A dual enclosure including an inner housing inside an outer housing is provided for an optical bench supporting a plurality of optical elements. An air gap is provided between the inner and outer housings. The inner housing may act as a heat spreader for isothermal operation, and the outer housing may act as a heat insulator. The optical bench may be disposed within the inner housing on a supporting element or elements, which thermally and mechanically decouple the optical bench from the inner housing.