Drew A. Pommet

Novel joint transform correlator architecture using bacteriorhodopsin optically addressable spatial light modulators

A novel, all-optical joint transform correlator using bacterior- hodopsin (bR) spatial light modulators is presented. This architecture employs relatively inexpensive white light sources and He-Ne lasers to exploit the photoinduced anisotropic properties of the bacteriorhodopsin films. Due to the high spatial resolution of bacteriorhodopsin films, the system offers the possibility of being reduced to a compact size. Advan- tages and limitations of the system are described and comparisons to previously reported optical correlators using bR films are discussed. The authors believe that this is the first time an all bacteriorhodopsin based optical correlator is reported.

A homomorphic filtering method for imaging strongly scattering penetrable objects

This paper describes a new method for determining the structure of strongly scattering penetrable objects having permittivity fluctuations with scales comparable to the illuminating wavelength. We are concerned with the case when small wavelength or weakly scattering approximations, such as the Born or distorted wave Born approximations, or slowly varying approximations such as the Rytov approximation, are not valid. The problem is formulated as one of recovering, in principle, a quantitative image of the objects permittivity distribution function from a set of perturbed images. Each perturbed image is obtained by backpropagating the scattered field measured around the object for different illumination directions. These backpropagated images are filtered in the differential cepstral domain to recover the object permittivity distribution, and we show reconstructions from both simulated and real microwave scattered data. >

Minimal data collection: imaging from limited-angle data using prior knowledge

We describe a method for generating a high resolution image or target identifier from limited sampled noisy Fourier data. These data are assumed to be collected from either limited-angle tomographic data or limited-angle scattering data. In extreme cases of, for example, only backscatter data being measured, little useful image information can be deduced directly from the available measurements. However, if some a prior knowledge about the support and/or internal features of the object can be assumed, this information can be incorporated into a spectral estimation technique we refer to as the PDFT. This technique has a closed form solution that estimates the image and is easily regularized in the Miller-Tikhonov sense. We have studied how the availability of less and less data affects the resulting image quality when using the PDFT. We explain the trade-offs between reducing the number of measurements (e.g. for time or radiation exposure considerations) and the resulting image fidelity. We also discuss how little data need be measured to be able to identify a given object when good a priori information is available. Examples using real data are presented.

Compact optical correlator for machine vision with optically addressed bacteriorhodopsin spatial light modulator

We describe a compact optic correlator architecture which does not require a CCD camera to input the image to be interrogated. The white light illuminated image can be polarized and imaged directly onto a thin bacteriorhodopsin film which modulates the films birefringence. Read out of this written information can be achieved using a low power diode or HeNe laser in order to put the image information onto a coherent wavefront. Architectures with the bR film in the input and Fourier plane are considered using performance measures such as the fidelity of feature identification and speed.

Optically induced ordering in microparticle suspensions

From fundamental concepts of electromagnetic theory a mathematical development on the forces between radiating bodies is presented. A method is developed that evaluates the stationary volume energy density as a function of particle separation. A rudimentary description of particle scattering yields data that correspond to the sinusoidally varying force that has been shown to act on particles under intense illumination as a function of their proximity.

Optical imaging from scattering data: imaging from Fourier-intensity data

We discuss the problem associated with obtaining an image of an object from the magnitude of its Fourier transform. This problem arises in many imaging applications. We discuss some new ideas developed to address this problem and describe constraints on the object function that can lead to its Fourier transform having only real zeros, thereby eliminating the phase retrieval problem.

The dual twin image effect from a waveguide hologram

A new phenomenon called the dual twin image effect is reported. The mechanisms of the dual twin image effect and the twin image effect are discussed. A sandwich-like waveguide hologram unit, which can be used for fingerprint recognition, is described and verified experimentally.

New Model for the Mutual Enhancement of Nonlinear Optical Phenomena in Composite Media

We consider an optically linear fluid containing nanoparticles in which quantum confinement effects permit a controlled saturable absorbance to be exploited. We also incorporate the effects of neighboring particles on the local field that any one particle experiences, when calculating the effective permittivity of that particle close to resonance. Since the particles are free to move, under the influence of the Lorentz force, one can alter their spatial distribution as a function of the local field gradients. The particles will move closer together in regions of high electric field, further increasing the local field in the vicinity of any one of these particles, if their permittivities are higher than that of the host fluid. The particles move apart if the reverse is true.

Ray-Tracing Approach to Computer-Generated Holography for Precision 3D Beam Patterns

Computer-generated holography [1, 2, 3] is a well known way to produce holograms. It is widely used in integrated optics [4], for holographic components [5, 6], in medical detection [7], for image-enhancement in electronic microscopes [8], and for three-dimensional displays [9, 10]. Most of the computer-generated holograms (CGHs) described in existing papers are Fourier holograms which are generated using the FFT (Fast Fourier Transform) [11, 12]. In this paper, a method which is based on ray tracing is described and demonstrated. This method can encode and reconstruct not only two-dimensional but also three-dimensional objects.

Photonic crystal fabrication by way of coherent microparticle interaction

A method for determining steady-state particle density distribution resulting from an incident standing-wave field is discussed. A brief review of photonic crystals relates their established properties and their symmetry along with spectral relationships using 1D eigenvalue equations. Electrostatic interactions between neutral but polarizable particles are derived from Maxwells equations and the Lorentz force equation. The role of the stress tensor in electromagnetic propagation is discussed. Macroscopic van der Waals forces are described in terms of the Maxwell stress tensor, and equations for the microscopic van der Waals forces between two parallel dipoles are given for in- phase and out-of-phase cases. Spatial distribution of the electric field magnitude for the two cases are illustrated. Possible applications are described.