Active jitter suppression of optical structures

This paper presents the results of experiments involving jitter suppression of optical components. Acoustic disturbances and structurally transmitted vibration contribute to the jitter of optical systems such as lasers. Active and passive methods must be used to suppress jitter from entering the optical train. An experimental test bed is constructed to study the effects of acoustic disturbances on an optical system. A laser source is directed onto a light-detecting target by way of a turning mirror and fast-steering mirror (FSM). The FSM, actuated by three piezoelectric stacks, provides tilt in both the elevation and azimuth axes. Both mirrors are exposed to an acoustic disturbance. The objective is to use knowledge of the acoustic-structural interaction to design a controller that precisely points the laser. To achieve this, several control methodologies are studied. A servo control loop around the FSM is designed using an H-2 approach. By feeding back the laser beam position to the FSM, the jitter is reduced by a factor of 2.5. Feedforward methods are also explored using microphones and accelerometers as disturbance sensors. Acoustic noise control is studied as a means of reducing the sound pressure level in the proximity of the optics. Sound pressure sensed by a microphone was fed to a loudspeaker and the loop was closed with an H2 optimal controller.