Wayne Robert Tompkin

Passive one-way aberration correction using four-wave mixing

We have demonstrated a passive method for recovering an optical image that has been degraded by being passed through a thin phase-aberrating medium. This method relies on a point source situated near the object of interest to sample the aberration impressed upon the wave front. Degenerate four-wave mixing in fluorescein-doped boric acid glass was used to reconstruct the wave front.

Enhancement of the nonlinear optical properties of fluorescin doped boric-acid glass through cooling

We examine, both theoretically and experimentally, the temperature dependence of the nonlinear optical response of fluorescein doped boric-acid glass. The third-order nonlinear susceptibility is increased by an order of magnitude over its room temperature value to greater than 10 esu by cooling the sample to a temperature below 200 K.

Nature of the interference pattern produced on reflection at a phase-conjugate mirror

We show theoretically and experimentally that the positions of the fringes produced by interference between a wave incident upon a phase-conjugate mirror and the wave leaving the mirror depend on the phase associated with the incident wave. This result is in contrast to that obtained when an ordinary metal mirror is used, in which case the interference pattern is found to beindependent of the phase of the incident wave.

Nonlinear optical properties of fluorescein in boric-acid glass

Abstract Fluorescein in boric-acid glass has an extremely low saturation intensity measured in saturated absorption and phase conjugation experiments to be of the order of 10 mW cm 2 . The time evolution of the long-lived luminescence is highly nonexponential, leading to a nonlorentzian spectral hole of width ∼750 millihertz in the absorption profile measured in a pump-probe experiment.

Time reversal of Berry’s phase by optical phase conjugation

We examine experimentally the time-reversal properties of Berry’s geometrical phase in one of its optical manifestations, Pancharatnam’s phase, through the use of optical phase conjugation. The time-reversal symmetry of the total optical system is broken by a nonreciprocal element, a Faraday rotator. Nevertheless, we find that the geometrical part of the phase acquired by an optical wave in passing through the system still respects time-reversal invariance.

Interference pattern produced on reflection at a phase-conjugate mirror. II: Experiment

The nature of the fringe pattern produced by interference between a wave incident upon a phase-conjugate mirror and that leaving the mirror has been studied experimentally for a phase-conjugate mirror based on degenerate four-wave mixing. The fringe locations are found to depend on the phase of the wave incident upon the mirror, in agreement with recent theoretical predictions but in contrast to the results observed for the interference pattern produced on reflection at an ordinary metal mirror. The phases of the waves that pump the phase-conjugate mirror are shown to provide the reference with respect to which the phase of the incident wave is determined.

Zero-order gratings for optically variable devices

We present the results of the application of zero-order diffraction gratings for optical variable devices (OVDs) for document security. Zero-order gratings have periods which are smaller than the wavelength of light; to describe accurately the optical properties of the zero-order gratings, we have applied rigorous electromagnetic theory, which we have compared to experimental measurements. We studied the diffractive behavior of zero-order grating varies locally in a predetermined manner. In the latter case, the resulting surface profile can exhibit variations in the diffraction properties, for example, a moire pattern. Furthermore, we have developed diffractive surface-reliefs which are a combination of a high-frequency, zero-order grating with large-period gratings, the addition of the zero-order grating to a large-period grating results in a surface relief with novel diffractive properties.

Color-shifting features for optically variable devices

The simultaneous engineering of diffractive structures and amterial systems enables innovative appraoches for realizing iridescent color shifts for Optically Variable Devices (OVDs) for document secrity. In a first exmaple, we dmonstrate the interplay between a color-shifting coating, whichfunctions inreflection,a nd embossed gratings,w ith effects inthe first and hgher diffraction orders. In a second exmpale, we demosntrate novel surface-releif, zero-order gratingw hich show a color shift, e.g. green to red, uponrotation by 90 degrees. In a third example, we explore the use of combination gratings to realize color-shifting and color-contrast features. These color-shifting features are integrated within OVD designs in which an observer can easily check the behavior of the feature and verify the authenticity of the document.

Achromatic features for optically variable devices

We have studied the use of achromatic features in Optically Variable Devices (OVD) for document security applications. We present various forms of matt structures as we have implemented them in OVD designs. By tailoring the scattering characteristics of the surface relief, we have created OVDs which appear in various intensities of white or gray, and whose brightness can vary as the viewing conditions are changed. Furthermore, we have realized surface reliefs which appear bright and colorless when viewed within a predetermined solid angle and appears dark in all other viewing directions. The gratings appear bright and colorless when viewed from one side of the grating normal; however, when these gratings are rotated by 180 degrees in their plane, the gratings appear dark. We will show gratings of this type, where the surface reliefs have been engineered so that the bright and colorless appearance covers an enlarged solid angle.

Perceptual information from OVD diffraction security devices

The criteria by which optically variable devices are judged are aesthetic, semantic, security, ergonomic, and physical/chemical. This paper addresses ergonomic aspects which relate to the human vision and perceptual-cognitive system. Applying some pertinent rules may help greatly to improve the image visual information for easier, more straight-forward reception of a persistent security message. We consider two important aspects of the human visual system that help to determine the ergonomic response to visual displays created using optical diffraction. The human visual system aspect treats the retinal source of information, which is the retinal signal produced when an image of the external world is projected on the retina. The other aspect is the underlying information-processing mechanism of our brains and its constructive operations, which yields the final perceptual information. In this paper we consider information processing methods hidden in the biology of our cognition system. Findings on the relationship between physiology and psychology, sensory results and the activities of the optic pathway and subjective brightness sensations can be applied directly in designing images. Some effects are demonstrated by video tape.