Re: how the laser happened

On Tue, 25 Jun 2024 11:50:05 +0100, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:

On 21/06/2024 14:05, john larkin wrote:

There was a thread somewhere above about photon wave/particle duality.
 
 
This is worth reading:
 
https://www.amazon.com/How-Laser-Happened-Adventures-Scientist/dp/0195153766
 
Einstein, in one of his fits of genius, predicted in around 1916 that
under the right conditions, a photon could pass by an excited atom and
the atom would kick in another photon, or add to the wave amplitude,
depending on how you feel about these things. He called it stimulated
emission. He also declared that the laws of thermodynamics made this
effect impossible to use in practical situations.
 
In 1951, Charles Townes invented a work-around trick and built the
maser, a gaseous microwave oscillator. His superiors thought he was
crazy to dispute Einstein and almost threw him out of grad school, but
it worked.

>
More interesting still nature beat him to it.
>
The natural source W3(OH) dense molecular cloud which has hydroxyl
masers pumped by UV bright young stars embedded in it.
>
Very bright ultra narrow band point sources on a fuzzy nebulous object.
>
https://articles.adsabs.harvard.edu/pdf/1981MNRAS.194P..25S
>

What's interesting is that any decent neon sign shop could have built
a HeNe laser in 1920.

>
They would have needed to make the mirror just cavity right though.

I know a guy who built a HeNe. It wasn't hard.

T>

A nitrogen gas UV pulsed laser is possible just by getting the pressure
right and creating the  population inversion. Self starting - there was
a (dangerous) experiment in SciAm Amateur Scientist column to do it
sometime in the 1970's. June 1974 in fact - cover shows the BZ reaction.
>
https://www.scientificamerican.com/article/the-amateur-scientist-1974-06/
>
The failure to discover fullerenes in soot was a lot more surprising
since they were there all the time since the invention of fire just
waiting to be extracted by benzene. For a long time space dust had a
spectrum that could not be reproduced on Earth by any known compound.
>
Much like Helium was in the sun but more pervasive.

Too many powerful old farts declare things to be impossible.