing angle of focusing laser radiation onto a flat target. Numerical calculations showed that the increase in angle of focusing brought the mean angle of incidence of laser radiation closer to the optimal angle corresponding to the maximal efficiency of the resonance absorption mechanism and, as a result, increased the fraction of absorbed laser energy in the energy of fast electrons and increased the number of fast electrons. In turn, the increase in the energy and number of fast electrons resulted in an increase in the number of fast electrons involved in the formation of a self-consistent electric field at the target edge and led to the growth of the field strength, which, eventually, was the reason for the increase in the number and energy of fast ions.     

Visible-laser acceleration of relativistic electrons in a semi-infinite vacuum

We demonstrate a new particle acceleration mechanism using 800 nm laser radiation to accelerate relativistic electrons in a semi-infinite vacuum. The experimental demonstration is the first of its kind and is a proof of principle for the concept of laser-driven particle acceleration in a structure loaded vacuum. We observed up to 30 keV energy modulation over a distance of 1000 lambda, corresponding to a 40 MeV/m peak gradient. The energy modulation was observed to scale linearly with the laser electric field and showed the expected laser-polarization dependence. Furthermore, as expected, laser acceleration occurred only in the presence of a boundary that limited the laser-electron interaction to a finite distance.     

Laser heating of biological tissue with blood vessels: Modeling and clinical trials

The spatial distribution of the energy absorbed by a unit volume of a laser-irradiated biological tissue is calculated by the Monte Carlo method. Based on these calculations, the temperature fields in biological tissues subjected to laser radiation at 810 nm are modeled. The temperature fields in subcutaneous blood vessels are modeled separately taking into account the inhomogeneous volumetric distribution of heat sources inside the vessels. The results of the modeling showed that laser heating can be efficiently used both for small-diameter and large vessels. Experimental clinical trials of therapy of vascular skin changes by pulsed diode laser radiation (at 810 nm) confirmed these results.     

Kinetics of laser-induced surface melting and oxide removal in single-crystalline Ge

The process of oxide removal in crystalline Ge using a pulsed ultraviolet laser has been studied by means of real-time reflectivity measurements with nanosecond resolution. The interaction of laser radiation with a clean, oxide-free surface has been characterized and the inhomogeneous and homogeneous energy density melting thresholds of c-Ge for 193 nm radiation have been determined. The values are 180 and 370 mJ/cm², respectively. We have demonstrated that it is possible to remove an oxide overlayer by irradiation in vacuum and to produce a surface that shows the same response to laser radiation as a smooth, oxide-free, chemically cleaned surface. Under certain specific irradiation conditions it is even possible, after removing the oxide overlayer, to produce an enhanced crystalline quality in the near-surface region compared to that obtained upon chemical cleaning as evidenced by Rutherford backscattering/channeling measurements.     

Numerical modeling of laser–matter interaction in the region of “low” laser parameters

The interaction of laser radiation with matter leads to the certain kinds of modelling of its surface or volume. These effects have been demonstrated for a lot of materials, even causing the formation of new scientific and industrial domain, which is undoubtedly laser material processing and as well as laser cleaning of artworks. Those applications lie in the so-called “low' region of laser energy densities, represented for short laser pulses by power densities below 10⁹ W/cm². Paper presents set of equations describing in one-dimensional (1D) model phenomena accompanying to laser–matter interaction. Target geometry includes two and four layers of different materials, irradiated by ns laser pulses. Effects of radiation absorption and transport, heat conductivity, target transit to plastic state, melting and evaporation are taken into consideration. The part of the paper is devoted to the discussion of numerical results, selected in such a way to illustrate the phenomenon of radiation interaction with materials as well as to show, in whole, possibilities of computer simulation methods.     

The role of virtual photons in nanoscale photonics

The fundamental theory of processes and properties associated with nanoscale photonics should properly account for the quantum nature of both the matter and the radiation field. A familiar example is the Casimir force, whose significant role in nanoelectromechanical systems is widely recognised; the correct representation invokes the creation of short‐lived virtual photons from the vacuum. In fact, there is an extensive range of nanophotonic interactions in which virtual photon exchange plays a vital role, mediating the coupling between particles. This review surveys recent theory and applications, also exhibiting novel insights into key electrodynamic mechanisms. Examples are numerous and include: laser‐induced inter‐particle forces known as optical binding; non‐parametric frequency‐conversion processes especially in rare‐earth doped materials; light‐harvesting polymer materials that involve electronic energy transfer between their constituent chromophores. An assessment of these and the latest prospective applications concludes with a view on future directions of research.     

The Concept of an Erosion Monitor for In-Vessel ITER Components with the Use of a Pulsed Laser

The erosion monitor is the ITER diagnostic system designed to control the erosion and deposition of materials on the plasma-facing components of the vacuum vessel under the influence of particle flows and radiation from the plasma. The required accuracy and range of measurements can be achieved using the two-frequency speckle interferometry method. However, because of vibration of the installation, the images should be taken in such a short time that is not provided by existing CMOS cameras. In this paper, it is proposed to use an interferometer based on a pulsed solid-state laser with a tunable radiation wavelength, and methods for recording interferograms under vibration conditions are considered. The required laser parameters are estimated; the expected results are analyzed.

     

Antiangular ordering of gluon radiation in QCD media

We investigate angular and energy distributions of medium-induced gluon emission off a quark-antiquark antenna in the framework of perturbative QCD as an attempt toward understanding, from first principles, jet evolution inside the quark-gluon plasma. In-medium color coherence between emitters, neglected in all previous calculations, leads to a novel mechanism of soft-gluon radiation. The structure of the corresponding spectrum, in contrast with known medium-induced radiation, i.e., off a single emitter, retains some properties of the vacuum case; in particular, it exhibits a soft divergence. However, as opposed to the vacuum, the collinear singularity is regulated by the pair opening angle, leading to a strict angular separation between vacuum and medium-induced radiation, denoted as antiangular ordering. We comment on the possible consequences of this new contribution for jet observables in heavy-ion collisions.