Home – Home – Jornals – Atmospheric and Oceanic Optics 2016 number 2

The XII International Conference on pulsed lasers and their applications "Atomic and Molecular Pulsed Lasers AMPL" was held in Tomsk on September 14-18, 2015. Subjects of the Conference were traditionally devoted to results of theoretical and experimental studies of physical and chemical processes in laser active media; the newest active media and pumping methods; new laser technologies; fundamental topics of laser physics; application of lasers in science, engineering, medicine, and other spheres; discussion of problems and difficulties in development of laser-based equipment; new optical technologies.

Spectral and amplitude-temporal characteristics of plasma of a pulse-periodic nanosecond discharge initiated by runaway electrons in nitrogen in a pressure range 30-760 torr are investigated. Voltage pulses (U = 13 kV, FWHM is 10 ns, front duration is 4 ns, negative polarity, f = 60 Hz) applied to a cathode made of aluminum. The cathode had a cone form. Diameter of cone base, apex angle, and corner radius of cone apex were 6 mm, 30°, and 0.2 mm, respectively. A flat anode was located at distances of 2 and 6 mm from the cathode apex. Waveforms of voltage pulses, discharge current, radiation intensity, and spectra of discharge plasma were registered. At an interelectrode distance of 2 mm, colored jets of metal vapor were observed near the cathode apex throughout the pressure range. Size of jets was about 1 mm. Intense lines of atoms (Al I) and ions (Al II) of aluminum with wavelengths of 394.4; 396.15 nm and 622.62; 623.17; 704.21; 705.66; 706.36 nm were registered, respectively. Luminescence duration (> 2 ms) of the both was larger than the discharge current duration (~ 1 ms).

This work reports the fabrication of composite transparent ceramics consisting of Nd:YAG as the central part and Cr⁴⁺:YAG as the edge cladding. The central part of ceramics was shaped into 14-mm-diameter disk or 11-mm-side square and an outer diameter of the edge cladding was 18 mm or 23 mm, respectively. The central part of ceramics exhibited an optical transmittance of  84% at a wavelength of 1.06 µm. The concentration of Cr⁴⁺ in Cr⁴⁺:YAG ceramics with three different compositions was evaluated using measured transmission spectra and known absorption cross sections. Taking into account the infeasibility condition for self-excitation, the optimal composition of edge cladding was estimated to be 2.5 mol.% Cr + 0.5 mol.% Ca + 97 мол.% YAG.

The results of experimental studies of the gas mixture (laser active medium) effect on the generation energy and overall efficiency of excimer discharge ArF- (193), KrCl- (223), KrF- (248), and XeCl lasers (308 nm) operating on gas mixtures without the use of a buffer gas are presented. The optimal (in terms of maximum radiation energy) ratio of the gas components of the active media of excimer lasers are found, at which the efficient operation is achieved with a sufficiently high output power of the laser radiation. It is experimentally confirmed that for the rare gas halide discharge pumped excimer lasers the presence of a buffer gas in the active medium is not required for efficient laser operation. For example, in the binary excimer laser gas mixtures containing working rare gas and halogen-containing gas, for pulsed gas-discharge excimer lasers operating on electronic transitions of excimer ArF*, KrCl*, KrF*, and XeCl* molecules pumped by a transverse electric space discharge at reduced pressure a buffer-free gaseous mixture, laser pulse energy of up to 170 mJ and high pulsed laser power of up to 24 MW have been attained for the first time. The maximum total efficiency in an experiment for binary gas mixtures of KrF and XeCl lasers has reached 0.8%.

Results of numerical simulation of exciting a copper vapor laser (CVL) by a pulse-periodical inductive (electrodeless) discharge are presented. A variant of CVL with a ring active volume of the discharge chamber is studied. It is shown that such a chamber to a higher degree satisfies all the requirements for pumping by the inductive method than an ordinary cylindrical chamber. High output characteristics of lasing obtained in the numerical simulation confirm the possibility of CVL efficient pumping by the new inductive method.

Evolution of spatial and energy characteristics of start pulse with energy of 0.8 mJ and duration of 2 ps in the amplifier of THL-100 laser system have been studied experimentally and by numerical simulation. Laser radiation energy E = 2 J was obtained experimentally. In this work we present a 3D amplification model of conically diverging laser beams, which takes into account the spatial inhomogeneity of the pump and the geometry of THL-100 laser system amplifier. Description and the test results of the model are submitted. At the start pulse energy of 0.8 mJ the calculated radiation energy at the amplifier output reaches 2.4 J. Simulation results show that maximal intensity of the laser radiation in this mode reaches P = 60 GW × сm^-2. Evolution of energy and space-time structure of the laser pulse in the amplifier was investigated. It is shown that in the ideal case (excluding the processes of nonlinear interaction of laser beam with the active medium), at the start pulse energy of 5 mJ, the energy of the laser radiation at the output of the amplifier is increased to E _out = 3.8 J. In this mode, the maximal radiation intensity reaches a value of I = 148 GW × сm^-2.

The experimental results of the study of population inversion in the resonant electronic transition B³П _g -A³å _u⁺ of nitrogen ions by optical pump of air and pure nitrogen by a femtosecond laser pulse at a wavelength of 950 nm are presented. It is shown that the inversion results from selective settling of N₂⁺ (B²å _u⁺,n¢=0) excited state during multiphoton excitation of the autoionization state of the nitrogen molecule with energy of 18.7 eV. Seed photons for superradiance at transitions of molecular nitrogen ions are photons of the axial supercontinuum occurring in a filament at the corresponding wavelengths. The mode of the superradiance at the wavelength  = 358.4 nm, referred to the transition of the CN molecules, was implemented.

The results of measurement and calculation of parameters of radiation at  = 475 nm after compression in glass are presented. It is shown that there are three ranges of the energy density of the radiation entering to the compressor. In the first range of low intensity (energy density is 1-5 mJ/cm²), the influence of non-linearity on the output beam parameters is insignificant. The second range of moderate intensity (energy density is 5-10 mJ/cm²) is characterized by a significant loss of energy during the propagation of the output beam. The third range of increased intensities (energy density is 20 mJ/cm² or more) is characterized by a complete destruction of the spatial structure and the spectral composition of the output beam.

In this work, we showed that doping of sesquioxide based ceramics (for instance, Y₂O₃) by heterovalent ions leads to altering of polarizations. It results in variation of refractive index and wave-front distortion due to presence of volumes with increased content of heterovalent ions. It also contributes to lowering of transmittance and increasing of scattering in ZrO₂-, HfO₂-, or CeO₂-doped Y₂O₃ ceramic samples.

Investigations of 1Nd : Y₂O₃ + 6HfO₂, 1Nd : Y₂O₃ + 10HfO₂, 3Yb_{: Y2O3 + 5ZrO2, and 5Yb :Y2O3 + 5HfO2 laser ceramics with typical optical inhomogeneities called "orange peel" are presented. The diameter and thickness of samples were, respectively, 11 and 1.7-2.0 mm. Characteristic sizes of optical inhomogeneities causing the effect of "orange peel" were in a range from 10 to 300 mm.}

Results of experimental investigations of dependence of energy, temporal, spectral, and spatial characteristics of inductive HF laser generation on pumping conditions are presented. Gas mixture of hydrogen with F₂ or NF₃ or SF₆ and their mixtures with helium and neon were used as an active medium. A maximum generation energy of 19 mJ in a gas mixture He :_{H2 : NF3 - 45 :1 : 4 under pressure of 42 Torr has been achieved. Pulse duration (FWHM) was 0.42 ms that corresponded to a pulse peak power of 45 kW. Spectral composition of inductive HF laser generation has been investigated for the first time. Lasing spectrum consisted of seven groups of bands near 2732, 2763, 2798, 2835, 2873, 2893, and 2913 nm. Lasing shape had a ring form with diameter of about 20 mm and thickness of 4-5 mm. The laser had high stability when operating in pulse periodic regime. The light pulse amplitude divergence was within 5-6%.}

Laser parameters in Не-Ar(Kr, Xe)-F₂ and He-F₂ gas mixtures under pumping by runaway electron preionized diffuse discharge (REP DD) are studied. It is shown that the REP DD can be a source of efficient laser emission on XeF^* and KrF^* molecules. Laser action on transitions of molecular fluorine in the VUV range at 157 nm was obtained in REP DD for the first time. It was shown that high uniformity of REP DD allows one to increase laser pulse duration on rare gas fluoride molecules. Laser parameters obtained in the REP DD are comparable with those obtained under pumping by commonly used transverse discharges with preionization.

Gasdynamic processes that take place at a pulse-periodic discharge initiated by runaway electrons in atmospheric pressure air were studied with a laser monitor based on a CuBr laser. Voltage pulses (U = 13 kV, FWHM is 10 ns, front duration is 4 ns, negative polarity, f = 60-3200 Hz) applied to a cone copper cathode with diameter of cone base, apex angle, and corner radius of cone apex of 6 mm, 30°, and 0.2 mm, respectively. A flat copper anode was located at a distance of 2 mm from the cathode. It was established that products of discharge plasma with copper vapors are transferred in radial direction along a surface of the flat anode during 2.5 ms to a distance of 24 mm. The temperature of air heated by the discharge in the moment of its expanding was ~ 1 × 10³ K. It was shown that use of the laser monitor in transmitted light allows obtaining contrast images of optical inhomogeneities that arise at a gas discharge.

In this paper, the investigation results of gain characteristics of a CuBr laser with an unstable cavity are shown. The effect of the losses in the feedback channel of the unstable telescopic resonator with lateral output radiation was investigated. The possibility of allocating one laser wavelength through the use of band-pass filters in the cavity feedback channel was demonstrated.