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The Faraday effect is a magneto-optic effect wherein a magnetic field applied to a Faraday material causes the axis of polarization of the linearly polarized light to rotate. A Faraday rotator is a device that rotates the angle of polarization of light by using the Faraday effect. Optical isolators using Faraday rotators have many uses in laser technology, such as for isolating stages of oscillator-amplifier systems and for discriminating against reverse-traveling waves in ring cavities. This invention relates to optical isolators and particularly to an ultraviolet optical isolator which utilizes a KDP-isomorph for rotating the polarization of ultraviolet radiation in the wavelength range from about 190 to about 350 nanometers (nm). In a preferred embodiment, the ultraviolet optical isolator comprises: an input polarizer for linearly polrizing an input beam of ultraviolet light in a first plane of polarization means for rotating the plane of polarization of the linarly polarized ultraviolet light from the input polarizer by substantially 45 degrees in a first direction a Faraday rotator including an optical element made of a KDP-isomorph crystal in which the plane of polarization of the rotated linearly polarized ultraviolet light from the rotating means is rotated about an optical axis of the optical element, a plurality of permanent magnets sequentially coupled together with altnerating polarities for developing a magnetic field along the optical axis of the optical element in order to cause the optical element to rotate the plane of polarization of the rotated linearly polarized ultraviolet light from the rotating means by substantially another 45 degrees in the first direction to a second plane of polarization substantially orthogonal to the first plane of polarization, and means for moving the optical element so that the optical element is always enclosed by the plurality of permanent magnets and an output polarizer for outputting the ultraviolet light in the second plane of polarization. An ultraviolet optical isolater which utilizes a KDP-isomorph crystal as optical element is disclosed.