Creation of Singlet Strontium Rydberg States Using ULE-stabilized Laser Systems*

The development of stable laser systems for creation of high-n strontium singlet Rydberg states via two-photon 5s^{2 1}S₀ → 5s5p ¹P₁ → 5sns ¹S₀ transitions is described.   The required radiation at 461 and 413 nm is generated using frequency-doubled diode laser systems whose fundamental outputs are stabilized using a single very-high-finesse ultralow expansion (ULE) cavity.  The lasers are tuned by directing a fraction of their fundamental output powers through fiber electro-optical modulators (EOMs) to generate sidebands that are then locked to the ULE cavity.  This allows the lasers to be tuned over frequency ranges of up to ~1GHz by varying the EOM drive frequency.  Whereas a similar scheme has been used to generate triplet strontium Rydberg atoms, the use of singlet Rydberg atoms results in a simpler excitation spectrum and, since S=0, simplifies the interpretation of observed phenomena.