Preparation and characterization of transparent Nd:YAG ceramics Z. LIBRANT 1 , J.K. JABCZYŃSKI *2 , H. WĘGLARZ 1 , A. WAJLER 1 , H. TOMASZEWSKI 1 , T. ŁUKASIEWICZ 1 , W. ŻENDZIAN 2 , and J. KWIATKOWSKI 2 1 Institute of Electronic Materials Technology, 133 Wólczyńska Str., 01-908 Warsaw, Poland 2 Institute of Optoelectronics, Military University of Technology, 2 Kaliskiego Str., 00-908 Warsaw, Poland Transparent Nd:YAG ceramics were produced by solid-state reaction of high-purity (4N) nanometric oxides powders, i.e., Al 2 O 3 ,Y 2 O 3 and Nd 2 O 3 . After sintering, mean grain sizes of 2% Nd:YAG samples were about 20 µm and their transparency were a bit worse than that of 0.9% Nd:YAG single crystal. Two types of active elements: rods and slabs were fabricated and characterized in several diode pumping schemes. In end pumping configuration as a pump source 20-W fiber coupled laser diode operating in low duty cycle regime (1 ms pump duration/20 Hz) was deployed. In the best case, 3.7 W of output power for 18 W of absorbed pump power, M 2 < 1.4 were demonstrated for uncoated ceramics Nd:YAG rod of f 4´3mm size in pre- liminary experiments. For the ceramics of two times lower Nd dopant level above 30% slope efficiency was achieved. In case of Nd:YAG ceramic slab side pumped by 600-W laser diode stack above 12 W was demonstrated with slope efficiency of 3.5%. Keywords: lasers, neodymium, lasers, solid states, optical ceramics. 1. Introduction Since the advent of high quality ceramic Nd:YAG [1–5] in the end of last century, the tremendous progress in technol- ogy and applications of ceramic materials in laser technol- ogy has been observed up to nowadays [6–33]. Two types of ceramics processing were successfully demonstrated: l “wet” method developed by Yanagitani and Ueda group [4–8], l “dry” method developed by group of Ikesue and Taira [1–3,9]. The ceramics made of polycrystalline Y 3 Al 4 O 12 [1–5,14, 15,32,33], Lu 3 Al 4 O 12 [13], Y 2 O 3 [6,8,16,18,19,21,22], and Y 3 ScAl 4 O 12 [9] doped with neodymium, ytterbium, chro- mium, and erbium were prepared and showed excellent per- formance in experiments. The optical ceramics can be pro- duced till now from the cubic crystals, however, intensive ef- forts are continued to produce ceramics from anisotropic crystals as vanadates or sapphires. Some other crystalline ma- trices as semiconductors, e.g., ZnSe [10], or fluorides [11] have been processed in the ceramics form in last years. In the same time, the basic investigations of optical, laser, thermal and mechanical properties of Nd:YAG ceramics were carried out. For the Nd:YAG ceramics of matured technology their benefits in comparison to the crystalline Nd:YAG can be summarized as follows [33]: l larger possible dimensions, l less time required for fabrication (days instead of weeks required for growing single crystal boules), l particular shapes can be made, in order to optimize per- formance parameters, l higher concentrations of optically active ions are possible, l uniform distribution of optically active ions, l low or no residual stress birefringence, l much higher fracture toughness and shatter resistance, l more than one type of material (e.g., central core of Nd:YAG ceramics with undoped YAG outer region) can be included in a single laser rod, l tailored distribution of optically active ions is possible. Several types of efficient diode pumped lasers made of ceramic materials as microchips [23], composite Q-swit- ched lasers [31], mode-locked lasers [13,21,22,24], high power oscillators [25,26,30,32] were demonstrated. Due to unique properties of advanced engineered ceramic Nd:YAG square slabs produced by Konoshima, the highest reported power of 67 kW in 2×diffraction limits was demonstrated in 2006 [32]. The aims of this paper were short description of applied technology and preliminary characterization of the ceramics elaborated at the Institute of Electronic Materials Technol- ogy. In Sect. 2, brief description of applied technology is given. In the next Sect., the results of optical and laser characterisation are presented. 2. Preparation of ceramic Nd:YAG samples The Nd:YAG ceramics of nominal 1% and 2% Nd dopant were produced by a solid-state reaction of high-purity (4N) nanometric oxides powders, i.e., Al 2 O 3 ,Y 2 O 3 , and Nd 2 O 3 . Two commercially available oxides were used, alumina 72 Opto-Electron. Rev., 17, no. 1, 2009 OPTO-ELECTRONICS REVIEW 17(1), 72–77 DOI: 10.2478/s11772-008-0060-x * e-mail: jjabczynski@wat.edu.pl