Optical frequency standards for time and length applications

Abstract

The last decade has witnessed tremendous progress in research on optical frequency metrology. Optical frequency standards using optical lattice and single-ion trap technologies have reached levels of stability and accuracy that surpass the performance of the best Cs fountain atomic clocks by orders of magnitude. Optical frequency standards are also used for various applications including length metrology. Optical frequency measurement and links using optical frequency combs and optical fibres play important roles in the development of optical frequency standards. This article introduces optical frequency standards recommended by the International Committee for Weights and Measures (CIPM) along with updates provided by recent research results. Frequency ratio measurements and remote frequency comparisons are addressed in relation to the work whose goal is to redefine the second. Optical frequency standard and optical frequency comb applications are also described.

Atomic clocks for geodesy

“…Since this review is intended for physicists interested in geodetic applications of optical atomic clocks as well as for geodesists curious about the capabilities of clocks and their comparison, it provides a basic introduction and description of the state-of-the art aimed for readers of the respective other field. Further details can be found in recent reviews on optical clocks (Margolis 2010, Ludlow et al 2015, Hong 2017) and on clocks in the context of geodesy (Delva andLodewyck 2013, Denker et al 2017). The broader physics background of frequency standards and physical geodesy can be found in text books e.g.…”

Accurate laser frequency locking to optical frequency combs under low-signal-to-noise-ratio conditions

“…Self-referenced optical frequency combs provide an accurate optical frequency reference over a wide optical bandwidth [6,10,11]. They can be used to measure or stabilize the frequency of continuous-wave (CW) lasers in many applications such as state-of-the-art optical-frequency metrology [4,17], precision spectroscopy [12], laser cooling of atoms [7,19], exciting rovibrational transitions in cold molecules [22], measurement of the frequency of stabilized lasers for length metrology [13], etc. This relies on exploiting the beat note between the CW laser and a tooth of the comb, either by frequency counting or by phase locking [5,12,14].…”

High‐stability optical frequency transfer with all‐fiber architecture for optical lattice clocks

“…The current definition of the second goes back half a century; the attainable accuracy has improved at a pace of one digit in 10 years, and now is 16 digits (uncertainty: 10 −16 ) . However, aiming at further improvement of frequency standards in terms of accuracy and stability, researchers explore optical frequency standards in an optical frequency band (10 15 Hz) exceeding the conventional microwave frequency (10 10 Hz) . Research in frequency standards was spurred with realization of optical frequency measurement using optical frequency combs around 2000, and there already appeared optical atomic clocks with uncertainty of 10 −18 , thus outperforming cesium atomic clocks in attainable accuracy.…”

“…1 However, aiming at further improvement of frequency standards in terms of accuracy and stability, researchers explore optical frequency standards in an optical frequency band (10 15 Hz) exceeding the conventional microwave frequency (10 10 Hz). 2 Research in frequency standards was spurred with realization of optical frequency measurement using optical frequency combs around 2000, 3,4 and there already appeared optical atomic clocks with uncertainty of 10 −18 , 5-8 thus outperforming cesium atomic clocks in attainable accuracy. Particularly, optical lattice clocks 9 use multiple atoms so that quantum projection noise-limited stability determined by the number of atoms can be improved, and high-accuracy frequency can be realized within a short averaging time.…”