Ultra-coherent semiconductor lasers for metrology

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This project involves the development of compact and robust laser sources with the high performance required for metrology and quantum technology applications, enabled by the unique properties of hybrid semiconductor lasers: wavelength engineerable lasers with very high finesse cavities and ultra-narrow fundamental linewidth. Such lasers have very low intensity and frequency noise compared to other lasers so long as the photon lifetime exceeds the carrier lifetime; however, in conventional formats this means that the external cavity must be a few cm long and therefore subject to environmental noise. Linewidths below a few kHz are usually achieved via active stabilisation to an external reference, most often a Fabry-Perot. We have recently reported semiconductor disk lasers with sub-kHz linewidths at novel wavelengths for atom cooling applications, which is record performance for this laser type; however, to date we have used relatively standard free-space laser resonators, external frequency references, and standard locking schemes. These add bulk and complexity to a compact semiconductor laser system and are subject to drift. Having demonstrated the potential of these lasers for cold-atom metrology we will now take advantage of their low intrinsic noise and unique intracavity dynamics for much more compact frequency locking schemes.Aim: to apply a range of semiconductor and optical engineering techniques combined with novel laser architectures to significantly reduce the volume and improve the stability of ultra-coherent semiconductor laser systems for metrology.