In a multi-pass laser optical system orthogonal polarization of any two immediately adjacent optical passes allows suppression of internal parasitics caused by overlap of laser radiation on successive passes through a laser oscillator or amplifier, allowing increased operating efficiency and closer spacing of adjacent optical paths.

A laser device having an improved resonator utilizes a single rigid base component for a light reflector coating that defines and forms the end terminals of the resonator cavity, means being provided for translating and reflecting the laser beam between linear light paths that respectively terminate at the mirror surfaces provided by the coating. Various embodiments are shown and in which one or more prisms are used to fold the laser beam between offset and parallel light paths. The end terminal forming mirror surfaces may be coplanar and face in a common direction in the base component, or the mirror surfaces may be provided on opposite side surfaces of the component. Where the base component is made from transparent material the terminals may also be defined by the inside and outside surfaces of the coating. The use of figured surfaces in the unitary structure is contemplated and the use of mirror clusters for folding the beam is also contemplated. The rigid base component may be provided by a prism, a solid state laser rod, the envelope for a fluid lasing medium or any suitable rigid unitary structure that has an appropriate surfaces arrangement for the contemplated use.

A method and apparatus for producing preferential polarization of the output light beam from a laser of the kind having a three surface retroreflector comprises mounting the three reflecting surfaces of the retroreflector so that the surfaces are orthogonal in the retroreflector. The preferential polarization is obtained by controlling the combined effects of the orientation of the retroreflector assembly, with respect to the axis of the beam, and the selection of the coatings on the three reflecting surfaces.

The invention relates to means for generating a laser beam with an essentially constant angle of divergence over a wide range of operating conditions. The invention further relates to a method of generating such laser beam. The oscillator-amplifier laser system of the invention comprieses in combination an optical resonator, a first active medium and first optical means located within said resonator for generating an oscillator beam; a second active medium for amplifying said oscillator beam and a second optical means external to said resonator. Said first and second optical means have each, according to the invention, a predetermined optical power which maintains a constant divergence-angle of the output beam, even under variations in the induced optical power of the active media. Thus, there is provided an oscillator-amplifier laser system provided with optical means resulting in a beam having an essentially constant divergence angle over a wide range of operating conditions, and particularly over a wide range of repetition rates.

A folded Q-switched laser cavity uses total internal reflections of prisms to fold the intracavity beam. The index of refraction and the orientation of the prisms are selected to induce a predetermined phase delay between the two orthogonal polarization components of the linearly polarized intracavity beam. The predetermined phase delay rotates the intracavity beam polarization to an orthogonal direction such that an intracavity polarizer rejects the beam and the laser is held off from lasing. An electro-optic Q-switch cell is intermittently turned "on" whereby a second predetermined phase delay is induced onto the intracavity beam. The combination of the two predetermined phase delays results in a beam polarization orientation that is not rejected by the polarizer and the laser is not held off from lasing.