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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: how the laser happened
Date: Wed, 26 Jun 2024 13:55:29 +1000
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On 26/06/2024 1:19 am, john larkin wrote:
> 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.

When I was a graduate student I put together an He laser tube with 
Brewster angle windows, and getters, and loaded it with the right gas 
mix. It did produce the right sort of glow when I ran a discharge through it

The friend who was going to fabricate the metalwork to locate the tube 
between the two properly aligned mirrors didn't get as far.

>> 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.

Many more ill-informed half-wits make the alternative mistake


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