Abstract

A laser marking process is described which is based upon a unique phenomenon of photothermally transforming oriented microcrystallites of a vapor-deposited dichroic dye. It is shown that writing with linearly polarized laser light on an oriented film improves contrast and sensitivity over the unoriented film. The improvement stems from the increased optical sensitivity when an oriented film of one polymorphic form of the dye is photothermally transformed by irradiation with suitably oriented linearly polarized laser light. It is shown that the laser marking process proceeds via three stages. At low power the laser pulse causes a crystal-crystal transformation within microcrystallites of an oriented film of the dichroic dye. At medium power the dye also migrates and coalesces around nucleating sites in the written spot during the crystal transformation process. At the highest powers the unovercoated film ablates. A simple polishing process is described for producing large areas of oriented thin vapor-deposited films.

© 1984 Optical Society of America

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