Manufacture of High Efficiency Surface Relief Computer Generated Holograms
Doctoral thesis, 1992
This thesis treats design, manufacture, evaluation and applications of computer-generated surface relief holograms - kinoforms. These diffractive, phase-only, planar optical components are characterized by high efficiency, design flexibility, light weight and small size. They can further be reproduced at low cost. These properties make kinoforms particularly well suited for integration with diode lasers, optical fibers and micro-electronic circuits. Given its desired diffraction properties, the kinoform phase structure is computer-calculated using iterative Fourier-transform algorithms. Initially the kinoforms were realized photolithographically, using a computer-controlled grey-scale laser mask generator of our own design. Later, due to the excellent lateral accuracy and resolution, we turned to direct-writing electron-beam lithography (EBL). A problem with that technique is scattering of exposing electrons, which reduces the resolution (the proximity effect). A method was devised to determine the electron point-spread function by measuring the optical diffraction from EBL-manufactured test structures. With the gained information the negative influence of the proximity effect could be reduced by properly modifying the electron exposure doses. With repeated development of the exposed kinoforms optimum relief depths were reached. Manufacture of high-performing array illuminators was demonstrated. Resist kinoforms were further used in successful Nd:YAG-laser micro-machining experiments.