Abstract
The increasing performance of optical lattice clocks has made them attractive for scientific applications in space and thus has pushed the development of their components including the interrogation lasers of the clock transitions towards being suitable for space, which amongst others requires making them more power efficient, radiation hardened, smaller, lighter as well as more mechanically stable. Here we present the development towards a space-compatible interrogation laser system for a strontium lattice clock constructed within the Space Optical Clock (SOC2) project where we have concentrated on mechanical rigidity and size. The laser reaches a fractional frequency instability of 7.9 × 10−16 at 300 ms averaging time. The laser system uses a single extended cavity diode laser that gives enough power for interrogating the atoms, frequency comparison by a frequency comb and diagnostics. It includes fibre link stabilisation to the atomic package and to the comb. The optics module containing the laser has dimensions 60 × 45 × 8 cm3; and the ultra-stable reference cavity used for frequency stabilisation with its vacuum system takes 30 × 30 × 30 cm3. The acceleration sensitivities in three orthogonal directions of the cavity are 3.6 × 10−10/g, 5.8 × 10−10/g and 3.1 × 10−10/g, where g ≈ 9.8 m/s2 is the standard gravitational acceleration.
Highlights
The increasing performance of optical lattice clocks has made them attractive for scientific applications in space and has pushed the development of their components including the interrogation lasers of the clock transitions towards being suitable for space, which amongst others requires making them more power efficient, radiation hardened, smaller, lighter as well as more mechanically stable
We report on the design and characteristics of a clock laser system, which is the iteration in the pursuit of space applications
The stability of the laser was assessed by comparing it to a reference stationary clock laser system, based on an ultra-stable long cavity, that was operating at the same frequency
Summary
The increasing performance of optical lattice clocks has made them attractive for scientific applications in space and has pushed the development of their components including the interrogation lasers of the clock transitions towards being suitable for space, which amongst others requires making them more power efficient, radiation hardened, smaller, lighter as well as more mechanically stable. Some efforts have been made in this direction with new designs targeting force-insensitivity[13,14,15,16], compactness and transportability[17] and space readiness[18] The importance of such lasers was boosted by European Space Agency (ESA), which has launched the Space Optical Clock (SOC) projects, developing generations of mobile lattice clocks towards space applications. The clock laser is used for the interrogation of the clock transition (natural linewidth 1.2 mHz21) and it needs to have an intrinsic narrow linewidth This ultra-high stability of the laser’s frequency is typically obtained by stabilising it to a high finesse Fabry-Pérot cavity. The cavity should be as insensitive as possible to external vibrations that would change the distance between the mirrors
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