Random Laser Action in Nd:YAG Crystal Powder Jon

This work explores the room temperature random stimulated emission at 1.064 mu m of a Nd:YAG crystal powder (Neodymium-doped yttrium aluminum garnet) in a very simple pump configuration with no assistance from an internal mirror. The laser threshold energy as a function of pump beam area and pump wavelength has been measured, as well as the temporal dynamics of emission pulses. The absolute energy of stimulated emission and the absolute laser slope efficiency have been measured by using a method proposed by the authors. The results show a surprising high efficiency that takes the low Nd3+ ion concentration of the crystal powder into account.This work has been partially supported by the Spanish Ministerio de Economia y Competitividad, MINECO project MAT2013-48246-C2-2-P, the Basque Country Government, project IT-943-16, and Saiotek S-PE11UN072 and S-PC13UN017

Influence of Upconversion Processes in the Optically-Induced Inhomogeneous Thermal Behavior of Erbium-Doped Lanthanum Oxysulfide Powders

The efficient infrared-to-visible upconversion emission present in Er-doped lanthanum oxysulfide crystal powders is used as a fine thermal sensor to determine the influence of upconversion processes on the laser-induced thermal load produced by the pump laser and to assess the potentialities of this material in order to obtain anti-Stokes laser-induced cooling. The analysis of the upconversion emission and excitation spectra as well as the decay curves indicates that energy transfer upconversion is the main mechanism responsible for the green (S-4(3/2)) and red (F-4(9/2)) upconversion luminescence. The dependence on temperature of the intensity ratio of upconversion emission from thermally-coupled H-2(11/2) and S-4(3/2) levels of Er3+ in the 240-300 K temperature range has been used to estimate a relative sensitivity of 1.09 x 10(-2) K-1. Thermal measurements performed on the powder samples by using a thermal infrared camera exhibit a very inhomogeneous heat distribution at the sample surface due to the random distribution of the pumping energy inside the sample as well as to the random properties of the thermal field. The analysis of both spectroscopic and thermal measurements show that after a transient heating induced by the background absorption, cooling of discrete regions by means of anti-Stokes processes can be observed.This work was supported by the Spanish Government under project MAT2013-48246-C2-2-P and Basque Country Government IT-943-16. Macarena Barredo-Zuriarrain acknowledges an FPI grant from the Spanish Government