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Experiments made in a parallel-plate arrangement, where one of the plates is the ground plane and the other a positively charged dielectric sheet, show that at low air pressure the dielectric injects streamers onto the surrounding air. The similarities and differences between the streamers thus produced and those emitted from electrodes are discussed. The streamers here obtained were found to have diameters and speeds that are clearly dependent on pressure. Often the streamers were seen to decelerate markedly to the point of coming to a complete stop and on occasions even returning back to the dielectric they came from. The deceleration and the reflection of the streamers are attributed to a virtual anode created by the electrostatic image of the head's charge behind the ground plane. Field calculations performed corroborate this hypothesis. Through the use of an equation of motion of the positive head, it is then possible to obtain an estimate of the magnitude of its charge. The charge thus obtained was found to be in the 2.5–26 nC range.

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We present here the implementation and characterization of a rhodamine dye laser pumped by a pulsed, high-power solid-state laser. The employed dye consisted of a solution of rhodamine 6G in ethanol at different concentrations. To maximize the laser efficiency the second harmonic of a pulsed Nd: YAG was used to collinearly pump the cavity. In particular, the effect of rhodamine concentration and pump energy on the laser emission were investigated. The laser emission obtained was found to have, on average, a width at half maximum (FWHM) of 12 nm. It was found, for example, that the wavelength of the output line varies linearly with the dye’s concentration. Under the employed experimental conditions, maximum efficiency of 12% is obtained with a concentration of 2.5×10−7 mol/l rhodamine in alcohol.