The Laser

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Einsteins realisation?

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that from one photon two is gotten so we can amplify light.

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L

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is distance between mirrors, m is integer.

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23 Terms

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Einsteins realisation?

that from one photon two is gotten so we can amplify light.

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L

is distance between mirrors, m is integer.

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First step for Laser creation

Absorption: When electrons in the ground state absorb a photon with certain energy then it can move to a higher state, if the energy difference between ground and excited state is same as photons energy.

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Spontaneous emission

The electron goes back to the ground state after some time and emits a photon of defined energy.

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Population inversion

To get a high intensity light we need to create a lot of numerous excited electrons in a material then invest energy from outside into the material (laser pumping)

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Stimulated emission

Einstein that we could induce emission, when a photon with energy that satisfies Bohrs condition for electrons in excited state is emitted by electron in excited state.

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LASER

Light amplification by stimulated emission of radiation

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Example of three level system

Ruby laser, the medium is chromium doped synthetic sapphire

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What do we need for Laser oscillators?

gain medium, intensive electron excitation, positive feedback and optical resonator.

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Resonance condition?

2L = m(wavelength)

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Explain Monochromatic attribute of Laser

narrow bandwidth

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Coherence of Lasers?

create interference even in big path differences.

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How is laser Collimated

Has a narrow beam with little divergence

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What is Power density for laser lights

has higher power density (E/At) than ordinary light

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How is laser polarized?

ultrashort pulses

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Pulse length of Q-switched lasers

100 - 200ns

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Example of 4 level system

He-Ne laser

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Classification of lasers

By gain medium, by operation and by energy

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Types of lasers by operation

Pulse lasers and continuous wave

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Comparison of pulse lasers and continuous wave

Pulse lasers produce series of pulses at certain width and frequency until stopped

Continuous wave releases constant output over interval of seconds

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Medical application of Lasers

Surgical operations, retinal laser surgery, gene surgery

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Metastable state

Short lived high energy state that spontaneously drops to a low energy state with long lifespan

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How to achieve laser pumping

Thermal excitation, optical excitation and electric discharge