High-power frequency-stabilized laser for laser cooling of metastable helium at 389 nm

A high-power, frequency-stabilized laser for cooling of metastable helium atoms using the 2 S1 →3 P2 transition at 389 nm has been developed. The 389 nm light is generated by frequency doubling of a titanium:sapphire laser in an external enhancement cavity containing a lithium– triborate nonlinear crystal. With a maximum conversion efficiency of 75%, 1 W of useful 389 nm power is produced out of 2 W at 778 nm. While being stabilized to the 2 S1→3 P2 transition, the 389 nm frequency is tunable over ±150 MHz with respect to the field-free atomic resonance frequency. This is accomplished by Zeeman tuning of the absorption lines used in the frequency-stabilization scheme. The setup for saturated absorption spectroscopy in an rf discharge cell, used to stabilize the 389 nm laser to the atomic transition, is described in detail. © 2005 American Institute of Physics. fDOI: 10.1063/1.1865752g