OP: Semiconductor Materials for Extremely Nondegenerate Photonics and 2-Photon Gain

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Nontechnical Description: Typical lasers emit streams of single photons - small bundles of light - that are all at the same energy. In this project, the investigators are studying ways to make lasers simultaneously emit two photons at very different energies. This gives tremendous flexibility in controlling laser outputs, since one of the emitted photons can be at almost any desired energy, as long as the energy of the other is appropriately chosen. This may lead to semiconductor lasers that deliver radiation that is broadly tunable across the infrared spectrum. The availability of such lasers will impact a wide variety of applications, including sensing of pollutants in the atmosphere, biological imaging, microscopy, telecommunications, art restoration and laser radar. The research team is focusing on investigating the materials properties that enable lasers to emit light in this way, and on how to mitigate factors that cause light to be absorbed, as absorption of light could hinder laser operation. In particular, the use of nanometer-thick semiconductor layers for laser emission is being addressed. This research is largely carried out by graduate and undergraduate students who are members of the University of Central Florida's diverse student body. Technical Description: The research team aims to study the nondegenerate absorption and emission properties of semiconductors, particularly quantum wells, to verify the team's recent calculations that nondegenerate two-photon absorption or emission of Transverse Magnetic (TM)-polarized light is enhanced in quantum wells compared to bulk semiconductors. At the same time, the research team is characterizing the relevant loss mechanisms for nondegenerate two-photon gain and lasing, namely free-carrier absorption, Urbach-tail absorption and nondegenerate three-photon absorption, especially with a view to finding regimes where two-photon gain overcomes losses. Of greatest interest is the mid-IR spectral region where multiple semiconductors are appropriate for testing two-photon gain. Quantum-well systems with TM polarization attract particular interest because, at this polarization the two-photon transitions are calculated to be the most enhanced while free-carrier absorption can vanish. Additionally, unlike in bulk semiconductors, the enhancement of two-photon emission and three-photon absorption are expected to occur at different photon energies. However, each one of these processes needs to be carefully measured in order to build a practical picture of the overall losses.