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4 January 2008 Methods of controlling grooves profile and the duty cycle of gold transmission phase gratings
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It is known that rectangular grooves profile and various duty cycles (line to pitch) are required to attain maximum efficiency. The gold transmission phase gratings have been fabricated using holography and ion-beam etching techniques. The latent image monitoring technique and real time end-point detection technique were utilized to improve control of the shape of grooves and duty cycle during exposure and development, respectively. It is difficult to produce gratings with larger duty cycle in photoresist on gold for standing wave, nevertheless it is revealed in our work that the duty cycle can be more than 0.4 for the case for photoresist on gold substrates if development is stopped where the slope of the monitoring curve begins to drop off, not at the peak of the diffracted signal. In ion-beam milling, the influence of redeposition on the shape of grooves and duty cycle has been overcome by using a thin mask of Chromium with a comparatively low ion-etch rate and tilting and rotating substrates beneath the ion beam. Finally, some gold phase gratings with the duty cycles in the range of 0.25-0.45 have been obtained, whose duty cycle value is about 0.45, and their grooves profile is trapezoidal profile whose left and right facets are both more than 83 degrees approximately.
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Keqiang Qiu, Xiangdong Xu, Ying Liu, Yilin Hong, and Shaojun Fu "Methods of controlling grooves profile and the duty cycle of gold transmission phase gratings", Proc. SPIE 6832, Holography and Diffractive Optics III, 68322L (4 January 2008);


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