Several research groups published papers in 1965 describing holographic interferometry.[1][4][5][6] While the first observations of phenomena that could be ascribed to holographic interferometry were made by Juris Upatnieks in 1963[7] the essential feature of the process was not understood until the work of Powell and Stetson.[1] Their experiments were conducted over the period of October to December 1964, and they began with an investigation of the periodic coherence length of the HeNe laser being used.