Fiber lasers in MOPA configuration are a very flexible tool for micromachining applications since they allow to independently adjust the pulse parameters such as pulse duration, repetition rates and pulse energy while maintaining a constant beam quality. The developed fiber laser provides an average power of 11 W and maximum pulse energy of 0.5 mJ for a wide range of pulse parameters at diffraction limited beam quality. Its pulse duration and repetition rate are continuously adjustable from 10 ns to cw and from 10kHz to 1MHz respectively. Ablation experiments were carried out on stainless steel, nickel and silicon with the goal of optimizing removal rates or surface finish using nanosecond pulses of different parameters. Maximum removal rates are achieved on all three materials using relatively similar pulse parameters. For silicon, pulse duration of 320ns at 100kHz and 45mJ resulted in optimum removal. In single shot experiments on silicon a significant influence of the pulse duration was found with a distinct optimum for removal rate and surface finish. The optimum intensity at the work piece is in the range of 35MW/cm<sup>2</sup> to 70MW/cm<sup>2</sup>. Lower values are below the ablation threshold, while the plasma shielding effect limits considerable increases in removal rates for intensities exceeding 70MW/cm <sup>2</sup>.
We demonstrate a single transverse mode Yb-doped fiber laser that can be operated in a wide range of pulse lengths and repetition rates.
The pulsed 1064nm beam of a single mode diode laser is amplified by a three stage fiber amplifier. It consists of two stages that incorporate single-mode fibers and a third stage using LMA fiber. A monolithic setup is achieved by an adiabatic taper between the second and the third stage exciting only the fundamental mode in the LMA fiber. Variable pulse regimes were investigated in the range from 10kHz to 1MHz and CW. A maximum output energy of 0.5mJ and maximum peak power of 66kW were measured. Pulse trains consisting of four pulses with pulse spacing of 200, 500 and 1000ns and a pulse length of 10ns were also evaluated. The repetition rate of the train was set to 1kHz.