The performance of a pulsed D2O laser pumped longitudinally by a CO2laser and emitting at 385 &mgr;m is investigated numerically. These studies point out the limitations in pumping efficiency due to the ‘‘bottleneck’’ effect in the vibrational deexcitation of D2O. The influence of a buffer gas on the saturation behavior is discussed. The results of this numerical simulation are in good agreement with experimental measurements. Design parameters are predicted for a D2O laser system suitable for Thomson scattering diagnostics of a Tokamak plasma.