Eric J. Shrader

Elastomer-based diffractive optical modulator

In this paper, device structure and measurements on a diffractive optical modulator fabricated using a elastomer layer are reported. The device structure is fairly simple with an interdigitated bottom electrode, an elastomer layer, and a top electrode. Application of voltage to one of the bottom interdigitated electrodes causes an electrostrictive force, which, in turn, corrugates the elastomer layer. This method is used to create a configurable reflective phase grating that enables an analog control of the diffracted intensity. The major advantages of this method are the ease of fabrication and the simple device structure.

Optical beam position active sensing and control using acoustooptic satellite beams

This paper presents novel techniques and experimental results for precision active sensing and control of the position of a laser beam using dynamic acoustooptic diffraction patterns. Sensing of the acoustooptic (AO) diffraction pattern higher order beams is used to determine the position of the main optical beam (i.e., zero order beam) while minimally perturbing the main beam. In the experimental system a reduced Q acoustooptic modulator was used in the axial mode to generate symmetrically deviated +1 and -1 diffraction order satellite beams with a small fraction of the zero order power. Sensing the crossing time of scanned satellite beams past differential split bicell detectors to derive precise zero-crossing signals was used to precisely locate them and infer the main beam position. The symmetric configuration is particularly effective for accurately determining and calibrating the main beam position. A Bragg regime acoustooptic deflector was used to steer the position of the main beam over a range of angles, controlling it to a desired position, as well as stabilizing it by means of control of Bragg deflector RF frequency derived from the sensing signals. Experimentally, a 1 milli-radian angular divergence laser beam at 632.8 nm optical wavelength was controlled and settled to within (/spl plusmn/1/60) beam diameter in 1 sense/control feedback cycle of 80 msec. The cycle time was limited by the present control electronics; however, it could be much faster: fundamentally response time is limited by the acoustooptic beam transit time on the order of a microsecond. The general method of this paper could be applied at any optical wavelength where suitable acoustooptic modulators and photosensors can be obtained. The method can also be readily extended to operation in two axes, providing two-dimensional position sensing and control.

Electrostrictive elastomer based diffractive modulator for use as a variable optical attenuator

Device structure and measurements on an elastomer based MEMS modulator is reported. The configurable reflective phase grating responds to voltage and the surface corrugates to a sinusoidal pattern enabling analog control of the diffracted intensity.

Formation of very low resistance contact for silicon photovoltaic cells

A number of approaches have been developed in order to introduce a nickel-based contact layer between the silver electrode and n+ emitter layer, which can substantially reduce the specific contact resistance. One of them is to use a blanket sputtered nickel film as the contact layer and screen printed silver lines as an etch mask to pattern the underlying nickel film. This approach ensures the use of high quality nickel film as a contact layer to reduce the specific contact resistance, and also avoids the use of standard photolithographic process to reduce the cost. The result shows the specific contact resistance with this approach can be reduced by about two orders of magnitude compared to only using screen printed silver gridlines. The second approach is to use inkjet printed nickel nanoparticle inks instead of the sputtered nickel film to form the contact layer, enabling a very low cost inline process that can be easily implemented into current solar cell production line. The PC1D modeling result shows that the absolute efficiency of solar cells can be increased by up to 0.9% with the substantial reduction on contact resistance.

Numerical models of perfused hyperthermia phantoms

Finite difference numerical models based on bioheat transfer [H. H. Pennes, J. Appl. Physiol. 1, 93–122 (1948)] and incomplete countercurrent heat exchange [S. Weinbaum and L. M. Jiji, J. Biomech. Eng. 107, 121–139 (1985)] have been developed and tested. Predicted performance of hyperthermia phantoms heated by ultrasound applicators will be compared with actual performance to validate the models. The models will then be used as aids in designing ultrasound applicators to produce heat deposition patterns believed advantageous for hyperthermia treatment of experimental animals and patients. The 3D models admit adiabatic or isothermal boundaries and arrays of paired, straight tubules for counter current heat exchange. Results of parametric variations will be shown. Preliminary results obtained by using as inputs the design parameters for a proposed kidney phantom perfused at 110 ml/100 g (of tissue‐equivalent gel) per minute have yielded satisfactory time constants on the order of 150 s. When the simulated u...