| |
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.
Videos about interference phenomena
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.
Videos about diffraction phenomena
- 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.
|
