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Sharda University, Greater Noida
B.Tech.-1st Term, 2022-2023, CSE, Sec.-A
Engineering Physics-I, PHY125
Assignment, Unit-2
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 ( )
( (
) ) 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
acrater 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.
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 105km from the earth. Calculate (a).
the angular spread of the beam and (b). the areal spread when it reaches the moon.
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 corresponding to the
coherent length and (b). coherent time.
10. Explain the systematic diagram, Energy level diagram and working of He-Ne LASER
in detail.
11. Explain the advantages and disadvantages of semiconductor LASER over gas and
solid-state LASER.
12. A laser beam has a power of 50mw. It has an aperture of 5 x 10-3 m and it emits light
of wavelength 7200 A0. The beam is focused with a lens of focal length 0.1 m.
Calculate the area and the intensity of the image.
