We have proposed, designed, manufactured and tested low loss dielectric micro-lenses for infrared (IR) radiation based on a dielectric metamaterial layer. This metamaterial layer was created by patterning a dielectric surface and etching to sub-micron depths. For a proof-of-concept lens demonstration, we have chosen a fine patterned array of nano-pillars with variable diameters. Gradient index (GRIN) properties were achieved by engineering the nano-pattern characteristics across the lens, so that the effective optical density of the dielectric metamaterial layer peaks around the lens center, and gradually drops at the lens periphery. A set of lens designs with reduced reflection and tailorable phase gradients have been developed and tested, demonstrating focal distances of a few hundred microns, beam area contraction ratio up to three, and insertion losses as low as 11%.
A method of determining the constants of propagation for ultrasonic waves in gases, by use of the Pierce interferometer, was devised by Hubbard, and application of it extended to a limit of two megacycles by his various students. Herein is described a new interferometer which carried these investigations to the four-megacycle region. Alignment of the piston and crystal to the order of one light fringe was attained and maintained by employing Newton and Haidinger optical fringe systems. Velocities were measured to an accuracy of one-tenth of one percent, and absorption and reflection coefficients to fifty percent in air and CO2. The limit of accuracy in both cases was determined by the measurement of length, as measured to one micron with a micrometer screw. Preliminary measurements on H2 gave evidence of molecular dispersion between four and eight megacycles.
The method of determination of the optimum frequencies for active sonar without knowledge of the absolute values of the sonar-set parameters, but only of their frequency dependence, appears to have been originated by J. W. Horton in about 1945 and is to be found in his recent text. This theory has been simplified and extended to include search rate,time-processing gain, and the ratio of echo-to-noise-plus-reverberation. The inclusion of these new factors only slightly modifies the results obtained by maximizing echo-to-noise ratio alone because of the dominant effect of the frequency dependent exponential attenuation term in the transmission loss. Because of the octave or greater width of the maxima and the lack of precision in the knowledge of the frequency dependencies, the optimum frequencies should be looked on only as broad regions. For longer-range and hence lower-frequency active sonata operating at their optimum frequencies the energy of the pulse required per unit area or volume searched increases rapidly with the design range to a high exponent for the cases considered. This corollary is probably of little practical significance since the cost of operating power is usually small compared to other costs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.