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In a ray trace calculation of the rms radius of the spot formed in the image plane of an optical system by a point source object, a decision must be made as to how many rays will be traced to obtain the result. As the number of rays is increased, the rms spot radius is generally found to decrease, apparently approaching a definite lower limit as the number of rays becomes very large. This paper examines the question of how many rays must be traced and what their geometrical distribution within the aperture should be to approach the limiting value of the rms spot radius for an infinite number of rays within an accuracy of approximately 1%.

It has been widely observed that when a multimode gas laser is employed in photomixing experiments, the heterodyne signal amplitude depends on the optical path length difference between the paths traversed by the two light beams. In this paper, a simple phenomenological model of multimode gas laser radiation is used to calculate the dependence of the heterodyne signal amplitude on optical path length difference for various numbers of oscillating axial modes in a multimode gas laser. The results have important implications for the design of optical heterodyne receivers.

This paper deals with the properties of the images of truncated one-dimensional periodic bar targets formed by aberration-limited optical systems. Attention is directed to the problem of determining how many bars are required at a given spatial frequency in order to obtain an image which closely approximates that for an infinite-chain periodic bar target. Numerical calculations are carried out for the case of an aberration-limited, glancing-incidence x-ray telescope.