Large waist cavity for ultra-narrow transition spectroscopy

Cavity enhanced spectroscopy on ultra-narrow transitions in atoms and molecules is a promising tool for frequency stabilization of clock lasers. However, the small beam waist of a typical cavity can effectively reduce the number of atoms in the system or introduce transit time broadening in the less controlled molecular systems. We present a cavity design with an internal telescope optimized to increase the waist from about 0:5 mm to 5 mm while still maintaining a convenient range of tuning parameters. Its usefulness in three separate spectroscopic systems is clarified.