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Resources and multimedia

Short video sequences showing some optical phenomenon.

Videos on polarization of light

• Linear polarization

A beam of natural light passes through a linear polarizer. To verify that the transmitted light is linearly polarized, we use a second polarizer (analyzer). In the video we observe how, when rotating the analyzer, the intensity of the transmitted light changes between its extinction (polarizers with crossed axes) and a maximum value (polarizer and analyzer' axes parallel). Note that the two orientations of the analyzer that cancel the intensity differ by 180º.

• Circular polarization

When a beam of natural light passes through two crossed linear polarizers, we observe light extinction. If we place a quarter-wave plate with its axes making 45º with the polarizers' axes, we obtain circularly polarized light. In these conditions, the endpoint of the electric-field vector traces a circumference, and therefore its projection onto any polarization direction is constant.
In the video we observe how the intensity of the transmitted light remains constant when the analyzer is rotated.

• Calcite anistropic behavior

We have a light beam which is normally incident on a uniaxial medium, in this case a plane-parallel calcite crystal. In the video we observe how this light beam divides in two, and we also see that these two rays have orthogonal polarizations. The latter is justified by showing the image formation of two images that appear and disappear when changing the orientation of a linear polarizer. In order to see them better, in the video we show an enlargement of the crystal while rotating the analyzer.

In the video we can see a Young interference experiment using a Fresnel biprism. Note the equally spaced bright and dark fringes. As we change the visualization plane, the fringe spacing changes. When we get too close, we see two images of the light source. If we then eliminate the biprism, we can see the light source, which is in this case a sodium lamp.

In the video we can see the interference image of a Fabry-Perot interferometer when illuminated by a mercury light source. In the image we can see non-equally spaced rings, whose radii change when the distance between the two plates of the set-up is modified. Note that different series of rings appear, due to the fact that the mercury light is polychromatic.
The contrast of the image is very good because the inner surfaces of the interferometer have a very high reflection coefficient.

Interference distribution in a Fabry-Perot interferometer illuminated by a laser

In the video we can see the interference image of a Fabry-Perot interferometer when illuminated by a He-Ne laser. In the image we can see non-equally spaced rings, whose radii change when the distance between the two plates of the set-up is modified.
The contrast of the image is very good because the inner surfaces of the interferometer have a very high reflection coefficient.

In the video we can see the screen of a spectrophotometer. A thin film is illuminated by a light beam, whose wavelength changes between 400 and 1100 nm. The graph on the screen shows the plate transmittance as a function of the wavelength.
Note the non-periodic oscillating behavior of the function, as predicted by the theory.

In the video we can see the interference image of a Michelson interferometer when illuminated by a sodium light source. In the image we can see non-equally spaced rings, whose radii change when the distance between the mirrors of the set-up is modified. Note the loss of contrast for certain distance ranges, as a consequence of the sodium light doublet. These two very close wavelengths generate two ring series that for certain distances compensate one another.

In the video we can see the interference image of a Michelson interferometer when illuminated by a mercury light source. In the image we can see non-equally spaced rings, whose radii change when the distance between the mirrors of the set-up is modified. Note that different series of rings appear, due to the fact that the mercury light is polychromatic.

In the video we can see the interference image of a Michelson interferometer when illuminated by a laser. In the image we can see non-equally spaced rings, whose radii change when the distance between the mirrors of the set-up is modified.

• Fresnel diffraction. Screw edge

A screw edge is illuminated by a plane wave. The wavelength of the light source is 633 nm. We place the video camera at a distance from the aperture of about 20 cm, and we take the image without lens. The video shows the evolution of the Fresnel diffraction when the camera is moved away from the object to a distance of a meter and a half. Note that the light distribution is not uniform, in contrast to Geometrical Optics prediction, despite the fact that at short distances we can still recognize the shape of the object.

• Fresnel diffraction of a circular object

A circular aperture 2 mm in diameter is illuminated by a plane wave. The wavelength of the light source is 633 nm. We place the video camera at a distance from the aperture of about 20 cm and we take the image without lens. The video shows the evolution of the Fresnel diffraction when the camera is moved away from the object to a distance of a meter and a half. Note that the light distribution is not uniform, in contrast to Geometrical Optics prediction, despite the fact that at short distances we can still recognize the shape of the object.

• Fresnel diffraction of a square object

A square aperture with a side of 2 mm is illuminated by a plane wave. The wavelength of the light source is 633 nm. We place the video camera at a distance from the aperture of about 20 cm and we take the image without lens. The video shows the evolution of the Fresnel diffraction when the camera is moved away from the object to a distance of a meter and a half. Note that the light distribution is not uniform, in contrast to Geometrical Optics prediction, despite the fact that at short distances we can still recognize the shape of the object.

• Transition from Fresnel to Fraunhofer diffraction conditions. Slit

In this video we can see the transition from the Fresnel to Fraunhofer diffraction. A slit is illuminated by a plane wave. The camera that registers the intensity is initially near the aperture. We then move the camera away until we reach the conditions for the Fraunhofer diffraction. As these conditions are only reached at infinite distances, the experiment was done by using a converging lens.

• Transition from Fresnel to Fraunhofer diffraction conditions. Square

In this video we can see the transition from the Fresnel to Fraunhofer diffraction. A square object is illuminated by a plane wave. The camera that registers the intensity is initially near the aperture. We then move the camera away until we reach the conditions for Fraunhofer diffraction. As these conditions are only reached at infinite distances, the experiment was done by using a converging lens.