1. total internal reflection
critical
angle

2. A little light is also reflected.
When light travels from an optically denser medium to a less dense medium, rays are bent away from the normal. The incident substance has a larger refractive index than the other substance
For a larger angle of incidence, more light is reflected as well as the refracted ray being bent further from the normal
When the critical angle, c, is reached it produces an angle of refraction of 900 c
A little light is also reflected.
For angles of incidence greater than the critical angle,
TOTAL INTERNAL REFLECTION occurs. θ θ
N.B. The angle of incidence
= The angle of REFLECTION

3. TOTAL INTERNAL REFLECTION
weak reflected
ray
As the angle of incidence
increases towards the critical
angle ( glass = 420 ) the
refracted ray gets weaker
and the reflected ray gets
stronger.

4. Critical angle depends upon the refractive indices of the media1 2 C
Critical angle depends upon the refractive indices of the media
HENCE
If medium 2 is air, n2 = 1, and so

5. 1 2 C
For Water
AIR
WATER
C = 48.80
C = 41.80
For Crown Glass

6. Finding the Critical Angle…
1) Ray gets refracted
2) Ray still gets refracted
4) Ray gets internally reflected
3) Ray still gets refracted (just!)
THE CRITICAL ANGLE

7. Why do diamond sparkle?
* high refractive index
Critical angle =?
* Colours are spread out more and
TIR occurs many times inside the diamond before emerging

8. End probe containing coherent bundle, incoherent bundle, lens and surgical instruments
Controls
Eyepiece
Light injected here
ENDOSCOPE
This is an endoscope image of the inside of the throat. The arrows point to the vocal chords

9. The endoscope is inserted into a body cavity,
which is then illuminated
through an in coherent
bundle of fibres
A lens over the end
of the other bundle
is used to form an
image of the body

10. A coherent bundle means that the fibre ends at each end
must be in the same relative positions

11. A COHERENT BUNDLE: A bundle of optical fibres in which the relative spatial coordinates of each fibres are the same at the two ends of the bundle. Such a bundle are used for the transmission of images.
A NON-COHERENT FIBRE bundle, as you would expect, does not have this precise matrix alignment since they need only transmit light for illumination purposes. They are cheaper to produce.

12. FIBRE OPTIC COMMUNICATIONS
PROBLEM: Input light rays cannot be precisely parallel.
core
cladding
Rays taking different paths will take different times to travel along the fibre, resulting in the jumbling of the signal.
Solution : Monomode fibre only 5μm in diameter

13. Optical fibres
in communications
Purpose?

14. Optical fibres
in communications

15. Optical fibres
in communications

16. Pulse broadening with spectral dispersion
Pulse out with spectral dispersion
Pulse in - white light

17. Pulse broadening with spectral dispersion
Pulse out with spectral dispersion
Pulse in - white light

18. Pulse broadening with spectral dispersion
Pulse out with spectral dispersion
Pulse in - white light

19. Other uses of total internal reflection
1) Endoscopes (a medical device used to see inside the body):
2) Binoculars and periscopes (using “reflecting prisms”)

20. Hot Desert Sand
air layers
THE MIRAGE
Water
for my hump!
Air layers closer to the sand are hotter and less dense. Light from the sky is successively bent until a critical angle is reached and then total internal reflection occurs.
A mirage "water" illusion is seen because the mind initially interprets the light rays reaching our eyes as having come along a straight path originating from the ground. Thus, the image of that patch of sky we see "on the ground" is interpreted as a surface "pool of water."