CMR Institute of Technology Jan 2015 - May 2015 // Engineering Physics -14PHY22 // Sem 2- // Assignment # 05 – Lasers // Submission Due: 23/3/2015 ANSWER NEATLY AND LEGIBLY on A4 sheets only and not in sheets torn from a book. Sketch diagrams wherever relevant. Explain your notations explicitly and clearly.

ON the top of the first page, write your Name, Class, Section, Roll No., Due Date and Date of Submission. An incomplete assignment is not acceptable for submission. Once you submit your assignment, you will be expected to answer all the questions there INDEPENDENTLY. You may be asked to answer any question of the assignment in the class.

1. Explain the terms i) Stimulated emission ii) population inversion iii) metastable state iv) resonant cavity v) pumping. 2. Obtain an expression for Energy density of radiation under equilibrium conditions in terms of Einstein’s coefficients. 3. Describe principle, construction of CO2 laser and explain its working with the help of energy level diagram. 4. What are semiconductor lasers? Describe the construction and working of gallium-arsenide laser along with applications. 5. Describe briefly the applications of lasers in welding, cutting and drilling. 6. Write a note on measurement of pollutants in the atmosphere using laser. 7. What is holography? Describe recording and reconstruction process in holography with the help of suitable diagrams. 8. The ratio of population of two energy levels is 1.059 ×10-30. Find the wavelength of light emitted at 330K 9. Find the ratio of population of the two energy levels in a medium in thermal equilibrium if the transition between them produces light of wavelength 694.3 nm. Assume the ambient temperature as 27oC. 10. A He-Ne laser is generating laser beam of power 4 mW. Calculate the number of photons emitted by the laser. Given the wavelength of the emitted radiation is 680nm.