For nearly 25 years, the research group of Prof. Diddams has pioneered the development and use of the optical freuqency combs for the most precice measurements in spectroscopy, sensing and atomic timekeeping. Research听topics we pursue include ultrafas laser science and engineering,听precision timing, optical clocks, astronomy, nonlinear optics, nonlinear nano-photonics, microwave听photonics, and spectroscopy from the UV to THz. In relocating from NIST to the University of Colorado in 2023, we are ramping up new experiments, while continuing much of our earlier work. Check back often as we will be updating this page to capture all the current research efforts.
Optical Clocks and Precise Timing
Optical atomic clocks keep time at the femtosecond level, which is the intrinsic timescale of light. 听These clocks have demonstrated frequency stability and accuracy at the 10-18听level form the basis for next-generation time standards. 听Our work aims to harness this precision for fundamental tests of physics, the generation of ultra-precise timing signals, and the development of optical clock technolgies for application outside the research lab.
Optical clocks听
Beginning with the introduction of the frequency comb technology that enables the counting of optical cycles of light,听PI Diddams and his group have advanced the development of optical clocks and clock networks.听These have been used for the most accurate measurements of atomic frequency ratios and for tests of fundamental physics. A new focus is to focus on the engineering of these clock systems to make them more robust and operational beyond the research lab. 听We have a new project in which we will take an optical clock to the highest peaks of Colorado and compare back to a reference clock in Boulder to perform the bets test Einstein's general relativity. 听(more coming soon)
Low-noise microwave generation
Our group has pioneered the technique of听optical frequency division and used optically-stabilized frequency combs to generate ultra-low noise microwave signals鈥攑ossessing phase noise and timing jitter significantly lower than what is achievable with the best conventional electronic sources. This research involves the development of the frequency comb sources and the critical understanding of the limitations of听high-speed photodetection, as well as ways to understand and circumvent the quantum limitations. (more coming soon)
Mm-wave time transfer
Optical techniques have听shown the highest performance of any time-transfer approach. 听However, optical field suffer from poor atmospheric transmission in bad weather and the requirements for point and tracking are very challenging. 听As an alternative, we are beginning to explore time transfer techniques with mm-wave (30-300 GHz) carriers. The high frequency of mm-waves provides a compromise between听high timing precision and technological maturity.
As part of this work, our lab continues to develop and refine techniques for optically-referenced stable mm-wave generation. 听These approaches听are based on a combination of Er:fiber, EO and microcomb technologies.
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- S. A. Diddams, J. C.听 Bergquist,听 S. R. Jefferts and C. W. Oates, 鈥淪tandards of time and frequency at the outset of the 21st century,鈥� Science, 306, 1318 (2004).听听听听
- K. Beloy, et al., 鈥淔requency Ratio Measurements with 18-digit Accuracy Using a Network of Optical Clocks,鈥� Nature 591, 564 (2021).听听
Frequency Comb听Technology
鈥婨lectro-optic Combs
Electrooptic combs are optical frequency combs generated using the electrooptic effect. They involve modulating an optical carrier with a periodic听electrical signal using electrooptic modulators. The modulated signal is then sent through a nonlinear medium which generates new frequencies in addition to the original carrier. These new frequencies form the evenly spaced spectral lines of the electrooptic comb, providing a precise and controlled series of optical frequencies. We utilize electrooptic combs for a wide variety of interesting metrology problems such as exoplanet detections, mm-wave generation, and electrooptic sampling.
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- Pooja Sekhar, Connor Fredrick, David R. Carlson, Zachary Newman, Scott A. Diddams, 鈥�20 GHz fiber-integrated femtosecond pulse and supercontinuum generation with a resonant electro-optic frequency comb,鈥澨�(2023).听鈥�
- D. R. Carlson, D. Hickstein, W. Zhang, A.J. Metcalf, F. Quinlan, S. Diddams, and S. Papp, 鈥淯ltrafast electro-optic light with subcycle control, Science 361, 1358 (2018).听听听
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Nonlinear Nanophotonics
The impact of lasers on our world has been tremendous, as they are crucial in various fields such as manufacturing, medicine, remote sensing, and optical communications. Photonic integrated circuits have also allowed for significant advances in optical systems with applications in signal processing, data transmission, precise timekeeping, and LiDAR. Certain optical crystals exhibit strong nonlinearities that allow for the manipulation of light through second harmonic generation, four-wave mixing, spontaneous parametric down-conversion, and other nonlinear processes. By exploiting these nonlinear properties, one can tune to frequencies needed for quantum sensors and quantum metrology. Harnessing these nonlinearities on nanophotonic platforms allows for more efficient frequency conversion and听lower SWaP-C. We work toward developing our own nanophotonic device recipes for novel quantum metrology.
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- Tsung-Han Wu, Luis Ledezma, Connor Fredrick, Pooja Sekhar, Ryoto Sekine, Qiushi Guo, Ryan M. Briggs, Alireza Marandi, Scott A. Diddams, 鈥淰isible to Ultraviolet Frequency Comb Generation in Lithium Niobate Nanophotonic Waveguides,鈥澨�(2023).听听
- T. J. Kippenberg, R.L. Holzwarth and S.A. Diddams, 鈥淢icroresonator based optical frequency combs,鈥� Science 332, 555 (2011).听听
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Frequency Comb Spectroscopy
Spectroscopy is essential for studying molecular properties and gaining control over molecular quantum states. The development of compact frequency combs from the infrared to听ultraviolet听spectral regions constitutes an important step in furthering fundamental spectroscopy and atmospheric sensing.听Our group works on developing infrared combs allowing for听precision spectroscopic measurements addressing both vibrational and rotational states of molecules. We also have generated spectrally broad UV-visible combs听through the use of high-harmonic generation and cascaded harmonic generation mechanisms in nonlinear crystals to probe the electronic states of molecules.听
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- D. M. B. Lesko et al., 鈥淎 six-octave optical frequency comb from a scalable few-cycle erbium fibre laser鈥�, Nature Photonics 15, 281 (2021),听
- Henry Timmers, Abijith Kowligy, Alex Lind, Flavio C. Cruz, Nima Nader, Myles Silfies, Gabriel Ycas, Thomas K. Allison, Peter G. Schunemann, Scott B. Papp, and Scott A. Diddams, "Molecular fingerprinting with bright, broadband infrared frequency combs," Optica 5, 727-732 (2018).听听听
- A. S. Kowligy, H. Timmers, A. J. Lind, U. Elu, F. C. Cruz, P. G. Schunemann, J. Biegert, and S. A. Diddams, 鈥淚nfrared electric-field sampled frequency comb spectroscopy,鈥� Science Advances 5, eaaw8794 (2019).听听听
Frequency Combs for Astronomy
The search for exoplanets around nearby stars is driven by profound scientific questions about planetary formation, evolution, diversity, and the potential for extraterrestrial life. Finding an exo-Earth remains challenging due to the required radial-velocity precision at the level of 10 cm/s.听Many sources of noise, such as instrumental systematics and contamination from Earth鈥檚 atmosphere and stellar activity, complicate attempts to reach this level of precision. Improving the instrumental RV precision to disentangle the effects from these noise sources requires precise, accurate, and highly stable calibration sources. In this regard, laser frequency combs听have emerged as an ideal calibration source.听Our group is exploring simple and robust approaches to developing 10+ GHz astrocombs that can operate autonomously at a remote telescope site.
- A. J. Metcalf, et al., "Stellar spectroscopy in the near-infrared with a laser frequency comb," Optica鈥�6, 233-239 (2019).听听听
- D. A. Fischer, et al. 鈥淪tate of the Field: Extreme Precision Radial Velocities,鈥澨� Publications of the Astronomical Society of the Pacific, 128, 066001 (2016)听听听
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