Experiments were performed on a CO(2) laser with an annular resonator. The objective of these experiments was to control the polarization in an annular laser and to verify computer code predictions. A Mylar pellicle was placed in the annular leg, and its angular orientation with respect to the optical axis was varied. The pellicle had different transmittances for horizontal and vertical polarizations and also had stress-induced birefringence. At small angles of incidence in the pellicle, the birefringence dominated, and the output had a complicated nature. However, at large angles of incidence, the transmittance difference forced the laser into a well-defined mode for which the near field was horizontally polarized at the top and bottom and the two sides and vertically polarized at intermediate locations. The experimental results were in good agreement with the computer code calculations.

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A diamond turned aluminum cone was coated with a multilayer dielectric coating which was designed to produce a 90° phase shift at 10.6 μm between the S and P components on reflection.

A pulsed C02 electric discharge fast flowing gain medium is used to test three unstable resonators which are forced to oscillate in an L=3 azimuthal mode. This Higher Order Azimuthal Mode Unstable Resonator (HAMUR) could be used to form a "natural mode" resonator which would be uneffected by support struts neccessary in an annular gain medium. Six equally spaced intracavity radial struts, and a suitable diameter on axis obscuration, produce 180 degreee phase changes between adjacent sectors of the six sector near field pattern, and six radial lobes in the far field with no on axis intensity. A phase plate, constructed by applying a half step coating to every other adjacent sector, corrects the far field.

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