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Note for Applied Physics - Phy By Suman Kumar Acharya

  • Applied Physics - Phy
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1. The wavelength of a He-Ne LASER generating 3.14 mW power is 632.8 nm. When it is in operation, the number of photons emitted per minute is ………… . [ BPUT_20016-17_1st SEM_Regular_2Marks] Soln: (Ans.) [Given power ; Wavelength . Energy of a single photon Number of photons per second the He-Ne laser emit is So, Number of photons the He-Ne laser emitted per minute (i.e. 60 seconds) is ] 2. Write two applications of LASER. [ BPUT_20016-17_1st SEM_Regular_2Marks] Soln: Many applications are there. We can write any two.  A wide variety of interferometric techniques.  Raman spectroscopy.  Laser induced breakdown spectroscopy.  Atmospheric remote sensing.  Investigating nonlinear optics phenomena.  Holographic techniques employing lasers also contribute to a number of measurement techniques.  Lasers have been used aboard spacecraft such as in the Cassini-Huygens mission.  In astronomy, lasers have been used to create artificial laser guide stars, used as reference objects for adaptive optics telescopes. 3. What does LASER stand for? Describe in detail, the components, principle of operation and working of a Ruby LASER. [ BPUT_20016-17_1st SEM_Regular_10Marks] 4. Q: Differentiaate between spontaneous emission and stimulated emission of radiation. Soln:  Spontaneous Emission: It is polychromatic radiation. Stimulated Emission: It is monochromatic radiation.  Spontaneous Emission: Less intensity. Stimulated Emission: High intensity.  Spontaneous Emission: Less directionality, so more angular spread during propagation. Stimulated Emission: High directionality, so less angular spread during propagation.  Spontaneous Emission: Specially and temporally incoherent radiation.

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Stimulated Emission: Specially and temporally coherent radiation.  Spontaneous Emission: It takes place when excited atoms make transition to lower energy level voluntarily without any external stimulation. Stimulated Emission: It takes place when a photon of energy equal to stimulates an excited atom to make transition to lower level. 5. A semiconductor diode laser has a peak emission wavelength of 1.55 eV. Soln: Given wavelength 1.55 1.55 m Band gap , where & velocity of light Plank’s constant . Find its band gap in m/s Js So   eV [1eV= ] 0.8 eV (Ans.) 6. Calculate the wavelength of emitted radiation from GaAs which has a band gap of 1.44 eV. Soln: Band gap 1.44 eV 1.44 [1eV= ] We know   [as 8633 Plank’s constant Js and m m/s] velocity of light 8633 (Ans.) 7. How many photons per second a low power(1mW) He-Ne laser emit(λ=633 nm)? Soln: Given power ; Wavelength Energy of a single photon Number of photons per second the He-Ne laser emit is . (Ans.) 8. The wavelength of a He-Ne LASER generating 3.14 mW power is 632.8 nm. When it is in operation, calculate the number of photons emitted per minute. Soln: Given power ; Wavelength . Energy of a single photon Number of photons per second the He-Ne laser emit is So, Number of photons the He-Ne laser emitted per minute is (Ans.)

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MCQ: 1. Laser light is produced due to (a) Interference of light radiation (c) light amplification by stimulated emission of (b) Spontaneous emission of light (d) diffraction phenomenon 2. Which laser was invented first? (a) Semiconductor laser (c) He-Ne laser (b) Ruby laser (d) CO2 laser 3. Which of the following is a gas laser? (a) CO2 laser (c) Semiconductor laser (b) Ruby laser (d) Dye laser 4. Two different light sources are sending light and spots from both beams on a screen is obtained. Which of the following statements is true? (a) The broad and faint spot is a laser while the bright and narrow spot is an ordinary light. (b) The broad and bright spot is a laser while the narrow and low intensity spot is an ordinary light. (c) The broad and low intensity spot is an ordinary light while the narrow and highly intense spot is a laser light. (d) Actually both the spots will merge into each other and form an interference patterns. 5. A highly coherent beam is produced. The beam is (a) Laser light (b) Ordinary light electrodes. (c) converged light from the sun (d) spark produced between the gap of two 6. Which of the following conditions is very essential for the production of laser light? (a) Spontaneous emission process (c) Population inversion process (b) Stimulated emission process (d) All of the above. 7. Which is of the following is not a pumping process? (a) Optical pumping (c) Chemical pumping

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(b) Electrical pumping (d) Thermal pumping. 8. Which of the following scheme does not produce lasing action? (a) Two-level scheme (c) Four-level scheme (b) Three-level scheme (d) Five-level scheme. 9. High-power laser light is obtained from (a) CO2 laser (c) He-Ne laser (b) Semiconductor laser (d) Ruby laser. 10. Pulsed laser light is produced from a (a) Ruby laser (c) CO2 laser (b) Carbon laser (d) none of the above. 11. Which of the following is not a laser property? (a) Coherence (c) Extreme brightness (b) Highly directional (d) Divergence. 12. Production of laser does not include (a) Active medium flat mirror (c) one highly silvered and other partially silvered optically (b) Two highly silvered optically flat mirrors 13. Which source of light is brightest? (a) Sunlight (c) Arc light (b) Laser light (d) Flash light. (d) optical cavity.

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