An electro-optical apparatus for transforming a single frequency linearly polarized laser beam into a beam having a pair of collinear orthogonally polarized components each having a different frequency, said apparatus comprising:
- means for providing said single frequency linearly polarized beam as a first external input beam to said apparatus;
- means for providing an electrical signal of frequency .function..sub.0 ;
- acousto-optical means operatively connected to said electrical signal providing means for transforming said electrical signal into an acoustic beam within said acousto-optical means, said acoustic beam having a direction of propagation, said acousto-optical means being disposed for receiving said first external input beam within said acousto-optical means as a first internal input beam, said first internal input beam being ordinarily polarized, said acousto-optical means further comprising means for transforming said first internal input beam into a first intermediate beam, said first intermediate beam being ordinarily polarized and having a direction of propagation nominally normal to said direction of propagation of said acoustic beam in the region of said acoustic beam, said acousto-optical means still further comprising means for transforming said first intermediate beam into second and third intermediate beams during passage through said region of said acoustic beam, said second intermediate beam having a direction of propagation, frequency, and polarization which is substantially the same as that of said first intermediate beam, said third intermediate beam being extraordinarily polarized, said second and third intermediate beams having a frequency difference equivalent to said electrical signal frequency .function..sub.0 and having a relatively small difference in direction of propagation, said acousto-optical means further comprising means for causing said second and third intermediate beams to exit the acousto-optical means as first and second exit beams, said first and second exit beams having the same direction of propagation and orthogonal polarizations, with a difference in frequency equivalent to said electrical signal frequency .function..sub.0 and having a small relative displacement with respect to each other, said first exit beam having the same polarization and frequency as said second intermediate beam, said second intermediate beam having the same polarization and frequency as said first external input beam, said second exit beam having the same polarization and frequency as said third intermediate beam, said first and second exit beams and said first external input beam each having an associated intensity, the sum of said intensities of said first and second exit beams being nominally the same as said intensity of said first external input beam;
- and
- means for adjusting said intensity of said first exit beam relative to said intensity of said first external input beam;
- whereby said single frequency, linearly polarized laser beam is transformed into said beam having said pair of collinear orthogonally polarized components with a high diffraction efficiency.