Many inertial confinement target designs have the fuel as a frozen spherical shell of hydrogen isotopes. One method of manufacturing these targets would be to produce the spherical shell first. In this paper we report on an experimental study on the production of spherical shells of liquid and solid hydrogen. These shells are made by acoustically breaking up a jet of superheated liquid hydrogen into drops and at the same time cavitating a bubble in the center of each drop. The resulting growth of the bubbles by evaporation produces the spherical shells. The size and the aspect ratio of the spherical shells are found to be affected by several parameters. The mass of the drop depends on the diameter of the nozzle from which the jet emerges. Also, varying the frequency of the acoustic excitation gives some control of the droplet size. The aspect ratio depends most strongly on the liquid temperature and the droplet-chamber pressure. Increasing the temperature or lowering the pressure increases the aspect ratio of the shell. If the pressure is lowered below the triplet-point pressure of hydrogen, the shells freeze forming a spherical shell of solid hydrogen.
High-power 1 -100 kW industrial lasers typically undergo thermally-induced optical effects that change the laser beam and laser beam delivery to the work piece. Knowledge of any changes such as focal shift may be important for particular welding or cutting processes. Conventional beam profile diagnostic methods are not practical and fall short at such high powers. A new profiling technique that uses Rayleigh scatter from the beam overcomes the power obstacle and allows laser characterization that was previously impossible to perform.In high-power laser welding and cutting applications operating over "long" times at the minute scale, the delivery optics are heated and typically the focal spot shifts in position, and the spot size and other beam parameters also change. The higher the power, the greater the shift, and this could be critical to the process. With observed focal shifts on the order of 0
The effect of intense pulses of laser-produced x rays upon the reflective and diffractive properties of metal mirrors and multilayered mirrors (artificial crystals) have been inves tigated. Laser pulses from a Nd-glass pulsed laser system of 25 ns pulse width and 50 3 energy were focused onto a copper target to generate the required x-ray pulses. A polished planar sample of nickel was used to reflect the 1.0 to 1.3-keV x rays onto photographic film, The x-ray flux onto the mirror (at grazing incidence angles near 3.5°) was split into two adjacent fields with a beryllium filter over one field and with an equal thickness beryl lium filter placed over the film holder covering the adjacent field. Thin pieces of Kimfol were used as debris shields ahead of the mirror sample. This technique provided an insitu nomalization since both a low intensity and a high intensity irradiation caa he simultane ously achieved on adjacent portions of the sample. A similar technique was used to study reflection by a multilayer sample of carbon-tungsten carbide layering and 19,6A° spacing.Experimental details and the results obtained are presented.;.ij^iy mSM^mmmtmmf
The discovery of Rayleigh Scattering by 3rd Baron Rayleigh, John William Strutt, served an explanation of why the sky is blue during the daytime and different hues of orange, pink, and purple in the early morning hours and at dusk. But it was only recently that this phenomenon has been applied to the measurement of high-powered lasers. Only through the measurement of the laser source and laser system can the user of the laser fully understand its performance and then start to control the processes in which they are used. Key laser parameters which ensure a successful process include output power or energy at the work piece, spot size or beam waist size, spot size location (over time), in addition to M2 or Beam Parameter Product values. Since the beginning of the application of the highpowered laser, and with recent steady increases in continuous-wave power, measurement has proved to be more and more problematic. This paper will discuss how the signal of the laser produced from Rayleigh Scattering can put to rest any concerns by the laser user of damaging their laser measurement equipment. The high-power laser user can now obtain dynamic characteristic measurements, instantly from beam
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