Femtosecond laser-induced ZnSe nanowires on the surface of a ZnSe wafer in water

We present a simple route for ZnSe nanowire growth in the ablation crater on a ZnSe crystal surface. The crystal wafer, which was horizontally dipped in pure water, was irradiated by femtosecond laser pulses. No furnace, vacuum chamber or any metal catalyst were used in this experiment. The size of the nanowires is about 1-3 μm long and 50-150 nm in diameter. The growth rate is 1-3 μm/s, which is much higher than that achieved with molecular-beam epitaxy and chemical vapor deposition methods. Our discovery reveals a rapid and simple way to grow nanowires on designed micro-patterns, which may have potential applications in microscopic optoelectronics.     

Femtosecond laser ablation of crystals SiO2 and YAG

Damage threshold of crystals SiO₂ and YAG against 60-900 fs, 800 nm laser pulses are reported. The breakdown mechanisms were discussed based on the double-flux model and Keldysh theory. We found that impact ionization plays the important role in the femtosecond laser-induced damage in crystalline SiO₂, while the roles of photoionization and impact ionization in YAG crystals depend on the laser pulse durations.     

Femtosecond laser-induced damage in reflector

We have investigated the damage for ZrO₂/SiO₂ 800 nm 45° high-reflection mirror with femtosecond pulses. The damage morphologies and the evolution of ablation crater depths with laser fluences are dramatically different from that with pulse longer than a few tens of picoseconds. The ablation in multilayers occurs layer by layer, and not continuously as in the case of bulk single crystalline or amorphous materials. The weak point in damage is the interface between two layers. We also report its single-short damage thresholds for pulse durations ranging from 50 to 900 fs, which departs from the diffusion-dominated scaling. A developed avalanche model, including the production of conduction band electrons (CBE) and laser energy deposition, is applied to study the damage mechanisms. The theoretical results agree well with our measurements.     

Mechanisms of femtosecond laser-induced breakdown and damage in MgO

Single-shot laser damage threshold of MgO for 40-986 fs, 800 nm laser pulses is reported. The pump-probe measurements with femtosecond pulses were carried out to investigate the time-resolved electronic excitation processes. A theoretical model including conduction band electrons (CBE) production and laser energy deposition was applied to discuss the roles of multiphoton ionization (MPI) and avalanche ionization in femtosecond laser-induced dielectric breakdown. The results indicate that avalanche ionization plays the dominant role in the femtosecond laser-induced breakdown in MgO near the damage threshold.     

Inversion Formula for the Dunkl-Wigner Transform and Compactness Property for the Dunkl-Weyl Transforms

We define and study the Fourier-Wigner transform associated with the Dunkl operators,and we prove for this transform an inversion formula.Next,we introduce and study the Weyl transforms W_σ associated with the Dunkl operators,where cr is a symbol in the Schwartz space S(R~d×R~d).An integral relation between the precedent Weyl and Wigner transforms is given.At last,we give criteria in terms of σ for boundedness and compactness of the transform W_σ.     

Standing electron plasma wave mechanism of void array formation inside glass by femtosecond laser irradiation

We investigate the mechanism of formation of periodic void arrays inside fused silica and BK7 glass irradiated by a tightly focused femtosecond (fs) laser beam. Our results show that the period of each void array is not uniform along the laser propagation direction, and the average period of the void array decreases with increasing pulse number and pulse energy. We propose a mechanism in which a standing electron plasma wave created by the interference of a fs-laser-driven electron wave and its reflected wave is responsible for the formation of the periodic void arrays. PACS 61.80.Ba; 42.65.Re; 42.70.Ce; 61.72.Qq; 52.35.Mw     

Hydroxylamine derivative in Purex process Part VIII. The kinetics and mechanism of the redox reaction of N-methylhydroxylamine and vanadium(V)

The kinetic properties of the oxidation-reduction reaction between N-methylhydroxylamine (NMHAN) and vanadium(V) in nitric acid medium has been studied by spectrophotometry at 23.1 °C. The rate equation of the redox reaction was determined as -d[V(V)]/dt=k[V(V)] [NMHAN] by investigating the influence of concentration of NMHAN, acidity, ionic strength and the ratio of initial concentration of V(V) to NMHAN on the reaction. The rate constant of the reaction k> = 0.818±0.051 (mol/l)^–1·s^–1 at the ionic strength of 1.00 mol/l. The activation energy of the redox reaction was calculated to be 39.6 kJ/mol. A possibly radical mechanism of the redox reaction between NMHAN and V(V) has been suggested on the basis of electron spin resonance (ESR) spectra of nitroxyl radical, i.e., CH₃

Dunkl Multiplier Operators on a Class of Reproducing Kernel Hilbert Spaces

We study some class of Dunkl multiplier operators; and we establish for them the Heisenberg-Pauli-Weyl uncertainty principle and the Donoho-Stark''s uncertainty principle. For these operators we give also an application of the theory of reproducing kernels to the Tikhonov regularization on the Sobolev-Dunkl spaces.     

Microwave synthesis of 1-aryl-1H-pyrazole-5-amines

A microwave-mediated synthesis of 1H-pyrazole-5-amines utilizing 1?M HCl at 150?°C was developed in order to provide products in a matter of minutes with minimal purification. Most reactions are complete in only 10?min and can be isolated via a simple filtration without the need for further purification by column chromatography or recrystallization. This method tolerates a range of functional groups and can be performed on milligram to gram scales.