Lasers and Coherent Light

In the introduction to this chapter we gave an intuitive explanation of the origin of nonlinear optical effects and stressed the key role played by high power lasers and coherent light beams. These two concepts are defined here. We will describe one specific characteristic of laser light, namely the absorption saturation, and finally we will discuss susceptibility and frequency conversion of light. 

Laser light differs from conventional light, such as that from the sun or fluorescent lights. There are obvious differences laser light is extremely bright and nearly monochromatic in nature. It propagates as directional beams. But there are also more subtle differences, the 

Let us consider an atomic gas laser where the energy between the f and i levels is v0 = (Ef - E) h. The electric field associated with light in this laser oscillator is given by 

The position, r, of an atom moving in the laser oscillator with a velocity, v, is given by r -vt + rn, and the interaction between this atom and the electric field of the light reflecting the 

The phase of light emitted from atoms is independent. 

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But the advent of lasers and coherent light techniques opened a rich arsenal of spectroscopic tools which make it possible to study spectral lines in gas samples free of first order Doppler broadening.(1,2) Two conceptually different approaches have so far been used very successfully ... 

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