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Sugar Syrups

What it shows:

Certain materials (sugar in this experiment) are optically active because the molecules themselves have a twist in them. When linearly polarized light passes through an optically active material, its direction of polarization is rotated. The angle of rotation depends on the thickness of the material and the wavelength of the light.

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Circular Polarization

What it shows:

A linear polarizing filter followed by a quarter-wave plate whose slow and fast axes are at 45° to the axis of the polarizer becomes a circular polarizing filter, and incident unpolarized light emerges as circularly polarized light. This will not work if the order of the polarizer and wave plate is reversed. A quarter-wave plate converts circularly polarized light into linearly polarized light.

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Polarization by Scattering

Simulation of atmospheric scattering and polarization of sunlight using slide projector and aquarium containing milky water.

What it shows:

Unpolarized light passing through a fluid is scattered; the scattered light being partially or completely plane polarized. For scattering by particles of comparable size to the wavelength of the light, this process is called Rayleigh scattering. The wavelength dependence of this type of scattering is responsible for blue skies and red sunsets.

How it works:

Unpolarized white light from a...

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Brewster's Angle

What it shows:

When unpolarized light is reflected from a non-metallic surface, the reflected ray is plane polarized parallel to the reflecting surface if

θi + θr = 90°

or

tanθi = n

where θi = incident ray (Brewster's angle), θr = refracted ray, n = refractive index

How it works:

We use a black vinyl sheet 1m×4m as the reflecting surface, which has a Brewster angle of 57°. A theatrical spot lamp 1 is used to give a 50cm circle...

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Rayleigh's Criterion

What it shows:

The criterion for the resolution of two sources is that the central maximum of the single slit interference pattern of one source falls on the first minimum of the pattern of the second source.

How it works:

Each laser beam passing through the slit will form a diffraction pattern on the screen. With the aperture closed down, the pattern will be spread out and the central maxima of both sources will overlap giving a blurry image. Opening up the aperture and the diffraction patterns will get narrower, until the point...

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Edge Diffraction

What it shows:

A point light source will produce seemingly sharp shadows which turn out to be not at all sharp when viewed under magnification. Narrow interference bands are seen within the shadow of a straight edge while more complicated shapes yield more complicated interference bands and striations.

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Hear the Wall Bend

What it shows:  A room-size laser interferometer with audio signal output. A standing wave is produced whenever a wave is reflected back on itself. A resonant cavity requires a second reflection so that the twice reflected wave has the opportunity to be in phase with the original wave. Here, laser light is reflected from a half-silvered mirror (mounted on a wall) so as to return to the laser and be reflected again by the laser. Movement of the wall by half a wavelength is sufficient to change the cavity formed between laser mirror and wall mirror from one resonant...

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Thin Film Interference

What it shows:

Waves reflecting from two surfaces can interfere constructively and destructively. In this case it is light waves that are being reflected from the front and rear surfaces of thin soap or oil films. The interference produces a pattern of beautiful colors in white light, or dark and light bands in monochromatic light.

How it works:

Our two most visually dramatic illustrations of thin film interference use either a soap film suspended in air from a 19 cm diameter circular frame, or a very thin layer of oil floating on top of water....

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Frustrated Total Internal Reflection

What it shows:

In quantum mechanics, it is possible for a particle to tunnel through a potential barrier because its wave function has a small but finite value in the classically forbidden region. Here we use FTIR as an optical analog of this quantum mechanical phenomenon.

How it works:

A 45°-90° prism will deflect a beam of light by total internal reflection. When two such prisms are sandwiched back-to-back and pressed together, the air-glass interface can be made to vanish and the beam then propagates onward undisturbed. This transition, from...

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Bucket of Light

What it shows:

A beam of laser light can be trapped inside a stream of water by suffering total internal reflection—the aquatic equivalent of a fiber optic cable.

How it works:

A stream of water flows from a hole in the side of a soda bottle (figure 1). The critical angle of 49° is such that...

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Fishtank TIR

What it shows:

A simple qualitative demonstration of total internal reflection using a laser beam.

tank

How it works:

Using a fish tank suitably doped with a scattering agent (see Setting it Up), a ray of light from a laser beam can probe the water-air...

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Hot Road Mirage

What it shows:

There are various types of mirages possible, the details depending on whether the hot air is above or below the cool air and how sharp the transition is from cool to warm. This demonstration simulates what happens when a dark asphalt road gets much hotter than the air around it--the air next to it becomes hotter than the higher air and light traveling through this temperature gradient is bent so much that it appears reflected. The shimmering water on a road's surface or the blue oasis in the desert are natural examples of blue skylight being...

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Hotplate Mirage

What it shows:

A beam of light is distorted due to turbulent convection currents in air. This is a model of atmospheric distortion that affects seeing conditions in ground based optical and infrared astronomy.

How it works:

Turbulent air is provided by an electric stove ring, that heats the air above it as the warm earth dues to air sitting above it. The turbulent currents set up alter the refractive index of the air in a disordered and rapidly changing way. Light from a point source passing through these conditions is blurred...

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