“…In 1978, we were first to suggest that a further increase in the optical damage threshold of mirror surfaces of high power optics (HPO) based on porous (micro capillary) structures is possible when liquid alkali metals and their alloys are used as coolants [1,2,3,4,5]. Prospects of utilising liquid alkali metal coolants in HPO were determined by the possibility of achieving a high heat transfer coefficient in the porous structure due to a favourable combination of thermo physical properties of liquid alkali metals.…”