Suppose I have 2 lasers. 1 emits light of exactly 500 THz and the second emits light of a frequency exactly 1 hertz higher. A semitransparent mirror is used to superimpose the 2 beams and create a composite beam. The beam is directed to a detector which detects the intensity of the beam fluctuating in 1 second cycles as the 2 sources come in and out of phase with each other. Now here's the part I'm not sure about. During the time that the 2 sources are out of phase both light beams still exist and still travel together without effecting one another. They become undetectable when they are out of phase because when they encounter a charged particle they try to push it in opposite directions, and therefore have no effect on it. Therefore the light cannot interact with matter when it is out of phase. The out-of-phase beams go straight through the detector without interfering with it. If I place a long glass rod on the far side of the detector the glass will slow the propagation of the shorter wavelength more then that of the longer wavelength. Eventually the 2 waves should be in phase again and therefore detectable to a second detector. If all this reasoning is true then it is possible to cause coherent light to go through an otherwise opaque object by introducing a second coherent source that interferes destructively with the first. Is this correct or is there an error in my reasoning?