Observation of power drop and low threshold due to beam waist shrinkage around critical configurations in an end-pumped Nd : YVO4 laser

Under pumping spot size less than that of the cavity mode, we observed a de crease of the fundamental mode power in an end-pumped solid-state laser whe n the cavity length was adjusted approaching certain critical resonator con figurations where the transverse modes are degenerate. In the proximity of these configurations, we found, for the first time to our knowledge, that t he laser exhibits a relatively low threshold pump power together with an un expected far-field beam profile and shrinking beam waist. (C) 1999 Elsevier Science B.V. All rights reserved.