Path: ...!Xl.tags.giganews.com!local-1.nntp.ord.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Thu, 27 Jun 2024 14:05:08 +0000 From: Joe Gwinn Newsgroups: sci.electronics.design Subject: Re: how the laser happened Date: Thu, 27 Jun 2024 10:04:57 -0400 Message-ID: References: <3ihm7j9kruqmsg57svadl10araoahldqrn@4ax.com> User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Lines: 125 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-EL9PtY9aK4rFS59+FZogx6hchScH71+rZOat5vFGgLzkrLlGmWGQQgfkGqRfyVmQFMiTOBTbRKPm14s!cMclDUyR0oySa9Qp8sHeOLCOE6WFyYRFTRcj31P22YeRC9awIg+7+dcfjUBKkatvnHBqh1E= X-Complaints-To: abuse@giganews.com X-DMCA-Notifications: http://www.giganews.com/info/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 6436 On Wed, 26 Jun 2024 20:07:12 -0700, john larkin wrote: >On Thu, 27 Jun 2024 02:49:37 -0000 (UTC), Phil Hobbs > wrote: > >>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 > >My switching power supply filters are usually dominated by the first >inductor. It has to let some tolerable ripple current into the >downstream caps, has to not saturate, and must not get too hot in the >minimum expected air stream, from core loss and copper loss. And fit >available space and not cost too much and be available for purchase. > >I'll often have a secondary high-current ferrite bead to reduce EMI >spikes, typically maybe a per cent of the main inductance. > >None of that is classic filter theory. > >Only Spice can predict the power supply load response. It's too >nonlinear for classic filter theory. Yes, this is exactly how all the radar power engineers of my acquaintance solve the problem. LT Spice is their standard tool. >There are cheap tricks to compensate the control loop, once the big >power stuff is designed. Yep. Joe Gwinn > >