  We describe the operation of a free-space confocal optical microscope
operated in a dilution refrigerator. The microscope is installed on a cold
insertable probe to enable fast sample exchange while the refrigerator is held
at low temperatures. A vector magnet provides a 6 T field normal to the sample
and 1 T fields at arbitrary angles. A variety of optical microscopies and
spectroscopies, including photoluminescence, Raman, magneto-optical Kerr
effect, and spin relaxometry measurements are described, and some of the
challenges associated with performing these measurements at milliKelvin
temperatures are explored.
