How Lasers Work #24

00:00:00: We usually start these deep dives with, well a pretty massive stack of material.

00:00:05: Oh yeah!

00:00:05: Usually it's like huge research papers or investigative article right?

00:00:10: Or sometimes an entire non-fiction book that we've promised to distill down for you.

00:00:14: but today uh... You sent us something that completely breaks the mold.

00:00:19: It really does.

00:00:19: Its definitely not a stack.

00:00:21: No its'a single sheeted paper.

00:00:22: and honestly looking at I kinda thought there had been printing error.

00:00:26: i mean..it definitely looks like mistake at first glance.

00:00:29: It just completely challenges the basic expectation of what an educational source is even supposed to be.

00:00:34: Right,

00:00:35: because well here's exactly what's printed on this single piece of paper you send us.

00:00:39: at the top there's a header that says excerpts from how lasers work.

00:00:44: Just that one line?

00:00:45: Yeah.

00:00:46: and then right below that The actual excerpt Is just the title again How Lasers Work.

00:00:52: That's it!

00:00:52: That literally six words excerpts From how lasers works.

00:00:56: How lasers work?

00:00:57: It's

00:00:58: the absolute definition of a minimalist document.

00:01:00: Okay,

00:01:00: so let's unpack this because it feels like a prank

00:01:03: A little bit.

00:01:04: Yeah!

00:01:04: It's like walking into a fancy restaurant sitting down and The waiter hands you This beautiful leather-bound menu.

00:01:10: Right You open it up You're ready to read about the steaks And seasonal vegetables And printed right in the middle Of the blank page Is just the word food

00:01:20: Just Food.

00:01:21: That is great analogy.

00:01:22: So how do we even begin To analyze a source that announces its topic, but provides absolutely zero mechanics.

00:01:31: I mean are we just looking at the cover of a missing book?

00:01:34: Well what's fascinating here is that the document in it's extreme brevity...it kind acts as pure declaration of intent.

00:01:41: Okay

00:01:41: how so

00:01:42: It strips away all the preliminary throat clearing That usually accompanies a textbook.

00:01:48: Even without the underlying physics, the text How Lasers Work establishes a definitive educational premise.

00:01:54: So it's telling us what we're supposed to learn even if he doesn't teach you?

00:01:58: Exactly!

00:01:58: It tells this exactly with missing information is meant to achieve which is demystifying specific technology

00:02:04: but does not actually de-mystify anything just like point at mystery.

00:02:11: Honestly, sometimes identifying the boundary of your own ignorance is the most important first step.

00:02:15: Okay

00:02:16: that's fair.

00:02:16: The phrase how something works?

00:02:18: Is a promise.

00:02:19: it says you know You currently look at this technology as black box And the goal is to break that box open.

00:02:26: Right?

00:02:26: So by providing only the title, The Source distills the entire educational endeavor down to the identification of a gap in your knowledge

00:02:34: which has really interesting feeling because I see lasers all the time

00:02:37: oh everywhere.

00:02:38: check out scanners laser pointers

00:02:40: our code readers exactly.

00:02:42: i just accept them as background reality.

00:02:45: but staring at this piece of paper im basically forced that if you asked me to actually explain the physics of a laser pointer, I would completely freeze up.

00:02:54: Most people will.

00:02:56: The title creates an intellectual vacuum.

00:02:58: when confronted with clearly labeled gap in understanding our natural inclination is want fill it.

00:03:04: We

00:03:05: hate the vacuum

00:03:06: we really do.

00:03:07: If the document had just dumped the physics on immediately You might have skimmed

00:03:11: right?

00:03:11: Probably.

00:03:12: But by withholding the information, it forces you to consciously acknowledge that gap before even attempting crossing.

00:03:18: It makes you hyper-aware of what you don't know which I think brings us into the weirdest part in paper...which is framing.

00:03:25: The source explicitly calls itself excerpts plural

00:03:30: Right.

00:03:30: And if we connect this to the bigger picture, The very presence of the word excerpts guarantees that a larger comprehensive body of text exists out there somewhere.

00:03:40: Because you can't have an excerpt of nothing

00:03:42: Exactly!

00:03:43: An excerpt cannot exist in isolation.

00:03:45: It's a fragment cut from a large hole.

00:03:48: So what does all mean for us?

00:03:50: Is the author playing a trick on us, or is this just a placeholder?

00:03:53: Like a signpost pointing to knowledge?

00:03:55: we're supposed.

00:03:55: go find ourselves.

00:03:56: Well think about that arrow in which you live right now.

00:03:58: We are dealing with severe information overload.

00:04:01: Oh for sure.

00:04:02: So providing only title might actually be ultimate way of avoiding overwhelming reader.

00:04:07: It forces your to acknowledge specific topic without demanding immediately process like dense scientific data.

00:04:14: So it's gentle tap on shoulder instead fire hose.

00:04:17: That's a perfect way to put it, yeah.

00:04:19: Okay well I appreciate the gentle tap and i appreciate the profound minimalist philosophy of this six-word document.

00:04:26: but i'm not going to sit here for an hour analyzing the ontological weight of a blank page...

00:04:31: ...I wouldn't blame you?

00:04:32: The title promised to explain how lasers work!

00:04:38: I think

00:04:43: that's the only logical next step, honestly.

00:04:46: The document challenged us to seek the answers.

00:04:48: so let's seek them.

00:04:50: Let's actually break open a black box.

00:04:52: So where do we even start?

00:04:54: Laser is an acronym.

00:04:57: What does it stand for and how can you give us road map for mechanics?

00:05:01: Laser stands for light amplification by stimulated emission of radiation

00:05:05: Light Amplification By Stimulated Emission Of Radiation.

00:05:08: That's one.

00:05:09: Okay, light and amplification.

00:05:11: i get Radiation sounds scary, but I assume we just mean radiating light not like nuclear fallout.

00:05:17: Correct in physics radiation Just means the emission of energy as electromagnetic waves or moving subatomic particles.

00:05:25: okay Visible light is a form of electromagnetic radiation.

00:05:29: heat radiating from a stove Is radiation?

00:05:32: It doesn't mean it's radioactive Or dangerous in the nuclear sense.

00:05:35: good to know because that word always puts me on edge.

00:05:39: But it's those middle words stimulated emission that sound like the actual secret sauce here.

00:05:43: They

00:05:43: absolutely are.

00:05:44: but

00:05:45: before we get to this stimulated part We probably need to talk about light itself, right?

00:05:49: Like how is a light coming out of a laser pointer fundamentally different from the light coming Out Of say The flashlight on my phone?

00:05:57: so To understand the difference you really need to understand How light behaves.

00:06:01: your phones.

00:06:01: flashlight or just a standard light bulb produces what we call incoherent light.

00:06:06: Incoherent,

00:06:06: like a bad argument?

00:06:07: Similar

00:06:08: concept actually!

00:06:09: Incoherant Light is just chaotic.

00:06:11: Chaotic

00:06:11: how?!

00:06:12: Well... A light bulb generates light by heating up the filament until it glows or by exciting gas.

00:06:18: randomly It's throwing out photons which are fundamental particles of light in every conceivable direction.

00:06:23: Just a total spray of photons

00:06:25: Exactly and not only they're going all directions but there also huge mix different wavelengths which means a mix of different colors.

00:06:35: Right, because white light from the bulb is just all Smashed together

00:06:39: precisely and furthermore the light waves are completely out of phase with one another.

00:06:44: how to face?

00:06:44: Yeah, imagine a wave pool at a water park.

00:06:46: where?

00:06:47: A hundred different kids or jumping in at totally random times.

00:06:51: Oh I've been in that pool.

00:06:52: It's a mess right.

00:06:53: you get a choppy chaotic messy surface.

00:06:56: The peaks of some waves cancel out the troughs of other ways.

00:07:00: That is incoherent light.

00:07:02: it's scattered its mixed And it diffuses very quickly over distance

00:07:06: which is exactly why a flashlight beam gets washed.

00:07:08: hide and dim.

00:07:09: the further away you point it, just spreads out.

00:07:11: Exactly!

00:07:12: A laser on other hand produces coherent light that is highly organized.

00:07:16: Okay what makes it organize?

00:07:17: First

00:07:17: its monochromatic mono meaning one chroma meaning color.

00:07:22: a laser beam consists of one single highly specific wavelength of light.

00:07:26: So if this red laser is purely Red There's no rogue blue or green photons mixed in there at all.

00:07:32: Just

00:07:32: one pure wavelength, second it is highly directional.

00:07:36: the photons are all traveling in exactly the same direction tightly parallel to each other

00:07:41: so they don't spread out

00:07:42: right.

00:07:43: and third-and this is true definition of coherence The waves are perfectly in

00:07:49: phase meaning the peaks and valleys light waves line up perfectly.

00:07:54: yes

00:07:54: Back to the wave pool analogy.

00:07:56: Instead of a hundred kids jumping in randomly, imagine a massive mechanical paddle that pushes water all at once...

00:08:03: Like the ones they use for surfing pools?

00:08:05: Exactly!

00:08:06: Every single wave crests at the exact same moment and hits the trough At the exact say moment.

00:08:11: because they are in phase their amplitudes actually add together.

00:08:15: They reinforce each other creating a much more powerful focused way.

00:08:20: Okay, so a light bulb is a chaotic crowd of people walking in different directions bumping into each other but a laser is a military parade.

00:08:27: That's a great visual!

00:08:29: Everyone marching in perfect lockstep wearing the same uniform heading in the exact same direction...

00:08:33: that's a perfect way to visualize it.

00:08:35: so, The real question becomes how do you get nature which usually prefers chaos and randomness?

00:08:41: To organize light into a perfect synchronized marching band?

00:08:45: Right because if I just heat something up like we said It glows randomly.

00:08:50: How do we actually force the order?

00:08:52: i'm guessing this brings us down to the atomic level.

00:08:55: It does.

00:08:55: We have to look at the atoms themselves, specifically the electrons orbiting the nucleus of the atoms.

00:09:00: This takes us way back to Niels Bohr and his model of the atom from the early twentieth century.

00:09:05: Oh man!

00:09:06: The classic diagram we all saw in high school chemistry... ...the nucleus in middle and electron spinning around it on little tracks like planets around sun Right-

00:09:14: the planetary model.

00:09:16: While quantum mechanics has shown that model is a bit over simplification its actually still best conceptual tool for understanding lasers.

00:09:23: Okay

00:09:23: so How does it work for this?

00:09:25: In the model, electrons don't just orbit anywhere they please.

00:09:28: They are restricted to specific fixed orbits which we call energy levels or energy states.

00:09:35: Meaning...they're quantized!

00:09:37: They can be on step one of a ladder but not hover in between steps

00:09:43: Exactly.

00:09:44: and nature is fundamentally lazy.

00:09:46: It always seeks lowest possible energy state

00:09:49: Relatable vary.

00:09:50: So under normal conditions, the electrons in an atom are hanging out in the lowest available orbit closest to the nucleus.

00:09:58: we call this The

00:10:00: Ground State.

00:10:02: But if you pump energy into that atom let's say you flash a really bright light at it or run an electrical current through.

00:10:12: When it absorbs energy, It gets excited and jumps up to a higher orbit.

00:10:17: A higher-energy state.

00:10:18: You jump sort of run in the ladder?

00:10:19: Yes!

00:10:20: But remember nature is lazy.

00:10:22: The electron doesn't want stay In that excited high-energy State...it's unstable Up there

00:10:27: Right..It takes effort To hold on.

00:10:28: Its like holding heavy weight Above your head.

00:10:30: Eventually you're gonna drop it.

00:10:32: So after tiny fraction Of second The electrons spontaneously drops Back down into ground state.

00:10:37: And Energy has to be conserved right?

00:10:39: You can't just disappear.

00:10:41: So when the electron drops back down, where does that extra energy go?

00:10:45: It releases it in the form of a photon—a tiny packet of light.

00:10:48: Ah!

00:10:49: That's what the light comes from —the electrons jumping down from the upper runs of the ladder.

00:10:53: Exactly... This process is called spontaneous emission…it happens all around us.

00:10:59: Like where?

00:11:00: Well, when a neon sign glows it's because electricity is forcing the electrons in the neon gas up to high energy state and they are spontaneously dropping back down spitting out photons of red light in random directions at random times.

00:11:14: Okay

00:11:15: so spontaneous emission gets us light but Disorganized like bulb light.

00:11:21: kids jumping in the pool randomly, right?

00:11:23: Because every atom and that neon tube is acting independently.

00:11:26: The electrons drop whenever they feel like it firing photons In every direction.

00:11:30: to get a laser we need synchronization.

00:11:32: We need something more than just spontaneous emission.

00:11:35: We

00:11:35: need the s-inlaser.

00:11:36: Stimulated emissions

00:11:38: Right.

00:11:38: so how does that work?

00:11:39: well for this we actually owe a massive debt.

00:11:41: Albert Einstein by

00:11:43: Einstein.

00:11:43: Seriously, I was associated him with relativity, EMC or black holes.

00:11:48: He worked on lasers.

00:11:50: Well he didn't build a laser but in nineteen seventeen...he published paper on the quantum theory of radiation where theoretically predicted the process of stimulated emission

00:11:59: In nineteen seventeen.

00:12:00: Yeah!

00:12:01: He mathematically proved that there had to be another way for an atom release a photon.

00:12:05: Okay so how does Einstein's version work?

00:12:08: Imagine you have an atom were electron is already in excited state.

00:12:12: It's sitting up there on the higher rung, hanging on getting ready to spontaneously drop.

00:12:17: Okay I'm picturing it.

00:12:19: now imagine a stray photon comes flying along and this photon happens to have the exact same amount of energy as

00:12:28: So an incoming photon approaches and already excited at them.

00:12:31: Right, when that specific incoming photon interacts with the excited electron it doesn't just bounce off It actually stimulates the electron forcing to drop into ground state right then in there.

00:12:42: It basically knocks it of a ladder.

00:12:43: Essentially yes!

00:12:45: And when that electron drops what does is do?

00:12:48: it emits a photon to shed its excess energy.

00:12:51: But wait,

00:12:51: now we have two photons?

00:12:52: We've got the original one that came flying in and then new one that the electron just spit out!

00:12:56: Exactly.

00:12:57: but here is the magic...the true miracle of quantum mechanics that makes lasers possible.

00:13:03: That new photon isn't exact perfect clone of the original photon.

00:13:08: Wait, a

00:13:09: perfect clone?

00:13:09: A perfect clone!

00:13:10: It has the exact same wavelength it travels in the exact Same direction and its waves are perfectly in phase with the original Photon.

00:13:18: Wow...It's as if The first Photon recruited a partner And now they're marching side-by-side In perfect lockstep.

00:13:24: That is wild.

00:13:26: So one Photon goes in hits an excited atom and two identical synchronized photons come out.

00:13:31: that is stimulated emission.

00:13:32: I see where this going now, because if you have those two clone photons marching along and they run into more excited atoms...

00:13:38: They stimulate the atoms to drop!

00:13:40: And NOW YOU HAVE FOUR PERFECT CLONE PHOTONS, THEN THOSE FOUR HIT FOUR MORE EXCITED ATOMS AND YOU HAVE EIGHT, THAN sixteen thirty-two sixty four.

00:13:48: That's

00:13:48: a chain reaction

00:13:49: An optical avalanche.

00:13:51: The marching band is recruiting more members at exponential speed and everyone perfectly in step.

00:13:56: So this is the light amplification part of the acronym.

00:13:59: You've got it, that avalanche of identical perfectly in phase photons Is the laser beam?

00:14:05: Okay That makes perfect sense but let me push back for a second here.

00:14:07: sure if stimulated emission is a fundamental law physics predicted by Einstein way Back in nineteen seventeen Why aren't lasers just happening naturally all The time?

00:14:18: why doesn't a campfire suddenly turn into a laser beam?

00:14:21: That is the crucial question, and it's why it took over forty years from Einstein's theory to the invention of The First Working Laser.

00:14:29: Forty

00:14:30: years!

00:14:30: Yeah...the roadblock has something called a population inversion.

00:14:34: Population

00:14:35: inversion?

00:14:36: Sounds like a demographic crisis.

00:14:38: It's a statistical problem really at the atomic level.

00:14:41: Remember when I said nature was lazy And most electrons want be in ground state.

00:14:45: Right They prefer the couch.

00:14:47: Well, if you shine light through a normal chunk of material... ...a photon is far more likely to hit an atom that's in the ground state.

00:14:54: When a photon hits the ground-state atom The atom just absorbs the photon.

00:14:59: Using its energy to jump up into the excited state The photon is destroyed.

00:15:04: Ah!

00:15:05: So Normal Matter acts like a sponge for Light not an amplifier?

00:15:09: The photons get eaten by the lazy atoms.

00:15:11: Exactly

00:15:12: Absorption dominates.

00:15:13: If you have one hundred atoms Ninety-nine of them are usually in the ground state, and maybe one is randomly excited.

00:15:19: So if you send a photon in it's going to get absorbed long before it finds that one excited atom... ...to trigger a stimulated emission?

00:15:26: The avalanche gets stopped before can even start!

00:15:29: To create a laser you have somehow invert that natural population.

00:15:32: Yes

00:15:33: You need to create an artificial situation where there're more atoms in the excited states than on the ground.

00:15:39: you need to push the majority of the electrons up the ladder and hold them there so that when a photon comes along, it encounters a target-rich environment for stimulated emission.

00:15:48: So...you basically have to pump a massive amount energy into this system all at once to get everyone excited simultaneously?

00:15:55: That's exactly!

00:15:56: The energy source is called THE PUMP.

00:15:59: It can be a massive flash of intense white light an electrical discharge or even chemical reactions

00:16:05: And its only job is create that inversion.

00:16:07: The pump's entire job is to violently force the atoms out of their lazy ground state into excited states, creating population inversion.

00:16:16: Okay so let us walk through an actual physical anatomy of a laser device then... We have the PUMP to provide energy!

00:16:23: What else do we actually need?

00:16:24: You NEED

00:16:24: TO GAIN MEDIUM!

00:16:25: This IS THE ACTUAL MATERIAL CONTAINING THE ATOMS YOU'RE GOING TO EXCITE!

00:16:28: It'S THE BATTLEGROUND WHERE THE AVELANCHE HAPPENED!

00:16:30: What kind of material works for a game medium?

00:16:33: can it be just

00:16:34: anything?!

00:16:35: In

00:16:36: theory, yes.

00:16:37: There's actually a famous joke among physicists that you can make a laser out of anything if you pump it hard enough including a block of Jell-O.

00:16:44: Wait really?

00:16:44: JELL-O Yeah and they have made edible lasers out of gelatin.

00:16:48: That is hilarious.

00:16:49: Edible Laser

00:16:50: It Is.

00:16:51: But practically You need material with very specific atomic structure that allows electrons to stay in slightly prolonged excited state which called a metastable

00:17:01: state.

00:17:02: Why does it need to be prolonged?

00:17:03: Because if they drop down too fast, you just can't build up the population inversion.

00:17:07: You can't get enough of them at the latter at that same time.

00:17:09: So they had to hang on that upper ladder rung Just a fraction of second longer than normal waiting for the avalanche to hit them

00:17:15: Exactly.

00:17:16: Common gain mediums include certain types of crystals like ruby or gases Like a mixture helium and neon Or semiconductors like gallium arsenide.

00:17:27: Okay so we have the game medium Let's say cylinder of ruby crystal And we have the pump maybe like a spiral-shaped flash tube wrapped around the ruby to blast it with light, right?

00:17:38: We pumped the energy in.

00:17:39: The electrons jump up.

00:17:40: way of population inversion...the Avalanche starts but wait!

00:17:45: What's the

00:17:45: problem?!

00:17:46: The atoms in the crystal are facing all different directions.

00:17:49: Right if a random spontaneous emission kicks off the avalanche weren't the photons just cascade sideways and shoot out the sides of the Ruby cylinder?

00:17:58: They absolutely will.

00:17:59: And that is exactly why the third crucial component of a laser's required, which is the optical cavity or the resonator?

00:18:06: The optical cavity!

00:18:07: What does that

00:18:08: mean?

00:18:08: Mirrors... It's essentially two mirrors placed at exactly opposite ends of the gain medium facing inward at each other.

00:18:15: Oh this is the hull-of-mirror trick.

00:18:17: Exactly

00:18:18: think about what happens you fire the pump The population aversion is achieved.

00:18:23: A few electrons spontaneously drop, firing photons in random directions.

00:18:28: and the ones that shoot out the sides of the ruby cylinder just leave this system and are lost

00:18:32: right.

00:18:32: they produce uh little bit of scattered light but nothing special.

00:18:36: But the photons that happen to be traveling perfectly straight down the central axis of the cylinder.

00:18:42: Those photons hit the mirror at the end and they bounce back, travel back through incredibly excited target-rich gain medium.

00:18:49: as

00:18:50: they travel trigger stimulated emission.

00:18:53: one photon becomes two to become four for become eight.

00:18:57: They reach opposite mirror, bounce back and sweep thru the medium again.

00:19:01: Eight becomes sixteen

00:19:04: thirty two sixty four bouncing back and forth, plowing through the excited atoms sweeping up more and more clone photons with every single pass.

00:19:14: It's a brilliant feedback loop because the mirrors are perfectly parallel.

00:19:19: only the photons that are traveling perfectly straight back-and-forth survive the journey.

00:19:23: And what happens to the others?

00:19:25: Any photons going at even a slight angle will eventually bounce off of edge be lost.

00:19:29: So the mirrors don't just amplify the light, they physically align it.

00:19:33: They filter out the chaotic directions and enforce a strict discipline of marching band.

00:19:38: Exactly!

00:19:39: The cavity geometry dictates extreme directional focus on laser beam.

00:19:44: Photons bounce back-and forth millions times in fraction of second building up an unimaginably intense perfectly coherent perfectly aligned wave of light between two mirrors.

00:19:55: But if they're just bouncing back and forth between two mirrors totally trapped inside the crystal, how do we get the laser beam out?

00:20:02: That is the final elegant trick.

00:20:05: The mirror at one end of the cavity is hundred percent reflective a perfect mirror.

00:20:10: but the mirror on the other hand is partially transmissive.

00:20:13: Partially

00:20:13: transmissives meaning what

00:20:15: it's about.

00:20:16: ninety nine percent reflective in one percent transparent.

00:20:18: Oh so that's tiny fraction of the avalanche leak through

00:20:22: exactly.

00:20:24: The avalanche builds up to such an intense level of trapped energy that the one percent Focused beam

00:20:35: that escaping one percent is the laser beam.

00:20:38: you see it.

00:20:39: Is?

00:20:39: That is staggering.

00:20:41: The beam they can cut through steel or shoot to the moon?

00:20:43: He's just a tiny leakage from an even more violent storm of light trapped inside the machine.

00:20:49: It's harnessing chaos and forcing it into perfect resonant order.

00:20:52: Okay, I really have to know who actually built the first one because Einstein came up with a math in nineteen seventeen.

00:20:59: But turning that math into mirrors and crystals sounds like an engineering nightmare.

00:21:03: It was a huge challenge.

00:21:05: Throughout the nineteen fifties, A lot of very brilliant physicists were racing to build an optical maser.

00:21:10: Maser being microwave amplification by stimulated emission of radiation.

00:21:15: So they started with microwaves?

00:21:16: Yeah Right!

00:21:17: They had figured out how do it with invisible microwaves but doing it with visible light which has much shorter faster wavelengths Was considered incredibly difficult.

00:21:27: Teams at Bell Labs and Columbia University were working furiously on it.

00:21:31: So who won the race?

00:21:32: An underdog named Theodore Mayman.

00:21:34: in nineteen sixty, he was working at Hughes Research Laboratories in California.

00:21:39: What's fascinating is that maymen defy the conventional wisdom of all the prominent physicists set the time.

00:21:45: How so like?

00:21:45: what did you do differently?

00:21:47: well the big academic teams.

00:21:48: we're mostly trying to use complex mixtures of gases To create the population inversion.

00:21:53: Mayman wanted to use a solid, crystal specifically synthetic pink ruby.

00:21:58: The Ruby

00:21:58: Laser?

00:21:58: Yes!

00:21:59: A lot of experts had published papers claiming that ruby was mathematically unsuitable for achieving population inversion.

00:22:05: They said the energy levels were wrong That it would absorb too much its own light.

00:22:09: But Maymon just ignored them.

00:22:11: He ran his own calculations and realized they are wrong.

00:22:14: he took small cylinder of synthetic ruby polished ends perfectly flat And silvered them as mirrors One fully-silvered, one partially-silvert.

00:22:23: So he built the optical cavity right onto the crystal itself?

00:22:27: Exactly!

00:22:28: Then for the pump... He didn't use some massive continuous electrical discharge—he looked at photography equipment.

00:22:34: Photography?

00:22:35: Yeah…He

00:22:36: took a high power spiral shaped Xenon flash tube —the kind used for high speed strobe photography and wrapped it around the ruby cylinder.

00:22:43: …So just hit with this massive split second burst of incredibly bright white

00:22:48: light?!

00:22:48: Right

00:22:49: On May, sixteenth, nineteen-sixty, Maimon charged up the capacitors fired the flash lamp and pulsed that intense white light into the ruby.

00:22:56: And it worked!

00:22:57: The chromium atoms in the rubie absorbed the light jumped to excited state.

00:23:01: as they dropped the stimulated emission bounced back & forth between silver dens

00:23:06: In.

00:23:06: what actually came

00:23:07: out?

00:23:07: A pulse of pure coherent deep red light...the first artificial laser beam in human history.

00:23:13: That must have been an incredible moment A totally new form of light that didn't exist anywhere in nature.

00:23:42: Ouch.

00:23:42: Yeah, so Maimon ended up publishing it in the British journal Nature where was a very brief roughly three hundred word article.

00:23:50: Wow!

00:23:51: The Three Hundred Word Article changed the world.

00:23:54: Maybe our six-word document from today's source isn't so crazy after all.

00:23:57: Revity

00:23:57: can contain multitudes right?

00:23:59: What is really humorous though is public and scientific reaction to laser in nineteen sixty.

00:24:05: How do they react?

00:24:06: Today?

00:24:06: we know lasers are backbone of modern civilization But when Mayman unveiled it, the press called it a death ray.

00:24:13: And the scientific community notoriously dubbed The Laser

00:24:18: A Solution Looking for a Problem.

00:24:21: That has to be one of the worst technological predictions of all time.

00:24:24: It's definitely up there.

00:24:26: They had invented a way to create perfect pure focused light but they hadn't yet imagined what they could use it For...it was beautiful piece of physics with no immediate commercial application.

00:24:38: It's hard to even wrap my head around that because today lasers are literally everywhere.

00:24:43: Let's transition into how they're actually used, How do we get from Theodore Mamon's pulsing red ruby To like the barcode scanner at my grocery store or the fiber optic internet cables under the ocean?

00:24:56: To understand applications We have look at how laser technology evolved away from just solid crystals!

00:25:02: The Ruby Laser was a pulsed laser.

00:25:04: it fired in short powerful bursts because the flash tube had to recharge and The ruby would get too hot if you tried to run it continuously,

00:25:10: right?

00:25:11: If you pump too much energy into a crystal constantly.

00:25:13: It's just gonna shatter

00:25:14: or melt exactly.

00:25:15: So the next major breakthrough was the gas laser specifically the helium neon laser Invented very shortly after Maman's Ruby laser by Ali Javan at Bell Labs.

00:25:25: How is a gas laser different?

00:25:26: instead of a solid crystal the game medium Is a glass tube filled with a mixture of helium and neon gases.

00:25:34: And instead of a flash lamp, the pump is a continuous electrical current running through the gas.

00:25:39: Much like a neon sign.

00:25:40: Okay I can picture that The

00:25:42: electrical current excites the helium atoms which then crash into the neon atoms transferring their energy and pushing the neon in to that crucial metastable excited state.

00:25:51: So the population inversion happens on the gas?

00:25:53: Yes!

00:25:54: Because it's a gas It doesn't overheat.

00:25:56: the same way a crystal does.

00:25:58: The helium neon laser could run continuously.

00:26:02: It produced a steady unbroken beam of red light.

00:26:05: This is the classic Red Laser Beam you saw in grocery store.

00:26:08: barcode scanners for decades.

00:26:10: Okay, bar code scanners that's a perfect example Of a problem the laser eventually solved.

00:26:15: how exactly does a laser read?

00:26:16: A barcode?

00:26:17: because to me it just looks like a solid red line flashing across my cereal box.

00:26:21: It relies entirely on the lasers coherence and tight focus.

00:26:25: A barcode is a series of black lines and white spaces.

00:26:29: A normal light bulb would just cast a wide wash-of-light over the whole bar code, And it'd be very hard for a sensor to distinguish sharp edges from the line.

00:26:36: It's a blurry reflection!

00:26:38: Right... But a laser can focus down into an incredibly tight spot—a fraction of a millimeter wide.

00:26:43: The scanner uses rotating mirrors to quickly sweep that tiny laser dot across the barcode.

00:26:49: Ah, so it's not actually a solid line of light at all.

00:26:51: It is just single dot moving incredibly fast.

00:26:54: Exactly!

00:26:55: As the tiny dots sweeps across... ...it hits white spaces and reflects strongly back into a light sensor in scanner.

00:27:02: When its hit black line The Black ink absorbs red laser light And reflection drops to zero.

00:27:08: So the sensors are reading a rapid fire sequence Of bright reflection No reflection Bright reflection Which computer translates into binary code Ones & zeros.

00:27:18: perfectly synchronized binary data enabled solely by the fact that the laser light doesn't spread out and blur the edges?

00:27:24: That is brilliant.

00:27:25: It's using light as a highly precise physical probe, which actually reminds me of another massive application CDs DVDs And Blu-ray discs.

00:27:35: Oh absolutely

00:27:36: completely revolutionised how we store information in concerned media.

00:27:41: I know there's laser on my old disc man but How does light read music?

00:27:44: This is where we get into semiconductor lasers or laser diodes.

00:27:48: These are the most common lasers on earth today.

00:27:51: They don't use gas tubes, or ruby crystals.

00:27:54: they Use microscopic chips of semiconductor material like silicon or gallium arsenide layered together

00:28:00: Like a computer chip.

00:28:01: Very similar By creating a junction between two different types of semiconductor materials One with extra electrons and one with deficit of electrons called holes.

00:28:10: You can pass tiny electrical current through the chip

00:28:13: and what does that do?

00:28:14: The electrons in holes recombine at the junction, dropping to a lower energy state and emitting photons.

00:28:19: And if you polish the microscopic edges of the chip to act as mirrors...

00:28:23: You get an optical cavity on a microscopic scale!

00:28:25: ...you get a laser beam coming out of a speck of material the size of grain of salt.

00:28:30: That is insane A microscopic marching band.

00:28:33: And because they are so small and require little power They could be put inside consumer electronics.

00:28:39: So let's look at a CD.

00:28:41: The surface of a seedy is not smooth.

00:28:44: If you looked at it under a microscope, It's long continuous spiral track of microscopic bumps and flat areas.

00:28:52: We call them pits & lands

00:28:53: For like a microscopic vinyl record.

00:28:55: but instead of physical needle tracing the grooves its laser

00:28:59: Exactly!

00:29:00: The Laser diode shines focus beam onto the spinning disk.

00:29:03: When the laser hits a flat land light reflects perfectly straight back into sensor

00:29:08: Makes sense

00:29:09: But when it hits a pit, the depth of the pit is engineered to be exactly one-quarter the wavelength of the laser light.

00:29:15: One quarter the wavelength?

00:29:16: Why's that specific math

00:29:18: important?".

00:29:18: Because of interference!

00:29:20: When the light hits the pit... ...the light has to travel slightly further down to bottom and back up.

00:29:25: The total extra distance at travels is one half of a wave length A quarter down....a quarterback.

00:29:30: So the light bouncing out of this pit Is now exactly half a wavelength out of sync with the light balancing off flat surface next to it.

00:29:37: Yes And what happens when the peak of one wave aligns with a trough of another wave?

00:29:42: They

00:29:42: cancel each other out, just like kids in the Wave Pool jumping perfectly out-of-sync to flatten water.

00:29:48: It's called destructive interference.

00:29:50: So as the CD spins The laser reflects brightly off lands But it hits edge of pit.

00:29:56: Interference causes light intensity to drop sharply.

00:30:00: The sensor reads these rapid changes in light intensity As ones and zeros digital audio.

00:30:06: That is an incredibly elegant use of quantum mechanics just to listen to the Backstreet Boys in nineteen ninety nine.

00:30:12: It really is and The evolution of that technology shows why wavelength matters so much.

00:30:17: CD's used infrared lasers which have relatively long wavelengths Which

00:30:21: means the pits had to be relatively large So the laser could actually feel them

00:30:24: right.

00:30:25: a laser can't focus on something smaller than its own wavelength.

00:30:28: it would Be like trying To read Braille with an oven mitt, so a cd Can hold about seven hundred megabytes Of data.

00:30:34: But in the nineteen nineties, scientists figured out how to make laser diodes that emitted red light which has a shorter wavelength than infrared.

00:30:42: And shorter wave length means smaller sharper optical needle Exactly!

00:30:46: With a Red Laser they could make the pits smaller and pack the spiral track much tighter.

00:30:51: The CD became DVD holding four point seven gigabytes.

00:30:54: A massive jump in storage just by changing color of lights.

00:30:58: And

00:30:58: Holy Grail was blue laser.

00:31:00: Blue light has a much shorter wavelength than red, but building a blue laser diode was notoriously difficult.

00:31:05: It took decades of material science to figure out how to grow gallium nitride crystals perfectly enough to laze in the blue spectrum.

00:31:13: Shuji Nakamura won The Nobel Prize for finally cracking it in the nineteen nineties.

00:31:17: and the blue laser means even smaller pits microscopic

00:31:21: pits that allowed for the Blu-ray disc which holds twenty five to fifty gigabytes all driven by the quest for shorter and shorter curcumin wavelengths.

00:31:30: It's fascinating how the physical property of the light wave dictates the limit of technology.

00:31:34: But data storage on disks is almost obsolete now, right?

00:31:37: We stream everything!

00:31:39: Which brings us to the internet—none of this streaming works without lasers does it?

00:31:43: Fiberoptics.

00:31:44: FiberOptics is arguably the most vital application for laser in human history —the entire backbone of global Internet built on

00:31:52: it.

00:31:52: How did that work?

00:31:54: I know fiber optics are basically just really long, thin tubes of glass.

00:31:58: How does shooting a laser down-a-glass tube connect me to a server in Japan?

00:32:02: It works on the principle called total internal reflection.

00:32:05: If you shine a light into a pane of glass at shallow enough angle The light doesn't pass through the glass.

00:32:11: it reflects off inside surface as if were perfect mirror.

00:32:15: Oh, like when you were underwater in a swimming pool and look up the surface from sharp angle it looks like a silver mirror.

00:32:20: Exactly!

00:32:21: An optical fiber is a strand of glass incredibly pure and incredibly thin about the diameter human hair.

00:32:28: You take an infrared laser diode and pulse on-and off billions per second

00:32:33: Translating internet data emails video calls into flashes of light.

00:32:38: Those flashes of coherent light enter the glass fiber.

00:32:41: Because the light is coherent and directional, it travels in a tight beam.

00:32:45: When hit's curve of fiber hits at shallow angle perfectly reflecting off inside walls bouncing its way down cable

00:32:54: speed.

00:32:55: because glass so pure far purer than window glass dozens of miles before it starts to fade and needs to be amplified.

00:33:04: We have massive bundles of these glass hairs wrapped in steel cables laid across the bottom of the ocean floors connecting the continents, millions of lasers flashing billions times a second carrying all the data of

00:33:16: humanity.".

00:33:16: It's mind-boggling.

00:33:18: we took Mayman's pulsing red crystal and turned into an nervous system for the entire planet but reading or transmitting data.

00:33:31: What about when lasers are used as brute force tools?

00:33:34: Like what?

00:33:35: Well, I've seen videos of lasers cutting through thick sheets of steel in car factories.

00:33:39: How does light slice metal?

00:33:41: that requires a completely different scale of power.

00:33:44: For industrial cutting, we often use carbon dioxide or CO-II lasers.

00:33:48: Or high power solid state fiber lasers.

00:33:51: A

00:33:51: carbon dioxide laser?

00:33:52: Yes!

00:33:52: The gain medium is a mixture of gases primarily CO-I.

00:33:56: When pumped with electricity the CO- II molecules vibrate and achieve population inversion emitting an incredibly intense beam of infrared light.

00:34:06: This isn't milliwatts of power like a laser pointer.

00:34:08: We are talking kilowatts of continuous optical power.

00:34:11: Wow, so when you focus a kilowatt of infrared light onto a sheet of steel What actually happens at the atomic level is just melting this deal?

00:34:19: It's melting it and often vaporizing it.

00:34:21: The laser is focused by lens down to a pinpoint on the surface of the metal.

00:34:25: because the light Is coherent all that energy is concentrated into an infinitely small area.

00:34:31: The metal absorbs the intense infrared radiation.

00:34:34: The atoms in steel begin to vibrate violently, and

00:34:37: heat is just atomic vibration.

00:34:39: Exactly!

00:34:40: The steel instantly melts, and the center of focal point actually boils into a vapor.

00:34:50: Usually there is high pressure jet of assist gas like oxygen or nitrogen blowing coaxially with the laser beam.

00:34:57: So it's pushing metal out of

00:34:58: way.

00:34:58: This gas physically blows molten metal from cut zone leaving perfectly clean razor sharp edge.

00:35:05: It essentially light saber but industrialized

00:35:08: It is!

00:35:09: Its touchless machining.

00:35:10: There's no saw blade to dull, No physical pressure to warp the metal.

00:35:14: You can program a computer To steer the beam and cut incredibly intricate shapes Out of titanium steel or Kevlar With microscopic precision.

00:35:23: That precision makes me think Of medicine Because we don't just Cut steel with lasers We cut human tissue Which sounds terrifying When you consider what you Just described with boiling metal.

00:35:32: How do use laser on someone's eye Without blinding them?

00:35:35: Medical lasers are a perfect example of tuning the tool to the tissue.

00:35:39: You wouldn't use a continuous high-power CO₂ laser for delicate eye surgery, it causes way too much thermal damage to surrounding cells.

00:35:46: The heat conducts outward and burns the tissue

00:35:49: Right.

00:35:50: you definitely don't want burn scar on your cornea.

00:35:52: So something like LASIK Eye Surgery where we wanna reshape the cornea.

00:35:56: to fix nearsightedness We used an excimer laser Excimer?

00:36:00: What does that mean?

00:36:01: It stands for excited dimer.

00:36:03: It uses a mixture of reactive gases like argon and fluorine, which only bond together when they are electrically excited.

00:36:10: When they drop back down to the ground state The molecule falls apart and emits a photon in the ultraviolet spectrum.

00:36:16: Ultraviolet light not infrared Like that cutting lasers.

00:36:20: Why is that distinction important?

00:36:22: Because ultraviolets light has very short wavelength an incredibly high photon energy.

00:36:28: it interacts with organic tissue In a fundamentally different way than infrared.

00:36:33: Infrared heats things up by making molecules vibrate.

00:36:36: Ultraviolet photons carry so much raw energy that when they hit a biological molecule, They don't heat it!

00:36:42: They literally shatter the carbon-carbon molecular bonds

00:36:46: that break the chemistry of this cell itself.

00:36:48: Exactly, it's a process called photoablation.

00:36:51: The laser pulse hits the surface of the cornea... ...the molecular bonds snap and the microscopic layer of tissue instantly turns into gas and floats away.

00:36:59: There is almost zero heat transfer to cells underneath.

00:37:03: So its cold cut.

00:37:04: A cold perfectly precise cut The eczema laser pulses hundreds of times a second, vaporizing microscopic layers of cells one by one slowly sculpting the curvature of the cornea until the eye can focus perfectly.

00:37:16: The precision is less than a fraction human hair.

00:37:19: It's astonishing!

00:37:20: We're using quantum mechanics of stimulated emission to perform molecular level surgery on

00:37:26: And we are continually finding new ways to apply this precision.

00:37:30: The future of lasers is moving into realms that honestly sound like science fiction.

00:37:34: Oh, give me a preview.

00:37:35: where's the technology going next?

00:37:36: We've got communications cutting surgery.

00:37:40: what's the next frontier?

00:37:41: one major frontier is nuclear fusion-the quest for clean limitless energy

00:37:46: using lasers to create a star on earth.

00:37:48: essentially yes.

00:37:49: at the national ignition facility in california they use.

00:37:56: It's a building the size of three football fields.

00:37:59: They take single, weak infrared laser pulse and split it into a hundred ninety-two separate beams.

00:38:05: they run those beams through miles of glass amplifiers boosting their energy exponentially creating

00:38:11: massive synchronized army of photons

00:38:13: that convert these beans in to ultraviolet light focus.

00:38:16: all one hundred ninety two beam simultaneously onto target sizes peppercorn.

00:38:21: Inside that peppercorn is frozen hydrogen fuel.

00:38:23: What happens when a hundred and ninety two stadium-sized leasers hit at peppercorns exactly the same time?

00:38:28: The outer surface of the capsule instantly explodes outward.

00:38:32: According to Newton's third law, every action has an equal and opposite reaction... ...the rest of the capsules violently driven inward!

00:38:39: The implosion compresses the Hydrogen field to densities one hundred times greater than lead heating it millions of degrees.

00:38:47: The exact conditions inside the core The

00:38:49: hydrogen atoms are forced together, they fuse into helium and release a massive burst of clean nuclear energy.

00:38:56: They recently achieved ignition where the reaction produced more energy than the lasers pumped in to it.

00:39:02: It's crucial first step toward limitless clean energy And relies entirely on perfect synchronization of laser light.

00:39:08: That is just incredible.

00:39:10: this scale from peppercorn to three football fields of amplifiers

00:39:14: On other end of spectrum, lasers driving future autonomous vehicles LightR technology.

00:39:20: LightR, like radar but with light

00:39:22: Exactly!

00:39:23: Light detection and ranging.

00:39:25: Self-driving cars have LiDAR units spinning on their roofs.

00:39:29: They shoot out millions of invisible infrared laser pulses every second in a three hundred sixty degree arc.

00:39:36: Those pulses hit cars pedestrians trees and road signs And bounce back to a sensor.

00:39:41: Because light travels at a constant speed the computer can calculate exactly how long the pulse took to bounce back.

00:39:47: Right.

00:39:48: It measures the time of flight...of the photon.

00:39:50: By doing this millions times a second, The car builds perfect real-time three D map around it with millimeter precision!

00:39:59: It sees the world purely through laser reflection.

00:40:04: And finally space communication.

00:40:06: Right now we communicate satellites and rovers using radio waves But radio waves spread out and carry relatively low amounts data.

00:40:13: NASA is aggressively testing optical communications, using lasers to transmit data across the solar system.

00:40:19: Because the laser beam stays tightly focused even over millions of miles?

00:40:23: Yes!

00:40:24: A laser beam fired from Mars would spread out a little bit by the time it reaches Earth but its vastly more focus than a radio wave.

00:40:31: and because the frequency of light so much higher then radio you can pack exponentially more data into a laser beam.

00:40:38: We will be able to stream high-definition video live from astronauts on Mars directly back using interplanetary fiber optics without the

00:40:47: fiber.

00:40:47: Just a coherent beam of focans cutting through the vacuum of space.

00:40:51: It's along way from red light blinking in a ruby crystal.

00:40:53: in nineteen sixty

00:40:55: it really is.

00:40:55: we've gone from Niels Bohr atomic ladders to Einstein stimulated emission, To Theodore Mamons ruby flash tube to fiber optic internet molecular eye surgery and now Interplanetari communication.

00:41:08: And all of it, literally ALL OF IT hinges on the simple quantum mechanic trick of making one photon clone itself perfectly.

00:41:14: The mastery of coherence... taking the chaotic nature in the universe and forcing into perfect synchronized order.

00:41:20: Which

00:41:21: honestly brings me back to a document sitting at our desk between us-the absolute minimalist joke that you sent for this deep dive excerpts from how lasers work.

00:41:32: How lasers work

00:41:33: is a very productive provocation.

00:41:35: I have to say

00:41:35: it really was.

00:41:37: we could've looked at this six word document laughed and thrown in the trash.

00:41:41: We could spend an hour trying to analyze the font or the margins But instead, we took the bait.

00:41:46: The document pointed out a gap And we spent his time filling It.

00:41:50: built the rest of the excerpt.

00:41:51: it highlights something fundamental about why?

00:41:53: We bother trying to learn these dense subjects in the first place.

00:41:57: The hunger for knowledge is activated by the realization of ignorance.

00:42:01: Exactly!

00:42:03: Before we wrap up, I want to leave you with one final thought... We spent this whole time diving into the staggering mechanics of quantum physics and optical engineering but a deep dive has come close…

00:42:13: And the mechanism of text remains?

00:42:15: Yes So here's something for you all to mull over as go about your day.

00:42:20: Consider the power of a title standing completely on its own.

00:42:24: How does the mirror isolated phrase, how lasers work instantly trigger your brain to realize there's a gap in your own knowledge?

00:42:31: The title acts as a mirror reflecting your own lack of understanding back at you.

00:42:36: Perhaps the true value of a source that provides absolutely no answers is that it compels you independently and freely To seek out the rest of the excerpts on your own.

00:42:44: It forces you to build the cathedral yourself.

00:42:46: So until next time keep looking for those missing pages Keep interrogating the silences And keep exploring them.

00:42:51: app Even when paper completely blank.

00:42:54: We will catch you on the next deep dive.