Phase Conjugation

	Phase Conjugation Phase conjugation is a physical transformation of a wave field where the resulting field has a reversed propagation direction but keeps its amplitudes and phases. Description It is distinguished from Time Reversal Signal Processing by the fact that phase conjugation uses a holographic or parametric pumping whereas time reversal records and re-emits the signal using transducers. * Holographic pumping makes the incident wave interact with a pump wave of the same frequency and records its amplitude-phase distribution. Then, a second pump wave reads the recorded signal and produces the conjugate wave. All those waves have the same frequency. * In parametric pumping, the parameters of the medium are modulated by the pump wave at double frequency. The interaction of this perturbation with the incident wave will produce the conjugate wave. Both techniques allow an amplification of the conjugate wave compared to the incident wave. As in time reversal, the wave re-emitted by a phase conj ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Time Reversal Signal Processing Time Reversal Signal Processing has three main uses: creating an optimal carrier signal for communication, reconstructing a source event, and focusing high-energy waves to a point in space. A Time Reversal Mirror (TRM) is a device that can focus waves using the time reversal method. TRMs are also known as time reversal mirror arrays since they are usually arrays of transducers. TRM are well-known and have been used for decades in the optical domain. They are also used in the ultrasonic domain. Overview If the source is passive, i.e. some type of isolated reflector, an iterative technique can be used to focus energy on it. The TRM transmits a plane wave which travels toward the target and is reflected off it. The reflected wave returns to the TRM, where it looks as if the target has emitted a (weak) signal. The TRM reverses and retransmits the signal as usual, and a more focused wave travels toward the target. As the process is repeated, the waves become more and more focused on ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Holographic Pumping Holography is a technique that enables a wavefront to be recorded and later re-constructed. Holography is best known as a method of generating real three-dimensional images, but it also has a wide range of other Holography#Applications, applications. In principle, it is possible to make a hologram for any type of Holography#Non-optical holography, wave. A hologram is made by superimposing a second wavefront (normally called the reference beam) on the wavefront of interest, thereby generating an interference pattern which is recorded on a physical medium. When only the second wavefront illuminates the interference pattern, it is diffracted to recreate the original wavefront. Holograms can also be Computer-generated holography, computer-generated by modelling the two wavefronts and adding them together digitally. The resulting digital image is then printed onto a suitable mask or film and illuminated by a suitable source to reconstruct the wavefront of interest. Overview and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Parametric Pumping Parametric may refer to: Mathematics Parametric equation, a representation of a curve through equations, as functions of a variable Parametric statistics, a branch of statistics that assumes data has come from a type of probability distribution * Parametric derivative, a type of derivative in calculus Parametric model, a family of distributions that can be described using a finite number of parameters Parametric oscillator, a harmonic oscillator whose parameters oscillate in time Parametric surface, a particular type of surface in the Euclidean space R3 Parametric family, a family of objects whose definitions depend on a set of parameters Science * Parametric process, in optical physics, any process in which an interaction between light and matter does not change the state of the material Spontaneous parametric down-conversion, in quantum optics, a source of entangled photon pairs and of single photons Optical parametric amplifier, a type of laser light source that em ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Transducer A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and control systems, where electrical signals are converted to and from other physical quantities (energy, force, torque, light, motion, position, etc.). The process of converting one form of energy to another is known as transduction. Types * Mechanical transducers, so-called as they convert physical quantities into mechanical outputs or vice versa; * Electrical transducers however convert physical quantities into electrical outputs or signals. Examples of these are: a thermocouple that changes temperature differences into a small voltage; a linear variable differential transformer (LVDT), used to measure displacement (position) changes by means of electrical signals. Sensors, actuators and transceivers Transducers can be categorized by wh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Acoustic Phase Conjugation Acoustic phase conjugation is a set of techniques meant to perform phase conjugation on acoustic waves. Techniques Acoustic phase conjugation can appear in a solid when the sound velocity is modulated by an electromagnetic field. The generation of the conjugate wave can be seen as the decay of a photon into two phonons, as seen on the diagram. The two phonons have opposite wave vectors k and -k (they will propagate in opposite directions) and a frequency two time smaller than that of the photon. Parametric pumping techniques can be performed in several media: * In piezoelectric crystals, a nonlinear piezoelectric effect will produce a modulation of fractions of a percent. * In magnetic crystals, a modulation of dozens of percent can be reached through the magneto-acoustic coupling, which can be improved by combining the magnetostriction and spin reorientation transition effects or using the magnetoacoustic resonance. A "supercritical" or "giant" amplification, up to 80 dB, can be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Optical Phase Conjugation Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in ''nonlinear media'', that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity is typically observed only at very high light intensities (when the electric field of the light is >108 V/m and thus comparable to the atomic electric field of ~1011 V/m) such as those provided by lasers. Above the Schwinger limit, the vacuum itself is expected to become nonlinear. In nonlinear optics, the superposition principle no longer holds. History The first nonlinear optical effect to be predicted was two-photon absorption, by Maria Goeppert Mayer for her PhD in 1931, but it remained an unexplored theoretical curiosity until 1961 and the almost simultaneous observation of two-photon absorption at Bell Labs and the discovery of second-harmonic generation by Peter Franken ''et al.'' at University of Michigan, both shortly after the constru ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]