The polarimetric properties of an adjustable two plate quarter-wave system have been investigated. Multiple beam interference within single wave-plates has been taken into account. It has been shown that different adjustments are needed to produce left-handed and right-handed circular polarized coherent light. Laser light polarization conversion by the systems consisting of two birefringent mica plates has been investigated experimentally. The high-quality circularly polarized light with the

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... ensity-related ellipticity higher than 0.99 has been produced.