Breking laserstraal in water

Door met een laserlicht in troebel water te schijnen, kun je zien hoe het licht breekt (afbuigt) onder water.

Met de lasdraad kun je de positie van de laserstraal in het luchtruim aangeven. De lasdraad maakt de breking beter zichtbaar.

4. Gradual Refraction (Optics of the Mirage)
Use hot tap water to fill the tank this time. Stir in the usual amount of scattering agent, and allow the water to settle. When the water is once again still, carefully drop about 10 sugar cubes into the warm water, spacing them as evenly as possible along the bottom of the tank. Don’t worry if the spacing is a little uneven.

Allow 10-20 minutes for the cubes to dissolve in the undisturbed water. Do not stir the water during this time. The cubes will not dissolve completely, but the result will be a sugar solution concentration gradient from the bottom to the top of the tank. Direct the laser horizontally through the water near the top of the tank. It should be unaffected and pass through as expected.

Maintain the horizontal aim as you lower the beam to deeper and deeper depths of water. As you get close to the bottom of the tank, the beam will appear to arc downward into the sugar.

This gradual refraction results from a gradient in the index of refraction. The gradient in the index of refraction arises from the gradient in the concentration of the sugar solution. 

Gradual refraction is the optics behind mirages, where the index of refraction gradient coincides with the temperature gradient of the air above the surface of the ground.
Finally, stir the water thoroughly. Once the sugar is distributed uniformly, the gradient no longer exists and gradual refraction no longer occurs.