Comparison Between a Gas Lens and Its Equivalent Thin Lens

Gas lenses have been studied for their potential use as focusing elements in beam waveguides.1-2-3'4 Two earlier papers 2,3 were concerned with the study of the optical properties of a particular gas lens (see Fig. 1) and came to the conclusion that certain types of gas lenses behave as optically thin lenses. The equivalent thin lens approximating the optical properties of the gas lens is not flat but deformed to fit the shape of the principal surface of the gas lens. The definition of the equivalent thin lens is based on the optical properties of the gas lens for input rays parallel to the optical axis. For those rays the two lenses are optically equivalent by definition. This equivalence need not necessarily hold true for arbitrary input rays. To show that the equivalent lens can replace the gas lens for arbitrary input rays is the purpose of this paper. For the purpose of optical waveguides a gas lens can be replaced by an equivalent thin lens if the ray trajectories through many gas lenses coincide reasonably closely with the ray trajectories through the equivalent thin lenses. A computer simulated experiment was conducted to determine the ray trajectories through 100 gas lenses and through 100 equivalent lenses and to compare their results. It will be shown in this paper that the two ray trajectories are very nearly the same. This result allows us to use the equivalent thin lenses to study the light guidance properties of gas lenses. This replacement is particularly desirable to examine the wave optics properties 1339