Abstract
A phase-controlled spatial light modulator to split one laser pulse into tens of thousands of mini rays, each propagating into a designed direction to form a 3D point cloud, has been proposed and demonstrated recently. The original experimental design needs a beamsplitter to couple the femtosecond laser light to the phase-controlled spatial light modulator. Thus, only one-fourth of the incoming laser light is used in the volumetric lithography after two reflections with the beamsplitter. This study proposes a tilted coupling scheme between the femtosecond laser and the phase-controlled spatial light modulator. Because no beamsplitters are required in the new scheme, the useful laser energy is four times higher than the original scheme, and the required exposure time to cross-link polymer through two-photon absorption is sixteen times shorter.
A new mathematical model has also been developed to generate the phase diagram on the phase-controlled spatial light modulator to diffract light into the required directions to form voxels in the designed 3D point clouds. The new mathematical model considers the tilted incoming laser light and the required adjustment to ensure mini rays arrive at the voxel locations simultaneously to trigger two-photon absorption. The resulting phase diagram for projecting vertical lines, tilted lines, and micro pyramids with the new mathematical model for the tilt coupling scheme is presented. The resulting lithography results and the possible future improvements considering the diffraction of mini rays are also discussed.
