CAREER: Mid-infrared Intersubband Polaritonics

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The goal of this program is to develop fundamentally new mid-infrared optical sources based on strong quantum interactions between light and extremely thin layers of semiconductors for applications in medicine, industry, and homeland security. Optical devices operating in the mid-infrared portion of the electromagnetic spectrum (3-30 microns) enable sensitive imaging and detection because many molecules exhibit specific and strong absorption spectra at these wavelengths. One of the primary challenges of developing mid-infrared sources for these applications is that the physical process that generates light is very inefficient. Our approach to improving the efficiency of mid-infrared optical sources is to engineer strong quantum mechanical interactions between light and matter, creating quantum states that are simultaneously light and matter excitations, and to study these hybrid states when the device is electrically pumped. In doing so, our desire is to develop a set of tools for these optoelectronic devices by demonstrating techniques for engineering, fabricating, characterizing, and controlling devices that incorporate strong light-matter interactions. Beyond advancing mid-infrared technologies, this program also addresses education and diversity in science, technology, engineering, and mathematics by developing and hosting Engineering Days that are built around hands-on optics-based challenges for students at local schools.This program aims to improve the radiative quantum efficiency of mid-infrared optoelectronic devices. However, far from incremental improvements to existing devices such a quantum cascade lasers, our approach seeks the development of fundamentally new devices based on electrically injected polariton states that arise from strong light-matter interactions between the photon field in a resonator and electronic intersubband transitions between the quantized states of quantum wells integrated into the resonator. These novel optoelectronic devices will provide a new approach for wide-bandwidth, high-power incoherent sources needed for applications in mid-infrared sensing and imaging. Our approach is an integrated theoretical, computational, and experimental effort to (1) investigate mid-infrared microcavities, (2) improve coupling of photons with mid-infrared intersubband transitions, and (3) implement efficient electrical injection of intersubband polariton states. We will investigate a range of cavity and conduction band designs in both GaAs- and InP-based material systems. All of our materials will be grown by molecular beam epitaxy and fabricated into devices in a state-of-the-art nanofabrication facility. We will characterize the devices using Fourier transform spectroscopy as a function of temperature, resonator and conduction band design, and electrical pumping power. Our efforts will lay the groundwork for integrating mid-infrared intersubband polaritons into optoelectronic devices. Furthermore, efficient electrical injection of intersubband polariton states will also benefit the development of ultra-tunable quantum cascade lasers, while the investigation of the limits of light-matter coupling will be of interest to the mid-infrared detector and quantum optics communities. The end result of this program is ambitious: the development of electrically injected intersubband polariton emitters with more than four orders of magnitude improvement in the emitted power and efficiency compared to existing mid-infrared intersubband emitters.