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Sample Exam Paper

MPY301Sample Examination Paper — I

Course: Laser Physics (MPY301)Programme: M.Sc. Physics (Electronics Specialization) — Semester III
Time: 3 HoursMaximum Marks: 70

General Instructions:

  1. All questions in Section A are compulsory.
  2. Attempt any two parts from each question in Section B.
  3. Attempt any two questions in full from Section C.
  4. Draw energy-level diagrams wherever applicable.

Section A — Short Answer (Compulsory)

  1. Distinguish between spontaneous and stimulated emission. (2 marks)
  2. Define population inversion. Why is it not possible in a two-level system? (2 marks)
  3. What are the main components of a laser system? (2 marks)
  4. Name any two solid-state lasers with their operating wavelengths. (2 marks)
  5. What is the basic principle of holography? (2 marks)
  6. Define numerical aperture of an optical fibre. (2 marks)
  7. What is LIDAR? State one application. (2 marks)

Section B — Attempt any two parts of each

  1. Derive the relation between the Einstein A and B coefficients and explain their physical significance. (5 marks)
  2. Explain the difference between three-level and four-level laser systems, with suitable examples. (5 marks)
  3. Describe the construction and working of the He-Ne laser with an energy level diagram. (5 marks)
  4. Explain the construction and reconstruction of a hologram, and describe two applications of holography. (5 marks)
  5. Explain saturation spectroscopy and how it achieves Doppler-free resolution. (5 marks)

Section C — Attempt any two questions in full

  1. Discuss in detail the concept of population inversion. Explain, with energy-level diagrams, why three-level systems are inherently less efficient than four-level systems, using the Ruby and Nd:YAG lasers as examples. (10 marks)
  2. Describe the construction, working and applications of the CO2 laser. Compare its suitability for industrial materials processing with that of the Nd:YAG laser. (10 marks)
  3. Explain the principle, construction and reconstruction process of a hologram in detail. Discuss Holographic Non-Destructive Testing (HNDT) and holographic data storage as applications. (10 marks)
  4. Describe the propagation mechanism of light in an optical fibre and explain the roles of fibre amplifiers and fibre-optic sensors in modern communication and sensing systems. (10 marks)
  5. Discuss laser applications in materials processing — cutting, welding, alloying and laser hardening — explaining the underlying physical mechanism in each case. (10 marks)