Performance study of highly efficient 520 W average power long pulse ceramic Nd:YAG rod laser Ambar Choubey n , S.C. Vishwakarma, Sabir Ali, R.K. Jain, B.N. Upadhyaya, S.M. Oak Solid State Laser Division, Raja Ramanna Centre for Advanced Technology, Indore 452013, India article info Article history: Received 10 October 2012 Received in revised form 5 March 2013 Accepted 25 March 2013 Keywords: Ceramic Nd:YAG laser Laser pump chamber Laser resonator abstract We report the performance study of a 2% atomic doped ceramic Nd:YAG rod for long pulse laser operation in the millisecond regime with pulse duration in the range of 0.5–20 ms. A maximum average output power of 520 W with 180 J maximum pulse energy has been achieved with a slope efficiency of 5.4% using a dual rod configuration, which is the highest for typical lamp pumped ceramic Nd:YAG lasers. The laser output characteristics of the ceramic Nd:YAG rod were revealed to be nearly equivalent or superior to those of high-quality single crystal Nd:YAG rod. The laser pump chamber and resonator were designed and optimized to achieve a high efficiency and good beam quality with a beam parameter product of 16 mm mrad (M 2 ∼47). The laser output beam was efficiently coupled through a 400 μm core diameter optical fiber with 90% overall transmission efficiency. This ceramic Nd:YAG laser will be useful for various material processing applications in industry. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction High average power and milliseconds (ms) pulse duration Nd: YAG laser systems are of great interest in various industrial and scientific applications [1–6]. In such systems, highly doped cera- mic Nd:YAG rod seems to be a better option to replace single crystal Nd:YAG, if one can generate higher pulse energy (∼100 J) with higher peak power (∼ few kW). In such lasers, three primary groups of solid state host materials are used, namely, single crystals, glasses and ceramics. Among these host materials, Nd: YAG single crystal is the most widely used laser media. But, Nd: YAG single crystals grown by the conventional Czochralski method have its own insurmountable disadvantages such as expensive, time-consuming, small size, and low doping concentration of Nd 3+ ions and for Nd 3+ -doped glass materials, although it is very easy to get large size and high concentration, but its thermal conductivity and gain are quite low and the laser efficiencies are not satisfactory in comparison with single crystals for CW or high frequency and long pulse operation. Fortunately, with the breakthrough preparation, novel ceramic media combines the predominance of single crystals and glasses. It not only contains good thermal, mechanical and spectral properties as fine as single crystal but can also be made with large size and high doping concentrations [7,8]. Ikesue et al. were the first to develop transparent polycrystal- line Nd:YAG ceramics for laser media [9]. Later on, Lu et al. demonstrated the generation of 1.46 kW of CW output power using diode pumping of ceramic Nd:YAG rods in 2002 [8]. Since then, a tremendous amount of effort has been made to realize high power ceramic Nd:YAG lasers suitable for the various industrial and defense applications. Further, Heller [10] demonstrated gen- eration of 67 kW of output power from ceramic Nd:YAG laser at the Lawrence Livermore National Laboratory and Bishop [11] demonstrated generation of 100 kW of output power from ceramic Nd:YAG laser, but these lasers have been operated in the heat capacity mode. Recently, Liu et al. have generated 2.44 kW of CW output power using diode pumping of ceramic Nd:YAG disc [12]. A detailed review of ceramic laser materials has been carried out in Ref. [13–16]. However, most of these reports on high power ceramic Nd:YAG lasers are based on diode pumping. On the other hand, long pulse and high peak power Nd:YAG lasers still depend on flash lamp pumping in place of diode laser pumping as the long pulse (ms), high peak power operation of laser diodes is restricted by the thermal run away problem [17]. Further, flash lamp pumped systems are much more rugged and cost effective than the diode lasers for material processing application. Thus, the lamp pumped long pulse Nd:YAG laser systems are still important in the present scenario for various material processing applications. Saiki et al. [18] have reported lamp pumped CW ceramic Nd:YAG laser for space applications, but in their report output power was limited to a few milliwatts only. In case of lamp pumped ceramic Nd:YAG lasers, removal of heat load from laser material is an important issue. If the heat load is not removed efficiently, temperature Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/optlastec Optics & Laser Technology 0030-3992/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.optlastec.2013.03.015 n Corresponding author. Tel.: +91 731 244 2303; fax: +91 731 244 2300. E-mail addresses: ambarchoubey@rrcat.gov.in, sslddiv@yahoo.co.in (A. Choubey). Optics & Laser Technology 51 (2013) 98–105