The present invention is a beam scanner for use about a nonlinear optical crystal for frequency conversion. The scanner oscillates the high power laser beam passing through the crystal to reduce heat damage and does not change the direction or the position of the beam upon exiting the scanner. A pair of thick optical plates are affixed to a driven axle being parallel to the laser beam direction. The first plate is mounted at a given angle to the axle and the second plate is mounted at the same but negative angle to the axle so that they are mirror images about the crystal. As the axle rotates, the laser beam moves through the crystal in a cylindrical pattern and due to the manner of mounting the plates, the exiting laser beam is not displaced from the original beam direction or position. The beam scanner may be inserted into an existing optical resonator, for example, without modifications thereto.