No abstract

Time-resolved studies of the vacuum-uv emissions from neon and helium-neon mixtures were made using a single-photon counting technique. Excitation of the atoms was provided by a pulsed beam of 250-keV electrons. Measurements in neon were carried out at the wavelengths of the resonance states Ne(~P&) and Ne( P&). Collision coefficients for the destruction of Ne(P&), Ne(P&), and Ne(P2) atoms in neon were determined. The two-body collision coefficient for deexcitation of Ne(P&) atoms to the Ne(P&) state is 5.5 &&10 sec / Torr. Atoms in the Ne(3P&) level undergo twoand three-body collisions with neon groundstate atoms. The deexcitation rate for the transition Ne(P&) to Ne(P2) is 1.80~10 sec / Torr. The three-body collision coefficient for Ne(~P&) is 6.0 sec~/Torr2. Metastable Ne(3P&) atoms are collisionally excited to the Ne(3P&) state at the rate 160 sec t/Torr, and they are destroyed in three-body collisions with rate coefficient 0.60 sec t/Torr2. The twobody deexcitation frequency for Ne(P&) and twoand three-body collision coefficients for Ne(P2) are in agreement with the results of Phelps. Studies of the emissions from He-Ne mixtures were performed at relatively high helium pressures of 200 and 400 Torr, respectively. At each helium pressure controlled amounts of neon impurity were added. Timeresolved measurements were nmde at the wavelengths of the He(2i$) rnetastable, the helium continuum emissions, and at the wavelengths of Ne(iP&) and Ne(3P&). The decay constants for He(2~$) and Ne(P&) are shown to be consistent with resonant excitation transfer from He(2 $) to the Ne(3s2) laser level (Paschen notation). The pressure dependence of the emissions from Ne(3P&) in helium is governed primarily by collisional deexcitation to the metastable Ne(P2) state. The two-body collision coefficient for the destruction of Ne(P&) atoms by helium is 8.3 X10 sec /Torr.

An automated measurement technique to measure the surface impedance, Zs=Rs+iXs, as a function of temperature is presented. Based on the dielectric resonator measurement technique, a general purpose approach is developed which does not neglect dielectric loss and can accommodate a variety of sample sizes and measurement frequencies. By employing a parallel-plate geometry which has a known electromagnetic solution, both the surface impedance of the sample and the induced surface current can be related quantitatively to the measured Q, the resonant frequency, and the applied power. Although the measurement sensitivity depends on the system design and choice of materials, comprehensive equations are presented which serve as a useful tool for designing the system and simulating the measurement. Using a sample size of 1×1 cm2 and a measurement frequency of 19.6 GHz, a measurement uncertainty of 420 μΩ for Rs and 4800 μΩ for ΔXs is demonstrated. For superconducting samples, this translates to a measurement uncertainty of 105 μΩ for Rs and 2400 μΩ for ΔXs at 10 GHz, which is sufficient for routine measurements. Methods to improve the resolution and uncertainty of this measurement technique are discussed, and a general scheme to fully automate this measurement via computer is demonstrated.

A simple comparative technique to characterize surface electrical resistance of small metallic samples at submillimeter wavelengths is presented. A quasioptical hemispherical resonator, fed by an optically pumped far-infrared laser is used, with the sample serving as the plane mirror. The cavity developed combines a small beam size at the sample, enabling measurements on samples with widths as small as 5 mm, with a large quality factor Q, so that surface resistance losses are readily measurable. This cavity uses a simple new geometry that feeds the cavity through a single small coupling hole that also serves as a system of monitoring energy storage in the cavity by means of a single external beamsplitter. An alternate approach of inserting an internal beamsplitter into the resonator was found to be unacceptable due to excessive losses and alignment problems.