ABSTRACT

CONTENTS 21.1 Introduction ................................................................................................ 318 21.2 Photon Diffraction ...................................................................................... 319

21.2.1 Young’s Experiment....................................................................... 320 21.2.2 Bragg Relation ................................................................................ 323 21.2.3 Fraunhofer Diffraction .................................................................. 324 21.2.4 Fresnel Diffraction ......................................................................... 325

Summary .............................................................................................................. 329 References ............................................................................................................330

Any discussion of the nature of light must include a reminder that whenever we make the observation of light (photons), we only observe particle-like properties. This chapter provides a reiteration that we don’t need wave-like properties to scattered photons to describe phenomena such as diffraction or refraction of light. This chapter updates the original ideas of Duane, later revived by Landé, which provided a description of light diffraction without making reference to a wave nature. These are updated using terminology more common to quantum electrodynamics which describes the interaction of particles in terms of the exchange of virtual photons. Diffraction is described in terms of an ensemble of distinct, probability weighted paths for the scattered photons. The scattering associated with each path results from the quantized momentum exchange with the scattering lattice attributed to the exchange or reflection of virtual photons. The probability for virtual particle exchange/reflection is dependent upon the allowed momentum

states of the lattice determined by a Fourier analysis of the lattice geometry. Any scattered photon will exhibit an apparent wavelength inversely proportional to its momentum. Simplified, particle-like descriptions are developed for Young’s double slit diffraction, Fraunhofer diffraction and Fresnel diffraction. This description directly accounts for the quantization of momentum transferred to the scattering lattice and the specific eigenvalues of the lattice based upon the constraints to virtual photon exchange set by the Uncertainty Principle, ∆pi = h/ℓi.