Laser
P.K.Ghatak, M.D.
Lasers are so well known today that most people have forgotten that they stand for Light Wave Application by the Stimulated Emission of
Radiation.
In
1916, Einstein suggested that under proper circumstances, atoms could release excess energy as light, spontaneously or when
stimulated by light.
Rudolf
W. Ladenberg in Germany, the first scientist, had observed stimulated
emission in 1928. He did not foresee any practical use of the Laser, if
only he knew what a future the Laser was going to have!!
Science
of Laser:
Atoms
of all substances are in constant motion, vibrate, and rotate.
The
nucleus of atoms is made up of Protons and Neutrons. Electrons
move around the nucleus in several circular orbits(currently
considered in the form of a cloud). Electrons with low energy circle
close to the nucleus and electrons with high energy in the distal
orbits. Elections remain in their own orbits, unless they are
disturbed by an energy that makes them either gain energy and move to
an outer circle, or lose energy and move to an inward circle. Those
electrons which gained energy, returned to the initial state after a time. The excess energy is emitted as an electromagnetic radiation.
That emitted radiation has different wavelengths, moves in different
directions, and is unpredictable. To produce Laser light, all the
photons must be the same wavelength, travel in the same direction
and the same color. This is achieved by the Stimulated Emission.
Stimulated
Emission:
Stimulated
emission occurs when electrons, in an excited state, interact with a
photon (light particle) and emit a second photon with the same
energy, frequency, color, and move in the same direction as the incident
photon. The produced photons then stimulate further and excite more
atoms, leading to a cascade and amplification.
Population
Inversion:
Population
inversion occurs when more electrons exist in an excited/higher
energy state compared to those in a resting state. Only those
electrons in an excited state can be used to produce photons by
stimulated emission.
Mechanism
of Laser Production:
A
laser is created when electrons of glass, crystal, or gas absorb
energy and reach an excited state and then the excess energy is
released as laser.
The
energy source is heat, electricity, or light. A vacuum tube equipped
with a highly reflective mirror at one end and a semi-silver mirror
(allows some light to pass and the rest reflected back) to the other
end. The source material is enclosed inside the tube
By
switching on the energy source, the electrons inside the tube gain
energy and emit excess energy as photons of the same wavelengths of
the energy source and move back and forth by the reflecting mirrors,
making more and more electrons in the excited state and population
inversion occurs. This process generates a Laser of uniform wavelengths, that travel in the same direction and of the same color.
Types
of Lasers.
Lasers
are of 5 main types: Gas, Solid state, Fibers, Liquid or Dye, and
Semiconductor lasers.
The
medical lasers are also several. The main medical lasers are:
Carbon dioxide Laser, used in cutting and destroying tissues and
tumors.
Nd: YAG
laser I used where deeper penetration of tissues is required.
Excimer
Laser. Used in LASIK corneal surgery.
Diode
Laser. Used in Dental surgery and also used as a hair removal agent.
Medical
Laser and Pioneers of Users.
Theodore
Maruim, a physicist and electrical engineer, while pursuing a PhD, experimented with the Laser. In 1920, he used Laser as his thesis. He is
credited with inventing the Laser.
Dr.
Charles Campbell, an Ophthalmologist at Presbyterian Hospital in NYC, used Ruby laser in 1961 to destroy an angioma of the retina.
Leon
Goodman in 1963 used a ruby laser in his dermatological practice.
Dr.
Peter Kiefhaber uses an Argon laser to perform photocoagulation of a bleeding
Gastric ulcer. He also used Nd: YAG laser later for GI bleeding.
In
1976, Hofstetter utilized lasers in urology surgery.
A few
examples of Laser use in medicine.
Laser is used for cutting skin and tissues and coagulation of bleeding vessels.
In cutting excess gum tissues. Burning off unwanted pigmented skin
lesions. Liposuction, Cosmetic plastic surgery, Lithotripsy, Laser
mammography, and Prostectomy. In the laboratory, from biochemical
analysis of a biological sample by a Spectroscope.
Today's
industrial world would not advance much without the laser. From a
laser pointer in the lecture theater to the high-speed
telecommunication, and to heat up gas to generate plasma within the
circular tube of CERNS(Organisation
européenne pour la recherche nucléaire), will come to a screeching halt, if
the laser generation is magically taken away.
Automotive
manufactures and metal structural fabricators are heavy users of
lasers. Military hardware and the “Star Wars” defense and offensive
weapons based on precision, pinpoint accuracy and the speed of light
for their effectiveness. You will be able to add a lot further to this
list, if you recall the use of laser in your activities in a single day.
*******************************
