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The light of a laser does diminish at the square of the distance but the cone is very, very narrow. This is because laser light is collimated. The production

The light of a laser does diminish at the square of the distance but the cone is very, very narrow. This is because laser light is collimated. The production of laser light occurs in an optical cavity that where uncollimated light is reflected back into the cavity. I would really just be quoting wikipedia so I included the link. A parabolic antenna also collimates the energy, reducing the size of the cone that the energy is spread over. This allows things like point-to-point communication and narrow-field radio telescopy. The "power" of a transmitter is the effective radiated power so a transmitter using 1 watt might spread that out over a wide area, but with low power in each direction, or collimate it to a narrow area but with relatively high power in that one direction. https://en.wikipedia.org/wiki/Collimated_beam https://en.wikipedia.org/wiki/Collimated_beam https://en.wikipedia.org/wiki/Optical_cavity https://en.wikipedia.org/wiki/Optical_cavity https://en.wikipedia.org/wiki/Parabolic_antenna https://en.wikipedia.org/wiki/Parabolic_antenna https://en.wikipedia.org/wiki/Effective_radiated_power https://en.wikipedia.org/wiki/Effective_radiated_power

colanderman 3y ago
Cones are still subject to inverse square. What matters more is that the focal length is much longer (effectively infinite) with a collimated beam -- that is, the (virtual) tip of the cone is very far behind the light generating element. Inverse square only applies at distances from the source much greater than the focal length.
mlyle 3y ago
And just to add a little more-- Laser beams at short distances don't fall off inverse square and may even increase in intensity (decrease in spot size) with distance. But in the end, beam dispersion/the diffraction limit wins and the power density is inverse square. (I can focus a big light down to a smaller spot; but ultimately the light is going to be spreading out. This can be true for radio, too, with weird things happening close).

colanderman 3y ago

Cones are still subject to inverse square. What matters more is that the focal length is much longer (effectively infinite) with a collimated beam -- that is, the (virtual) tip of the cone is very far behind the light generating element. Inverse square only applies at distances from the source much greater than the focal length.

mlyle 3y ago

And just to add a little more-- Laser beams at short distances don't fall off inverse square and may even increase in intensity (decrease in spot size) with distance. But in the end, beam dispersion/the diffraction limit wins and the power density is inverse square. (I can focus a big light down to a smaller spot; but ultimately the light is going to be spreading out. This can be true for radio, too, with weird things happening close).