Abstract: A method for thermally conditioning an optical element includes irradiating the optical element with radiation, not-irradiating the optical element with the radiation, allowing heat flow between the optical element and a conditioning fluid that is held in a conditioning fluid reservoir, and providing a fluid flow of the conditioning fluid, to supply thermally conditioned fluid to the reservoir. A flow rate of the fluid during the irradiating of the optical element is lower than a flow rate of the fluid when the optical element is not-irradiated.

Abstract: A mirror module is provided with comprising a reflective element, a supporting base element attached to the reflective element, and a heat exchange element for transferring heat to and/or from the mirror module. The mirror module, more in particular the reflective element, is stabilized against possible deformation due to a thermal load. The stabilized mirror module comprises heat pumps, for example Peltier elements, for transferring heat between the heat exchange element on one hand and the reflective element and the base element on the other hand, more in particular for cooling the reflective element. A method is provided to stabilize a mirror module wherein a heat flow is measured to stabilise the shape of a reflective element.

Abstract: A method for thermally conditioning an optical element includes irradiating the optical element with radiation, not-irradiating the optical element with the radiation, allowing heat flow between the optical element and a conditioning fluid that is held in a conditioning fluid reservoir, and providing a fluid flow of the conditioning fluid, to supply thermally conditioned fluid to the reservoir. A flow rate of the fluid during the irradiating of the optical element is lower than a flow rate of the fluid when the optical element is not-irradiated.