N. N. Il’ichev

Generation of an Electrical Signal Upon the Interaction of Laser Radiation With Water Surface

A new physical effect lying in the generation of an electrical signal (ES) upon the interaction of IR laser radiation with the water surface at a laser fluences lower than the plasma formation threshold is studied. An ES amplitude exceeding 15 V is detected. A one-to-one relationship between the observed effect and the bulk explosive boiling of water is established, and a qualitative interpretation is proposed. In the case of irradiation of an open surface, the ES is generated due to bulk explosive boiling accompanied by the evacuation and splashing of the surface layer, the destruction of the double electric layer on the surface, and the spread of an electrified vapor-drop mixture (balloelectric effect). When the surface is covered with a transparent plate, ES generation can be caused by the charge separation upon the detachment of the water surface from the plate by a vapor bubble resulting from boiling and the displacement of the charged water surface upon the expansion and contraction of the bubble.

Nonlinear transmittance of ZnSe :Fe2+ crystal at a wavelength of 2.92 μm

ZnSe crystals doped with Fe2+ ions are produced with the diffusion method under the conditions for thermodynamic equilibrium of solid ZnSe, solid Fe, and vapors (SZnSe-SFe-V). The transmittance of the samples is varied from 7 to 50% (in the absence of the antireflection coating) for a wavelength of about 3 μm. It is demonstrated that the transmittance of the ZnSe:Fe2+ crystals increases with an increase in the energy density of the high-power laser radiation with a wavelength of 2.92 μm. An equation that describes the propagation of the resonant radiation in a medium with saturable absorption at an arbitrary ratio of the radiation pulse duration to the relaxation time of the medium is introduced for the analysis of the experimental dependence of the transmittance on the energy density.

EPR diagnostics of laser materials based on ZnSe crystals doped with transition elements

The electron paramagnetic resonance (EPR) spectra observed in laser materials based on zinc selenide (ZnSe) crystals doped with transition elements have been analyzed and identified. It has been shown that, in addition to working impurities (Cr2+, Co2+, or Fe2+), the diffusion layer exhibits EPR spectra of accompanying impurities due to the diffusion of transition elements (chromium, cobalt, or iron) used in the preparation of active materials for quantum electronics (lasers, switches) operating in the mid-infrared range. EPR diagnostics of these impurities can be used in the development of appropriate regimes for minimizing concentrations of accompanying impurities that adversely affect the performance characteristics of laser materials. It has been found that, during the diffusion of transition metals, ions of the accompanying impurity Mn2+, which is characterized by extremely informative EPR spectra, are embedded in the crystal lattice. It has been proposed to use these ions as ideal markers to control, on the electronic level, the crystal structure of the active diffusion layer.

Explosive boiling in water exposed to q-switched erbium laser pulses

Pressure signals generated in water under the action of erbium laser pulses (100–200 ns, 2.94 μm) are investigated with lithium niobate piezoelectric transducer. For the first time multiply short (subnanosecond) pressure pulses standing against smooth pressure background are observed when the laser intensity exceeds explosive boiling threshold.

Cobalt diffusion during doping of ZnSe single crystals

Cobalt diffusion into single crystals of the compound semiconductor ZnSe has been studied under the conditions of the SZnSe-SCoSe-LZn-V phase equilibrium at temperatures from 700 to 970°C, and the diffusion coefficients of cobalt in (100)-and (111)-oriented single-crystal samples of zinc selenide have been determined as functions of temperature. The diffusion rate of cobalt along the [111] direction is shown to exceed that along [100].

Photoacoustic and evaporation pressure signals in water irradiated with erbium laser pulses

Pressure signals in water exposed to erbium laser pulses with a duration of 200 ns, a wavelength of 2.94 µm, and an intensity modulated with a period of ∼ 5 ns due to mode beats were studied. It was found that the amplitude of the high-frequency component of the pressure signal, caused by this modulation, reproduces the behavior of the smooth component of the laser pulse shape at low irradiation intensities. As the intensity increases, behavior of the high-frequency signal amplitude is more complicated, showing significant decrease at certain instants of laser pulse exposures. Such behavior can be caused by the simultaneous effect of photoacoustic and evaporation mechanisms of pressure generation in irradiated liquid.

Effective 2.5-μm ZnSe:Cr2+ laser with transverse laser pumping

Effective lasing is obtained in the transversely pumped ZnSe single crystals that are doped with Cr2+ ions using diffusion methods. A Q-switched Er3+-doped glass laser with a radiation wavelength of 1.54 μm is used for pumping. The resulting laser energy is 150 μJ at an absorbed pump energy of 600 μJ, so that the efficiency is 25% and the slope efficiency is 29%. An increase in the gain (up to the superluminescence level) due to the application of the transverse pumping of the active element with a substantially non-uniform distribution of the dopant is discussed.

Diffusion coefficient of Fe2+ in single-crystal ZnSe

The diffusion coefficient of Fe in single-crystal ZnSe has been measured in the temperature range 886–995°C. The 995°C diffusion coefficient is (47 ± 5) × 10−11 cm2/s, and the average activation energy for Fe diffusion is 2.9 ± 0.3 eV.

Hafnia-yttria-alumina-silica based optical fibers with diminished mid-IR (>2 µm) loss

Fabrication details and basic characteristics of a set of novel multimode hafnia-yttria-alumina-silicate (HYAS) core-glass based fibers, one of which is co-doped with bismuth (Bi), for the mid-IR (> 2 µm) spectral range are reported. It is demonstrated that fibers of this type possess low fundamental loss in the spectral range beyond 2 µm, lowered by fewer times as compared to conventional silica-based ones, even at moderate (units of mol.%) co-doping with hafnium. This makes them attractive for versatile mid-IR applications. Furthermore, HYAS core-glass fiber co-doped with Bi is revealed to have all the signs of ‘active’ (fluorescing) Bi-related centers, thus being suitable for lasing/amplifying in the near-IR spectral range.

CO oxidation with oxygen of the catalyst and gas-phase oxygen over (0.5−15)%СоО/СеО2

The CO adsorption species on Co3O4 and (0.5-15%)CoO/CeO2 catalysts have been investigated by temperature-programmed desorption and IR spectroscopy. At 20°C, the largest amount of CO is adsorbed on the 5%CoO/CeO2 sample to form, on Com2+On2+ clusters, hydrogen-containing, bidentate, and monodentate carbonate complexes, whose decomposition is accompanied by CO2 desorption at 300 and 450°C (1.1 × 1020 g–1). The formation of the carbonates is accompanied by the formation of Co+ cations and Co0, on which carbonyls form. The latter decompose at 20, 90, and 170°C to release CO (2.7 × 1019 g–1). Part of the carbonyls oxidizes to CO2 upon oxygen adsorption, and the CO2 undergoes desorption at 20°C. Adsorbed oxygen decreases the decomposition temperature of the H-containing and bidentate carbonates from 300 to 100-170°C and maintains the sample in the oxidized state, which is active in subsequent CO adsorption and oxidation. CO oxidation by oxygen of the catalyst diminishes the activity of the sample in these processes and increases the decomposition temperature of the carbonate complexes. Taking into account the properties of the adsorption complexes, we concluded that the H-containing and bidentate carbonates are involved in CO oxidation by oxygen of the catalyst at ~170°C under isothermal conditions. The rate limiting step is the decomposition of the carbonates, a process whose activation energy is 65-74 kJ/mol.