Optical atomic clocks and frequency combs
Atomic clocks are essential for a wide range of applications, including GPS systems, telecommunications, and scientific research requiring ultra-precise timekeeping. These clocks are typically based on the high-frequency energy transitions of atoms, such as cesium or rubidium. A key advancement in atomic clock technology is the use of optical frequency combs, which enable precise measurements of optical frequencies in the THz range. Compared to traditional microwave-based atomic clocks, optical clocks can provide significantly more precise timekeeping. Frequency combs are used to link optical frequencies to radio frequencies, which, unlike optical frequencies, can be measured by electronic systems.
Challenges of optical clocks
Optical clocks offer unprecedented precision and stability, far surpassing traditional atomic clocks. However, for the ultimate performance these optical clocks are largely confined to laboratory use due to their complexity and sensitivity. They require ultra-stable lasers, intricate cooling and trapping techniques for atoms or ions, and precise environmental control to prevent disturbances. The delicate nature of these systems makes them challenging to deploy outside controlled settings, limiting their practical use in everyday applications.
Vescent and DFM: A case study in optical source innovation
To demonstrate the feasibility of building a highly stable optical clock using commercial off-the-shelf components, Vescent and DFM combined Vescent’s FCC-100 frequency comb with DFM’s acetylene-stabilized fiber laser, Stabiλaser 1542ε, and evaluated the performance of the resulting 100 MHz clock signal.
Performance results
The performance of clocks is often evaluated from their relative frequency instability over time in terms of the so-called Allan deviation.
The black data points in the figure show the measured Allan deviation of the frequency difference between the 100 MHz output of DFM’s passive hydrogen maser used for realization of the national timescale UTC(DFM) and the output from a DFM-Vescent optical clock. Thus, the black data points are the quadratic sum of the frequency instability of both the maser and the optical clock. The blue line is the manufacturer’s specifications for the maser. The data shows that the optical clock performs significantly better than the hydrogen maser specifications up to 10 000 s, but clearly the maser performance is also better than its specifications. These data underscore the potential of compact reliable optical clocks in pushing the boundaries of atomic clock performance.
Additional data can be found in the white paper here.