Total reflection

Green DPSS laser bouncing around in a water glass. This is a 5mW laser, cheaply available at dealextreme. Thanks to a small drop of milk the beam is clearly visible. The tiny drops of fat scatter some of the light back to the camera.

Category:

Science & Technology

Tags:

• laser
• milk
• water
• total reflection

[Ryalnotch]

Okey thanks for replying but i mean after the light source is shut off with the light bouncing back and forth inside.. ehm lets say a spherical object. Is that possible? :)

[zupnikal]

@Ryalnotch: Ahhhh. Well, practically no. Even if you had perfect reflection, there is still absorption in the material. And if you eliminated that somehow, you have self-diffraction of the laser beam (google for Gaussian Beam). Essentially the laser beam spreads laterally as it travels, which also changes the angle of incidence on the surface again. Parts of the beam would escape. Your asking for a ring-resonator. These things do exist. But once you shut of the light source, it's dead.

[zupnikal]

@Ryalnotch: Part 2: Just do the math. Assume you have a ring resonator with 4 mirrors with the beams bouncing inside a square with a circumference of 1m. Speed of light is 3*10⁸m/s. Assume the mirrors have 99.999% reflectivity. Now you can easily calculate how many bounces it takes until you end up with 50% power left (69314 bounces or 17329 round-trips). The time it takes for that is just 17329m / 3*10⁸ m/s = 57.7µs.

[Ryalnotch]

Just a theoretical question, is it possible to get TOTAL reflection so that the light stays within a reflecting object?

[zupnikal]

@Ryalnotch: Of course. That is what happens in optical glass fibers used in telecommunication. To make it works you need a core with a higher refractive index than the cladding and stay below the critical angle (flat incidence). The angle can easily be calculated with Snell's Law.

[zupnikal]

@Ryalnotch: If you need something more fancy, look at 'Fresnel Equations'. These also cover different polarizations.

[ciferusbux]

two drop of water and quad closed

[CamouflageCow]

It reminds me of a transmutation circle

[koffeekage]

it reminds me of a Radar CRT

[zupnikal]

The important reflection actually takes place at the boundary between glass and air, not between water and glass!