In this paper we present a high repetition rate experimental platform for examining the spatial structure and evolution of Biermann-generated magnetic fields in laser-produced plasmas. We have extended the work of prior experiments, which spanned over millimeter scales, by spatially measuring magnetic fields in multiple planes on centimeter scales over thousands of laser shots. Measurements with magnetic flux probes show azimuthally symmetric magnetic fields that range from 60 G at 0.7 cm from the target to 7 G at 4.2 cm from the target. The expansion rate of the magnetic fields and evolution of current density structures are also mapped and examined. Electron temperature and density of the laser-produced plasma are measured with optical Thomson scattering and used to directly calculate a magnetic Reynolds number of $1.4\times {10}^4$ , confirming that magnetic advection is dominant at $\ge 1.5$ cm from the target surface. The results are compared to FLASH simulations, which show qualitative agreement with the data.

The plasma parameters of laser-ablated Zirconium (Zr) using a Langmuir probe technique have been investigated by employing a Q-switched Nd:YAG laser (532 nm, 6 ns) at various irradiances ranging from 8.6 to 15.5 GW/cm2. All the measurements have been performed under an ultra-high vacuum condition while keeping the probe at a fixed distance of 4 mm from the target. By varying the biasing voltages from 1 to 75 V, the corresponding values of electric currents are measured by the probe on the oscilloscope. Laser-induced Zr plasma parameters such as electron temperature, electron number density, plasma potential, Debye length, and thermal velocity have been evaluated from I–V characteristic curves of Langmuir probe data. It is found that both the electron temperature and thermal velocity of Zr plasma reveal an increasing trend from 18 to 41 eV and 2.8 × 108 to 4.3 × 108 cm/s, respectively, with increasing laser irradiance which is attributed to more energy deposition and enhanced ablation rate. However, the electron number density of Zr plasma exhibits a non-significant increase from 6.5 × 1014 to 6.7 × 1014 cm−3 with increasing irradiance from 8.6 to 10.9 GW/cm2. A further increase in irradiance from 12 to 15.5 GW/cm2 causes a reduction in the number density of Zr plasma from 6.1 × 1014 to 5.6 × 1014 cm−3 which is attributed to the formation of thick sheath, ambipolar electric field, and laser-supported detonation waves (Shock front). Scanning electron microscope analysis has been performed to reveal the surface morphology of irradiated Zr. It reveals the formation of cracks, ridges, cones, and grains. It was observed at high irradiances the ridges are vanished, whereas cones and cracks are dominant features. By controlling plasma parameters, surface structuring of materials can be controlled, which has a vast range of applications in the industry and medicine.

Interaction of extreme ultraviolet (EUV) pulses of high intensity with gases results in the creation of non-thermalized plasmas. Energies of the driving photons and photoelectrons are sufficient for creation of excited states, followed by emission of the EUV photons. In most cases, decay times of these states are short comparing to the driving EUV pulse. It means that just after stopping of the driving pulse, the EUV emission corresponding to the excited states should also stop. From our earlier measurements in the optical range, however, it can be concluded that lifetimes of such plasmas exceed a time duration of the driving pulse even two orders of magnitude. Hence, it can be expected that the time duration of the EUV emission can be also significantly longer than the irradiation time. In this work, EUV-induced, low-temperature helium (He), krypton, and xenon plasmas were investigated. EUV emission from these plasmas was studied, using a specially prepared detection system, allowing for time-resolved measurements, in selected spectral ranges. The detection system was based on a paraboloidal collector and a semiconductor photodiode, sensitive for the EUV photons. For spectral selection, the corresponding filters or multilayer mirrors were employed. In most cases, the time duration of the EUV emission was significantly longer than the driving EUV pulse. In case of He plasmas, the emission corresponding to excited atoms was detected even hundreds of nanoseconds after the irradiation. It was also shown that the corresponding time profiles depended on densities of gases to be ionized.

Irradiation of gases with intense pulses of extreme ultraviolet (EUV) can result in the formation of low-temperature plasmas. During the time of irradiation, various non-thermal processes driven by the EUV photons and photoelectrons take place, leading to the creation of excited states of atoms and ions. Fast relaxation of these states should result in EUV emission within a time comparable to the driving EUV pulse. On the other hand, from our earlier works, a time duration of the emission in an optical range is over an order of magnitude longer. It can be thus expected that the time of EUV emission can be also relatively long. In this work, time-resolved measurements of the EUV emission from low-temperature plasmas induced in He, Ne, and Ar gases were performed. Due to a low intensity of the emitted radiation, a specially prepared detection system, based on an EUV collector and an EUV sensitive photodiode, was employed. In all cases, a time duration of the EUV emission was much longer compared with the driving EUV pulse. Time profiles of the corresponding signals were specific for particular gases. In case of He and Ne plasmas, these time profiles varied with initial densities of gases to be ionized. The corresponding dependence was especially visible in case of plasmas induced in helium. In case of Ar plasmas, such dependence was not revealed.

In this work, extreme ultraviolet (EUV) emission, from EUV induced, low-temperature microplasmas, were investigated. To perform temporal measurements of the EUV pulses of low intensity, in a medium vacuum, under the pressure of the order of 0.1–0.01 mbar a special detection system was prepared. The system was based on an EUV collector and a semiconductor detector, sensitive for the EUV photons. The collector consisted of two identical grazing incidence, paraboloidal mirrors, and allowed to focus a part of the radiation emitted from the microplasma onto the detector surface. An absorption filter, mounted between the collector and the detector, allowed for selection of an interesting wavelength range. Plasmas were created by irradiation of small portions of gases, injected into the vacuum chamber, using a laser produced plasma EUV source. Three gases were used for the EUV induced plasma formation: neon, krypton, and xenon. Low-temperature plasmas, created in these gases, contained multiply charged ions, emitting radiation in similar wavelength ranges. Two detectors, AXUV20HS1 and AXUVHS5, were used for the measurements. It was shown that differences between the corresponding signal profiles, obtained using both detectors, were not very significant. Moreover, it was demonstrated that the duration of the EUV emission from plasmas, created in different gases, were comparable with the duration of the driving EUV pulse. The longest EUV emission was observed for Kr plasmas, approximately 1.5 times the full width half maximum of the driving EUV pulse.

In this work, a comparative study of low-temperature plasmas, induced in a gaseous nitrogen by photoionization of the gas using two different irradiation systems, was performed. Both systems were based on laser-produced Xe plasmas, emitting intense extreme ultraviolet (EUV) radiation pulses in a wide wavelength range. The essential difference between the systems concerned formation of the EUV beam. The first one utilized a dedicated ellipsoidal mirror for collecting and focusing of the EUV radiation. This way a high radiation fluence could be obtained for ionization of the N2 gas injected into the vacuum chamber. The second system did not contain any EUV collector. In this case, the nitrogen to be ionized was injected into the vicinity of the Xe plasma. In both cases, energies of emitted photons were sufficient for dissociative ionization, ionization of atoms or even ions. The resulting photoelectrons had also sufficiently high energy for further ionizations or excitations. Low-temperature plasmas, created this way, were investigated by spectral measurements in the EUV, ultraviolet (UV) and visible (VIS) spectral ranges. Time-resolved UV/VIS spectra, corresponding to single-charged ions, molecules, and molecular ions, were recorded. Numerical simulations of the molecular spectra were performed allowing one to estimate vibrational and rotational temperatures of plasmas created using both irradiation systems.

Suprathermal electrons produced by laser–plasma interactions at 0.53-μm laser wavelength have been investigated using 19 electron spectrometers. The targets were 2- and 10-μm-thick Al foils, while the laser average intensities were 2 × 1013 and 7 × 1014 W/cm2. A double temperature distribution was observed in the electron energy spectrum: the lower electron temperature was below 25 keV, whereas the higher was ~50 keV. The angular distribution of the total suprathermal electron energy approximately obeyed the Gaussian distribution, peaking along the k vector of the incident laser beam for perpendicular incidence. Furthermore, the conversion rate of laser energy into escaped suprathermal electron energy over the π sr solid angle was ~10−4 at $\sim \!\!10^{14} \; {\rm W}/{\rm c}{\rm m}^{\rm 2}$, increasing almost linearly with the laser intensity.

The effects of shape and thickness of a tin surface layer and of the energy of a 170 ps neodymium:yttrium-aluminum-garnet laser pulse on the conversion efficiency (CE) into extreme ultraviolet emission in the 13.5 nm region is investigated. Whereas a CE of up to 1.16% into the 2% reflection band of multilayer Mo/Si optics was measured for a bulk Sn target at a laser energy of 25 mJ, significant CE enhancement up to 1.49% is demonstrated for a 200-nm-thick Sn layer on a microstructured porous alumina substrate.

A laser ion source (LIS) is a promising candidate as an ion source for heavy-ion inertial fusion (HIF), where a pulsed ultra-intense and low-charged heavy ion beam is required. It is a key development for a LIS to transport laser-produced plasma with a magnetic field to achieve a high-current beam. The effect of a tapered magnetic field on laser-produced plasma is demonstrated by comparing the results with a straight solenoid magnet. The magnetic field of interest is a wider aperture on a target side and narrower aperture on an extraction side. Based on the experimentally obtained results, the performance of a scaled LIS for HIF was estimated.

A new approach is proposed to analyze Bremsstrahlung X-rays that are emitted from laser-produced plasmas (LPP) and are measured by a stack type spectrometer. This new method is based on a spectral tomographic reconstruction concept with the variational principle for optimization, without referring to the electron energy distribution of a plasma. This approach is applied to the analysis of some experimental data obtained at a few major laser facilities to demonstrate the applicability of the method. Slope temperatures of X-rays from LPP are determined with a two-temperature model, showing different spectral characteristics of X-rays depending on laser properties used in the experiments.

The effects of axial magnetic field on the properties of the ions ejected from Nd:YAG laser (wavelength = 1064 nm, pulse duration = 6 ns) produced expanding Cu plasma were investigated. A plane Cu target, without and with 0.23 T axial magnetic field at its surface, was irradiated in the fluence range of 2–24 J/cm2. The ions emitted along the target surface normal were analyzed with the help of ion collector and time-of-flight electrostatic ion energy analyzer. The integrated ion yield, highest ion charge state, average ion energy, and energy of individual ion charge states were found to increase by application of the magnetic field. The initial parameters of the non-equilibrium plasma such as average ion charge, equivalent potential, electron temperature, electron density, Debye length, and transient electric field were estimated from the experimental results obtained without and with application of the magnetic field. The increase of ion yield and ion charge state by application of magnetic field are most probably due to the trapping of electrons in front of the target surface, which boosts up the electron impact ionization process. The ion energy increment due to the magnetic field is discussed in the frame work of electrostatic model for ion acceleration in laser plasma.

Comparative study of CO2 laser-produced tin-droplet plasma with and without pre-pulse laser has been presented. A pre-pulse laser and the CO2 laser was combined and focused to tin-droplet with a diameter of 180 µm. The emitted Sn ions were detected by several Faraday cups to obtain angular distribution of ions in the laser-produced tin-droplet plasma. The influence of pre-pulse laser energy and delay time between pumping laser and pre-pulse laser on the ion characteristics was investigated. It is illustrated that ion average kinetic energy from CO2 laser-produced plasma (LPP) can be reduced when the tin-droplet target has been replaced by the preformed Sn plasma. The obtained optimal delay time with the lowest ion average kinetic energy is about hundreds of nanoseconds. The ion time-of-flight spectra show a twin peak structure in laser-irradiating preformed Sn plasma. And a superimposed Maxwell–Boltzmann (MB) distribution is proposed to describe this twin peak ion time-of-flight spectra. The fitting results quite agree with the raw ion time-of-flight spectra in current experiment. Then, the fitted plasma temperatures and mass-center velocities with various delay times in laser-irradiating preformed plasma are obtained, and the fitted plasma temperatures can be comparable with ion average kinetic energy in double-pulse LPP, which justified the rationality using this superimposed MB distribution.

The influence of plasma shielding effect induced by ambient gas pressure and laser intensity on the laser-produced Cu plasma parameters, signal-to-background ratio (S/B) and expansion are experimentally and numerically investigated. A Q-switched Nd:YAG laser at 1064 nm at various intensities ranging from 2 to 7.1 GW/cm2 intensity (40–150 mJ) is used to produce Cu plasma in air, argon (Ar), helium (He), and neon (Ne) ambient gas at various pressures ranging from 5 to 1000 mbar. Laser-induced breakdown spectroscopy reveals that spectral radiation, S/B, electron temperature, number density, and front edge velocity of the plasma have an increasing trend up to a certain value of laser intensity and gas pressure. Afterwards, a saturation trend is achieved, which is attributed to the shielding and self-regulation effect. The numerical modeling of the laser-produced Cu plasma in the presence of air at atmospheric pressure is carried out using the MULTI radiation hydrodynamics code. We have shown that the feature of plasma shielding effect observed in the experiments can be reproduced using a continuum hydrodynamics model. Laser intensity at about 3.5 GW/cm2 is found to produce the highest S/B at 1000 mbar air. He, Ne, air, and Ar show the best S/B, respectively and the best S/B is found for air, Ar, He, and Ne at 10, 5, 10, and 20 mbar, respectively. The expansion of plasma plume is studied using a simple and effective technique based on probe laser absorption and scattering method. The plasma plume expansion through He, Ne, air, and Ar at 1000 mbar pressure has the highest velocity, respectively. The simulated results of strong shock wave model and Rankine–Hugoniot jump condition are fitted to the experimental data, which are then used to estimate the values of the ablation parameters.

The overview of the recent results for discovery and investigations of a very exotic phenomenon – optical mirage in the X-ray spectral range – is presented. It was found that the mirage could be created in the form of coherent virtual point source, emerging in the vicinity of the second plasma in two-stage oscillator-amplifier X-ray laser. The X-ray source-mirage, rigidly phased with the initial radiation of generator, occurs only when amplification takes place in the amplifier plasma and leads to the appearance of the interference pattern in the form of concentric rings in the spatial profile of the output X-ray laser beam. The equation describing the emergence of X-ray mirage was found, numerical solution of which shows that its formation is similar to that of the optical mirages observed at propagation of light rays through an inhomogeneously heated air. Obtained results have already demonstrated novel comprehension into the physical nature of amplification of X-ray radiation, opening additional opportunities for X-ray interferometry, holography, and other applications, which require multiple rigidly phased sources of coherent radiation.

The paper is a continuation of research carried out at Prague Asterix Laser System (PALS) related to the shock ignition (SI) approach in inertial fusion, which was carried out with use of 1ω main laser beam as the main beam generating a shock wave. Two-layer targets were used, consisting of Cu massive planar target coated with a thin polyethylene layer, which, in the case of two-beam irradiation geometry, simulate conditions related to the SI scenario. The investigations presented in this paper are related to the use of 3ω to create ablation pressure for high-power shock wave generation. The interferometric studies of the ablative plasma expansion, complemented by measurements of crater volumes and Kα emission, clearly demonstrate the effect of changing the incident laser intensity due to changing the focal radius on efficiency of laser energy transfer to a shock wave and fast electron emission. The efficiency of the energy transfer increases with the radius of the focused laser beam. The pre-plasma does not significantly change the character of this effect. However, it unambiguously results in the increasing temperature of fast electrons, the total energy of which remains very small (<0.1% of the laser energy). This study shows that the optimal radius from the point of view of 3ω radiation energy transfer to the shock wave is the maximal one used in these experiments and equal to 200 µm that corresponds to the minimal effect of two-dimensional (2D)-expansion. Such a result is typical for the ablation process determined by electron conductivity energy transfer under the conditions of one-dimensional or 2D matter expansion without any appreciable effect due to energy transfer by fast electrons. The 2D simulations based on application of the ALANT-HE code and an analytical model that includes generation and transport of hot electrons has been used to support of experimental data.

Experimental data are presented showing maximum carbon C6+ ion energies obtained from nm-scaled targets in the relativistic transparent regime for laser intensities between 9 × 1019 and 2 × 1021 W/cm2. When combined with two-dimensional particle-in-cell simulations, these results show a steep linear scaling for carbon ions with the normalized laser amplitude a0 ($a_0 \propto \sqrt ( I)$). The results are in good agreement with a semi-analytic model that allows one to calculate the optimum thickness and the maximum ion energies as functions of a0 and the laser pulse duration τλ for ion acceleration in the relativistic-induced transparency regime. Following our results, ion energies exceeding 100 MeV/amu may be accessible with currently available laser systems.

The effect of laser intensity on characteristics of the plasma ablated from a low-Z (CH) planar target irradiated by a 250 ps, 0.438 µm laser pulse with the intensity of up to 1016 W/cm2 as well as on parameters of the laser-driven shock generated in the target for various scale-lengths of preformed plasma was investigated at the kilojoule Prague Asterix Laser System (PALS) laser facility. Characteristics of the plasma were measured with the use of 3-frame interferometry, ion diagnostics, an X-ray spectrometer, and Kα imaging. Parameters of the shock generated in a Cl doped CH target by the intense 3ω laser pulse were inferred by numerical hydrodynamic simulations from the measurements of craters produced by the shock in the massive Cu target behind the CH layer. It was found that the pressure of the shock generated in the plastic layer is relatively weakly influenced by the preplasma (the pressure drop due to the preplasma presence is ~10–20%) and at the pulse intensity of ~1016 W/cm2 the maximum pressure reaches ~80–90 Mbar. However, an increase in pressure of the shock with the laser intensity is slower than predicted by theory for a planar shock and the maximum pressure achieved in the experiment is by a factor of ~2 lower than predicted by the theory. Both at the preplasma absence and presence, the laser-to-hot electrons energy conversion efficiency is small, ~1% or below, and the influence of hot electrons on the generated shock is expected to be weak.

This paper reports on properties of a plasma formed by sequential action of two laser beams on a flat target, simulating the conditions of shock-ignited inertial confinement fusion target exposure. The experiments were performed using planar targets consisting of a massive copper (Cu) plate coated with a thin plastic (CH) layer, which was irradiated by the 1ω PALS laser beam (λ = 1.315 μm) at the energy of 250 J. The intensity of the fixed-energy laser beam was scaled by varying the focal spot radius. To imitate shock ignition conditions, the lower-intensity auxiliary 1ω beam created CH-pre-plasma which was irradiated by the main beam with a delay of 1.2 ns, thus generating a shock wave in the massive part of the target. To study the parameters of the plasma treated by the two-beam irradiation of the targets, a set of various diagnostics was applied, namely: (i) Two-channel polaro-interferometric system irradiated by the femtosecond laser (~40 fs), (ii) spectroscopic measurements in the X-ray range, (iii) two-dimensional (2D)-resolved imaging of the Kα line emission from Cu, (iv) measurements of the ion emission by means of ion collectors, and (v) measurements of the volume of craters produced in a massive target providing information on the efficiency of the laser energy transfer to the shock wave. The 2D numerical simulations have been used to support the interpretation of experimental data. The general conclusion is that the fraction of the main laser beam energy deposited into the massive copper at two-beam irradiation decreases in comparison with the case of pre-plasma. The reason is that the pre-formed and expanding plasma deteriorates the efficiency of the energy transfer from the main laser pulse to a solid part of the targets by means of the fast electrons and the wave of an electron thermal conductivity.

We investigated the expansion dynamics of laser-produced plasmas expanding into an axial magnetic field. Plasmas were generated by focusing 1.064 μm Nd:YAG laser pulses onto a planar tin target in vacuum and allowed to expand into a 0.5 T magnetic field where the field lines were aligned along the plume expansion direction. Gated images employing an intensified charge-coupled device showed focusing of the plasma plume, which were also compared with results, obtained using particle-in-cell modeling methods. The estimated density and temperature of the plasma plumes employing emission spectroscopy revealed significant changes in the presence and absence of the 0.5 T magnetic field. In the presence of the field, the electron temperature is increased with distance from the target, while the density showed opposite effects.

In this work, plasma is produced by irradiating a Ti target with 10 ns pulsed Nd:YAG (λ = 1064 nm) laser. The laser fluence at the target was varied in the range of 2–20.3 J/cm2. The ion signal from freely expanding Ti plasma in vacuum was characterized with the help of ion collector and time-of-flight electrostatic energy analyzer. The ion charge state was found to increase with the laser fluence and maximum available ion charge in this fluence range is Ti4+. A correlation between the intensities of various ion charge states was observed, which indicates that higher charge states are most probably produced through stepwise ionization mechanism. It is also observed that charge state distribution of plasma can be controlled by variation of the laser fluence. In addition, energy distribution of ion charge states Tin+ (n = 1–4) is measured by varying back plate voltage of the electrostatic energy analyzer for a fixed laser fluence of 20.3 J/cm2. Ions energy distributions were in the range of 0.36–3.0 keV and the most probable ion energy was found to increase linearly with ion charge state. The estimated equivalent potential at the laser fluence of 20.3 J/cm2 is about 310 V. These results are in good agreement with the predictions of electrostatic model of ion acceleration in laser plasma.