2005 Conference on Lasers and Electro-Optics Europe

Interaction between Nd3+ and Yb3+ ions in epitaxial YAG laser wave2uide

A. Wnuka, K. Kopczynskib , J. Sarnecki', M. Malinowskic"a, J. Mlynczakb, Z. Mierczykb

aInstitute ofElectronic Materials Technology, 01-919 Warsaw, 133 Wolczynska Str, e-mail: artur.wnuk(,wv.plbInstitute ofOptoelectronics, Military University of Technology 00 908 Warsaw,e-mail: kkoPczi'n(aixwat.waw. l

Institute ofMicroelectronics and Optoelektronics, Warsaw University ofTechnolozy, 75 Koszykowa Str.00-662 Warsaw, Poland, e-mail: m.malinowskiraelka.pw.edu.pl

Rare earth doped epitaxial gamet films have been demonstrated to have excellent laser properties. One of thecandidates for PDFA pump is, Yb+Nd:YAG waveguide laser LD pumped at 810 nm and operating at 1.03 gm as aresult of efficient energy transfer from Nd3+ to Yb3+ ions [ 1,21. In the case of garnet films the liquid phase epitaxy (LPE)is the most powerful epitaxial technique for producing low loss (<0.05 dB/cm) planar waveguide lasers. In our study weemployed LPE to grow, from a supersaturated molten garnet-flux high temperature solution, Nd+Yb:YAG/YAGwaveguides layers on <111> oriented YAG substrates. Standard isothermal LPE dipping technique has been used [3,41.The creation ofYAG waveguide on YAG substrate requires an increase of the refractive index difference between filmand substrate. For this purpose the substitution of aluminum by gallium was employed. The introduction of a largeconcentration of Ga3+ ions into the films causes a necessity of lattice mismatch compensation with a small optically inertion like Lu3+ in y3+ sites. Thus, the composition of waveguide films could be described as Y3_x_y_tNd.YbyLutAl5_,Gaz012

We have investigated the IR and visible emissions of Yb+Nd:YAG waveguide layers excited by 810 nm laserdiodes and have observed, to the first time, of our best knowledge, strong amplification of the up-converted Nd3+emission by Yb3+ presence. The IR and up-conversion emission of waveguides with different concentration ofNd3+ andYb3+ have been characterized in terms of absorption, fluorescence and fluorescence lifetime measurements. The visiblefluorescence (fig. 1) and IR (fig.2) spectra ofNd+Yb+Ga+Lu:YAG layer pumped at 810 nm are presented. In fig. 1 threebands of emission centered at 910, 1063, and 1340 nm corresponding to the (4F3/2_*419/2), (4F3/2-_4J111/2) and (4F3/2_*4 13/2)transitions of Nd3+ and one band centered at 1030 nm corresponding to the (2F5/_+2F7/2) transition of Yb3+ ions arepresented. We analyzed the mechanisms of the energy transfer from Nd3+ to Yb3+ ions for different concentration ratioof Yb3+/Nd3+.

Nd ('G47->4i9 )

(U ~~~~~~~~~~~~~~~~~~~~~~~~~~~~_1

C Yb cooperativeYb('F5-z- F7 C emission

C ~~~~~~~~~~~~~~03 Nd (4F5->'10) E Nd ( G,0->4I,52 )

EW _>4' Nd 4Ga1'>I

800 900 1000 1100 1200 1300 1400 1500 1600 460 480 500 520 540 560 580 600 620 640 660 680 700 720Wavelensth fnml Wavelenqth [nml

Fig. 1. The NIR emission spectra ofNdYb:YAG Fig. 2. Up-conversion fluorescence spectra ofepitaxial waveguide excited at 810 nm NdYb:YAG epitaxial waveguide excited at 810 nm

In the visible range of spectra (fig.2) we observed three bands of Nd3+ up-conversion emission from the 4G712 levelcentered at 540, 600, and 670 nm and also band of cooperative emission of Yb3+ at about 500 rm. We investigatedpossible pathways of the up-conversion excitation, especially we analyzed the amplification of the Nd3+ up-conversionby energy transfer from Yb3+ to Nd3+ ions. Model of the observed optical transitions in active ions was proposed andverified using the rate equations.References[11 N.Sugimoto, Y.Chishi, Y.Katoh, M.Shimokozo and S.Sudo, Appl.Phys.Letters 67, 582-584, 1995[21 M.Shimokozo, N.Sugimoto, A.Tate and Y.Katoh, Appl.Phys.Letters 68, 2177-2179, 1996[31 B. Ferrand, B. Chambaz, M. Couchaud, Optical Materials 11, 101-114, 1999[41 M.Malinowski, J.Samecki, R.Piramidowicz, P.Szczepaniski, and W.Wolin'ski, Optoelectronic. Rev. 9, 67-74, 2001

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