In 1975 i've got the job in lab constructing middle power one mode CO2 lasers for outer space object location (they used C and O isotopes for reducing losses in atmosfere). The main joke for newbies of our lab's boss (Yuri Vasilievich Pechenin) was to breathe sigarette smoke from mouth into focus area of operating laser (1 to 3 kilowatt output radiation ordinary). And there was a question: Why was the smoke rocketed from focus area in opposite direction (from focus to laser)? I don't remember the reason. Who can help?