Extended list of materials and tips:
- A plastic bottle (that you do not need anymore)
- A jug (same capacity as the bottle or larger)
- A drill (be careful; make sure the hole is smooth and well rounded)
- A stand (or anything you can put your bottle on so it is higher than the table)
- A yellow highlighter
- A blue laser pointer (we used a 405 nm 5 mW laser, avoid shining in the eyes)
Delving a little deeper into the physics:
In our fountain, we can observe that the beam of light follows the stream, instead of continuing through it in a straight line. This has to do with total internal reflection: instead of being refracted into the air at the air/water interface, the laser beam reflects back into the stream of water. This is the basic principle underlying how optical fibers work. [1,2] The fact that we can see the beam to begin with is not trivial. The role of the highlighter ink is to make the beam visible. The high-energy, near-UV blue light emitted by the laser hits the ink particles. Some of it is scattered by those particles, while some of it is absorbed by them. As the ink molecules are fluorescent, they re-emit light in the yellow-green region of the spectrum, around 510 nm for standard yellow highlighters, often based on pyranine.  In the end, the light that comes out of the fountain is both guided and wavelength-shifted towards the green – exactly like in the optical fibers found in the ATLAS Tile Calorimeter.  The Tile Hadronic Calorimeter is one of the many layers of the ATLAS detector. It is the heaviest part of the experiment, with 420 000 plastic scintillating tiles located in 128 modules like the one in the video, arranged into a circle 8.5 m in diameter.  It is one of two calorimeters in the ATLAS experiment; calorimeters measure the energy of the particles created during the collisions.
Links for further information :
-  Dianna Cowern, How to control light with water, YouTube (2016). The use of optical fibers in communication.
-  Daniel Colladon, Sur les réflexions d’un rayon de lumière à l'intérieur d’une veine liquide parabolique, La Nature (1842). First publication reporting the phenomenon of light being guided by a water jet, by a professor of physics at the University of Geneva.
-  Compound Interest, The chemistry of highlighter colors, compoundchem.com (2015). How highlighters work.
-  ATLAS Experiment website, Outreach about the two calorimeters in the detector, atlas.cern.
-  Ana Henriques, The ATLAS Tile Calorimeter, ANIMMA Conference Proceedings (2015). Overview of the Tile Calorimeter.
-  Alexander Solodkov, The ATLAS Tile Hadronic Calorimeter Production, calibration and performance, LHC Days in Belarus Workshop (2018). More detailed information about the scintillating tiles and wavelength-shifting fibers in the Tile Calorimeter.