A system to control and stabilize the output of visible laser diodes was developed and used to measure the velocity distribution of lithium atoms in a laser cooling experiment. Circuitry was designed and built for controlling the diode temperature and current, and optical feedback from a grating was used to further tune the laser and to narrow its lineshape. In the experiment, atoms from a thermal lithium beam were slowed to near zero velocity using a multi-frequency relay chirp technique.