Laser

LASER. At the first instant the name reminds me of my childhood days when I used to fancy about sci-fi robots, extra-terrestrials and heroes with mighty powers. I still remember watching numerous shows like Startrek or Galactica back in the 90s. An integral part of all those shows was the “Laser” which was used either in the form of weapons of mass destruction by perilous space beings or even in the form of “teleporters”.

Little did I know that the laser had even more important and mind boggling applications in our daily lives than in amusing but apocryphal science fictions. From checking out the shopping at the supermarket to precision hospital surgery, from printing our homework to communicating along thin strands of glass---laser is all around us.

SPECTACULAR LASER SHOWS ARE A COMMON PUBLIC ATTRACTION TODAY

LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. Most lasers share the following components:

1. A lasing medium
2. An energy source
3. A resonator

Conventional lasing mediums consist of mixtures of helium and neon gases. In normal conditions the atoms of the gases are all in their ground states. The lasing medium is enclosed within a discharge tube with highly reflecting mirrors at two ends of the tube along with arrangements for the application of high voltages.

This high voltage arrangement acts as an energy source. When a high voltage is applied across the ends of the tube containing the gas, an electric current is caused to flow through it, thereby exciting the electrons in the atoms of the lasing medium to higher energy levels---a situation termed as Population Inversion.

When the excited atoms decay to the ground state, they emit photons of light spontaneously. However, if this photon of light then meets another excited atom, it stimulates the excited atom to drop to its ground state. In this process, another photon of light is emitted (by stimulated emission).

THE SCHEMATIC DIAGRAM SHOWS: 1. LASING MEDIUM

2. ENERGY SOURCE; 3,4. MIRROR RESONATORS; 5. EMERGENT LASER LIGHT

Einstein showed in his papers that both the stimulating and the stimulated photons have:
The same wavelength
The same phase
The same direction of travel

The emitted photons can be allowed to bounce back and forth along the axis of the tube by means of highly reflecting mirrors which act as resonators. This avalanche effect produces more and more photons until a beam of monochromatic laser light is allowed to emerge from any one end of the discharge tube.
----
By Mahmud Hasan
The Aftermath Publications
----
The Aftermath Publications, Issue 3
----