Abstract
We analyze the interference field formed by two electromagnetic plane waves (with the same frequency but different wave vectors), and find that such field reveals a rich and highly non-trivial structure of the local momentum and spin densities. Despite the seemingly-planar and extensively-studied character of the two-wave system, we find that it possesses a transverse (out-of-plane) helicity-independent spin density, and also a transverse polarization-dependent momentum density with unusual physical properties. The polarization-dependent transverse momentum represents the so-called Belinfante spin momentum, which does not exert the usual optical pressure and it is considered as `virtual' in field theory. We perform analytical estimations and exact numerical simulations of the interaction of the two-wave field with probe Mie particles. The results of these calculations clearly indicate the straightforward detectability of the unusual spin and momentum properties in the two-wave field and strongly motivate their future experimental verifications.
Highlights
It is well known, since the seminal works by Poynting [1], that light carries momentum and angular momentum (AM) [2,3]
Despite the seemingly planar and extensively studied character of the two-wave system, we find that it possesses a transverse helicity-independent spin density and a transverse polarization-dependent momentum density with unusual physical properties
Despite the seemingly planar and thoroughly studied character of the two-wave system, we discover that such a field possesses a transverse helicity-independent spin density and a transverse polarization-dependent momentum with nontrivial physical properties
Summary
Since the seminal works by Poynting [1], that light carries momentum and angular momentum (AM) [2,3]. Typical plane-wave or Gaussian-beam states exhibit longitudinal momentum associated with the wave vector k and longitudinal (k-directed) spin AM associated with the degree of circular polarization (helicity) σ This is in accordance with the “naive” but intuitively clear picture of photons as particles carrying momentum and spin. Local momentum and angularmomentum densities in structured (i.e., non-plane-wave) optical fields can demonstrate unusual features, which have recently attracted considerable attention These are “supermomentum” with values higher than ħk per photon [4,5,6,7,8], transverse (i.e., orthogonal to k) helicity-independent spin AM [9,10,11,12,13], and transverse helicity-dependent momentum [10,14,15]. These intriguing results, supported by both analytical theory and exact numerical simulations, call for experimental verification
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