Test: Laser - Mechanical Engineering MCQ

Coherence is an important characteristic of laser beam because in laser beams, the wave trains of same frequency are in phase/ Due to high coherence it results in an extremely high power.

The atoms of Ruby are excited with the help of photons emitted with the help of photons emitted by an external optical source. The atoms absorb energy from photos and raises to excited state. Therefore Ruby laser is an example of optical pumping.

Laser beam has very high intensity, directional properties and coherence. When it is focussed on a particular area for a long time, then the area alone will be heated and the other area will remain as such. This is called thermal effect.

 E = hc/ʎ
Therefore, ʎ = hc/E
ʎ = 4430.8 Å

E = hc/ʎ
E = 4.006×10^-19 Joules
Number of photons required = (1 Joule)/(4.006×10^-19 )
N = 2.4961×10¹⁸/m³

Since Nd YAG laser has a higher thermal conductivity than other solid state lasers, it lends itself for generation of laser pulses at a higher pulse repetition rate or a quasi continuous wave operation.

 When population inversion is achieved, the majority of atoms are in the excited state. This causes amplification of the incident beam by stimulated emission. Thus the laser beam is produced.

In laser surgery, without knife, bloodless operation, cutting tissues etc can be made, hence laser is
called non-material knife.

A DVD player contains a laser. By moving the lens longitudinally, different depths can be reached in the disc. In order to make room for a lot of information on every disc, the beam has to be focused on as small an area as possible. This cannot be done with any other light source.

 Before laser maser was used. It stood for microwave amplification by stimulated emission of radiation. This was based of Albert Einstein’s principle of stimulated emission. It was used in atomic clock.