Applied Physics I: Chapter 10: Applied Optics - Lasers
Characteristics of Laser
Since an ordinary light spreads in all directions, the intensity reaching the target is very less.
CHARACTERISTICS
OF LASER
Directionality:
Ordinary
light spreads in all directions and its angular spread is 1 metre/metre. But,
it is found that laser is highly
directional and its angular spread is 1 mm/metre. For example the laser
beam can be focused to a very long distance with a few divergence (or) angular
spread.
Divergence
(or) Angular spread is given by (ϕ) = r2‒r1
/ d2‒d1 degrees.
Where
d1,d2 are any two distances from the laser source emitted
and r1, r2 are the radii of the beam spots at a distance
d1 and d2 respectively as shown in Fig.10.1.
Intensity:
Since
an ordinary light spreads in all directions, the intensity reaching the target
is very less. But in the case of laser, due to high directionality the
intensity of laser beam reaching the target is of high intense beam. For
example, 1 milli watt power of He‒Ne laser appears to be brighter than the
sunlight.
Monochromatic:
Laser
beam is highly monochromatic (i.e) the wavelength is single, whereas in
ordinary light like mercury vapour lamp, many wavelengths of light are emitted.
Coherence:
It
is an important characteristics of laser beam. In lasers the wave trains of the
same frequency are in phase (i.e) the radiation given out is in mutual
agreement not only inphase but also in the direction of emission and
polarization. Thus it is a coherent beam. Due to high coherence
it results in an extremely high power.
There
are two types of Coherence viz.
1. Temporal coherence.
1.
Temporal coherence refers to the coherence between the two points of same wave
at different time, as shown in Fig. 10.2.
2.
Coherence length is small.
3.
Coherence time is less
2. Spatial coherence
1.
Spatial coherence refers to the coherence between two points in different waves
over a time 't', as shown in Fig. 10.3.
2.
Coherence length is large
3.
Coherence time is more.
Due
to these peculiar properties of laser, it has wide engineering and medical
applications.
Applied Physics I: Chapter 10: Applied Optics - Lasers : Tag: Applied Physics : - Characteristics of Laser
Applied Physics I: Chapter 10: Applied Optics - Lasers
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