I read laser beams get wider, like a few feet wide by the time they hit the moon, Is that a manufacturing limit, or just something about the physics of laser light? Is a perfect laser beam that doesn’t get wider possible?

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I read laser beams get wider, like a few feet wide by the time they hit the moon, Is that a manufacturing limit, or just something about the physics of laser light? Is a perfect laser beam that doesn’t get wider possible?

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Anonymous 0 Comments

It’s not just about getting wider- can’t you get a really good lens and focus it at some ideal distance and get it to a zero-width point?

Nope. [Diffraction limits](https://courses.physics.illinois.edu/phys214/fa2013/lectures/lecture5.pdf) show the limit of all optical systems. Even if the lenses are “perfect”.

It’s the same rule behind Rayleigh Criterion limiting the angular resolution of a telescope.

The larger the initial beam, nonintuitively, makes the minimum spot size smaller. Starting with a beam twice as wide and using a lens twice as wide will reduce the minimum spot size by 50% for a given distance. But then the beam is starting out wide dia and gets smaller and smaller to its minimum at the focal point, then gets wider. So if you didn’t know what distance to focus at exactly, the beam is even less Star-Wars-ish and makes a more prominent bowtie/hourglass shape.

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