Patent ID: 8817229

Claim:
A method of thermally conditioning an optical element operating in a vacuum environment, wherein said optical element comprises a first body having at least one optical surface and at least one heat transfer surface, the method comprising: controlling a temperature of a second body to a desired temperature, the second body comprising a second heat transfer surface of a form complementary to that of the first heat transfer surface; dynamically controlling the first body in position and/or orientation with a first actuator coupled to the first body via a first linkage; positioning the second body adjacent the first body and dynamically controlling the second body in position and/or orientation with a second actuator coupled to the second body via a second linkage so as to maintain the first and second heat transfer surfaces in a substantially constant arrangement without contact between the bodies; and delivering a gas as a heat transfer medium into a heat transfer space defined by the first and second heat transfer surfaces, while controlling the pressure of the gas in the heat transfer space to be at a predetermined value between about 30 Pa and about 300 Pa.