A novel method for discriminating and selecting a specific high order mode is presented. It is based on introducing spiral phase elements into a laser resonator, so as to improve the output beam quality over that when the laser operates with multi-modes, and yet maintain a relatively high output power. The theoretical analysis, along with experimental results with CO and Nd:YAG lasers are presented. The results reveal that a 50% increase of laser output power over that operating with 2 TEM mode is possible. q

Transverse mode selection in a longitudinal continuous wave CO 2 laser with a nominal power of 125 W Rev.

Abstract-We demonstrate the advantageous use of highly dispersive ( 450 ps nm km), high-order-mode (HOM) fiber modules for true time delay applications. Along with their low insertion loss, very low phase ripple (root mean square 0 3 over 0-20 GHz), and high immunity to nonlinear effects, the high dispersion values facilitate the construction of devices with relatively short fibers, resulting in improved tolerance of the radio frequency delay to thermal changes. The implications of multiple path interference effects in HOM modules are also studied and shown to be very small.

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