Laser system for secondary cooling of 87Sr atoms

A laser system with a narrow generation line for secondary laser cooling of ⁸⁷Sr atoms has been developed and investigated. It is planned to use ultracold ⁸⁷Sr atoms loaded in an optical lattice in an optical frequency standard. To this end, a 689-nm semiconductor laser has been stabilised using an external reference ultrastable cavity with vibrational and temperature compensation near the critical point. The lasing spectral width was 80 Hz (averaging time 40 ms), and the frequency drift was at a level of 0.3 Hz s^-1. Comparison of two independent laser systems yielded a minimum Allan deviation: 2 × 10^-14 for 300-s averaging. It is shown that this system satisfies all requirements necessary for secondary cooling of 87Sr atoms using the spectrally narrow ¹S₀ — ³P₁ transition (λ = 689 nm).