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The heterogeneous nature of energy deposition by ionizing radiation can be used to advantage by pulsing an electron beam at low dose per pulse and high pulse rates. Track overlap is avoided for a short period of time, sufficient to allow an essentially heterogeneous polymerization to take place. High pulse rates appear to maintain this advantage by terminating the incipient homogeneous kinetics while re-initiating the heterogeneous kinetics. Polymerization by this method shortens the residence time necessary for full conversion but beyond 50% conversion, there may no longer be any advantage in a diffusion-limited system. Lower temperature also helps to reduce termination in the early phase of polymerization.

Development of Integral Images 3M has invented integral image products that have true 3-D appearance and exhibit full motion parallax. We will present the optics of the materials and analysis of image quality.

3M has developed a proprietary laser process for creating three-dimensional images that appear to float above and/or below the plane of a substrate containing an array of microlenses. During the imaging process the laser records a microscopic image of the desired three-dime nsional pattern in the material located at the focal point of each microlens in the array. The images exhibit motion parallax comparable to that seen from holograms and are easily visible in a wide range of ambient lighting conditions. The images are theref ore similar, but not identical, to integral images, first proposed in 1908 by Lippmann. The fidelity of these fl oating images requires maintaining exact registration between the microlens array and the corresponding microimage array. In addition, the use of an ablative laser process for the production of the microimages enables the production of microi mage features smaller than the diffraction limit (up to approximately 50,000 dpi). The images are therefore very difficult to simulate, counterfeit, or modify and are highly desirable as an overt security feature. 3M has scaled up the floating imag e process to produce images in Confirm • Retroreflective Security Laminate to au thenticate passports and driver’s license s and in retroreflective license plate sheeting as the Ensure • Virtual Security Thread to authenticate vehicle re gistration. This allows addition of features to a secure document that are easily veri fiable, using only the human eye, by a large and widely disperse population to create an identity document that is easily identified as genuine. Keywords: integral photography, three-dimensional image, floatin g image, overt security, authentication, laser imaging

Three-dimensional images may be produced by a number of methods, the earliest being integral photography. The basic concept involves exposing a photographic emulsion to light scattered from an object through a fly's eye lens to produce an array of micro-images, one behind each lenslet. An observer viewing the composite image through the lenslet array sees a three-dimensional representation of the object. Over the past 5 years, 3M has applied laser technology to the creation of three-dimensional virtual images using the integral photography approach. The virtual images made by this process can be observed by a viewer with the unaided eye in either reflected or transmitted light. The images display large movement as an observer's viewing perspective changes and have a distinct on/off-viewing angle beyond which the image cannot be seen. The fidelity of the virtual images requires maintaining the registration of the substrate lenslets and the micro-images produced by the laser imaging process. This makes the images difficult to copy or modify and an ideal, cost-effective candidate for an overt security feature.

Exposure of oriented, semicrystalline polymers, such as poly(ethylene terephthalate), poly(ethylene naphthalate) and polyimides, to the output of pulsed light sources, such as excimer lasers or short pulse flashlamps, at energy densities less than the ablation threshold can produce an amorphous layer on the polymer surfaces. Time resolved spectroscopy has shown that this amorphous layer is produced by a transient heating of the surface region to temperatures exceeding the polymer melting point (300-500 degree(s)C) resulting in rapid melting and the production of the thin disordered surface layer. Static SIMS, XPS, and infrared spectroscopy measurements have shown that this surface amorphization occurs without any decomposition or crosslinking of the polymer surface. The amorphous layers produced by this rapid thermal process provide increased adhesion of a wide range of coatings and films to the treated polymers due to the increased fracture toughness of their disordered morphology. The amorphous surface layer also can antireflect the polymers, provide increased autoadhesion, and increase coating penetration into the treated polymer substrates. This last characteristic can be exploited to provide photoimaging properties, as negative photoresists, to polyimides. The rapid thermal surface modification technology shows potential for economic industrial implementation, using short pulse flashlamps, provided that reliable, large-scale flashlamp systems can be made available.

Infrared spectra of NO adsorbed on single-crystal Pt (111) and polycrystalline Pt foil have been measured over a temperature range 100 to 473 K and at adsorbant pressures from 5 × 10−10 to 1 Torr. Relatively intense absorption bands have been found over the wavenumber range 1450–1780 cm−1, the wavenumber depending on the temperature, coverage and, apparently, the presence of impurities. A model based on an assumed interaction force constant coupling NO molecules adsorbed on adjacent sites accounts quantitatively for most of the spectroscopic observations.

Infrared spectra of NO adsorbed on an annealed polycrystalline Pt surface have been measured at temperatures between 300 and 673 K and under pressures of gas-phase NO between 10 −3 and 1 Torr. The spectra show that the NO adsorbate is in equilibrium with the gas phase at elevated temperatures. A model based on strong vibrational coupling between NO molecules adsorbed on adjacent Pt atoms is proposed to explain the observed spectra.

We have studied the infrared reflection-absorption spectrum of an adsorbate formed when an annealed polycrystalline Pt foil, presumably having a (111) surface structure, is exposed to ammonia gas at pressures in the range 0.1–10 torr. Isotopic substitution establishes that the adsorbate contains N2 in addition to NHx species. There is also CN present in the adsorbate, presumably formed by reaction of nitrogen with carbon impurities on the surface.