Quantum Cascade Laser Frequency Modulation for Trace Gas Detection
Student: Harry Burton III
Delaware State University
Major: Applied Optics
Degree Level: Master of Science
Internship Site: NASA Goddard Space Flight Center, Greenbelt, Maryland
Mentor: Eduard Luzhanskiy
Abstract: Quantum Cascade Lasers (QCLs) can be designed to operate anywhere from the Mid-IR to THz spectrum, and with their small size, tunable frequencies, and high energy output makes them an excellent choice for Trace Gas Detection. During the course of this internship, our job was to construct a laser system capable of producing low enough beat frequencies that could be detected via a spectrum analyzer. After the internship, the QCL would then undergo experimentation into detecting various molecules. Research and experimentation into QCLs will allow them to be used in both Earth science and future planetary NASA missions. QCLs are relatively new within the field of spectroscopy and operate on a principle different from that of common p-n junction diode lasers. In a diode laser, conduction band electrons jump into a valence band hole and emit a photon whose wavelength is determined by the band gap energy of the semiconductor, known as an interband transition. With QCLs, a conduction band electron can make a series of jumps in a staircase-like potential existing in the conduction band, emitting an identical photon in each transition. Here, a single electron emits a cascade of photons leading to the formation of a high-power laser. Transitions within a QCL take place from subband-to-subband inside a quantum well, continuing into the next quantum well, and so on. Thus, these are referred to as intersubband transitions.
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