Abstract
Lasers emit a narrow beam of light which, for many applications, is often required to be expanded and then collimated. A common type of device used for this purpose is a lens telescope in which a pin-hole is placed at the common focal point of the two lenses. In dye laser cavities, dispersion through a number of prisms gives an expanded beam. The divergence of a laser beam can also be achieved by a convex reflecting surface like a polished steel ball. Here the capability of a small steel ball as an inexpensive, simple and convenient laser-beam expander has been investigated experimentally. It has been shown, with the help of shearing interferograms and Ronchigrams, that the aberrations introduced from on-axis as well as off-axis illumination of the ball are less than 1/4 of a fringe.
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