A new technology platform for compact and nearly maintenance-free laser sources from the femtosecond to the nanosecond time scale has been developed utilizing highly efficient Yb:fiber amplifiers and allowing application-customized use in industrial laser micromachining. The basis of this technology is the patented use of multimode fibers with TEM00 output characteristics, enabling high gain and efficient amplification, while maintaining high-quality focusing and precision positioning of the beam. In this paper, we present results of these fiber amplifier deve l-opments from the femtosecond pulse to the nanosecond pulse regime.
First, we describe femtosecond chirped-pulse amplification of seed pulses from a mode-locked fiber laser. In this way, microJoule pulses (200 – 500 fs) with high repetition rate (250 kHz) can be produced without using a Ti:Sapphire amplifier. Next, we present fiber amplification of picosecond pulses generated from a gain-switched laser diode, resulting in microJoule level pulses of 50 ps duration in the kHz range.
Finally, a unique laser seeder/amplifier design is presented, enabling online temporal tuning of laser pulses between 4 and 20 ns without changing pulse energy (at 10 - 20 kHz). This is achieved by utilizing high-speed control circuitry to adjust pulse duration, repetition rate and pulse energy independently. The goal of “tailoring” the pulse length is to adjust the final energy input to a given dimension of a sample structure that needs to be processed. The pulse shape can be controlled to produce rectangular pulse forms with <1.5 ns rise/fall times, which allows micro processing of very thin structures without damaging the underlying materials. Integration of the resultant output pulses into material processing systems can be achieved easily using a polarization-maintaining delivery fiber. Some results of micromachining using pulses from these flexible, fiber-based laser sources are described.