LEGO LASER OPTICAL BENCH 1: Wave Nature of Light

The nature of light was a topic of hot debate in Newton's day, the argument raging between one group (Newton and Pierre Gassendi among them) who were steadfast proponents of the corpuscular theory (light is a particle) and an opposing group (including Newton's historical nemesis, Robert Hooke and Christiaan Huygens) who promoted the wave theory of light.

One of the most famous bits of folklore surrounding this great debate is the story of Simeon Poisson, who argued vehemently against the wave theory of light. Poisson's argument stemmed from a calculation he had made that showed the wave theory of light predicted the existence of a bright spot in the geometric center of the shadow of a circular illuminated object. As far as Poisson was concerned, that was crazy talk!

As with all good arguments in science, experiments rapidly put data on the table to help settle the debate. "Poisson's Spot" (named, I think, to annoy him) was shown to exist, and the wave theory of light gained ground. It would hold sway as the dominant description of light until the Annus Mirabilis (1905) when Einstein demonstrated that the photoelectric effect could be explained with a particulate theory of light.

Lego Optical Bench

Optical experiments are easy to conduct at home, especially with the use of common laser pointers.

While simple equipment setups can be jury-rigged with common household implements (cups, ticky tacky, tape, etc), I found it convenient to create an adjustable optical bench using Lego bricks. The bench consists of 4 pieces:

  • Rail -- this carries each of the other elments, keeps them aligned, and allows distances to be adjusted
  • Laser carriage -- this holds a laser pointer horizontal and rigid, and has a mechanism for holding the switch depressed
  • Element carriage -- this holds an optical target on a bench that can be height adjusted to put the target in the laser path.
  • Screen carriage -- a simple runner to hold a white screen for projection of the laser beam

Here are a few images of the optical bench. Click on pictures for a larger view!

rail thumb rail thumb rail thumb
bench thumb laser thumb element thumb
element thumb screen thumb screen thumb

Poisson Spot

My first effort with the Lego optical bench was to illuminate the head of a straight pin in an effort to produce a visible Poisson Spot.

It was reasonably easy to see a spot, as well as significant diffraction around the edges of the pattern, especially when projected over long distances. The hardest part was capturing an image of the spot using my simple point and shoot digital camera!
redspot thumb redspot thumb
greenspot thumb greenspot thumb
green diffract thumb green diffract thumb

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