Panniculectomy: an alternative approach to the revision of a difficult stoma.

AIM: We describe a modified abdominoplasty technique as an alternative approach to the revision of a difficult stoma. METHOD: A patient with a retracted colostomy secondary to change in abdominal wall contour following significant weight loss was treated with this technique. The patient had previous colostomy revision with marlex mesh insertion for combined parastomal and massive ventral hernia repair. A preoperatively marked crescent shaped left upper quadrant segment of skin and subcutaneous fat was excised and the defect was approximated in multiple layers. This shifted the stoma opening cephalad and eliminated the cutaneous crease that originally made it difficult to obtain a proper stoma seal. RESULTS: At one year follow up the patient was extremely satisfied with the results and was able to properly pouch the stoma. CONCLUSION: Modified abdominoplasty can be used as an alternative, low morbid approach in dealing with selected patients with difficult stoma problems.

Observation of collisionless shocks in laser-plasma experiments.

The propagation in a rarefied plasma (n(e) < or approximately 10(15) cm(-3)) of collisionless shock waves and ion-acoustic solitons, excited following the interaction of a long (tauL approximately 470 ps) and intense (I approximately 10(15) W cm(-2)) laser pulse with solid targets, has been investigated via proton probing techniques. The shocks' structures and related electric field distributions were reconstructed with high spatial and temporal resolution. The experimental results were interpreted within the framework of the nonlinear wave description based on the Korteweg-de Vries-Burgers equation.

Revisiting nonlocal electron-energy transport in inertial-fusion conditions.

Correct modeling of the electron-energy transport is essential for inertial confinement fusion target design. Various transport models have been proposed in order to extend the validity of a hydrodynamical description into weakly collisional regimes, taking into account the nonlocality of the electron transport combined with the effects of self-generated magnetic fields. We have carried out new experiments designed to be highly sensitive to the modeling of the heat flow on the Ligne d'Intégration Laser facility, the prototype of the Laser Megajoule. We show that two-dimensional hydrodynamic simulations correctly reproduce the experimental results only if they include both the nonlocal transport and magnetic fields.

Comparison of laser ion acceleration from the front and rear surfaces of thin foils.

The comparative efficiency and beam characteristics of high-energy ions generated by high-intensity short-pulse lasers (approximately 1-6 x 10(19) W/cm2) from both the front and rear surfaces of thin metal foils have been measured under identical conditions. Using direct beam measurements and nuclear activation techniques, we find that rear-surface acceleration produces higher energy particles with smaller divergence and a higher efficiency than front-surface acceleration. Our observations are well reproduced by realistic particle-in-cell simulations, and we predict optimal criteria for future applications.

Picosecond time-resolved X-ray absorption spectroscopy of ultrafast aluminum plasmas.

We have used point-projection K-shell absorption spectroscopy to infer the ionization and recombination dynamics of transient aluminum plasmas. Two femtosecond beams of the 100 TW laser at the LULI facility were used to produce an aluminum plasma on a thin aluminum foil (83 or 50 nm), and a picosecond x-ray backlighter source. The short-pulse backlighter probed the aluminum plasma at different times by adjusting the delay between the two femtosecond driving beams. Absorption x-ray spectra at early times are characteristic of a dense and rather homogeneous plasma. Collisional-radiative atomic physics coupled with hydrodynamic simulations reproduce fairly well the measured average ionization as a function of time.

Ultralow emittance, multi-MeV proton beams from a laser virtual-cathode plasma accelerator.

The laminarity of high-current multi-MeV proton beams produced by irradiating thin metallic foils with ultraintense lasers has been measured. For proton energies >10 MeV, the transverse and longitudinal emittance are, respectively, <0.004 mm mrad and <10(-4) eV s, i.e., at least 100-fold and may be as much as 10(4)-fold better than conventional accelerator beams. The fast acceleration being electrostatic from an initially cold surface, only collisions with the accelerating fast electrons appear to limit the beam laminarity. The ion beam source size is measured to be <15 microm (FWHM) for proton energies >10 MeV.

Complete characterization of a plasma mirror for the production of high-contrast ultraintense laser pulses.

Improving the temporal contrast of ultrashort and ultraintense laser pulses is a major technical issue for high-field experiments. This can be achieved using a so-called "plasma mirror." We present a detailed experimental and theoretical study of the plasma mirror that allows us to quantitatively assess the performances of this system. Our experimental results include time-resolved measurements of the plasma mirror reflectivity, and of the phase distortions it induces on the reflected beam. Using an antireflection coated plate as a target, an improvement of the contrast ratio by more than two orders of magnitude can be achieved with a single plasma mirror. We demonstrate that this system is very robust against changes in the pulse fluence and imperfections of the beam spatial profile, which is essential for applications.

Spatial uniformity of laser-accelerated ultrahigh-current MeV electron propagation in metals and insulators.

The evolution of laser-generated MeV, MA electron beams propagating through conductors and insulators has been studied by comparing measurement and modeling of the distribution of MeV protons that are sheath accelerated by the propagated electrons. We find that electron flow through metals is uniform and can be laser imprinted, whereas propagation through insulators induces spatial disruption of the fast electrons. Agreement is found with material dependent modeling.

Heating of thin foils with a relativistic-intensity short-pulse laser.

K-shell x-ray spectroscopy of sub-100 nm Al foils irradiated by high contrast, spatially uniform, 150 fs, Ilambda (2)=2 x 10(18) W microm(2)/cm(2), laser pulses is obtained with 500 fs time resolution. Two distinct phases occur: At /=500 fs the resonance transitions dominate. Initial satellites arise from a large area, high density, low temperature (approximately 100 eV) plasma created by fast electrons. Thus, contrary to predictions, a short, high intensity laser incident on a thin foil does not create a uniform, hot dense plasma.

MeV ion jets from short-pulse-laser interaction with thin foils.

Collimated jets of carbon and fluorine ions up to 5 MeV/nucleon ( approximately 100 MeV) are observed from the rear surface of thin foils irradiated with laser intensities of up to 5 x 10 (19)W/cm(2). The normally dominant proton acceleration could be surpressed by removing the hydrocarbon contaminants by resistive heating. This inhibits screening effects and permits effective energy transfer and acceleration of other ion species. The acceleration dynamics and the spatiotemporal distributions of the accelerating E fields at the rear surface of the target are inferred from the detailed spectra.

X-ray emission of a xenon gas jet plasma diagnosed with Thomson scattering.

We present the results of a benchmark experiment aimed at validating recent calculation techniques for the emission properties of medium and high-Z multicharged ions in hot plasmas. We use space- and time-resolved M-shell x-ray spectroscopy of a laser-produced gas jet xenon plasma as a primary diagnostic of the ionization balance dynamics. We perform measurements of the electron temperature, electron density, and average charge state by recording simultaneous spectra of ion acoustic and electron plasma wave Thomson scattering. A comparison of the experimental x-ray spectra with calculations performed ab initio with a non-local-thermodynamic-equilibrium collisional-radiative model based on the superconfiguration formalism, using the measured plasma parameters, is presented and discussed.

L-band x-ray absorption of radiatively heated nickel.

Absorption of L-M and L-N transitions of nickel has been measured using point projection spectroscopy. The x-ray radiation from laser-irradiated gold cavities was used to heat volumetrically nickel foils "tamped with carbon" up to 20 eV. Experimental spectra have been analyzed with calculations based on the spin-orbit split arrays statistical approach and performed for each ionic species Ni5+ to Ni11+. Using a least-squares fit, this method provides an ion distribution broader than at local thermodynamic equilibrium, which is explained by spatial and temporal temperature gradients. A major improvement in the simulation of the absolute value of transmission is obtained with a resolved transition array statistical calculation that reproduces the experimental spectrum with the nominal areal mass density by taking into account the saturation of narrow lines.

Time-resolved plasma spectroscopy of thin foils heated by a relativistic-intensity short-pulse laser.

Time-resolved K-shell x-ray spectra are recorded from sub-100 nm aluminum foils irradiated by 150-fs laser pulses at relativistic intensities of Ilambda(2)=2 x 10(18) W microm(2)/cm(2). The thermal penetration depth is greater than the foil thickness in these targets so that uniform heating takes place at constant density before hydrodynamic motion occurs. The high-contrast, high-intensity laser pulse, broad spectral band, and short time resolution utilized in this experiment permit a simplified interpretation of the dynamical evolution of the radiating matter. The observed spectrum displays two distinct phases. At early time, < or =500 fs after detecting target emission, a broad quasicontinuous spectral feature with strong satellite emission from multiply excited levels is seen. At a later time, the He-like resonance line emission is dominant. The time-integrated data is in accord with previous studies with time resolution greater than 1 ps. The early time satellite emission is shown to be a signature of an initial large area, high density, low-temperature plasma created in the foil by fast electrons accelerated by the intense radiation field in the laser spot. We conclude that, because of this early time phenomenon and contrary to previous predictions, a short, high-intensity laser pulse incident on a thin foil does not create a uniform hot and dense plasma. The heating mechanism has been studied as a function of foil thickness, laser pulse length, and intensity. In addition, the spectra are found to be in broad agreement with a hydrodynamic expansion code postprocessed by a collisional-radiative model based on superconfiguration average rates and on the unresolved transition array formalism.

Direct observation of the ponderomotive force effects in short-scale-length laser plasmas by frequency-domain interferometry.

We report on single-shot frequency-domain interferometric measurements showing space- and time-resolved ponderomotive electron density profile steepening of a short-scale-length ultraintense laser-produced plasma. The density gradient scale length is varied by applying a time-delayed laser prepulse. The measured absolute position of the critical density surface is found to be in agreement with one-dimensional hydrodynamic simulations for the range of scale lengths studied.

Non-thermal melting in semiconductors measured at femtosecond resolution.

Ultrafast time-resolved optical spectroscopy has revealed new classes of physical, chemical and biological reactions, in which directed, deterministic motions of atoms have a key role. This contrasts with the random, diffusive motion of atoms across activation barriers that typically determines kinetic rates on slower timescales. An example of these new processes is the ultrafast melting of semiconductors, which is believed to arise from a strong modification of the inter-atomic forces owing to laser-induced promotion of a large fraction (10% or more) of the valence electrons to the conduction band. The atoms immediately begin to move and rapidly gain sufficient kinetic energy to induce melting--much faster than the several picoseconds required to convert the electronic energy into thermal motions. Here we present measurements of the characteristic melting time of InSb with a recently developed technique of ultrafast time-resolved X-ray diffraction that, in contrast to optical spectroscopy, provides a direct probe of the changing atomic structure. The data establish unambiguously a loss of long-range order up to 900 A inside the crystal, with time constants as short as 350 femtoseconds. This ability to obtain the quantitative structural characterization of non-thermal processes should find widespread application in the study of ultrafast dynamics in other physical, chemical and biological systems.

Study of the ion-distribution dynamics of an aluminum laser-produced plasma with picosecond resolution.

The ion-distribution dynamics of an expanding aluminum plasma produced by a nanosecond laser pulse at moderate intensity (10(13) W cm(-2)) is studied by point-projection x-ray absorption spectroscopy with unprecedented, picosecond, time resolution. We show that the ionic populations measured as a function of distance to the target and at different probing times differ markedly from those predicted by widely accepted collisional radiative models coupled to hydrodynamic simulations. We discuss the effects of radiation, conduction, and expansion cooling on the spatiotemporal ionic distribution evolution.

Single-shot spectral interferometry with chirped pulses.

We present a method for obtaining time-resolved measurements of the amplitude modulation and the phase shift of a chirped probe pulse interacting with a femtosecond-laser-produced plasma. Based on spectral interferometry, the technique allows for single-shot measurements and keeps the temporal resolution associated with the full bandwidth of the probe pulse. We demonstrate the efficiency of this technique by probing femtosecond-laser breakdown of plastic targets.

Comparison of measured and calculated X-ray and hot-electron production in short-pulse laser-solid interactions at moderate intensities.

Ultrashort pulse laser-solid interaction experiments with 4x10(16) W/cm(2),120 fs, 45 degrees incidence angle, p-polarized pulses are theoretically analyzed with the help of 1(1/2)-dimensional (1(1/2) D) particle-in-cell (PIC) simulations. The laser impinges upon preformed plasmas with a precisely controlled density-gradient scale-length. PIC electron distribution functions are used as an input to 3D Monte Carlo simulations to interpret measured electron distributions and Kalpha radiation emission. Satisfactory agreement between the experimental and simulation results is obtained for the measured absorption coefficient, the energy distribution of the back-scattered hot electrons, the hot-electron temperature in the bulk of the target, and the Kalpha yield, when the preplasma scale-length is varied.

Hot-electron distribution functions in a subpicosecond laser interaction with solid targets of varying initial gradient scale lengths.

We have studied the distribution function of the hot electrons produced during the interaction of a 120-fs, 60-mJ, 800-nm wavelength and a p-polarized laser pulse with bilayered Al/Fe targets. The main pulse interacts with a preformed plasma, obtained with a controlled prepulse, whose density gradient scale length has been measured. The electron distribution function is characterized by means of the Kalpha emission of the two materials of the target as a function of the Al-layer thickness. The low-energy region (<50 keV) of the hot-electron distribution function shows no dependency in shape on the gradient scale length, but only a variation in the total number of the generated electrons. The comparison between the experimental results and the particle-in-cell and Monte Carlo calculations of the electron distribution function and the Kalpha emission is gratifying.

Children's self-report of postoperative pain intensity and treatment threshold: determining the adequacy of medication.

OBJECTIVE: Many studies have shown indirectly that children are undermedicated for postoperative pain. In this study, we used a pain self-report scale to examine this more directly. METHODS: We performed a survey with 63 children who were postoperative from minor, uncomplicated surgery. Using the self-report scale, we determined the pain intensity at time of interview, the worst pain experienced postoperatively, and the intensity of pain that the subject felt to warrant pharmacologic intervention (the "treatment threshold"). A subgroup of 48 children was asked to indicate on the scale the intensities that represented mild, moderate, and severe pain. RESULTS: Mean (SD) pain at time of interview was 1.9 (1.7) on the 0-6 scale. Mean worst postoperative pain was 3.8 (1.8). The mean for treatment threshold was 3.2 (1.8). We found gender differences in regard to the judgments about the intensities representing mild, moderate, and severe pain, with girls rating these lower than did boys. Twenty-five percent of subjects reported pain that was mild, 29% reported moderate pain, and 46% reported severe pain. CONCLUSIONS: We found that 51% of subjects were undermedicated for postoperative pain, being required to suffer pain that was above their treatment threshold. By determining each subject's treatment threshold and estimate of moderate pain, we have better defined the intensity at which pain becomes clinically significant.