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From: Martin Brown <'''newspam'''@nonad.co.uk>
Newsgroups: sci.electronics.design
Subject: Re: how the laser happened
Date: Tue, 25 Jun 2024 11:50:05 +0100
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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.

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.


-- 
Martin Brown