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In solid-state laser emission, the spectral width mainly depends on two factors: frequency shift and broadening due to the short duration of the spikes. The latter being more important as the emitted wave train is shorter and the envelope slope steeper, it is of interest to consider an O-switched laser. The importance of the frequency shift compared to spectral width is determined for single pulses by measuring variations of the emitted wavelength as a function of time. Experiments are carried out by using a high-speed rotating mirror camera. The time resolution is about 3.2 nsec. Some results are reported, deduced from streak photographs of Fabry-Pérot rings. For a particular mode, a wavelength shift of the order of 3 x 10(-3) A in 50 nsec was detected; this shift is not a linear function of time.

The article endeavors to bring back to life Pasteur's years as a teenage boy, based on his correspondence with his parents and on the philosophy homework he undertook during his school days. These materials reveal an authoritarian, moralizing young man who bore the strong mark of his education and his father's personality but who was also endowed with a spirit of curiosity, already imbued with the rational faith that would characterize the entirety of his scientific works.