Stephen Cognetta ’15


Chemical and Biological Engineering

Project Title

Development of Quantum Cascade Lasers for Atmospheric Carbon Isotope Ratio Detection

This summer I interned at the Center for Mid-InfraRed Technologies for Health and the Environment (MIRTHE) in Princeton, where I worked with Professor Claire Gmachl and her team to identify characteristics about lasers. I helped with developing quantum cascade laser technology, specifically Distributed Feedback Quantum Cascade (DFB QC) lasers. DFB QC lasers offer a reliable and efficient way to sense gases such as carbon dioxide or water vapor. To ensure specified detection of these gases, however, QC lasers must exhibit single-mode behavior (which means that the lasers target a specific wavenumber in the mid-infrared spectrum). This allows the laser to be used for environmental applications, such as detecting leakage from carbon sequestration. We tested a number of different DFB QC lasers to determine the operating conditions under which they exhibited single-mode behavior (parameters such as current and temperature). Throughout my internship, I learned how to use the equipment in the lab. In particular, I focused on operating the LIV (Light, current, voltage) setup and Fourier Transform Infrared Spectrometer, both were instrumental in characterizing lasers. The main portion of my research was directly involved with the graduate students and Professor Gmachl, which exposed me to both electrical engineering and the research field. I will definitely consider my experience when applying to graduate school.

Internship Year


Project Category

Climate and Energy


Princeton University, Princeton, NJ


Claire Gmachl, Professor, Electrical Engineering