Time evolution of the pulsed HF chemical laser system. I. Kinetic modeling - rotational nonequilibrium

A detailed model of a pulsed F + H₂ → HF + II laser is used to investigate the kinetic behaviour of the system and to provide input data for a thermodynamic analysis of its time evolution. The rate equations for all relevant vib-rotational level populations and photon densities are solved for various initial conditions without using the rotational equilibrium assumption. The results of the kinetic model are in good agreement with the experimental results of Berry in which high inert gas pressure was used to enhance rotational relaxation. The effects of specific kinetic processes on the time evolution of the molecular populations and the laser output are evaluated by varying the inert gas pressure and by “switching on and off” the influence of various kinetic factors. The laser efficiency ranges between ≈ 1 to 2 photons per molecule. The major rate process enhancing the efficiency is rotational relaxation. The reduction in laser efficiency due to vibrational relaxation is ≈ 20%.     

Nonlinear distortions in the current modulation of non-self-pulsing and weakly self-pulsing GaAs/GaAlAs injection lasers

Nonlinear distortion characteristics of GaAs/GaAlAs injection lasers under analog current modulation were experimentally investigated. In non-self-pulsing lasers, relaxation oscillation (R.O.) plays a heavy role in generating harmonic distortions, in good agreement with theory. Additional distortions generated by microwave mixing in weakly self-pulsing lasers make such lasers unacceptable for wideband analog transmissions unless suitable negative feedback is applied. With such measure taken, both fundamental and the harmonic responses of a self-pulsing laser is indistinguishable from that of a laser with no R.O. resonance.     

Frequency marker based on moiré deflectometry

We propose a new method for frequency marking based on measuring the diffraction angle by moiré deflectometry. The method is demonstrated experimentally.     

Emanation thermal analysis study of Na-montmorillonite and montmorillonite saturated with various cations

Emanation thermal analysis (ETA) and thermogravimetry measured in the range 20–1000°C was used to characterize the thermal behaviour of Na-montmorillonite (Upton Wyoming, USA) and homoionic montmorillonite samples prepared by saturation with cations Li⁺ , Mg²⁺ , Al³⁺ , respectively. It was confirmed that the presence of cations used for montmorillonite saturation (Li⁺ , Mg²⁺ , Al³⁺ ) influenced the thermal behaviour of the samples. The results that indicated the decrease of radon release rate corresponding to a collapse of the interlayer space between the silicate sheets after water release and the crystallization of meta-montmorillonite in the respective temperature intervals were compared. From the ETA results it followed that the thermal stability of intermediate microstructure depends on the type of exchanged cation. A mathematical model was used to evaluate the ETA data.     

The use of thermo-XRD-analysis in the study of organo-smectite complexes

Summary Thermo-XRD-analysis is applied to identify whether or not the adsorbed organic species penetrates into the interlayer space of the smectites mineral. In this technique an oriented smectite sample is gradually heated to temperatures above the irreversible dehydration of the clay, and after each thermal treatment is diffracted by X-ray at ambient conditions. In the thermal treatment of organo-clays, under air atmosphere at temperatures above 250°C, the organic matter is in part oxidized and charcoal is formed from the organic carbon. In inert atmosphere e.g. under vacuum above 250°C the organic matter is pyrolyzed and besides small molecules, charcoal is formed. If the adsorbed organic compound is located in the interlayer space, the charcoal is formed in that space, preventing the collapse of the clay. A basal spacing of above 1.12 nm suggests that during the adsorption the organic compound penetrated into the interlayer space. Thermo-XRD-analyses of montmorillonite complexes with anilines, fatty acids, alizarinate, protonated Congo red and of complexes of other smectites with acridine orange are described. To obtain information about spacings of the different tactoids that comprise the clay mixture, curve-fitting calculations on the X-ray diffractograms were adapted.     

Thermal analysis of the interaction between stearic acid and pyrophillite or talc. IR and DTA studies

Pyrophyllite and talc sorb stearic acid on edge surfaces. The grinding of clay-stearic acid associations in the presence of alkali halides converts some of the acid into the ionic form, this occurring more readily with talc than with pyrophyllite. Heating in a closed or semi-closed system causes dissociation of stearic acid adsorbed on talc, but not on pyrophyllite. The infrared absorption frequencies of the adsorbed ionic form vary with the clay mineral and the amount of water present. The thermal stabilities of the clay-stearic acid associations depend on the rate of escape of the acid, which is determined by the strength of bonding to the clay and the nature of the system, and on the degree of dissociation of the acid on the clay surfaces.

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Zusammenfassung Pyrophyllit und Talk adsorbieren Stearinsäure an den Kantenoberflächen. Beim Verreiben von Ton-Stearinsäure-Assoziaten in Gegenwart von Alkalihaliden wird ein Teil der Säure in die ionische Form überführt, und zwar leichter mit Talk als mit Pyrophyllit. Aufheizen im geschlossenen oder halbgeschlossenen System bewirkt eine Dissoziation der an Talk, aber nicht der an Pyrophyllit adsorbierten Stearinsäure. IR-Absorptionsfrequenzen der adsorbierten ionischen Form sind abhängig vom Tonmineral und der anwesenden Wassermenge. Die thermische Stabilität der Ton-Stearinsäure-Assoziate hängt von der Geschwindigkeit der Abgabe der Säure ab, die durch die Stärke der Bindung an das Tonmineral, also der Natur des Systems, und durch den Dissoziationsgrad der Säure an der Tonmineraloberfläche bedingt ist.

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Study of thermally treated dickite by infrared and micro-Raman spectroscopy using curve-fitting technique

The products of dickite heated in air at 1000 to 1300°C were studied using curve-fitting of transmission and photoacoustic infrared and micro-Raman spectra. The spectra were compared with those of mullite, Al-spinel, corundum, cristobalite, amorphous silica and meta-dickite. Bands that characterize crystalline phases appeared at 1100°C and became stronger with increasing temperature. Mullite, Al-spinel, corundum and amorphous silica were identified by their characteristic bands. The characteristic IR bands of cristobalite overlap those of mullite and amorphous silica, and its presence was therefore established from intensity ratios of the appropriate bands. The research clearly demonstrated the advantage of using curve-fitting for the identification of high temperature phases in the study of the thermal treatment of kaolin-like minerals by infrared and Raman spectroscopy. This technique seems to be a useful method for materials analysis in the ceramic industry.This revised version was published online in November 2005 with corrections to the Cover Date.     

Nonparaxial equation for linear and nonlinear optical propagation

The formalism of coupled-mode theory, specialized to the continuum of radiation modes, allows us to extend the standard parabolic wave equation to include nonparaxial terms and vectorial effects, and, in particular, to generalize the nonlinear Schr?dinger equation that describes propagation in the presence of an intensity-dependent refractive index.