Achromatic phase retarder arrangement

Claim 1

In an achromatic phase retarder arrangement comprising at least one prismatic body with two total reflection surfaces and a source of a light beam directed toward said body, the improvement wherein the body has a light entry surface at an angle of incidence (α) different from 90° to the incidence direction of the light beam, wherein the light beam has an incident angle (α) at the light entry surface so that the difference between the angles of refraction of the short wavelength light and a medium wavelength light or the difference between the angles of refraction of medium wavelength light and long wavelength light is identical with the difference between the corresponding angles of incidence (θ K , θ S , θ L ) at the first total reflection surface according to the relation: |arc sin (sin α/n.sub.S)-arc sin (sin α/n.sub.K)|=|θ.sub.S -θ.sub.K | or |arc sin (sin α/n.sub.L)-arc sin (sin α/n.sub.S)|=|θ.sub.L -θ.sub.S | wherein α is the angle of incidence of the light entry surface, n L is the refractive index for medium wavelength light, n K is the refractive index for short wavelength light, θ L is the angle of incidence for long wavelength light, θ S is the angle of incidence for medium wavelength light, θ K is the angle of incidence for short wavelength light, and φ=θ S +arc sin (sin α/n S ), and wherein a first total reflection surface of the body makes an angle (φ) with the light entry surface, the two angles (α, φ) being selected so that, for a light beam of short wavelength, refracted at the light entry surface, an angle of incidence (θ K ) results at the first total reflection surface, which is larger than the angle of incidence (θ L ) of a refracted light beam of a longer wavelength, and a second surface of total reflection of the body is parallel to the first surface of total reflection, and a light exit surface of the body refracts the refracted and reflected light beams (1 L , 1 S , 1 K ) and is parallel to the light entry surface.