Influences of high intensity pumping for laser threshold intensity K. Kato 1 , H. Okunishi 1 , M. Nishio 1 , A. Maruko 1 , K. Shimabayashi 1 , K. Kyomoto 1 , T. Yoshida 1 , S. Inayoshi 2 , M. Morioka 2 , S. Yamagata 2 , and S. Kawato 1,3 1 Graduate School of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui, Fukui 910-8507, Japan 2 Faculty of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui, Fukui 910-8507, Japan 3 Research and Education Program for Life Science, University of Fukui, 3-9-1 Bunkyo, Fukui, Fukui 910-8507, Japan kentokato.m17@gmail.com, kawato@u-fukui.ac.jp Abstract: Influences of high intensity pumping were studied for the laser threshold intensity. The normalized laser threshold intensities are decreased by strong thermal focusing due to the high pump intensity. © 2014 Optical Society of America OCIS codes: (220.0220) Optical design; (120.6810) Thermal effects; (140.3580) Lasers, solid- state; (140.3615) Lasers, ytterbium; (350.6830) Thermal lensing References and links 1. S. Matsubara, T. Ueda, T. Takamido, S. Kawato, and T. Kobayashi, “Nearly quantum-efficiency limited oscillation of Yb:YAG laser at room temperature”, Advanced Solid-State Photonics, TOPS (Optical Society of America), (2005). 2. S. Matsubara, T. Ueda, S. Kawato, and T. Kobayashi, “Highly Efficient Continuous-Wave Laser Oscillationin Microchip Yb:YAG Laser at Room Temperature” , Japanese Journal of Applied Physics, Vol.46, L132-L134 (2007).. 3. S. Matsubara, T. Ueda, M. Inoue, M. Tanaka, K. Otani, S. Kawato, and T. Kobayashi, “High Efficiency Cavity Dumped Operation of Yb:YAG Laser at Room Temperature”, Advanced Solid-State Photonics, Technical Digest (Optical Society of America), paper MB13 (2006). 4. M. Takama, S. Matsubara, T. Ueda, M. Inoue, M. Tanaka, K. Otani, S. Kawato, and T. Kobayashi, “Highly efficient nanosecond-pulse Yb:YAG laser”, Smart Processing Technology, 281-283 (2007). 5. M. Nishio, A. Maruko, M. Inoue, M. Takama, S. Matsubara, H. Okunishi, K. Kato, K. Kyomoto, T. Yoshida, K. Shimabayashi, M. Morioka, S. Inayoshi, S. Yamagata, and S. Kawato, “High-efficiency cavity-dumped micro- chip Yb:YAG laser”, Proceedings of SPIE PLD, in press (2014). 6. M. E. Innocenzi, H. T. Yura, C. L. Fincher and R. A. Fields “Thermal modeling of continuous‐wave end‐ pumped solid‐state lasers”, Appl. Phys. Lett. 56, 1831 (1990) 7. k. kato, M. Nishio, K. Shimabayashi, A. Maruko, H. okunishi, T. Yoshida, K. Kyomoto, M. Morioka, S. Inayoshi, S. Yamagata, and S. Kawato, "Influences of high intensity pumping for laser threshold intensity," in Advanced Solid State Lasers, OSA Technical Digest (Optical Society of America) paper AM5A.18. (2014) 8. W. P. Risk, "Modeling of longitudinally pumped solid-state lasers exhibiting reabsorption losses", J. Opt. Soc. Am. B 5, 1412-1423 (1988) 1. Introduction In recent years, short pulse lasers are required to have high efficiency, high pulse energy, high peak power, and high repetition rates. To achieve these properties, it is important that the laser gain medium has long fluorescence lifetime, high quantum efficiency, broad gain spectrum, and a capability of laser diode pumping. Ytterbium (Yb)-doped media are believed as one of the most promising media to satisfy these needs. However, their weak point on the laser efficiencies exist as the quasi-three or -four laser loss which is caused by thermal population at the lower laser level. The high gain architecture, which includes high gain operation and precise compensation of thermo-optic effects by high intensity pumping, is useful to overcome the loss which includes the quasi-three (or –four) laser loss and the high gain architecture increase the laser efficiencies at room temperature. To our knowledge, the highest optical-to-optical