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Periodic surface structures on aluminium are produced by femtosecond laser pulses for efficient excitation of surface electromagnetic waves using a strong objective (NA = 0.5). The local electromagnetic field enhancement on the structures is measured using the technique of surface-enhanced Raman scattering from pyridine molecules.

Regenerative amplification of single and multiple ultrashort subpicosecond UV pulses in a wide-aperture KrF amplifier with an unstable confocal resonator was investigated on the GARPUN-MTW hybrid laser system. Amplitude-modulated 100-ns long UV radiation pulses with an energy of several tens of joules were obtained at the output of the system. The pulses were a combination of a quasi-stationary oscillation pulse and a train of amplified ultrashort pulses (USPs) with a peak power of 0.2–0.3 TW, which exceeded the power of free-running lasing pulse by three orders of magnitude. The population inversion recovery time in the active KrF laser medium was estimated: τc ≤ 2.0 ns. Trains of USPs spaced at an interval Δt ≈ τc were shown to exhibit the highest amplification efficiency. The production of amplitude-modulated UV pulses opens up the way to the production and maintenance of extended plasma channels in atmospheric air.

The problem of the production of extended (~1 m) plasma channels is studied in atmospheric air by amplitude-modulated laser pulses of UV radiation, which are a superposition of a subpicosecond USP train amplified in a regenerative KrF amplifier with an unstable confocal resonator and a quasi-stationary lasing pulse. The USPs possess a high (0.2–0.3 TW) peak power and efficiently ionise oxygen molecules due to multiphoton ionisation, and the quasi-stationary lasing pulse, which has a relatively long duration (~100 ns), maintains the electron density at a level ne = (3–5) × 1014 cm—3 by suppressing electron attachment to oxygen. Experiments in laser triggering of high-voltage electric discharges suggest that the use of combined pulses results in a significant lowering of the breakdown threshold and enables controlling the discharge trajectory with a higher efficiency in comparison with smooth pulses. It was shown that controlled breakdowns may develop with a delay of tens of microseconds relative to the laser pulse, which is many orders of magnitude greater than the lifetime of free electrons in the laser-induced plasma. We propose a mechanism for this breakdown, which involves speeding-up of the avalanche ionisation of the air by negative molecular oxygen ions with a low electron binding energy (~0.5 eV) and a long lifetime (~1 ms), which are produced upon cessation of the laser pulse.

During six decades of quantum electronics, a vast majority of new types of quantum generators have been developed. Although the principle of population inversion has united different ranges of electromagnetic spectra (and respective quantum generators), the existence of the title laser without the population inversion, makes that the exception had confirmed the rule, i. e. that this title deserves to be discussed further. Developing of formalisms describing the operation of quantum generators, by now have produced several approaches, which must have a quantum mechanics base. For the practical reasons, negative coefficient of absorption is acquired using classic electromagnetics as well, however for the population purposes, quantum representation must be entered. A few levels of formalisms will be set in this paper, linked to quantum generators accenting the optical portion of the spectra. The lowest level descriptions are based on lumped circuits. This could be expanded to equivalents of other physical problems, using program packages developed for the electrical engineering application purposes (Spice, etc.). Schematics are defined at the macro as well as micro equivalent levels (atomic – electronic levels). The kinetic equations with simpler approach will be considered as well as simplified laser equations based on quantum/ semi-quantum approach. The use of Fourier analysis or other appropriate transformations leads to formulating the main five laser equations which serve as the base for various working regimes of quantum generators and amplifiers (free generation regime, Q switch, synchronization, operation with filters, two modes regime, regime with losses, etc.). The Lyapunov stability theorem has to be included here, etc. For some of the chosen types of quantum generator, analytical modeling will be analyzed as well as the results of program packages developed for the lasers dynamics, regimes and parameters. The systems pumped with electronic beams (relativistic) will be considered and the nuclear physics statements discussed which must be included at the beginning, in order to consider further necessary parts of the condensed – solid state theory and laser techniques, after slowing down towards thermal energies. Existing program packages provide fast modeling and visualization of laser energy distribution, temperature, modes, etc. in active material with or without the resonator. A modeling will be performed for the specified geometries and a temperature distribution in active material will be captured during operation of a chosen laser system. Different pump geometries will be compared. Contemporary lasers with the shortest existing pulse durations demand new formalisms. Areas of nonlinear optics and quantum electrody-namics, Glauber states and similar, are areas that have to be included. Two main formalisms thermodynamical and quantum mechanical with transition probabilities using perturbation methods and secondary quantization naturally had to be complemented if the Brillouin, Raman, Compton, soliton, fiber and other lasers are included more generally.

A two-cascade frequency conversion of CO-laser radiation is demonstrated in a single sample of a nonlinear ZnGeP2 crystal. The crystal is pumped by a repetitively pulsed cryogenic lowpressure CO laser operating on ~150 vibration – rotational transitions in the wavelength range 5.0 – 7.5 μm, which corresponds to the frequency range of a half octave. In the first conversion cascade, generation of second harmonic and sum frequencies of various pairs of CO-laser radiation give ~350 emission lines in the wavelength range 2.5 – 3.7 μm. In the second cascade, by mixing the radiation converted in the first cascade with the residual radiation of the CO laser we have obtained ~90 lines in the range 4.3 – 5.0 μm and more than 80 lines in the range 7.5 – 8.3 μm. Thus, using a single sample of the nonlinear ZnGeP2 crystal pumped by the radiation of a single CO laser we have produced a source of broadband (more than one and a half octaves) laser radiation, simultaneously operating at ~670 lines in the wavelength range 2.5 – 8.3 μm.

The filamentation of IR and UV laser pulses has been studied numerically and experimentally for different initial beam focusing geometries, and linear electron density profiles along the plasma channel of filaments have been obtained. The results demonstrate that changes in laser beam focusing have a stronger effect on filament and plasma channel parameters for UV radiation than for IR radiation. Focusing causes individual high fluence regions produced by refocusing to merge to form a continuous extended filament with a continuous plasma channel.

This paper examines the propagation of focused femtosecond gigawatt laser pulses in air under normal and reduced pressure in the case of Kerr self-focusing and photoionisation of the medium. The influence of gas density on the beam dimensions and power and the electron density in the plasma column in the nonlinear focus zone of the laser beam has been studied experimentally and by numerical simulation. It has been shown that, in rarefied air, the radiation-induced reduction in the rate of plasma formation diminishes the blocking effect of the plasma on the growth of the beam intensity in the case of tight focusing. This allows higher power densities of ultrashort laser pulses to be reached in the focal waist region in comparison with beam self-focusing under atmospheric pressure.

The prepared samples were characterized by reflection and transmission spectra of broadband visible-range radiation, and the volume fraction of substances introduced into pores of artificial opals is estimated. It is found that the introduction of solid-state nanoparticles with negative real part of the permittivity into opal pores results in a decrease in the effective refractive index and a short-wavelength shift in the spectral position of the stop band in artificial opal.

Quasi-periodic nano- and microstructures have been formed on silicon surface using IR ( l » 744 nm) and UV ( l » 248 nm) femtosecond laser pulses. The influence of the incident laser fluence and the number of pulses on the structured surface topology has been investigated. The silicon nanostructuring thresholds have been determined for the above-mentioned wavelengths. Modulation of the surface relief at the doubled spatial frequency is revealed and explained qualitatively. The periods of the nanostructures formed on the silicon surface under IR and UV femtosecond laser pulses are comparatively analysed and discussed.

This work examines the effect of high-power femtosecond laser pulses on Ni/Cu bilayer foils produced by electrodeposition. We consider nanostructures formed at different laser beam parameters and under different ambient conditions. The surface nanostructures obtained in air and water have mostly the form of quasi-periodic ripples with a characteristic period of 400 — 450 and 370 — 390 nm, respectively, at a laser wavelength of 744 nm, whereas the nanostructures produced in ethanol and benzine have the form of spikes, typically spaced 400 — 700 nm apart. Femtosecond laser nanostructuring of metals is for the first time proposed, and experimentally tested, as a viable approach to producing anti-reflective coatings on the surface of polymer replicas.

Gradual evolution of self-induced silicon surface topology from one-dimensional ridge-like to two-dimensional spike-like nanogratings and then to isotropic sets of micro-columns was observed by evenly increasing IR and UV femtosecond laser irradiation dose. This topological evolution exhibits clear indications of consequent melting and vaporization processes being set up during the prolonged laser irradiation. Monotonously decreasing cumulative IR and UV femtosecond laser-nanostructuring thresholds may indicate an increase of optical absorbance of the laser-nanostructured silicon surfaces versus the increasing laser dose, consistent with the consequent onset of the abovementioned thermal modification processes.

A compact capacitive transverse RF-discharge-pumped slab CO laser with cryogenically cooled electrodes, which operates both in the cw and repetitively pulsed regimes, is fabricated. The laser operation is studied in the free running multifrequency regime at the vibrational – rotational transitions of the fundamental (V + 1 → V) vibrational bands of the CO molecule in the spectral region from 5.1 to 5.4 μm. Optimal operation conditions (gas mixture composition and pressure, RF pump parameters) are determined. It is shown that only gas mixtures with a high content of oxygen (up to 20% with respect to the concentration of CO molecules) can be used as an active medium of this laser. It is demonstrated that repetitively pulsed pumping is more efficient compared to cw pumping. In this case, quasi-cw lasing regime can be obtained. The maximum average output power of ~12 W was obtained for this laser operating on fundamental bands and its efficiency achieved ~14 %. The frequency-selective operation regime of the slab RF-discharge-pumped CO laser was realised at ~ 100 laser lines in the spectral region from 5.0 to 6.5 μm with the average output power of up to several tens of milliwatts in each line. Lasing at the transitions of the first vibrational overtone (V + 2 → V) of the CO molecule is obtained in the spectral region from 2.5 to 3.9 μm. The average output power of the overtone laser achieved 0.3 W. All the results were obtained without the forced gas mixture exchange in the discharge chamber. Under fixed experimental conditions, repetitively pulsed lasing (with fluctuations of the output characteristics no more than ±10 %) was stable for more than an hour.

The method of multifrequency laser probing is developed which can be used for diagnostics of the temperature and population of vibrational levels in gas mixtures containing CO molecules in excited vibrational states. The method is tested by studying the dynamics of the gas temperature and population of vibrational levels of the CO molecule in gas mixtures excited by a pulsed discharge. It is shown that the method provides the reduction of the gas temperature measurement error down to 3%. It is found that the population of lower vibrational levels in the CO–O2 mixture can exceed the population of levels in CO–He and CO–N2 laser mixtures by several times.

Small-signal gain (SSG) dynamics G(t) in the active medium of a pulsed laser amplifier operating on the v+1→vP(J) vibrational–rotational transitions of the CO molecule, including high (v > 15) vibrational transitions, is studied experimentally. It is demonstrated that as the vibrational number increases from 7 to 31, G changes with time slower, while Gmax decreases in this case by three times. It is found that at a fixed value of v the rate of the SSG rise increases with increasing the rotational number J > 6. It is shown that in oxygen-containing gas mixtures (CO:O2 = 1:19) the value of Gmax at low vibrational levels (for v < 13) can substantially exceed Gmax in mixtures containing nitrogen (CO:N2 = 1:19) instead of oxygen. It is found that the efficiency (47%) of a CO laser on mixtures with a high concentration of oxygen considerably exceeds the efficiency (30%) of a CO laser operating on a nitrogen-containing mixture.

Lasing parameters of a rf discharge-pumped CO laser in a subsonic gas flow with subsequent cooling of the laser medium in a supersonic flow are studied. The output power of the laser achieved 2.1 kW for the efficiency up to 21% in the spectral range 4.9–5.7 μm corresponding to the V+1→V fundamental vibrational transitions in the CO molecule. The laser output power at the V+2→V first vibrational overtone transitions (2.6–2.7 μm) was 50 W. Possible ways of improving the laser design for generating radiation at higher overtone transitions of the CO molecule are discussed.

The absorption/emission spectral regions of SO, SO2, SO3, S2O and HSO are analyzed for the range from UV (λ ≥ 0.2 µm) to IR (λ < 30 µm) and are compared with the atmospheric transmission spectrum. It is shown that many vibrational bands of the compounds considered fall into atmospheric transmission windows. For the vibrational bands of SO, SO2, SO3, S2O, and HSO molecules there are some gases which hinder the absorption diagnostics of the indicated compounds. These interfering gases are natural components of atmospheric air as well as specific gases of aircraft engine exhaust. It is found that the least influence of the interference takes place in the 2400–2700 cm−1 IR region. The spectroscopic techniques used for the detection of aircraft engine exhaust compounds are briefly reviewed, with much consideration given to SO2. The IR absorption spectra of SO2 and other gases are calculated for the conditions of the aircraft engine nozzle exit. Narrow spectral intervals suitable for SO2 detection in a hot flow are determined. An analysis is made for the detection capabilities of CO2 lasers (including isotope CO2 lasers) and CO lasers (both fundamental band and first-overtone ones) as applied to SO2 detection in aircraft engine exhaust.

The method of intracavity laser spectroscopy using a Co:MgF2 laser is applied to record the absorption spectra from the first excited a1Δg state of gaseous molecular oxygen at the a1Δg → b1Σg+ transition at 1.91 μm. The gas flow from a chemical singlet oxygen generator with a known concentration of singlet oxygen O2 (a1Δg) was supplied to the cavity of the Co:MgF2 laser. The absorption line intensities are measured for five spectral lines of the Q-branch of the 0–0 vibrational band for the a1Δg → b1Σg+ transition. The O2 (b1Σg+ → a1Δg) transition probability calculated from these data was (1.20 ± 0.25) × 10-3 s-1.

The electrical and spectroscopic characteristics of electron-beam-sustained discharge (EBSD) in oxygen and oxygen-containing gas mixtures are studied experimentally under gas pressures up to 100 Torr in a large excitation volume ({approx}18 L). It is shown that the EBSD in pure oxygen and its mixtures with inert gases is unstable and is characterised by a small specific energy contribution. The addition of small amounts ({approx}1%-10%) of carbon monoxide or hydrogen to oxygen or its mixtures with inert gases considerably improves the stability of the discharge, while the specific energy contribution W increases by more then an order of magnitude, achieving {approx}6.5 kJ L{sup -1} atm{sup -1} per molecular component of the gas mixture. A part of the energy supplied to the EBSD is spent to excite vibrational levels of molecular additives. This was demonstrated experimentally by the initiation of a CO laser based on the O{sub 2} : Ar : CO = 1 : 1 : 0.1 mixture. Experimental results on spectroscopy of the excited electronic states O{sub 2}(a{sup 1{Delta}}{sub g}) and O{sub 2}(b{sup 1{Sigma}}{sub g}{sup +}), of oxygen formed in the EBSD are presented. A technique was worked out for measuring the concentration of singlet oxygen in the O{sub 2}(a{supmore » 1{Delta}}{sub g}) state in the afterglow of the pulsed EBSD by comparing with the radiation intensity of singlet oxygen of a given concentration produced in a chemical generator. Preliminary measurements of the singlet-oxygen yield in the EBSD show that its value {approx}3% for W {approx} 1.0 kJ L{sup -1} atm{sup -1} is in agreement with the theoretical estimate. Theoretical calculations performed for W {approx} 6.5 kJ L{sup -1} atm{sup -1} at a fixed temperature show that the singlet-oxygen yield may be {approx}20%, which is higher than the value required to achieve the lasing threshold in an oxygen-iodine laser at room temperature. (laser applications and other topics in quantum electronics)« less

The gain dynamics in the active medium of an overtone CO laser operating on the transitions between high vibrational levels is studied experimentally and theoretically. The gain dynamics is measured on the vibration — rotation transitions of the CO molecule [the P(12) spectral line in the vibrational bands from 20 → 18 to 36 → 34] in CO — He and CO — N2 laser mixtures. The maximum small-signal gain was 0.43 m-1. The theoretical model of the CO laser was significantly improved. It was shown that multiquantum and asymmetric VV-exchange processes should be included in the analysis of the population dynamics of high vibrational levels of the CO molecule.

Experiments have been performed at hybrid Ti:sapphire/KrF laser facility GARPUN-MTW to develop a novel technique to create a hollow-core sliding-mode plasma-filament waveguide for directed transfer of microwave radiation. Efficient multiphoton air ionization was produced by a train of picosecond 1-TW UV pulses at 248 nm wavelength, or by amplitude-modulated 100 ns pulse combining a short-pulse train with a free-running 1-GW pulse, which detached electrons off O2− ions. Multiple filamentation of UV laser radiation in air was observed, and filamentation theory based on resonance-enhanced ionization was developed to explain the experimental results.

Resonant absorption of first-overtone (FO) CO laser radiation by atmospheric water vapor and various organic and nonorganic pollutants is discussed. Suitable ro-vibrational lines are selected for their potential use in traditional spectroscopic schemes of atmospheric pollution diagnostics. Nonlinear atmospheric absorption of intense multiline FO CO laser radiation is simulated and laser-induced changes in absorption spectra are demonstrated. Absorption coefficients of a few substances on several FO CO ro-vibrational lines are experimentally measured. A comparative analysis of spectral characteristics of an FO CO laser and an HF (DF) laser demonstrates that the potential of FO CO laser applications for spectroscopic detection of various molecular trace gases is greater than that of HF and DF lasers.

Characteristics of a pulsed, multifrequency electroionisation CO laser operating on the first vibrational overtone of the CO molecule are studied experimentally and theoretically. It is shown experimentally that a pulsed, multifrequency overtone CO laser is an efficient source of coherent radiation in the 2.5–4.1-μm region whose specific output reaches 50 J l-1 amagat-1 and the electro-optical efficiency amounts to 11 %. A theoretical analysis based on experimental data shows the feasibility of obtaining overtone emission with efficiency as high as ~20 %. The alternation of the intensity of vibrational bands in the overtone CO laser is discussed. This effect is caused by the cascade mechanism of formation of the emission spectrum. The comparison of experimental data with calculations showed that they agree well with respect to spectral and energy characteristics of the overtone CO laser. Moreover, it revealed the necessity of refinement of the kinetic model of the active medium of the CO laser for obtaining an adequate description of time parameters of a laser pulse.

The kinetics of exchange by vibrational quanta is studied theoretically and experimentally in highly excited CO molecules by analysing the recovery time of the inversion population on the selected vibrational-rotational transitions in a doubly Q-switched pulsed CO laser. A model of vibrational kinetics that takes into account the multiquantum vibrational exchange between CO molecules in the temperature range between 100 and 300 K is described in detail for the first time. This model is compared with the model of single-quantum vibrational exchange. Good agreement between experimental data and theoretical calculations performed using the model of multiquantum vibrational exchange is the first direct confirmation of the validity of this model.

Tunable single-line first-overtone (FO) CO lasing on wavelengths from 2.7 up to 4.2 μm corresponding to overtone vibrational transitions from 13→11 up to 38→36 on 413 ro-vibrational lines was experimentally obtained. A parametric study of energetic and spectral characteristics of the single-line FO CO laser was carried out. Energy distribution over ro-vibrational lines was measured. The maximum specific output energy (SOE) came up to ∼3 J/l Amagat, with single-line output efficiency being up to 0.6%. For the first time, a multi-quantum theoretical model was used to describe the tunable single-line FO CO laser. This multi-quantum approach demonstrated better agreement between theoretical calculations and observed experimental data for laser output as a function of vibrational quantum numbers.

A review of reports made on the International Forum on Advanced High-Power Lasers and Applications, which was held at the beginning of November 1999 in Osaka (Japan), is presented. Five conferences were held during the forum on High-Power Laser Ablation, High-Power Lasers in Energy Engineering, High-Power Lasers in Civil Engineering and Architecture, High-Power Lasers in Manufacturing, and Advanced High-Power Lasers. The following trends in the field of high-power lasers and their applications were presented: laser fusion, laser applications in space, laser-triggered lightning, laser ablation of materials by short and ultrashort pulses, application of high-power lasers in manufacturing, application of high-power lasers in mining, laser decommissioning and decontamination of nuclear reactors, high-power solid-state and gas lasers, x-ray and free-electron lasers. One can find complete information on the forum in SPIE, vols. 3885-3889.

The temporal dynamics and efficiency of phase-conjugate reflection in the course of intracavity degenerate four-wave mixing of radiation from a pulsed frequency-selective electron-beam-sustained CO laser was investigated experimentally and theoretically. The energy efficiency of the phase-conjugate reflection in the experiments reached 1.5 - 2.5% for a CO laser emitting as a result of one vibrorotational transition, diminishing on expansion of the emission spectrum of the laser. Comparison of the experimental and calculated data indicates the dominant role of the resonance amplitude phase-conjugation mechanism in the active medium of a CO laser. (nonlinear optical phenomena)

Millimeter-long filaments and accompanying luminous plasma and defect channels created in fused silica (FS) by single focused femtosecond laser pulses with supercritical powers were probed in situ using optical imaging and contact ultrasonic techniques. Above the threshold pulse energy E opt = 5 μJ corresponding to a few megawatt power levels pulses collapse due to self-focusing, producing channels filled by electron-hole plasma and luminescent defects, and exhibits predominantly compressive pressure transients. Analysis of the optical and ultrasonic response versus the laser pulse energy suggests that filamentary pulse propagation in the channels occurs with considerable dissipation of about ∼10 cm -1 . The predominant ionization mechanism is most likely associated with avalanche ionization, while the main mechanism of optical absorption is free-carrier absorption via inverse Bremsstrahlung interaction with the polar lattice.

Numerical simulation is used as the basis of an analysis of nonlinear optical properties of the active medium in intracavity four-wave mixing of the radiation of a pulsed electron-beam-controlled discharge CO2 laser on saturated-gain and refractive-index diffraction gratings. The reflection coefficient of the phase-conjugated signal is determined for various cavity Q-factors, specific input energies, and pressures of the laser-active mixture. A comparison is made of the theoretical and experimental results. It is found that the rate of formation of amplitude gratings is governed primarily by the initial population inversion and by the intensities of the interacting waves. It is shown that transient phase gratings make the dominant contribution to the phase-conjugate reflection coefficient at high pressures of the mixture.

Parametric study of a first-overtone (FO) CO laser was carried out both experimentally and theoretically. A special optical filter was used for suppression of fundamental band lasing. The theoretical model is in satisfactory agreement with the experiment for a laser operating on a He-containing gas mixture. The maximum FO CO laser efficiency of 5.5% and specific output energy (SOE) of ∼20 J/l Amagat were obtained for a laser resonator with rather high useless optical losses, FO CO lasing taking place from 13→11 up to 30→28 vibrational transitions ( λ =2.7–3.6 μm). Important influence of intracavity water vapor on the output characteristics of FO CO laser and its spectrum, in particular, is discussed. Both theoretical and experimental results indicate that the FO CO laser efficiency up to 15–20% and SOE up to 50–80 J/l Amagat can be obtained.

An experimental investigation was made of the interaction of radiation from a frequency-selective pulsed electron-beam-controlled discharge CO laser on polymer materials (nylon and polyethylene terephthalate) with intense absorption bands near the wavelength ~ 6 μm. The parameters of the interaction (geometry and method of irradiation of a material; temporal, spectral, and energy characteristics of the laser radiation) corresponding to the appearance of microstructures of different types on the surface of the processed material were determined. An analysis was made of the relationship between the structural changes in the materials at the microscopic level and visual macroscopic changes in the physical properties of the samples processed by laser radiation.

The high-frequency temporal structure of probe-laser and phase-conjugated signals, generated in the course of degenerate four-wave mixing of long pulses from CO2 and CO lasers in their own inverted media, was investigated experimentally with nanosecond resolution throughout the whole pulse. Single-frequency (corresponding to one vibrational — rotational transition) and multifrequency pulses of ~10 — 20 μs and ~ 200 — 300 μs durations, generated respectively by electron-beam-controlled discharge CO2 and CO lasers, had a complex temporal dynamics with a depth of modulation up to 100%. In one round-trip period (~100 ns) the pulses from these CO2 and CO lasers consisted of several spikes (free-running mode) or of one spike (self-mode-locking with the aid of a plasma mirror) of τ0.1 ~10 ns duration. The temporal dynamics of the phase-conjugated signal also had a complex structure, differing from the probe signal structure over longer (in excess of 100 ns) and shorter time intervals. The relative influence of the amplitude and phase mechanisms of the formation of transient diffraction gratings in the active medium, and also the influence of large- and small-scale diffraction gratings, and of the temporal synchronism on the dynamics of the phase-conjugated signal were considered.

A pulse-periodic electron-beam-controlled CO laser, operating at room temperature, was constructed. The active laser volume was 3.4 litres, the pressure in the CO : N2 : He = 1 : 6 : 7 laser mixture was varied within the range 0.3–0.6 bar, and the duration of the pump current pulses was 7 μs. The laser cavity was formed by a concave copper mirror (r = 9 m) and a dielectric mirror (on a plane-parallel ZnSe substrate) with a reflection coefficient of 97%. The repetition frequency of the pump and output pulses was varied within the range 1–50 Hz. The maximum output radiation energy delivered by a single pulse, the specific output energy, and the lasing efficiency, were 24.4 J, 18 J litre-1 bar-1, and 4.6%, respectively. The average output radiation power was ~1 kW when the repetition frequency of the output pulses was 45 Hz. Ways of improving further the output power of this laser and its possible applications were considered.

An experimental study of a four-wave interaction in the active laser medium was made for long (10–103 μs) pulses emitted by electron-beam-controlled-discharge CO2 and CO lasers. Linearly polarised probe radiation from a CO2 (CO) laser was directed into the intracavity inverted medium of the laser itself. The radiation reflected back by the active medium was recorded in the near-field and far-field zones. Phase conjugation was confirmed by reconstruction of the spatial pattern of the radiation field in the near-field zone and of the angular divergence of the radiation in the far-field zone. The energy coefficient representing phase conjugation by reflection reached 2% for the CO2 laser and 0.2% for the CO laser. The time dependence of the phase-conjugation power coefficient was analysed.

The research-and-development effort on CO lasers and applications of these lasers in Russia are reviewed. Various types of cw, pulsed, and periodic-pulse CO lasers have been developed in various laboratories. Sealed-off, water-cooled cw CO lasers with an output power of 5-10 W, pumped by a self-sustained electric discharge, are being used successfully in the manufacture of electronic devices and in medicine. The output power of fast-flow cryogenic cw CO lasers with a self-sustained discharge ranges up to ~1 kW. The use of electron-beam pumping has made it possible to develop pulsed electron-beam-sustained (EBS) CO lasers with an energy up to ~1 kJ and also to develop cw and periodic-pulse EBS CO lasers with a power of 10 kW and an efficiency up to ~40%. Research on pulsed electron-beam-sustained CO lasers has been the scientific foundation for the construction of CO laser systems of the (master oscillator)-amplifier type and periodic-pulse CO lasers. A CO laser system with an output energy ~200 J and an output beam divergence of 2·10−4 rad has been developed. Requirements on the effective gain in the active medium and on the transport through atmospheric air of multifrequency output pulses from CO laser with various spectral and temporal characteristics have been formulated. A supersonic EBS CO laser with a peak power ~105 W and a 10-kW periodic-pulse EBS CO laser with subsonic flow have been developed. The latter laser generates pulses with an energy ~100 J and a repetition frequency up to 100 Hz. The EBS CO lasers with injection of the laser mixture in the liquid phase are discussed. Lasers using nuclear ionization of the active medium are also discussed.

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.

Generation of free-carrier plasma and filamentation of the ultra-short laser pulse were investigated and modeled. Experimental results of filamentation are supported by numerical model which takes into account accumulation of refractive index modifications due to multi-pulse exposure. A contact acoustic monitoring technique was employed to perform spatially-resolved in situ detection of micro-plasma formation and filamentation of focused femtosecond laser pulses with critical and sub-critical powers in glass. The recorded acoustic signals reveal freecarrier generation mechanisms associated with the formation of plasma and filamentation of the propagating laser pulses. Optical opacity of the plasma region, which sets in at the irradiance of a few kJ/cm 3 (close to the dielectric breakdown threshold) using pulse focusing optics with numerical aperture NA = 0.75, reveals its critical character, and allows the estimation of acoustic pressure in the ~GPa range. The pressure depended on the irradiance as P ~ I 0.59 . In the case of loose focusing (NA = 0.035) filamentation of fs-pulses occurred at sub-critical plasma density with P ~ I. Detection and interpretation of these acoustic signatures thus enable real-time in situ monitoring of optical ionization, pulse filamentation in bulk dielectrics under the irradiation by femtosecond laser pulses.

An experimental and theoretical investigation was made of the small-signal gain in a pulsed electron-beam-controlled N2O laser. The gain was found to exceed ~ 1 m−1. A comparison of the experimental and calculated gain values was used as the basis for estimating the pumping efficiency of N2O molecules in an electron-beam-controlled discharge and the relaxation constant of the upper active level. The lasing frequency of the N2O laser was tunable in spectral ranges corresponding to vibrational–rotational transitions from R (46) to R (2) and from P (2) to P (46). The laser output energy, at its maximum in the distribution over the rotational numbers, was ~ 8 J (~ 16 J liter−1 amagat−1).

Small-signal gain time behavior for cryogenic pulsed e-beam sustained discharge CO laser amplifier on high (V>15) fundamental band vibrational transitions was studied experimentally for different CO containing gas mixtures including ones typical for CO lasers and amplifiers (CO:He and CO:N2), and CO:O2 used for singlet delta oxygen production.

Time behavior of gas temperature in CO containing gas mixture excited in pulsed electron-beam sustained discharge (EBSD) was experimentally studied under different experimental conditions. To study time behavior of gas temperature, the fact that the gas temperature is equivalent to the rotational temperature of gas molecules was used. Rotational distribution of the excited states of CO molecule was reconstructed from measured small-signal gain dynamics on different ro-vibrational transitions. The time behavior of small-signal gain was obtained with probe low-pressure CW CO laser for ten ro-vibrational spectral lines. Gas mixtures CO:He=1 :4 and CO:N2=1:9 typical for a CO laser were used. It was demonstrated that gas temperature grew from 1 10 K (initial temperature) up to 45O K for the first hundred microsecond after EBSD beginning and was staying at this value for a long time (more than 1 ms) for both gas mixtures. EBSD pulse duration was -3Oj.ts. The method of reconstruction of gas temperature time history was also applied for oxygen gas mixture CO:02=1:20 at gas pressure 0.04 atm, which was used for obtaining singlet delta oxygen in EBSD. The method can be used for diagnostic of non-equilibrium gas mixtures containing CO molecule.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Singlet delta oxygen (SDO) production in a pulsed e-bearn sustained discharge (EBSD) ignited in molecular oxygenwith carbon monoxide stabilizing this discharge is theoretically and experimentally studied. Temporal behavior of SDOconcentration and yield in the EBSD afterglow is analyzed. Experimentally measured SDO yield for oxygen mixture 02:Ar:CO= 1 : 1 :0.05 at total gas pressure 30 Ton comes up to 7% at specific input energy (SIE) of —3.O kJ/(l atm(02+CO)), whereas its theoretical value riches -17.5%. The efficiency of SDO production is theoreticallyanalyzed as a function of the STE. 1. INTRODUCTION Molecular oxygen in the first excited electronic state 02(a1 Ag), so-called singlet delta oxygen (SDO), is an energy donorfor atomic iodine in an oxygen-iodine laser (OIL)[1]. It used to be produced in a chemical generator [1]. One of the alternative methods of the SDO production is an electric discharge (see, for instance, [2-4]), the SDO yield being sensitive to the E/N parameter. The latter should be close to 1O16

Last years, CO laser physics has been advanced by researches of CO overtone laser operated on high vibrational levels. An extension of kinetic model to multi-quantum vibration-vibration exchange and development of fully self-consistent model of CO laser are described. The theoretical model developed is verified by comparison with experimental data on overtone CO laser characteristics and laser gain dynamics. Current status of experimental achievements in CO laser characteristics in both fundamental and overtone bands are reported.

Absorption spectra of chemically produced singlet oxygen O2(α1Δg) in the vicinity of 1.91 μm wavelength were recorded by intracavity laser spectroscopy technique. The line strengths for Q-branch transitions of the (0,0) band of the b1Σg-α1Δg system were measured. Measurements of the O2(α1Δg) yield for an electric discharge are presented.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Electric properties and spectroscopy of an e-beam sustained discharge (EBSD) in oxygen and oxygen gas mixtures at gas pressure up to 100 Torr were experimentally studied. The pulsed discharge in pure oxygen and its mixtures with noble gases was shown to be very unstable and characterized by low input energy. When adding small amount of carbon monoxide or hydrogen, the electric stability of the discharge increases, specific input energy (SIE) per molecular component being more than order of magnitude higher and coming up to 6.5 kJ/(l atm) for gas mixture O2:Ar:CO = 1:1:0.1. The results of experiments on spectroscopy of the singlet delta oxygen O2(a1Δg)(SDO) and O2(b1Σg+) states in the EBSD are presented. The calibration of the optical scheme for measuring the SDO absolute concentration and yield using the detection of luminescence of the SDO going from a chemical SDO generator was done. The preliminary measurement of the SDO yield demonstrated that it was ~3% for the SIE of ~1 kJ/(l atm), which is close to the results of theoretical calculations for such a SIE. Theoretical calculations demonstrated that for the SIE of 6.5 kJ/(l atm) the SDO yield may reach ~20% exceeding its threshold value needed for oxygen-iodine laser operation at room temperature, although a part of the energy loaded into the EBSD goes into the vibrational energy of the molecular admixture, (which was experimentally demonstrated by launching a CO laser operating on an oxygen-rich mixture O2:Ar:CO = 1:1:0.1 and measuring its small-signal gain).

The problem of development of a singlet delta oxygen O 2 ( 1 Δ g ) (SDO) generators alternative to chemical one needs application of the accurate methods of measuring the SDO concentration. A chemical SDO generator providing efficient operation of a chemical oxygen-iodine laser (COIL) is proposed to be used as a reference source for absolute calibration of the system measuring the SDO concentration. The principle of the COIL operation results in the threshold and output COIL parameters make it possible to evaluate the SDO yield with a satisfactory accuracy. A convenient sparger chemical SDO generator was applied as a reference source for absolute calibration of detectors of dimole (λ=634nm) and b→X (λ=762 nm) radiations. The values of b-state concentration formed in a longitudinal electric discharge were evaluated. The intracavity laser spectroscopy (ICLS) was absolutely calibrated for measuring the SDO concentration. ICLS method has a very high sensitivity and makes it possible to monitor the absorption corresponding to the O 2 ( 1 Δ g )→O 2 ( 1 Σ g + ) (λ = 1.91 μm) transition. The cross-sections of lines of the Q - branch of the vibrational 0-0 band of the a 1 Δ g → b 1 Σ g + transition of molecular oxygen were measured. The method developed was applied to measure the concentration of singlet oxygen produced in the microwave discharge. He - Ne laser (λ = 633 nm) was used for absolute calibration of a system monitoring the dimole radiation. The rate constant of the process responsible for dimole emission was measured. The value obtained k d =7.34•10 -23 cm 3 /s is in agreement with literature.

Radio frequency (RF)-excitation of carbon monoxide (CO) in a supersonic cavity with only a 10 cm gain length has yielded an observed fundamental band (Δv=1) multi-line lasing output power of 2.1 kW utilizing a one-pass resonator, with an electrical efficiency of 21%. More importantly, this work generated 50 W of overtone multi-line lasing around 2.7 micron. This was the first time lasing on CO overtone bands (Δv=2) had been demonstrated with a RF-pumped supersonic system.

The process of laser ablation of fused and crystal silica and natural silicates induced by pulsed CO2 laser irradiation (total pulse duration of 35 μs, laser pulse rise time of 0.1 μs, pulse energy of 10 J) has been studied. By action of focused laser radiation at the surface of samples the appearance of erosion plume at the irradiated surface take place. For study of ablation regimes the frame image of laser induced plume by use of high speed photography method with 2 microsecond expose of each frame have been made. It has been observed the formation of two different type of laser plume during laser pulse action. First type plume represents a long narrow plume with the onset close to start of laser pulse. The maximal length of this plume is about of 20 millimeter. The second type of plume represents a conical plume with the onset, which is late from laser pulse start for a few microsecond. The first type plume expands in to laser beam direction. The second type plume expands normal to the surface. The velocity of laser plume particles by means of measurements of moment transferred into samples during laser pulse action has been measured. It has been obtained, that value of this velocity varies in region of (l÷3)103 m/s in dependence of laser fluency value. The appearance of first time plume have a threshold which equal to 0.30 kJ/cm2 whereas the appearance of second type plume have not a such threshold and may take place at low laser fluency. We believe, that the first type plume connects with the selective ablation of SimOn complexes whereas second type plume connects with the thermal heating caused by dissipation of laser energy in to system of low frequency acoustics phonons.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An idea to replace singlet delta oxygen (SDO) generator working with wet chemistry by electric discharge generator has got much attention last years. Different kinds of discharge were examined for this purpose, but without a great success. The existing theoretical models are not validated by well-characterized experimental data. To describe complicated kinetics in gas discharge with oxygen one needs to know in detail processes involving numerous electronic excited oxygen molecules and atoms. To gain new knowledge about these processes experimental studies were made on electric discharge properties in gas mixture flow with independent control of inlet SDO concentration. The theoretical model extended to include minor additives like oxygen atoms, water molecules, ozone was developed. Comparison with careful experimental measurements of electric characteristics along with gas composition allows us to verify the model and make theoretical predictions more reliable. Results of numerical simulations using this model for an electron-beam sustained discharge are reported and compared with the experimental data.

Electric properties and spectroscopy of an e-beam sustained discharge (EBSD) in oxygen and oxygen gas mixtures at gas pressures up to 100 Torr was experimentally studied in large excitation volume (~18 liter). The discharge in pure oxygen and its mixtures with noble gases was shown to be very unstable and characterized by low input energy. When adding small amount of carbon monoxide or hydrogen, the electric stability of the discharge increases, specific input energy per molecular component being higher more than order of magnitude and coming up to 6.5 kJ/(l atm). Theoretical calculations demonstrated that for the experimental conditions the singlet delta oxygen yield may reach ~20% exceeding its threshold value needed for oxygen-iodine laser operation at room temperature. The results of experiments on spectroscopy of the singlet delta and singlet sigma oxygen states in the EBSD are presented.