We describe a method for frequency narrowing commercial high power diode la
sers from 2 to 0.1 nm bandwidth with modest loss of power (< 2 dB). The res
ulting laser light is well suited for spin-exchange optical pumping, and we
demonstrate that the polarization produced by a 2.5 W narrowband laser exc
eeds that of a 15 W array by 40% in our optical pumping system. (C) 2000 Am
erican Institute of Physics. [S0003-6951(00)00411-3].