a605_1.pdf CTuHH2.pdf
Submitted to CLEO-2007
Solid State Laser
A Highly Efficient Quasi-Continuous-Wave Diode-Pumped Nd: YAG Rod Laser with a 3.8 kW Output Qinjun Peng, Xiaodong Yang, Yong Bo, Qianjin Cui, Hongbo Zhang, Yuanpu Lu, Xiaofu Zhang, Jialin Xu, Dafu Cui, Zuyan Xu Optics physics lab, institute of Physics, Chinese Academy of Sciences,Beijing,100080 China. (
[email protected])
Abstract: A Quasi-Continuous-Wave (QCW) Nd:YAG-rod laser with a 3.8kW output and a 54% optical-optical efficiency is demonstrated by the stable zone control of resonator, which overcomes the limitations of thermal lens effect of Nd: YAG rod. ©2007 Optical Society of America
OCIS codes: (140.3410) laser resonators; (140. 3480) lasers, diode-pumped; (140.3580) lasers, solid-state
1. Introduction Many applications of solid state laser in material processing, study of front sciences require a high average output power with high efficiency and high beam quality. For obtaining simultaneously the three “high” result (high average output power, high efficiency and high beam quality), various techniques have been developed [1-4]. Hereinto, multi-rod resonators for high power solid state lasers with improved beam quality have been discussed by Prof Weber [4]. By using several rods inside the same resonator, the output power range can be increased without reducing the beam quality. However, when the number of the rod in the resonator exceeds 6, the laser operation very easily enter unstable zone of resonator and the output power was limited when the pump power is increased because of the thermal lens of laser crystal rod if the parameters of resonator are not optimal. So the stable zone control of resonator is vital for multi-rod laser system. In the paper, a 7-rod resonator with a suitable choice of resonator parameters for stable zone control which overcomes the limitations of thermal lens effect of Nd: YAG rod, is demonstrated. The diode-pumped solid-state laser presents an average output power of 3.8 kW with an optical-optical efficiency of 54% at a repetition rate of 1.1 kHz (QCW) and a pulse width of 120 µs, and the beam quality is estimated to ~15 mm mrad. 2. Experiments and Results H R L a se r H e a d 1
L a se r H e ad 2
L a se r H e a d 6
L a se r H e a d 7
OC
L a se r H ea d 3 -5 N d :YA G R o d
N d :YA G R o d
N d :YA G R o d
Fig.1 the experimental setup, HR: high reflection mirror, OC: output coupler
N d :YA G R o d
Fig.2 The gain distribution
The experimental setup of 7-rod resonator is shown in Fig. 1. Seven identical laser heads are placed in a flat-flat resonator with an optical cavity length L=700mm. The transmittance of the output coupler (OC) is 90%. For one laser head [3], five QCW 2D LD arrays (each 2D LD array containing ten, 1-cm long diode bars arranged in 2
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a605_1.pdf CTuHH2.pdf
Submitted to CLEO-2007
Solid State Laser
rows) symmetrically surround the Nd:YAG rod (7 mm in diameter and 100 mm in length with 0.6 at % Nd3+ doping concentration). Each laser head is capable of outputting 1 J in a 120µs pulse at a repetition rate of over 1.1 kHz. The distance between the LD bars and the side surface of the Nd:YAG rod is optimized by use of our ray-tracing code, so that the uniform gain distribution in the Nd:YAG rod and the higher efficiency can be obtained simultaneously. The gain distribution is shown in Fig 2. A suitable arrangement of rods and mirrors must be made in the system for obtaining largest range of stable oscillation. A symmetric plane-plane resonator, in which the 7 rods must be separated by L/7, and the mirror-rod distance must be L/14, is used. Fig. 3 is the calculated stable zone of resonator by ABCD matrix method. The ft is the thermal focus of crystal rod, and wR1(ft) is the beam waist. Any other arrangement (See Fig.3 b-d) seem impossible because the range of stable zone becomes un-continuous, which is difficult to span the unstable zone. Thus it will reduce the efficiency.
Fig.3 a: the rod-rod distance R=100, the mirror-rod distance M=50; b: R=100, M=60; c: R=100, M=40; d: R=110, M=50.
The experimental output power is shown in Fig. 4 and 5, corresponding to the arrangement in Fig3. a and b, respectively. We obtain 3.8kW output based on the arrangement in Fig.3 a. However, it is difficult to realize the high output power, as shown in Fig.5, if the parameter of resonator is not suitable for multi-rod laser system.
Fig. 4 the experiment results for R=100, M=50
Fig. 5 the experiment results for R=100, M=60
3. References [1] K.Furuta, T. Kojima, S. Fujikawa, J. Nishimae, “Diode-pumped 1 kW Q-switched Nd:YAG rod laser with high peak power and high beam quality”, Appl. Opt, 44, 4119-4123 (2006). [2] G. D. Goodno, H. Komine, S. J. McNaught, S. B. Weiss, S. Redmond et al, “Coherent combination of high-power zigzag slab lasers”, Opt. Lett, 31 1247-1249. (2006) [3] X.D. Yang, Y. Bo, Q.J. Peng, H.L. Zhang, A.C. Geng, Q.J. Cui, Zh.P. Sun, D.f. Cui, Z.Y Xu, “High-beam-quality, 5.1 J, 108 Hz diode-pumped Nd:YAG rod oscillator-amplifier laser system”. Opt. Commun 266, 39-43. (2006). [4] K. P. Driedger, R. M. Ifflander, and H. weber, “multi-rod resonators for high power solid state lasers with improved beam quality,” IEEE. J. Quant. Electron. 24, 665-674 (1988).
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