Light and Optics

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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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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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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Double Refraction

What it shows:

A birefringent substance will split unpolarized light into two polarized rays with different refractive indices and different velocities. A crystal of calcite demonstrates this phenomenon.

Double Refraction...

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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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Poisson's Spot

Diffraction produces a bright spot where Poisson believed there would be darkness.

Poisson's Spot

What It Shows

Edge diffraction around a 1/8" diameter steel ball bearing results in a visible spot in the center of its shadow. In 1818 this result—to the chagrin of Siméon D. Poisson—...

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Single Photon Interference

Wave/particle duality observed in Young's double slit experiment with camera sensitive to individual photons.

What it shows:
In this demonstration we perform the double-slit interference experiment with extremely dim light and show that even when the light intensity is reduced down to several photons/sec, the audience can see the familiar Young's double-slit interference pattern build up over a period of time. This addresses the question of how can single photons interfere with photons that have already gone through the apparatus in the past, or with those that...

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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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