Development of a compact mode-locked ECDL for precision frequency comparison experiments at 780 nm

Abstract

Nowadays, cold atom-based quantum sensors such as atom interferometers are leaving the optical labs [1, 2], thus allowing fundamental physics to be tested in space. The use of different quantum objects such as Potassium (K) and Rubidium (Rb) ultra-cold quantum gases enables tests of the Universality of Free Fall (UFF) [1-4]. While narrow linewidth lasers emitting at 767 nm and 780 nm are used to build the corresponding atom interferometers, determination of any relative acceleration of the quantum ensembles can be realized by employment of a suitable frequency comb measuring the frequency difference between those lasers [5]. Further, the micro-gravity environment demands a highly compact, robust and power efficient setup. Here, we present an important step to reduce the complexity of the laser system employed. Instead of using e.g. a fiber-based frequency comb [6], we employ a compact semiconductor laser consisting of a specifically designed diode chip and some passive components developed to generate a frequency comb in the wavelength range of interest.