Friday is here, and the "A Taste of Science for the Weekend" corner is back — number 85.
This time: lasers, ytterbium, and some of the engineering marvels hidden inside the Iron Beam system.
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A laser is created when perfectly identical light rays travel together in the same direction, and the challenge of producing one stems from the inherently random nature of light.
Light is produced when an atom absorbs energy and its outer electrons jump to a higher energy level — orbiting the nucleus at a greater distance.
An atom in this state is excited and unstable. The electrons tend to return to their original energy level, releasing the excess energy as a photon of light. This process is random and emits photons in all directions.
To create a laser, you must charge a gas or solid material with enough energy to excite its atoms into an unstable state, then inject photons at a precise frequency that causes the electrons to relax and release additional photons.
The emitted photons are coherent (identical) to the incoming photons. All the photons are bounced back and forth between mirrors through the medium, causing the number of identical photons to grow continuously until a laser beam is produced.
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Despite enormous investment over the years, attempts to develop an effective and sustainable laser-based interception system have failed time and again.
Project Nautilus delivered operational successes, but it relied on energy generation through a violent chemical reaction involving toxic chemicals and massive storage tanks, which made it operationally impractical.
A central difficulty stems from the need to focus the laser to as small a diameter as possible over distances of kilometers through the atmosphere.
The heat generated in the process distorts the shape of the laser source itself and of the beam it emits. Dust particles, turbulence, rain, and fog distort and absorb the beam in the air.
Another problem is thermal blooming — the more intense the beam, the faster it heats the air in its path, turning it into a kind of lens that scatters the beam.
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Iron Beam is a formidable and extraordinarily complex engineering achievement.
Its laser source is a bundle of long, transparent fibers containing ytterbium.
Ytterbium is an element that is difficult and expensive to produce, and its great advantage as a laser source is that only a small fraction of the energy fed into it is lost as heat.
The fiber bundle is immersed in a cooling liquid. The great advantage of the fibers is that their surface area is exceptionally large relative to their volume, enabling highly efficient heat dissipation.
Photons travel back and forth along each fiber, stimulating the release of more and more photons, and each fiber emits a laser beam from its end at a slightly different wavelength from the other fibers.
The laser beams from all the fibers pass through a diffraction grating. The grating slightly adjusts the angle of each wavelength passing through it, thereby combining all the beams into a single beam of an extremely small diameter.
This beam then passes through a telescopic system that expands it to 450 millimeters, and then refocuses it onto the target.
The system also detects in real time the beam returning from the target, calculates the deviation caused by atmospheric disturbances, and continuously adjusts the focus of the source beam to compensate for the distortion.
The end result is the ability to combine several dozen lasers into a single, uniform laser beam with a power of 100 kilowatts, at a range of 10 kilometers, with a spot no larger than a coin.
These figures represent only a tiny fraction of the engineering genius embedded in this system — one that will protect the lives of millions of people around the world in the years to come.
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On a more personal note: despite being a technological system, Iron Beam moves me to tears every time I watch it.
It is a remarkable concentration of the finest qualities of Israel — pure genius, the achievement of the impossible, the defense of the homeland, and the commemoration of one of our best sons who fell in battle while his father was helping to build it.
Shabbat Shalom 😊
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