Cr:LiSAF Laser Yields Femtosecond Blue Pulses Blue Pulses

A femtosecond Cr:LiSAF laser emitting 12 mW of blue light has achieved much higher electrical-to-optical efficiencies than Ti:sapphire sources. Demonstrated by researchers at St. Andrews University in the UK, the laser converted 1 percent of its 1.2-W electrical drive into 429-nm light. Ti:sapphire lasers, in comparison, convert only about 0.05 percent of input into near-infrared output.

As reported in the Aug. 12 issue of Optics Express, the St. Andrews researchers used relatively thick (3- to 5-mm) KNbO₃ crystals in a single-pass, extracavity arrangement to double the laser's 860-nm fundamental. Although thicker crystals generate the second harmonic more efficiently, they also can incur a larger group velocity mismatch and temporal broadening of femtosecond pulses. Even with the thicker crystals, the instrument demonstrated 543-fs pulse widths.