Wavefront reversal

Potential applications of wavefront reversal with frequency doubling or multiplication include C18] (i) wavelength... 

Optical phase conjugation, also referred to as time reversal or wavefront reversal, is a technique involving the creation of an optical beam that has the variations in its wavefront, or phase, reversed relative to a reference beam. If the optical field is represented as the product of an amplitude and complex exponential phase,... 

Figure 2.73. Illustration of electron wave propagation through a linear array of atoms, showing the constructive interference of forward/reverse wavefronts to form standing waves.

After raising the wall temperature in both sides, a sharp wave front develops and propagates toward the center of the physical domain which separates between the heat-affected zone from the thermally undisturbed zone (see Figure 8.13). The two thermal wavefronts from both sides collide with each other at the center of the film. After the collision, the center temperature is amplified, and reverse thermal wavefronts take place and travel toward both sides of the thin film. When thermal wave-front reaches both side walls, the film temperatures at the side walls exceed the imposed wall temperature, called temperature overshoot. For thick film, the wavefronts do not show reverse temperature waves after meeting the center of the thin film. 

C) corresponds to the maximum intensity, but the presence of a lens at this plane does not influence the focused beam wavefront and there is no change in transmittance. At point D lensing has an effect that is the reverse to that of (B) the size of the beam in the far held is decreased and the transmission through the aperture is increased. A characteristic S-shaped Z-scan curve (a valley followed by a maximum of transmittance) is obtained. This shape is reversed in the case of negative 2-... 

The mode patterns of a laser oscillating in some of the lowest-order modes of rectangular symmetry are shown in Fig.12.4. These should be compared with the diagrammatic representation of electric fields shown in Fig.12.2. The higher-order modes clearly have more extended field distributions and consequently higher diffraction losses than the lower-order modes, as we have already remarked. The wavefronts of these modes contain one or more phase reversals of Ti arising from the particular form of the Hermite or Laguerre polynomial which determines the field distribution. 

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