A method and apparatus are provided to modulate a beam of laser light. An acousto-optic modulator (AOM) is positioned to receive continuous-wave (CW) laser light at an angle approximating the Bragg angle. Fine tuning of the modulation is then used to compensate for any variations in the actual angle from the Bragg angle. A photodiode provides a feedback signal that may be used to tune or adjust the operation of the AOM. The photodiode is positioned to receive laser light at the first order diffraction and provide a signal indicative of the magnitude of the first order diffraction laser light produced by the AOM. The photodiode signal is coupled to an RF frequency generator so that the RF frequency may be adjusted to vary the acoustic wave in the AOM to compensate for any variations in the Bragg angle.