It is the short form of Light Amplification by Stimulated Emission of Radiation. The inventor said Laser is a marriage of optics and electronics. Lasers are also called optical Masers. Here M stands for microwave. The absorption and emission of electromagnetic radiation by materials is used for making Laser. The Frequency of lasers is 10*14 to 15 Hz.

Absorption

When a photon of energy hv = E2-E1 is incident on a material then atom in the lower energy level E1is absorbed that energy and come to energy level E2, this is called induced or stimulated absorption.

Stimulated Emission

From the energy level E2 the atom may come to the lower energy level E1, then one photon energy is emitted this is called stimulated emission. When the photon is absorbed it disappears, the emitted photon energy has the same energy as that of absorbed photon, to conserve energy and will be in phase with incident photon to conserve momentum.

Principle of Laser

The action of laser is based on the principle of stimulated emission of an atom

When an atom in excited state gets  a photon, it emits a photon with same energy. Now we have two photons this two photon incidents on two atoms then they emits two more photons, now there will be four photons with same energy this goes on in a chain, giving a number of photons having same energy. This increases the intensity of radiation and amplification due to stimulated emission is achieved. Now we have more photons than absorbed.

For lasing action we need more than two energy levels

Optimum Condition for Lasing action

For laser operation the following basic requirements must be satisfied.

  1. Density of incident photon should be large
  2. A21/B21 must be very large. A21 and B21 are Einstein constants
  3. There must be optical feedback at the ends of the medium to form a resonant cavity in order to get powerful laser beam

Properties of Laser Light

Directionality

It is highly directional due to stimulated emission. There may be deviation due diffraction. This can be measured by the full angle beam divergence. For a typical laser beam has divergence less than 10*-5

Intensity

It is highly intense and can be sharply focused. The energy is concentrated In a small area.

Coherence

Photons coming out of the laser beam have zero phase difference that is it is travelling parallel.

Parts of Laser

Lasing materials are crystal gas or semiconductor. A source of energy is needed for lasing material. An optical cavity is needed, which consists of reflectors or concave mirrors.

Different kinds of Lasers

Solid state laser, Gas laser, Liquid laser, semi conductor laser,

Applications of Lasers

It is used in material processing, laser welding, laser drilling, laser cutting, in surgery, in precision measurement.

It is also used in bar code reading, in DVD players, in printers, in medial experiments.

Conclusion

Laser is a modern technology development, which is very useful in everyday life. This is not harmful. A tube fitted with concave mirrors to reflect light.