A light beam can be confined and guided along a straight or gently curved path through a gas by appropriate control of temperature gradients in the gas. Two types of guides that take advantage of convection to assist in this temperature control are described. One is composed of a continuous, warm, open helix within a cooler outer pipe containing the gas. The other is a series of gas lenses, in each of which the gas is warmed as it moves through an opposing pair of short focusing tubes to the base of a short warm chimney. The gas rises in the chimney and is then cooled, whereupon it falls through ducts that return it to the focusing tubes. Experiments were performed on each type and the relative merits of the two types are compared. An approximate mathematical analysis of the operation of the second type is presented.
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Uncertainty derived from assumption that knife-edge test will give
wavelength uncertainty in optical path differences between marginal ray and axial ray with 0.6 μ light when there are no aberrations.
Asymmetric aberration that would be described by adding a term proportional to y3 to Eq. (1) “sagging lens aberration,” adds significantly to uncertainty in Cs.
Strong spherical aberration observed; approximate value near axis recorded.
Some of the previously reported temperature differences1 were too small because of a faulty microvolt meter. New data were taken using a bridge circuit with the thermocouples.
Table II
Physical properties of gases at 300°K and 1 atm pressure.a
Most of the data are from the International Critical Tables (McGraw-Hill Book Company, Inc., New York, 1930) vols. 5 and 7. Some values are interpolated.
Information compiled by T. Phillips of Allied Chemical Company. Morristown, New Jersey (private communication).
Figures estimated from data on other similar compounds with approximate scaling relations.
From molecular weight and ideal gas relation.
Table III
Measured performance of chimney lens at 1 atm pressure.
See first footnote to Table I for criterion of uncertainty.
Marked spherical aberration made measurement uncertain. The figures given are for the region near the axis.
Table IV
Computed performance of chimney lens at same temperature differences as in Table III.
Note that zm is much greater than the length (3.8 cm) of the warm part of the focusing tube in this case. Hence computed convergence should be greater than that observed near the axis. The fact that it is less is probably due to inaccuracy in some of the estimated physical constants for C4F10.
Uncertainty derived from assumption that knife-edge test will give
wavelength uncertainty in optical path differences between marginal ray and axial ray with 0.6 μ light when there are no aberrations.
Asymmetric aberration that would be described by adding a term proportional to y3 to Eq. (1) “sagging lens aberration,” adds significantly to uncertainty in Cs.
Strong spherical aberration observed; approximate value near axis recorded.
Some of the previously reported temperature differences1 were too small because of a faulty microvolt meter. New data were taken using a bridge circuit with the thermocouples.
Table II
Physical properties of gases at 300°K and 1 atm pressure.a
Most of the data are from the International Critical Tables (McGraw-Hill Book Company, Inc., New York, 1930) vols. 5 and 7. Some values are interpolated.
Information compiled by T. Phillips of Allied Chemical Company. Morristown, New Jersey (private communication).
Figures estimated from data on other similar compounds with approximate scaling relations.
From molecular weight and ideal gas relation.
Table III
Measured performance of chimney lens at 1 atm pressure.
See first footnote to Table I for criterion of uncertainty.
Marked spherical aberration made measurement uncertain. The figures given are for the region near the axis.
Table IV
Computed performance of chimney lens at same temperature differences as in Table III.
Note that zm is much greater than the length (3.8 cm) of the warm part of the focusing tube in this case. Hence computed convergence should be greater than that observed near the axis. The fact that it is less is probably due to inaccuracy in some of the estimated physical constants for C4F10.
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