'Superlattice' Laser Achieves Record Power in the Mid-IR

Michael K. Robinson

MURRAY HILL, N.J. -- Lucent Bell Laboratories researchers have reported measuring peak power of 750 mW from a pulsed 8-µm laser at liquid nitrogen temperatures.
The device, a quantum cascade laser based on superlattice crystal structures, produced 30 mW of power at its highest operating temperature, 33 °C, according to the group's report, published in the May 2 issue of Science magazine.
The higher power is a record for a semiconductor laser in the mid-infrared, reported the research team led by Gaetano Scamarcio, Federico Capasso and Carlo Sirtori. And the device's power could be even higher than that: The group's detector is only 50 percent efficient, so its actual power at 196 °C could be close to 1.5 W, according to Capasso, head of Bell Labs' quantum phenomena and device research.
The device's peak output far exceeds traditional lead salt diodes of similar frequency. "No other semiconductor laser has come even close to this performance in the 4- to 12-µm range," Capasso said.
In the Science paper, the team also reported another pulsed superlattice laser at 11.2 µm; members planned to present their results at the Conference on Lasers and Electro-Optics last month.
The superlattice is an artificial crystal, which the Bell Labs team has engineered to lase at a specific frequency, depending upon the thickness of the crystal's quantum well and barrier layers.
Infrared lasers are useful in medical testing, military countermeasures, pollution monitoring, combustion diagnostics and industrial process control. Capasso said that while discussing applications for the superlattice lasers is premature, he expects them to be similar to other infrared lasers. "There is potentially a large market for laser-based sensors," he added.
Capasso said the device's high power is a significant advantage, but the design also seems to be more robust than other options in the IR. The superlattice laser could be scaled into the far-infrared wavelengths as well. The disadvantage is the need for cryogenic cooling, a drawback common to most mid-infrared lasers.
The group's next steps will be to reduce the device's threshold density and increase its operating temperature.