QCL Features Higher Power, Wider Tuning Range

Combining a tunable laser with an on-chip amplifier has enabled a versatile and powerful tool for spectroscopy and other applications.

A team from Northwestern University demonstrated a single-mode quantum cascade laser (QCL) emitting at a wavelength near 4.8 μm by integrating an asymmetric sampled grating distributed feedback tunable laser with an optical amplifier.

With this architecture, the laser demonstrated output power an order of magnitude greater than its predecessors, and the tuning range was enhanced by more than a factor of two.

Schematic of a single-chip laser system developed in the lab of professor Manijeh Razeghi. Courtesy of the McCormick School of Engineering, Northwestern University.

In pulsed mode, the system demonstrated >5 W output over a 270-nm spectral range. The researchers reported that refinement of the geometry led to continuous operation with a single-mode spectral coverage of 300 nm and a maximum continuous power of 1.25 W. The output beam was shown to be nearly diffraction-limited, even at high amplifier current.

The work was led by and builds upon the research of professor Manijeh Razeghi, who in 2012 developed a widely tunable single-chip mid-infrared (MIR) laser.

One important application of the laser system is for MIR spectroscopy for identification of chemicals. Because Razeghi's system is highly directional, the high power can be used more efficiently, allowing for the greater ability to detect chemicals. It also allows for standoff application, which keeps personnel physically distant from potentially dangerous environments. The technology could also benefit free-space optical communications and aircraft protection.

Funding came from the U.S. Department of Homeland Security Science and Technology Directorate, National Science Foundation, Naval Air Systems Command and NASA. The research was published in Applied Physics Letters (doi: 10.1063/1.4938005).