In-Situ Metrology of Large Segmented Detector Based on Modified Optical Truss

To precisely map cosmic structures and capture time-domain events, future large survey telescopes will be equipped with segmented detectors that greatly expand their field of view. Segment flatness and assembly accuracy will be essential for them to make accurate observations. Instead of physically measuring distances between adjacent mirror surfaces, our modified optical truss enables the angle (slope) between them to be calculated. Furthermore, we calculated the relative tilt and piston between the segmented detectors. The modified optical truss can measure the flatness of a mosaicked detector before and after it is assembled into a telescope. We reduced the volume, weight, and power of our device compared with earlier versions. Its angular accuracy is now better than 0.1 arcsecs, and, at a maximum scope of 500 µm, the linear accuracy of the new truss is better than 25 µm. In fact, accuracy and testing ranges are comparable to instruments found in optics labs.