We describe frequency locking of a diode laser to a two-photon transition o
f rubidium using the Zeeman modulation technique. We locked and tuned the l
aser frequency by modulating and shifting the two-photon transition frequen
cy with ac and de magnetic fields. We achieved a linewidth of 500 kHz and c
ontinuous tunability over 280 MHz with no laser frequency modulation. (C) 2
000 Optical Society of America OCIS codes: 020.7490, 140.2020, 300.6260.