In this Letter we discuss the observation of a pattern of concentric annuli formed as a result of thermal effects upon a light beam. To our knowledge, this is the first time such patterns have been reported.
When a beam of light passes through an absorbing medium whose refractive index decreases as a function of temperature, the medium behaves as a negative lens. Gordon et al.1 observed this phenomenon by placing a cell containing an absorbing liquid between the mirrors of a helium-neon laser. The absorption constants for several liquids with very low absorbencies have been determined using this effect.2 Rieckhoff3 measured the increase in the diameter of a light beam that passed through a thermal self-defocusing liquid placed external to the laser inter-ferometer. Recently Leite et al.4 demonstrated that this effect may be used as a power limiting device.
In the early part of January, 1993, engineers and historians at Georgia Tech joined together to draft a proposal to SUCCEED, a national engineering education coalition funded by the National Science Foundation. This mvel collaboration of academics who do not ususally work together;imagined an evenmental course that would integrate humanities and engineering education in order to provide a braod context for understanding the role of engineering and the engineering profession in modem society. Primarily aimed at beginning students in electrical engineering, this pilotproject would develop a set of modular units, each one of which incorporate materials on engineering design or on issues related to engineering professionalism, and which would link that information to economic, political or social considerations. In this fashion, the creative work of engineers, past and present9 could be analyzed both in terms of technical detail and in terms of the human context in which engineering always takes place. The course was presented at Georgia Tech for the$rst time in the Spring Quarter of 1995, and it will be repeated in the Winter Quarter, 1996. We present here a progress report that describes the planning, organization and objectives of the course, and that concludes with some observations on the work yet to be done in order to make the course materials we have developed usable by others.
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