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Effect of Lower Level Lifetime on the Pulse Width of Passively Q-switched Nd:YAG/Cr4+:YAG Microchip Lasers
Y-X. Wang, J-X. Chang, L-Y. Cao, C-Y. Cai, S-W. Wang, Z-Y. Wang, Q. Zhou, S-J. Shi, J. Su and Q. Qiu

Modelling of pulse operation for passively Q-switched Nd:YAG/ Cr4+:YAG microchip lasers with finite lower level lifetime is presented. The computed pulse width with finite lower level lifetime is longer than that with infinitely fast lower level relaxation. With the proposed model, lower level lifetime of Nd:YAG could be estimated by measuring pulse width of such microchip lasers. The pulse width of three different microchips are measured. The measured data and computed data matched in high degree for lower level lifetime of approximately 100 ps. The ratio of computed pulse width with this model to that with conventional model becomes larger as the cavity lifetime decreases. The ratio is larger than two for cavity lifetime smaller than 40 ps in optimum condition for short pulse width. Effect of finite lower level lifetime should be considered in the design of short pulse microchip lasers, especially sub-nanosecond lasers.

Keywords: Nd:YAG/Cr4+:YAG laser, microchip laser, passively Q-switched, diode-pumped, short pulse width, low level lifetime, rate equation

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