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Based on our experimental study of spectral characteristics of an improved compact CO laser system, the prospects of using such a laser system for solving urgent problems of atmospheric sounding were demonstrated. An increase in the number of laser lines due to intracavity generation of the second harmonic and sum-frequencies in a nonlinear zinc germanium phosphide (ZnGeP2) crystal enriches capabilities of the laser. It was shown that such a CO laser system with frequency conversion in ZnGeP2 crystal can be used for detection and measuring concentration of at least 14 minor natural and pollution gases components of the atmosphere. The advantages and disadvantages of various laser operation modes, and the prospects for using its radiation for atmospheric remote sensing in various spectral ranges are discussed.

Broadband sum frequency conversion of a slab RF discharge Q-switched CO laser system was performed with two BaGa2GeSe6 crystals resulting in its spectrum lying within 1.7–6.0 μm spectral range. The first BaGa2GeSe6 crystal was located in the CO laser cavity and operated as both CO laser sum frequency (second harmonic) generator and laser output coupler. Another BaGa2GeSe6 crystal was applied for external third harmonic generation, i.e. as sum frequency generator for fundamental CO laser radiation and its sum frequencies obtained within the cavity. Peak powers of fundamental CO laser radiation, its second and third harmonics were up to 4.7 kW, 100 W and 0.5 W, respectively.

Q-switched slab RF-discharge multiline CO laser with broadband frequency conversion in BaGa2GeSe6 and ZnGeP2 crystals was developed. The laser system operated within 2.5-6 μm wavelengths and it was tested for absorption measurement of atmosphere gases.

Analysis of experimental data obtained in study of cryogenic CO laser with glow discharge and cryogenic slab CO laser with RF discharge showed that oxygen concentration in laser mixture is much less than in initial gas mixture. With low oxygen content, ozone plays role of supplier of electrons in cryogenic discharge. Since ionization potential of ozone is somewhat higher than that of oxygen, and ozone quickly condenses on cold walls of cryogenic discharge, conversion of O2 to O3 is accelerated. In addition, in plasma-chemical reactions, ozone regenerates carbon monoxide after dissociation. Acceleration of ozone generation in cryogenic barrier discharge was experimentally demonstrated.

Different frequency conversion processes in the mid-IR were experimentally studied with slab RF discharge CO and CO2 lasers and various nonlinear crystals ZnGeP2, GaSe, BaGa2GeSe6, AgGaSe2 and PbIn6Te10 : second and third harmonic generation of CO laser; sum and difference frequency generation of CO and CO2 lasers. Mid-IR emission on hundreds of narrow spectral lines from 1.7 μm to 19.3 μm was obtained

Nonlinear frequency conversion of broadband mid-IR radiation of different molecular gas lasers by various nonlinear crystals converting their multi-line emission into broadband radiation on sum and difference frequencies within ∼ 1.7 – 17 micron is discussed.

Q-switched cryogenically cooled slab RF discharge CO laser operating in multi-line mode, single-line mode with a diffraction grating, and also with frequency selection by special spectral filters situated both outside and inside the laser cavity was experimentally studied. Characteristics of CO lasing on individual ro-vibrational spectral lines produced by this laser with various cavities under the same active medium and pump parameters were compared. Application of output couplers with a relatively narrow spectral band of high transmittance compared to the non-selective CO laser range of operation, but with high reflection in the rest of the range, was effective for obtaining narrow-band multiline lasing. For selection of the long-wave part of Q-switched CO laser spectrum, which was needed for frequency conversion into the long-wave mid-IR when mixing with CO2 laser emission, application of a broadband spectral filter with a very low reflection coefficient in the spectral range where lasing was necessary to be suppressed (sort of a step function) proved to be efficient being installed outside the laser cavity.

Super-broadband mid-IR laser systems are under development in the Gas Lasers Lab of the Lebedev Physical Institute. These systems consist of different sorts of molecular gas lasers and various nonlinear crystals converting multi-line emission of those lasers into broadband radiation on sum and difference frequencies. As frequency converters, both main mid-IR nonlinear crystals such as ZnGeP2, GaSe, AgGaSe2 and new ones such as BaGa2GeSe6, PbIn6Te10 are applied. As radiation sources, repetitively-pulsed Q-switched lasers pumped by both longitudinal DC discharge and transverse slab RF discharge emitting microsecond pulses, and also actively mode-locked e-beam sustained discharge lasers emitting nanosecond pulses are applied. It was experimentally demonstrated for the developed laser systems to emit broadband radiation on hundreds spectral lines covering mid-IR range from ~1.7 to ~17 micron due to sum and difference frequency generation including third harmonic generation.

Mode-locking with an acousto-optic modulator was for the first time demonstrated for a repetitively pulsed (150 Hz) slab RF discharge CO2 laser. The mode-locked CO2 laser emitted trains of 5.5 ns pulses following with 27.25 MHz repetition rate. Mode-locking also affected the laser pulses envelope in respect to free-runing mode. The numerical estimation of the laser system scalability indicated an opportunity to develop a very compact CO2 laser emitting sub-nanosecond pulses.

Q-switched repetitively pulsed cryogenic slab RF discharge CO laser output characteristics (its spectrum, peak power and pulse duration) were studied for various active medium compositions and pump pulse energies. It was found that small addition of N2 increased output peak power at the same other parameters. The highest peak power of this CO laser facility ~ 4 kW was obtained for gas mixture CO:O2:N2:He with O2:N2 concentration ratio 1:4 as about in the atmospheric air. It was shown that the atmospheric air as the active gas mixture component can be applied instead of pure nitrogen and oxygen without the laser peak power loss.

Surface topography, phase composition and compressive residual stresses were characterized in surface layers of α + β titanium alloys VT6 (Ti–6Al–4V) and VT16 (Ti–3Al–4.5V–5Mo) nanotextured by 744-nm, 120-fs-laser pulses. The relative content of β-phase, along with the residual compressive stresses, increases significantly in both these materials over the depth ~0.2 μ in the nanotextured surface layer comprised by nanograins and remains almost unchanged at higher depths of 1–2 μ in bulk. The laser-driven α → β phase transformation is related to the combined effect of ultrafast heating/cooling, strong (multi-GPa) shock waves, chemical segregation and nanograin formation induced during the ablative surface nanotexturing.

Thin aluminum film homogeneously heated by intense IR femtosecond laser pulses exhibits on the excitation timescale consequent fluence-dependent rise and drop of the IR-pump self-reflectivity, followed by its final saturation at higher fluences F > 0.3 J/cm2. This prompt optical dynamics correlates with the initial monotonic increase in the accompanying laser-induced electron emission, which is succeeded by its non-linear (three-photon) increase for F > 0.3 J/cm2. The underlying electronic dynamics is related to the initial saturation of IR resonant interband transitions in this material, followed by its strong instantaneous electronic heating via intraband transitions during the pump pulse resulting in thermionic emission. Above the threshold fluence of 0.3 J/cm2, the surface electronic heating is balanced during the pump pulse by simultaneous cooling via intense plasma removal (prompt ablation). The relationship between the deposited volume energy density in the film and its prompt electronic temperature derived from the self-reflection measurements using a Drude model, demonstrates a kind of electron “liquid–vapor” phase transition, driven by strong cubic optical non-linearity of the photo-excited aluminum.

Difference frequency generation under mixing of repetitively-pulsed CO- and CO2-laser radiation in AgGaSe2, BaGa2GeSe6 and PbIn6Te10 nonlinear crystals was studied. Efficiency and refractive indices were examined for this frequency conversion into the long-wave domain of ∼12-20 µm in the mid-IR. The highest frequency conversion efficiency of 10-4 was obtained for a relatively new PbIn6Te10 crystal, which is an order of magnitude higher than previous results.

We have developed a new method for manipulating nanotopology and chemical composition of titanium surfaces by a scanning femtosecond laser beam with an asymmetrical spatial fluence distribution. Using of a common Gaussian laser beam leads to formation of combined nano- and micro-scale surface topologies owing to superimposition of different laser beam parts during the surface scanning. In contrast, beam shaping results in presumable surface structuring at specific laser fluences yielding in “clean” surface structures. In a simple case, cutting of a half beam perpendicular to the scanning direction enables to eliminate surface nanotopology, leaving less oxidized, cleaner and smoother microspikes, just by changing the scanning direction. Optimal experimental conditions were revealed to obtain in air the topologically and chemically different surface structures using the asymmetrical femtosecond laser beam and the opposite scanning directions.

The space-time dynamics of thermal melting, subsurface cavitation, spallative ablation, and fragmentation ablation of the silicon surface excited by single IR femtosecond laser pulses is studied by timeresolved optical reflection microscopy. This dynamics is revealed by monitoring picosecond and (sub)nanosecond oscillations of probe pulse reflection, which is modulated by picosecond acoustic reverberations in the dynamically growing surface melt subjected to ablation and having another acoustic impedance, and by optical interference between the probe pulse replicas reflected by the spalled layer surface and the layer retained on the target surface. The acoustic reverberation periods change during the growth and ablation of the surface melt film, which makes it possible to quantitatively estimate the contributions of these processes to the thermal dynamics of the material surface. The results on the thermal dynamics of laser excitation are supported by dynamic measurements of the ablation parameters using noncontact ultrasonic diagnostics, scanning electron microscopy, atomic force microscopy, and optical interference microscopy of the modified regions appearing on the silicon surface after ablation.

Nanostructured near-IR antireflective layer was produced on a GaAs slab surface by direct femtosecond laser fabrication of a surface diffraction grating. The single nanostructured layer on the GaAs slab reduces its total reflection at the wavelength λ ≈ 2.5 μm by 42 %, in agreement with the second-order approximation of the effective medium theory, with negligible increase of its absorbance.

Compact repetitively pulsed cryogenically cooled slab RF discharge CO laser with double path V-type laser resonator equipped with external Q-switch system based on rotating mirror was developed and studied. The laser produced IR (λ∼5–6 μm) radiation pulses of −1+2 μs duration (FWHM), peak power up to ∼3 kW and pulse repetition rate up to 130 Hz. Averaged output laser power reached 0.4 W, the laser spectrum consists of ∼80 simultaneously generating laser lines with individual peak power up to 80 W.

Color marking of rough or smooth metal (Al, Cu, Ti) and semiconductor (Si) surfaces was realized via femtosecond laser fabrication of periodic surface nanorelief, representing one-dimensional diffraction gratings. Bright colors of the surface nanorelief, especially for longer electromagnetic wavelengths, were provided during marking through pre-determined variation of the laser incidence angle and the resulting change of the diffraction grating period. This coloration technique was demonstrated for the case of silicon and various metals to mark surfaces in any individual color with a controllable brightness level and almost without their accompanying chemical surface modification.

Femtosecond laser nanostructuring at low fluences produces a onedimensional quasiperiodic grating of grooves on an aluminum surface with a period (≈0.5 μm) that is determined by the length of a surface elec� tromagnetic wave. The structure of the grooves of the surface nanograting is formed by regular nanopeaks fol� lowing with a period of about 200 nm. Some nanopeaks manifest craters at their tops. It is suggested that nanopeaks are formed due to the frozen nanoscale spallative ablation of a nanolayer of an aluminum melt in quasiperiodic regions corresponding to interference maxima of the laser radiation with the surface electro� magnetic wave. The periodicity of the appearance of nanopeaks along grooves is due to the previously pre� dicted mechanism of cavitation deformation of the melt surface in the process of macroscopic spallation ablation. However, in this case, cavitation is coherent (similar to a nearcritical spinodal decay) rather than spontaneous. DOI: 10.1134/S0021364011160065

Superstrong shock waves of multimegabar level generated during ablation of an aluminum surface by intense (

One-dimensional quasi-periodic nanogratings with spacings in the range from 160 to 600 nm are written on a dry or wet titanium surface exposed to linearly polarized femtosecond IR and UV laser pulses with different surface energy densities. The topological properties of the obtained surface nanostructures are studied by scanning electron microscopy. Despite the observation of many harmonics of the one-dimensional surface relief in its Fourier spectra, a weak decreasing dependence of the first-harmonic wavenumber (nanograting spacing) on the laser fluence is found. Studies of the instantaneous optical characteristics of the material during laser irradiation by measuring the reflection of laser pump pulses and their simulation based on the Drude model taking into account the dominant interband absorption allowed us to estimate the length of the excited surface electromagnetic (plasmon-polariton) wave for different excitation conditions. This wavelength is quantitatively consistent with the corresponding nanograting spacings of the first harmonic of the relief of the dry and wet titanium surfaces. It is shown that the dependence of the first-harmonic nanograting spacing on the laser fluence is determined by a change in the instantaneous optical characteristics of the material and the saturation of the interband absorption along with the increasing role of intraband transitions. Three new methods are proposed for writing separate subwave surface nanogratings or their sets by femtosecond laser pulses using the near-threshold nanostructuring, the forced adjustment of the optical characteristics of the material or selecting the spectral range of laser radiation, and also by selecting an adjacent dielectric.

The propagation of focused femtosecond laser pulses with supercritical peak powers in air has been investigated by the methods of optical visualization, profilometry, and calorimetry. Laser pulses with supercritical powers create a bundle of submillimeter filaments with a diameter of about 5 µm ahead of the lens focus; the maximum number of filaments in the beam cross section and their length increase linearly and sublinearly, respectively, with the radiation peak power. The optical visualization and calorimetry indicate that the plasma channels of filaments are optical contrast (a plasma density of 1018–1019 cm−3), ensuring the refraction of laser radiation incident on them.

One-dimensional quasiperiodic structures whose period is much smaller than the wavelength of exciting radiation have been obtained on a titanium surface under the multipulse action of linearly polarized femtosecond laser radiation with various surface energy densities. As the radiation energy density increases, the one-dimensional surface nanorelief oriented perpendicularly to the radiation polarization evolves from quasiperiodic ablation nanogrooves to regular lattices with subwave periods (100–400 nm). In contrast to the preceding works for various metals, the period of lattices for titanium decreases with increasing energy density. The formation of the indicated surface nanostructures is explained by the interference of the electric fields of incident laser radiation and a surface electromagnetic wave excited by this radiation, because the length of the surface electromagnetic wave for titanium with significant interband absorption decreases with an increase in the electron excitation of the material.

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 obtaining a high specific input energy in an electron-beam sustained discharge ignited in oxygen gas mixtures O2 :A r :C O (or H2) at the total gas pressures of 10–100 Torr was experimentally demonstrated. The specific input energy per molecular component exceeded ∼ 6k J l −1 atm −1 (150 kJ mol −1 ) as a small amount of carbon monoxide was added into a gas mixture of oxygen and argon. It was theoretically demonstrated that one might expect to obtain a singlet delta oxygen yield of 25% exceeding its threshold value needed for an oxygen–iodine laser operation at room temperature, when maintaining a non-self-sustained discharge in oxygen gas mixtures with molecular additives CO, H2 or D2. The efficiency of singlet delta oxygen production can be as high as 40%.

The filamentation of focused beams at wavelength of 800 and 248 nm in air is studied experimentally and numerically. The results indicate that relatively tight focusing can lead to the coalescence of individual regions of high fluence and high plasma density that result from multiple refocusing, whereas in the case of weak focusing such regions are separated in the pulse propagation direction. The lower multiphoton ionization order in the case of UV radiation leads to a stronger effect of geometric focusing on filament formation. We show the possibility to control the parameters of femtosecond laser plasma filaments by introducing astigmatism in laser beam wavefront. Strong astigmatism can lead to the splitting of the channel into two separate regions. We demonstrate that the self-phase modulation in the thin passthrough dielectric plate decreases the distance to the filament start in air and increases the length of plasma channel.

An influence of pass-through optics on femtosecond laser pulse filamentation in ambient air is analyzed for the first time both experimentally and numerically. Propagation of high-power femtosecond laser pulse through solid optical elements introduces spatiotemporal phase modulation due to the Kerr effect. This modulation may have a strong ef-fect on the pulse filamentation in air. We demonstrated that the phase modulation obtained in the thin pass-through dielectric plate reduces the distance to the filament onset and increases the plasma channel length, 4 pages, 4 figures

Studies of the vibration-vibration (VV) exchange in CO molecules excited up to vibration quantum numbers v = 20 have been performed both theoretically and experimentally. A new kinetic model which takes into account the multi-quantum VV exchange in the temperature range T = 100-300 K is described for the first time. A description is given of the experimental methodology allowing for studies of the effects of the relaxation of the vibrational distribution after a sudden disturbance. The disturbance of the vibrational distribution is produced by a Q-switched short pulse of single line radiation in fundamental band. The relaxation is studied by measuring the laser pulse energy of the second pulse initiated by resonator Q-switching produced with a variable time delay relative to the first pulse. A set of kinetic rate constants accepted in the model for various gas temperatures, vibration level numbers and number of exchanged vibration quanta from 1 to 4 is presented. The good agreement between the experimental data and the results of the advanced theory is the first direct evidence in support of the multi-quantum exchange model.

We have demonstrated for the first time that an array of nanoantennas (central nanotips inside sub-micron pits) on an aluminum surface, fabricated using a specific double-pulse femtosecond laser irradiation scheme, results in a 28-fold enhancement of the non-linear (three-photon) electron photoemission yield, driven by a third intense IR femtosecond laser pulse. The supporting numerical electrodynamic modeling indicates that the electron emission is increased not owing to a larger effective aluminum surface, but due to instant local electromagnetic field enhancement near the nanoantenna, contributed by both the tip's lightning rod effect and the focusing effect of the pit as a microreflector and annular edge as a plasmonic lens., 4 pages, 3 figures

An influence of plasma channel created by a filament of focused UV or IR femtosecond laser pulse ({\lambda}=248 nm or 740 nm) on characteristics of other plasma channel formed by a femtosecond pulse at the same wavelength following the first one with varied nanosecond time delay was experimentally studied. A dependence of optical transparency of the first channel and plasma density of the second channel on the time delay was demonstrated to be quite different for such a double UV and IR femtosecond pulses., Comment: 5 pages, 3 figures

Non-self-sustained electric discharge and electric breakdown were triggered and guided by a train of ultrashort sub-TW ultraviolet (UV) pulses overlapped with a long free-running UV pulse of a hybrid Ti:Sapphire - KrF laser facility. Photocurrent sustained by this train is two orders of magnitude higher, and electric breakdown distance is twice longer than those for the discharge triggered by the long UV pulse only. When transporting the laser radiation over the long distance, UV filaments of ~ 100 m length were observed.

Superimposed one-dimensional quasiperiodic gratings with multiple periods \ensuremath{\Lambda} \ensuremath{\approx} 110--800 nm well below or comparable to the pump laser wavelength of 744 nm, and ridge orientations perpendicular to the linear polarization of infrared femtosecond laser pulses, were fabricated after multiple near-threshold laser shots on a planar surface of quasimonocrystalline graphite in ambient air. The broad range of the grating periods corresponds to the large number of spatial Fourier harmonics of the final nanorelief (up to $m=7$th order, ${\ensuremath{\Lambda}}_{m}\ensuremath{\approx}800$ nm/$m=110--800$ nm), qualitatively representing the nonsinusoidal profile of the laser-induced intermediate surface relief (the set of periodic, broadly spaced narrow nanotrenches), which provides the corresponding multiangle diffraction of the incident femtosecond laser pulses. Experimental measurements and modeling of the transient optical constants of the photoexcited graphite justify the excitation, at the first stage, of the first-order (${\ensuremath{\Lambda}}_{1}\ensuremath{\approx}800$ nm) surface plasmon-polaritonic (SPP) wave on the photo-excited initial planar graphite surface becoming metallic via photo-generation of dense electron hole plasma ($\ensuremath{\sim}{10}^{21}$ cm${}^{\ensuremath{-}3}$). Such an SPP wave provides intermediate nanorelief in the form of the nonsinusoidal surface grating via its interference with the incident laser wave, resulting under near-threshold laser irradiation conditions in the highly localized surface ablation of the material in the interference maxima. During the next stage, the multiperiod subwavelength nanogratings develop through the multiangle diffraction of the multiple incident laser pulses on the intermediate nonsinusoidal surface grating.

In this work femtosecond laser photo-excitation of GaAs is studied numerically. The transient plasma densities photogenerated during the pumping IR fs-laser pulses were evaluated having in mind experimental data of time-resolved reflectivity measurements of transient bandgap shifts. Theoretical modeling employing quantum kinetic formalism based on a generalized Boltzmann-type equation, including one/multi-photon photo-excitation, Joule heating and free-carrier absorption, interband excitation, impact ionization, Auger recombination of electron-hole plasma, thermal exchange with the lattice, etc. is performed. For the first time the effect of enhancement of ionization by transient bandgap renormalization (BGR) is considered both experimentally and theoretically. The energy spectra of the electron distribution function and the time dependence of the electron density are calculated and the key role of BGR in the transient electron-hole plasma dynamics is pointed out.

Compact slab repetitively-pulsed RF discharge overtone CO laser is developed. Results of parametric study of the laser with cryogenically cooled electrode system operating in sealed-off mode are reported. The average output power of the laser was up to 0.5 W with maximal efficiency of ~1.5 %. More than ~80 ro-vibrational overtone CO laser lines (summarizing two spectral ranges 2.5-3.1 μm and 3.1-4.2 μm corresponding to two sets of laser resonator mirrors used in the experiments) were observed. Start-up experiments on development the laser head of new design with enlarged active medium length (40 cm) were carried out. Preliminarily the output power of the overtone CO laser with the new laser head reached 0.75 W at the efficiency up to 1 %.

Results of experimental and theoretical study of singlet delta oxygen (SDO) production in transverse gas flow RF slab discharge for an electric discharge oxygen-iodine laser are presented. The electric discharge facility operating in both pulse-periodic and CW mode was manufactured: gas flow duct including multi-path cryogenic heat exchanger, dielectric slab channel, and slab electrode system incorporated in the channel for RF discharge ignition. Experiments on SDO production in transverse gas flow RF discharge were carried out. SDO production depending on gas mixture content and pressure, gas flow velocity, and RF discharge power was experimentally studied. It was shown that SDO yield increased with gas pressure decrease, gas flow deceleration and helium dilution of oxygen at the same input power. CW RF discharge was demonstrated to be the most efficient for SDO production as compared to pulse-periodic RF discharge with the same averaged input power. SDO yield was demonstrated to be not less than 10 percent. The model developed was further modified to do simulations of CW and pulse periodic RF discharges. A reasonable agreement between experimental and theoretical data on SDO production in CW and pulse-periodic RF discharges in oxygen is observed.

Recent experiments on applications of high‐intensity femtosecond pulses for studying multi‐photon and tunnel ionization of different gases, including air, are discussed. Mechanisms of non‐linear absorption and ionization of pure atomic argon and molecular nitrogen gases by UV femtosecond laser pulses were studied using photogalvanic and photoacoustic technique. The effect of the intermediate Rydberg resonance, its dynamic Stark perturbation and ponderomotive up‐shift of the first ionization potential of argon atoms and nitrogen molecules by the intense laser pulses has been revealed by observing an increase of a power slope of ion yield from three to four at increasing laser intensity. The photoacoustic technique was also applied for studying the effect of tunnel ionization of air by IR femtosecond laser pulses with sub‐critical peak power in the range of intensity ∼0.5–20 PW/cm2. Saturation of ultrasonic signals at near‐atomic laser fields, which is well described by ADK model, is observed.

Results of experimental and theoretical study of singlet delta oxygen (SDO) production in transverse gas flow RF slab discharge for an electric discharge oxygen‐iodine laser are presented. The electric discharge facility operating in both pulse‐periodic and CW mode was manufactured: gas flow duct including multi‐path cryogenic heat exchanger, dielectric slab channel, and slab electrode system incorporated in the channel for RF discharge ignition. Experiments on SDO production in transverse gas flow RF discharge were carried out. SDO production depending on gas mixture content and pressure, gas flow velocity, low‐frequency modulation of RF power and RF discharge power was experimentally studied. It was shown that SDO yield increased with gas pressure decrease, gas flow deceleration and helium dilution of oxygen at the same input power. CW RF discharge was demonstrated to be the most efficient for SDO production at the same averaged input power of RF discharge. SDO yield was demonstrated to be not less than...

One‐dimensional quasi‐periodic structures whose period is much smaller than the wavelength of exciting optical radiation have been obtained on a titanium surface under the multi‐shot action of linearly polarized femtosecond laser radiation at various surface energy densities. As the radiation energy density increases, the one‐dimensional surface nanogratings oriented perpendicularly to the radiation polarization evolve from quasi‐periodic ablative nano‐grooves to regular lattices with sub‐wavelength periods (90–400 nm). In contrast to the preceding works for various metals, the period of lattices for titanium decreases with increasing energy density. The formation of the indicated surface nanostructures is explained by the interference of the electric fields of incident laser radiation and a surface electromagnetic wave excited by this radiation, as shown by our transient reflectivity measurements and modeling, because the length of the surface electromagnetic wave for titanium with significant interband ...

We have successfully fabricated in vitro femtosecond laser micro‐incisions inside cornea and—for the first time—inside sclera mildly pre‐cleared by a biocompatible and clinically safe (non‐toxic) natural agent (replacive refractive index‐matching 40%‐glucose solution in water), with the tissues taken as fresh cool cuts of human cadaver eyes, and reported on basic operational conditions of the micro‐surgical procedures.

Parametric study of a slab first-overtone carbon monoxide laser was performed. The compact slab first-overtone CO laser with active volume 3x30x250 mm 3 was excited by a repetitively pulsed capacitive RF discharge (81 MHz or 60 MHz) with pulse repetition rate 100-500 Hz. The laser electrodes were cooled down to 120 K. Gas mixtures CO:O 2 :N 2 :He with different component contents at gas pressures 15-22 Torr were used. Two laser resonator mirrors sets were used in the experiments on multiline lasing. More than 100 spectral lines within the spectral range ~2.5-4.0 μm with maximum single line average output power 12 mW were observed. Total output power of the slab firstovertone CO laser came up to 0.3 W, with maximum laser efficiency 0.5%. Special details of long time output laser power behavior are discussed.

Mechanisms of nonlinear absorption and ionization of pure atomic argon and molecular nitrogen gases by UV femtosecond laser pulses were studied using photogalvanic and photoacoustic techniques. The effect of the intermediate Rydberg resonance, its dynamic Stark perturbation and ponderomotive upshift of the first ionization potential of argon atoms and nitrogen molecules by the intense laser pulses has been revealed by observing an increase of a power slope of ion yield from three to four at increasing laser intensity.

Overtone lasing and fundamental band tuning was for the first time obtained in a slab carbon monoxide laser. The compact slab CO laser with active volume 3×30×250 mm3 was excited by a repetitively pulsed capacitive RF discharge (81.36 MHz) with pulse repetition rate 100-500 Hz. The laser electrodes were cooled down to 120 K. Gas mixture CO:Air:He at gas pressures 15-22 Torr was used. An optical scheme "frequency selective master oscillator - laser amplifier" was applied for getting fundamental band tuning. Single line lasing with average power up to several tens of mW was observed on ~100 rotational-vibrational transitions of CO molecule within the spectral range ~5.0 - 6.5 micron. Multiline overtone lasing was observed on ~80 spectral lines within the spectral range ~2.5 -4.0 micron, with maximum single line average output power 12 mW. Total output power of the slab overtone CO laser came up to 0.3 W, with maximum laser efficiency 0.5%. Results of parametric studies of the overtone CO laser including complicated time behavior for laser pulses on different overtone vibrational-rotational transitions are discussed.

The multi-stage hybrid laser system producing ultrashort pulses of radiation with peak power ~10 14 - 10 15 W now under developing at the Lebedev Physical Institute of the Russian Academy of Sciences is discussed. The distinctive feature of the laser system is direct amplification of ultrashort pulses produced by solid state laser system, first going through a prism stretcher with negative dispersion, in gas active medium without using a rather expensive and complicated grating compressor of laser pulses. Two hybrid schemes are being developed now based on the amplification of femtosecond pulses of the third harmonic of Ti:Sapphire laser at the wavelength 248 nm in the active medium of KrF laser amplifier, and on the amplification of the second harmonic of Ti:Sa laser at the wavelength 480 nm in the active medium of photochemical XeF(C-A)laser excited by VUV radiation of an e-beam pumped Xe 2 lamp. The final stage of the laser system is supposed to be an e-beam pumped facility with a laser chamber of 60 cm in diameter and 200 cm long in the case of KrF laser, and with another laser chamber of 30-40 cm in diameter put into the former one in the case of XeF(CA) laser. The parameters of such e-beam facility are close to those of previously developed at the Institute of High- Current Electronics: electron energy ~600 keV, specific input power ~ 300-500 kW/cm 3 , e-beam pulse duration ~ 100- 200 ns. A possibility of using Kr 2 F as an active medium with saturation energy 0.2 J/cm 2 for amplification of ultrashort laser pulses is also under consideration. There was theoretically demonstrated that the energy of a laser pulse at the exit of the final stage of the laser system could come up to ~ 17 J with pulse duration ~50 fs in the case of KrF laser, and ~75 J with pulse duration of 25 fs in the case of XeF laser. Two Ti:Sa laser systems producing ~50 fs pulses with energy ~0.5 mJ at the wavelength 248 nm and ~5 mJ at the wavelength 480 nm have been already developed and are being now installed at the Lebedev Institute. Preliminary experiments on amplification of UV femtosecond pulses were carried out with electric discharge KrF laser amplifier.

First experiments on fundamental band CO lasing in sealed-off cryogenically cooled slab facility with RF discharge excitation were carried out. Repetitively pulsed and CW modes of RF discharge excitation were studied. The laser output characteristics for different slab geometries were compared. Average output power achieved 12 W. Lasing efficiency came up to ~14 %. The output laser spectrum was observed within wavelengths range 5.08-5.34 µm. Stable lasing was obtained for more than one hour.

The multi-stage hybrid laser system producing ultrashort pulses of radiation with peak power ~10 14 - 10 15 W now under developing at the Lebedev Physical Institute of the Russian Academy of Sciences is discussed. The distinctive feature of the laser system is direct amplification of ultrashort pulses produced by solid state laser system, first going through a prism stretcher with negative dispersion, in gas active medium without using a rather expensive and complicated grating compressor of laser pulses. Two hybrid schemes are being developed now based on the amplification of femtosecond pulses of the third harmonic of Ti:Sapphire laser at the wavelength 248 nm in the active medium of KrF laser amplifier, and on the amplification of the second harmonic of Ti:Sa laser at the wavelength 480 nm in the active medium of photochemical XeF(C-A)laser excited by VUV radiation of an e-beam pumped Xe 2 lamp. The final stage of the laser system is supposed to be an e-beam pumped facility with a laser chamber of 60 cm in diameter and 200 cm long in the case of KrF laser, and with another laser chamber of 30-40 cm in diameter put into the former one in the case of XeF(CA) laser. The parameters of such e-beam facility are close to those of previously developed at the Institute of High- Current Electronics: electron energy ~600 keV, specific input power ~ 300-500 kW/cm 3 , e-beam pulse duration ~ 100- 200 ns. A possibility of using Kr 2 F as an active medium with saturation energy 0.2 J/cm 2 for amplification of ultrashort laser pulses is also under consideration. There was theoretically demonstrated that the energy of a laser pulse at the exit of the final stage of the laser system could come up to ~ 17 J with pulse duration ~50 fs in the case of KrF laser, and ~75 J with pulse duration of 25 fs in the case of XeF laser. Two Ti:Sa laser systems producing ~50 fs pulses with energy ~0.5 mJ at the wavelength 248 nm and ~5 mJ at the wavelength 480 nm have been already developed and are being now installed at the Lebedev Institute. Preliminary experiments on amplification of UV femtosecond pulses were carried out with electric discharge KrF laser amplifier.

Fluence dependences of IR and UV reflectivity of femtosecond laser pulses on a HOPG surface demonstrate their saturation in a certain fluence range, starting from 0.2 J cm−2, where single-shot non-linear plasma emission is detected by electric probe measurements. This correlation between prompt solid-state optical/electronic dynamics and electron–ion plasma emission indicates prompt 'freezing' of surface electronic dynamics via its plasma-emission cooling and simultaneous ultrafast shallow laser ablation of the surface. Strong HOPG disordering is observed in Raman spectra for laser fluences, exceeding the plasma emission threshold.

First experiments on fundamental band CO lasing in sealed-off cryogenically cooled slab facility with RF discharge excitation were carried out. Repetitively pulsed and CW modes of RF discharge excitation were studied. Average output power achieved 12 W. Lasing efficiency exceeded 10 %. The output laser spectrum was observed within wavelengths range 5.08-5.34 µm. Stable lasing was obtained for tens minutes. Keywords: CO laser, slab RF discharge, cryoge nic cooling, sealed-off, repetitively pulsed

Singlet delta oxygen O2a1Dg (SDO) production in a slab discharges ignited in oxygen gas mixtures was experimentally studied. An influence of gas mixture content and input electric power on SDO yield was analyzed. In self-sustained RF slab discharge SDO yield of 10±5 % was measured by comparison luminescence intensity of SDO going from a chemical generator and SDO generated in electric discharge. SDO yield of 7.2 % was measured by intracavity laser spectroscopy method. It was demonstrated that the choice of electrodes material is very important. Experiments on SDO production in slab non-self-sustained discharge with external ionization by repeating high-voltage pulses were carried out. SDO concentration was measured by the method of intracavity laser spectroscopy. The measured concentration of SDO was about 1.5×1016 cm-3, with SDO yield of ~10.6 %. A development of electric discharge oxygen-iodine laser with SDO production in long electrodes slab discharge is discussed.