Latest / Talking Science / Lasers – Light in Lockstep

Transcript

Lasers – Light in Lockstep · Talking Science

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Right now, I mean literally right this second,
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beneath the Atlantic Ocean, there are these pulses
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of invisible light firing millions of times per
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second. Yeah, racing through these hair -thin
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glass cables just to bring this very audio to
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your ears. Exactly. And without degrading at
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all, we just treat it as a mundane utility, you
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know? Like, we rely on the exact same technology
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to scan our groceries, entertain our cats, and
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perform delicate eye surgery. Oh, totally. And
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what's wild is that what we treat as this simple,
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everyday tool actually relies on a bizarre, mind
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-bending quirk of quantum physics. Right. Something
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Albert Einstein predicted over a century ago.
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Exactly. So today our mission for this deep dive
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is to take a word you toss around casually every
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single day and unpack the beautiful science hiding
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right inside it. That word is laser. We stick
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it on razors to sound futuristic, but we easily
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forget it's actually an acronym. Yeah, you really
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do. OK, let's unpack this. It stands for light
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amplification by. Stimulated emission of radiation.
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Which is quite the mouthful. It really is. I
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mean, the moment you string those words together,
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it sounds incredibly intimidating, like the title
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of a graduate level physics thesis. Yeah. But
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we are going to walk through exactly what that
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means at an unhurried, comfortable pace. You
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do not need any kind of science or engineering
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background to follow along today. By the time
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we finish, the mechanics behind that acronym
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will make complete. intuitive sense well i am
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definitely holding you to that yeah because light
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amplification by stimulated emission of radiation
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feels like a lot to chew on it does yeah so logically
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to understand why we would ever need to amplify
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light through this specific process, we probably
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first need to understand the default state of
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things, right? Right. The everyday light around
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us, like the light bouncing off the walls right
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now, is actually quite messy, isn't it? Oh, it
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is completely chaotic. We really need to look
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at the anatomy of ordinary light to appreciate
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the contrast. OK. Because when you look at the
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light radiating from, say, a standard lamp in
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your room or just the sunlight streaming through
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your window, your eyes perceive it as smooth,
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continuous and white. Yeah, it looks perfectly
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clean. But on a physical level, it is a tremendous
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jumble. Ordinary white light contains many different
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colors all mixed together. Like a big soup. Exactly.
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And when physicists talk about those different
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colors, what they're actually describing are
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different wavelengths. Light travels in tiny
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waves, you know, cresting and dipping. Right.
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And a wavelength is literally just the physical
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distance between the peaks of those microscopic
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waves. So our brains just interpret those different
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physical distances between the wave crests as
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different colors. That's it. Yeah. Like red has
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a wider gap between peaks. Blue has a shorter
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gap. And the white light from my lamp is just
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a massive mashup of all those different gaps
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and colors smashed together. That is the perfect
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way to look at it. You have all these different
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wavelengths layered over each other. Okay, got
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it. Furthermore, those waves are completely out
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of step. Like one wave is cresting while another
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is dipping at total random. Oh, so there's no
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rhythm to it. None at all. And to make matters
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even more disorganized, the light is spraying
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out in every conceivable direction. It spreads
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out from the bulb, fanning wider and wider, which
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means the energy weakens drastically the further
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it travels. It's like being in a noisy milling
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crowd at a train station during rush hour. Yes.
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There is a ton of collective energy in that room,
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but there is zero coordination. Everyone's walking
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in different directions at different speeds,
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just bumping into each other to catch different
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trains. The energy is totally diffuse. Exactly.
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And what's fascinating here is that if ordinary
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light is your chaotic train station crowd, laser
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light is a highly disciplined army marching in
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perfect synchronized formation. Oh, wow. A laser
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strips away all that chaos because it possesses
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three very specific unique qualities. And what
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are those? First, instead of that mashup of different
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colors, a laser is monochromatic. Mono meaning
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one. Right. It is a single, pure color. Just
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one specific wavelength. So we've cleared out
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the train station. We only have one specific
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type of person walking at one specific speed.
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Second, all of those light waves are perfectly
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in step with one another. They crest and dip
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in absolute lockstep. Okay. The scientific term
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for the state is being coherent. When light is
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coherent, the peaks of the waves align perfectly,
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reinforcing each other rather than canceling
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each other out. Coherent, meaning they are moving
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as one unified, synchronized entity. You've got
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it. And third, because the light is coherent
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and single -colored, it travels in a tight, extremely
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narrow beam that barely spreads. Unlike the lamp
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spring everywhere. Exactly. A normal flashlight
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beam spreads out and fades into shadows after
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a few dozen feet. A specialized laser beam, though,
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can maintain a tight enough focus to shoot across
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an entire room, or even carry its energy all
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the way to reflectors placed on the moon by Apollo
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astronauts. Wait, really? To the moon. Yeah.
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Without fanning out into uselessness, that marching
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army coordination is the entire secret to its
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power. But organizing a chaotic crowd of millions
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of people into a disciplined marching army sounds
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like a complete logistical nightmare. It really
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does. If light naturally wants to burst out in
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random directions at random wavelengths, what
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physical force could possibly compel trillions
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of light waves to suddenly align in... Perfect
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lockstep. Well, to find that force, we have to
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travel back to 1917. Okay. Einstein's era. Yep.
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Long before anyone had the technology to build
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a physical laser, Albert Einstein was working
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out the theoretical physics of how light interacts
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with matter. Right. He is the one who figured
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out the stimulated emission part of our acronym,
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the S and E in laser. Okay. I was wondering when
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we get to the acronym. So to follow Einstein's
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logic, we need to understand a foundational rule
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about how atoms work. behave. An atom can absorb
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and hold energy, but it cannot just hold any
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random amount. It can only hold energy at very
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specific fixed levels. I usually picture that
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like the rungs on a ladder. Oh, that's a great
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visual. Like you can stand firmly on the first
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rung or you can climb up to the second rung,
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but you can't just, you know, hover in the empty
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air between the rungs. The energy levels are
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discrete. That analogy works perfectly for the
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energy states. When an atom absorbs some form
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of outside energy like heat or light, One of
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its electrons makes a quantum leap up to a higher
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rung on that ladder. Okay, makes sense. When
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the atom is sitting in that elevated state, physicists
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call it an excited atom. So excited just means
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the atom is energized. It absorbed some juice
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from its environment and bumped up a rung. Exactly.
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But atoms are inherently lazy. Really? Yeah.
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They do not want to hold on to that extra energy
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forever. Nature always prefers stability and
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balance. So eventually, that excited atom is
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going to drop back down to its original rung.
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And it has to put that energy somewhere. Right.
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And when it falls, it has to get rid of that
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borrowed energy. It releases it by spitting out
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a tiny single pack. packet of light, which is
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known as a photon. A photon. Okay, so the atom
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gets excited, jumps up the ladder, eventually
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gets tired of holding the energy, drops back
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down, and spits out a photon of light to balance
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its ledger. That's exactly it. And this process
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is happening all around us all the time. It's
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called spontaneous emission. Okay, spontaneous.
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It is the exact mechanism making a neon sign
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glow on a diner window. Electricity excites the
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neon atoms, and then they drop back down, spontaneously
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emitting photons. But they do this whenever they
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please. Right. Randomly, in all directions. Hold
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on. Let me push back on this. Sure. If the atom
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naturally wants to drop to a lower energy state
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anyway, and it's doing so randomly, why wouldn't
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hitting it with more energy just add to the chaos?
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If the goal is a disciplined army, how did Einstein
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use these totally random, unpredictable atomic
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drops to create perfect order? That is the exact
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paradox Einstein solved. He theorized that spontaneous
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random emission isn't the only way an atom can
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release its photon. Oh. There is a second, highly
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coordinated method. Think about a pair of acoustic
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tuning forks. Okay. If you have two tuning forks
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pitched to the exact same note and you strike
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the first one so it rings out, bringing it near
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the second one will cause the second fork to
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start vibrating and ringing in perfect sympathy.
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Right. The sound waves from the first stimulate
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the second. Because they share the exact same
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frequency, the energy transfers perfectly. Yeah,
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I've seen that in music class. Einstein realized
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atoms operate on a similar principle of resonance.
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If an atom is already sitting up on that higher
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rung -like, it's already excited. And a photon
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with the exact right energy happens to pass by,
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that passing photon acts like the struck tuning
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fork. Oh, wow. It literally tickles the excited
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atom, stimulating it into dropping down the ladder
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early. It forces the atom to give up its stored
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energy right at that exact moment. Yes. And crucially,
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because it was triggered by resonance, the new
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photon that the atom emits isn't random. It comes
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out as a flawless, perfect twin of the passing
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photon that triggered it. A twin. Same exact
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color traveling in the exact same direction and
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cresting and dipping perfectly in step. Unbelievable.
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This is stimulated emission. The passing photon
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stimulated the atom to emit its own matching
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photon. Here's where it gets really interesting,
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though. Yeah. Because you started with one. passing
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photon, but now you have two identical photons
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traveling side by side. Totally coherent. Exactly.
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And if those two twins pass by two other excited
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atoms, they stimulate those atoms to drop their
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energy. Now you have four identical coherent
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photons. Right. Those four sweep past more atoms
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and become eight and eight become 16. It's a
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cascading domino effect. Right. Which brings
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us to the amplification part of the acronym,
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right? The A in laser. You got it. You are amplifying
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the amount of light. By triggering this avalanche
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of stimulated twins, you're building that massive
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flood of photons that are all marching in perfect
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lockstep. You are amplifying light by the stimulated
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emission of radiation. And the word radiation
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in this context just refers to the radiating
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light waves. Laser. Laser. The beautiful mechanics
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of the acronym are fully revealed. That is so
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cool. However, understanding the physics on a
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chalkboard is very different from building a
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device that can trap light and atoms and actually
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force them to do this. Yeah, I can imagine. Einstein
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published this math in 1917, but it took over
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four decades for engineers to construct a physical
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chamber that could execute the theory. Right,
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because knowing how the dominoes fall is great,
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but building a track that forces them to fall
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infinitely. without losing momentum, that is
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an entirely different engineering challenge.
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Totally. How did they finally build the machine?
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in the real world? Well, to manufacture a working
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laser beam, you have to execute two major physical
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tricks. First, you need a substantial population
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of atoms and you need the vast majority of them
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to be excited and sitting on that top rung ready
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to be stimulated. Physicists refer to this unnatural
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state as a population inversion. A population
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inversion. I assume that's because in a normal
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population of atoms, most are just chilling at
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the bottom rung. Right. They prefer being lazy.
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So you have to invert the natural order so the
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majority are holding extra energy, creating this
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target -rich environment for a passing photon
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to stimulate. Exactly. And to force that inversion,
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you have to pump an immense amount of energy
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into whatever material you are using. You might
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blast it with high -voltage electricity or bombard
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it with a tremendously bright, intense flash
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of ordinary light. Just giving them a ton of
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juice. Yes. This aggressive pumping shoves the
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atoms up the ladder. That achieves your inversion.
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Okay, what's the second trick? The second trick
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is managing the photons once they start replicating.
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You need to give them a space to build up their
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numbers exponentially. You accomplish this by
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placing two precisely aligned mirrors facing
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each other, sandwiching your excited atoms in
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the middle. So it functions almost like an optical
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echo chamber. Oh, that's a fantastic description.
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Instead of a sound wave bouncing off canyon walls
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and slowly dying out, the light is trapped. It
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bounces back and forth between those two mirrors,
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sweeping through the population of excited atoms
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over and over. With every single pass, it triggers
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more and more twins, amplifying the intensity
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until you have this overwhelming, dense concentration
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of coherent light. An optical echo chamber is
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exactly it. The light sweeps back and forth,
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organizing more and more atoms into the marching
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army. But a perfectly sealed chamber of light
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is useless to us if we can't extract the beam.
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Oh, right. It would just stay trapped forever.
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Exactly. So the final elegant detail of the machine
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involved those mirrors. One mirror is 100 % reflective,
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but the mirror on the opposite end is engineered
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to be slightly less than perfect. It's intentionally
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flawed so it doesn't reflect everything. Right.
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It might reflect, say, 99 % of the light, but
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it allows a tiny 1 % fraction to leak through
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the glass. Ah. as that intense perfectly coordinated
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avalanche of photons aggressively bounces back
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and forth a thin sustained sliver of it escapes
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through that imperfect mirror wow and that highly
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disciplined stream of pure coherent light is
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the laser beam. Which brings us to the actual
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physical birth of the laser. Yeah. The person
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who finally solved this engineering puzzle and
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built the first working prototype was an American
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physicist named Theodore Maiman back in 1960.
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Right, and Theodore Maiman constructed his device
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by housing his atoms in a small, solid, cylindrical
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rod of synthetic ruby. Ruby? Yeah. He wrapped
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a coiled flash lamp around the ruby rod. When
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he fired the lamp, the intense burst of light
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pumped the ruby atoms into that population inversion.
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Okay, the first... trick. He had silvered the
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ends of the ruby to act as his mirrors. And out
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of one end emerged the world's first concentrated
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beam of pure red laser light. It's just a gorgeous
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visual, isn't it? This glowing synthetic ruby
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crystal firing a perfectly straight beam of crimson
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light across a laboratory. It really is. But
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what I find so incredibly funny about this milestone
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is the broader historical reaction to it at the
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time. Oh, yeah. If we connect this to the bigger
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picture of mid -century science, the reaction
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is deeply ironic. Yeah. When Mayman unveiled
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this working laser to the press and the scientific
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community in 1960, they were profoundly underwhelmed.
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There was actually a running joke at the time
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that Mayman's laser was a solution looking for
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a problem. Meaning, congratulations on your neat
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little glowing ruby, Ted, but what on earth is
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anyone supposed to actually do with this? Exactly.
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It was viewed as a highly sophisticated parlor
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trick, like an elegant demonstration of quantum
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physics that had absolutely no practical utility
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for everyday human life. Which has to rank as
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one of the most spectacularly short -sighted
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judgments in the history of technology. Oh, without
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a doubt. They had absolutely no idea that this
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useless gadget was going to fundamentally rewrite
15:02
modern civilization. The ubiquity of the laser
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today really stems from a crucial realization
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engineers made shortly after Mayman's success.
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Which was? The acronym laser only requires atoms.
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It dictates nothing about ruby atoms specifically.
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You can achieve a population inversion in countless
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different materials. For example, instead of
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a solid crystal, you can use a tube of mixed
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gases. For decades, the bright red beam scanning
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barcodes at your local supermarket checkout was
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generated by a helium neon gas laser. The classic
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glass window at the grocery counter. We all remember
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that glow. But the true explosion in how we use
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lasers came when we figured out how to shrink
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them down, right? Yes, the revolution really
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arrived with semiconductor lasers, commonly called
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laser diodes. Instead of giant glass tubes or
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synthetic crystals requiring massive flash lamps,
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engineers figured out how to create the echo
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chamber inside a microscopic chip of silicon
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-like material. That's wild. These laser diodes
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are roughly the size of a single grain of rice.
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Furthermore, they don't need external light to
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pump the atoms. They generate laser light directly
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from a tiny trickle of electrical current. So
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a component the size of a grain of rice that
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costs pennies to manufacture is what allows a
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video game console to read the microscopic bumps
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on a disc or a computer mouse to track movement
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across a desk. Yes. But the impact goes so far
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beyond consumer electronics. Let's talk about
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the internet. You mentioned fiber optic cables
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earlier. Why is a laser absolutely necessary
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to send internet data across an ocean? Why couldn't
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we just pulse a really bright LED light down
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a glass tube? Because if you pumped ordinary
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light down a transatlantic cable, it would fail
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completely. Remember our chaotic train station
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crowd? Oh, right. Ordinary light is messy. It
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spreads out, it bounces at random angles, and
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the different wavelengths travel at slightly
16:55
different speeds through glass. If you pulsed
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a complex internet signal using ordinary light,
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the data would smear and degrade into absolute
17:02
static before it traveled even a few miles. The
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signal would blur together because the light
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waves aren't coherent. Exactly. But laser light
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is the disciplined army. It is a single wavelength,
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entirely coherent, traveling in a tight beam.
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Right. When we pulse laser light down a hair
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-thin fiber optic cable, it bounces cleanly along
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the interior of the glass through a process called
17:24
total internal reflection. The waves stay tightly
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packed and perfectly synchronized. Wow. That
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purity is the only reason we can shoot terabytes
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of data from New York to London in milliseconds
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without the information degrading. That cohesion
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is also what makes lasers. is so devastatingly
17:42
effective in heavy industry and medicine, isn't
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it? Oh, absolutely. Because the light waves don't
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spread out, you can run a laser through a magnifying
17:48
lens and focus all of that energy down to a microscopic
17:52
pinpoint. If you do that with ordinary light,
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you might get enough heat to start a campfire.
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Right. But if you do it with a high -powered
17:58
industrial laser, you're concentrating thousands
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of watts into an area the size of a pinhead.
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The localized heat is so intense it instantly
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vaporizes thick steel plates in car factories.
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Or, on a much more delicate scale, surgeons utilize
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that exact same pinpoint focus. Right, like we
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mentioned earlier. They use specialized lasers
18:19
to slice through tissue, instantly cauterizing
18:22
and sealing blood vessels as they go, or to painlessly
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ablate and reshape the microscopic curves of
18:27
the human cornea during eye surgery. You are
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wielding energy with sub -millimeter precision.
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And beyond industry and medicine, Lasers have
18:36
become our ultimate ruler for measuring the universe,
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haven't they? Like the LEGO observatory, which
18:41
detects gravitational waves, relies entirely
18:43
on the laser's purity. Yes. Gravitational waves
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are literal ripples in the fabric of space and
18:49
time caused by massive cosmic events like black
18:52
holes colliding. Mind -blowing stuff on its own.
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When those ripples pass through Earth, they stretch
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and squeeze our planet by amounts vastly smaller
18:59
than the width of an atomic nucleus. You cannot
19:02
measure a change that unimaginably small with
19:04
physics. So how do they do it? Instead, physicists
19:07
fire kilometers -long laser beams down vacuum
19:10
tubes. Ah, because the laser is a single Pure
19:14
wavelength marching in perfect lockstep. It acts
19:17
as an unchangeable microscopic ruler. Yes. If
19:20
space itself stretches even a fraction of an
19:22
atom, the laser's journey takes slightly longer,
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the lockstep waves shift out of alignment, and
19:28
the scientists can detect the ripple. You could
19:30
only ever achieve a measurement that precise
19:32
with light that is completely ordered and coherent.
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So what does this all mean? When you take a step
19:38
back and survey the trajectory of this technology,
19:41
it is staggering. It really is. In 1960, a massive
19:45
room full of high voltage laboratory equipment,
19:48
precision mirrors, and synthetic ruby rods was
19:51
required to generate a single beam of coherent
19:53
light. Today, that exact same quantum manipulation
19:56
has been shrunk down into a throwaway component
19:59
we scatter through the world like confetti. It
20:01
is the ultimate quiet triumph of theoretical
20:03
science, from a laboratory curiosity mocked as
20:06
a solution looking for a problem, to the invisible
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thread sewing global communication, manufacturing,
20:11
and modern medicine together. And to summarize
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the journey, everything we've unpacked today
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traces back to one elegant physical reality.
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Light and lockstep. An ordinary lamp emits a
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chaotic, desperate jumble of energy. A laser
20:24
persuades countless atoms to sing their energy
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out in perfect, synchronized unison. Which brings
20:30
us right back to you listening to this deep dive.
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Whether you are using a plastic pointer to entertain
20:35
a pet, receiving sight -saving surgery, or just
20:38
relying on the undersea glass cables delivering
20:40
this very audio to your device right now, you
20:43
are interacting directly with an abstract physics
20:46
equation sketched out in 1917. Incredible. isn't
20:50
it? Einstein saw the resonance. Mayman built
20:52
the ruby trap. And now manipulating quantum states
20:54
is just a mundane part of your daily routine.
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And this raises an important question, something
20:58
for you to mull over as you go about the rest
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of your day. Let's hear it. Since the laser was
21:03
once completely dismissed by the brightest minds
21:06
of the 1960s as a useless parlor trick, what
21:09
incredibly dense, seemingly pointless theoretical
21:12
physics equations being fiercely debated in obscure
21:15
university laboratories today are secretly the
21:18
blueprints for the throwaway, everyday gadgets
21:20
of our future. What a fantastic thought to end
21:23
on. the chaotic crowd transforming into a synchronized
21:26
army, all thanks to some carefully tickled atoms.
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Thank you so much for joining us on this deep
21:30
dive into the hidden world of lasers, and as
21:32
always, keep asking questions and stay curious.