Neodymium glass waveguide lasers

Abstract

Generation and amplification characteristics are presented for solid-state lasers with neodymium silicate glass waveguides (60μm and 1 mm in diameter clad with passive envelopes) as their active elements. Their characteristics have been studied, and the possibility of obtaining powerful stimulated radiation with a predetermined radiation field distribution in the near zone was demonstrated. The optical coupling of separate waveguide active elements, causing the synchronous generation of groups of active elements, was also investigated. The essential role played in generation and amplification by the short-lived color centers developing in silicate glasses exposed to the violet component of the pumping spectrum was demonstrated. These IR-absorbing centers give rise to Q-switching of the waveguide resonator, resulting in emission of periodic giant pulses. When these color centers were absent, a quasi-continuous generation mode with relaxation oscillations was realized. The short-lived color centers can be described as weakly coupled excitons with a potential well depth of ~0.1 eV. Interaction of the photons emitted by neodymium with such color centers leads to their induced decay, causing bleaching and Q-switching. The influence of the color centers on amplification in active waveguides appeared significant: along with the light pulse amplification an appreciable (more than twofold) shortening of the amplified pulses was observed. A study of the sequence of ultrashort pulses revealed that the main reason for pulse compression is the induced decay of the short-lived color centers after absorbing part of the amplified pulse leading edge. Part of the amplified pulse leading edge is used in annihilating short-lived color centers, while the remainder is amplified more effectively due to lower color center losses.