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Tunneling Analog

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...

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Optical Analog of Uncertainty Principle

What it shows:

In the Heisenberg uncertainty relation, the momentum of a particle cannot be known with any greater accuracy than h/∆x where h is Planck's constant and ∆x is the uncertainty in spatial position. The more you localize its spatial position, the less certain you become about its momentum. An optical illustration for this is the diffraction of light though a slit.

How it works:

For a laser beam, the transverse momentum is pretty well known (i.e. it's zero) but you have no localization of its spatial x coordinate. You...

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Electron Diffraction

What it shows:

Louis de Broglie predicted that matter under certain circumstances would exhibit wave-like properties. A proof of this is the repeat of X-ray diffraction experiments using electrons, whose de Broglie wavelengths at high accelerating potentials are similar to X-ray wavelengths. Here we accelerate electrons into crystal targets and get diffraction patterns identical to those from X-ray diffraction.

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Tether-ball Catastrophe

What it shows:

An accelerated electric charge radiates energy. So according to classical physics, an electron in orbit about an atomic nucleus should emit electromagnetic radiation by virtue of its orbital motion. As it radiates energy, the radius of its orbit decreases. The electron should spiral into the nucleus amidst a burst of radiation in about 10-16 seconds.

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Syrup Tube

What it shows:

Linearly polarized light, propagating down a long glass tube filled with corn syrup, is made to rotate its direction of polarization by the optically active corn syrup. The intensity of the 90° scattered light varies dramatically, in a periodic manner, along the length of the tube -- the intensity being zero when the dipole radiators oscillate in the line of sight direction, and maximum intensity when they oscillate perpendicular to the line of sight. Scattered light is most intense when the electric field vector is perpendicular to the line of sight.

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Photoelasticity

What it shows:

Normally isotropic substances can become birefringent when under stress. This property can be used in stress analysis.

How it works:

To use birefringence in stress analysis, the sample is placed between two crossed Polaroids. The first Polaroid produces a linearly polarized light source for the sample. This source has components split into ordinary and extraordinary rays; the differing velocities of these rays in the sample creates a phase difference which is color dependent. The second Polaroid takes components of...

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Malus' Law

What it shows:

Polaroid filters absorb one component of polarization while transmitting the perpendicular components. The intensity of transmitted light depends on the relative orientation between the polarization direction of the incoming light and the polarization axis of the filter and is described quantitatively by Malus' cos2θ intensity law.

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Polarization by Absorption

What it shows:

Polaroid filters absorb one component of polarization while transmitting the perpendicular components. The intensity of transmitted light depends on the relative orientation between the polarization direction of the incoming light and the polarization axis of the filter.

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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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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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