Narrow linewidth VCSELs for high-resolution spectroscopy

A future generation of high-performance low-power atomic systems is expected to require VCSEL linewidths below 10 MHz for compatibility with the natural atomic linewidth (5 MHz for cesium) that is realized with atomic beams, trapped atoms, and trapped ions. This paper describes initial efforts at Sandia to reduce VCSEL linewidth by increasing the effective cavity length of an 850-nm monolithic VCSEL. In particular, two aspects of VCSEL design will be discussed: the Q of the VCSEL cavity, and the linewidth enhancement factor of the active region material. We report a factor of two linewidth reduction, from 50 MHz for our standard oxide-aperture VCSEL to 23 MHz for an extended-cavity VCSEL.