Non-planer, image rotating optical parametric oscillator

Abstract

An Optical Parametric Oscillator (OPO) that includes optical elements located and oriented to form a non-planer, image-rotating ring cavity. To provide a high quality well shaped output beam, the OPO comprises a plurality of reflecting surfaces, designed to rotate the resonating beam by 90 degrees for each round trip in the cavity. Preferred embodiments include a first non-linear crystals and a similar second non-linear crystal mounted side-by-side on a single rotating stage. To minimize the adverse effects of walk-off, a reflecting unit is positioned to cause the output of the first crystal to be reflected into the second crystal. The two crystals are aligned so as to cause walk-off produced in the first of the two crystals to be cancelled by opposite walk-off produced in the second crystal.

What is claimed is: 
     
         1 . An optical parametric oscillator for converting, with at least one nonlinear crystal, a laser pump beam into a signal beam and an idler beam, said signal and idler beams defining two OPO beams, said oscillator comprising:
 A) a non-planer ring resonance cavity comprising:
 1) a nonlinear crystal unit pivotally positioned within the cavity so as to receive the pump beam and to convert energy of the pump beam into the signal and idler beams with both signal and idler beams propagating in directions common to the pump beam; 
 2) plurality of reflecting elements together providing at least six reflecting surfaces, wherein:
 I) at least four of the reflecting elements are oriented to rotate one or both OPO beams by 90 degrees on each pass of the rotated OPO beam or beams through the cavity, and 
 II) two of the reflecting surfaces are oriented to receive the pump beam and the OPO beams after each first pass through a first portion of the nonlinear crystal unit and to reflect the pump beam and the OPO beams so as to pass a second time through a second portion of the nonlinear crystal unit in order to cancel, on the second pass, walk-off produced by the first pass; 
 
 B) a pump beam deflector positioned to deflect the pump beam into the resonance cavity; 
 C) a polarization correcting element positioned within the cavity and adapted to rotate the polarization of the one or both rotated beams back to its or their un-rotated polarization on each pass, of the one or both rotated OPO beams, through the cavity; 
   
       wherein wavelengths of the signal and idler beams are dependent of the pivot position of the nonlinear crystal unit. 
     
     
         2 . The optical parametric oscillator as in  claim 1  wherein said at least six reflecting surfaces consists of no more than six reflecting surfaces. 
     
     
         3 . The optical parametric oscillator as in  claim 1  wherein the nonlinear crystal unit is comprised of a single non-linear crystal. 
     
     
         4 . The optical parametric oscillator as in  claim 1  wherein the nonlinear crystal unit is comprised of two substantially similar non-linear crystals mounted together and adapted to pivot as a unit about a common axis. 
     
     
         5 . The optical parametric oscillator as in  claim 3  and further comprising a rotation stage adapted to pivot the two crystals about the common axis to adjust the wavelength of the rotated beam. 
     
     
         6 . The optical parametric oscillator as in  claim 2  and further comprising a rotation stage adapted to pivot the single non-linear crystal about an axis to adjust the wavelength of the rotated beam. 
     
     
         7 . The optical parametric oscillator as in  claim 1  wherein the two reflecting surfaces, oriented to receive the pump beam and the OPO beams after each first pass through a first portion of the nonlinear crystal unit and to reflect the pump beam and the OPO beams so as to pass a second time through a second portion of the nonlinear crystal unit in order to cancel, on the second pass, walk-off produced by the first pass, are two surfaces of a prism. 
     
     
         8 . The optical parametric oscillator as in  claim 7  wherein the prism is a roof prism. 
     
     
         9 . The optical parametric oscillator as in  claim 1  wherein the two reflecting surfaces, oriented to receive the pump beam and the OPO beams after each first pass through a first portion of the nonlinear crystal unit and to reflect the pump beam and the OPO beams so as to pass a second time through a second portion of the nonlinear crystal unit in order to cancel, on the second pass, walk-off produced by the first pass, are two mirrors. 
     
     
         10 . The optical parametric oscillator as in  claim 1  wherein the crystal unit is adapted for type II OPO operation. 
     
     
         11 . The optical parametric oscillator as in  claim 1  wherein the oscillator is adapted for oscillation of the signal beam. 
     
     
         12 . The optical parametric oscillator as in  claim 1  wherein the oscillator is adapted for oscillation of the idler beam. 
     
     
         13 . The optical parametric oscillator as in  claim 1  wherein the polarization correcting element is an achromatic half waveplate. 
     
     
         14 . The optical parametric oscillator as in  claim 1  wherein the pump beam is a 1064 nanometer laser beam produced by a Q-switched Nd-YAG laser. 
     
     
         15 . The optical parametric oscillator as in  claim 1  wherein the pump beam source is a second harmonic 532 nanometer laser beam produced by a Q-switched Nd-YAG laser. 
     
     
         16 . The optical parametric oscillator as in  claim 1  wherein the pump beam source is a third harmonic 355 nanometer laser beam produced by a Q-switched Nd-YAG laser. 
     
     
         17 . The optical parametric oscillator as in  claim 11  wherein the at least four of the at least seven reflecting surfaces are surfaces of mirrors. 
     
     
         18 . The optical parametric oscillator as in  claim 11  where at least one crystal is placed outside the OPO cavity to amplify the OPO energy. 
     
     
         19 . The optical parametric oscillator as in  claim 1  wherein the at least four of the reflecting elements are oriented to rotate one or both OPO beams by 90 degrees on each pass of the rotated OPO beam or beams through the cavity includes at least one prism. 
     
     
         20 . The optical parametric oscillator as in  claim 19  wherein the at least one prism is three prisms.