Applying CO2 and ytterbium fiber lasers to high-performance production of refractory oxide nanopowders

The main features of obtaining refractory oxide nanopowders using a repetitively-pulsed CO2-laser (10,6 µm) with an average radiation power of 500 W or a CW ytterbium fiber laser (1,07 µm) with a radiation power of up to 700 W are considered. In particular, the influence of pressure, buffer gas composition and average radiation power on the size of nanoparticles and the productivity of their obtaining were studied. Depending on the thermophysical properties of the material, in atmospheric pressure air the productivity of nanopowder synthesis varies from 15 – 23 g/h (YSZ) to 350 g/h (WO3). The mass yield of nanopowder obtained upon evaporation of one target is usually is 30 wt. % of the weight of the initial target. The obtained nanopowders contain weakly agglomerated nanoparticles of spherical shape. The average size of nanoparticles 11 – 20 nm weakly depends on their material. The most important features of using a CW ytterbium laser to obtain nanopowders of refractory oxides are their high transparency for radiation of 1,07 μm, as well as the spraying of many melt droplets. These features led to a reduction in the productivity of nanopowder production and its mass yield. On the other hand, the scattering of laser radiation in porous of the initial target and its concentration in some regions makes it possible to efficiently evaporate oxide targets from materials with a refractive index of more than 1.7 – 1.75. The transition to a repetitively-pulsed mode of radiation (pulse duration 120 μs, square waveform, and peak power 600 W), an increase in the spot diameter and the speed of beam movement over the target surface made it possible to significantly reduce droplet spattering and increase the yield of Nd: Y2O3 nanopowder from 9,7 to 30 wt.% of the weight of the initial target. However, a twofold decrease in the average radiation power led to the fact that the productivity of obtaining the nanopowder was only 15 g/h. Thus, to obtain nanopowders of refractory oxides, it is desirable to use a quasi-CW fiber ytterbium laser, which is specially designed for operation in a repetitively pulsed mode. The obtained nanopowders YSZ, Nd: Y2O3, Al2O3, etc. are used for the manufacture of ceramic solid electrolytes of the YSZ type and highly transparent laser ceramics.

Pulse Рhotochemical Decomposition of Phenol in Wastewater

Photochemical decomposition of phenol with a concentration of 5 to 24 mg/L using hydrogen peroxide and ultraviolet irradiation (UV/H2O2) was studied. Xenon flash lamp was chosen as a radiation source. It emits high-intensity continuous-spectrum radiation in a wide wavelength range from 200 to 1000 nm. The effect of the initial concentration of hydrogen peroxide and the source average radiation power on the phenol destruction rate were studied. An extremum in the dependence of the phenol decomposition rate constant on the initial concentration of hydrogen peroxide was found. Kinetic model of the process based on the obtained data was developed. It was tested by predicting phenol destruction rate with the different process parameters and gave good accuracy.

D.Sc. in Chemistry, Head of the Labora tory, Siberian Physical-Technical Insti tute of Tomsk State University

The article considers and analyzes an important stage in the development of laser systems for metal vapor from the point of view of biomedical applications. Since the advent of the first generation of domestic medical facilities with pulsed lasers on metal vapors, in particular, copper vapors (LSM), which were created in the FSUE “Research and Production Enterprise ‘Istok’”, not much time has passed. Now similar studies are widely developed and include a variety of uses, for instance, in oncology for treatment with photodynamic therapy (PDT), angioplasty of intravascular destruction of atherosclerotic lesions, dermatology and cosmetology for the treatment of facial skin defects, as well as otorhinolaryngology, gynecology, proctology, urology, and others. In that cases, doctors use the Yantar-2Fand Yakhroma-2 installations, developed on the basis of the “Kurs” LPM with radiation wavelengths λ = 510.6 nm and 578 nm and the average radiation power Prad= 5–10 W and tunable in wavelengths in the range of λ = 620–670 nm. Laser radiation is delivered to the affected area of a bio-object using a flexible light-guide cable with a diameter of 400, 600 or 800 μm fiber, which is one of the most convenient medical instruments. A compact and air-cooled medical installation of the new generation “Yakhroma-Med” based on the pulsed LPM “Kulon” with an average radiation power at the output of the light-guide cable Prad= 1–3 W uses in dermatology and cosmetology (together with the Lebedev Physics Institute of the Russian Academy of Sciences). Today, YakhromaMed is the leader in non-ablative technologies and is optimal for removing vascular, pigmented and unstained skin defects, treating acne and smoothing wrinkles. It is used in more than 100 clinics in Russia and abroad. Moreover, for scientific and practical medicine in the field of oncology, low-intensity laser therapy and surgery, dermatology and cosmetology, etc., a compact air-cooled industrial multifunctional high-intensity medical unit “Kulon-Med” (similar to Yakhroma-Med) based on two pulsed lasers was developed: LM “Kulon” with an average radiation power Prad= 10 W and LVRK with radiation tunable in wavelengths in the range λ = 620–750 nm and radiation power Prad= 1–3 W (together with Ltd. NPP VELIT, Kurchatov Institute and the Hertzen Hermitage Research and Development Institute). The laser radiation is transported using four flexible light-guide cables with a conductive quartz fiber diameter of 400 and 600 μm, which makes it possible to perform a therapeutic and prophylactic procedure simultaneously in several rooms. Medical facilities of this class have been put in many medical institutions. This report on the use of CVL in medicine says only about the developments in theMoscow region.

Means for generating ultra-wideb and radio-frequency emissions with semiconductor field generators

The paper considers the perspective of using powerful semiconductor subnanosecond electrical pulse generators as radiation modulators. We give the data on determining the amplitude-time and spectral radiation parameters of a synchronous active antenna array, the angular divergence of the array radiation. We also estimate the efficiency of converting the electric excitation energy of the antennas into the energy of the directed ultra-wideband radiation in the main directional lobe. Findings of the research show that the effective peak radiation power of the terawatt level is reached at the excitation power of the gigawatt level, and the effective average radiation power of tens of megawatts is achieved with the primary power consumption of modulators of tens of kilowatts.