The laser is an optical amplifier that works on the principle of stimulated emission of radiation. Einstein first predicted stimulated emission in 1917, but it was not utilized until the 1950s when the maser was developed. In 1960, Maiman built the first laser, a ruby laser, and shortly after the first gas laser was developed. The basic components of a laser are an active medium to amplify light, an excitation mechanism to energize the medium, and optical resonators with at least one mirror to provide feedback. Common laser types include He-Ne, CO2, and semiconductor lasers which have various applications like optical storage, surgery, manufacturing.

1. LASERS

2. Theory of Lasing
1.Introduction (Brief history of laser)
The laser is perhaps the most important optical
device to be developed in the past 50 years. Since
its arrival in the 1960s, rather quiet and
unheralded outside the scientific community, it
has provided the stimulus to make optics one of
the most rapidly growing fields in science and
technology today.

3. The laser is essentially an optical amplifier. The word
laser is an acronym that stands for “light amplification by
the stimulated emission of radiation”. The theoretical
background of laser action as the basis for an optical
amplifier was made possible by Albert Einstein, as early as
1917, when he first predicted the existence of a new
irradiative process called “stimulated emission”. His
theoretical work, however, remained largely unexploited
until 1954, when C.H. Townes and Co-workers developed a
microwave amplifier based on stimulated emission
radiation. It was called a maser.

4. Following the birth of the ruby and He-Ne lasers, others devices followed
in rapid succession, each with a different laser medium and a different
wavelength emission. For the greater part of the 1960s, the laser was
viewed by the world of industry and technology as scientific curiosity.
In 1960, T.H.Maiman built the first laser device
(ruby laser). Within months of the arrival of Maiman’s
ruby laser, which emitted deep red light at a
wavelength of 694.3 nm, A. Javan and associates
developed the first gas laser (He-Ne laser), which
emitted light in both the infrared (at 1.15mm) and
visible (at 632.8 nm) spectral regions..

5. Einstein’s quantum theory of radiation
In 1916, according to Einstein, the interaction of radiation
with matter could be explained in terms of three basic
processes: spontaneous emission, absorption and stimulated
emission. The three processes are illustrated and discussed in
the following:

6. The Three Process
E1
E2
hυ
(a) Absorption
hυ
(b) Spontaneous emission
hυ
(c) Stimulated emission
In
hυ
Out
hυ
E2
E2
E1 E1
Absorption, spontaneous (random photon) emission and stimulated
emission.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)

7. Stimulated Emission

8. BASIC LASER COMPONENTS
High Reflectance
Mirror (HR)
Output Coupler
Mirror (OC)
Active
Medium
Output
Beam
Excitation
Mechanism
Optical Resonator
Laser-Professionals.com
19/04/158

9. He-Ne laser
•Medium excited by large electric discharge, flash pump or continuous
high power pump
•In gas, atoms characterized by sharp energy levels compared to solids
•Actual lasing atoms are the Neon atoms
Pumping action:
Electric discharge is passed through the gas
Electrons are accelerated, collide with He and He atoms and excite them
•Laser medium is mixture of Helium and Neon gases in the ratio 10:1
to higher energy levels

10. He-Ne Laser

11. The CO2 LASER:
•Lasers discussed above – use transitions among various excited electron
states of an atom or ion
•CO2 laser – uses transition between different vibrational states of CO2
molecule
●
•One of the earliest Gas lasers
•Highest power continuous wave laser currently available
•
•The filling gas within the discharge tube consists primarily of:
Carbon dioxide Hydrogen Nitrogen Helium
(proportions vary according to a specific laser)

13. Typical Application
of LaserThe 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!

14. Metal cutting

15. LASER RETINA OPERATIONS AND
SCANNING