Mode-Locked Laser Hits High Power

Aaron J. Hand

Engineers at Spectra-Physics Lasers Inc. have hit a new high for visible output powers in a laser based on saturable Bragg reflector technology. The frequency-doubled, quasi-continuous-wave (CW) Nd:YVO₄ laser can sustain an output of 38 W at 532 nm, at least 10 W higher than previous results, said Bruce Craig, marketing manager.

The saturable Bragg reflector is made up of a saturable absorber atop a Bragg mirror. With a saturable loss modulation of a few percent, the absorber becomes transparent at high peak intensities, allowing the laser light to pass through to the reflector.

The quasi-CW, mode-locked output offers higher stability than a Q-switched laser, Craig said. "In a Q-switched laser, each pulse is different from the previous one in that it builds up from noise every time," he said. With a saturable Bragg reflector, a small amount of energy leaks out of the output coupler on each round trip, providing a well-defined relationship from one pulse to the next.

The output is well-suited to efficient harmonic generation. So, although achieving this power level in a green laser is a significant step, he said, Spectra-Physics engineers plan to extend the technology to 355- and 266-nm lasers to compete with CW gas lasers in a variety of applications.