Outgassing of contamination in large quantity was observed in a helical TE CO2laser housed in an acrylic (Perspex) chamber. This considerably reduced the sealed operational life of the device. In a helium‐free mixture the laser energy initially improved and then reduced with time, while in the mixtures with helium it reduced monotonically. Water vapor seemed to be the main constituent in the contamination. By circulating the contaminated gas through a trap at dry‐ice temperature, the water vapor was condensed, enhancing the sealed‐off life of the device.