CAREER: Chip-Scale, Field-Resolved Detection of Mid-Infrared Light

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The mid-infrared portion of the electromagnetic spectrum is of fundamental interest to biological, chemical, and physical science. The mid-infrared (MIR) consists of electromagnetic waves with wavelengths from around 3 to 20 millionths of a meter. In this spectral region, virtually all molecules exhibit absorption resonances, and these resonances constitute molecular fingerprints. Accordingly, for around the past hundred years, MIR light has been used for sensing, with recent applications ranging from environmental monitoring to protein characterization. In the past few decades, there have been revolutionary advances in ultrafast MIR laser sources, that is, laser systems producing brief pulses of MIR light. Such ultrafast MIR sources offer new, exciting opportunities for enhancing MIR sensing technologies. The first goal of this project is to develop novel detectors specifically tailored for ultrafast MIR laser sources. These detectors will enable the measurement of light fields of MIR laser pulses in the time-domain. Such field-resolving detectors will enable MIR sensing with improved resolution, as well as provide novel capabilities to study the dynamic behavior of MIR absorption resonances. The second goal of this project is to promote engineering education engineering student retention. Towards this end, online educational content will be developed for graduate students working with ultrafast laser technology; novel educational strategies emphasizing the “we do” component of the gradual release of responsibility pedagogical model will be explored at the undergraduate level; and outreach events, promoting engineering and photonics, will be held for local students at the K-12 level. At all levels, the underlying themes of the research program will be integrated into the educational efforts. Mid-infrared (MIR) spectroscopy is ubiquitous in sensing applications across virtually all scientific disciplines. MIR spectroscopic tools primarily rely on frequency-domain techniques: in a MIR spectroscopic system, infrared light illuminates a sample, and the frequency spectrum of the transmitted light is measured. Absorption resonances are then extracted from the measured spectrum, and information about the sample is thereby obtained. In contrast to conventional MIR spectroscopy, at longer wavelengths, ultrafast laser systems have enabled time-domain spectroscopic techniques. For instance, in terahertz time-domain spectroscopy, terahertz waves irradiate a sample, and ultrafast laser pulses are used to measure the time-dependent electric field of the transmitted terahertz radiation. Such field-resolved measurements can provide unique, dynamical information as well as dramatically improved resolution compared to frequency-domain techniques. The goal of this project is to extend such time-domain, field-resolved detection to chip-scale platforms operating in the MIR. Specifically, in this project, chip-scale, optical detectors capable of resolving the instantaneous electric field of incident ultrafast MIR laser pulses will be developed. These chip-scale detectors will leverage sub-optical-cycle, strong-field photoemission currents from nanoscale metallic antennas to sample MIR laser pulses in the time-domain with exceptional resolution. These field-resolving detectors will provide revolutionary capabilities for future MIR spectroscopic systems and impact a broad range of scientific, medical, and industrial applications.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.