No abstract

This is the third in a series of related reports on (1) nonstable behavior of widely used ionization gauges, (2) causes of nonstability and nonreproducibility in widely used Bayard–Alpert (BA) gauges, and (3) a stable and reproducible BA gauge design with approximately a tenfold improvement in both stability of gauge calibration after thousands of hours of operation and reproducibility gauge-to-gauge compared to older design BA gauges and inverted magnetron gauges. Computer simulation of electron and ion trajectories utilizing a program named simion was used to optimize the design. A grounded conducting shield of closely controlled dimensions completely surrounds the cathodes and anode. The anode has partial end caps on both ends. Dual, independently tensioned, thoria coated iridium ribbon cathodes are precisely positioned so that the flat emitting surfaces face imaginary axes laterally displaced from the anode axis by a small amount. The cathodes are relatively short compared to the anode. A 0.040 in. diam ion collector and an emission current of 100 μA help extend the upper pressure measuring limit to above 1×10−2 Torr and provide an x-ray limit of 1.6×10−10 Torr. With a 0.005 in. diam ion collector and an emission current of 4 mA, the x-ray limit is 1.4×10−11 Torr and the upper pressure measuring limit is above 1×10−3 Torr. This new technology, called Stabil-Ion technology, provides sufficient stability and reproducibility to justify storing accurate calibration data for a specific Stabil-Ion system or averaged data from a set of nominally identical systems in electronic memory. Thus, the typical nonlinearities in sensitivity and purposeful changes in emission current or gas type do not significantly affect the accuracy of pressure indication. Consequently, accurate real time readout of pressure and stable process control are provided by the new design.

Equations (27a) and (27b) were originally solved numerically by M. Sargent III and some of his results are shown in Ref. 7. We gladly acknowledge his assistance on the numerical part of this problem and his sharing of some of the difficulties. The coefficient on the right-hand side of Eq. (49) A'P /S has the dimensions of number density && (dipole moment) /angular momentum.In Eq. (39) for the classical model, the coefficient on the right-hand side can be written in the form N(ea) /2m(cue)a where "a" is the length of the pendulum, "ea" is the dipole moment, and m(~a)n is the angular momentum.'4The possibility of a "cyclotron maser" was first suggested by Schneider IJ. Schneider, Phys. Bev. Letters 2, 504 (1959)] and first realized A theoretical model for the pressure dependence of the intensity of a gas laser is presented in which only velocity-changing collisions with foreign-gas atoms are included. This is a special case where the phase shifts are the same for the two atomic-laser levels or are so small that deflections are the dominant effect of collisions. A collision model for hard-sphere repulsive interactions is derived and the collision parameters, persistence of velocity and collision frequency, are assumed to be independent of velocity. The collision theory is applied to a third-order expansion of the polarization in powers of the cavity electric field (weak-signal theory). The resulting expression for the intensity shows strong pressure dependence. The collisions reduce the amount of saturation and the laser intensity increases with pressure in a characteristic fashion. It is recommended that the best way to look for this effect is to make the measurements under conditions of constant relative excitation.

A model for a laser oscillator in which the atoms of the active medium do not collide during their radiative lifetimes has been used by Lamb. His theory predicts that as the cavity frequency is tuned through atomic resonance, there can be a dip in the intensity of the laser radiation. In the present work this model is generalized by allowing the atoms to collide while they radiate. The general formulation of the collision problem is presented for thermally moving neutral atoms interacting with a standing-wave cavity mode, and it is then applied to the calculation of the intensity profile for some simple collision models. It is found that as the pressure increases, not only is the "dip" broadened and made less deep, but it is also shifted and becomes asymmetric. Some observations by Cordover on pressure effects are found to be in satisfactory accord with this theory.