Optics & Laser Technology 34 (2002) 357–362 www.elsevier.com/locate/optlastec Experimentaldeterminationofeectivestimulatedemission cross-sectioninadiodepumpedNd:YVO 4 micro-laserat1064nmwith variousdopingconcentrations PranabK.Mukhopadhyay * ,J.George,S.K.Sharma,K.Ranganathan,T.P.S.Nathan Center for Advanced Technology, Solid State Laser Laboratory MPS-3, Indore, MP 452 013, India Received 8 January 2002; accepted 22 February 2002 Abstract A practical method is described and used for determination of the eective stimulated emission cross-section (e )inanoperatingdiode pumpedNd:YVO4 micro-laser at 1064 nm with various doping concentrations. In this method a micro-laser is formed by keeping a small piece of the sample in a plane–plane resonator under semi-monolithic conguration and a ber coupled diode laser (808 nm) was used for pumping. The pump power induced thermal lensing eect was used to make the cavity stable. In thermally stabilized solid-state lasers the cavity parameters change dynamically with the pump power and hence the overlap integrals become a function of the absorbed pump power. In our method the overlap integrals were estimated by measuring the thermal lens focal length at the threshold. The value of e of Nd:YVO4 crystal with dierent doping concentrations obtained by this method were in well agreement with the reported values. ? 2002 Elsevier Science Ltd. All rights reserved. PACS: 42.60.Lh; 42.60.Da; 42.60.By; 42.55.Rz Keywords: Solid-state laser; Thermal lens; Diode pumping; Plane–plane cavity; Stimulated emission cross-section 1. Introduction Theeectivestimulatedemissioncross-section( e )isan important parameter for the assessment of a laser crystal. Knowledge of the  e is essential in evaluating laser sys- tem parameters such as maximum gain, saturation power and optimum output mirror reectivity [1,2]. In case of end-pumped solid-state 4-level laser systems, the thresh- old pump power is inversely proportional to the eective stimulated emission cross-section of the lasing crystal [3]. Thereareseveralexperimentalmethodsreportedinliterature [1–5]forndingthe  e valueofacrystalatthelasingwave- length.Thespectroscopictechnique[4]formeasurementof stimulated emission cross-section require determination of uorescentbranchingratiosandtheuorescentquantumef- ciency of the 4 F 3=2 level which are usually dicult to de- termine [2]. The laser pumped laser technique [1,2] is an easier method for determination of  e and is free from the ∗ Corresponding author. Fax: +91-731-488891. E-mail address: pkm@cat.ernet.in (P.K. Mukhopadhyay). complications involved in spectroscopic method. However, this is an indirect method, which can only provide a rel- ative measurement of  e . In this method, the  e value of thereferencematerialshouldbeknownveryaccuratelyand the measurement setup must be identical for both the sam- ple and the reference material. Moreover, if the reference material is not optically good due to the growing process or due to some other reasons it may lead to erroneous re- sult.Inaddition,thepumppowerandmechanicalstressin- ducedlensingeectsarealsonottakenintoaccount,which may not guarantee the identical mode volume for the sam- ple and reference materials. Mermilloid et al. [5] and more recently Wang et al. [6] reported direct measurement of  e value of several Nd 3+ doped materials. In these methods, plano-concave resonator was used for laser oscillation and the cavity mode area was calculated from the resonator pa- rameters. However, these methods are also not accounting for the pump power induced thermal lensing eect in the crystal and due to this the value of the cavity waist radius calculated from the resonator parameters may be dierent fromtheactualwaistradius.Moreover,intheirmethod,the 0030-3992/02/$-see front matter ? 2002 Elsevier Science Ltd. All rights reserved. PII:S0030-3992(02)00028-2