Download PTU Laser Overview_0 Question Bank

Overview - Laser

1. Define Laser - coherent source of light
2. Characteristic properties of laser light - monochromatic, unidirectional, highly intense
and coherent

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3. Full form of laser
4. What is coherence - its two types - temporal n spatial (define and give significance)
5. Define - population inversion, lifetime of an energy state, metastable state
6. Principle of laser - Stimulated emission - emission which requires external help -
happens before the lapse of lifetime of energy state

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7. Spontaneous emission - happens by itself after the lapse of lifetime of energy state
8. Discuss Einstein theory of matter and radiations - relationship amongst various Einstein
coefficients - define Einstein Coefficients, give their physical significance and their units.
9. Give conditions of lasing action
10. Components of laser - (i) Laser medium (should be able to achieve population

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inversion, can be solid, liquid, gas) (ii) Pump (device to supply energy to create population
inversion) - its types ( optical, electric discharge, electric, chemical) (iii) Optical Resonator
(composition - two plane parallel mirrors with common principal axis, one fully polished
and other is partially polished ; working - makes the photons oscillate between two
mirrors and number of photons grows, positive feedback device as well as help to select

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one frequency /wavelength to be amplified based on 2l=n?.
11. 3-level laser : Ground state and Lower lasing level coincide with each other; normal
excited state and upper lasing level (metastable state) separately defined eg Ruby laser
12. 4-level laser : All the four levels, ground state, lower lasing level, upper lasing level and
normal excited state separately defined. Continuous Output. e.g. He-Ne, CO

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2

13. Explain construction and working (energy level diagram) of Ruby laser.
14. Explain Construction of He-Ne laser and CO
2

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laser.
15. Explain working using energy level diagram of He-Ne laser and CO
2
laser.
16. Why He and Ne are mixed together?

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17. How He-Ne laser is better than Ruby laser?
18. Why CO
2
and N
2

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are mixed together?
19. Why He is added in the mixture of CO
2
and N
2

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in

CO
2
laser?

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20. Construction and working (energy level diagram) of diode laser.
21. Applications of He-Ne laser
22. Applications of CO
2
laser

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23. Applications of diode laser
24. Applications of lasers in general
25. Disadvantages of lasers
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