Measuring the Transverse Spin Density of Light

Abstract

We generate tightly focused optical vector beams whose electric fields spin around an axis transverse to the beams' propagation direction. We experimentally investigate these fields by exploiting the directional near-field interference of a dipole-like plasmonic field probe, placed adjacent to a dielectric interface, which depends on the transverse electric spin density of the excitation field. Nearto far-field conversion mediated by the dielectric interface enables us to detect the directionality of the emitted light in the far-field and, therefore, to measure the transverse electric spin density with nanoscopic resolution. Finally, we determine the longitudinal electric component of Belinfante's elusive spin momentum density, a solenoidal field quantity often referred to as 'virtual'.

Linear and angular momenta in tightly focused vortex segmented beams of light (Invited Paper)

“…Typically, these negative energy flows are linked to the occurrence of transverse vortices [17][18][19][20][21][22] . Additionally, a negative longitudinal component of p s , which is linked to the occurrence of transverse components of s, has been demonstrated in various optical systems consisting of propagating [12,14] or evanescent waves [5] . In this work, we investigate the occurrence of a negative longitudinal component of p o , a phenomenon sometimes referred to as 'backflow' [21,[23][24][25] , in tightly focused composite beams consisting of two spatially separated vortices with opposite charge and circular polarization of opposite handedness.…”

“…A deep understanding of this type of light-matter interaction is particularly important in highly confined and/or structured electromagnetic fields [6][7][8] . Recently, this led to a growing interest in the theoretical description [5,[9][10][11] and measurement [12,13] of the individual constituents of LM and AM occurring in various nano-optical systems. In general, it is convenient to define these dynamical quantities locally, when complex three-dimensional field distributions are considered.…”

“…The spin LM density p s , sometimes referred to as Belinfante's spin momentum density [5,[12][13][14][15] , is defined by the curl of the spin AM density s,…”

Accurate Feeding of Nanoantenna by Singular Optics for Nanoscale Translational and Rotational Displacement Sensing

“…The singularity usually refers to the discontinuity or undefined value in the light field itself. Around these singularities of the fields, rapidly spatially varying field patterns occur, which has led to new applications such as high-precision nanoscale metrology and superresolution imaging [13,[15][16][17][18][19][20][21][22][23].In this Letter, we use two different kinds of singularities: The so-called V-point polarization singularity in an azimuthally polarized beam [24][25][26] and the phase singularity in a Hermite-Gaussian beam to precisely excite one individual element of two identical parallel metallic nanorod antennas separated by a deep subwavelength gap. The precise alignment of the singularity with the two nanorods gives an accurate feeding of them far beyond the diffraction limit.…”

“…The singularity usually refers to the discontinuity or undefined value in the light field itself. Around these singularities of the fields, rapidly spatially varying field patterns occur, which has led to new applications such as high-precision nanoscale metrology and superresolution imaging [13,[15][16][17][18][19][20][21][22][23].…”