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Merely a curious fool contemplating how plausible it would be to cut the Eiffel Tower in half with a massive laser (you know, for fun). What kind of laser would it take to cut an iron girder from about 260m away and is this something that's possible to build?

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    $\begingroup$ Did you calculate the energy required to cut through a unit mass of steel? Did you calculate the cross-section of the steel half-way up the Eiffel Tower? Otherwise you're just asking someone else to do a pile of work for you without you contributing anything! $\endgroup$
    – Transistor
    Commented May 10 at 18:28
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    $\begingroup$ What is the attenuating medium in that 260m. What is the thermal conduction of the girder? What is the diffraction of the beam. What is the focal radius of the beam? What is the emissivity of the target over the entire range of temps up to melting? what will be the convective and radiative losses? Kind of complicated. $\endgroup$
    – Phil Sweet
    Commented May 10 at 19:13

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Laser weapons are making a comeback, specifically for targeting cheap drones in the new age of warfare. Lots of variables to consider more than just power.

  1. There is lots of public information available about the star wars program from the 1980s where lasers were planned to shoot down missiles. See the Strategic Defense Initiative wiki page and its reference links.
  2. Also lots of information on the laser weapon wiki page.
  3. The wavelength of the weapon changes how different targets absorb the energy. Near Infrared is a good choice for steel at roughly 1000nm.
  4. The wavelength also influences how quickly the laser spreads into a wider and wider beam called diffraction. The longer the wavelength the quicker it spreads apart.
  5. The width of the beam at the target establishes how much metal must be melted. Laser cutting tools obviously seek to minimize the width of the beam in the target to maximize the cut speed.
  6. Lots of other variables to consider like angles, controlling the beam, feedback, etc.

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