To get a steady beam of light you can use a flashlight or laser pointer. If using the flashlight, tape it down securely into the back of a shoe box, and turn it on. Poke a small hole where the light is most concentrated.
Caution: do not stare into laser pointer beam. It can seriously damage your eyes!
Twist the bottle and align the beam so it shines through the bottle and out the duct tape hole.
When all your pieces are in place and aligned just uncork the soda bottle, and watch the flow glow.
There is nearly total internal reflection of light bouncing off the inside edges of the water stream.
This is why light travels so far through glass fiber optic communications cables carrying telephone calls, TV shows, and Internet traffic.