Sous-titres (83)
0:07Dropping out of light speed,
0:08a fleet of rebel spaceships is greeted
by a frenzy of laser blasts—
0:13illuminating the sector
with brilliant bursts of light.
0:18Science fiction has shown us
scenes like this for decades,
0:22but the lasers in our daily lives
seem far less dazzling and destructive.
0:27Laser eye surgery can cut tissue, and
laser cutters can shape wood or plastic,
0:33but neither seems strong enough
to pierce a spaceship.
0:38And laser pointers are more likely
to annoy a cat than an evil empire.
0:43So could sci-fi laser weaponry ever exist?
0:48And how do lasers even work
in the first place?
0:52Lasers are devices
that produce laser beams,
0:55which are ultimately just a form of light.
0:58But these beams have special properties.
1:02the ordinary light from this
incandescent bulb
1:05is composed of a rainbow of colors,
1:07each of a different wavelength.
1:09And the particles that make
up the light, called photons,
1:13randomly emanate outward
in all directions.
1:17Laser beams, on the other hand,
are much more organized.
1:21They're generated through a process
called stimulated emission,
1:25which is part of the acronym
that gave this tech its name.
1:29Every laser houses a few photons,
and when the device is turned on,
1:34it begins exciting a large number
of electrons.
1:39Stimulated emission begins
when these particles collide,
1:44causing each electron to emit a second
synchronized photon of the same color.
1:50This photon then strikes
other excited electrons,
1:54which in turn emit more and more
of the same type of photon.
2:00Eventually, this chain reaction generates
an organized stream of light particles
2:06known as a laser beam.
2:09Stimulated emission imbues these beams
with two unique properties.
2:14They’re monochromatic,
2:15meaning their light is composed
of a single color.
2:19And they’re coherent,
2:21meaning their light waves
are all synchronized
2:24and travel in the same direction.
2:27These two traits give laser
beams all kinds of special abilities.
2:32Whereas the light from a standard bulb
spreads out to fill a room,
2:36coherent laser beams stay narrow,
2:40allowing some to travel over distances
as large as thousands of kilometers.
2:46Coherence also makes laser beams great
for carrying information.
2:51Since their light waves
are perfectly synchronized,
2:54it's easy to detect
any changes in the beam.
2:58For example, when you
shine laser light on a barcode,
3:02the scanner can precisely
measure the reflected light
3:06and convert the pattern
of black and white into data.
3:10We can also encrypt a Morse code-like
chain of data into laser light
3:16by creating the beam in short pulses,
3:19and laser light’s high frequency lets it
carry much more information
3:26Scientists rely on the precision
of laser measurements
3:30in guidance systems
that help robots navigate;
3:33spectroscopy tools that study
the composition of different materials;
3:38and even in a gravitational
wave observatory
3:42that measures ripples in space-time.
3:45Being monochromatic and coherent
3:48are also what gives laser beams
their destructive potential.
3:52Whereas ordinary light distributes
its energy across a large physical space
3:57and a spectrum of colors,
3:59laser light concentrates its energy
into a narrow, single-color beam.
4:05However, there are limits to how
powerful these beams can get.
4:10First, stimulated emission
is incredibly fragile.
4:14As lasers increase in power,
the more internal heat they generate.
4:19Heat de-excites electrons,
4:22rendering them unable to participate
in the chain reaction
4:26that produces laser light.
4:28So when there's too much excess heat,
4:30the mechanism gets disrupted
and the laser stops working.
4:35Furthermore, while laser beams
can travel huge distances,
4:39doing so causes the beams to get
scattered and absorbed
4:43by air molecules and other particles,
4:47weakening the light
until it disappears entirely.
4:51For all these reasons,
4:52blasters and laser cannons will likely
remain in the realm of science fiction.
4:59However, this doesn't
mean lasers can't hurt us.
5:02On a clear night, laser beams can damage
small nearby targets
5:07like drones, mortar shells, and balloons.
5:11High power lasers found in factories,
machine shops, labs, and medical clinics
5:17can instantly burn and cut nearby skin.
5:22And even the humble laser pointer
can damage eye tissue
5:26with continued exposure.
5:28So while lasers can't
take down a starship,
5:32they still need to be used
with care and caution.
