{wiki}

https://physics.stackexchange.com/questions/450654/how-atomic-clock-works/726135#726135[How atomic clock works? answer] by <Ciro Santilli> on <Physics Stack Exchange>.

\Video[https://www.youtube.com/watch?v=p2BxAu6WZI8]
{title=How an atomic clock works, and its use in the global positioning system (GPS) by <EngineerGuy> (2012)}
{description=Shows how conceptually an atomic clock is based on a <feedback loop> of two <hyperfine structure> states of <caesium> atoms (non-<radioactive> <caesium-133> as clarified by the <Wikipedia> page). Like a <quartz clock>, it also relies on the <piezoelectricity> of quartz, but unlike the <quartz clock>, the <quartz> is not shaped like a <tuning fork>, and has a much larger resonating frequency of about 7 <MHz>. The feedback is completed by producing <photons> that <resonate> at the right frequency to excite the <caesium>.}

\Video[https://www.youtube.com/watch?v=eOti3kKWX-c]
{title=Inside the <HP> 5061A Cesium Clock by <CuriousMarc> (2020)}
{description=
A similar model was used in the <Hafele-Keating experiment> to test <special relativity> on two planes flying in opposite directions. Miniaturization was key.

Contains a disposable tube with 6g of <Caesium>. You boil it, so when it runs out, you change the tube, 40k USD. Their tube is made by <Agilent Technologies>, so a replacement since that opened in 1999, and the original machine is from the 60s.

Detection is done with an <electron multiplier>.

https://youtu.be/eOti3kKWX-c?t=1166 They compare it with their 100 dollar <GPS> disciplined oscillator, since <GPS> <satellites> have <atomic clocks> in them.
}

\Video[https://www.youtube.com/watch?v=Tc_tDVbjCQk]
{title=Quick presentation of the <atomic clock> at the <National Physical Laboratory> (2010)}
{description=Their super accurate setup first does <laser cooling> on the <caesium> atoms.}


Atomic clock

{wiki}

\Video[https://www.youtube.com/watch?v=lVu11WWrNbQ]
{title=How Microwaves Work by National MagLab (2017)}
{description=A bit meh. Does not mention the word <cavity magnetron>!}

\Video[https://www.youtube.com/watch?v=kp33ZprO0Ck]
{title=How a Microwave Oven Works by <EngineerGuy>}
{description=Cool demonstration of the <standing waves> in the cavity with <#cheese>!}


Microwave oven

{tag=Technology}
{wiki}

= Fiber optics
{synonym}

\Video[https://www.youtube.com/watch?v=7qkizPs2kdw]
{title=The Story of Light by <Bell Labs> (2015)}
{description=Gives some ideas of the history of <fiber optics>. Features: Herwig Kogelnik.}

\Video[https://www.youtube.com/watch?v=0MwMkBET_5I]
{title=<Fiber optic cables> by <EngineerGuy>}

\Video[https://www.youtube.com/watch?v=0DCrIAxEv_Y]
{title=<Fiber optics> fundamentals by <#Shaoul Ezekiel>}
{description=
2008 at <MIT>. Theory and demonstration.
* https://youtu.be/0DCrIAxEv_Y?t=560[]:
  * on smaller wavelengths, loss is due to <#Rayleigh scattering>
  * on longer wavelengths, loss is due to material absorption
  Terefore, the 1.5 micrometer window truly is the minimum.
}


Ciro Santilli @cirosantilli 35

 Incoming links: EngineerGuy