Stable pulsed operation of Lissajous structured beams by Nd:YVO4/Cr4+:YAG laser in a concave–convex resonator

Abstract

A Nd:YVO4/Cr4+:YAG laser with a symmetric concave–convex cavity ensuring strong intracavity beam focusing on the absorber is designed for stable pulsed operation of Lissajous structured modes with transverse patterns as Lissajous figures. Setting the cavity length to fulfill the criterion for efficient passive Q switching (PQS), as well as to meet the accidental degenerate conditions, Lissajous pulsed beams with well-defined structures and good temporal stability are created under two-dimensional off-axis pumping. Although the multi-transverse-mode oscillation inevitably induces asynchronous pulsation and leads the short-term pulse profiles to reveal parasitic effects, the overall long-term behavior of Lissajous pulses can be kept regular with amplitude fluctuations ≤15% and pulse-to-pulse timing jitter ≤5%. With the maximum peak power exceeding 500 W at a pump power of 4.5 W, the PQS Lissajous modes are further transformed into trochoidal pulsed beams to realize high-order and high-peak power structured vortex fields.