Bessel Beams: The Coolest Physics Phenomena That Technically Don’t Exist

Bessel Beams are impossible to create, can’t be destroyed, and don’t diffract. In other words, physics has discovered yet another thing that makes no sense.

Bessel beams bear the name of Friedrich Bessel, a man whose life straddled the late eighteenth and early nineteenth centuries. And yet he helped create something that seems like it should be from the 24th century. Right now, Bessel beams are used as optical tweezers in microbiology — literally, they are beams of light that can move tiny things like cells. But someday they’ll probably be used as tractor beams. It’s an impressive feat for things that don’t really exist.

Bessel beams are lasers that behave very differently from ordinary lasers. Consider how the typical laser pointer behaves, creating a small red dot where you point it. Instead of a single point on a wall, Bessel beams create a bullseye: one dot surrounded by concentric rings. The number of rings is some indication of the strength of the beam. Many commercial Bessel beam devices create beams with about eleven rings. The ideal Bessel beam would have an infinite amount – because an ideal Bessel would use an infinite amount of energy. Since infinite energy isn’t available, the true Bessel beam doesn’t actually exist. Right now, we’re working with knock-offs, but we’re still doing impressive work.

Unlike a typical laser beam, a Bessel beam does not diffract and get larger as the beam gets farther from its point of origin. Your pen-sized laser pointer creates a tiny dot on your wall because the wall is relatively nearby. If your laser pointer were focused on the moon, and its beam were visible, you wouldn’t see a red dot; you’d see an entire red moon. That household laser will spread so widely that the beam would be wider than the Moon’s diameter. Bessel beams don’t do that. In an ideal Bessel beam, although the rings around the dot spread out, the central beam itself stays focused. Real-world Bessels don’t stay focused forever, but they do hold together a great deal more than the average laser.

One of the most prized attributes of Bessel beams is the fact that the central core of the beam can be blocked, without interrupting the beam. The laser essentially self-heals by using the rings which were not blocked. It’s the optical terminator. It’s also the idea building block for a tractor beam because it won’t drop its load just because a stray space rock zooms through its beam.

Read how Bessel Beams are made and what they are used for here Bessel Beams:

This entry was posted in Physics. Bookmark the permalink.