A new optical metric, termed resist deformation factor (RDF), to represent deformation of three-dimensional (3D) resist profile has been introduced into a source and mask optimization (SMO) flow to mitigate defects caused by a reactive ion etching (RIE) process at the lithography stage. Under the low-k1 lithography conditions with both a highly-coherent source and a complicated mask, the 3D resist profile is subject to top-loss or bottom footing, resulting in hotspots and/or defects after the RIE process. In order to represent the 3D resist profile on a fast lithography simulation, a sliced latent image along resist depth direction is used to define RDF as the ratio of integrated optical intensities within the resist pattern to those around its surrounding area. Then the SMO flow incorporating the RDF into its cost function is implemented to determine both a source and a mask as the 3D resist profile is less likely to deform. The result of new SMO flow with RDF shows 30% improvement of resist top-loss.
Brighter far-field pattern of a phase-locked Nd:YAG microchip laser array was obtained by the Talbot effect in a three-mirror cavity. The laterally coupled Nd:YAG microchip laser array produced a pair of spots with sharper peaks with an angular separation of (lambda) /d in its far-field, where d is the distance between the adjacent sources, indicating an out-of-phase spatial mode coupling was improved. The far- field spot size is reduced by a factor of 9.3 compared with that obtained by incoherent pile of the individual microchip laser outputs. We demonstrated that the far-field pattern is improved by enhancing the self-imaging with side mirrors which make the array source disguise an infinity. A mode selecting slit placed right after the crystal is also effective to stabilize the out-of-phase mode.
A Nd:YAG microchip laser array is developed and the spatial phase correlation among each the microchip laser is attained utilizing the Talbot effect in a three-mirror cavity configuration. The laterally coupled Nd:YAG microchip laser array produces a pair of spots with angular separation of (lambda) /d in its far field, where d is the distance between the adjacent sources, corresponding to an out-of-phase spatial mode coupling. The far field spot size is reduced by a factor of 4.7 compared with that obtained by incoherent adding of the individual microchip lasers. Although an external mirror positioned at the 1/4 Talbot distance from the microchip lasers source is very effective to introduce the coherence among the laser chips, the present long Talbot distance limits the output laser power due to the extremely high diffraction loss in the auxiliary cavity. Smaller beam sizes for each microchip lasers will decrease the filling factor and improve the efficiency in the Talbot cavity.
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