Efficient second harmonic generation by a femtosecond pulse far from phase matching

Highly efficient second harmonic generation by a femtosecond pulse under the condition of group matching in the absence of phase matching was obtained. Second-order dispersion and cubic nonlinearity of the propagation medium were considered. The cubic nonlinearity is necessarily required for the generation to be efficient. The results obtained open up a fundamental opportunity for the efficient cascade generation of optical harmonics to be realized.     

Chemistry of α -hydroxylaminooximes

The direction taken by the reaction of -hydroxylaminooximes (prepared by the action of hydroxylamine on -halogenoketones) with aldehydes depends on the geometric configuration of the oxime group, cis isomers reacting with benzaldehyde to give N -substituted -phenylnitrones and with acetaldehyde to give derivatives of 4H-1, 2, 5-oxadiazine. Anti--hydroxylaminooxime and acetaldehyde give substituted 1 -hydroxy-3-imidazolin-3-oxide. The structures of the compounds synthesized check by analyses of their UV and IR spectra.For Part VI see [1].     

Achieving high-efficiency second harmonic generation in a sequence of laser pulses with random peak intensity. Part I. Efficient generation in optical fibers

The study examines the possibility of suppressing peak intensity fluctuations in a sequence of fixed-energy femtosecond pulses using so-called cascade second harmonic generation (SHG). In Part I we consider the propagation of light pulses in an optical fiber with quadratic and cubic nonlinearity. We show that, for a given fiber length, high mean efficiency of frequency conversion can be achieved simultaneously with minimum intensity fluctuations. __________ Translated from Prikladnaya Matematika i Informatika, No. 27, pp. 5–24, 2007.     

Improving the optical performance of InGaN light-emitting diodes by altering light reflection and refraction with triangular air prism arrays

The effect of triangular air prism (TAP) arrays with different distance-to-width (d/w) ratios on the enhancement of light extraction efficiency (LEE) of InGaN light-emitting diodes (LEDs) is investigated. The TAP arrays embedded at the sapphire/GaN interface act as light reflectors and refractors, and thereby improve the light output power due to the redirection of light into escape cones on both the front and back sides of the LED. Enhancement in radiometric power as high as 117% and far-field angle as low as 129° are realized with a compact arrangement of TAP arrays compared with that of a conventional LED made without TAP arrays under an injection current of 20 mA.     

Spontaneous switching in cavityless optically bistable systems

Relaxation cavityless optical bistability is studied when a semiconductor is exposed to light quanta with an energy exceeding the transition energy and the free-electron relaxation time depends on temperature. The numerical analysis of dynamic equations for temperature and free-electron density demonstrates that 11 regimes of light-semiconductor interaction are possible. The regimes are classified in terms of the features of temperature-intensity characteristic curves, namely, by the number and arrangement of instability and quasistability segments and by the presence or absence of bistability. It is found that both the upper and the lower branch of a bistable characteristic curve may be unstable, which results in spontaneous switchings between the respective states. Similarly, if the upper state is unstable and the lower state is stable, a small perturbation of the parameters (free-electron temperature and density) near the former causes the transition to the oscillatory regime. If the upper state is unstable and a small perturbation of the lower (stable) state excites a damped oscillation, spontaneous switchings result if the fluctuating temperature exceeds some critical value for the lower state.     

Kinetics and products of the reactions of ozone with toluene and its derivatives in acetic anhydride

The reactions of ozone with toluene and its derivatives in acetic anhydride were studied. It was found that competing parallel reactions of ozone with the aromatic ring and substituents occurred in the ozone-arene-acetic anhydride system. The ratio between these reaction paths depended on the arene structure and reaction conditions. The selectivity of the oxidation of toluene and its derivatives at the methyl group varied from 0 to 40%. The fraction of aromatic products decreased as the number of methyl groups at the ring was increased. Tri- and tetramethylbenzenes were oxidized only at the aromatic ring. The stability of an aromatic system increased upon the introduction of electron-acceptor substituents into the benzene ring. Aminotoluenes and hydroxytoluenes were oxidized with ozone mainly at the NH₂ and HO groups; however, as in the case of toluene, the aromatic ring and methyl group became the main directions upon their acylation. The oxidation of the methyl group in acetic anhydride in the presence of sulfuric acid was finished at the step of the formation of the acylated derivatives of benzyl alcohols and benzaldehydes, which are resistant to the action of ozone.