tailieunhanh - Dictionary of Material Science and High Energy Physics Part 8

Tham khảo tài liệu 'dictionary of material science and high energy physics part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | medium mostly rare earth atoms like Nd Yb Er etc. will also gain importance due to their high power capabilities compactness and reliability. In the Free-electron laser in which the radiation given off by accelerated electrons is used the wavelength range extends further into the VUV as well as the longer wavelengths. laser cooling Is the reduction of the temperature of atoms in the gas or bulk phase by means of laser radiation. Most often the cooling is associated with a reduction in the speed of the atoms and a narrowing of their velocity distribution. Laser cooling can be performed by irradiating the atoms with light red-detuned from the atomic resonance. Each absorption process transfers a momentum kick to the atoms. This is followed by spontaneous emission. The latter has no net-effect since it occurs randomly in a 4n radian. Due to the red-detuning of the laser beam the atom is more likely to absorb from a laser beam which is counterpropagating with the atom leading to a slowing of the atom. In order to keep the decelerating atom on resonance with the laser the atom or the laser frequencies must be tuned. The former can be achieved with a spatially varying magnetic field see Zeeman slower the latter by sweeping the frequency of the lasers in synchronous with the loss in velocity. See also magneto-optical trap. laser fluctuations Are fluctuations in phase and amplitude of a laser. Intensity and phase fluctuations stem from spontaneous emission. The photons in a laser follow the Poisson statistics and scale with the square root of the photon number. The phase undergoes a random walk which is also termed the phase diffusion. Phase locking allows the locking of the phases of two lasers with respect to each other. laser fusion A process in which intense lasers are used to implode a pellet containing thermonuclear fuel. The power delivered by the lasers causes the surface material of the pellet to ablate which compresses and then heats the material in the center of