is fire opaque to laser pointers ?

[Widdekind]

is fire opaque, to EM radiation ?

 

can you project a laser-pointer, through the flame, of (say) some cigarette lighter, or a candle ?

 

 

 

 

 

http://www.astro.princeton.edu/~burrows/classes/514/opac.2.ps

 

As a thought experiment, if the cores of big bright blue super-massive stars are ~1 g/cm3, ~100MK, then the Kramers' Opacity implies a mean-free-path of ~10-100m...

 

so if you could somehow bury yourself inside the center of some super-massive star, then w/ some sort of super-dark star-glasses you could see through the star, like fog on a football field, from post to post

 

are those numbers accurate, for said supermassive stars ?

[Enthalpy]

The flame of my propane or butane lighter is very transparent to the red light of my laser pointer. No perceivable difference at the laser's spot. Nor do I see any spot from the laser's light on the flame.

 

When I had protected a thin sheet of copper from a blowtorch by having water on the other side, the transferred power density was compatible with thermal radiation from acetylene+oxygen, but maybe the transfer was by contact after all. Or the hotter flame is more opaque.

[swansont]

It's possible that because it's a plasma, it will attenuate light more readily than a transparent gas would. But to ask whether it's opaque is a poorly-formulated question, because it's not a yes or no answer; it would depend on the thickness of the flame.

[Widdekind]

http://www.physicsforums.com/showthread.php?t=203289&page=3

 

fire = "semi-plasma", ionization % = PPB

 

if fire was 100% ionized, then the equations would imply perceivable opacity... but the attenuation distance [math]\equiv 1/\rho \kappa \propto 1/\rho^2[/math]

 

so PPB => km's to attenuate

 

i tried flashlight + match => no shadow from flame, no obscuration thru the flame from flashlight

[John Cuthber]

A candle flame glows because it has a lot of hot soot in it.

That soot will absorb some light (and re emit it).

How much will depend on how big and how sooty the flame is.

A quick experiment showed that the attenuation was small with a common household candle flame.

 

Nothing to do with stars.

[Widdekind]

jet-fighter exhaust is still "too cold" to be highly ionized, and so still presents little opacity:

 

http://community.warplanes.com/wp-content/uploads/2010/06/Lockheed-F-35-Lightning-IIside.jpg

 

i think the same is sayable, for space shuttle thrusters, through which one can see the other in-side surface of the nozzle

 

 

 

what would be least unlike stars, would be ion thrusters... perhaps people have ascertained the opacity of ion-thruster-exhaust streams ?