accordingly. If A// = 6 (for example, A// = 2tt for a cylinder, if / = radius, but the one-dimensional argument is then inaccurate), then Fig. 3a would correspond to 1 Torr and Fig. 3b to p = 20 Torr. For any given p, the variations of T with a and b are mostly due to the quantity 1/5, or variations in the heat conductivity of the mixture, which can vary over a range of 6 to 1, whereas F' varies only from 0.81 to 1. Evidently overheating may curtail high-pressure operation of the laser system. II.3. Inversion Population Evaluation of T yields /V100 by Eq. 4, and the inverted population TV = Nooi - /V100 can be estimated from Eqs. 3 and 4. Computer plots of N on a-b planes for different pressures are shown in Fig. 4. The ratios a and b vary over the range 10~4 to 104, and N is on a linear scale. Where N is negative, the plots indicate zero. The values assumed are C = 100, F = 0.5, A/l = 1, Tw = 300 K. When the effect of Br2 deexcitating the CO2 is omitted (the Zc4Br2 term), the values of N are an order of magnitude greater. Also, failure to include the depletion terms results in N's too high for low p, and low a: for example, if p = 0.001 Torr, and a = 10”3, b = 10”2, the estimated N001 = 1013, whereas there are only 3.5 x 1010 molecules of CO2 present. The depletion terms result in the flattening of the graphs at low p and low a, so that /VOoi < CO2. The drop in N at high values of a is the effect of the lower level filling up because of temperature rise for increased CO2 content (Fig. 3b). The temperature rise gets rapidly worse as p increases and results in the lower level exceeding the upper level at about 1 Torr for A/l = 1. On recalculating N with A/l = 6, the curves for p = 10”3, 10 2, and 101 Torr are indistinguishable from the above, consistent with the low temperature rise at lower p (Fig. 3). However, the values in the 1-Torr plot are about
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