E. M. Dianov

Microscopic mechanisms of photosensitivity in germanium-doped silica glass

The photosensitivity of germanium-doped silica glass fibers and related phenomena, namely photoinduced second harmonic generation and refractive index change, attract considerable interest. In the present paper the microscopic mechanisms of the photosensitivity, which are based on photoionization and structural transformation, are considered. The recent experimental results, which reveal the role of excited triplet state of germanium oxygen deficient defect in the photosensitivity of germanium-doped glass, are discussed.

Influence of PbO concentration on photoinduced second-harmonic generation in lead glasses

We report experimental studies of photoinduced second-harmonic generation (SHG) in lead glasses with different PbO concentrations. The dependencies of photoinduced second-harmonic saturation efficiency on PbO concentration and calculated third-order nonlinearity are observed. The optical concentration of PbO for photoinduced SHG is found to be approximately 50 wt%. Experimental results are interpreted on the base of photovoltaic model.

Test of photovoltaic model of photoinduced second-harmonic generation in optical fibers

It is shown that second-harmonic generation efficiency in a photovoltaic model depends on the relationship of illuminated size to grating period. Model test experiments are proposed and realized. To explain the photo-induced second-harmonic generation (SHG) in glass optical fibers, two groups of models have been suggested, some based on separation of charges and appearance of a strong electrostatic field the others based on orientation of defects. However, a strong electrostatic field (approximately equals 104 V/cm) appears also in the last models. That is why neither the experiment on the discovery of such a field nor the experiment on the measurement of the component (chi)(2) tensor ratio gives an answer to the preference of either model. This paper shows that the efficiency of SHG by a (chi)(2) grating, resulting from a coherent photocurrent, depends strongly (approximately equals (r0/(Lambda) )-4) on the ratio of the transverse size r0 of the light beam, used for the grating preparation, and the grating period (Lambda). So we think that an experiment on SHG in a bulk sample to check this point will make it possible to clear up the mechanism of (chi)(2) grating formation. Another possibility is an experiment with the (chi)(2) grating writing by pump and second-harmonic waves, propagating in opposite directions in a fiber. In this case the grating period will decrease to (lambda)p/4 approximately equals 0.25 micrometers.

Evidence for different photovoltaic mechanisms of photoinduced second-harmonic generation in semiconductor microcrystallite-doped and lead glass

Evidence for different microscopic mechanisms of coherent photovoltaic effect in lead glass and semiconductor microcrystallite-doped glass is obtained by temperature studies of photoinduced second harmonic generation.

Photoinduced second-harmonic generation in titanium and cerium-doped lead silicate glasses

Photoinduced second harmonic generation in titanium and cerium doped lead-silicate glasses at different infrared preparation intensities is reported. The influence of dopants on second harmonic conversion efficiency is discussed.