Proceedings Article | 25 March 1996
Proc. SPIE. 2652, Practical Holography X
KEYWORDS: Holograms, Diffraction gratings, Electron beam lithography, Optical design, Light sources, Light, Wavefronts, Image quality, Photoresist materials, Semiconductors
The e-beam lithography commonly used in the semiconductor industry is used to create large format grating image holograms. Delicate and bright images with extremely fine features can be generated using this newly developed method. In this paper, a quantitative and qualitative analysis related to the grating image hologram is discussed in detail. Using the optimized condition derived based on the quantitative analysis, the e-beam lithography technique commonly used to generate semiconductor masks has been implemented to create images with extremely fine features. The optimized condition together with the simplistic nature of the grating written to the image, the grating image holograms generated will be bright and colorful under white light illumination. The above mentioned generic characteristics plus the optimized condition obtained from our analysis make the e-beam lithography technique a versatile and powerful method in creating image holograms. High end products such as kinegrams can be easily implemented by using this technique. Furthermore, kinegrams with extremely fine features to generate a continuous and smooth imaging effect can be effectively created by this newly developed technique. The orientation and the pitch of the grating written to the grating image hologram determines two important characteristics of the grating image. More specifically, the grating orientation determines the viewing angle while the grating pitch determines the color projected to the viewer. As the grating image hologram is typically being illuminated by an inclined incident white light, the incident light beams will be diffracted into a colorful curved surface extending from the illuminated grating pixel. Taking a realistic extended illuminating light source into consideration, a single grating pixel actually will diffract the illuminating light cone into a colorful surface ensemble. With this understanding, it is possible for us to design the grating image hologram using the colorful surface ensemble as one of the design parameters available to us. In other words, we can use the colorful surface ensemble to shape the final image created by illuminating the grating image hologram with prespecific extended white light conditions. Two grating image holograms, one of which is a 5 by 5 centimeters square grating and the other a 3.5 centimeters by 2 centimeters elliptical kinegram, were successfully created by utilizing the analysis mentioned above. It was discovered that the limitation of the field size available to today's e-beam machine poses an important design consideration. That is, when field stitching is required to create a large area grating image hologram, the images being written should be carefully chosen so as to minimize the mismatch effect among the junction of each field. The two newly completed holograms showed that with the design methodology presented in this article, high quality large area grating image holograms can be created.
