Re: The sound of a laser.
From: Ian (not_at_here_at_hotmail.com)
Date: 10/17/04
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Date: Sun, 17 Oct 2004 12:36:27 GMT
i suspect the sound reported from any high energy laser is more likely to be
the crack due to the relaxation of the dielectric in the capacitors. Itd
have to be some energy/(not power) level to heat the air up enough to
produce a shock wavefront. Still... if you dress it up enough and give it a
swishy name, theres bound to be some hi-fi nut with a turntable and valve
amp that would think it was the best tweeter he'd ever heard ie inertialess.
"Helpful person" <rrllff@yahoo.com> wrote in message
news:87946313.0408200441.785a361b@posting.google.com...
> "David Prokopetz" <sirbob@penguinking.com> wrote in message
news:<2ol510Fbmdq4U1@uni-berlin.de>...
> > Hi.
> >
> > Physics newbie question here: what does a laser sound like? Some
sources
> > I've read claim that a sufficiently powerful laser would ionise the air
> > along its path and produce a "crackle" or "pop" noise, while others
claim
> > that regardless of power, a laser has to be of a particular colour to
ionise
> > the air and thus produce a sound - but fail to mention what that colour
is.
> > Is any of this information accurate?
> >
> > As a follow-up question, if a laser actually can make noise, is there an
> > easy way to derive an approximate relationship between how powerful the
> > laser is and how loud it is?
> >
> > Thanks,
> >
> > - David Prokopetz.
>
> At high instantaneous laser powers the ossilating electric field in
> the beam can ionize gasses, including air. An easy way to
> experimentally investigate this is to bring a laser beam to a focus in
> gasses of varying pressures. Vary both the gas pressure and focal
> length of the lens. Longer lens focal lengths result in lower
> electric fields at the focus. It will be necessary to use a pulsed
> laser with short pulse lengths as this maximizes the instantaneous
> electric field.
>
> The sound of the electric breakdown is a loud crack.
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