acta physica slovaca

Abstract: Dc and hf gas discharges used in industrial devices are strongly nonlinear media whose characteristics and behavior critically depend on the type of the device and on the way and the amount of energy injected into the system. Consequently, considering a certain industrial device, it is possible to select, by gradually changing the injected energy, the working regimes that offer the most suitable conditions for a certain practical applications. The consideration of the nonlinear behavior of gaseous conductors (plasmas), created in dc and hf electric fields, and implicitly of the self-organizing phenomena at their origin become important for certain applications.

Abstract: In this work, we have studied the composition of polymer thin films prepared by plasma polymerisation and d.c. magnetron sputtering. We investigated two sets of samples, one set Ag composite layers and the second set nitrogen containing plasma polymers, both deposited on the silicon substrate. The Rutherford Backscattering Spectrometry and Elastic Recoil Detection Analysis measurement was used to characterize the composition and to determine the element depth profiles in the deposited layers.

Abstract: The application of a microwave plasma process operated at atmospheric pressure to the decomposition of volatile organic compounds has been investigated. This microwave plasma system consists of a 2.45 GHz magnetron detached from a household microwave oven, a directional coupler, a three-stub tuner, a tapered waveguide terminated by a movable plunger, and plasma flame section where a quartz tube with a copper nozzle is located. In this system, the organic compounds such as toluene and trichloroethylene can be decomposed in the way of thermal incineration as well as by the reactions with a variety of active species formed during plasma discharge. The effect of feed gas flow rate on the decomposition was significant because it changed the gas temperature, but the initial concentration of the organic compound in the range of 210-2,100 ppm did not largely affect the decomposition efficiency. The principal byproduct was nitrogen oxides because this system was operated at high temperature. To improve the decomposition of the organic compounds, argon was used as a plasma-assisting gas, together with the air-like feed gas mixture. Large enhancement in the decomposition efficiency of the organic compounds was achieved by the use of argon.

Abstract: The paper is devoted to a computer study of morphological properties of thin composite films. A computer experiment was suggested for testing of suitable methods of morphological analysis of the films. A computer model was prepared to study the 3D structural properties on the basis of 2D projections or sections. A special attention is devoted to covariance method.

Abstract: Dense Plasma Focus, a device invented more than 30 years ago, is until now one of the most bright and efficient source of ionizing radiation (neutrons, soft and hard X-rays, electron and ion streams). Being relatively cheap and flexible (energy stored in condenser battery and driving the phenomena from 0.2 kJ up to 1MJ) DPF fits very well to a number of applications in different fields e.g. nanotechnology, material science, defectoscopy, biology, medicine etc.. Already investigated and existing applications of DPF, as well as those of future potential are presented and discussed in the paper. Specific demands for radiation sources based on DPF principle to be used in above mentioned fields, problems encountered and methods how to overcome them are briefly indicated.

Abstract: Polyester cord threads, which are used as a reinforcing materials of rubber blend, have been treated in atmospheric-pressure H$_{2}$O plasma in order to enhance their adhesion to rubber. The atmospheric-pressure H$_{2}$O plasma was generated in an underwater diaphragm discharge. The plasma treatment resulted in approximately 100\% improvement in the adhesion. Scanning electron microscopy investigation indicates that not only introduced surface polar groups but also increased surface area of the fibres due to a fibre surface roughening are responsible for the improved adhesive strength.

Abstract: Waveforms of the first negative current pulses in a short negative point-to plane gap in pure argon and argon with SF$_{6}$ admixture have been investigated with a nanosecond time resolution at a gas pressure 50 kPa as a function of applied gap voltage and content of SF$_{6}$ in the mixture. We have made an attempt to explain the differences in the discharge development in pure argon and in argon with admixture of SF$_{6}$ based on the observed changes of the pulse shape. The experimental results obtained will be discussed in context with existing computer simulation models.

Abstract: A general procedure for correct two-centre Coulomb Green's function is given. It is motivated by the incorrect formula of Liu. We start with partial expansion of Green's function in terms of spheroidal functions. Various expansions of regular and irregular radial Coulomb spheroidal functions are also presented. The paper also contains two-centre Green's function for continuous spectrum. This article may be considered as a basis for the three-centre Coulomb problem, which we aim to study in future.

Abstract: Gain clamping is demonstrated in single-pass and double-pass long wavelength band erbium-doped fiber amplifiers (L-band EDFAs). A C/L-band wavelength division multiplexing (WDM) coupler is used in single-pass system to generate a laser at 1566 nm. The gain for the amplifier is clamped at 15.5 dB with gain variation of less than 0.2 dB from input signal power of $-40$ to $-14$ dBm with almost negligible noise figure penalty. However, the flatness of gain spectrum is slightly degraded due to the un-optimisation of erbium-doped fiber (EDF) length. The advantage of this configuration is that the oscillating light does not appear at the output port of the amplifier. A highly efficient gain-clamped L-band EDFA with improved noise figure characteristic is demonstrated by simply adding a broadband conventional band fiber Bragg grating (C-band FBG) in double pass system. The combination of the FBG and optical circulator has created laser in the cavity for gain clamping. By adjusting the power combination of pumps 1 and 2, the clamped gain level can be controlled. The amplifier gain is clamped at 28.1 dB from $-40$ to $-25$ dBm with gain variation of less than 0.5 dB by setting the pumps 1 and 2 at 59.5 and 50.6 mW, respectively. The gain is also flat from 1574 nm to 1604 nm with gain variation of less than 3 dB. The corresponding noise figure varies from 5.6 to 7.6 dB, which is 0.8 to 2.6 dB reduced compared to those of unclamped amplifier.