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The search for Earth-like exoplanets with the Doppler radial velocity (RV) technique is an extremely challenging and multifaceted precision spectroscopy problem. Currently, one of the limiting instrumental factors in reaching the required long-term 10−10level of radial velocity precision is the defect-driven subpixel quantum efficiency (QE) variations in the large-format detector arrays used by precision echelle spectrographs. Tunable frequency comb calibration sources that can fully map the point spread function (PSF) across a spectrograph’s entire bandwidth are necessary for quantifying and correcting these detector artifacts. In this work, we demonstrate a combination of laser frequency and mode spacing control that allows full and deterministic tunability of a 30 GHz electro-optic comb together with its filter cavity. After supercontinuum generation, this gives access to any optical frequency across 700–1300 nm. Our specific implementation is intended for the comb deployed at the Habitable-Zone Planet Finder (HPF) spectrograph and its near-infrared Hawaii-2RG array, but the techniques apply to all laser frequency combs (LFCs) used for precision astronomical spectrograph calibration and other applications that require broadband tuning.
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High-precision optical time and frequency transfer
High-precision optical time and frequency transfer is accomplished by a collection of laser-based techniques that achieve time dissemination with subpicosecond instabilities and frequency dissemination with instabilities below one part in 1016. The ability to distribute and compare time and frequency at these precisions enables current optical timing networks such as interconnected optical atomic clocks for the redefinition of the second, relativistic geodesy, and fundamental physics tests as well as time and frequency dissemination systems for large-scale scientific instruments. Future optical timing networks promise to expand these applications and enable new advances in distributed coherent sensing, precise navigation, and more. The field of high-precision optical time and frequency transfer has made significant advances over the last 20 years and has begun to transition from technique development to deployment in applications. Here, we present a review of approaches to high-precision optical time and frequency transfer. We first present a brief overview of the metrics used to assess time and frequency transfer. We then provide a discussion of the difference between time transfer and frequency transfer and review the various technical noise sources. We also provide a background on the optical frequency comb and its role in optical time and frequency transfer for additional context. The next sections of the paper cover specific time–frequency transfer techniques and demonstrations beginning with time and frequency transfer over fiberoptic links including continuous-wave (CW) laser-based frequency transfer, CW-laser-based time transfer, and frequency-comb-based time transfer. We then discuss approaches for time and frequency transfer over free-space including pulsed-source time transfer, CW-laser-based frequency transfer, and frequency-comb-based time transfer. Since no known existing review article covers frequency-comb time transfer over free-space, we provide additional details on the technique. Finally, we provide an outlook that outlines outstanding challenges in the field as well as possible future applications.
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- Award ID(s):
- 2016244
- PAR ID:
- 10589697
- Publisher / Repository:
- Advances in Optics and Photonics
- Date Published:
- Journal Name:
- Advances in Optics and Photonics
- Volume:
- 17
- Issue:
- 2
- ISSN:
- 1943-8206
- Page Range / eLocation ID:
- 375
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1364/AOP.545290
