Advent Of High Power Lasers Research Articles

Investigation of warm dense matter using time-resolved X-ray absorption spectroscopy with third- and fourth- generation light sources

The advent of high-power lasers has provided insights into laboratory high energy density (>1011 J/m3) physics. In particular, the properties of warm dense matter (WDM) with temperatures of 104–106 K and near-solid densities is a research area that has garnered significant interest recently. However, owing to the high temperatures and pressures associated with WDM, the measurement of fundamental properties is difficult, and insufficient data has been a significant setback in WDM research. Herein, we review recent developments in time-resolved X-ray absorption spectroscopy with synchrotron and X-ray free electron lasers for WDM research. Various physical properties, such as atomic bonding, electronic structures, electron–phonon coupling, and thermal conductivity of various elements in WDM conditions are investigated via this noble X-ray technique at various time scales from 100 ps to 100 fs.

Direct electron acceleration in multi-kilojoule, multi-picosecond laser pulses

The physics mechanism behind the acceleration of electrons to energies much higher than the laser ponderomotive potential is reported. While electrons with these energies have been observed for the last twenty years at the one percent level, it is only with the recent advent of high power lasers with extended pulse durations, large focal spots, and high intensities that significant numbers (>10%) of the so-called “superponderomotive” electrons have been observed. Evidence is provided that the dominant acceleration mechanism of superponderomotive electrons is direct acceleration by the electromagnetic (EM) wave of the laser as they co-propagate in an under-dense plasma; one-dimensional particle-in-cell simulations yield electron spectra with typically ten times the ponderomotive temperature. Direct acceleration requires tens of plasma wavelengths of under-dense plasma, as well as pulse durations of tens of plasma periods, conditions that can be found in large focal spot multi-picosecond laser pulses. It is shown that the plasma simply provides the source of accelerated electrons and a variety of methods to inject a significant population of electrons into the EM waves at relativistic energy.

Analytical estimates of proton acceleration in laser-produced turbulent plasmas

With the advent of high power lasers, new opportunities have opened up for simulating astrophysical processes in the laboratory. We show that second-order Fermi acceleration can be directly investigated at the National Ignition Facility, Livermore. This requires measuring the momentum-space diffusion of 3 MeV protons produced within a turbulent plasma generated by a laser. Treating Fermi acceleration as a biased diffusion process, we show analytically that a measurable broadening of the initial proton distribution is then expected for particles exiting the plasma.

Effect of Laser Settings and Irrigation Rates on Ureteral Temperature During Holmium Laser Lithotripsy, an In Vitro Model.

Ureteroscopic laser lithotripsy requires irrigation for adequate visualization and temperature control during treatment of ureteral stones. However, there are little data on how different irrigation and laser settings affect the ureteral wall and surrounding tissues. This effect has become an important consideration with the advent of high-powered lasers. We therefore evaluated the effect of laser settings and irrigation flow on ureteral temperature in an in vitro setting. To mimic ureteroscopic laser lithotripsy, we simulated clinically relevant irrigation flow rates and fired a Holmium:Yttrium-aluminum-garnet (Ho:YAG) laser while monitoring "intraureteral" temperature. The probe tip of a thermometer was placed 1 mm from the tip of a 200 μm laser fiber, which was fired for 60 seconds at 0.2 J/50 Hz, 0.6 J/6 Hz, 0.8 J/8 Hz, 1 J/10 Hz, and 1 J/20 Hz within a tubing system that allowed for specified room temperature flow rates (100, 50, and 0 mL/minute). We recorded temperatures every 5 seconds. The maximum temperature was noted, and each laser/flow trial was duplicated. Averaged maximum temperatures were compared using analysis of variance across irrigation settings. At 100 cc/minute, only the 1 J/20 Hz laser setting produced a significantly higher maximum temperature (p < 0.01), although this finding was not clinically significant at a maximum of 30.7°C. At a lower irrigation rate of 50 cc/minute, the 1 J/20 Hz setting was again the only significantly higher maximum temperature (p < 0.05), although this temperature crossed the toxic threshold at a maximum of 43.4°C. With no flow, all maximum temperatures reached over 43°C, with 0.8 J/8 Hz, 1 J/10 Hz, and 1 J/20 Hz each statistically higher than the lower-energy settings (p < 0.05). The maximum temperature at 1 J/20 Hz with no irrigation was over 100°C. Despite increasing laser settings, adequate irrigation can maintain relatively stable temperatures within an in vitro ureteral system. As irrigation rates decrease, even lower power laser settings produce a clinically significant increase in maximum temperature, potentially causing ureteral tissue injury.

MHD Models and Laboratory Experiments of Jets

Jet research has long relied upon a combination of analytical, observational and numerical studies to elucidate the complex phenomena involved. One element missing from these studies (which other physical sciences utilize) is the controlled experimental investigation of such systems. With the advent of high-power lasers and fast Z-pinch machines it is now possible to experimentally study similar systems in a laboratory setting. Such investigations can contribute in two useful ways. They can be used for comparison with numerical simulations as a means to validate simulation codes. More importantly, however, such investigations can also be used to complement other jet research, leading to fundamentally new knowledge. In the first part of this article, we analyze the evolution of magnetized wide-angle winds in a collapsing environment. We track the ambient and wind mass separately and describe a physical mechanism by which an ionized central wind can entrain the ambient gas giving rise to internal shells of molecular material on short time scales. The formation of internal shells in molecular outflows has been found to be an important ingredient in describing the observations of convex spurs in P-V diagrams (Hubble wedges in M-V diagrams). In the second part, we present astrophysically relevant experiments in which supersonic jets are created using a conical wire array Z-pinch. The conically convergent flow generates a standing shock around the axis which collimates the flow into a Mach ∼ 30 jet. The jet formation process is closely related to the work of Canto et al. (1988) for hydrodynamic jet collimation. The influence of radiative cooling on collimation and stability is studied by varying the wire material (A1, Fe, and W).

A future ICE (thermonuclear, that is!)

The advent of high-powered lasers has created quite a stir among nuclear physicists, who are enthusiastically examining the prospects of using these devices in a new approach to the problem of creating ultrahigh-temperature plasmas to maintain and control thermonuclear fusion. The idea of building ``modern internal combustion engines'' (ICE) based on this form of clean, efficient, and powerful energy was examined by Edward Teller at the 7th International Quantum Electronics Conference, Montreal, Canada, during May 8-11, 1972, where he deliberated upon the overwhelming engineering problems to be solved before such an engine could be realized. Dr. Teller's exciting commentary would have been lost had it not been for the attendance of Spectrum staff writer Marce Eleccion and the kind assistance of James R. Packard of the 3M Co., who tape-recorded Dr. Teller's remarks. Subsequently, Dr. Teller and Mr. Eleccion edited the tapes to produce this article. At the conference itself, the famed thermonuclear expert's unique sense of humor was exhibited when the session chairman (in his introductory remarks) confessed to the audience that he did not really know the content of the upcoming presentation, to which Dr. Teller replied: ``I might perhaps start by saying that I don't know either what I am going to tell you, and for that reason, I will listen very carefully and recommend the same to you.''