We report a novel technique to broaden and reshape the spectrum of picosecond laser pulse based on the seeder of gain switch laser diode and Yb3+-doped fiber amplifier (YDFA). From compensating the seed spectrum with the gain of YDFA, the seed pulse of 7 nm bandwidth is broadened to 20 nm, and the flat top spectral shape is obtained as well. A self-made fiber coupled tunable filter is used to realize the tunable output laser with the wavelength range from 1053 nm to 1073 nm and the line width of 1.4 nm.

Nanodots forming dense assembly on a substrate are difficult to characterize in terms of size, density, morphology and cristallinity. The present study shows how valuable information can be obtained by a combination of electron microscopy techniques. A silicon nanodots deposit has been studied by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) to estimate essentially the dot size and density, quantities emphasized because of their high interest for application. High resolution SEM indicates a density of 1.6 × 1012 dots/cm2 for a 5 nm to 10 nm dot size. TEM imaging using a phase retrieval treatment of a focus series gives a higher dot density (2 × 1012 dots/cm2) for a 5 nm dot size. High Resolution Transmission Electron Microscopy (HRTEM) indicates that the dots are crystalline which is confirmed by electron diffraction. According to HRTEM and electron diffraction, the dot size is about 3 nm which is significantly smaller than the SEM and TEM results. These differences are not contradictory but attributed to the fact that each technique is probing a different phenomenon. A core-shell structure for the dot is proposed which reconcile all the results. All along the study, Fourier transforms have been widely used under many aspects.

A characterization of Semi-insulating Polycrystalline Silicon (SIPOS) layers deposited from SiH4 on SiO2 is presented, as a function of growth and annealing conditions (time and temperature), in order to better understand the processes involved in nucleation of silicon nanocrystals. Correlation between optical and XPS measurements allows determination of the starting composition of the amorphous material. After annealing, Fourier transform infrared (FTIR), ultraviolet-visible and Raman spectroscopies have been used to determine the structural and optical characteristics of the resulting material. Thermal treatment promotes a phase separation, modifying the layer properties and degrading the electrical insulation characteristics. Concentration of the silicon dioxide phase increases, whereas elemental silicon precipitates into nanocrystals which nucleate near the interface with the underneath SiO2. Their density depends of the initial silicon content in the SIPOS layer, and some directions such as <1I1> and <220> grow preferentially whereas other directions such as <311> show a slower growth. As the percentage of oxygen increases, the formation of precipitates is less marked.