K. N. Taylor

Charge transfer pumping of the helium‐nitrogen laser at atmospheric pressures in an electrical avalanche discharge

An atmospheric electrical avalanche (AEA) laser, stabilized by displacement current preionization, has been developed to support the study of the collisional pumping of the N/sup 2/(+), B yields X, electronic transition by the kinetic step He/sup 2/(+) + N/sup 2/ + He yields N/sup 2/+(B 2 Sigma sub u) + 3He. With proper preionization, the AEA laser has been operated at a PRF of 1 to 30 Hz in an avalanche mode at 100 to 200 A/cm/sup 2/. and E/p of 5 v/cm/torr. At pressures from 1 to 8 atm an essentially uniform, 30 cm/sup 3/. volume containing a high concentration of He/sup 2/(+) has been produced. Resulting laser output pumped by the charge transfer reaction has exceeded 1MW peak power at 427.8 nm. in a 4 nsec pulse. Efficiency with respect to the electrical power flowing through the laser tube has exceeded 2% and output pulse energies have exceeded 1% of the input pulse of energy dissipated in the laser tube.

Gain and saturation of the nitrogen ion laser

In this work a dilute nitrogen plasma pumped by charge transfer from He+2 has been operated as a pulsed optical amplifier. In the experimental system used two synchronously excited plasmas were produced by preionized discharges in an atmospheric electrical avalanche device switched by hydrogen thyratrons so that repetitive operation to 30 Hz would be possible. The plasmas were electrically connected in a transverse series circuit to provide a phase delay in their excitation comparable to the optical transit time between them. Laser output at 427.8 nm from the first discharge coupled to the fields in a self‐excited oscillator geometry was threaded through the second along its 85‐cm longer dimension. Calibrated attenuation of the beam from the oscillator subsequently input to the amplifier provided data on the overall amplification ratio to which the two adjustable parameters of a simple model were fit. From these parameters overall small‐signal gains as large as 2×106 were found together with saturation in...

Mössbauer effect measurement of the recoil‐free fraction for 57Fe implanted in a nanophase diamond film

The Mossbauer effect was used to investigate films of nanophase diamond (NPD) implanted with isotopically pure 57Fe at a dose of 5×1016 atoms/cm2 and an energy of 20 keV. When defects and voids created by the implantation were repaired with an overcoating layer of NPD, the recoil‐free fraction at room temperature for these samples was found to be fdia=0.94±0.06 with a corresponding Debye temperature of 1140 K. This relatively high value for f makes NPD films a promising host matrix for microgram quantities of Mossbauer isotopes.

Tissue fusion bursting pressure and the role of tissue water content

Tissue fusion is a complex, poorly understood process which bonds collagenous tissues together using heat and pressure. The goal of this study is to elucidate the role of hydration in bond efficacy. Hydration of porcine splenic arteries (n=30) was varied by pre-fusion treatments: 24-48 hour immersion in isotonic, hypotonic, or hypertonic baths. Treated arteries were fused in several locations using Conmeds Altrus thermal fusion device and the bursting pressure was then measured for each fused segment. Artery sections were then weighed before and after lyophilization, to quantify water content. Histology (HE, EVG staining) enabled visualization of the bonding interface. Bursting pressure was significantly greater (p=4.17 E-ll) for the hypotonic group (607.6 ± 83.2mmHg), while no significant difference existed between the isotonic (332.6 ± 44.7mmHg) and hypertonic (348.7 ± 44.0mmHg) treatment groups. Total water content varied (p=8.80 E-24) from low water content in the hypertonic samples (72.5% weight ± 0.9), to high water content in the hypotonic samples (83.1% weight ± 1.9), while the isotonic samples contained 78.8% weight ± 1.1. Strength differences between the treated vessels imply that bound water driven from the tissue during fusion may reveal available collagen crosslinking sites to facilitate bond formation during the fusion process. Thus when the tissue contains greater bound water volumes, more crosslinking sites may become available during fusion, leading to a stronger bond. This study provides an important step towards understanding the chemistry underlying tissue fusion and the mechanics of tissue fusion as a function of bound water within the tissue.

Dyes pumped by the nitrogen ion laser

Abstract Coumarin derivatives, 6, 30, and 102, were excited in a simple dye laser by the output at 427.8 nm from a nitrogen ion laser pumped by charge transfer from He + 2 . Tuning ranges and stabilities of the dyes are reported.

A regenerative power amplifier operating on the blue‐green line of the nitrogen ion laser

Operation of the nitrogen ion laser as an optical regenerative amplifier driven by a master oscillator allows the output to be effectively switched into the blue‐green region of the spectrum. In this work an amplifier containing a dilute plasma of nitrogen ions was pumped by thermolecular charge transfer from He2+ produced by an intense e‐beam propagating through several atmospheres pressure of gas mixture. The injection of relatively broadband output from a dye laser oscillator caused the output from the amplifier to switch entirely into the (0,2) vibrational component of the B→X electronic transition of N+2 at 470.9 nm. An output linewidth of 0.007 nm was achieved together with the early saturation of the laser transition needed for the extraction of power from the amplifier at optimal efficiency.

Status and issues in the development of a γ-ray laser. II: Giant resonances for the pumping of nuclei

A γ-ray laser would stimulate the emission of radiation of wavelengths below 1 A from excited states of nuclei. However, the anticipation of a need for high pump powers tended to discourage early research and the difficulties in demonstrating a device were first assumed to be insurmountable. Over the past decade, advances in pulsed-power technology have changed these perceptions and studies have built a strong momentum. A nuclear analog of the ruby laser has been proposed and many of the component steps for pumping the nuclei have been demonstrated experimentally. A quantitative model based upon the new data and concepts has shown the γ-ray laser to be feasible if some real isotope has its properties sufficiently close to the ideals modeled. The greatest positive impact upon feasibility has come from the discovery of giant resonances for pumping nuclei that greatly reduce the levels of pump power needed.

Status and issues in the development of a gamma-ray laser (Invited Paper)

Recent advances in theoretical and experimental research concerned with the feasibility of the gamma-ray laser are reviewed. The discussion covers the principal concepts, pump calibration, giant pumping resonances, and the development of a laser model. A quantitative model based on new data and concepts demonstrates the feasibility of the gamma-ray laser.

Status and Issues in the Development of a Gamma-Ray Laser

A gamma-ray laser would stimulate the emission of radiation at wavelengths below 1 A from excited states of nuclei. However, the difficulties in realizing such a device were considered insurmountable when the first cycle of study ended in 1981. Nevertheless, research on the feasibility of a gamma-ray laser has taken a completely new character since then. A nuclear analog of the ruby laser has been proposed and many of the component steps for pumping the nuclei have been demonstrated experimentally. A quantitative model based upon the new data and concepts of this decade shows the gamma-ray laser to be feasible if some real isotope has its properties sufficiently close to the ideals modeled.

A novel parameter for predicting arterial fusion and ablation in finite element models

Tissue fusion devices apply heat and pressure to ligate or ablate blood vessels during surgery. Although this process is widely used, a predictive finite element (FE) model incorporating both structural mechanics and heat transfer has not been developed, limiting improvements to empirical evidence. This work presents the development of a novel damage parameter, which incorporates stress, water content and temperature, and demonstrates its application in a FE model. A FE model, using the Holzapfel-Gasser-Ogden strain energy function to represent the structural mechanics and equations developed by Cezo to model water content and heat transfer, was created to simulate the fusion or ablation of a porcine splenic artery. Using state variables, the stresses, temperature and water content are recorded and combined to create a single parameter at each integration point. The parameter is then compared to a critical value (determined through experiments). If the critical value is reached, the element loses all strength. If the value is not reached, no change occurs. Little experimental data exists for validation, but the resulting stresses, temperatures and water content fall within ranges predicted by prior work. Due to the lack of published data, additional experimental studies are being conducted to rigorously validate and accurately determine the critical value. Ultimately, a novel method for demonstrating tissue damage and fusion in a FE model is presented, providing the first step towards in-depth FE models simulating fusion and ablation of arteries.