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Magnetic Properties of Endohedral Fullerenes
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
Panagiotis Dallas, Reuben Harding, Stuart Cornes, Sapna Sinha, Shen Zhou, Ilija Rašović, Edward Laird, Kyriakos Porfyrakis
Many modern technologies, such as communications and navigation, rely on precise and stable frequency standards (Vig, 1993). For example, high-frequency stability is necessary in communication systems to ensure that the transmitter and receiver remain synchronized. This is particularly important for jamming-resistant communications that work by coordinated hopping over different frequencies. In navigation applications, such as global navigation satellite system (GNSS) receivers, high-stability frequency standards could improve positional accuracy in signal-degraded environments (Misra, 1996). The most stable clocks work by locking an electronic oscillator to a reference frequency provided by an atomic transition (Riehle, 2004) as shown in Figure 16.6a. Since atomic transition frequencies are fixed by nature, this reduces the influence of manufacturing variation and drift and results in a highly stable and reproducible output frequency. Such a system is commonly called an “atomic clock”. For portable atomic clocks, size, weight and power (SWaP) are important parameters in addition to stability (Vig, 1993).
Single-ion, transportable optical atomic clocks
Published in Journal of Modern Optics, 2018
Marion Delehaye, Clément Lacroûte
The schematic single-ion clockwork is illustrated Figure 1. The clock laser frequency is compared to an optical transition frequency in a single, laser-cooled trapped ion and corrected using an optical frequency corrector such as an acousto-optical modulator (AOM). The output of this corrector is the optical clock output signal, which is locked to an ultra-stable Fabry-Pérot (FP) cavity at short times (s - 10 s, see Section 4) and to the ion at longer times. It constitutes an optical frequency standard, which can be used and distributed directly for applications such as optical frequency comparisons, precision spectroscopy, relativistic geodesy, etc. Using an optical frequency comb, it can also be transferred to the radiofrequency (RF) domain, where it can form the basis of a timescale [63,64]. In that regard, the useful signal of an optical atomic clock is actually the RF signal, which is why the optical frequency comb used to transfer the stabilized frequency from the optical to the RF domain should be taken into consideration in the overall setup volume (see Section 7.1).