Coherent electromagnetic waves

Transmission is accomplished by the emission of coherent electromagnetic waves in free space from one or more radiating elements that are excited by RF currents. Although, by definition, the radiated energy is composed of mutually dependent magnetic and electric vector fields, it is conventional practice to measure and specify radiation characteristics in terms of the electric field only. 

As it is known, a laser (optical quantum generator) generates coherent electromagnetic waves. It operation is based on the forced emission of photons under the... 

L. Tsang, J.A. Kong, Effective propagation constants for coherent electromagnetics waves in media embedded with dielectric scatterers, J. Apply. Phys. 53, 7162 (1982)... 

V. Twerski, Coherent electromagnetic waves in pair-correlated random distributions of aligned scatterers, J. Math. Phys. 19, 215 (1978)... 

V.K. Varadan, V.N. Bringi, V.V. Varadan, Coherent electromagnetic waves propagation through randomly distributed dielectric scatterrers, Phys. Rev. 19, 2480 (1979)... 

In contrast to coherent radiation emitted by laser sources, incoherent or non-co-herent radiation is characterized by elementary electromagnetic waves that do not have any phase relation in space and time. The production of incoherent excimer radiation in the UV or VUV region of the electromagnetic spectrum is made pos-... 

It is worth noting that coherency of the electromagnetic wave elastically scattered by the electron establishes specific phase relationships between the incident and the scattered wave their phases are different by n (i.e. scatterred wave is shifted with respect to the incident wave exactly by 7J2). 

Thin Films. When geometric optics cannot be applied, coherence effects require that electromagnetic wave theory be applied until extremely thin films are treated. For example, the normal reflectance R of a thin nonabsorbing film of refractive index n, on a substrate with refractive index n2 is found to be... 

The definition of the coherency and Stokes vectors explicitly exploits the transverse character of an electromagnetic wave and requires the use of a local spherical coordinate system. However, in some cases it is convenient to introduce an alternative quantity, which also provides a complete optical specification of a transverse electromagnetic wave, but is defined without explicit use of a coordinate system. This quantity is called the coherency dyad... 

The output of an interferometer are the so-called complex visibilities, also called spatial coherence function. When observing an object with an interferometer, the light intensity / is the result of the superposition of electromagnetic waves coming from the apertures. Considering an instrument with two apertures P and P2, the corresponding electric fields at the apertures are Ei (t) and 2 (t), respectively. At the recombination point Q, the intensity of the recombined signal is... 

The end of the nineteenth century was a proud period for physics, which seemed to finally achieve a state of coherence and clarity. At that time, physicists believed that the world consisted of two kingdoms a kingdom of particles and a kingdom of electromagnetic waves. The motion of... 

Interferometry is a process in which the superposition of two or more waves (beams) of sufficiently coherent electromagnetic radiation provides information about the waves and/or their differences. 

Finally, in this section, possible frequencies for the excitation of coherent vibrations should be considered. Originally special reference was made to membrane oscillations as their high polarization will then yield coherent electric oscillations (cf. Ref. 7, with earlier literature). Since the thickness of a membrane is about 10" cm and its elastic constant is equivalent to a velocity of sound of about lO cm/s, a frequency of the order of 10 Hz was expected, corresponding to electromagnetic waves in the millimeter region. When based on proteins or DNA, however, both higher and lower frequencies may be expected. 

The mixer consists of a photodetector and a local oscillator. We are interested in determining the signal-to-noise ratio at the output of the photodetector. The input electric field consists of three plane, parallel, coincident electromagnetic waves, which are assumed to be polarized and to impinge normally on the photodetector. Spatial first-order coherence is assumed over the detector aperture. The total incident electric field , may therefore be written as... 

Cerenkov light is a coherent electromagnetic shock wave emitted when a charged particle travels through a medium at speeds greater than the speed of light in the mediiun. 

As a last point in this chapter we will address the coherence properties of hght The concept of coherence is related to the stabihty, or predictability, of the phase of an electromagnetic wave. Therefore, in the broadest sense, coherence is defined as the property of waves (or wave-like states like wave packets) that... 

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