This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Pumping Mechanism”.
1. Optical pumping happens via ___________
a) Spontaneous emission
b) Spontaneous Absorption
c) Stimulated emission
d) Stimulated Absorption
Explanation: In optical pumping, a highly intense radiation from an optical flash tube is incident on the active medium, raising the atoms to a higher energy state through stimulated absorption.
2. Pumping is done in order to achieve __________
a) Steady state
b) Population inversion
d) Photon emission
Explanation: Pumping is the process of raising the atoms or molecules of the active medium to a higher energy state so that the stage of population inversion can be achieved.
3. Which pumping method is used in He-Ne laser?
a) Optical Pumping
b) Electrical Excitation
c) Chemical Pumping
d) Direct Conversion
Explanation: Generally, in He-Ne laser, an electric discharge is used to excite the atoms of the active medium. This process is known as Electrical Excitation and is normally used in gas lasers.
4. Direct conversion of electrical energy into radiation takes place in ___________
a) Ruby laser
b) ND: YAG
d) He-Ne laser
Explanation: In Light Emitting Diodes (LED) and semiconductor lasers, direct conversion of electrical energy into radiation takes place. This process of pumping is called as Direct conversion.
5. At least 2 levels are required in a crystal to achieve population inversion.
Explanation: Population inversion takes place in crystals with a minimum three-level system. Two level system is not suitable for achieving population inversion because in that case the population of both the levels would remain same as B12 = B21.
6. Which of the following is a four-level laser?
a) ND: YAG
d) Semiconductor laser
Explanation: He-Ne laser is a four-level laser. Whenever an electric discharge is passed through the gas, the helium atoms gets to higher energy states, as the concentration of helium atoms is higher to achieve population inversion.
7. The meta-stable state have a larger lifetime then lower energy state.
Explanation: The meta-stable states have an unusually long lifetime. It is due to this that the number of atoms if higher in meta-stable state then in lower energy state, which causes population inversion.
Explanation: After pumping, the atom will get excited to the exited state. After that, as the lifetime of the exited state is lower, it will drop to the meta-stable state.
9. The output of a laser has pulse duration of 30 ms and average output power of 1 W per pulse. How much energy is released per pulse if wavelength is 6600 Å?
a) 0.001 J
b) 0.002 J
c) 0.003 J
d) 0.004 J
Explanation: As we know, Energy = Power X Time
= 1 W X 30 X 10-3s
= 0.003 J.
10. What is the region enclosed by the optical cavity called?
a) Optical Region
b) Optical System
c) Optical box
d) Optical Resonator
Explanation: The optical cavity resembles an oscillator as it provides feedback of the photons by reflection, at the mirrors. Therefore, the area enclosed inside the optical cavity is called optical resonator.
Sanfoundry Global Education & Learning Series – Engineering Physics.
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