3 ms·

I always wonder what happens to the energy that goes past the target and heads out into space. Seems like an upper limit on these things. :-) That said, if the

I always wonder what happens to the energy that goes past the target and heads out into space. Seems like an upper limit on these things. :-) That said, if the Russo-Ukranian war has shown us anything it is that drones, even ones that are either unarmed or carrying around one or two grenades, are a credible threat. Both from the role of "forward observer" for indirect fire, and "precision low yield bombardment." Clearly opportunities in locating drones at a distance as well.

giantrobot 4y ago
The light that doesn't hit the target has to travel through a hundred miles of atmosphere before getting to space. Between diffraction of the beam and all that atmosphere only a fraction of the light will make it out of the atmosphere.
everyone 4y ago
Perun released a video on drones in Ukraine today https://youtu.be/AlpZf1hpQYM https://youtu.be/AlpZf1hpQYM
- ChuckMcM 4y ago
  This was fabulous! Thanks for the reference.
bamboozled 4y ago
There’s a commonly held misconception that lasers “go forever”. I’m not sure how practically true that is in a vacuum, but I understand why the person said it.
- TeMPOraL 4y ago
  Like all light, they do go forever. Like all light, they disperse, following the inverse square rule. Unlike with an omnidirectional source (e.g. a lightbulb), for the purposes of inverse square rule the source of the laser beam is an imaginary light source far behind the emitter, and far more powerful than it; this makes the beam seem to disperse slower, but disperse it does.
  - jjtheblunt 4y ago
    Wouldn’t lightbulb power fade with an inverse cube?
    - j16sdiz 4y ago
      It is inverse square https://home.ifa.hawaii.edu/users/barnes/ASTR110L_S03/inversesquare.html https://home.ifa.hawaii.edu/users/barnes/ASTR110L_S03/invers...
      - jjtheblunt 4y ago
        thanks for the link. oh, easy way to see it is surface area of a sphere, 4 pi r^2.
        TeMPOraL 4y ago
        Correct. The light emitted at a particular point in time forms a section of a spherical surface; as that light travels out, it's like the whole sphere is inflating - the surface area covered by the light remains a fixed fraction of the entire sphere's surface, and so in absolute terms, it grows proportional to r². This means the surface density (light per m²) drops with r². There's probably a nicer way to describe it. If I remember correctly, there's a similar explanation for other phenomena following inverse-square rule, including attraction forces such as gravity, as that r² comes from something forming a surface expanding in space. Inverse cube would give you total energy/power contained in a volume, which isn't usually the interesting quality when talking about radiation. Also, this is why strength of radar return signal drops with fourth power of the distance to target: the illuminating beam drops with 1/r² to target, and then the reflection drops with 1/r² again when traveling back.

giantrobot 4y ago

The light that doesn't hit the target has to travel through a hundred miles of atmosphere before getting to space. Between diffraction of the beam and all that atmosphere only a fraction of the light will make it out of the atmosphere.

everyone 4y ago

Perun released a video on drones in Ukraine today https://youtu.be/AlpZf1hpQYM https://youtu.be/AlpZf1hpQYM

ChuckMcM 4y ago
This was fabulous! Thanks for the reference.

bamboozled 4y ago

There’s a commonly held misconception that lasers “go forever”. I’m not sure how practically true that is in a vacuum, but I understand why the person said it.

TeMPOraL 4y ago
Like all light, they do go forever. Like all light, they disperse, following the inverse square rule. Unlike with an omnidirectional source (e.g. a lightbulb), for the purposes of inverse square rule the source of the laser beam is an imaginary light source far behind the emitter, and far more powerful than it; this makes the beam seem to disperse slower, but disperse it does.
- jjtheblunt 4y ago
  Wouldn’t lightbulb power fade with an inverse cube?
  - j16sdiz 4y ago
    It is inverse square https://home.ifa.hawaii.edu/users/barnes/ASTR110L_S03/inversesquare.html https://home.ifa.hawaii.edu/users/barnes/ASTR110L_S03/invers...
    - jjtheblunt 4y ago
      thanks for the link. oh, easy way to see it is surface area of a sphere, 4 pi r^2.
      - TeMPOraL 4y ago
        Correct. The light emitted at a particular point in time forms a section of a spherical surface; as that light travels out, it's like the whole sphere is inflating - the surface area covered by the light remains a fixed fraction of the entire sphere's surface, and so in absolute terms, it grows proportional to r². This means the surface density (light per m²) drops with r². There's probably a nicer way to describe it. If I remember correctly, there's a similar explanation for other phenomena following inverse-square rule, including attraction forces such as gravity, as that r² comes from something forming a surface expanding in space. Inverse cube would give you total energy/power contained in a volume, which isn't usually the interesting quality when talking about radiation. Also, this is why strength of radar return signal drops with fourth power of the distance to target: the illuminating beam drops with 1/r² to target, and then the reflection drops with 1/r² again when traveling back.