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 S-3(1)-> 3 P-3(2) 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 S-3(1)-> 3 P-3(2) 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. (C) 2005 American Institute of Physics.