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A Single Free-Running Dual-Comb MIXSEL for Fast and Precise Distance Measurements

Multiheterodyne techniques in science and technology promise unsurpassed precision in many fields of application such as dual-comb spectroscopy or light detection and ranging (LIDAR) [1–2]. Complexity, performance and cost can be greatly improved with dual-comb semiconductor disk lasers (SDL). Integration of the active semiconductor gain of a vertical exteral-cavity surface emitting laser (VECSEL) with the saturable absorber of a semiconductor saturable absorber mirror (SESAM) in the same epitaxial structure leads to the modelocked integrated external-cavity surface emitting laser (MIXSEL) [3]. The MIXSEL allows modelocking in a simple straight cavity. With two intracavity birefringent crystals, the initially unpolarized cavity beam is seperated by polarization [4]. When optically pumping two spots on the semiconductor chip, the dual-comb MIXSEL emits two orthogonally polarized optical frequency combs (OFCs) with a slight difference in pulse repetition rate which can be freely adjusted (Fig. 1a). The common cavity leads to an intrinsically high mutual coherence between the two OFCs, making the dual-comb MIXSEL the ideal source for dual-comb spectroscopy [5] and other field-deployable multiheterodyne beatnote techniques.