Energy absorbed by spherical‐shell targets irradiated using the KMSF ellipsoidal‐mirror illumination system at powers on target of up to 1.0 TW has been measured using a thermopile differential calorimeter. Data are presented for 1.06 and 0.532‐&mgr;m laser light, for glass and low‐atomic‐number PVA targets, and for laser configurations with and without a plasma spatial filter.