Effect of the Thermal Rise Time of Diode Pump Modules on the Cold-Start Turn-on Time of a Yb-doped Fiber Amplifier

Beam-combinable, high-power, narrow-linewidth Yb-doped fiber amplifiers are presently being evaluated as high energy laser weapons where the rapid turn-on of the amplifiers is critical. These amplifiers are optically pumped at the narrow 976nm, high-absorption peak of ytterbium. The fiber amplifier turns on when the emission spectra of the diode pump modules significantly overlap the 976nm Yb absorption peak. The thermal wavelength tuning behavior of two types of laser diode sources was analyzed to predict the cold-start turn-on-time of a fiber amplifier. Turn-on-times of ~4ms and ~4s were predicted for a fiber amplifier employing a laser diode bar directly attached to a micro-channel cooler and a single emitter package cooled by a cold plate, respectively.