A high power D2O laser, pumped by a single mode CO2laser, has been optimized to produce 1 &mgr;s pulses at 385 &mgr;m. Pump energies up to 100 J were available using ane‐beam preionized CO2amplifier at 2.5 atm. Far infrared pulse energies of 140 mJ in multimode and 40 mJ in single mode operation have been obtained from a 4‐m unstable resonator. During parametric studies the influence of operating pressure, spatially inhomogeneous pump intensity, resonator feedback as well as saturation effects have been investigated.