Compact-sized excimer laser with two-side preionization

Compact-sized monopulse excimer laser with the foot-print equal to only 250×80 mm, total height 250 mm and beam axis height 50 mm was designed. Output energy at the wavelength 308 nm (XeCl* mixture) is 5 mJ, maximal repetition rate – 1-2 pulses per second, beam divergence – 8 milliradians. The small foot-print, small axis height of beam in combination with low weight of laser (5 kg) allow this laser to be used in various optical schemes, where traditional, typical bulky ecximer lasers are unapplicable. Moreover, small dimensions, low weight in combination with low energy consumption (a few watts) allow them to be used in clear “field” conditions. Beside abovementioned characteristics, the designed laser differs from the traditional ones by two-side preionization that has a “spark” character near the “hot” massive electrode and the so-called “capacitive” or “barrier” one under the ground grid. This two-side preionization provides both igniting and sustaining of wider discharge thus allowing to reach beam with higher symmetry – its cross-section is 15×20 mm²

Voids’ layer structures in silicon irradiated with high doses of high-energy helium ions

Structural and optical properties of single crystal silicon irradiated with 27.2 MeV helium ions by using fluences Ф ≥ 10¹⁶ ion/cm² were studied at various beam currents. It was found that at currents 0.25 to 0.45 μА, heavily damaged layers containing voids were formed in ion path in Si and behind it. The number of layers in the ion path region depends on the beam intensity. With increasing the beam current up to ~1 μA, the layer structures consisting of voids were observed only in the ion path. As helium is poorly soluble in Si, during implantation it collects in the gas-filled vacancy complexes. We consider that, like to the case of keV-ion implantation at fluences of Ф ≥ 10¹⁶ ion/cm² , an amorphous layer is created in the ion stopping region at annealing. Moving by recrystallization fronts on both sides of the amorphous layer, vacancy clusters are collected inside, coalesce and form voids. It is a combination of high energy and high fluence helium implantation that can form layered structure with voids in silicon, as observed by us. At present, there is no strict explanation of the mechanism of voids’ ordering (forming of superlattice of them). Especially, it concerns the void layer formation beyond helium ion path. The concept of mobile solitons is used. Formation of the “lattice” from the voids leads to swelling of the material. Further researches are necessary to understand these processes and control them

Spectral control of powerful diode lasers with enhanced output by external cavity based on volume holographic grating

To achieve the maximum efficiency in single-frequency lasing mode of laser diode with external cavity, it is necessary to minimize losses in the optical system for the output beam and to provide the optimal frequency-selective feedback. In this paper, we have investigated the scheme of an external cavity diode laser (ECDL) based on phase volume holographic grating (VHG). Angular and spectral selectivities of the holographic grating allow to adjust the optical feedback with low losses in the cavity, and it can be used for the frequency narrowing of diode-array bars. Here, the optimal parameters of VHG and the temperature dependence of the diode laser bar spectrum have been studied, and the proposals on VHG design have been developed

Numerical Method for Solving the Inverse Problem of Quantum Scattering Theory

We present a new numerical method for solving the problem of the reconstruction of interaction potential by a phase shift given on a set of closed intervals in (l,k)-plane, satisfying certain geometrical ”Staircase Condition”. The method is based on the Variable Phase Approach and on the modification of the Continuous Analogy of the Newton Method

Status of child population health — the future of the country (part 1)

The article of the team of scientists of pediatricians and organizers of pediatric health care of Ukraine is devoted to the study of the main trends in the health status of children over last 22 years. The results of the analysis of the incidence and prevalence of diseases among Ukrainian child population, infant mortality rates over the past two decades demonstrates that they remain significantly higher than the average European indicators against the background of a progressive decrease in the number of child population at 3,16 million people. The prevalence of childhood diseases in Ukraine over past 22 years has grown by 41 %, the incidence of childhood diseases arose by 36 %. The article considers the ways of solving a number of new social and medico-ecological problems that negatively affect child health

Child health status — the future of the country (part 2)

The article deals with the problems of increasing the incidence and prevalence of childhood diseases during 1994–2016 against the background of a global reduction in the staffing of children’s specialists by 1.7 times, with an extremely inadequate supply of the regions of the South-East, Donetsk and Luhansk regions. All of this has a negative impact on the proper medical care of the child population, including the detection of childhood diseases. The authors substantiate the need to restore the personnel and material-technical potential of the pediatric service, the development of modern diagnostic and treatment technologies, the preservation of immunization and the prevention of disability of common childhood diseases that is an important component of the national health care and safety system of the country as a whole

State of the Climate in 2012

International audienceEditors note: For easy download the posted pdf of the State of the Climate for 2012 is a very low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download