Jeffrey D. Kmetec

Measurement techniques for laser parameters relevant to materials processing

Many micromachining operations, particularly in the electronics sector, utilize pulsed solid-state UV lasers. These processes demand high levels of stability, as the yield and quality relate directly to the repeatability of each laser pulse. Critical stability issues arise with single-pulse processes (e.g. repair), situations requiring bursts of pulses (e.g. drilling), and continuous pulsing applications (e.g. cutting). To realize optimal stability specific design choices must be made, certain transient problems must be solved, and pulse energy measurements must be standardized. Solid-state UV lasers originate as infrared lasers, and nonlinear optics converts the infrared to the UV. This conversion introduces instability. Performing the conversion within the infrared laser cavity suppresses the instability, relative to performing the conversion outside of the laser cavity. We explain this phenomenon. Ideally, a versatile and stable solid-state laser can generate pulses in many formats. Thermal effects tend to prevent this versatile ideal, resulting in transient problems (unstable pulse trains), or less than optimal performance when the laser is pulsing continuously. Many methods of measuring pulse energy exist. Each method can produce surprisingly different results. We compare various techniques, discuss their limitations, and suggest an easily implemented pulse energy stability measurement.

>10 Watt fiber laser source with 0.5-5 MHz repetition rate and 0.5-1.5 nsec pulse width

The trend in micro-machining lasers is toward greater average power and higher repetition rate, in order to increase throughput, with pulse energy and peak power held roughly constant, as determined by the small scale of the feature. At repetition rates beyond 500 kHz, conventional high-power Q-switched Nd lasers will reach fundamental limits. We demonstrated a fiber-based oscillator-amplifier architecture which produces pulse repetition rates in the 0.5 - 5 MHz range and pulse durations in the 0.5 - 1.5 nsec range. The oscillator is a compact (35 cm3 package) passively Q-switched Nd:YVO4 laser oscillating at a single frequency. By amplifying this laser in fiber, we demonstrated 10-W average power at the two wavelengths of 914 nm and 1064 nm. At 1064-nm, Yb-doped large mode area fiber will allow scaling of average power to over 100 Watts, with peak power of tens of kW, in a diffraction-limited beam. Excellent conversion will be possible to visible and UV using the robust nonlinear material LBO. By opening up a new range of repetition rates and pulse lengths, at IR, visible and UV wavelengths, in a high power design that has the packaging and efficiency advantages of fiber, new micro-machining applications may be enabled.

1.5-TW 10-Hz Ti:sapphire laser system: design and performance

We describe a complete solid state 1.5 terawatt, 150 femtosecond laser system operating at 10 Hz repetition, based on titanium-doped sapphire amplifiers and use of the technique of chirped-pulse amplification (CPA). The design and performance of the system is described. Special emphasis on the tunability of the system from 760 nm to 860 nm is also discussed.

150 fs, 1.5 TW, 10 Hz Ti:Al2O3 Laser System

A 1.5 terawatt, 150 femtosecond Tksapphire (Тi:Al2Оз) laser system operating at 10 Hz repetition, tunable from 760 to 860 nm is described. The system design was based on regeneradve/multi-pass amplifiers and the technique of chirped pulse amplification.