Search

Laser patterning of thin films of materials is widely used for the fabrication of one-, two- and three-dimensional functional nanomaterials. Using structured laser beams with a complex structure of amplitude, phase, and polarization distributions allows one to significantly simplify and speed up the procedure of manufacturing nano- and microstructures with a complex shape, such as a spiral structure. Here, we demonstrate the use of vortex laser beams with a helical wavefront for the realization of spiral mass transfer in azopolymer films. The polarization sensitivity of this material allows us to demonstrate the formation of different three-dimensional structures in the case of linearly or circularly polarized vortex beams of different orders. The presented theoretical analysis shows that the profile of the fabricated structures is defined by the structure of the longitudinal component of the incident radiation, and thus can be easily controlled with the polarization state of the radiation without the need to change the amplitude-phase structure of the beam.

The spin Hall effect of light is a manifestation of angular momentum conservation in the process of spin-orbit interaction of light. This optical Hall effect is exhibited in tight focusing of a circularly polarized asymmetric input beam as a shift of the center of gravity of the focal spot in the transverse plane, perpendicular to the direction/axis of symmetry breaking. It is commonly established that the direction of this shift depends on the sign of the spin. Here we show, for the first time, to the best of our knowledge, both analytically and by numerical simulation, that different Cartesian components of an asymmetric circularly polarized focused beam shift in opposite directions by different amounts. Moreover, these shifts depend on the type and degree of the asymmetry and thus can be tuned/controlled. We show how these field components' shifts are related to spin and orbital angular momentum shifts. These findings shed new light on the spin optical Hall effect, facilitate new/simpler ways to measure it, and may broaden the gamut of its applications in manipulation and trapping of particles by light and precision metrology.

We show that by breaking the symmetry of a beam subjected to tight focusing, namely by obscuring half of it or, equivalently, shifting the beam away from the lens axis, it is possible to obtain novel light properties in the focal spot which, to the best of our knowledge, have not been observed before. For example, a linearly polarized beam half-obstructed or shifted from the axis generates longitudinal and transverse electrical field components, both of which peak on-axis. The ratio of the intensities of these two components can be tuned by changing the shift distance, the size, and the azimuthal location of the displaced incoming beam. Moreover, such symmetry breaking of a linearly polarized beam acts as a catalyst for producing distributions of circular polarization/longitudinal spin angular momentum, as well as orbital angular momentum, in the focal plane. The simple method for generating co-incident longitudinal and transverse components with a controllable ratio may find applications in laser machining, particle manipulation, etc.

We consider a new type of vector beam, the vector Lissajous beams (VLB), which is of double order ( p , q ) and a generalization of cylindrical vector beams characterized by single-order p . The transverse components of VLBs have an angular relationship corresponding to Lissajous curves. A theoretical and numerical analysis of VLBs was performed, showing that the ratio and parity of orders ( p , q ) affect the properties of different components of the electromagnetic field (EF) (whether they be real, imaginary, or complex). In addition, this allows one to engineer the imaginary part of the longitudinal component of the electromagnetic field and control the local spin angular momentum density, which is useful for optical tweezers and future spintronics applications.

Complex-shaped light fields with specially designed intensity, phase, and polarization distributions are highly demanded for various applications including optical tweezers, laser material processing, and lithography. Here, we propose a novel (to the best of our knowledge) optical element formed by the twisting of a conic surface, a twisted microaxicon, allowing us to controllably generate high-quality spiral-shaped intensity patterns. Performance of the proposed element was analyzed both analytically and numerically using ray approximation and the rigorous finite difference time domain (FDTD) solution of Maxwell's equation. The main geometric parameters, an apex cone angle and a degree of twisting, were considered to control and optimize the generated spiral-shaped intensity patterns. The three-dimensional structure of such a microaxicon cannot be described by an unambiguous height function; therefore, it has no diffraction analogue in the form of a thin optical element. Such an element can be produced via direct laser ablation of transparent targets with structured laser beams or direct laser writing via two-photon photopolymerization and can be used in various micro- and nano-optical applications.

We suggest an annular field with linear polarization and a binary sectored phase for the formation of the inverse energy flux with an increased area of action. The possibility of the formation of a reverse energy flux over large areas in the focal domain at tight focusing of a linearly polarized field with the binary phase is shown theoretically and numerically. Moreover, the area increases with the number m. The proposed approach is simple, because linearly polarized radiation is the most common among laser sources and does not require additional devices for polarization transformations. The binary phase also provides ease of manufacture of phase plates with a high diffraction efficiency and high damage threshold. The results will be useful in optical manipulations and processing.

Low- and ultralow-energy tightly focused 200 fs, 515 nm donut-shaped laser pulses at 0.25 and 0.65 NA focusing were used for single-shot ablative pulse-energy scalable nanopatterning of 50 nm thick gold film and the following plasmonic excitation of dye monolayer photoluminescence (PL) in the fabricated nanostructures, respectively. The same pulses at much lower, non-ablative nanojoule energies, and the same focusing and linear, azimuthal, or radial polarizations provided efficient spectrally and symmetry-matched excitation of both localized and delocalized surface electromagnetic modes in the separate, ring-like through holes and their arrays in the film envisioned by our modeling, thus resulting in a polarization-sensitive yield of rhodamine 6G dye PL. The demonstrated consistency between the symmetries of the donut-shaped low-energy photo-exciting laser beam, its polarization state, and the donut-shaped gold nanostructures, produced by the same beam at high, ablative pulse energies, paves the way to smart, self-consistent nanofabrication and plasmonic sensing, when the structured light interacts with the consistently structured matter.

We report on high-quality infrared (IR)-resonant plasmonic nanoantenna arrays fabricated on a thin gold film by tightly focused femtosecond (fs) laser pulses coming at submegahertz repetition rates at a printing rate of 10 million elements per second. To achieve this, the laser pulses were spatially multiplexed by fused silica diffractive optical elements into 51 identical submicrometer-sized laser spots arranged into a linear array at periodicity down to 1 μm. The demonstrated high-throughput nanopatterning modality indicates fs laser maskless microablation as an emerging robust, flexible, and competitive lithographic tool for advanced fabrication of IR-range plasmonic sensors for environmental sensing, chemosensing, and biosensing.

Multi-sector broadband diffractive optical elements (DOEs) were designed and fabricated from fused silica for high-efficiency multiplexing of femtosecond and nanosecond Gaussian laser beams into multiple (up to one 100) optically tunable microbeams with increased high-numerical aperture (NA) focal depths. Various DOE-related issues, such as high-NA laser focusing, laser pulsewidth, and DOE symmetry-dependent heat conduction effects, as well as the corresponding spatial resolution, were discussed in the context of high-throughput laser patterning. The increased focal depths provided by such DOEs, their high multiplexing efficiency and damage threshold, as well as easy-to-implement optical shaping of output microbeams provide advanced opportunities for direct, mask-free, and vacuum-free high-throughput subtractive (ablative) and displacive pulsed-laser patterning of various nanoplasmonic films for surface-enhanced spectroscopy, sensing, and light control.

We report on a remarkable property of azimuthally (radially) polarized light beams containing a vortex or an orbital angular momentum: upon tight focusing of a first-order vortex beam, the subwavelength spot has a shape of an electric (magnetic) dipole rotating at an optical frequency. For beams with a vortex of order m, the generated pattern is propeller-shaped and rotates at a 1/m fraction of the optical frequency. The applications include petahertz control of electrical or optical conductance between two electrodes or waveguides of two-terminal junctions.

We show that it is possible to generate transversely random, diffraction-free/longitudinally invariant vector optical fields. The randomness in transverse polarization distribution complements a previously studied one in intensity of scalar Bessel-type beams, adding another degree of freedom to control these beams. Moreover, we show that the relative transversely random phase distribution is also conserved along the optical axis. Thus, intensity, phase, and polarization of Bessel-type beams can be transversely random/arbitrary while invariant upon propagation. Such fields may find applications in encryption/secure communications, optical trapping, etc.

We study the sharp focusing of differently polarized low-order and high-order beams, including Bessel and Laguerre-Gaussian (LG) modes, to compare them using several criteria: the size of a light spot, the intensity ratio of the central peak and sidelobes, and the intensity of the longitudinal electric field component. The experiments performed using the near-field microscopy techniques are in general agreement with the results of the numerical simulation. We have validated the growth of the longitudinal component in the focus for high-order modes at moderate NA=0.6-0.8, and essential lower sidelobes of Bessel modes, in comparison with LG modes.

We show that general-form optical cavities are able to perform the temporal differentiation of optical signals. Analytical relationships to account for the scattering losses for such a cavity's characteristics are deduced on the basis of temporal coupled-mode theory. A compact nanocavity-aided differentiator based on a ridge photonic crystal waveguide is designed.

We propose a new approach to generating a pair of initial beams for a polarization converter that operates by summing up two opposite-sign circularly polarized beams. The conjugated pairs of vortex beams matched with laser modes are generated using binary diffractive optical elements (DOEs). The same binary element simultaneously serves two functions: a beam shaper and a beam splitter. Two proposed optical arrangements are compared in terms of alignment complexity and energy efficiency. The DOEs in question have been designed and fabricated. Natural experiments that demonstrate the generation of vector higher-order cylindrical beams have been conducted.

We show that, by adding a π-phase shift to one-half of a linearly polarized beam, the roles of the transversal and longitudinal field components of the focused beam are interchanged, resulting in better focusing of the longitudinal component in the direction perpendicular to the phase jump line. For this component the scheme produces a spot with FWHM >15% smaller than a spot generated with either linearly or radially polarized light for any NA. The scheme has a similar advantage when applied to circularly polarized light, and it holds for both a plane wave and a realistic case of a Gaussian incident beam. This technique may find applications when using recording media responsive to the longitudinal field only, particularly in read/write for optical storage where the resolution in one transverse dimension is most important.

A new family of paraxial laser beams that form an orthogonal basis is discussed. When propagated in uniform space, these beams preserve their structure to scale. The intensity distribution profile for such beams is similar to that for the Bessel modes, representing a set of alternating bright and dark concentric rings. The complex amplitude of these beams is proportional to the degenerate (confluent) hypergeometric function, and therefore we term such beams hypergeometric (HyG) modes. The HyG modes are generated with a liquid-crystal microdisplay.

We derive analytical expressions containing a hypergeometric function to describe the Fresnel and Fraunhofer diffraction of a plane wave of circular and ringlike cross section by a spiral phase plate (SPP) of an arbitrary integer order. Experimental diffraction patterns generated by an SPP fabricated in resist through direct e-beam writing are in good agreement with the theoretical intensity distribution.