The threshold power for CO2‐laser‐induced gas breakdown in helium has been studied at many pressures in the range of 50–700 Torr by using laser pulses of two different lengths. These measurements show that electron diffusion losses play an important role at these pressures. The experimental data can be quantitatively accounted for by taking into account both diffusion losses and the finite length of the laser pulse. In addition, it is found that the breakdown threshold power is significantly lowered when longer laser pulses are used and that elastic losses appear to play an important role at pressures above 500 Torr.