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Tham khảo tài liệu 'crc press - dictionary of material science and high energy physics - d. basu (2001) episode 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | ated field. The signal and generated fields are therefore subject to a phase matching condition which does not apply to the propagation of the input fields O 1 and 2. As opposed to other schemes of frequency generation by the interaction of coherent beams such as lasing without inversion no population transfer is occurring within the atomic or molecular system. A special case offour wave mixing is the degenerate four wave mixing which leads to phase conjugation. In this case the two incoming fields with the same frequency are copropagating through the medium which causes a stationary grating to build up. It can be shown that the generated field is the phase conjugate of the signal beam and consequently co-propagates with respect to it. From a viewpoint of a quantized field one photon out of each of the pump beams is annihilated a photon in the phase conjugate wave is generated and the signal beam gets amplified. fractional charge An electric charge less than that of the electron generally by a factor expressible as a rational fraction made of small integers. The quasiparticles in the fractional quantum Hall effect e.g. are believed to possess fractional charges. fractional quantum numbers Quantum numbers associated with quasiparticles in certain systems that are simple fractions of the numbers for elementary particles. See fractional charge. fractional statistics Term used to describe certain field theories in which the wave function of the many-particle system does not get multiplied by 1 or -1 during the exchange of any two particles as would be the case for Bose or Fermi statistics respectively. Instead the wave function is multiplied by a phase factor with a phase angle that is a fraction of n. fragmentation function In a high momentum transfer reaction a recoiling quark-parton will eventually hadronize. The fragmentation function represents the probability that a quarkparton of a specific type will produce a hadron in an interval dz about z where z is the .
