We propose an approach to stabilize the parameters of filament-generated infrared light bullet against pulse- to-pulse fluctuations in three domains: spectral, spatial and energy, by means of amplitude modulation of the initial laser beam. We studied the single-shot angle-wavelength spectra of filament-generated supercontinua for a beam modulated by a four-hole opaque mask and a beam without additional modulation. We demonstrated that amplitude modulation of the initial beam improves the bullet pulse-to-pulse stability in all the three domains with the bullet energy stability reaching as high as fivefold enhancement.

A method of wide-range X-ray and electron spectrometry of plasma formed by a femtosecond laser pulse with a peak intensity of over 1018 W/cm2 on the surface of a solid-state target is experimentally considered. Measurements of a flow of charged particles and quanta were carried out using thermoluminescent detectors based on LiF(Mg, Ti) that accumulate a dose, in front of which magnets were additionally installed to isolate the X-ray component. The spectra were obtained on the basis of the method for determining the accumulated dose of a detector depending on the thickness of the filter installed in front of it. The data have been restored in the range from 10 keV to several megaelectronvolts. The “temperatures” of the hot electron components of laser plasma have been determined, which are 160 and 1500 keV and may be related to the effects of particle acceleration in the dense-plasma region, as well as the temperatures during propagation of radiation in a cloud of subcritical density.

We propose a novel method for changing the length of laser wakefield electron acceleration in a gas jet using a cylindrical blast-wave created by a perpendicularly focused nanosecond laser pulse. The shock front modifies the wake significantly and stops interaction between the laser pulse and accelerated electron bunch, allowing one to directly control the interaction length and avoid dephasing. It also improves the electron beam quality through the plasma lensing effect between the two shock fronts. We demonstrated both experimentally and numerically how this approach can be used to form a quasimonoenergetic electron bunch with controlled energy and improved divergence as well as tracking changes in the bunch parameters during acceleration.

We report the results of experimental and computational studies on the formation of electron beams by ultrashort terawatt laser pulses. Various acceleration regimes—direct laser acceleration (DLA), laser wake field acceleration (LWFA), and hybrid variants—are discussed. A possibility of controlling the processes occurring during such interactions with an additional nanosecond laser pulse is demonstrated: formation of a plasma with the required density and profile, change in the electron beam emission direction, and improvement of the beam emittance. Possible applications of such tabletop accelerators in the study of photonuclear processes, for the generation of unipolar pulses of extreme amplitude in the terahertz range of the spectrum, etc., are discussed.

The simultaneous laser-driven acceleration and angular manipulation of the fast electron beam is experimentally demonstrated. The bunch of multi-MeV energy charged particles is generated during the propagation of the femtosecond laser pulse through the near-critical plasma slab accompanied by plasma channeling. Plasma is formed by the controlled breakdown of a thin-tape target by a powerful nanosecond prepulse. The electron beam pointing approach is based on the refraction of a laser pulse in the presence of a strong radial density gradient in the breakdown of the tape with a small displacement of the femtosecond laser beam relative to the breakdown symmetry axis. A shift of several micrometers makes it possible to achieve beam deflection by an angle up to 10 degrees with acceptable beam charge and spectrum conservation. This opens up opportunities for in-situ applications for scanning objects with an electron beam and the multistage electron beam energy gain in consecutive laser accelerators without bulk magnetic optics for particles. Experimental findings are supported by numerical Particle-In-Cell calculations of laser-plasma acceleration and hydrodynamic simulations.

Various methods and approaches of efficient bunched high energy particles accelerations are discussed with the use of few terawatt-class lasers interacting with tailored under-critical plasma.

Generation of a collimated electron bunch with energy of a few MeV is demonstrated experimentally during propagation of 1 TW 10 Hz femtosecond laser radiation through a near-critical plasma formed from a micrometer-scale liquid jet (ethanol) target by ablation and boring with an intense nanosecond pulse. Hydrodynamic and particle-in-cell simulations reveal the evolution of the plasma cloud and help to identify the acceleration mechanism, which is related to self-modulated laser Wakefield acceleration during nonlinear propagation of laser radiation through plasma. The measured bunch divergence is at the level of 0.04 rad with high shot-to-shot stability. The total charge of the particles with energy above 1.6 MeV was estimated at similar to 15 pC. The simplicity and robustness of the target design allows for enhanced pulse repetition rate with suppressed debris formation.

We demonstrate that modulation of the initial beam by a simple four-hole amplitude mask allows to enhance pulse-to-pulse stability of the red wing of filament-generated supercontinuum. In particular, we focus our attention on the spectral position and width, angular coordinate and energy of the brightest red-shifted maximum in the spectrum of a loosely-focused filament in air. This maximum, corresponding to a Raman bullet, bears about $40 \%$ of the initial pulse energy and is of interest for applications. The enhancement in pulse-to-pulse stability of the bullet parameters reaches 1.7 times for the bullet spectral position and width, 3.4 times for its angular position and 4.5 times for its energy.

Results of experimental investigation of charged particles generation and X-ray emission under relativistic interaction of laser pulse with $\left(\mathrm{C}_{2} \mathrm{H}_{6}\right) \mathrm{N}$ clusters are presented. Energy spectra of protons, ions and electrons are examined, revealing few hundreds of MeV particles.

We observed huge, almost two orders of magnitude, increase in the energy of the forward terahertz (THz) emission by the long femtosecond filament if transverse electrostatic field is applied along its full length. This proves summation of emission both from different parts of a single filament and from multiple filaments. The observed THz radiation has a narrow angular shape with a maximum in the direction of laser radiation and a spectrum in the range of 0.05–0.3 THz with a maximum at about 0.1 THz. Numerical simulations based on the UPPE well explain the experimental findings.

Compact laboratory neutron sources play a crucial role in both fundamental physical research and practical applications, such as neutron radiography and spectroscopy. One of the most promising strategies to develop such a source is the use of laser-plasma accelerators of electrons or ions and the subsequent initiation of nuclear reactions (γ,n), (p,n), or (d,n) with the release of neutrons. In this study, we propose a neutron source based on (γ,n) photodisintegration reactions and characterize it using an electron beam from a 1‑TW laser-plasma accelerator. The maximum neutron flux reaches 105 neutrons/s srad at a laser-radiation efficiency of 106 neutrons/J. While maintaining efficiency and increasing the energy of the laser pulse by a factor of 10, the neutron flux becomes sufficient for several applications. To investigate neutron production using electron beam parameters measured in experiments, we conduct numerical Monte Carlo simulations. Recording the number of neutrons generated in an experiment can be used to estimate the charge and average energy of accelerated electrons. The simulation results show good agreement with values measured by standard beam-diagnostic tools, confirming the accuracy of our approach.

The X-ray emission of relativistic laser plasma was investigated in the spectral range from XUV to gammas by a set of detectors and techniques. Thermal and hot electron components generation was studied in dependence of the peak laser intensity and contrast of the laser pulse.

Generation of terahertz (THz) radiation in the interaction of laser pulse with intensity ∼5 × 10 18 W cm −2 with a controlled preplasma, created by an additional laser pulse interacting with a 16 μ m film target, was studied. The mechanism of generation of THz radiation in the frequency range 1–5 THz was found to be coherent transition radiation of accelerated electrons transversing the rear plasma-vacuum boundary. Angular distribution of the THz radiation changes with the delay between main pulse and prepulse due to different regimes of electron acceleration, while THz radiation spectrum reflects the spatial size of the preplasma cloud and may be used for diagnostics purposes. THz radiation energy reaches ∼0.1 mJ in 1–5 THz spectral range, corresponding to 0.2% conversion efficiency, and increases linearly with laser pulse energy.

The high charge electron beam is generated at interaction of 1 TW laser pulse with gas target tailored by nanosecond prepulse forming a shock wave. Propagation of intense femtosecond pulse through complex plasma slab accelerates electrons up to 10 MeV. The debris free target has potential to kHz laser application and electrons energy enhancement using more powerful femtosecond laser pulse.

A new approach is proposed to form a jet with submicron aggregates for femtosecond laser neutron generation under nonlinear interaction with relativistically intense laser pulse. Aggregates are formed through the rapid expansion into vacuum of the supercritical mixture of CO 2 + CD 3 OD (3:1). For the first time, fusion neutrons (2.45 MeV) with a peak output of 3 × 10 3 neutron/pulse/4 π and efficiency of 6 × 10 4 neutron J −1 were obtained under interaction of Ti:Sa laser pulse having 3 × 10 18 W cm −2 intensity with submicron aggregates produced from supercritical CO 2 + CD 3 OD mixture.

This paper presents results of experimental study of the stochastic and regularized filamentation of terawatt femtosecond radiation on a distances 1–40 m in the atmosphere. The robust array of femtosecond filaments were observed if the initial beam was modulated with four hole amplitude mask and each sub beam contains peak power in the certain range. The distance of a stable spatial structure formation was found to be much less than the value deduced from the Marburger formula. It was shown that the distance of filament array formation is determined by the laser radiation diffraction at each hole in the amplitude mask.

Multiple filament’s formation on a long atmospheric path was studied for an amplitude modulation of the terawatt femtosecond beam with the four and six hole masks. Filaments appeared at the distance that is determined by the Fresnel lens formed by a hole, not by the self focusing theory for the unrestricted (Gaussian like) beam. This lens focuses 1/3 of the energy passing through the hole to the beam spot ≈1 mm in diameter. The robust multifilament array 10–15 m in length was observed if the energy per hole was ≈1-1.5 mJ (pulse duration 50 fs), while each hole produces bundle of a few filaments at higher energies.

The effect of the size of the rods at the structured silicon target surface on the parameters of the plasma produced when the target is exposed to a high-contrast femtosecond laser pulse with an intensity of 2 × 10 18 W cm −2 is investigated. It is shown that irradiation of a target with subwavelength rods (∼ 100 nm in diameter) provides a significant (up to 250 keV) increase in the temperature of hot plasma electrons and their number in comparison with those obtained in the case of a plane target. It was found that in this case the yield of hard X-ray radiation increases several-fold. The observed effect can be attributed to increased absorption and particle motion in a complex field near plasma nonuniformities. It is shown that the presence of rods with a characteristic size of ∼ 1 μm promotes an increase in the production efficiency of multiply charged silicon ions. The result obtained is apparently associated with the radiation penetration between the rods and with collisional ionisation of particles as they fly into vacuum from deeper target layers.