A New Dysprosium Laser: 5.5-im Oscillation in The Dy3+:RbPb2CI5 Crystal atRoom Temperature.

A. G. Okhrimchuk, L. N. Butvina, E. M. Dianov, I. A. ShestakovaFiber Optics Research Center, GPI ofRAS, 38 Vavilov Str., Moscow 119333, Russia

okhrim@o.gpi.ru

N. V. Lichkova, V. N. Zagorodnev,Institute ofMicroelectronics Technology, RAS, Chernogolovka, Moscow region 142432, Russia.

A.V. ShestakovElements ofLaser Systems Co., 3 Vvedensky Str., Moscow 117342, Russia

Solid-state lasers operating on electronic transitions in rare-earth ions are very attractive as bright sources for mid-IRapplications, because of simplicity and durability of such type lasers. Now in practice implementation an operationwavelength of such laser does not exceed 3 gim. The progress in technology of low-phonon energy and moisture-resistantmatrixes for rare earth ions is required to overcome this problem. We consider that promising candidates in this concern arecrystals of the MePb2Hal5 class, where Me = K or Rb, and Hal =Cl or Br [1,2]. They are moisture-resistant, and thiscircumstance beneficially distinguishes these crystals from other low-phonon chloride and bromide crystals, which could bedoped with rare earth ions. The Dy3 is a promising active ion for mid-IR, because it has series of closely spaced multipletsseparated by 1500...2500 cm-1 and intense absorption bands in the near IR suitable for pumping to these multiplets.

A 6 - mm diameter cylindrical boule of the RbPb2Cl5 (RPC) crystal was grown by the vertical Bridgman method in asilica tube crucible. A 3 - cm long laser crystal was made. Concentration of Dy3 ions in the crystal was determined by theinductively coupled plasma mass spectroscopy and was as much as 2*1019 cm

Unpolarized absorption spectrum of the RPC:Dy3 crystal consisted of spin-allowed intense absorption bands in0.75... .2.8 gm range and was found to be analogous to those of the KPb2Cl5:Dy3 crystal [1]. Emission properties wereinvestigated under pumping to the most intense absorption band, centered at 1.3 gim, corresponding to transition from the6H15/2 ground state to the overlapping and thermalized 6F11/2 and 6H9/2 multiplets. We used for this a flash-lamp pumpedpulsed Nd:YAG laser, operating in the free running multimode regime at 1.319 and 1.338 gm wavelengths duringspectroscopy and oscillation experiments. Pump pulse duration was as much as 80 gs (WFHIM). We found, that theRPC:Dy3 crystal has six luminescent transitions centered at 1.32 gim, 1.75 gim, 2.44 gim, 2.9 gim, 4.3 gm and 5.5gm.Investigations of luminescence kinetics led to a conclusion that a kinetics curve was single exponential for each band. Decaytimes of the 6F,1/2+6H9/2 6H1/2 and 6H13/2 multiplets were found to be 0.51 ms, 5.6 ms and 13 ms correspondingly. Branchingrations pi (i=1,2,3) for luminescence originating from the 6F1/2+6±H1/2 multiplet were obtained from luminescence spectra andfound to be 0.006, 0.079 and 0.915 for transitions to the 6H1/2,6HI3/2 and 6H15/2 multiplets correspondingly. The 6F11/2+6H9/2>* 6H1/2 transition emission cross section was estimated by Fuchtbauer-Ladenburg formula and found to be as much as0.5*10-20 cm2 at the maximum of the band.

For oscillation experiments at room temperature we had a two-mirror resonator for the 5.3-5.7 ptm wavelength rangeconsisting of a concave HR mirror of 5-cm curvature radius and a flat output coupler. Cavity length was equal to 4.2 cm. Thepump beam, focused by 8 cm -focus lens to 300 gm diameter spot, passed through the dichroic HR mirror and pumped thelaser crystal through its end. Since the laser crystal had no AR coating, its orientation was precisely tuned to reduce lossescaused by reflections on the crystal surfaces. Pulses of oscillation were obtained at the center of the emission band at 5.54gm with non-selective output coupler of 2.9% transmittance. Threshold pump energy was as much as 20 mJ, and undermaximal pump energy of 45 mJ the output oscillation energy was measured to be 23 gJ. Nearly 60% ofpump energy wasabsorbed in the laser crystal. For one pump pulse we have observed a series of separate oscillation pulses within timeinterval of the pump pulse. Such deep modulation of the output pulse could be explained by the low relaxation rate of thelow laser level 6H1/2.

Thus we demonstrated mid-IR lasing in a new laser crystal - RbPb2Cl5:Dy3 . It is a promising active media fordeveloping of reliable and durable solid-state lasers, which could be tunable in the 5... .6 gm wavelength range matching to atransparency window of atmosphere.

References.1. M. C. Nostrand, R. H. Page, S. A Payne, L. J. Isaenko, and A. P. Yelisseyev, "Optical properties of Dy3+- and Nd3+- dopedKPb2Cl5", JOSA B 18(3), P.264-276, 2001.2. K.Nitsch, M.Dusek, M.Nikl, K.Polak and M.Rodova, "Ternary Alkali Lead Chlorides: Crystal Growth, Crystal Structure,Absorption and Emission Properties", Prog. Crystal Growth and Charact., 30, P.1-22 (1995).