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
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.
Can’t speak for particle accelerators, but as someone who has worked for a brief time in photonics, the simplest answer is usually because the equipment needs to fit in a confined space, so you’re going to have to turn eventually.
We actually do have gentle curves all the time, the most notable example being fiber optic cables. In fact in a more general case we have what are called waveguides which carry not just light (fiber optic cables themselves are a specific type of waveguide), but other waveguides carry microwaves or even sound.
Regardless of what the waveguide actually carries, a concept borrowed from electronics is the idea of impedance, which can be thought of as an electric resistance, but also has a frequency dependent component (meaning, the amount of impedance depends on the frequency of the electronic signal).
Well, whenever the signal (whether it be radio, sound, electrical etc.) reaches another medium of a different impedance, the impedance change causes a reflection coefficient. So for example, you had a waveguide/optic cable of a certain kind of impedance, and it connects to another waveguide of a different impedance. At the connection point, if the impedances are mismatched, there will be signal reflection. If there are too many of these reflections, the signal gets distorted and/or it makes mathematic modeling much more complicated.
Changing the medium is one way to change the impedance, but also changing geometry can also change the impedance. Consider a gentle bend, the outside circumference is more than the inside circumference. The impedance matching can sometimes get pretty complicated like this. Great lengths are taken to ensure that transmission lines are balanced, meaning they have the same geometry throughout, and same length, etc.
Obviously, it’s not possible for two transmission lines (sending and returning) to be completely identical in all situations. We actually have devices called “baluns” (BALanced-to-UNalanced, or BALancing-UNitS) that specifically exist to help interface two unbalanced lines. But this adds extra complexity and is best avoided if possible. But going around a 90-degree corner of a square is easily calculatable, compared to some arbitrary geometry that requires complex calculus to solve.
Additionally, you actually see more gentle curves in fiber optics than in other kinds of waveguides because fiber optic cables don’t have nearly as much impedance as other kinds of waveguides, to the point it’s practically negligible.
Laser beams and particle accelerators are two very different technologies. A particle accelerator is usually a giant circle shape where you can run your particle around and around, all the while accelerating it, to get it moving insanely fast.
With lasers and other optical systems, a lot of the path the laser follows is just “cable management”. You need to get your laser from one piece of equipment to another, so you use mirrors to bounce it. It’s kinda like asking why do the water pipes in our houses make so many turns. Plumbers just run the pipes in a way where they all fit together and get the water where it needs to go. Same thing with the light in an optical system.
As someone who’s also attended conferences with experts in their field, I can understand how confusing it can be to start from level 0. From what I understand, the mirrors and curves in particle accelerators and laser experiments are used to control and manipulate the beams. Straight lines may seem easier to control, but sometimes you need to bounce the beam off of certain materials or curving the path can help with focusing the beam. It’s all about precision and getting the desired outcome. Hopefully that helps simplify things a bit!
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