The results of experimental modeling of a wireless optical communication channel in an aquatic environment are presented, which were carried out on the basis of a laboratory installation for underwater communication, developed at MTUCI. The possibility of creating cheap and compact optical communication systems for high-speed data transmission at distances up to 100 m has been demonstrated. The necessity of using the technology of quantum key distribution for information security is shown. The key elements required for the implementation of the quantum distribution of cryptographic keys in the ocean are analyzed.
The possibilities of using plasma formed by laser radiation in Ge- and Si semiconductors to create plasma antennas are analyzed. The dependences of the amplitude of the emitted microwave signal in the range of 6-7.5 GHz on the laser power and the length of the irradiated section on the semiconductor plate, which served as a transmitting vibrating antenna, were obtained. It is shown that the amplitude of the transmitted signal during the formation of a plasma antenna in Si and Ge crystals can be increased by more than an order of magnitude. The proposed method for creating a semiconductor plasma antenna with initiation by laser radiation has great prospects for creating materials with controlled electromagnetic characteristics in the radio, microwave and THz spectral ranges.
This paper reports on first experimental study of a self-sustained volume discharge (SSVD) in c-C4F8. The discharge voltage and current oscillograms are taken over a wide range of gas pressures. How and why this discharge radically differs from that in other strongly electronegative gases is considered in terms of the theory of the vibrational relaxation in polyatomic molecules. For the first time an SSVD in c-C4F8 preheated by CO2-laser radiation has been investigated. The unusual behavior and temperature-dependent characteristics of this discharge are revealed. There is much discussion on the peculiarities of an SSVD in a preirradiated c-C4F8. To refine the static limiting field in c-C4F8 the static dielectric strength of c-C4F8 is measured on changing the gas pressure by nearly two orders of magnitude.
Characteristics of a laser on polycrystalline ZnS:Fe2+ subjected from two sides to diffuse doping at room temperature are investigated. The sample was pumped by a non-chain electrodischarge HF laser with the radiation pulse FWHM duration of ~140 ns. The diameter of pumping radiation spot on the surface of crystal was 3.8 mm. Further increase of the size of pumping spot was limited by parasitic generation arising due to a high concentration of Fe ions in the near-surface layer of sample at a relatively small depth of doping (short length of active medium). The output energy of ZnS:Fe2+ laser was 25.5 mJ at the slope efficiency with respect to the energy absorbed in the crystal of 20%. Characteristics of lasers on polycrystalline ZnS:Fe2+ and ZnSe:Fe2+ have been compared in equal pumping conditions. The slope efficiency of ZnSe:Fe2+ laser was 34%. At equal pumping energy absorbed in the samples, the duration of ZnSe:Fe2+ laser radiation pulse was longer than that of ZnS:Fe2+ laser. Possibilities of increasing the efficiency of ZnS:Fe2+ laser operation at room temperature by improving the technology of sample manufacturing and reducing the duration of pumping pulse are discussed.
Generation characteristics of laser on polycrystalline ZnSe:Fe2+ samples doped by the diffusion method have been investigated at room temperature under the pumping by an electrodischarge HF laser. With the sample doped from two sides (working surfaces) the obtained generation energy was E=253 mJ with the slope efficiency ηsl=33% and efficiency with respect to the absorbed energy ηabs≈28% at the elliptical shape of the pumping spot of dimension a×b=6.8×7.5 mm. It was established that possibilities of further increase of generation energy on samples of this type by increasing the pumping spot area (at a constant density of the pumping energy) are limited by developing parasitic generation that is inherent in lasers with disk geometry. First investigation results are presented for a laser on the polycrystalline sample produced by the technology capable of providing zero doping component concentration on the surface and a maximal concentration at the centre of the sample (sample with "internal doping"). Prospects are discussed for increasing the generation energy of ZnSe:Fe2+ laser at room temperature by developing multilayer samples on the bases of the doping technique mentioned.
The burning voltages of a self-sustained volume discharge (SSVD) in SF6 and SF6-C2H6 mixtures subjected to a 10.6 μm pulse CO2 laser irradiation are measured on varying the laser fluences and delays between the laser and voltage applications over a wide range. These voltages are found to considerably increase as the specific absorbed laser radiation energy increases. The observed effect is treated in terms of enhanced electron attachment due to the capturing of electrons by vibrationally excited molecules of SF6. Also given are the results of measuring the burning voltages in a non-irradiated confined SSVD in the same mixtures versus the specific electric energy deposited. Most plausible scenarios of vibrational relaxation in SF6 are qualitatively discussed and, on this basis, some inferences about the peculiarities of electron attachment to vibrationally excited molecules of SF6 are drawn. At lowest values of the specific absorbed laser radiation energy, realized in the present experiments, no significant impact on the discharge voltage was observed. Together with data on the burning voltages in a non-irradiated SSVD this fact has allowed some conclusions about the role of electron attachment to the discharge-produced vibrationally excited molecules of SF6. In particular the results obtained appear to give no evidence for the electron impact vibrational excitation of SF6 is capable of considerably affecting the operating characteristics of current electric discharge non-chain chemical HF lasers using SF6 and SF6-based mixtures.
The feasibility of producing continuous laser sparks (CLSs) with a resistance per unit length of 100-400 Ω/cm by focusing radiation from CO2 laser with a conical mirror is demonstrated. The laser energy input per unit length required for this is experimentally found to be equal to ~200 J/m. The possibility to efficiently control the trajectory of an electric discharge by means of a CLS is demonstrated. A CLS is found to be an analogue of a high-conductivity metal rod during the electric breakdown and electric potential transfer. The effect of polarity in the electric breakdown of air gaps between the CLS plasma channel and a metal rod is discovered and interpreted. The transverse structure of the CLS conductivity is investigated. Most likely the CLS conductivity at the initial state is due to the photoionization of air by the radiation of primary nuclei of the optical breakdown.
This paper reports on the physics of a self-sustained volume discharge without preionization, self-initiated volume discharge (SIVD), in working mixtures of nonchain HF(DF) lasers. Dynamics of SIVD in discharge gaps of different geometry is thoroughly described. The mechanisms of restricting current density in a diffuse channel in electric discharges in SF6 and SF6 based mixtures determining the possibility of the existence of SIVD were suggested and analyzed using simple models. It is shown that the most probable mechanisms are the electron impact dissociation of SF6 and other mixture components, electron-ion recombination and electron attachment to vibrationally excited SF6 molecules. Starting from a comparison analysis of the rate coefficients of these processes, it was found that the electron-ion recombination is capable of compensating for electron detachment from negative ions by electron impact. It is established that SIVD can be observed not only in SF6, but in other strongly electronegative gases, e.g., in C3F8 and C3HCl3. Analysis is given of the factors determining uniformity of active medium in nonchain HF(DF) lasers. Some special features of operating nonchain HF(DF) lasers with small, 2÷6cm, apertures are carefully examined and the results of measuring the nonchain HF(DF) laser divergence are presented. Consideration is given to the problem increasing the aperture and discharge volume of nonchain HF(DF) lasers and, based from the experimental results, the possibility is shown of increasing their energy to a level of ~ 1kJ and above.
This paper reports on investigating self-sustained volume discharge (SSVD) characteristics in CH3I, C3H7I, C4H9I, CF3I and their mixtures with SF6 and N2, employed as buffer gases, and with O2. The investigations performed in the plane-plane electrode system displaying high electric field edge enhancement have shown that in C3H7I, C4H9I and their mixtures with SF6, N2 and O2 SSVD is realized in the form of a self-initiated volume discharge (SIVD)- SSVD with no any preionization. Addition of SF6 or N2 in C3H7I, C4H9I leads to increasing the discharge stability, the latter being not adversely affected by addition of O2 in amounts of up to 300% of the iodide partial pressure. The fact that SSVD in C3H7I and C4H9I develops in the form of SIVD is indicative of these discharges to be promising for creation of high power pulsed and pulsed-periodic COIL. SIVD has been performed at total mixture pressures of up to 72 Torr and energy depositions of up to 130J/l in a volume of 1.5 l. The performed experimental modeling involving laser geometry of the discharge gap gives firm evidence that SIVD is promise for being used in creation of pulse and pulse-periodic COIL.
A role of UV preionization in non-chain HF(DF) lasers has been investigated. The influence of preionization on the discharge uniformity and on the duration of stable burning of a self-sustained volume discharge (SSVD) in working mixtures of non-chain HF lasers as a function of the energy stored in capacitors are comprehensively studied. Also presented are discharge photographs taken under identical conditions with and without preionization. It is shown that SSVD characteristics and laser energy are scarcely affected by preionization if the discharge lasts more than 150ns and the cathode surface area is in excess of 300 cm2. In HF lasers with the cathode surface area and discharge duration of less than 300cm2 and 150ns, respectively, preionization is essential for nothing but stabilization of the discharge voltage and breakdown delay and for improving discharge uniformity. If the opposite takes place preionization has no influence on the laser characteristics.
This paper reports on the physics of a self-sustained volume discharge without preionization, self-initiated volume discharge (SIVD), in working mixtures of nonchain HF(DF) lasers. Dynamics of SIVD in discharge gaps of different geometry is thoroughly described. The mechanisms of restricting current density in a diffuse channel in electric discharges in SF6 and SF6 based mixtures determining the possibility of the existence of SIVD were suggested and analyzed using simple models. It is shown that the most probable mechanisms are the electron impact dissociation of SF6 and other mixture components, electron-ion recombination and electron attachment to vibrationally excited SF6 molecules. Starting from a comparison analysis of the rate coefficients of these processes, it was found that the electron-ion recombination is capable of compensating for electron detachment from negative ions by electron impact. It is established that SIVD can be observed not only in SF6, but in other strongly electronegative gases, e.g., in C3F8 and C3HCl3. Analysis is given of the factors determining uniformity of active medium in nonchain HF(DF) lasers. Some special features of operating nonchain HF(DF) lasers with small, 2 divided by 6 cm, apertures are carefully examined and the results of measuring the nonchain HF(DF) laser divergence are presented. Consideration is given to the problem increasing the aperture and discharge volume of nonchain HF(DF) lasers and, based from the experimental results, the possibility is shown of increasing their energy to a level of approximately 1 kJ and above.
The paper studies a self-sustained volume discharge without preionization-self-initiated volume discharge (SIVD)--to excite non-chain HF lasers on SF6-C2H6 mixtures. Once initiated by a local discharge gap breakdown, SIVD is found to propagate then over the whole gap normally to the applied electric field through successively starting diffuse overlapping channels at a voltage close to the quasi- stationary value. With forming new channels, the current through those previously originated decreases. The volume occupied by SIVD tends to expand with increasing the energy released within the discharge plasma, whereas a discharge bounded by a dielectric surface shows a simultaneous increase both in burning voltage and current. All these features combined allow a concept to be put forward of the existence of certain restriction mechanisms depending on the specific energy released and not permitting the total deposited energy to pass through a single channel. It is suggested that SF6 dissociation by electron impact and the electron attachment to vibrationally excited SF6 molecules are just those mechanisms. Simple analytical models have been developed allowing these mechanisms to be qualitatively described.
Scaling problems are considered for non-chain HF laser operating on mixtures of SF6 and hydrocarbons in which a chemical reaction is initiated by self-sustained volume discharge. The possibility of obtaining a volume discharge in SF6 and in corresponding mixtures without preionization, i.e., self- initiated volume discharge (SIVD) is a new qualitative result in solving the scaling problem for non-chain lasers. The dynamics of SIVD evolution has been investigated. The possibility of obtaining SIVD is determined in SF6 by mechanisms that limit the density of current, are related to specific energy release, and prevent the total energy from flowing through a single channel. A simple mode is developed for calculating the discharge characteristics in non-chain laser. The model provides a good agreement with experiment data. The obtained energy of nonchain HF-laser is 407 J and that of DF-laser is 325 J with the electric efficiency 4.3 percent and 3.4 percent, respectively. A possibility is estimated of creating non-chain HF lasers with the output energy of the order of kilojoules and higher on the basis of experimental data obtained.
Initiation mechanisms of self-sustained volume discharge (SSVD) are analyzed in mixtures of SF6 with hydro-carbons (deuterocarbons). The possibility is shown to obtain SSVD in a large volume of SF6 and hydrocarbon (deuterocarbon) mixtures without preionization in the discharge gaps possessing high edge nonuniformity of electric field. The scaling characteristics of nonchain HF (DF) laser are investigated. The highest generation energy has been achieved, namely, 397 J for HF laser and 312 J for DF laser at the electric efficiency 3.8% and 3%, respectively.
It is established that higher stability of a self-sustained volume discharge (SVD) without pre-ionization in mixtures of SF6 with hydrocarbons (deuterocarbons) is explained by higher surface density of cathode spots and the corresponding reduction of the current across a spot. It is shown that SVD may occur in mixtures of SF6 with hydrocarbons (deuterocarbons) without special systems for gas pre- ionization in extremely compact system of electrodes. Wide- aperture non-chain HF (DF) lasers with high radiation energy can be created on this basis. Such laser with the aperture approximately 20 cm provided the generation energy 190 J in the case of HF and 152 J in the case of DF and the electric efficiency 3 and 2.4 %, respectively.
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