IOP PUBLISHING JOURNAL OF OPTICS A: PURE AND APPLIED OPTICS J. Opt. A: Pure Appl. Opt. 10 (2008) 104013 (5pp) doi:10.1088/1464-4258/10/10/104013 Efﬁcient and compact diode-side-pumped Nd:YLF laser operating at 1053 nm with high beam quality Niklaus Ursus Wetter, Eduardo Colombo Sousa, Fabiola de Almeida Camargo, Izilda Marcia Ranieri and Sonia L´ ıcia Baldochi Centro de Lasers e Aplicac ¸˜ oes—IPEN, S˜ ao Paulo, Brazil E-mail: nuwetter@ipen.br Received 5 March 2008, accepted for publication 21 May 2008 Published 28 August 2008 Online at stacks.iop.org/JOptA/10/104013 Abstract A very efﬁcient, diode-side-pumped Nd:YLF laser is demonstrated using a compact cavity design based on total internal reﬂection inside the gain medium. With one pass through the crystal using a single bounce at the pumped face, efﬁciency in excess of 40% in multimode operation was measured, giving 6.6 W of output power for 16.2 W of pump power. Using two bounces inside the crystal, the beam quality was improved to fundamental mode with 4.2 W of output power for 16.2 W of pump power. Keywords: solid state lasers, side pumping, Nd:YLF, beam quality (Some ﬁgures in this article are in colour only in the electronic version) 1. Introduction Nd:YLF displays good qualities as a host material due to its superior thermo-optical characteristics, especially at 1053 nm, where the weak thermal lensing provides for a high quality output beam [1]. For Q-switched and ampliﬁer applications, Nd:YLF is an attractive host material for near-infrared high power lasers because of its long storage lifetime. Recently, Nd:YLF has regained interest and some very high power lasers with good beam quality have been made with this material [2, 3]. The weak lensing observed under lasing conditions is a consequence of a refractive index decrease with temperature increase, creating a negative thermal lens, which partly compensates the positive thermal lens created due to expansion of the material [4]. Applications for Nd:YLF lasers include pumping of other solid-state lasers [5], medical treatment, industrial material processing, and LIDAR for pollution monitoring. The development of novel laser designs is strongly focused on scaling the output power while keeping high conversion efﬁciency and high beam quality in fundamental mode operation. The overlap between the excited region and the volume occupied by the laser mode in the active medium is one of the most important elements in optimizing the efﬁciency and the beam quality of a solid-state laser. Longitudinal pumping geometries provide optimal mode matching, resulting in high efﬁciency and high beam quality. Using the longitudinal pumping scheme, slope efﬁciencies of 50% [6] or higher can be achieved for Nd:YLF laser systems in fundamental output. However, in this pumping conﬁguration it is necessary to use a focused pump beam to maintain a good overlap between the laser and the pump beam, which restricts the pump power due to the risk of thermal fracture. One of the drawbacks of Nd:YLF is its low tensile strength (33 MPa), which limits the maximum pump intensity. Using a side pumping conﬁguration, the pump power can be increased, but this conﬁguration usually suffers from low efﬁciency when operating in TEM 00 mode because of the poor overlap between the pump beam and the intracavity beam. Slab laser designs with zig-zag optical path have been largely employed in laser development because of the advantages of these conﬁgurations, reducing the thermal induced focusing and birefringence [7]. Many design variations have been reported in the literature, in general, with the pump radiation quite distributed inside the crystal [8]. Zig-zag slab lasers can be scaled to the kilowatt level by 1464-4258/08/104013+05$30.00 © 2008 IOP Publishing Ltd Printed in the UK 1