A compact, robust, and transportable ultra-stable laser with a fractional frequency instability of 1 x 10-15

We present a compact and robust transportable ultra-stable laser system with minimum fractional frequency instability of 1 x 10(-15) at integration times between 1 and 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 Space-Time Explorer and QUantum Equivalence Principle Space Test (STE-QUEST) (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 cm x 20 cm x 30 cm. The acceleration sensitivities of the optical frequency in the three directions were measured to be 1.7x10(-11)/g, 8.0x10(-11)/g, and 3.9 x 10(-10)/g, and the absolute frequency instability was determined via a three-cornered hat measurement. Two additional cavity-stabilized lasers were used for this purpose, one of which had an instability sigma(y) < 4 x 10(-16) at 1 s integration time. The design is also appropriate and useful for terrestrial applications. (C) 2014 AIP Publishing LLC.