1 the outgoing laser beam will be frequency upshifted by the acoustic frequency u03bd acous and wavelength downshifted by the amount in equation 3 similarly for the negative first order diffracted beam m u2212 1 the outgoing laser beam will be frequency downshifted by the acoustic frequency u03bd acous and wavelength upshifted by the amount in equation 3 notably the zero order undiffracted beam m 0 will not experience a frequency or wavelength shift in order to avoid a continual frequency or wavelength shift as the laser beam passes through the bragg cell the positive first order diffracted beam can be returned through the bragg cell along the path of the negative first order diffracted beam thereby exactly canceling the frequency wavelength shift the laser will be frequency upshifted by u03bd acous and then frequency downshifted by u03bd acous for a zero net frequency shift thus in the preferred embodiment the invention comprises adding a bragg cell 10 with two highly reflecting mirrors 14 and 16 inside the laser cavity 12 in order to preserve the symmetry and efficiency of the bragg cell the bragg cell 10 is placed with its face nominally perpendicular to the incoming laser beam 26 from the gain medium from the left in fig1 as the laser beam passes through.