  A method for active control of the spatial profile of a laser beam using
adaptive thermal lensing is described. A segmented electrical heater was used
to generate thermal gradients across a transmissive optical element, resulting
in a controllable thermal lens. The segmented heater also allows the generation
of cylindrical lenses, and provides the capability to steer the beam in both
horizontal and vertical planes. Using this device as an actuator, a feedback
control loop was developed to stabilize the beam size and position.
