Opto-Electronics Review

Abstract

The review exposes basic concepts and manifestations of the singular and structured light fields. The presentation is based on deep intrinsic relations between the singularities and the rotational phenomena in light; it involves essentially the dynamical aspects of light fields and their interactions with matter. Due to their topological nature, the singularities of each separate parameter (phase, polarization, energy flow, etc.) form coherent interrelated systems (singular networks), and the meaningful interconnections between the different singular networks are analysed. The main features of singular-light structures are introduced via generic examples of the optical vortex and circular vortex beams. The review describes approaches for generation and diagnostics of different singular networks and underlines the role of singularities in formation of optical field structures. The mechanical action of structured light fields on material objects is discussed on the base of the spin-orbital (canonical) decomposition of electromagnetic momentum, expressing the special roles of the spin (polarization) and spatial degrees of freedom. Experimental demonstrations spectacularly characterize the topological nature and the immanent rotational features of the light-field singularities. The review is based on the results obtained by its authors with a special attention to relevant works of other researchers.

Correlation Optics, Coherence and Optical Singularities: Basic Concepts and Practical Applications

“…A characteristic feature of 3D fields is the existence of the longitudinal electric and/or magnetic components, commensurate to the usual transverse ones [23][24][25][42][43][44]. In paraxial beams, this fact is responsible for a set of fine effects concerning the polarization-dependent deviations from the geometric-optics beam trajectory [51][52][53].…”

“…Such points normally belong to specific lines or contours, closed within the observable regions or open (closed at infinity), where the field amplitude is zero. These objects demonstrate a complex of unique physical properties, due to which the same objects are referred to by various terms: phase singularities, wavefront dislocations, isolated amplitude zeros, optical vortices (OVs) [23][24][25][60][61]. A common example of the circular light beams of this sort is the Laguerre-Gaussian mode of a laser resonator [60][61][62], which spectacularly illustrates the main physical attributes: the helical dependence of the phase near the singularity core ~exp ± ilφ (13) where φ is the azimutal angle, the phase increment on a roundtrip near the core 2lπ where l is an integer topological charge of the singularity, and the transverse energy circulation due to which the beam carries an orbital angular momentum (OAM) with respect to the propagation axis, with the numerical value lħ per photon.…”

“…Each particle experiences a complex mechanical action caused by a complex of ponderomotive factors. In particular, the optical forces are associated with the optical field inhomogeneity and the internal energy flow (field momentum components) [23][24][25], which redistribute the particles to the regions of maximum light intensity. Additionally, there exists the photophoretic force associated with inhomogeneous heating of the absorbing particles [111][112][113][114], which moves the particles to the intensity minimum.…”

“…Its dependence on time is slow with respect to the oscillation period 2π/ω, which is reflected by the "slow-time" argument τ. The slow-time complex function E(R, τ) supplies a suitable instrument for description and analysis of such waves [23][24][25].…”

“…An important special class of light fields is the so called paraxial waves [23][24][25] where the physically selected longitudinal direction (propagation direction) z exists, and the rate of the field amplitude variations along z is much lower than that in the transverse (x, y) plane; in turn, the characteristic variations' scale in the transverse plane is much higher than the vacuum wavelength λ 2π/k (k ω/c is the wave number). In such situations, the electric vector is nearly transverse and can be described by the complex amplitude distribution…”