Ultrafast lasers have many important applications including frequency metrology, spectroscopy, imaging, communications, frequency conversion, and optical sampling. High brightness lasers are necessary for lidar, communications, and as pump sources for both solid-state and fiber lasers. Three main topics will be covered: modelocked semiconductor lasers, wavelength-beam combined eyesafe diode arrays, and a high power cryogenic Yb:YAG amplifier.
Semiconductor lasers are valued for their compactness, efficiency and wavelength tunability. However, it has been difficult to generate large pulse energies and average powers from electrically-pumped semiconductor lasers. A 1550-nm monolithic passively modelocked slab-coupled optical waveguide laser produced 10-ps pulses with an average power of 250 mW and a pulse energy of 58 pJ. This is a two-order-of-magnitude improvement in pulse energy over the performance of previously reported electrically pumped 1550-nm semiconductor lasers. Comparable results have been achieved at 980 nm.
Even with improvements in output power, an array of semiconductor lasers is often necessary to meet power requirements. Wavelength beam combining, similar to wavelength division multiplexing in communications, is a powerful technique for combining diode arrays and stacks with high brightness. At 1450 nm, a single bar, containing 25 elements, has been combined to yield an output power of 20 W with an M2 of 1.9 (fast axis) x 10 (wavelength-beam-combined dimension). This represents record brightness from a diode laser array at 1450 nm.
To generate even higher powers and pulse energies, a master-oscillator power-amplifier configuration based on a solid-state amplifier can provide an elegant solution. Cryogenic Yb:YAG has attractive thermo-optic properties, operates as a 4-level laser system, and provides high gain. A 300-W class, ps-pulsed master-oscillator power amplifier system based on cryogenic Yb:YAG has been demonstrated for high harmonic generation applications.