Ch. M. Briskina

DEGREE OF' COHERENCE AND DIMENSIONS OF THE GENERATION REGION OF POWDER LASERS

A degree of coherence of powder-laser radiation of 10–20% is estimated by the magnitude of the image contrast for a speckle, although cases are recorded where it attains 40–50%. It is found that as the average speckle intensity increases, the contrast decreases. It is established that the minimum, dimensions of the generation region in powders are 20–30 μm. Cases of existence of several generation centers simultaneously are noted. An attempt to interpret the results obtained is made.

ZnO random laser spectra under nanosecond pumping

Spectra of ZnO random lasers were obtained using a Peltier-cooled CCD camera Videoscan-285 at a single shot of nanosecond pumping. It was demonstrated that these spectra differ essentially from lasing spectra under picosecond pumping: as a rule, the line widths are significantly larger and the spectra often change essentially from shot to shot in a random manner on the same pumping spot. We suggest that large line widths can be the result of many lasing acts appearing during a single pumping pulse and of the lasing frequency changing in every lasing act. The random variations of spectra from shot to shot can be called forth by spontaneous emission fluctuations.

Simplified approach for modeling ZnO luminescence dependence on excitation level with and without surface plasmon resonance

The research of excitation level dependence of ZnO UV and visible luminescence was carried out. To describe the behavior of radiation intensity there was proposed the model based on the set of rate equations. The simultaneous equations include the set of parameters which characterizes processes participating in luminescence. The values of parameters were estimated using experimental dependence of luminescence intensity on excitation level. Proposed model can give the way for optimization of samples structure to maximize the effect of surface plasmon resonance influence on luminescence intensity.