Positioning of Optical Payload - SALT Telescope

摘要

A common problem in the large telescopes is the accurate positioning of the optical elements. In the Salt Telescope, there is no secondary mirror, but a light collection system mounted on an optical payload, which is dynamically positioned above the primary mirror. Fogale Nanotech has developed an optical ranging system, the LISE LS40-LD, which is derived from a commercial product, to measure the distance from the payload to the primary mirror, and adjust their relative position. The LISE system is a fibre optic low-coherence interferometre illuminated by an infrared broadband source. It consists in a control unit placed under the telescope and a small collimator mounted on the payload, which focuses the measurement beam on the mirror and collects the reflected light. The collimator is linked to the control unit by a 50 m long optic fibre. It measures a true absolute distance. The distance to measure is 13.505 m, the measuring range is +/-20 mm and the required accuracy is +/- 10 μm. The system has been installed on the Salt Telescope on July, 2003. The results shows that the specifications are met.