CO2 laser and sigarette smoke question

[Minich]

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?

 

[Integral]

Sure would like to see a video of this.

Unfortunatly in this day and age they will not let us any where near our lasers with a cigerett in hand (or mouth for that matter!)

 

[Minich]

Our boss wanted to show us that we work in proper place. And we worked with greate emotion and proud that we make best in the world lasers those days )

And lasers were not scientific installations only, they were produced in series at the plant. They were industrial lasers.

We were fascinated by creative atmosfere.We were aheard of laser groups in USSR, headed by Nobel Prize wiiners Basov and Prochorov (in CO2 line)..

I think video of those days are for restricted access only.

 

[dst]

Perhaps a hefty transfer of momentum from the photons? According to widely cited academic sources (XKCD) it takes 1.21GW/m^2 to levitate a squirrel of mass 0.7kg. Consider that gas particles have masses lower by several orders of magnitude ;)

Also, it might be a heat/pressure wave. When I place something into the focal point of a reasonably high powered laser it begins to emit white light.

 

[Minich]

To dst.

I remember it is connected with the temperature of spots on sigarett smoke bit and reactive force due to sigarette bit burning. But why is temperature on focus side higher?

Sigarette bit in laser beam is burning inhomogeneosly and behaves like rocket.

Excuse my poor english. I had never been outside former USSR and had never practice in written english.

 

[gareth]

I'll have a go at this;

If the laser spot hits the smoke particles they will heat up, if sufficient heat is imparted on the particles they will ionize forming a plasma.

This heated vapor at first directs pressure in all directions, however, the plasma absorbs most of the incident light, so the front of heated dusted partciles traveling towards the laser acts as an absorption front fot the laser energy, which in turn exerts pressure towards the laser.

In simple terms, there is an absorbing front created by the smoke plasma which travels towards the laser by the expansion of the heated gas.

Why doesn't it go in all directions? Simply because the point of absorption is getting closer and closer to the laser.

Does this help?