Talk:Point diffraction interferometer

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Definition of common path inteferometer[edit]

Please find a definition of common path interferometer. Common path only means common path length. The Michelson is a common path interferometer where the reference and test surfaces are spaced such that their distances from the source are very near equal. This allowed the use of simple and available light sources prior to the time of lasers which is when the term was originally defined. It just so happens that the vast majority of the common path length interferometers possessed certain other properties so after the introduction of lasers these other properties were lauded as inherent to common path interferometers when they actually are not. The ability to use a simple light source was a characteristic to appreciate when the term was coined. Beware the assumption that interferometers allowing incoherent light function also have the other properties that most common path interferometers have. The Michelson-Morley experiment was performed with a non-coherent source! (talk) 16:43, 17 October 2010 (UTC)