Multiple Focal Spots Research Articles

Spatial encoding of communication sequences with an ocean acoustic time-reversal mirror

With the at-sea demonstration of producing simultaneous multiple focal spots with a TRM, spatial encoding of communication sequences is now possible. We present the results of an ocean acoustic experiment in which we demonstrate that different communication sequences can be simultaneously sent to and decoded at individual receivers on a vertical array. This ‘‘multiple input, multiple output (MIMO)’’ process significantly increases the acoustic communications band rate. Various incoherent and coherent communication temporal coding schemes are employed together with this spatial procedure.

Symmetry enhancement and spot-size reduction through radial beam stacking in a multichannel CO/sub 2/ laser array

The beam quality of a diffusion-cooled RF-excited radial-geometry CO/sub 2/-slab-laser array is investigated. The system is shown to negate many of the disadvantages inherent with slab lasers, namely, asymmetric beams, multiple focal spots, and linear polarization. In addition, the effective spot size is reduced as a result of radial stacking of the individual asymmetric but azimuthally distributed, incoherent, output beamlets. A performance demonstration with sheet-metal cutting has produced excellent results in terms of kerf width, depth of penetration, and cut directionality. >