The present interpretation of photon is as: A photon = a quantum of radiation energy + energy hn, where the quantum of radiation energy constitutes the photon and provides the particle like physical existence to it, similarly, as the quantum of charge (-e) constitutes the electron and provides the particle like physical existence to it, and the energy hn enables the photon to travel with velocity c, spin with frequency n (which the photon obtains from the orbiting electron, from which the photon is emitted), scatter electron in Compton scattering, and eject electron penetrating into metals in photoelectric effect. The present interpretation of photon enables to provide very clear and complete explanations of all the phenomena related to photons, including the phenomena of interference and diffraction
The present interpretation of photon is as: A photon = a quantum of radiation energy + energy hn, where the quantum of radiation energy constitutes the photon and provides the particle like physical existence to it, similarly, as the quantum of charge (-e) constitutes the electron and provides the particle like physical existence to it, and the energy hn enables the photon to travel with velocity c, spin with frequency n (which the photon obtains from the orbiting electron, from which the photon is emitted), scatter electron in Compton scattering, and eject electron penetrating into metals in photoelectric effect. The present interpretation of photon enables to provide very clear and complete explanations of all the phenomena related to photons, including the phenomena of interference and diffraction
The idea of the photon has stirred the imaginations of physicists ever since 1905 when Einstein originally proposed the use of light quanta to explain the photoelectric effect. This concept is formalized in the quantum theory of radiation, which has had unfailing success in explaining the interaction of electromagnetic radiation with matter, seemingly limited only by the ability of physicists to perform the indicated calculations. Nevertheless, it has its conceptual problems—various infinities and frequent misinterpretations. Consequently an increasing number of workers are asking, “to what extent is the quantized field really necessary and useful?” In fact the experimental results of the photoelectric effect were explained by G. Wentzel in 1927 without the quantum theory of radiation. Similarly most electro-optic phenomena such as stimulated emission, reaction of the emitted field on the emitting atom, resonance fluorescence, and so on, do not require the quantization of the field for their explanation. As we will see, these processes can all be quantitatively explained and physically understood in terms of the semiclassical theory of the matter–field interaction in which the electric field is treated classically while the atoms obey the laws of quantum mechanics. The quantized field is fundamentally required for accurate descriptions of certain processes involving fluctuations in the electromagnetic field: for example, spontaneous emission, the Lamb shift, the anomalous magnetic moment of the electron, and certain aspects of blackbody radiation. (The Compton effect also fits here, but see later under references 8b and c.) Here we will outline how the photon concept originated and developed, where it is not required and is often misused, and finally where it plays an essential role in the understanding of physical phenomena. In our discussion we will attempt to give a logically consistent definition of the word “photon”—a statement far more necessary than one might think, for so many contradictory uses exist of this elusive beast. In particular consider the original coining of the word by G. N. Lewis: “[because it appears to spend] only a minute fraction of its existence as a carrier of radiant energy, while the rest of the time it remains an important structural element within the atom…, I therefore take the liberty of proposing for this hypothetical new atom which is not light but plays an essential part in every process of radiation, the name photon!” (our exclamation point). Clearly the present usage of the word is very different.
All electrons, nucleons, and other particles or quanta (because quantum mechanics is applied to all particles, these should be known as quanta) undergo a persistent spin motion without possessing any infinite energy source, and therefore, they should have a unique structure that maintains their spinning and provides all the properties that they display. Additionally, because nothing in nature occurs without a reason or purpose, there should be an explanation for their persistent spinning motion. The photons also possess spin motion that they derive from the orbiting electrons from which the photons are emitted, and not obtain from their unique structure. Therefore, purpose why all electrons, nucleons, and other particles possess persistent spin motion, and unique structures of electrons and nucleons have been determined. The results of the determination of the purpose why all electrons, nucleons, and other particles possess persistent spin motion provide very clear and complete explanations for all related phenomena. Present study is focused on to provide clear and complete understanding of the phenomena of interference and diffraction of electrons and photons.
It has already been noted (section 2.8) that high frequency electromagnetic radiation can exhibit particle-like behaviour. For example, in the sensitive type of detector known as a photomultiplier tube (described in Wehr and Richards, Physics of the Atom , 2nd edn, Addison-Wesley, section 10.5), a beam of low-intensity X-rays is detected as a sequence of isolated sharp pulses, such as would be produced by a stream of particles arriving at the detector. As was pointed out, it is not surprising that it is usually high-frequency radiation which travels in particle form; as shown in figure 2.39, a wave group of high-frequency radiation can be compressed into a very short time span. However, when we speak of a particle, we mean something more than an entity which arrives in a short time span. A particle has a definite size, or more exactly it has a well-defined energy and momentum. It was discovered around about 1900 that the same is true of an X-ray wave packet: all packets of a given frequency radiation carry the same energy and momentum. This revolutionary discovery means that we must treat the wave packets as particles on exactly the same footing as more familiar particles such as electrons. The electromagnetic particle is called a photon . There is a wealth of experimental evidence which may be used to define the properties of a photon. We shall be highly selective, however, and simply present two particularly clear-cut experiments, the photoelectric effect and Compton scattering, which enable one to define the energy and momentum of the photon in terms of the frequency and wave number of the corresponding wave. These experiments will be described in detail in section 4.1.
Although interferenceis intrinsically a classical wave phenomenon, the superposition principle whichunderlies all interference is also at the heart of quantum mechanics. Feynmanhas referred to interference as really “the only mystery” of quantum mechanics.Furthermore, in some interference experiments we encounter the idea of quantumentanglement, which has also been described as really the only quantum mystery.Clearly interference confronts us with some quite basic questions ofinterpretation. Despite its long history, going back to Thomas Young at thebeginning of the 19th century, optical interference still challenges ourunderstanding, and the last word on the subject probably has not yet beenwritten. With the development of experimental techniques for fast and sensitivemeasurements of light, it has become possible to carry out many of the Gedankenexperiments whose interpretation was widely debated in the 1920s and 1930s inthe course of the development of quantum mechanics. Although this articlefocuses entirely on experiments with light, interference has also been observedwith many kinds of material particles like electrons, neutrons, and atoms. For a given metal, there exists a certain minimum frequency of incidentradiation below which no photoelectrons are emitted. This frequency is calledthe threshold frequency. Increasing the frequency of the incident beam andkeeping the number of incident photons fixed increases the maximum kineticenergy of the photoelectrons emitted. The number of electrons emitted alsochanges because the probabilitythat each impacting photon results in an emitted electron is a function of thephoton energy. However, if just the intensity of the incident radiation isincreased, there is no effect on the kinetic energies of the photoelectrons.Ifthe photon energy is too low, the electron is unable to escape the material.Increasing the intensity of the light increases the number of photons in thebeam of light and thus increases the number of electrons excited but does notincrease the energy that each electron possesses. The energy of the emittedelectrons does not depend on the intensity of the incoming light (the number ofphotons), only on the energy or frequency of the individual photons. It isstrictly an interaction between the incident photon and the outermost electron.
The fundamental fact for quantum physics which has emerged from experimental investigations in the field is a double duality of wave and particle concepts. The wave theory of light, firmly grounded by the wave explanations of interference and diffraction and by Maxwell’s electromagnetic theory of light waves, is now recognized as giving but one aspect of the nature of radiation. The corpusclar aspect of radiation is revealed in the photoelectric effect and in the Compton effect. In these effects Planck’s constant appears as a universal constant which connects the wave and particle modes of description of the same radiation.
This chapter will explore Einstein’s theory of special relativity. In addition, readers will find the basic concept of radiation as waves and particles including photoelectric and Compton scattering effects. Definition of X-ray and behaviors under conservation of momentum and energy will be provided and discussed. Various photon and particle wavelengths will be explored with various examples to help readers understand how to apply basic quantum theory dealing with the de Broglie wavelength, wave equation, wave–particle duality, and the uncertainty principle.