The measurement of bending wave intensity in a two-dimensional structure

I.IntroductionOfallstructuralwaves,bendingwaveismostimportant.Itiseasilyexcitedandresultsinairbornenoiseradiation'Inpractice,itisnecessarytodeterminetheenergydistributionandpowertransmissionincoupledstructl1res.Bendingwaveenergycanbecalculatedfrombendingwaveaccelerationwhilebendingwavepowertransmissionischaracterizedbybendingwaveintensitywhichisavectorgivillgthemagnitudeanddirection.TheengineeringaPplicationofthevectorpropertyofbendingwaveilltensityisnumerous[1~3]buttheinvestigationinitispre…     

Interferometric measurement for the plasma produced by a Q-switched laser in air near the surface of an Al target

An analysis the plasma produced by a Q-switched laser in air near the surface of an Al target and a series of M-Z interferograms for the production and growth of the plasma for different delay time are reported. The causes of optical breakdown and calculated the electron density distribution in the plasma is also discussed.     

A modified moire interferometer for three-dimensional displacement measurement

This paper presents a new optical interferometric system, MMI-T/G, composed of a modified four-beam moire interferometer and a Twyman/Green interferometer. The MMI-T/G system can measure three-dimensional displacement fringe patterns with a single loading on the specimen, and the in-plane and out-of-plane displacement fields can be measured independently and defined clearly. The optical setup has the advantages of structural novelty, flexibility, and high fringe contrast. Moreover, the in-plane displacement sensitivity is twice of that of the normal moire interferometer. The measuring techniques to obtain the fringe patterns and displacement fields using the MMI-T/G system are described. The experimental results of thermal displacement of an electronic device are shown.     

Simulation of laser–plasma interactions and fast-electron transport in inhomogeneous plasma

A new framework is introduced for kinetic simulation of laser–plasma interactions in an inhomogeneous plasma motivated by the goal of performing integrated kinetic simulations of fast-ignition laser fusion. The algorithm addresses the propagation and absorption of an intense electromagnetic wave in an ionized plasma leading to the generation and transport of an energetic electron component. The energetic electrons propagate farther into the plasma to much higher densities where Coulomb collisions become important. The high-density plasma supports an energetic electron current, return currents, self-consistent electric fields associated with maintaining quasi-neutrality, and self-consistent magnetic fields due to the currents. Collisions of the electrons and ions are calculated accurately to track the energetic electrons and model their interactions with the background plasma. Up to a density well above critical density, where the laser electromagnetic field is evanescent, Maxwell’s equations are solved with a conventional particle-based, finite-difference scheme. In the higher-density plasma, Maxwell’s equations are solved using an Ohm’s law neglecting the inertia of the background electrons with the option of omitting the displacement current in Ampere’s law. Particle equations of motion with binary collisions are solved for all electrons and ions throughout the system using weighted particles to resolve the density gradient efficiently. The algorithm is analyzed and demonstrated in simulation examples. The simulation scheme introduced here achieves significantly improved efficiencies.     

A novel technique of laser measurement for the surface roughness

This paper describes a non-contact system for the surface roughness measurement without damage. It is suitable for various materials.     

Nonlinear propagation of an intense Laguerre–Gaussian laser pulse in a plasma channel

The nonlinear propagation of an intense Laguerre–Gaussian(LG) laser pulse in a parabolic preformed plasma channel is analyzed by means of the variational method. The evolution equation of the spot size is derived including the effects of relativistic self-focusing, preformed channel focusing, and ponderomotive self-channeling. The parametric conditions of the LG laser pulse and plasma channel for propagating with constant spot size, periodically focusing and defocusing oscillation,catastrophic focusing, and solitary waves are obtained. Compared with the laser pulse with fundamental Gaussian(FG)mode, it is found that the effect of vacuum diffraction is reduced by half and the effects of relativistic and wakefield focusing are decreased by a quarter due to the hollow transverse intensity profile of the LG laser pulse, while the effect of channel focusing is the same order of magnitude with that of the FG laser pulse. Thus, the matched condition for the intense LG laser pulse with constant spot size is released obviously, while the parameters of the laser and plasma for the existence of solitary waves nearly coincide with those of the FG laser pulse.     

Self-focusing of Hermite–Gaussian laser beams in plasma under plasma density ramp

Self-focusing of Hermite–Gaussian laser beams in plasma under plasma density ramp has been investigated. It is known that a laser beam shows an oscillatory self-focusing and defocusing behavior with the propagation distance. To overcome the defocusing, localized upward plasma density ramp is introduced, so that the laser beam attains a minimum spot size and maintains it with only a mild ripple. The density ramp could be important for the self-focusing of a Hermite–Gaussian laser by choosing the laser and plasma parameters appropriately. Self-focusing becomes stronger as the propagation distance increases. The behavior of beam-width parameters with the distance of propagation is presented graphically.     

Generation and measurement of complex laser pulse shapes in the SG-Ⅲ laser facility

The generation and measurement of complex ultraviolet laser pulse shapes is demonstrated in the SG-III laser facility. Relatively high contrast ratio of 300∶1 required by the physics experiment is achieved and successfully measured. Two continuous main shots validate the reproduction and the stability of the pulse shape, which provide solid foundation for precise physics experiment and laser power balance.     

Study of high precise measurement of large diameters by a dual frequency laser interferometer

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Radiative characteristics of a two-section laser structure based on a δ-doping superlattice

Spectral characteristics of a two-section laser structure with δ-doping active regions are studied theoretically. The wide range of tuning of the lasing wavelength is primarily related to specific characteristics of the gain spectra of n-i-p-i crystals: the dependence of the effective band-gap width of the superlattice on the level of excitation, the character of variation of the overlap integrals of the electron and hole wave functions, and broadening of the electronic spectra due to fluctuations of the electrostatic potential. Depending on the pumping currents in sections of the laser structure, the lasing wavelength can be tuned over a wide spectral range of the IR region in regimes of cw lasing, the transient regime, and the regime of regular pulsations. In the regime of self-sustaining pulsations, lasing is also possible at two wavelengths spaced well apart.     

Possible generation of a γ-ray laser by electrons wiggling in a background laser

The possibility of γ-ray laser generation by the radiation of wiggling electrons in a usual background laser is discussed.     

The technique of detecting the laser—ultrasonic vector displacement with a confocal Fabry—Perot interferometer waves in a plate

Generally,a confocal Fabry-Perot interferometer is only able to detect the out-of-plane component of a displhacement field;while the in-plane component often has the information about the material which cannot be found in this out-of-plane component.In this paper,based on a confocal Fabry-Perot interferometer set-up for detecting the out-of-plane component of a laser generated acoustic field.,a technique is developed to detect both the out-of-plane and inplane displacement components simultaneously with a novel two-channel confocal Fabry-perot interferometer.     

Absolute frequency measurement of the iodine-stabilized Ar<Superscript>+</Superscript> laser at 514.6 nm using a femtosecond optical frequency comb

The frequency of ¹²⁷I₂ hyperfine component a₃ of the P(13) 43-0 transition at 514.6 nm has been measured with an optical clockwork based on a femtosecond laser frequency comb generator. The measured frequency at an iodine pressure of 0.12 Pa is 67.3(0.75) kHz higher than the value of 582490603.38(15) MHz, adopted by the CIPM in 2003 [9] but is in a good agreement with the value measured by [29]. In our experiment we used H-maser reference frequency located at BNM-SYRTE Observatoire de Paris and transported to our laboratory by a 43 km optical fibre link. PACS 06.20.-f; 06.20.Fn; 06.30.Bp; 06.30.Ft     

“Small” models of relaxation of a dense inert-gas plasma

Problems of mathematical simulation of the relaxation kinetics of the plasma of dense inert gases are considered. A small model is constructed for the relaxation of helium plasma; the model takes into account the time dependences of the density and temperature of the electrons, of the gas temperature, and of the population of one effective excimer state. The results of the calculations agree with the preceding results of an analysis of a more detailed model (15 equations) at pressures higher than atmospheric. A small model for the relaxation of a xenon plasma is constructed and takes into account also the effective excited atomic state. The calculation results are compared with the experiments.Translated from Trudy Ordena Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 120, pp. 30–43, 1980.     

Specific features of excitations of “flow”-type self-oscillations in a two-component active medium of a fast-flow gas laser

The mechanism of “flow”-type self-oscillations in a two-component active medium of a flow laser with an unstable resonator is studied. It is shown that this mechanism is associated with the excitation of edge self-oscillatory in-phase perturbations of the medium components. These flow perturbations with low damping reach the optical axis of the resonator and result in an instability.     

Analysis of a 2D “liquid” plasma lattice

To study the structural and dynamical properties of a 2D dusty plasma lattice, a set of experiments were performed in an environment of radio frequency discharge. Based on the results of one of the experiments, pair correlation function, bond-orientational correlation function and mean square displacement of such a system were computed and analyzed. The bond-orientational correlation function is found to fit in with the law of e-r, and the mean square displacement is found to increase monotonously with time, both of which, together with the pair correlation function, indicate that the two-dimensional dusty plasma lattice formed in the experiment stayed in a "liquid" state.     

Generation of fast protons in moderate-intensity laser－plasma interaction from rear sheath

Forward fast protons are generated by the moderate-intensity laser--foil interaction. Protons with maximum energy 190~keV are measured by using magnetic spectrometer and CR-39 solid state track detectors along the direction normal to the rear surface. The experimental results are also modeled by the particle-in-cell method, investigating the time-varying electron temperature and the rear sheath field. The temporal and spatial structure of the sheath electrical field, revealed in the simulation, suggests that these protons are accelerated by target normal sheath acceleration (TNSA) mechanism.