Dual-comb generation made simple

A fully stabilized optical frequency comb (OFC) consists of equally spaced frequencies and can serve as a very precise ruler for optical frequency measurements. Optically pumped vertically emitting semiconductor lasers have successfully been modelocked over a wide spectral region from the visible to the mid-IR. Continuous-wave operation of these lasers has been successfully commercialized and have gained a strong interest for power scaling with optical pumping. A modelocked integrated external-cavity surface-emitting laser (MIXSEL) integrates both the gain and the saturable absorber layer within the same semiconductor wafer. The MIXSEL generates a modelocked pulse train from a linear straight cavity defined by the MIXSEL chip and the output coupler as the two end mirrors. In dual-comb operation, the initially unpolarized beam is split towards the semiconductor MIXSEL chip with an intracavity birefringent crystal. No active stabilization is required for dual-comb spectroscopy! This talk explains how this is possible, how well this works and for what it can be used.