It's a Basic concept of Laser on the basis of bandgap. I tried to explain on the easiest way the semiconductor and then i gave the view on Islamic perspective about Laser concept.

1. BISMILLAHIR RAHMANIR RAHIM
Presentation On:
Laser
Musanna Zahangir
International Islamic University Malaysia

2. OUTLINE:
1. What is Laser?
2. How does laser work?
i. Direct/Indirect Bandgap Semiconductors
ii. Radiative Transitions
3. Lasing Reqirements
4. Laser Types
5. Laser Structures
6. Unique Properties of Laser
7. Important Parameters of Laser
8. Application of Laser
9. Laser From Islamic Perspective

3. WHAT IS LASER?
(Light Amplification by Stimulated Emission of Radiation)
 A device that generates an intense beam of coherent
monochromatic light by stimulated emission of photons from
excited atoms or molecules.
 The LASER beam was invented by the physicist MAIMAN in
1960
 Laser is a source of highly directional monochromatic
coherent light

4. HOW DOES LASER WORK?
DIRECT AND INDIRECT SEMICONDUCTORS
• In direct bandgap semiconductor, the
recombination process releases light as
photons
• In Indirect bandgap semiconductors, a
change in electron momentum is required
for recombination to occur
Photon out

5. HOW DOES LASER WORK?
RADIATIVE TRANSITIONS
Optical Absorption
Spontaneous Emission
Stimulated Emission

6. Conduction Band
OPTICAL ABSORPTION
Ec
EvValance Band
Eg
ℎ𝑣

7. SPONTANEOUS EMISSION
Conduction Band
Valance Band
Ec
Ev
ℎ𝑣Eg

8. STIMULATED EMISSION
Conduction Band
Valance Band
Ec
Ev
ℎ𝑣
Egℎ𝑣
ℎ𝑣
The stimulated photons have unique properties:
• In phase with the incident photon
• Same wavelength as the incident photon
• Travel in same direction as incident photon

9. UNIQUE PROPERTIES OF LASER
 High Monochromaticity
 Highly Collimated Beam
 High power
 Wide Tuning Range
 Very Short Pulse Width

10. HIGH MONOCHROMATICITY
(NARROW SPECTRAL WIDTH)
 In Light Source ---
A plot of intensity versus wavelength and it has a certain width (∆λ)
 In Laser Device --- the width is extremely narrow and this means a
radiation of a monochromatic wave [2]

11. HIGHLY COLLIMATED BEAM
 To collimate the light beam of a typical source whose diameter is (2h)
and then to collect the light by a lens with a focal length of (f), the
angle of diversion (𝜃) would be given by (h) over (f)[2]
 For a laser source emitting a beam with a diameter of (D),
which angle of diversion (𝜃) that is very small, and is very
close to (λ) over (D) and that means we got a highly collimated
laser beam

12. Continuous Output (CW) Pulsed Output (P)
Energy(Watts)
Time
Energy(Joules)
Time
HIGH POWER
• The laser can be either continuous or pulsed. The
continuous laser power goes up to the range of
megawatts. Whereas, the pulsed power can reach the
range of exawatt, which is ten to the power 18-[13]

13. 10-13 10-12 10-11 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10 102
LASERS
200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 10600
Ultraviolet Visible Near Infrared Far Infrared
Gamma Rays X-Rays Ultra- Visible Infrared Micro- Radar TV Radio
violet waves waves waves waves
Wavelength (m)
Wavelength (nm)
Nd:YAG
1064
GaAs
905
HeNe
633
Ar
488/515
CO2
10600
XeCl
308
KrF
248
2w
Nd:YAG
532
Retinal Hazard Region
ArF
193
Communication
Diode
1550
Ruby
694
Laser-Professionals.com
Alexandrite
755
Wide Tuning Range
• Wide Tuning range means that laser has a broad range of
electromagnetic spectrum[15]

14. VERY SHORT PULSE WIDTH
 Lasers have a very short pulse width. It can goes down
to the range of femtosecond (ten to the power - 15)

15. LASING REQUIREMENTS
Direct Bandgap Semiconductor
Population Inversion
Optical Resonant Cavity

16. POPULATION INVERSION
 In thermal equilibrium 𝐸𝑐 > 𝐸𝑣,
𝐸𝑐 < 𝐸𝑣
 Population Inversion is the first important requirement for lasing
action to occur[3]
 If Electron concentation in the deplation region,NEc>NEv, then
the population inversion will be satisfied
 Another requirement is to enhance the stimulated emission over
spontaneous emission

17. OPTICAL RESONATOR
 An optical cavity,
resonating cavity is
an arrangement of
mirrors that forms a
standing wave cavity
resonator for light
waves. [14]

18. LASER TYPES
 According to the active material:
 Solid-state
 Liquid, gas
 Semiconductor lasers.
 According to the wavelength:
 Infra-red
 Visible
 Ultra-violet (UV) or x-ray lasers.

19. SEMICONDUCTOR LASER
 Stimulated, organized photon emission occurs when two
electrons with the same energy and phase meet. The two
photons leave with the same frequency and direction.
 A semiconductor laser is a laser in which a semiconductor
serves as a photon source
 The most common semiconductor material that has been used
in lasers is GaAs. Others are AlGaAs, GaP, InGaP, GaN,
InGaAs, GaInNAs, InP, GaInP
 According to the material used, mainly there are two types in
semiconductor laser:
(1)Homo-junction laser
(2)Hetero-junction laser

20. OTHER TYPES OF SEMICONDUCTOR LASER
o Edge-emitting laser diodes
o External cavity diode lasers
o Broad area laser diodes
o High-power diode bars
o High-power stacked diode bars
o Surface-emitting lasers (VCSELs)
o Surface-emitting external-cavity semiconductor lasers (VECSELs)
o Quantum cascade lasers

21. HOMOJUNCTION LASER
 The internal surfaces of the PN junction are polished to be mirrors[11]
 Two sides are roughened to prevent lasing across the diode cavity
 One side is cleaved to make it a highly reflective surface
 The last side is also cleaved, but it is made as a partially reflective
surface

22. HOMOJUNCTION LASER
 At thermal equilibrium, the energy band
diagram of the PN junction, P and N
shall be highly doped[11]
 If a forward bias Vf is applied, the Fermi
level of P will move down and the Fermi
level of N will move up
 If a forward bias increased into a
sufficient large voltage, high injection of
electrons and holes into the depletion
region occur
 Hence, NEc>NEv, and the population
inversion is satisfied

23. HETROJUNCTION LASER
 Hetrojunction laser is the Double-Hetrostructure (DH) Laser
 In which, a thin layer of a small bandgap semiconductor is
sandwiched between two larger bandgap semiconductors
 DH laser requires less current to obtain the population inversion
and to start lasing in the active region[11]

24. RECENT TECHNOLOGIES—
 By reducing the size of the active region—
 Researchers achieved:
 Quantum Well LASER
 Quantum Wire LASER
 Quantum Dot LASER
Hetrojunction Laser Quantum Well Laser

25. IMPORTANT PARAMETERS OF LASERS
 Laser Power
- maximum allowable power
 Peak power
- peak power for pulsed generation
 Wavelength
 Focal Spot Size
- the focal spot size determines the maximum
energy density that can be achieved when the
laser beam power is set
 Death Of Focus (DOF)
- DOF is the distance over which the focused
beam has about the same intensity
 Threshold Current

26. THRESHOLD CURRENT
 Lasing threshold is minimum
current that must occur for
stimulated emission[6]
 It is generally desirable that the
threshold current be as low as
possible, resulting in more
efficient device
 Thus, a threshold current is
one measure used to quantify
the performance of a laser
diode.

27. APPLICATION OF SEMICONDUCTOR LASER
 Optical communication---
 The portable optical telephone
 Multichannel stationary communication lines
 Optical detection and ranging and special automation systems-
 Range-finding
 Aitimetry
 Automatic-tracking systems
 Optical electronics----
 The emitter in an optron
 Logic circuits
 Address devices
 Holographic memory system
 Metrology
 Spectroscopy
 Material processing
 Pumping solid-state lasers
 Medical treatments

28. LASERS FROM ISLAMIC PERSPECTIVE
 Indeed, I swear by what you see. And by what you do not
see.[Surah Al-haqqah(69):38,39].
 Allah mentioned long time ago that we do not see some
particles and creatures. However, the verse doesn’t deny
the fact we could be able to see some of them later on.
Scientists discovered the range of the visible light which
can be detected by the human eye.
 All other waves out this range are not visible to our bare
eyes. However, the invention of laser and its applications
(such like laser microscopy) led to the discovery of many
tiny particles. Laser can also detect fast phenomena that
we were not able to catch
 In addition, laser application in astronomy helped
researchers to capture clearer images of distant galaxies.
For different applications, different lasers with different
bandgap are used.

29. LASERS FROM ISLAMIC PERSPECTIVE
 Everything We created is precisely measured.
[Surah Al-Qamar(54):49].
 All parameters and properties should be chosen
and used precisely. Allah says in Surat Al-
Qamar. We should remember and think about
the greatness of Allah who created everything
precisely.
 Especially when we study that the laser
wavelength decreases and the photons energy
increases when we use a larger bandgap
semiconductor.

30. References:
[1]: Solid State Electronic Devices, B.G. Streetman, S. Banerjee
[2]: Semiconductor Devices Physics and Technology, S.M.SZE.
[3]: An Introduction to Semiconductor Devices, D.Neamen
[4]: How a Laser Works – YouTube.
[5]: How can we achieve population inversion in an P-N diode -YouTube.
[6]: Energy and wavelength [https://faebianbatisman.wordpress.com].
[7]: Understanding Lasers and Fiberoptics, Prof.S.Ezekiel,MIT –YouTube
[8]: http://www.aml.engineering.columbia.edu/
[9]: https://en.wikipedia.org/wiki/Laser
[10]: https://www.teamwavelength.com/info/laserdiodedrivers.php
[11]: construction and working of semiconductor laser – YouTube
[12]: Stimulated Emission – YouTube
[13]: https://www.rp-photonics.com/semiconductor_lasers.html
[14]: Laser ppt – [https://www.slideshare.net/donpraju/laser-ppt]
[15]: Laser – [https://www.slideshare.net/viinnyy/laser]
[16]: Semiconductor Laser- [https://www.slideshare.net/ashiqshariff/]

31. THANKS FOR YOUR
PATIENCE