On the possibility of soliton-like double-frequency propagation of femtosecond pulses in an optical fiber under conditions of second harmonic generation

A soliton-like mode of double-frequency propagation of femtosecond pulses during second harmonic generation (SHG) in optical fibers is predicted on the basis of computer simulation. The essence of this mode is that, under certain conditions, the central part of the pulses of both the fundamental and the second harmonic waves propagate without a change in the intensity of either wave. This mode can be realized by either of two schemes of the SHG process. In the first scheme, the second harmonic enters a nonlinear medium with some definite input amplitude and definite phase shift with respect to the fundamental wave. In the other scheme, the second harmonic has a zero input amplitude and a phase shift is introduced into the interacting waves in particular cross sections of the medium.     

Catastrophic change in the efficiency of second harmonic generation by a high-intensity femtosecond pulse under phase mismatch

Earlier, computer simulation discovered the effect of catastrophic and asymmetric change in the efficiency of second harmonic generation by high-intensity femtosecond pulses under phase mismatch. Based on this effect, a simple method for experimentally verifying the existence of the frequency conversion bistable mode predicted earlier is proposed. The results of computer simulation are corroborated by analytical dependences obtained in the long-pulse approximation.     

Second harmonic generation by femtosecond pulses under the condition of nonzero amplitude of the double-frequency wave

Second-harmonic generation by femtosecond pulses in a medium with simultaneous action of the second-and third-order nonlinearities under the condition of group matching of interacting waves is analyzed. The problem is solved analytically within the long-pulse approximation, and possible generation modes are identified. In particular, it is shown that the presence of even a small second-harmonic signal (with the intensity comprising no more than 1% of that of the main wave) enables the maximal efficiency of energy conversion to be attained well before the intensities of interacting waves are increased by more than one order of magnitude due to the compression of pulses. This result is practically significant since it allows one to avoid the optical breakdown of the medium.     

Dynamics of Exciplex Formations and Dissociation in Organic Molecule Vapors

The discovery and investigation of exciplex luminescence in the polyatomic molecule vapors^1-4 is of great importance for better understanding of the relaxation mechanisms in bimolecular complexes formed due to the charge transfer between photo-excited organic molecules and other type of molecules in the ground state. The study of the vapor-phase exciplex emission from 9, 10-dicyanoanthracene in the presence of N, N-dimethylaniline (9, 10-DCA + DMA) showed⁴ that the exciplex stabilities, their luminescence properties and the relative efficiency of monomer and exciplex luminescence essentially depend on the excess of the vibrational energy of excited 9, 10-DCA molecules.     

Piezoelectric Current Generation in Wurtzite GaAs Nanowires

Generation of electric current is observed when GaAs nanowires with wurtzite crystal structure are bent by the probe of an atomic force microscope. The current originates from a piezo active phase in the nanowires due to the piezoelectric effect. Increasing of the piezo‐potential in bent nanowires enhances tunneling through the probe–nanowire Schottky barrier due to the thermionic field emission. Laser illumination amplifies short‐circuit current pulses by two orders of magnitude from 9 pA to 1 nA due to the piezo‐phototronic effect. Utilization of such piezo‐phototronic effect in GaAs nanowires is a solution to accelerate the efficiency of hybrid energy sources “piezoelectric nanogenerator ? solar cell” comprised of III–V nanowires.     

Formation of silver nanoparticles on polypropylene microfibrous carriers

Methods of physical and numerical experiments are used to investigate formation of quantum dissipative silver nanostructures on polypropylene microfibrous condensed-state carriers under two-stage activation by UV- and microwave radiation. For these two nanoprocessing stages, two different mechanisms of quantum activated silver nanoparticle relaxation are suggested, including dissipation of their energy into the polymeric matrix through the exciton femtosecond and phonon picosecond channels. A comparison of the results of mathematical modeling and physical experiments testifies to the adequacy of these models to the physical processes of self-assembly and self-organization of polymeric biomimetic fibrous material modified by silver nanoparticles.     

Taking the detail balance relations into account in the construction of approximations of kinetic equations

We propose an approach to the construction of approximations of kinetic equations of a lattice gas in the context of cluster approaches, taking account of the detail balance relations. This approach is applied to construct approximations for a one-component lattice gas on a homogeneous one-dimensional lattice, in which it is shown that in the absence of migration the additional requirement of unique solutions of the approximate equations leads to the well-known Kirkwood approximations in the context of the quasi-chemical approximations. We give the equations for a one-component lattice gas on a homogeneous rectangular lattice, describing a family of approximations satisfying these requirements and conditions on the additional relations needed to close the system. Bibliography: 5 titles. Translated fromProblemy Matematicheskoi Fiziki, 1998, pp. 96–112.     

Extended temperature range of absorptive optical bistability in semiconductors

Optical bistability based on the temperature dependence of the absorption coefficient in a semiconductor is considered. It is theoretically demonstrated that the upper bound of the thermostat temperatures at which the bistability is possible can be raised by a factor of three as against its conventional value reported in the literature. This can be achieved in the case of the Auger recombination of free electrons in semiconductors.     

Oxidation of 2,4-dinitrotoluene with ozone in the presence of a stop reagent

Liquid-phase oxidation of 2,4-dinitrotoluene with ozone in the presence of acetic anhydride as stop reagent and manganese(II) acetate as catalyst was studied. The major products of oxidation with ozone in acetic anhydride are 2,4-dinitrobenzyl alcohol (65.8%) and 2,4-dinitrobenzaldehyde (18.8%) in the form of the corresponding acetates. A reaction scheme accounting for the results obtained is considered.