Spectroscopic study of the cycling transition 4s[3/2](2)-4p[5/2](3) at 811.8 nm in Ar-39: Hyperfine structure and isotope shift

Doppler-free saturated absorption spectroscopy is performed on an enriched radioactive Ar-39 sample. The spectrum of the 3s(2)3p(5)4s[3/2](2)-3s(2)3p(5)4p[5/2](3) cycling transition at 811.8 nm is recorded, and its isotope shift between Ar-39 and Ar-40 is derived. The hyperfine coupling constants A and B for both the 4s[3/2](2) and 4p[5/2](3) energy levels in Ar-39 are also determined. The results partially disagree with a recently published measurement of the same transition. Based on earlier measurements as well as the current work, the isotope shift and hyperfine structure of the corresponding transition in Ar-37 are also calculated. These spectroscopic data are essential for the realization of laser trapping and cooling of Ar-37,Ar-39.