A phase-retrieval-based 4-dimensional diagnostic method is proposed to resolve the spatial and temporal evolution of plasma in air induced by ultrafast laser. The plasma evolution dynamics (from generation to relaxation) were temporally resolved across several hundred picoseconds, spanning 3 orders of magnitude in measurable electron density (10 15 to 10 18 cm −3 ). The proposed method provides comprehensive, microscopic, and instantaneous insight into the underlying physical mechanisms of nonlinear phenomena induced by femtosecond filament.

High aspect ratio holes in nickel-based alloys have significant applications in the film cooling of aircraft turbine engines. The high inlet temperature (>2200 degrees C) of the next generation turbine engine imposes stringent requirements on the cooling efficiency of its hot components such that the commercial macro-hole cooling with cooling efficiency <= 60% cannot meet the requirements. Micro cooling holes with diameter of similar to 0.1 mm are proposed to generate up to 90% cooling efficiency. However, current processing techniques face challenges of inefficient debris removal and debris redeposition on the inner walls, making it difficult and inefficient to fabricate high aspect ratio holes with diameters <= 0.1 mm. In this work, an aerosol assisted laser spinning method is proposed to fabricate free tapered or reverse tapered holes with diameters <= 0.1 mm and aspect ratios >= 20 in nickel-based alloys. The aerosol modulates the laser intensity distribution and the hole's perforation time is reduced by 35.6%. This study provides a cost-effective drilling efficiency improvement method for fabricating high aspect ratio micro-holes in opaque materials with broad applicability, particularly in processing micro cooling holes in turbine engines.

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.

The use of circularly polarized high-peak-power ultrashort pulses has various applications in extreme field science. Commonly used quarter-wave plates are unsuitable here, while multi-mirror schemes are technically complicated. We have demonstrated that simple PET film, 20.5µm thick, can be used to manipulate the polarization state of the high-peak-power beam and achieve ellipticity of up to 0.8 with negligible nonlinear phase distortion. Furthermore, the film can withstand 103 shots at an intensity of I=3⋅1012W/cm2 without sustaining visible damage. Thus, PET film is suitable for long-term use in a PW laser system, with a 20 cm beam diameter. We confirmed this experimentally by measuring the angular distribution of the second harmonic from the plasma channel created in an undercritical gas plume, with a 1 TW femtosecond Ti:Sa laser.

We demonstrate that amplitude modulation of a high-power femtosecond laser pulse allows to change fundamentally frequency-angular structure of the supercontinuum formed during the filamentation in both molecular and atomic gases. Particularly, modulation with a 4-hole mask strongly suppresses conical emission in the anti-Stokes wing of pulse spectrum with simultaneous enhancement in the Stokes band. We explain this phenomenon as a joint effect of diffraction, self-phase modulation and temporal pulse splitting of interfering beamlets formed by the modulation mask. Our results pave a way for tailoring the frequency-angular structure of filament-generated supercontinuum.

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.

We had numerically studied electron acceleration in the interaction of a terawatt laser pulse with a long-scale target with density approximately $10 \%$ of critical value. Based on PIC simulations, the mechanism of electron acceleration was found to be a combination of direct laser acceleration and laser wakefield acceleration. With the increase in pulse energy, a collimated electron beam with 1 nC charge can be obtained.

An O-shaped structure at wavelengths of 930–960 nm in the frequency–angular spectrum of the supercontinuum generated during the filamentation of a femtosecond laser pulse with a central wavelength of 740 nm on a 75-m path in air has been observed experimentally. This feature of the frequency–angular spectrum is due to the presence of the absorption band of water vapor in the range of 930–960 nm and the anomalous dispersion region associated with this absorption. This result opens prospects for the remote single-pulse detection of impurities in air.

We measured and simulated the spectrally resolved angular distributions of 0.3–1-THz emission from the two-color filament with its plasma length (∼40 mm) exceeding the dephasing length (∼25 mm) between the fundamental (740 nm) and the second harmonic (370 nm) pulses in air. We show that only the forwardly propagating on-axis terahertz (THz) radiation is sensitive to the variation of the phase offset φ between fundamental and second harmonics, while the ring-like THz beam carrying ≳80% of the overall THz yield is independent of φ. Utilization of the THz ring allows one to omit the tedious adjustment of the frequency-doubling crystal position in the experiment.

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.

We present a method for studying the dynamics of electron acceleration, based on interrupting the acceleration process by the shock wave front created by an additional nanosecond laser pulse. Experimentally obtained electron spectra at various stages of acceleration are provided, as well as confirming results from PIC modeling.

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.

A method for plasma channel characterization by optical plasma radiation was developed. The electron density of the unperturbed plasma was obtained from the backward stimulated Raman scattering spectrum, and the phase velocity of laser pulse inside the plasma channel was calculated from the second harmonic radiation angle.

The generation of high-power short laser pulses of ultrarelativistic intensity (over 10 20 W/cm 2 ) using the XCELS [1] infrastructure and their application to solve problems of laser-plasma interaction and acceleration of charged particles, as well as problems of quantum electrodynamics, require correct diagnostics of the laser pulse parameters in the interaction region upon sharp focusing. An approach is proposed for measuring the key parameters of the XCELS beam, such as its size in the caustic and the peak laser intensity. The proposed method is based on using the process of vacuum acceleration of charged particles—electrons and protons—from the focal volume. When using the distribution of the laser pulse fields near the focus using the Stratton-Chu diffraction integrals and the test particle method, the characteristics of accelerated electrons and ions (for example, the energies of accelerated particles and their emission angles) can be accurately quantified. The latter allows us to offer a practically accessible experimental method for diagnosing radiation in a single laser shot and the design of the XCELS experiment.

The interaction between a laser pulse with a peak power of 15 PW and a solid film target in the reflection and transmission regimes has been numerically studied. Frequency–angular radiation spectra in the THz range have been obtained and the parameters of accelerated electrons have been determined for these cases. The dimensionless strength of the THz field amounts to several units of a 0 , which may allow one to achieve relativistic intensities in the THz range after focusing.

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.