Transfer of Light Helicity to Nanostructures

Abstract

We discovered that chiral nanoneedles fabricated by vortex laser ablation can be used to visualize the helicity of an optical vortex. The orbital angular momentum of light determines the chirality of the nanoneedles, since it is transferred from the optical vortex to the metal. Only the spin angular momentum of the optical vortex can reinforce the helical structure of the created chiral nanoneedles. We also found that optical vortices with the same total angular momentum (defined as the sum of the orbital and spin angular momenta) are degenerate, and they generate nanoneedles with the same chirality and spiral frequency. DOI: 10.1103/PhysRevLett.110.143603 PACS numbers: 42.50.Tx, 42.50.Wk, 79.20.Ds, 79.20.Eb Light that has a helical wave front due to an azimuthal phase shift, expðiL Þ (where L is an integer known as the topological charge), carries orbital angular momentum, L@. Such light is referred as an optical vortex [1][2][3][4]. Optical vortices have been widely investigated for applications such as optical trapping and guiding [5][6][7], as well as superresolution microscopy [8,9]. Circularly polarized light has a helical electric field and a spin angular momentum, S@, associated with its circular polarization. Optical vortices with circular polarization exhibit both wave front and polarization helicities, and a total angular momentum, J@ [10-12], which is defined as the sum of the orbital and spin angular momenta. This angular momentum is evidenced by the orbital and spinning motions of trapped particles in optical tweezers.To date, several researchers have intensely studied the interaction of structured light, such as radially polarized beams, with plasmonic or metallic structures [13][14][15]. However, these previous studies mostly focused on optical properties, such as mode selection, plasmon focusing, etc., of plasmonic or metallic structures, including photonic crystals as well as plasmonic waveguides, prepared by conventional integrated photonic circuit techniques based on lithography and chemical etching. There are few reports on the use of structured light itself to form chiral structures on the nanoscale. Recently, we discovered that the helicity of a circularly polarized optical vortex can be directly transferred to an irradiated metal sample, resulting in the formation of chiral nanoneedles [16][17][18]. This is the first demonstration, to the best of our knowledge, of nanostructures created by structured light with angular momenta, and it clearly represents a new scientific phenomenon.We have also investigated control of the chirality of formed nanoneedles by changing the sign of the optical vortex helicity. Chiral nanostructures have the potential to form many new material structures [19], including planar chiral metamaterials [20,21] and plasmonic nanostructures [22,23]. They can also be used to selectively identify the chirality of chemical composites in nanoscale imaging systems, such as atomic force and scanning tunnel microscopes [24][25][26][27].However, it is currently unclear whe...

Direct laser printing of chiral plasmonic nanojets by vortex beams

“…Later, similar effects were used to produce chiral structures on the surface polymers [12][13][14] and semiconductors [15,16]. Based on their experiments with ablation of bulk tantalum targets [17], the authors revealed that mass transfer and handedness of the produced surface structures are associated with corresponding phase helicity (or OAM), while the polarization helicity (or SAM) accelerates/decelerates the movement of the molten material.…”

“…Recently, in a number of papers an alternative pioneering approach, employing optical radiation with specially designed intensity-, polarization-or phase states, was proposed for fabrication of chiral structures [9][10][11][12][13][14][15][16][17][18][19]. In particular, using inherent chirality of nanoparticles, synthesis of twisted nanoribbons through self-assembly in water solution under irradiation with continuous-wave circularly polarized laser radiation was demonstrated * alex.iacp.dvo@mail.ru [9].…”

Generation of Coherent Extreme-Ultraviolet Radiation Carrying Orbital Angular Momentum

“…In particular, helically phased light beams or optical vortices with a field dependence of exp (ilφ), where φ is the azimuthal coordinate and l an integer referred to as the topological charge, are currently among intensively studied topics in optics. These light beams, which carry orbital angular momentum (OAM) [17] that can be transferred to atoms, molecules, and nanostructures [18][19][20][21][22][23], have already been utilized at visible and infrared wavelengths in a wide variety of applications, ranging from micromanipulation [24], detection of spinning objects [25], microscopy [26], and optical data transmission [27][28][29]. Perhaps the most promising applications of vortex beams at short wavelengths are in x-ray magnetic circular dichroism, where different OAM states allow the separation of quadrupolar and dipolar transitions [30], photoionization experiments, where the dipolar selection rules are violated giving rise to new phenomena beyond the standard effect [31], and in resonant inelastic x-ray scattering, where vortex-beam-mediated coupling to vibrational degrees of freedom could provide important information on a wide range of molecular materials [32].…”

Generation of intense femtosecond optical vortex pulses with blazed-phase grating in chirped-pulse amplification system of Ti:sapphire laser

“…The twisted wavefront of an OV suggests that it possesses a well-defined orbital angular momentum (OAM), which was verified in 1992 by Allen et al [1]. Since the validation of the OAM in an OV, numerous promising applications [2][3][4][5][6][7] have been reported. Many studies have been carried out on monochromatic OVs, which have been widely used in the optical manipulation of molecules and nanoparticles [8][9][10].…”