OPTICAL SENSING: MIRTHE center aims to take mid-IR sensors to new heights

The National Science Foundation (NSF; Arlington, VA) is funding a new R&D center at Princeton University (Princeton, NJ) to develop mid-IR optical sensors for biomedical and environmental applications. Launched May 1 with $15 million in NSF funding over five years, MIRTHE (Mid-Infrared Technologies for Health and the Environment) is expected to attract additional financial support from corporate partners and other sources to conduct more than $40 million in research and educational activities over the next 10 years (see figure).

MIRTHE will be led by Claire Gmachl, associate professor of electrical engineering at Princeton, and will be fueled by quantum-cascade-laser technologies developed by Gmachl and her colleagues over the last several years. The center will combine the work of about 40 faculty members, 30 graduate students, and 30 undergraduates from the six core partner institutions: Texas A&M, the University of Maryland-Baltimore (UMBC), Rice University, Johns Hopkins University, and the City College of New York.

In 2004, Gmachl and her colleagues at Bell Labs, Texas A&M, Rice, and Princeton reported results on third-harmonic generation in a quantum-cascade laser (see www.laserfocusworld.com/articles/209682).¹ Since then, they have been working to improve the efficiency of the wavelength conversion, in particular by incorporating phase-matching into the waveguide design. One of the goals of the MIRTHE center is to use this technology to create mid-IR sensors that can detect minute amounts of chemicals in the atmosphere or exhaled in human breath. Given the maturity of the core laser and detector technologies, Gmachl says the sensors would be easier and less costly to produce.

“The sensors we are creating are like iPods compared to the tabletop-size computers of the past,” she said. “Today’s state-of-the-art sensors are very sensitive, but require an expert to operate and are bulky and expensive. MIRTHE’s vision is to make sensors with the same, or better, level of sensitivity at a fraction of the size and cost.”

One avenue of the center’s research is to develop mid-IR sensors that allow doctors to diagnose and monitor diseases—including lung, kidney and liver disorders—by measuring chemicals in a patient’s breath. Other MIRTHE participants will explore highly sensitive, low-cost sensors that monitor air quality, follow the evolution of greenhouse gases in the atmosphere, or detect chemical weapons. In addition, they will address various problems that hinder the development of mid-IR sensor technologies, including ways to improve sensitivity of the detectors using the same kind of physics that previously enabled physicists to slow light to tens of meters per second.

“Our goal is to detect a weak mid-IR signal from a tiny amount of chemicals amid a huge background of thermal radiation produced by all surrounding objects, including the body of the detector itself,” said Alexey Belyanin, assistant professor of physics at Texas A&M and part of the MIRTHE team.

Other proposed MIRTHE projects will focus on designing and fabricating integrated optical components to make a spectrometer on a chip. When combined with the laser and detector work of other groups, it will enable compact and affordable analysis of the mid-IR signature of materials for environmental, health, and process monitoring.

For more on optical-sensing applications, see the Optoelectronic World supplement, which follows p. 96.

REFERENCE

T.S. Mosely et al., Optics Express, Vol. 12, No. 13, June 28, 2004.