MODES OF OPERATION OF VARIOUS He-Ne LASERS AND CONFIGURATIONS Owen P. Smith, Worcester Polytechnic Institute; John W. Noe, Harold Metcalf, Department of Physics and Astronomy, Stony Brook University. The longitudinal and transverse mode characteristics of several types of helium-neon lasers were examined to better understand the operation of an open-cavity He-Ne laser. The lasers were aligned with a photodetector and a polarizer was placed in the beam path. The effects of the polarizer on the intensity vs. time profile was examined and several different characteristics of laser modes were studied. An open-cavity He-Ne laser was then built and its behavior under a variety of circumstances was examined. The laser was also modified for increased ease of use during experiments that involved changing the cavity length and for safety. This study showed that an open-cavity He-Ne laser can be a useful tool for examining the effects of various optical elements inside a cavity in addition to its instructional value as a demonstration piece for examining the stability criteria and modes of operation of lasers in general. This study was supported by NSF Grant No. Phy 99-12312.