Precision Radiometry for Incoherent Spectral Measurements (PRISM)
Abstract
Heterodyne techniques are amongst the most powerful ways of measuring radiation. By beating a signal with a strong local oscillator (LO), one coherently measures the spectrum of a light source with an excellent combination of sensitivity and resolution. As such, they are ubiquitous in science and technology. However, they have primarily been used to measure narrowband coherent sources, as the LO and signal must coexist within a limited detector bandwidth. Recent advances in light sources, detectors, and metrology have the potential to greatly increase the frequency resolution, spatial resolution, and sensitivity of heterodyne measurements, for the first time allowing for broad incoherent optical sources to be characterized with the ultimate spectral and spatial resolution. This MURI will leverage our team s interdisciplinary expertise in optical metrology, nanophotonics, astronomy, and quantum photonics to expand the fundamental limits of heterodyne spectroscopy. Using frequency combs, broadband light sources whose lines are phase-coherent, we will develop new schemes for measuring the spectra of incoherent sources with unprecedented bandwidth, frequency resolution, and spatial resolution. Blending the power of laser heterodyne radiometry with frequency comb techniques will significantly enhance the measurement of incoherent light sources and will enable a new level of precision in science and technology. The use of ultra-stable combs will unlock the possibility of broadband heterodyne Very Long Baseline Interferometry (VLBI) at optical wavelengths. Single-location instruments have a spatial resolution that is limited by the receiver size, but in VLBI, this is enhanced by coherently combining the output of multiple instruments. For example, the Event Horizon Telescope constructs images of black holes in the millimeter-wave. Performing optical VLBI at many frequencies with uncorrelated LOs at once would be a major undertaking, but correlated combs offer new opportunities. By developing the techniques needed to transfer the time from a single near-infrared comb to every frequency of interest, it will become possible to perform multispectral measurements with both high spatial and frequency resolution. This will be of use both for measurements of astronomical targets like proto-planetary disks and for DoD-relevant imaging. While multi-frequency heterodyne spectroscopy and VLBI present many opportunities, their ultimate limits are unknown. For example, while heterodyne spectroscopy is known to have quantum-limited sensitivity, it is uncertain how the sensitivity changes for comb LOs. PRISM will advance the fundamental understanding of heterodyne spectroscopy by establishing the theoretical framework for these limits and designing new quantum-enhanced systems to go beyond them. This will be done both in the multi-LO case and in the distributed case, leveraging new detector and source schemes in each case. Finally, we will use our techniques to perform several relevant demonstrations, advancing both fundamental science and defense-related applications.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 06, 2025
- Source ID
- FA95502410349
Entities
People
- David Burghoff
Organizations
- Air Force Office of Scientific Research
- United States Air Force
- University of Texas at Austin