Noncollinear tunable acousto-optic filter

A method for diffracting an incident nonpolarized light beam into two deflected light beams with mutually orthogonal polarizations, the said deflected light beams being spatially separated from each other and from the incident light beam, said method comprising the steps of exciting an acoustic wave in an optically birefringent crystal;

• passing the incident light beam through said crystal in a direction that is noncollinear with the group velocity of the acoustic wave;
• and, for at least one of said deflected light beams, selecting the direction of the acoustic wave such that the acoustic wavevector is in the same azimuth plane as the wavevector of the incident light, and in the said azimuth plane, the tangents to the locus of the wavevectors for the incident and diffracted light are parallel.

Apparatus for diffracting an incident light beam with a first polarization to a deflected light beam of second polarization that is orthogonal to the first polarization, said apparatus comprising:

• means for exciting an acoustic wave in an optically birefringent crystal;
• and means for passing a light beam through said crystal in a direction that is noncollinear with the group velocity of the acoustic wave, the direction of the acoustic wave being selected such that the acoustic wavevector is in the same azimuth plane as the wave-vector of the incident light, and in the said azimuth plane, the tangents to the locus of the wavevectors for the incident and diffracted light are parallel.

Apparatus for diffracting an incident nonpolarized light beam into two deflected light beams with mutually orthogonal polarizations, the said deflected light beams being spatially separated from each other and from the incident light beam, said apparatus comprising:

• means for exciting an acoustic wave in an optically birefringent crystal;
• and means for passing an incident light beam through said crystal in a direction that is noncollinear with the group velocity of the acoustic wave, for at least one of said deflected light beams, the direction of the acoustic wave being selected such that the acoustic wave-vector is the same azimuth plane as the wavevector of the incident light, and in the said azimuth, plane, the tangents to the locus of the wavevectors for the incident and diffracted light are parallel.