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Femtosecond low-energy Laguerre – Gaussian pulses of tightly focused visible laser radiation were employed for single-pulse ablative nanostructuring of a 50-nm thick gold film. Similar pulses of lower energy were employed for the efficient plasmonic photoluminescence excitation of a rhodamine 6G dye monolayer in the fabricated nanostructures. The consistency between the shape and polarisation symmetries of the low-energy laser beam, on the one hand, and the gold nanostructures produced by the same beam at a high radiation energy, on the other hand, opens the way to consistent nanostructuring and surface-enhanced analytical spectroscopy with the use of nanostructures.

the experimental modeling of high-pressure He-Ar gas laser with transverse pumping by a diode laser array was carried out. The plasma-chemical rate constants of collisional quenching of 4s argon levels with argon and helium atoms in high-pressure laser mixtures were for the first time obtained.

Specific features of ablation of a thin silver film with a 1-mm-thick layer of a highly transparent photoresist and the same film without a photoresist layer under single tightly focused femto- second laser pulses in the visible range (515 nm) are experimentally investigated. Interference effects of internal modification of the photoresist layer, its spallation ablation from the film surface and formation of through hollow submicron channels in the resist with- out its spallation but with ablation of the silver film lying under the resist are found and discussed.

The specific features of photofragmentation of sols of gold nanoparticles under focused femtosecond laser pulses in IR (1030 nm) and visible (515 nm) ranges is experimentally investigated. A high photofragmentation efficiency of nanoparticles in the waist of a pulsed laser beam in the visible range (at moderate radiation scattering) is demonstrated; this efficiency is related to the excitation of plasmon resonance in nanoparticles on the blue shoulder of its spectrum, in contrast to the regime of very weak photofragmentation in an IR-laser field of comparable intensity. Possible mechanisms of femtosecond laser photofragmentation of gold nanoparticles are discussed.

We use an absorption probe method to study collisional quenching of the metastable 5 s ′ [1/2] 0 (3P0) Kr atom in electron-beam-excited high-pressure Ar–Kr mixtures with a small content of krypton. The rate constants for plasma-chemical reactions Kr* + Kr + Ar → Kr 2 * + Ar((5.3 ± 0.8) ⋅ 10− 33cm6/s), Kr* + 2 Ar → ArKr* + Ar ((4.6±1.4)·10−36 cm6/s) and Kr* + Ar → products + Ar ((4.1±0.6)·10−15 cm3/s) are measured for the first time.

The processes of collision quenching of the resonance 5s[3/2]1o(3P1) state of the krypton atom are studied by the absorption probe method in electron-beam-excited high-pressure He – Kr mixtures with a low content of krypton. The rate constants of plasmochemical reactions Kr* + Kr + He → Kr*2 + He [(4.21 ± 0.42) × 10-33 cm6 s-1], Kr* + 2He → HeKr* + He [(4.5 ± 1.2) × 10-36 cm6 s-1] and Kr* + He → products + He [(2.21 ± 0.22) × 10-15 cm3 s-1] are measured for the first time. The rate constants of similar reactions are refined for krypton in the metastable 5s[3/2]2o (3P2) state.

Thermocavitation instability of a molten layer on a silicon surface was experimentally revealed in the form of a microscale surface crown-like feature produced by multiple infrared or visible femtosecond laser pulses near the spallation threshold fluence. The number of crown spikes varied versus the crown perimeter, monotonically increasing with increasing laser shot number. The instability dynamics was described in terms of the intermediate crown structures (the spike number) using the proposed thermocavitation model based on the Kuramoto-Sivashinsky hydrodynamic equation.

The evolution of an ensemble of point defects (vacancies and interstitials) produced by irradiating a tritium-saturated titanium target (sorbent film on substrate) with deuterium is considered. It is shown that when the concentration of defects exceeds a certain critical value, the film undergoes transition into a quasiperiodic bent state with simultaneous clustering of defect aggregates at the relief extrema, spontaneously created at the film – substrate interface and at the film free surface. The aggregation of vacancies leads to the formation of pores. The subsequent deadherence or rapture of the film in the regions of large pores at the film – substrate interface leads to irreversible degradation of the target. We discuss the possibility of suppressing this effect by nanostructuring a laser-induced nanorelief at the substrate surface before the sorbent film deposition. Different types of such a relief are experimentally demonstrated.

Nanobumps and nanoholes have been formed in gold and silver films with various thicknesses on a dielectric substrate by strongly focused single nanosecond pulses of a Nd:YAG laser. An apertureless dielectric fiber probe and an aspherical lens with a numerical aperture of 0.5 were used to focus laser radiation into a diffraction-limited spot on the surface of gold and silver films, respectively. Atomic force and electron microscopy studies have demonstrated that the shape and dimension of nanostructures, as well as the threshold parameters of laser radiation for their formation, are determined by the thickness of a modified film (“size effect”) and by the duration of a laser pulse owing to the lateral heat conduction in films (nonlocal energy deposition effect). Mechanisms of the dynamic formation of such structures in metallic films by nanosecond laser pulses due to phase transformations of their material have been discussed.

Mechanisms of formation of sub- and micrometre-scale holes in thin silver and chromium films of variable thickness by tightly-focused single nanosecond IR laser pulses with fluences in the range of 10 – 104 J cm-2 are studied by means of optical and scanning electron microscopy. At the minimal fluences above 5 J cm-2, the micrometre (2 – 5 μm in radius) holes are produced in these films, accompanying the lateral heat conduction in the film during the pump laser pulse, cavitation at the metallic/glass interface and subsequent explosive removal of the molten film. At the fluences of ~1 – 10 kJ cm-2 much larger (20 – 40 μm in radius) holes are formed in the film as a result of its heating by the erosive surface microplasma through the lateral heat conduction in the film during the plasma lifetime of the order of a few microseconds. Finally, at the maximal fluences (well above 10 kJ cm-2), the submillimetre holes were produced in these films by intense shock waves, generated in the erosive microplasmas. The comparative analysis of the formation mechanisms for sub- and micrometrescale holes in the same thin metal films by the single nano- and femtosecond laser pulses is provided.

We set forth an improved technique for the investigation of collisional quenching in high-pressure rare-gas mixtures, which relies on the absorption probing measurements of the decay rates of the excited states of these gases in the afterglow of a fast electron beam discharge. We determined more precisely the rate coefficients of the plasmochemical reactions Xe* + Xe + Ar → Xe2* and Xe*+Ar → products + Ar for the metastable (6s[3/2]20) and resonance (6s[3/2]10) levels of atomic Xe investigated in our earlier work. The rate coefficients for the reactions Xe(6s[3/2]20) + 2Ar → ArXe* + Ar((7.2±1.4)×10-36 cm6 s-1) and Xe(6s[3/2]10) + 2Ar → ArXe*((5.3±2.4)×10-36 cm6 s-1) were measured for the first time.

A Tandem electroionization laser facility consisting of two lasers with identical 10-l volumes of the active regions and different types of electron guns is described. In the first laser, a gun with a cold pointed cathode is used with an electron-current density of 1.7 A/cm2 and a pulse duration of 5 μs. The second laser has a gun with a directly heated cathode and a controlled duration of the electron-beam pulse.

The collision deactivation of the metastable 5s[3/2]2o(3P2) state of krypton atoms is studied by the absorption probe method in electron-beam-excited high-pressure Ar—Kr mixtures with a low krypton content. The rate constants of plasma-chemical reactions Kr* + Kr + Ar → Kr2* + Ar [(4.1±0.4)×10-33 cm6 s-1] and Kr* + 2Ar → ArKr* + Ar (less than 10-35 cm6 s-1) are measured for the first time and the rate constant of the reaction Kr* + Ar → products + Ar [(3.8±0.4)×10-15 cm3 s-1] is refined.

The first stage of the petawatt excimer laser project started at the P.N. Lebedev Physical Institute, implements a development of multiterawatt hybrid GARPUN-MTW laser facility for generation of ultra-high intensity subpicosecond ultraviolet (UV) laser pulses. Under this project, a multi-stage e-beam-pumped 100-J, 100-ns GARPUN KrF laser was upgraded with a femtosecond Ti:Sapphire front-end, to produce combined subpicosecond/nanosecond laser pulses with variable time delay. Attractive possibility to amplify simultaneously short and long pulses in the same large-scale KrF amplifiers is analyzed with regard to the fast-ignition, inertial confinement fusion problem. Detailed description of hybrid laser system is presented with synchronized KrF and Ti:Sapphire master oscillators. Based on gain and absorption measurements at GARPUN amplifier and numerical simulations with a quasi-stationary code, we are predicting that 1.6 J can be obtained in a short pulse at hybrid GARPUN-MTW Ti:Sapphire/KrF laser facility, combined with several tens of joules in nanosecond pulse. Amplified spontaneous emission, which is responsible for the pre-pulse formation on a target, was also investigated: its acceptable level can be provided by properly choosing staged gain or loading the amplifiers by quasi-steady laser radiation. Fluorescence and transient absorption spectra of Ar/Kr/F2 mixtures conventionally used in KrF amplifiers were recorded to find out the possibility for femtosecond pulse amplification at the broadband Kr2F (42Γ → 1,2 2Γ) transition, which benefits in 100 times higher saturation energy density than for KrF (B → X) transition.

The possibility of designing a highly efficient particle buncher for a laser accelerator by modulating electron flow with the alternating polyharmonic field of a laser beam is considered, with the flow being subsequently bunched in a spatially variable potential. Expressions for electron velocity and time of motion through the buncher are obtained in kinematic approximation. A numerical simulation of the electron motion in the buncher's three-frequency field demonstrates the possibility of optimizing the amplitudes of harmonics, which allows a bunch ±9° in width to contain up to 71% of the particles within the flow. A design for an experiment using a CO2 laser and frequency multipliers for verifying the bunching mechanism considered is proposed.

High-pressure lasers with Penning depletion of lower laser levels on the 3p-3s transitions in neon pumped by a fast electron beam are studied. High-power lasing at 703.2 and 724.5 nm on transitions that were not investigated earlier is reported for the first time. The energy parameters of lasers pumped by an electron beam with a current density of 1.7 A cm-2 are optimised (including the 585.2-nm laser) and the lasing dynamics of these lasers, as well as the dynamics of the small-signal gain and induced ('hot') absorption gain are studied.

The method of absorption probing was used to investigate collisional deactivation of resonant (6s'[1/210]) and metastable (6s'[1/2]00) states of the Xe atom in high-pressure Ar—Xe mixtures with low Xe concentrations. The rate constants were determined for the following plasma-chemical reactions: Xe(6s') + Ar → Xe*+ Ar [(1–2) × 10-14 cm3 s-1], Xe(6s') + 2Ar → ArXe* + Ar (less than 10-35 cm6 s-1), and Xe( 6s') + Xe + Ar → Xe2* + Ar [(3–3) × 10-32 cm6 s-1].

The energy characteristics of high-pressure (up to 10 bar) electron-beam-pumped lasers were optimised. These lasers operated on the basis of the 3p—3s transitions in the Ne I atom resulting in the emission at the wavelengths λ = 585, 703, and 725 nm when the active medium was pumped by an electron beam with the current density 1.7 A cm-2 in the form of pulses of 5 μs duration. A record specific output energy of 0.15 J litre-1 (energy of 1.5 J) was achieved at the 725 nm wavelength. The pressure dependence of the spectral width of the laser radiation was determined at λ = 585 and 725 nm.

The method of direct laser probing was used to investigate the time dependences of the small-signal gain of the active media of lasers based on the 3p—3s transitions in the Ne I atom. These media were pumped by an electron beam with a current density 1.7 A cm-2. The amplitudes of the small-signal gain of optimised (in respect of the output energy) laser mixtures were 1.7×10-2 and 1.0×10-2 cm-1 at the wavelengths 725 and 585 nm, respectively.

The absorption probing method was used in an investigation of the collisional deactivation of the 3s(1P1, 3P0, 3P1, and 3P2) states of the Ne atom in pure Ne and in its mixtures with Ar, Kr, and Xe. The rate constants of the formation of Ne2* excimers in collisions of Ne*(3s) with two neon atoms, and the total Penning and associative ionisation rate constants of argon, krypton, and xenon were determined. An estimate was obtained of the upper limit of the rate constant of the intramultiplet relaxation of the 3s states in collisions with neon.

The absorption probing method was used to investigate collisional deactivation of the 6s[3/2]10(3P1) state of the xenon atom in high-pressure He ? Xe mixtures with a low xenon concentration. Measurements were made of the rate constants of the following plasma-chemical reactions: Xe* + Xe + He ? Xe2* + He [(2.1 ? 0.2) ? 10-32 cm6s-1], Xe* + 2He ? HeXe* + He (less than 10-35 cm6s-1), and Xe* + He ? products + He (less than 3 ? 10-15 cm3s-1).

Time-resolved fluorescence of Ar/Kr/F 2 mixtures and transient absorption spectra were measured at Berdysh preamplifier module of GARPUN KrF laser facility pumped by 50 A/cm 2 , 350 keV, 100 ns e-beam. The experiments pursued an aim to obtain additional data on KrF laser kinetics, in particular, on the formation of Kr 2 F molecules and their influence on the absorption and extraction of KrF laser radiation in large-scale amplifiers. A possibility of femtosecond laser pulses amplification at broad-band Kr 2 F (4 2 G→1,2 2 G) transition is discussed.

Hydrodynamic regimes of KrF laser interaction with solid and thin-film targets in atmospheric and reduced pressure air were investigated at high-energy GARPUN installation. These experiments were performed with 100-J, 100-ns laser pulses in planar focusing geometry and compared with numerical simulations with ATLANT code to verify the concept of laser-driven shock tube (LST), which could accelerate a gas to hypersonic velocity and produce strong shock waves (SW). Laser beam was focused by a prism raster optical system that provided very uniform intensity distribution at moderate laser intensities q 1 GW/cm 2 over a square spot of ~ 1-cm size. Dynamics of laser-produced plasma and SW in a surrounding gas were investigated by means of high-speed photo-chronograph and streak camera in combination with shadow or schlieren techniques, time and space resolved spectroscopy in a visible spectral range. Both experiments and simulations confirmed that target evaporation and blow-up of expanding plasma are the main mechanisms of UV laser-target interaction in a surrounding gas. Planar shock waves with velocities up to 7 km/s towards the laser beam were observed in a normal density air and up to 30 km/s in a rarefied air. Acceleration of thin CH films of 1 to 50- µ m thickness was investigated both in a free-expansion and plasma-confined regimes with the highest achieved velocities up to 4 km/s. The SW damping law in a free space in dependently on laser intensity and air pressure c ould be a pproximated by a power law x ~ t

The method of absorption probing was used to determine the temporal behaviour of transient absorption in the active media of Penning lasers based on the 3p—3s transitions in the Ne I atom. The pumping was provided by an electron beam and the current density was 1.7 A cm-2. The efficiency of coupling out of radiation from a cavity containing an optimised laser mixture could exceed 80% for the transitions resulting in the emission at the wavelengths λ = 585 and 725 nm, and 50% for the λ = 703 nm transition.

Time-resolved scintillation technique and absolutely calibrated thermo-luminescence dosimeters have been applied to characterize bremsstrahlung x-ray emission from a large-aperture GARPUN KrF laser module pumped in a transverse geometry by double-sided e-beams stabilized by pulsed magnetic field of 0.1 T. It was produced by electrons with ~300 keV kinetic energy, 50 A/cm2 current density, and 100 ns pulse duration when they passed from vacuum diodes through foil windows into laser chamber and were decelerated in a working gas. Regularization algorithm was developed to reconstruct the bremsstrahlung spectra using experimental data on x-ray transmission through different absorbers. The energy fluence of ionizing radiation escaped onto laser windows has been measured. It was shown that a long-term degradation of optical transmission due to bremsstrahlung x-ray irradiation should be taken into account for KrF laser application in Inertial Fusion Energy.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A study was made of a high-pressure pulsed laser utilizing 3d?4p transitions in the Ar atom and emitting at wavelengths of 1.27, 1.79, 2.08 and 2.40?. When a 10-liter He?Ar active mixture was pumped by a beam of fast electrons, the output energy was 0.8J and the laser efficiency was > 1%. The electron-beam-controlled excitation method was realized for the first time in the case of He?Ar and Ne?Ar mixtures and the output energy was 1.5J. A study was made of the spectral composition of the radiation as a function of the experimental conditions.

An investigation was made of the influence of the addition of helium on the lasing and amplifying characteristics of an electron-beam-pumped Ar—Xe laser emitting in the near-IR part of the spectrum. The efficiency of this laser was far from maximal when the pressure of the two-component laser mixture was ~1 bar and the electron current density had the maximum (in the present investigation) value j~1.4 A cm-2. A major improvement in the energy parameters was obtained by reducing the electron current density or by adding helium to the active medium. The results obtained were interpreted by compensation of the excess pump power as a result of a reduction in the rates of the processes of mixing of laser-active levels by electron collisions on lowering the secondary-electron concentration in the former case or as a result of electron cooling in collisions with light helium atoms in the latter case. A record (for electron-beam-pumped lasers) efficiency of 4.5% was achieved with a mixture of the Ar : Xe=200:1 composition at a pressure of 1 bar for j=0.2 A cm-2.