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2003 Course Laser Applications in Instrumentation (Elective I)

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Total No. of Questions : 12] P1006 [Total No. of Pages : 3 [3664]-248 B.E. (Instrumentation & Control) LASER APPLICATIONS IN INSTRUMENTATION (Elective - I) (2003 Course) Time : 3 Hours] [Max. Marks : 100 Instructions to the candidates: 1) Answer 3 questions from Section-I and 3 questions from Section-II. 2) Answers to the two sections should be written in separate books. 3) Figures to the right indicate full marks. 4) Use of logarithmic tables, slide rule, Mollier charts, electronic pocket calculator and steam tables is allowed. 5) Assume suitable data, if necessary. SECTION - I Q1) a) What are the various processes due to which the small gain coefficients of laser get affected? Explain in detail. [8] b) Explain in detail how the axial modes and transverse modes of Laser output are formed. [8] OR Q2) a) Explain in detail the process of emission and absorption of radiation.[8] b) Calculate the value of population inversion required to give a gain coefficient of 1 per meter in a Nd:YAG laser with 1.06 micrometer for which the spontaneous life time is 230 microseconds, refractive index of 1.82 and line width of 3 THz. [8] Q3) a) Estimate the threshold current density of a GaAs junction laser of 0.84 micrometer wavelength, 14.5 THz line width, loss coefficient 3500 per meter, refractive index 3.6, dimensions length = 300 micrometer, thickness = 2 micrometer and internal quantum efficiency = 1. [9] b) Estimate the efficiency of a GaAs laser operating well above threshold. The refractive index of material is 3.6 and laser cavity length is 0.4 mm. The loss coefficient is 900 per meter length and the internal quantum efficiency is 0.75. [4] c) What are the steps that should be followed in a safe laser laboratory operation? [5] P.T.O. OR Q4) a) Explain the construction and working of He-Ne laser. [8] b) Calculate the efficiency of a He-Ne laser operating with a current of 10mA at a d.c. voltage of 2500 V and gives an optical power of 5 mW. [4] c) Calculate the threshold pumping power of a Nd: Glass laser for critical population inversion of 8 1021/m3 and spontaneous life time of 200 s. The upper level is at an energy of 1.5eV. [6] Q5) a) What are the basic optical interferometers? Explain each in short. [8] b) What is mean by Speckle Pattern? Describe speckle properties in short. [8] OR Q6) a) Write short note on White light interferometer. [8] b) What are the properties of speckle pattern? Describe each in short. [8] SECTION - II Q7) a) Explain the frequency domain processing of Doppler signal in detail.[8] b) What are the performance parameters of operation of laser velocimeter? Discuss. [8] OR Q8) a) What is the principle of operation of Laser velocimeter? Explain. [8] b) What are the two options for the electronic processing of the Doppler signal? Compare it. [8] Q9) a) Show that the frequency of the sagnac signal in RLG is proportional to the angular velocity of rotation. [8] b) Explain in detail the closed loop configuration of Fiber Optic Gyroscope. [8] OR Q10) a) What is Sagnac effect? Show how is the phase shift is proportional to the angular velocity. [8] b) What are the components required for all fiber FOG configuration? Explain each in short. [8] [3664]-248 -2- Q11) a) Write a short note on Holographic Interferometer. [9] b) What are different emulsions used to record the holograms? Mention the characteristics of it. [9] OR Q12) a) A thin strip of the hologram undergoing stress parallel to the x-axis is illuminated by a He-Ne laser. The fringes are localized in a plane having slope of 1.5 per unit length in x-direction and the fringe spacing is found to be 1 mm. Hence find the strain. [8] b) List out the applications of holographic interferometer that you know. Explain any one in detail. [10] [3664]-248 -3-

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