Nd 3 ion based self frequency doubling solid state lasers D. Jaque a , J. Capmany a , J.A. Sanz Garc  ıa a , A. Brenier b , G. Boulon b , J. Garc  ıa Sole ´ a a Departamento de Fisica de Materiales, C-IV Universidad Aut onoma de Madrid, Cantoblanco, 28049 Madrid, Spain b Laboratorie de Physico-Chimie des Mat eriaux Luminescents, Universit e Claude Bernard de Lyon 1 UMR 5620 du CNRS F-69622, Villeurbanne, France Abstract Spectral and laser properties of three non-linear crystals (LiNbO 3 , LaBGeO 5 and YAl 3 (BO 3 ) 4 ) activated with Nd 3 ions have been investigated. The main laser parameters (absorption and emission cross section, radiative lifetime and quantum eciency) are determined and compared by means of optical spectroscopy. Optical spectroscopy is also used to estimate losses due to second harmonic (SH) self-absorption, energy transfer, excited state absorption and non- equivalent Nd centres. Continuous wave laser properties of the crystals in the fundamental and SH wavelengths are investigated under similar cavity geometry and pumping conditions using a tunable Ti–sapphire pump laser. Ó 1999 Elsevier Science B.V. All rights reserved. PACS: 42.55.Xi; 78.55.Hx Keywords: Solid State Lasers; Frequency Doubling 1. Introduction The present interest in small compact diode- pumped lasers for the blue–green spectral domain has supported research on new solid state laser systems based on non-linear crystals. These crys- tals, when activated with trivalent rare earth ions, provide the possibility of realizing compact diode pumped visible lasers by internal frequency dou- bling of its fundamental infrared laser lines, so an additional non-linear crystal is not necessary. This type of systems is usually referred to as self fre- quency doubling (SFD) lasers. LiNbO 3 :MgO:Nd 3 was the first system to be operated as a continuous wave (CW) SFD laser in the visible [1]. Despite it has a high non-linear eective coecient (d eff  5.3 pm/V), the MgO codopant concentration (around 5.5 at.%) which is necessary to avoid the optical photorefractive damage, prevents the incorporation of a high Nd concentration and reduces the optical quality of the crystals. Thus, searching for new non-linear host crystals as well as new ways of reducing the optical damage [2] (such as codoping with Sc 2 O 3 ) in LiNbO 3 are key problems in this research field. In this work the experimental results obtained for the Nd 3 activated non-linear crystals (LiN- bO 3 :MgO, LiNbO 3 :Sc 2 O 3 , LaBGeO 5 and YAl 3 (BO 3 ) 4 ) are presented. These results emerge from a systematic study of the spectroscopy (en- ergy levels, absorption intensities, multicenters and excited state dynamics), laser gain and intracavity SH properties of these crystals. Optical Materials 13 (1999) 147–157 0925-3467/99/$ - see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 3 4 6 7 ( 9 9 ) 0 0 0 2 4 - 5