Transcript Total Reflection

Optics Phenomens
Total Internal Reflection
What is a total reflection?
Angles
Reality Aplications
The Optic Mirage
Everyday - Examples
What is a total reflection?
 A total reflection is the phenomenon that occurs when the light passes from a
transparent enviroment in another one without forming the reflected ray.
 When the incidence angle increase , the refraction angle increase in the same
time.
 The maxim value of the refraction angle is 90 degrees , when the incidence
angles beyond 90 degrees the light doesn't pass in the second enviroment , so
this is how the total reflection occurs.
Critical Angle
 The critical angle is the angle of incidence above which total internal reflection
occurs. The angle of incidence is measured with respect to the normal at the
refractive boundary.
 If the incident ray is precisely at the critical angle, the refracted ray is tangent to
the boundary at the point of incidence .
 if the fraction: is greater than 1, then arcsine is not defined—meaning that total
internal reflection does not occur even at very shallow or grazing incident angles.
 So the critical angle is only defined when is less than 1.
Angle Formula
Formula :
n2 - the refractive index of the less optically
dense medium,
 n1 - the refractive index of the more optically
dense medium.
Optical description
 Total internal reflections can be demonstrated using a semi-circular glass block. A
"ray box" shines a narrow beam of light (a "ray") onto the glass.
 The semi-circular shape ensures that a ray pointing towards the centre of the flat
face will hit the curved surface at a right angle; this will prevent refraction at the
air/glass boundary of the curved surface.
 At the glass/air boundary of the flat surface, what happens will depend on the
angle. Where θc is the critical angle measurement which is caused by the sun or a
light source (measured normal to the surface):
 If θ < θc, the ray will split. Some of the ray will reflect off the boundary, and some
will refract as it passes through.
 If θ > θc, the entire ray reflects from the boundary. None passes through. This is
called total internal reflection.
 This physical property makes optical fibers useful and prismatic binoculars
possible. It is also what gives diamonds their distinctive sparkle, as diamond has
an extremely high refractive index.
Phase shift upon
Total Internal Reflection
 A lesser-known aspect of total internal reflection is that the reflected light has an
angle dependent phase shift between the reflected and incident light.
 Mathematically this means that the Fresnel reflection coefficient becomes a
complex rather than a real number. This phase shift is polarization dependent and
grows as the incidence angle deviates further from the critical angle toward
grazing incidence.
 The polarization dependent phase shift is long known and was used by Fresnel o
design the Fresnel rhomb which allows to transform circular polarization to linear
polarization and vice versa for a wide range of wavelengths (colors), in contrast to
the quarter wave plate.
 The polarization dependent phase shift is also the reason why TE and TM guided
modes have different dispersion relations.
Reality Aplications
 The optics fiber is a aplication of this phenomen and with it's help we can lead the
refractive index of a liquid with the Abbe refractometer.
 The optic fibers , made of glas by successive and multiple total reflections lead on
long distance light signals.
 The red reflectors(catadioptrii) used on the cars and bicycles lights , which are
indebted of the total reflection of the light that came from the cars back headlights
make its presence felt.
Examples - Aplications
 Optical fibers, which are used in endoscopes and telecommunications.
 Rain sensors to control automatic windscreen/windshield wipers.
 Another interesting application of total internal reflection is the spatial filtering of
light.
 Prismatic binoculars use the principle of total internal reflections to get a very clear
image
 Some multi-touch screens use frustrated total internal reflection in combination
with a camera and appropriate software to pick up multiple targets.
 Gonioscopy to view the anatomical angle formed between the eye's cornea and
iris.
 Gait analysis instrument, Cat Walk,uses frustrated total internal reflection in
combination with a high speed camera to capture and analyze footprints of
laboratory rodents.
 Fingerprinting devices, which use frustrated total internal reflection in order to
record an image of a person's fingerprint without the use of ink.
 Flashlights lenses
The Optic Mirage
 it's a phenomen of atmospheric refraction which is due to density variation of the
air layers and therefore the refractive index of temperature.
 A light ray which comes obliquely downwards suffer a series of refractions with
a departure from the normal axis and then the total reflection phenomen , and
again refractions which it approaching to the normal axis.
In the everyday life
 Total internal reflection can be observed while swimming, if one opens one's eyes
just under the water's surface. If the water is calm, its surface appears mirror-like.
 Another very common example of total internal reflection is a critically cut
diamond. This is what gives it maximum sparkle.
 Total internal reflection of the green turtle can be seen at the air-water boundary.
How can we demonstrate it?
 One can demonstrate total internal reflection by filling a sink or bath with water, taking a
glass tumbler, and placing it upside-down over the plug hole (with the tumbler completely
filled with water).
 While water remains both in the upturned tumbler and in the sink surrounding it, the plug
hole and plug are visible since the angle of refraction between glass and water is not greater
than the critical angle.
 If the drain is opened and the tumbler is kept in position over the hole, the water in the
tumbler drains out leaving the glass filled with air, and this then acts as the plug.
 Viewing this from above, the tumbler now appears mirrored because light reflects off the
air/glass interface.
Biblyography
www.wikipedia.ro
Phisics manual & notebook
Our Team
Giurgiu Alexandru
Holhos Denisa
Slavu Andreea - Silviana