CAREER: Dynamic nanophotonic spectral and directional control of thermal emission

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Thermal emission, the electromagnetic waves emitted by all objects, is a ubiquitous feature of our world. Controlling emitted and absorbed thermal radiation is of paramount importance for a range of energy technologies and the sources of heat they rely on. Beyond energy technologies, from sensing to imaging and detection in dark environments, thermal sources serve also serve as a foundational technology for our ability to perceive the world around us. This project seeks to enable the dynamic tuning of both the spectrum and directionality of thermal emission. The research will illuminate new mechanisms to tune heat flows from sources using a combination of nanophotonic design and unique material properties over infrared wavelengths. These findings will enable new, more compact sources and detectors for infrared imaging and sensing, as well as improved materials platform to control heat flows for energy and heat transfer applications. The key research aims are closely integrated with education and outreach activities that seek to engage students from the high-school through graduate level through online videos and updated courses, as well as actively engaging community members in heat-vulnerable communities. These activities will feed back into the core research aims by identifying key technical capabilities needed as well as opportunities for new applications of the research findings.Thermal emission from conventional materials and devices is typically broad spectrum, isotropic and static in nature, with the emitted spectrum and intensity controlled by the emitter’s temperature. Due to these characteristics, dynamically controlling the spectral and directional characteristics of the emissivity of a thermal source is a challenging task, but of fundamental importance for infrared imaging and sensing, as well as heat transfer and energy applications. Typical approaches today involve using bulk optical elements, including spectral filters along with mechanical movement to move or re-orient a source, and alter its spectral characteristics to meet a target functionality. While recent progress has been made using photonic and metamaterials strategies to alter emissivity characteristics, dynamic control of both the spectrum and directionality of emitted thermal radiation remains an open challenge. This project will demonstrate gradient epsilon near zero-based thermal nanophotonic devices that can dynamically tune both their spectral and directional emissivity over long-wave infrared wavelengths. The PI will characterize graded doped semiconductor films and characterize their optical properties over infrared wavelengths. These films will then be configured into junction architectures to dynamically tune spectral and directional emission over large bandwidths and achieve strong electrical control of emissivity. Finally, the project will also demonstrate metasurfaces that can dynamically tune spectral, directional and polarization characteristics of emitted thermal radiation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.