20-11-2012, 01:35 PM
LASER (semiconducting Lasers)
LASER.ppt (Size: 663.5 KB / Downloads: 219)
For the Laser Course You Need:
A general reading on lasers:
A photocopy from a book by Watson p23-64 (easy read)
Population Inversion and Diode Laser:
A photocopy from Wilson and Hawkes
p 169- 182 (more advance reading)
P 204-223 (more advance reading)
A general reading + the optical fibre application + on laser diode
A photocopy from Kasap
p.159-166 (optical fibre)
P.181-196
EBB 424 Lecture Presentation
EBB 424 Short Lecture Notes summarising all of the above.
Information about the exam
Please study the pass year paper and all of the ‘typical exam questions’ presented to you in the lectures.
There will be 3.5 questions from Optoelectronics Part.
Compulsory for you to answer 2 questions from both part A and B.
Then choose one question from any parts.
Lecture: Laser
Able to state the definition of laser
Able to state the principle of population inversion
Able to explain the principle of semiconducting laser
Familiarise with the concept of light simulation and polarisation
Able to list down all materials criteria and materials selection for a given semiconducting laser compound.
Able to highlight several examples of the application of laser.
Typical Application of Laser
The detection of the binary data stored in the form of pits on the compact disc is done with the use of a semiconductor laser. The laser is focused to a diameter of about 0.8 mm at the bottom of the disc, but is further focused to about 1.7 micrometers as it passes through the clear plastic substrate to strike the reflective layer. The reflected laser will be detected by a photodiode. Moral of the story: without optoelectronics there will no CD player!
Definition of laser
A laser is a device that generates light by a process called STIMULATED EMISSION.
The acronym LASER stands for Light Amplification by Stimulated Emission of Radiation
Semiconducting lasers are multilayer semiconductor devices that generates a coherent beam of monochromatic light by laser action. A coherent beam resulted which all of the photons are in phase.
Another Typical Application of Laser – Fibre Optics
An example of application is for the light source for fibre optics communication.
Light travels down a fibre optics glass at a speed, = c/n, where n = refractive index.
Light carries with it information
Different wavelength travels at different speed.
This induce dispersion and at the receiving end the light is observed to be spread. This is associated with data or information lost.
The greater the spread of information, the more loss
However, if we start with a more coherent beam then loss can be greatly reduced.