a device and method for steering a laser beam to a focal point in target tissue requires generating a laser beam . diversions of the laser beam from a central beam path are minimized by a sequential arrangement of optical steering components . in order , the beam is first directed to the center of a z - scanning apparatus which will move the focal point in the medium in a z - direction . the beam is then passed to the center of a first galvanometric mirror which introduces focal point movements in the x - direction . a second galvanometric mirror then compensates for the x - direction movement by redirecting the beam to the center of a third galvanometric mirror where focal point movements in the y - direction are introduced .