I. H. Heon and J. H. Lee [14] studied the efficiency and threshold pump intensity of cw solar-pumped solid-state lasers. They worked on the Nd:YAG, Cr:Nd:GSGG, alexandrite and ruby lasers. For all laser materials the slope efficiency did not vary so much at the output mirror reflectances below 0.8, except for the 100 cm long laser rod. The dependence of the slope efficiency on the output mirror reflectances over 0.9 is, however, very strong; thus the slope efficiency reduces very rapidly with the increase of the reflectance. The threshold pump intensity decreases as the output mirror reflectance increases for all of the laser materials used in this work. It unexpectedly depends on the length of the laser rod, but does not at the reflectance near unity. The maximum achievable efficiency of Nd:YAG is estimated to be about 5 % with a 1 cm diameter laser rod when the pumping source is an air-mass-zero (AM0) solar radiation. Cr:Nd:GSGG crystal shows the maximum efficiency of about 12 % when the diameter laser crystal is 1 cm and when the threshold pump intensity at the output mirror reflectance of 99 % is about 100 AM0 s.c. The ruby crystal shows about 3 % slope efficiency but this crystal seems to have no practical worth due to its high threshold pump intensity. Alexandrite has a similar slope efficiency to Cr:Nd:GSGG; however, the threshold pump intensity depends very strongly on the output mirror reflectance so that the achievable effieciency is less than 10 % in the practical range for pump intensity. For all the laser materials used, the dominant deciding factor for the threshold pump intensity is the loss coefficient for a long laser rod