A transportable clock laser system with an instability of $1.6 \times 10^{-16}$

Abstract

We present a transportable ultra-stable clock laser system based on a Fabry-Pérot cavity with crystalline Al 0.92 Ga 0.08 As/GaAs mirror coatings, fused silica (FS) mirror substrates and a 20 cm-long ultra-low expansion (ULE ® ) glass spacer with a predicted thermal noise floor of mod σ y = 7 × 10 −17 in modified Allan deviation at one second averaging time. The cavity has a cylindrical shape and is mounted at ten points. Its measured sensitivity of the fractional frequency to acceleration for the three Cartesian directions are 2(1) × 10 −12 /(ms −2 ), 3(3) × 10 −12 /(ms −2 ) and 3(1) × 10 −12 /(ms −2 ), which belong to the lowest acceleration sensitivities published for transportable systems. The laser system's instability reaches down to mod σ y = 1.6 × 10 −16 Keywords Ultra-stalbe resonators • Clock laser system Among other applications, ultra-stable lasers as local oscillators largely determine the performance of optical clocks.