PHY125 UNIT-2 Assignment LASER PHYSICS
1. Explain the difference between the white light and the LASER light in
detail.
2. Explain the interaction of radiation with matter (absorbance, spontaneous
emission and stimulated emission) in detail.
3. Drive the relation
u
(
ν
)
=A/B
(exp
(
hν
kT
)
−1)
and show that from here laser action
is easily possible up to the infrared region. Take the example of λ=20cm
and λ=500nm.
4. Calculate the ratio of the population densities of upper and lower LASER
levels, assume that the material is in thermal equilibrium. It is given that
the wavelength separation between the energy levels is 1 micrometer at
the temperature of 295 K.
5. A laser beam λ= 6000Å on earth is focused by a lens (or minor) of
diameter 2m on to a crater on the moon. The distance of the moon is 4 x
108 m. How big is the spot on the moon? Neglect the effect of earth's
atmosphere. Ans: 1.44 x 104 m2.
6. Write the different applications of LASER. Explain one in detail.
7. A laser beam has a wavelength of 8 x 10-7 m and aperture 5 x 10-3 m. The
laser beam is sent to moon. The diastance of the moon is 4 x 105 km from
the earth. Calculate (a). the angular spread of the beam and (b). the areal
spread when it reaches the moon. Ans: (a) 1.6 x 10-4 radian, (b): 4.096 x
109 m2.
8. Explain the systematic diagram, Energy level diagram and working of
Ruby LASER in detail.
9. The coherence length for sodium light is 2.945 x 10-2 m. The wavelength
of sodium light is 5890 A0. Calculate: (a) the number of oscillations
