%0 Journal Article %T A compact, robust, and transportable ultra-stable laser with a fractional frequency instability of $1\times10^{-15}$ %A Qun-Feng Chen %A Alexander Nevsky %A Marco Cardace %A Stephan Schiller %A Thomas Legero %A Sebastian H£¿fner %A Andre Uhde %A Uwe Sterr %J Physics %D 2014 %I arXiv %R 10.1063/1.4898334 %X We present a compact and robust transportable ultra-stable laser system with minimum fractional frequency instability of $1\times10^{-15}$ at integration times between 1 to 10 s. The system was conceived as a prototype of a subsystem of a microwave-optical local oscillator to be used on the satellite mission STE-QUEST (Space-Time Explorer and QUantum Equivalence Principle Space Test, http://sci.esa.int/ste-quest/). It was therefore designed to be compact, to sustain accelerations occurring during rocket launch, to exhibit low vibration sensitivity, and to reach a low frequency instability. Overall dimensions of the optical system are $40\textrm{ cm}\times20\textrm{ cm}\times30\textrm{ cm}$. The acceleration sensitivities of the optical frequency in the three directions were measured to be $1.7\times10^{-11}/g$, $8.0\times10^{-11}/g$, and $3.9\times10^{-10}/g$, and the absolute frequency instability was determined via a three-cornered hat measurement. The design is also appropriate and useful for terrestrial applications. %U http://arxiv.org/abs/1410.5453v1