Spectroscopic and second harmonic generation properties of a new crystal: Yb-doped RbTiOPO 4 J.J. Carvajal a , R. Sol  e a , Jna. Gavald a a , J. Massons a , P. Segonds b , B. Boulanger b , A. Brenier c , G. Boulon c , J. Zaccaro d , M. Aguil  o a , F. D  ıaz a, * a F  ısica i Cristal®lografia de Materials, Universitat Rovira i Virgili, Pl. Imperial Tarraco, 1, Tarragona 43005, Spain b Laboratoire de Spectrom etrie Physique, Universit e Joseph Fourier, 38402 Saint Martin d’H eres, France c Laboratoire de Physico-Chimie de Mat eriaux Luminescents, Universit e Claude Bernard, 69622 Villeurbane, France d Laboratoire de Cristallographie, CNRS, 38042 Grenoble, France Received 30 October 2003; received in revised form 21 November 2003; accepted 5 December 2003 Available online 25 February 2004 Abstract RbTiOPO 4 single crystals doped with a concentration of 1.96 · 10 20 ionscm 3 of Yb 3þ have been grown. These crystals exhibit a large splitting of the 2 F 5=2 sublevels of Yb 3þ of about 70 nm, which is one of the largest crystal fields ever known for Yb-doped crystals. The larger compensation is ensured by a Nb-co-doping. As expected from the large splitting, a broadband fluorescence was observed around 1 lm, which is interesting for tunability and subpicosecond-pulse generation applications in the visible and in the infrared domains. The excited-state lifetime has a quite long value of 2.2 ms, which is favourable to get a high inversion of pop- ulation under CW pumping. Measurements of second harmonic generation have shown a correlation between the fundamental wavelength of angular non-critical phase-matching and the concentration of Nb and Yb. The conversion efficiency is of the order of that of RTP. Ó 2004 Elsevier B.V. All rights reserved. PACS: 42.70.Mp; 78.20.)e Keywords: Non-linear optics; KTiOPO 4 ; RbTiOPO 4 1. Introduction Using non-linear optical frequency processes in a la- ser material is a very promising way for the realization of compact all-solid-state laser sources. Few non-linear crystals doped with Nd 3þ have been yet considered [1]: LiNbO 3 (LNB), LaBGeO 5 , Ba 2 NaNb 5 O 15 , b-Gd 2 - (MoO 4 ) 3 , YAl 3 (BO 3 ) 4 (YAB), CaY 4 O(BO 3 ) 3 (YCOB) and CaGd 4 O(BO 3 ) 3 . More recently, Yb 3þ also appeared as a promising ion in the same range of emission wavelength close to that of Nd 3þ . Several highly efficient Yb-self-frequency doubling materials have been reported in YAB [2], LNB [3] and YCOB [4]. The strong laser efficiency of these crystals is due to the very simple energy level scheme of Yb 3þ : it is made up of only two levels, i.e. the 2 F 7=2 ground state and the 2 F 5=2 excited state. Moreover, there is no excited state absorption, which may reduce the effective laser cross-section, no up-conversion, no con- centration quenching and no absorption in the green. Finally, the intense Yb 3þ absorption lines are well suited for laser diode pumping near 980 nm from high-power InGaAs diode lasers, and the small Stokes shift between absorption and emission reduces the thermal loading of the material during the laser operation. KTiOPO 4 (KTP) has been established as a unique inorganic non-linear crystal for frequency conversion applications [5–8], in particular for frequency doubling of 1 lm Nd-lasers [5,9–11]. Furthermore, the doping of KTP with lanthanide elements using different techniques has been reported [12]. However, the concentration achieved in bulk crystals, limited to 5 · 10 17 –6 · 10 18 ionscm 3 , is weak. Higher concentrations of lanthanide ions have been obtained by different techniques: thermal * Corresponding author. Tel.: +34-977-559517; fax: +34-977- 559563. E-mail address: diaz@quimica.urv.es (F. D  ıaz). 0925-3467/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2003.12.009 Optical Materials 26 (2004) 313–317 www.elsevier.com/locate/optmat