Solution #2:
Dynamic Thermal Compensation
With this method of thermal compensation we use a scanning heating
laser: either a CO2 laser (absorbed in the optic's surface) or a solid
state 1.35 micron laser (absorbed in the bulk). Since the thermal time
constant of the optic is large (5 hours or more), a beam scanned across the
face at a sufficient speed (via a pair of galvanometer scanners),
modifying the dwell time in certain regions to
deposit heat where necessary), can be used to correct for essentially
arbitrary wavefront distortions (whose spatial extent is larger than the
size of the heating beam).
The control scheme for dynamic thermal compensation hinges on a high
resolution, three dimensional finite element model of the heating beam
acting on specific
"zones" of the optic. The model yields the optical path response for heating
in each particular zone, and the library of responses allows us to determine
the heat that must be deposited in each zone to generate an arbitrary
optical path distortion (usually one that corrects for the undesireable OPD
generated by thermal lensing).
Back to Thermal Compensation Home
Last modified: Mon Nov 29 22:35:36 EST 1999