Microholographic computer generated holograms for security applications: Microtags

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We have developed a method for encoding phase and amplitude in microscopic computer-generated holograms (microtags) for security applications. Eight-by-eight-cell and 12 x 12-cell phase-only and phase-and-amplitude microtag designs has been exposed in photoresist using the extreme-ultraviolet (13.4 nm) lithography (EUVL) tool developed at Sandia National Laboratories. Using EUVL, we have also fabricated microtags consisting of 150-nm lines arranged to form 300-nm-period gratings. The microtags described in this report were designed for readout at 632.8 nm and 442 nm. The smallest microtag measures 56 {mu}m x 80 {mu}m when viewed at normal incidence. The largest microtag measures 80 by 160 microns ... continued below

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30 p.

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Sweatt, W.C.; Warren, M.E. & Kravitz, S.H. January 1, 1998.

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  • Sandia National Laboratories
    Publisher Info: Sandia National Labs., Albuquerque, NM (United States)
    Place of Publication: Albuquerque, New Mexico

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Description

We have developed a method for encoding phase and amplitude in microscopic computer-generated holograms (microtags) for security applications. Eight-by-eight-cell and 12 x 12-cell phase-only and phase-and-amplitude microtag designs has been exposed in photoresist using the extreme-ultraviolet (13.4 nm) lithography (EUVL) tool developed at Sandia National Laboratories. Using EUVL, we have also fabricated microtags consisting of 150-nm lines arranged to form 300-nm-period gratings. The microtags described in this report were designed for readout at 632.8 nm and 442 nm. The smallest microtag measures 56 {mu}m x 80 {mu}m when viewed at normal incidence. The largest microtag measures 80 by 160 microns and contains features 0.2 {mu}m wide. The microtag design process uses a modified iterative Fourier-transform algorithm to create either phase-only or phase-and-amplitude microtags. We also report on a simple and compact readout system for recording the diffraction pattern formed by a microtag. The measured diffraction patterns agree very well with predictions. We present the results of a rigorous coupled-wave analysis (RCWA) of microtags. Microtags are CD modeled as consisting of sub-wavelength gratings of a trapezoidal profile. Transverse-electric (TE) and TM readout polarizations are modeled. The objective of our analysis is the determination of optimal microtag-grating design parameter values and tolerances on those parameters. The parameters are grating wall-slope angle, grating duty cycle, grating depth, and metal-coating thickness. Optimal microtag-grating parameter values result in maximum diffraction efficiency. Maximum diffraction efficiency is calculated at 16% for microtag gratings in air and 12% for microtag gratings underneath a protective dielectric coating, within fabrication constraints. TM-microtag gratings. Finally, we suggest several additional microtag concepts, such as two-dimensional microtags and pixel-code microtags.

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30 p.

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OSTI as DE98002763

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  • Other Information: PBD: Jan 1998

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  • Other: DE98002763
  • Report No.: SAND--98-0046
  • Grant Number: AC04-94AL85000
  • DOI: 10.2172/570182 | External Link
  • Office of Scientific & Technical Information Report Number: 570182
  • Archival Resource Key: ark:/67531/metadc696244

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  • January 1, 1998

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  • Aug. 14, 2015, 8:43 a.m.

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  • April 14, 2016, 5:47 p.m.

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Sweatt, W.C.; Warren, M.E. & Kravitz, S.H. Microholographic computer generated holograms for security applications: Microtags, report, January 1, 1998; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc696244/: accessed October 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.