In this paper we introduce experimentally the phenomenon of speckle and its interferometric applications. With the popularization of CCD sensors and webcams, it is now easy to acquire speckles patterns, to reduce them and exploit them. The material used here is what we could find easily in high schools. All Image processing mentioned in this article could be done using the free software called IRIS. Keywords are essentially diffraction, interference phenomena and Fourier optics. After presenting the characteristics of speckles we discuss the phenomenon of speckles interferences by analogy with the conventional 2 and N waves interferences. Finally, we apply interferometry to measure the angular separation between the components of a double star in drawing heavily on the historical experience of Antoine Labeyrie.

Doubly activated alkaline-earth phosphors are known to present luminescent and charge-storage properties. In this work, we investigate the photoluminescence (PL) and the optically stimulated luminescence (OSL) of the SrS:Ce,Sm phosphor by means of time-resolved spectroscopy with excitation laser pulses of 2 ps duration. By comparing the PL measurements obtained with direct UV excitation and the OSL experiments performed using infrared wavelength, it was possible to measure a charge conversion lifetime of about 2.5±1 ns. A luminescence lifetime of 36±1 ns has also been found. These measurements are presented and discussed in connection with applications where the speed of the SrS:Ce,Sm luminescence is a crucial parameter

Piezoelectric effects on the optical properties of GaN/AlN quantum dots have been investigated by both continuous-wave and time-resolved photoluminescence (TRPL) measurements. The increase in excitation density in CW-PL leads to a blue shift of the transition energy. The TRPL measurements reveal a very large blue-shift (0.6 eV) of the PL peak energy, which reduces with time delay in a complex way, due to the strong transition-energy dependence of the carrier recombination time. The results are discussed in terms of respective roles played by the population of excited levels and by the screening of internal electric fields by accumulation of electron-hole dipoles in the quantum boxes. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

GaAs samples doped with low indium and nitrogen contents were investigated by continuous-wave (CWPL) and time-resolved photoluminescence (TRPL) at low temperature (10 K). The simultaneous incorporation of doping amounts of both indium and nitrogen elements in GaAs creates new isoelectronic traps that are not present in indium-free GaAs:N. These traps are built from nitrogen-related defects of GaAs:N now perturbated by one additional indium atom. They are believed to involve a preferential <111> orientation of the In atom and of one N atom in near-neighbor positions. The experiments are consistent with the assumption that the clusters are perturbed by a single In atom but that a definitive assignment cannot be given without addition theoretical modeling. Optical feature characteristics of the exciton bound to these kinds of isoelectronic traps are reported: (i) the exciton fine structure with dipole-forbidden and dipole-allowed states and (ii) the train of phonon replicas that is typical of isoelectronic traps. The observation of the tine structure of the trapped excitons is made possible because of the thermodynamic equilibrium between the two populations of excitons (dipole-allowed and dipole-forbidden states) in the conditions of our measurement. It gives us a direct measurement of the short-range exchange interaction (∼0.7 meV). The TRPL experiments allow us to characterize the exciton recombination dynamics for the different isoelectronic traps and notably the transfer mechanisms of excitons among these various traps.