Computer-generated holograms (CGHs), such as those used in optical testing, are created by etching patterns into an optical substrate. Imperfections in the etching can cause small scale surface roughness that varies across the pattern. The variation in this roughness affects the phase and amplitude of the wavefronts in the various diffraction orders. A simplified model is developed and validated that treats the scattering loss from the roughness as an amplitude effect. We demonstrate the use of this model for engineering analysis and provide a graphical method for understanding the application. Furthermore, we investigate the magnitude of this effect for the application of optical testing and show that the effect on measurement accuracy is limited to 1 nm for typical CGHs.

http://www.loft.optics.arizona.edu/documents/journal_articles/Ping_Zhou_Coupling_of_surface_roughness_to_the_performance_of_computer-generated_holograms.pdf

Coupling of surface roughness to the performance of computer-generated holograms.

Diffractive optical elements are rapidly finding their way into many practical optical systems, and this has given rise to a spurt of research and developmental activities in this area. IN this paper, the history of these elements is first traced to get a perspective on their current state-of-the- art. The important features of this rapidly advancing field are then identified so that one does not get lost and can easily stick to one's guns while browsing through the maze of publications. Finally a glimpse of the fascinating future trends is given to stimulate further interest in the area.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Diffractive optical elements: past, present, and future

http://loft.optics.arizona.edu/documents/journal_articles/2009_ping_phddissertation.pdf

Error analysis and data reduction for interferometric surface measurements

Zone plate array lithography (ZPAL) in the X-ray or EUV regimes is one possible next-generation lithography solution because of its potential for high-resolution and maskless operation. To achieve a high throughput, Fresnel zone plates (FZPs) are integrated to form arrays of massively parallel exposure beams. FZP fabrication errors and uniformity can be serious issues in ZPAL systems, which are usually assembled and tested directly after zone plate arrays (ZPAs) are fabricated. The yield of this approach can decrease significantly with increasing beam number. A new ZPA design-to-manufacture flow that takes fabrication errors into account before the assembly process is proposed. The errors can be clearly screened by rigorous optical and lithography simulations. The effectiveness of the proposed approach is demonstrated by analyzing preliminary FZP designs of different zone numbers subject to imperfect zone width control. Simulation results indicate that FZPs with smaller zone numbers can tolerate larger radius deviations.

Fresnel Zone Plate Manufacturability Analysis for Direct-Write Lithography by Simulating Focusing and Patterning Performance versus Fabrication Errors

We have calculated the angle-resolved scattering from several phase only Fresnel zone plates (lenses) and Dammann gratings (beam splitters). We simulate manufacturing errors by random perturbations of the surface-relief pattern, and calculate the irradiance in the far-field by evaluating the Fresnel diffraction integral. Scattering from perturbations of the etch depth is found to be proportional to the square of the ratio of the perturbation divided by the wavelength. Random perturbations of the pattern edges in Fresnel zone plates causes more scattering with shorter wavelengths than with longer wavelengths, but in Dammann gratings this scattering is independent of wavelength. Scattering increases for either small apertures or small f-numbers; but does not depend on either the number of levels in a Fresnel zone plate, the pattern in a Dammann grating, or the form of the probability distribution function.

/pdf/light-scattering-from-binary-optics-4xrb1ypw2m.pdf

Douglas W. Ricks

Papers

Light scattering from binary optics