Abstract

All-optical production of quantum degenerate atomic gases has been one of the long-standing targets in laser cooling. We report a novel approach towards this direction based on a narrow-line laser cooling for strontium atoms. By employing two transitions with markedly different dipole moments, i e., the allowed ¹S₀^-1P₁(λ = 461 nm, γ = 2π × 32 MHz) and the spin-forbidden ¹S_0-³P₁ (λ = 689 nm, γ= 2π × 7.6 kHz) transition, thermal strontium atoms were Doppler-cooled down to 400 nK, or the photon recoil temperature, in a magneto-optical trap (MOT). Figure 1 shows the corresponding energy levels for cooling and trapping. The use of a narrow spin-forbidden transition successfully reduced the radiation trapping effects at a high atom density over 10^l2/cm³, thus enabling us to attain the hitherto high phase space density of 0.01[1] in a MOT.

© 2000 IEEE