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NNTP-Posting-Date: Tue, 25 Jun 2024 15:19:02 +0000
From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: how the laser happened
Date: Tue, 25 Jun 2024 08:19:03 -0700
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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.