Active surface correction of the Caltech Submillimeter Observatory (CSO) primary mirror has been accomplished. The
Dish Surface Optimization System (DSOS) has been designed and built to operate at the CSO, on Mauna Kea, Hawaii.
The DSOS is the only active optics system of its kind in the world. There are 99 steel rod standoffs that interface the
dish panels to its backing structure. Each standoff is now fitted with a heating/cooling assembly. Applying a controlled
potential to each of the 99 assemblies adjusts the surface of the dish. Heating elongates and cooling shortens the
standoffs, providing the push or pull on the primary's panel surface. The needed correction for each standoff, for a
given elevation, is determined from prior holography measurements of the dish surface. Without the DSOS the
optimum surface accuracy was 25-μm RMS, yielding a beam efficiency of 33% at the 350-μm-wavelength range. With
the DSOS on, this has been improved to 10-μm RMS. The best beam efficiency obtained is 56%, with an average beam
efficiency of 53%. The DSOS has been in operation on the CSO since February 2003. Observers using the SHARCII
(a 384 pixel submillimeter high angular resolution camera) and the 850 GHz heterodyne receiver, have been able to
detect new weak and/or distant objects including detection of an earth-massed planet in Fomalhaut with the help of this
unique active optics system.