Fig. 1: Extremely Large Telescope ELT Courtesy: ESO/L. Calçada

CEDRAT TECHNOLOGIES (CTEC) has been involved in the development and delivery of several piezo actuators and mechanisms for critical subsytem parts of the ELT structure and instrumentation like M5 filed stabilization unit and MICADO instrumentation. MICADO, a large multipurpose infra-red camera, is one of the first light instrument to be installed at the Extremely Large Telescope (ESO telescope) and an Adaptive Optics system to correct atmosphere defect will be realized at LESIA (Paris Observatory / CNRS). This AO system is based on a pyramid Wave Front Sensor to measure the wave front aberration with a very high accuracy. To linearize the signal and adapt the sensitivity of the sensor the focused image has to be modulated around the top of the pyramid optical component using a Fast Steering Mirror based on a piezo tip-tilt mechanism DTT40SM-SG (Fig.2). This FSM consists of a 50mm diameter and 8mm thickness glass mirror located in a pupil plane. To measure and correct fast change in the turbulent atmosphere, the system may run up to 500Hz with a stroke up to 2mrad in closed loop.In addition, CTEC has taken care to add a cover to ensure protection against excessive humidity in the environment, as well as a bracket to fix the modulation system with the mirror in a vertical position.Also, the FSM is equipped with strain gauges to measure the position of the angular deflection.

Fig. 2: Example of a Double Tip-Tilt DTT40SM