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26 February 2013 On the SBS threshold of optical pulse shapes compensated for gain saturation
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Nanosecond pulsed fiber laser sources have found multiple usages in material processing applications. Their reliability, flexibility, low cost, high average power and high beam quality are the reasons for their commercial success. With appropriate means, nanosecond fiber lasers based on a MOPA configuration can emit pulses with tailored shapes. This feature greatly increases the flexibility of the laser as it allows the emission of pulses of adjustable duration, complex pulse shapes such as bursts of short pulses, gain saturation-compensated shapes, chair-like shapes, or any other variations. Pulse shaping can have a significant impact on the ablation rate, the surface quality of the processed sample and different materials have been shown to respond differently to those pulse shape variations (the thermal conductivity of the material being a key parameter). Pulse shaping is also very valuable for optimizing the pulse energy from a system as it allows pre-compensation for the pulse distortion caused by gain saturation which tends to narrow the pulse duration, increase the peak power and associated SRS sensitivity. Through pulse shaping, one can achieve pulse energies that are significantly higher than the saturation energy of the amplifier while mitigating the detrimental effects of SRS. It is however important to consider the impact of pulse shape and pulse duration on the SBS threshold of an optical system. We have performed numerous SBS threshold measurements for pulses of varying duration and of varying levels of precompensation for gain saturation. We have demonstrated that pulse shapes with effective pulse duration of 40 ns have the lowest SBS threshold.
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Louis Desbiens, Vincent Roy, Marc Deladurantaye, and Yves Taillon "On the SBS threshold of optical pulse shapes compensated for gain saturation", Proc. SPIE 8601, Fiber Lasers X: Technology, Systems, and Applications, 86012V (26 February 2013);

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