Abstracts:The random laser differs from other types of laser in that its cavity is formed not by mirrors but by multiple scattering in a disordered gain medium. Over the course of ten years, random lasers have been attentive by many researchers in the world because their characteristics can lead to unique applications. This report presents the mechanism of random laser operation, classification, characteristics and prediction of different applications. Some research results of authors about random laser have also been noted in report.
We present two-beam and three-beam dynamical diffraction theories for strained multilayers, where no other approximations are used. We compare the resulting diffraction curves with the calculations using the conventional two-beam dynamical theory and by a kinematical approach. We show that between the diffraction maxima all the dynamical approaches used do not yield correct results and a two-dimensional formulation of the dynamical theory must be used.
R e p 31 mars 1980, prgsentation dkjiiiitifie 2 juin 1980RBsumk Nous dkcrivons les principes d'une methode originale d'enregistrement des variations de vitesse de propagation des ondes ultrasonores ; cette methode est fondee sur l'utilisation des proprietes de deformation d'un bilame piezoelectrique: cette deformation permet de commander la position d'un transducteur mobile afin de maintenir 1'CgalitC entre le temps de parcours d'une onde de reference dans un liquide et celui de I'onde se propageant dans l'echantillon CtudiC. La comparaison entre les temps de parcours est effectuke par comparaison de phase entre les signaux sinusoidaux. La technique uti!isbe permet d'atteindre une resolution de 100 ps pour des frequences situees dans le domaine 2-25 MHz. portant sur la deformation macroscopiquement Clastique de I'aluminium.
Nous donnons quelques rksultats extraits d'une etudeA new device for the measurement of ultrasonic velocity in solids Abstract A new instrument for the continuous recording of changes in ultrasonic velocity in solids is described. The system incorporates a two-layered piezoelectric device : its piezoelastic properties are used to control the displacement of a quartz transducer in order that the transit time through the reference liquid line equals that through the tested sample. The comparison of the transit times is done by a phase detection of the sine waves. The method leads us to a resolution of 100 ps in the range 2-25 MHz.Some typical results obtained during the elastic deformation of aluminium are reported.
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