Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Phil Hobbs Newsgroups: sci.electronics.design Subject: Re: how the laser happened Date: Thu, 27 Jun 2024 02:49:37 -0000 (UTC) Organization: A noiseless patient Spider Lines: 100 Message-ID: References: <3ihm7j9kruqmsg57svadl10araoahldqrn@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Thu, 27 Jun 2024 04:49:38 +0200 (CEST) Injection-Info: dont-email.me; posting-host="7fc924c350f1e0ccc961e321b1e2f196"; logging-data="2691732"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19PtrGbaR+g5mZqLN7BNqMd" User-Agent: NewsTap/5.5 (iPhone/iPod Touch) Cancel-Lock: sha1:E8hrdruUS/rFb8DeAHGnijK6AUw= sha1:1N1Osu7a9z/0EhFS6Ll+yIv3cKg= Bytes: 5211 john larkin wrote: > On Tue, 25 Jun 2024 17:43:56 -0400, Joe Gwinn > wrote: > >> On Tue, 25 Jun 2024 08:19:03 -0700, 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. >>> >>>> >>>> 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. >> >> . >> >> This is often paraphrased as "Science progresses one funeral at a >> time". >> >> Joe Gwinn > > I see the same thing in electronic design. People favor accepted > practice, validated in textbooks, and apply all their intelligence to > showing how new ideas won't work. > > A recent case is deciding that the LC's at the output of a switching > power supply are "a filter" so must follow classical filter theory, > pole-zeros and Butterworths and such. I tell them "It's just a power > supply." Classical filter theory is very useful for designing a power supply , as long as you don’t just wave some canned design over it like a dead chicken. Controlling rolloff and ringing over a wide range of conditions is easier with a bit of theory—you can estimate the overshoot via the Q of the network, for instance. Canned designs such as Butterworth, Chebyshev, and so on assume constant, resistive source and load. While that’s a useful fiction in lots of signal-level applications, it’s not remotely true in a power supply. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics