Time-tailored laser pulses: a new approach for laser micromachining and microfabrication processing

We describe novel designs for production of laser pulses from the nanosecond to the femtosecond regime which allow optimization to specific material processing requirements. These lasers are based on use of multimode Yb:fiber amplifiers (MM YDFA) to provide microJoule-level output in a single-mode beam. First, we present laser designs based on MM YDFA that produce 10 kHz - 5 MHz pulses of picosecond and femtosecond duration. Next, by seeding a MM YDFA with pre-shaped nanosecond laser diode seed pulses, we have created a laser that provides temporally nearly-rectangular output pulses. The duration is adjustable between 4 and 20 ns, with sharp rise times of <1.5 ns, and repetition rate of up to 20 kHz. Output pulse energy of >15 microJoules is maintained over the full tuning range. With this "tailorable" pulse design, control of laser energy deposition in confined laser interaction zones (“dosage”) can be user-optimized in real-time from the controller. For example, in biomedical microelectronics and other applications where the creation of micron-size features (in width and in depth) is required the user can adjust dosage in response to meas-ured structural changes over the material. Results of Si wafer and other material micromachining using this unique tem-porally-tailored pulsed laser are presented.