Title: Frequency Comb Spectroscopy with Coherent and Incoherent Light
Abstract: Optical frequency combs are a unique spectroscopic tool, providing an unparalleled combination of frequency accuracy, high-resolution and broad spectral coverage. In this talk, I will highlight our development of frequency comb spectroscopy techniques that apply to both the active detection of coherent laser light, as well as passive detection of incoherent thermal light. In the case of coherent spectroscopy, we have developed extremely broad bandwidth mid-infrared frequency combs that span from 3 microns to nearly 25 microns with repetition rates from 100 MHz to 10 GHz. These systems are being applied to high-speed dynamic gas sensing and hyperspectral microscopy with readout directly in the mid-infrared, or via up-conversion and electro-optic sampling with a second comb of few-cycle pulses at 1.5 micron. In a second case, we employ laser-based heterodyne radiometry to measure incoherent light sources in the near-infrared and introduce techniques for absolute frequency calibration with a laser frequency comb. Here we measure solar and atmospheric spectral features with signal-to-noise ratio that matches the fundamental quantum-limited prediction given by the thermal photon distribution and our system’s efficiency, bandwidth, and averaging time. Additionally, we perform direct heterodyne of incoherent thermal light with the frequency comb itself, thereby bringing the power of telecommunications photonics and the precision of frequency comb metrology to laser heterodyne radiometry, with implications for solar and astronomical spectroscopy, remote sensing, and phased-array imaging in the mid and near infrared.
About the Speaker: Scott Diddams holds the Robert H. Davis Endowed Chair at the University of Colorado Boulder, where he is also Professor of Electrical Engineering and Physics. He carries out experimental research in the fields of precision spectroscopy and quantum metrology, nonlinear optics, microwave photonics and ultrafast lasers. Diddams received the Ph.D. degree from the University of New Mexico in 1996. From 1996 through 2000, he did postdoctroral work at JILA, NIST and the University of Colorado. Subsequently, Diddams was a Research Physicist, Group Leader, and Fellow at NIST (the National Institute of Standards and Technology). In 2022 he transitioned to his present position where he also assumed the role of Faculty Director of the Quantum Engineering Initiative in the College of Engineering and Applied Science. As a postdoc Diddams built the first optical frequency combs in the lab of Nobel laureate John Hall, and throughout his career, he has pioneered the use of these tools for optical clocks, tests of fundamental physics, novel spectroscopy, and astronomy. His research has been documented in more than 750 peer-reviewed publications, conference papers, and invited talks. The work of Dr. Diddams and his research group has also been recognized by multiple awards. These include the Distinguished Presidential Rank Award, the Department of Commerce Gold and Silver Medals for "revolutionizing the way frequency is measured”, as well as the Presidential Early Career Award in Science and Engineering (PECASE), the OPTICA C.E.K. Mees Medal, the IEEE Photonics Society Laser Instrumentation Award, and the IEEE Rabi award. He is a Fellow of OPTICA (formerly OSA), the American Physical Society, and IEEE.
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