We provide performance information on the reduction of sidelobe levels in sparse linear phased arrays operating in the near-field. Iterative optimization techniques are used to choose inter-element spacings which reduce grating lobe magnitudes at select distances, and array configurations are generated with constraints on the minimum spacing between elements. The performance of these array configurations is then analyzed over a scan angle of 180 degrees. We show that it is possible to generate arrays which outperform the side-lobe level of far-field-optimized array configurations in the near-field by as much as 3 dB.
Optical pattern formation is studied far beyond threshold in a single-mirror feedback scheme using sodium vapor as the nonlinear medium. Patterns with twelve fundamental wave vectors arise from hexagons in a secondary bifurcation.Besides irregular patterns, quasipatterns and superlattices are obtained. Even after a tertiary bifurcation the patterns remain stationary. Fourier filtering experiments show that the harmonics of the fundamental wave vectors are essential for the stability of the secondary and tertiary patterns. A novel Fourier filtering technique is used for a measurement of the neutral stability curve and proves experimentally the existence of multiple instability regions existing due to the periodicity of the Talbot effect.
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