Laser

 

                                                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.

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