B.A. /B.Sc. (General) 4th Semester
Physics
Paper-B: Optics and Laser-II
Time Allowed: Three Hours] [Maximum Marks: 22
Note: - Attempt two questions from Section I, two questions from Section II, and six parts of the question in Section III. Only non-programmable calculators are allowed to be used.
SECTION-I
I. (a) Explain stimulated emission, spontaneous emission, and induced absorption. Derive relation between Einstein's spontaneous and stimulated emission coefficients.
(b) What are main features of Laser Light?
II. (a) What do you mean by broadening of spectral lines? Derive an expression for Doppler Broadening.
(b) Find the Doppler Broadening for 6328Ao laser transition in He-Ne Laser, assuming a single isotope of Ne20 and that the Laser operates at temperature of 373 K.
III. (a) What is population inversion ? Why is it essential and how is it achieved in a Laser?
(b) Explain the elementary theory of optical cavity.
SECTION-II
IV. (a) Discuss construction and working of Ruby Laser.
(b) What are applications of Lasers?
V. (a) Discuss construction and working of CO2 Laser with neat labelled diagram.
(b) Find the possible frequency spread when transition takes place from unstable upper state having life time 10-8 s.
VI. (a) What is Holography ? Describe recording of a hologram and reconstruction of image. How holography is different from ordinary photography?
(b) What are sources of attenuation of signal in optical fibres?
SECTION-III
VII. Attempt any six parts:
(i) Distinguish between LASER and MASER.
(ii) How does Laser light differ from the light from a filament lamp?
(iii) Can we obtain light amplification in absence of stimulated emission?
(iv) Define temporal coherence and spatial coherence.
(v) Do you think energy conservation is violated in Laser?
(vi) Define coherence time.
(vii) What is Laser pumping?
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