A. Riazi

Currents Induced in a Human Being for Plane-Wave Exposure Conditions 0-50 MHz and for RF Sealers

The currents induced in a human being were measured for plane-wave exposure conditions 0-50 MHz. These are used to point out that very large SARs may be set up in the wet tissues for the cross section of the ankle for standing human beings exposed to electric fields suggested in the ANSI C95.1-1982 RF safety guide. For these exposure conditions, foot currents on the order of 627 mA are projected for a human adult of height 1.75 m for the frequency band 3-30 MHz with the value increasing to 780 mA for 40 MHz. The corresponding ankle-section SARs are 182 and 243 W/kg. Using electromagnetic scaling concepts, SARs as high as 371 and 534 W/kg are projected for ten- and five-year old children, respectively, for f = 50.7 and 62.5 MHz, E = 61.4 V/m (1 mW/cm2) recommended by the ANSI C95.1-1982 RF safety guide. The paper also gives currents induced by two sealer models and three industrial RF sealers for a human being under grounded and insulated conditions. Though smaller than those for plane-wave irradiation conditions, these currents may be substantial for high leakage fields that are quite typical.

Image profile upon passage through a Fabry-Perot interferometer of large Fresnel number

Using two independent techniques, a determination is made of the quality of an optical image upon passage through a Fabry-Perot interferometer (FPI). Curves relating the Fresnel number, finesse, number of image elements, image frequency spectrum, and FPI transfer function are presented. It is determined that for interferometers of large Fresnel number, the phase shift per transit of each transverse mode plays a dominant role in distortiom of the image, unlike cases of low Fresnel number the power loss per transit is a significant factor. Based in the results, it is concluded that the value of employing an FPI in an configuration is limited by the amount of distortion which can be tolerated.

Imaging characteristics of a confocal cavity

Abstract Mode decomposition method is employed to determine the nature of image distortion on passage through a confocal cavity. It is shown that output image possesses either an even or an odd spatial symmetry, depending on resonance conditions. Possible methods of preventing image distortion are also discussed.

Image transfer through a Fabry-Perot interferometer

An experimental method for determining the transfer function and accompanying cutoff frequency of a Fabry-Perot interferometer (FPI) is described and a set of experimental results is presented. It is shown that upon passage through the FPI, the level of image distortion decreases with a decrease in cavity length (resulting in an increase in Fresnel number) when the FPI finesse is held constant. This phenomenon is in agreement with the theoretical prediction.

Twyman–Green interferometry for semi-quantitative analysis of homogeneity and nonlinearity of a mixing crystal

Application of Twyman–Green interferometry is extended to achieve semi-quantitative assessment of optical qualities of a nonlinear crystal. Interferograms of a proustite crystal are analyzed and effects of crystal imperfections on the conversion efficiency of a parametric upconversion system are evaluated.

Enhancement of coherent fields using resonant cavities

Abstract Expressions for power enhancement of a coherent image or a laser beam when resonated by an optical cavity are derived; and application of intracavity techniques to image upconversion systems is elucidated.

Threshold technique for measuring parametric upconversion efficiency

An experimental procedure which involves measurement of threshold values of infrared and upconverted powers for evaluating the quantum efficiency of a parametric upconverter is described. The threshold method is employed to determine the efficiency of a dye laser proustite upconversion system.

Laser synchronizer for parametric frequency conversion systems

A laser synchronization circuit, applicable to (optical) sum or difference frequency generation systems, is described. The laser synchronizer has yielded excellent results in preventing damage to the mixing crystal of an infrared‐to‐visible parametric upconverter.