17 May 2018 Pump modulated suppression of self pulsing in a pulsed fibre amplifier
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Abstract
We present an experimental study on the suppression of self pulsing in a single stage pulsed master oscillator power amplifier (MOPA), using pump modulation. Many applications require pulsed lasers operating at low repetition rate. Leaving the pump on for long duration without a seed pulse leads to accumulation of amplified spontaneous emission (ASE) and generation of a self-pulse that can damage the laser. For this experiment, the amplifier was fed with peak seed power of 500 mW having a pulse width and repetition rate of 100 ns and 10 kHz respectively. To study the effect of pump modulation on self-pulsing, we carried out the experiment with both a continuous pump and with a pulsed pump. The output was characterized using a constant fractional discriminator (CFD) that generated TTL pulses, in turn fed to a frequency counter. In case of a continuous pump of 2.4 W, with a low repetition rate of 10 kHz for the seed, we noticed self-pulsing of the MOPA. We obtained a maximum amplified signal output peak power of 162 W, or a pulse energy of 7.91 μJ. A further increase in pump power could lead to permanent damage to the system. In case of pulsed pump, the generated pump pulses were synchronized with the seed laser and had a 50 % duty cycle. The resulting output was again characterized with a CFD and counter. We were able to increase the pump power to 6.5 W with an output peak power of 160 W and pulse energy of 9.37 μJ without any sign of self-pulsing. Thus, using a simple method of pump modulation, we were able to reduce the accumulation of ASE and suppressed the phenomenon of self-pulsing at low repetition rates of the seed laser.
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I. Khan, I. Khan, B. Srinivasan, B. Srinivasan, A. Prabhakar, A. Prabhakar, } "Pump modulated suppression of self pulsing in a pulsed fibre amplifier", Proc. SPIE 10683, Fiber Lasers and Glass Photonics: Materials through Applications, 1068339 (17 May 2018); doi: 10.1117/12.2307474; https://doi.org/10.1117/12.2307474
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