Download AKTU B-Tech 3rd Sem 2018-2019 Laser Systems And Applications Roe 033 Question Paper

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Paper ID: 199304

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Time: 3 Hours

Roll No.

B TECH

(SEM-III) THEORY EXAMINATION 2018-19

LASER SYSTEMS AND APPLICATIONS

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Total Marks: 70

Note: 1. Attempt all Sections. If require any missing data; then choose suitably.

SECTION A

1. Attempt all questions in brief.
   1. What do you understand by Fermi Dirac Distribution function?
   2. What is temporal coherence?

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   3. A laser diode emits 150000 pulses per second. The duration of each pulse is 30ns. Calculate Duty cycle.
   4. What is the drawback of Ruby laser?
   5. Enlist the difference between Krypton ion laser and Argon ion laser.
   6. What are the losses associated in optical communication systems?
   7. Why pumping is necessary for laser action?

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   2 x 7=14

SECTION B

1. Attempt any three of the following:

   7x3=21

   1. What is black body radiation? On what factors does the black body radiation depend upon?

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   2. What is optical cavity? Calculate the loop gain with and without losses for optical cavity.
   3. Differentiate between continuous wave laser and pulse laser. Discuss various pulsating technique for a laser.
   4. With suitable diagram explain construction and working of Nd:Glass laser.
   5. How are lasers useful in material processing? Discuss laser cutting and laser welding process.

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SECTION C

1. Attempt any one part of the following:

   7x1=7

   1. Explain Bohr's theory of Hydrogen atom. If an electron transits from second orbit to the first orbit. Find the wavelength of electron in Hydrogen atom.
   2. Explain the physical significance of wave function ψ. Derive time-independent Schroedinger wave equation.

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2. Attempt any one part of the following:

   7x1=7

   1. Differentiate between spontaneous emission and stimulated emission. The output of a laser has a pulse duration of 60ms and average power is 1 watt per pulse. How much energy is released per pulse and how many photons does each pulse contain if the wavelength of laser beam is 6000Å.
   2. What is Q-switched laser? Explain various techniques used in Q-Switching.
3. Attempt any one part of the following:

   7x1=7

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   1. Why four level laser systems are more efficient than three level laser systems? Find the ratio of population of two energy states of the Ruby laser the transition between which is responsible of photon of wavelength 6928 Å. Assume ambient temperature is 18K.
   2. What are the main components of a laser? Briefly explain each component.
4. Attempt any one part of the following:

   7x1=7

   1. With a suitable schematic diagram explain the working of dye laser. How are dye lasers tuned?

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   2. Illustrate the construction and working of an excimer laser. Enlist the applications of excimer lasers.
5. Attempt any one part of the following:

   7x1=7

   1. How are lasers useful in the field of medicine? Briefly explain the application of lasers in Ophthalmology and general surgery.
   2. Discuss the principle of holography. Explain the construction and reconstruction of a hologram.

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Physical Constants

• Rest mass of Electron m = 9.1 x 10^-31 kg
• Rest mass of Proton m_p = 1.67 x 10^-27 kg
• Speed of light c = 3 x 10⁸ m/s

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• Plank's constant h = 6.63 x 10^-34 J-S
• Charge on electron e = 1.6 x 10^-19 C
• Boltzmann's Constant k = 1.38 x 10^-23 J/K