Apparatus for mounting an optical element in an optical system

Apparatus and methods for mounting an optical element to a mounting plate in an optical system. The optical element is adhesively bonded with a surface on the mounting plate by a radiation-curable adhesive and a radiation-transmissive member that provides an unobstructed optical path in the mounting plate for curing the radiation-curable adhesive. The adhesive accommodates differences in thermal expansion between the material forming the mounting plate and the material forming the optical element so as to maintain the position and angular orientation of the optical element relative to the mounting plate and so as to prevent damage to the optical element. The formulation of the adhesive forming the adhesive couplings may incorporate spacer elements operative for maintaining the spacing and parallelism between the optical element and the mounting plate.