PTU Latest Question Bank || Punjab Technical University
Overview - Laser
- Define Laser - coherent source of light
- Characteristic properties of laser light - monochromatic, unidirectional, highly intense and coherent
- Full form of laser
- What is coherence - its two types - temporal n spatial (define and give significance)
- Define - population inversion, lifetime of an energy state, metastable state
- Principle of laser - Stimulated emission - emission which requires external help - happens before the lapse of lifetime of energy state
- Spontaneous emission - happens by itself after the lapse of lifetime of energy state
- Discuss Einstein theory of matter and radiations - relationship amongst various Einstein coefficients - define Einstein Coefficients, give their physical significance and their units.
- Give conditions of lasing action
- Components of laser - (i) Laser medium (should be able to achieve population 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 one frequency /wavelength to be amplified based on 21=?.
- 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
- 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, CO2
- Explain construction and working (energy level diagram) of Ruby laser.
- Explain Construction of He-Ne laser and CO2 laser.
- Explain working using energy level diagram of He-Ne laser and CO2 laser.
- Why He and Ne are mixed together?
- How He-Ne laser is better than Ruby laser?
- Why CO2 and N2 are mixed together?
- Why He is added in the mixture of CO2 and N2 in CO2 laser?
- Construction and working (energy level diagram) of diode laser.
- Applications of He-Ne laser
- Applications of CO2 laser
- Applications of diode laser
- Applications of lasers in general
- Disadvantages of lasers
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