Lunar laser ranging using avalanche photodiode (APD) arrays

摘要

The Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) will improve range measurements to the moon by at least an order-of-magnitude, with the goal of achieving millimeter precision. Lunar ranging provides the most stringent tests of Einstein's strong equivalence principle, as well as placing the tightest constraints on the time evolution of Newton's gravitational constant. At the heat of APOLLO is an integrated constraints on the time evolution of Newton's gravitational constant. At the heart of APOLLO is an integrated array of avalanche photodiodes (APDs) developed at MIT Lincoln Laboratories. These devices are capable of detecting the arrival of a single photon with high temporal precision (< 100 ps), with detection efficiencies as high as 50%. The thin APD arrays have breakdown voltages in the neighborhood of 25 volts, active areas 20, 30, or 40 microns in diameter, placed on 100 micron centers in a square pattern. APOLLO will initially work with a 4 * 4 array, but may eventually upgrade to a larger format. The potential use of APD array technology in other areas of astronomy is briefly discussed.