Eli5: Why do laser experiments and particle accelerators have mirrors and curves or hard turns in their path?

Question

I am a layman who ends up attending a number of research conferences with experts in their field. I do my best to understand but I’m always starting at level 0.

These last few years I’ve heard researchers from TRIUMF and Oak Ridge, among others, talk about transmission of beams and seeing diagrams of the paths their beams transverse. Sometimes, like the particle accelerator at RAON, the path is straight but has a 90′ turn. And sometimes the path is curved and seems to have a number of things the beam is bounced off of.

I’ve also seen some lasers which seem to have the laser beam bounce all over the place. No straight line, no gentle curve, but what is probably 45′ angles and many many of them.

Are these steps (turns?) because they need to modify the beam? Are they adding or subtracting something from the beams? Are the beams getting more focused? Wouldn’t a straight line be easier to control and focus as opposed to adding turns and curves?

In: Physics

Answer 1

In regards to laser getting light to follow a gentle curve is hard you need a medium with a graduated index of refraction, and a bent single-mode fiber is an option. But direct angle change just requires a mirror.

One reason for having a long path with a lot of bouncing is that you need to delay a later pulse relative to another. There are likely a lot of 90-degree angles with the mirror at 45 degrees relative to the laser. It is an easy way to set up an experience. A straight line means you need a physically larger setup, a smaller setup with a mirror have practical advantages like you need a smaller room for the experiment.

For particle accelerators they are often curved into a circle so the particle can go around the acceleration many times and the speed can increase. You could build a single straight accelerator but it would need to be longer. The particles do not bounce in the circular accelerator, it is charged particles that are accelerated and the magnetic field turns them.

There are straight linear accelerators too, you do not get the same speed but they have other advantages. Small linear accelerators are a common way to create X-rays for medical applications. An old CRT display is a fundamental linear particle generator even if there are magnets to change the path of the electron beam to hit the right part of the display.