Chemical engineering of metamaterials to reduce optical losses is studied by first principle density functional
theory. Contribution of the surface states to optical losses is studied by calculations of the imaginary part of the
dielectric function for several organic molecules (water, methanol, and ethanol) adsorbed on the (111) surface of
Ag nano-slabs. Substantial modifications of optical functions of metallic nano-slabs in near infrared and visible
spectral regions, caused by surface states and molecular adsorption, are predicted, discussed, and compared to
Stimulated emission can be obtained in small volumes of scattering laser materials without cavity or any special optical design. Such sources of stimulated emission are known as random lasers. In random lasers, amplifying laser medium provides for gain, and scatterers (powder particles, air gaps between particles, etc.) provide for stimulated emission feedback. Above certain threshold pumping energy, the emission characteristics of random lasers change dramatically: the emission spectrum collapses to one or several narrow lines and one or several short emission pulses appear in response to a relatively long pumping pulse. Solid-state random lasers based on rare-earth doped dielectrics, dielectrics with color centers, semiconductors, scattering polymers, etc., offer challenging and not yet completely understood physics as well as promising applications, including express testing of laser materials, identification, and information processing. The focus of our presentation is on optically pumped neodymium random lasers. In particular, we discuss the dependence of the photon mean free path lt, the threshold energy density Eth/S and the slope efficiency in neodymium random lasers as a function of the mean particles size s. The experimental results are compared with the predictions of the developed models.
Stimulated emission in Nd0.5La0.5Al3(BO3)4 ceramic random laser was studied at different diameters of the pumped spot d. The developed heuristic model adequately describes the dependence of threshold pumping energy density versus d at d greater or equal to 150 micrometer. At small pumping beam diameter (less than 100 micrometer), very bright and strongly localized emission spot was observed in the center of the pumped area. The spectrum of the bright-spot emission appeared to be similar to that of 'continuum wave' light sources.