Electrons can act like light waves in many ways, but according to recent experiments, their wave-like effects don’t always correspond with light. The unexpected behavior occurs because electrons feel each other’s presence, while photons do not.
Newton thought that light was made up of particles, but then it was discovered, as we have seen here, that it behaves like a wave. Later, however (in the beginning of the twentieth century) it was found that light did indeed sometimes behave like a particle. Historically, the electron, for example, was thought to behave like a particle, and then it was found that in many respects it behaved like a wave. So it really behaves like neither. Now we have given up. We say: “it is like neither.” ere is one lucky break, however-electrons behave like light. e quantum behaviour of atomic objects (electrons, protons, neutron, photons, and so on) is the same for all, they are all ‘particle waves’ or whatever you want to call them.
We consider effects which occur when four-wave sum frequency generation and multiphoton ionization are induced by lasers tuned near a three-photon resonance and simultaneously near or at a dipole allowed four-photon resonance. In studies with unfocused laser beams, if the phase mismatch of the generated four-wave-mixing field is large and the related two-photon resonance for the absorption of a four-wave-mixing photon and a laser photon results in strong absorption of the four-wave-mixing field, a coherent cancellation occurs between the pumping of the resonance by two- and four-photon processes. This interference effect occurs when the first laser is tuned on either side of the three-photon resonance and \ensuremath{\Vert}\ensuremath{\Delta}krL\ensuremath{\Vert}\ensuremath{\gg}1, where \ensuremath{\Delta}kr is the mismatch and L is the length of the path of the laser beams in the gas. With focused laser beams large differences occur between ionization with unidirectional beams and with counterpropagating laser beams when \ensuremath{\Vert}\ensuremath{\Delta}krb\ensuremath{\Vert}\ensuremath{\gg}1, where b is the confocal parameter of the focused laser beams. Strong absorption of the four-wave-mixing field is shown not to be necessary for strong destructive interference with focused laser beams when the phase mismatch is large. This work also suggests an explanation for earlier experiments where the presence of a four-photon resonance enabled the generation of third-harmonic light in a positively dispersive wavelength region. We argue that this process can occur when the laser used to achieve the four-photon resonance is focused on the small z (z is the coordinate in the direction of propagation) side of the focal point of the laser responsible for the third-harmonic generation. In this way the absorption of the third-harmonic light on one side of the focal point is made much stronger than on the other side. Correspondingly, contributions to the third-harmonic field from the two sides of the focal point are unequal and cannot undergo complete destructive interference as would otherwise occur in a positively dispersive region.
At the atomic scale, the distinction between particles and waves breaks down. The realization, early in the twentieth century, that light consists of discrete packages, or “photons,” prompted the converse suggestion that particles could behave like waves. Confirmation of this idea came in 1927, from an experiment involving the scattering of electrons from a crystal. Today, “wave-particle duality” is central to quantum mechanics, and the wave properties of subatomic particles are widely used in microscopy and crystallography. Electron diffraction techniques are widely used to characterize atomic arrangements on solid surfaces and inside thin films, and to investigate the structures of molecules in gases. The dual nature of waves and particles is part of the “spookiness” of quantum mechanics, which cannot be explained in any classical way. It used to be that one could only imagine an experiment that would simultaneously demonstrate the particle and wave nature of electrons.
Wave-particle duality of light has dumbfounded physical scientists for centuries. Sir Isaac Newton contended that light was made up of individual particles while Hooke (who was utterly despised by Newton) wrote on the wave-like properties of light.[6] In 1801, Thomas Young’s double slit experiment demonstrated wavelike properties of light. In 1905, Einstein revisited the theory of light acting as a particle to resolve conflicts between the wave theory of light and certain experimental results such as the photoelectric effect.[11] Experiments confirming particle-like properties of light were not realized until later in the 20th century. In 1981, Grangier, Roger and Aspect published a paper titled Experimental Evidence for a Photon Anticorrelation Effect on a Beam Splitter: A New Light on Single-Photon Interferences. This paper reported on one of the first successful anticoincidence experiments which measured the particle-like behavior of light. The paper also reported on an experiment that used the same source and detection scheme as the anticoincidence experiment, which measured interference. Grangier, Roger and Aspect eloquently depicted the conundrum of the waveparticle duality of light. To what extent does this this complementary nature of light exist? How does light know when to display wave-like or particle-like properties? One popular answer to this was that light can ‘sense’ what the experiment is attempting to measure. Based on the initial ‘feel,’ light would decide whether or not it will display wave-like or particle-like behavior before entering the experiment. This hypothesis is aptly named the conspiracy theory.[2]