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An optical vortex possesses a ring-shaped spatial profile and orbital angular momentum (OAM) owing to its helical wavefront. This form of structured light has garnered significant attention in recent years, and it has enabled new investigations in fundamental physics and applications. One such exciting application is laser-based material transfer for nano-/micro-fabrication. In this work, we demonstrate the application of a single-pulse optical vortex laser beam for direct printing of ring-shaped structures composed of hexagonal close-packed, mono-/multi-layered nanoparticles which exhibit ‘structural color’. We compare and contrast the interaction of the vortex beam with both dielectric and metallic nanoparticles and offer physical insight into how the OAM of vortex beams interacts with matter. The demonstrated technique holds promise for not only photonic-based nano-/micro-fabrication, but also as a means of sorting particles on the nanoscale, a technology which we term ‘optical vortex nanoparticle sorting’.

We demonstrated ultrafast snapshot imaging with a sub-GHz framerate on the basis of our newly proposed recirculation-filtering method, which enables us to generate a wavelength-division multiplexed pulse train with a time interval in nanosecond regime.

We demonstrate the direct printing of an ultrafine microdot formed of gold nanoparticles by employing optical vortex laser induced forward transfer. Spin and orbital angular momentum induces the close-packing and sintering of gold nanoparticles.

We propose and demonstrate a novel vortex Airy beam which is a superposition of an Airy beam and its laterally sheared beam with a π/2 phase shift. This new-type of vortex Airy beam exhibits stable propagation dynamics, wherein its singular point closely follows its main lobe, unlike conventional vortex Airy beams. Notably, the orbital angular mode purity of this new vortex Airy beam is up to 10% better than that of a conventional vortex Airy beam. We anticipate that this new type of vortex Airy beam, which combines the characteristics of an optical vortex and a diffraction-free Airy beam, will facilitate new directions in applications such as microscopy, material processing and nonlinear optics.

We demonstrate a comprehensive quantitative analysis of vector beam states (VBSs) by using a vector field reconstruction (VFR) technique integrating interferometry and imaging polarimetry, where the analysis is given by a cylindrically polarized Laguerre–Gaussian (LG) mode expansion of VBSs. From test examples of cylindrically polarized LG mode beams, we obtain the complex amplitude distributions of VBSs and perform their quantitative evaluations both in radial and azimuthal directions. The results show that we generated (l, p) = (1, 0) LG radially polarized state with a high purity of 98%. We also argue that the cylindrically polarized LG modal decomposition is meaningful for the detail discussion of experimental results, such as analyses of mode purities and mode contaminations. Thus the VFR technique is significant for analyses of polarization structured beams generated by lasers and converters.

Laguerre–Gaussian (LG) vortex mode generations are demonstrated by employing the optical injection of a higher-order transverse mode into a vertical cavity surface emitting laser. In addition to the coherent LG injection, Hermite–Gaussian (HG) injection also enable LG mode generation, where the chirality is controllable by the HG mode angle of the injection beam. The result can be well understood when we consider the astigmatic Gouy phase shifts within the microcavity. HG induced vortex generation eases the symmetrical requirements of the cavity and thus extends flexibility as regards the design and fabrication of vortex lasers.

Subsequently to the previous generation of ultrashort and ultra-broadband optical-vortex (OV) pulses (pulse energy: several tens of μJ) in few-cycle regime, we performed the generation of axisymmetrically polarized pulses with spatial complex amplitude modulation, which is suitable for a broadband spectrum. The generation system employs the combination of spatial light modulators in the 4- f configuration and a space variant wave plate as a common path interferometer. The spatial light modulators in the 4- f configuration offer the spatial dispersion compensation with respect to wavelength; in addition, the common path interferometer provides the stability to perturbation. We experimentally demonstrated the generation of various axisymmetrically polarized pulses by applying modulations of fundamental and higher-order Laguerre-Gauss modes with high purity. The experimental results show that we are able to generate arbitral axisymmetrically polarized pulses with spatial complex amplitude modulation.

We proposed and constructed a system to realize broadband generation of arbitrary axisymmetrically polarized (AP) pulses with spatial complex amplitude modulation. This system employs the combination of a spatial light modulator in the 4-f configuration (4-f SLM), and a space variant wave plate as a common path interferometer. The 4-f SLM and the common path interferometer offer compensation for spatial dispersion with respect to wavelength and stability to perturbation, respectively. We experimentally demonstrated the various AP pulses generation by applying modulations of fundamental and higher-order Laguerre-Gauss modes, whose radial indices were, respectively, p = 0 and 1, with high purity, which showed that we were able to generate arbitral AP pulses with spatial complex amplitude modulation. This technique is expected to be applied in both classical and quantum communications with higher-order modes.

We discovered that a nanosecond optical vortex pulse can create a chiral cone-shaped monocrystalline silicon (Si) nanostructure (chiral Si nanocone) by transferring its optical angular momentum to a monocrystalline Si substrate. The fabricated Si nanocone, with a length of 4.8 µm and a tip curvature of ∼110 nm, was fully monocrystalline, and it had a spiral structure with an 86 nm line width on a conical surface. Furthermore, its chirality was also determined directly from the handedness of the optical vortex pulse. Such chiral Si nanocones may enable the development of novel silicon photonic devices as well as ultra-highly efficient photovoltaic devices.

The extended Stokes parameters for arbitrary cylindrically polarized beams are newly introduced to evaluate their quality. A set of the parameters, expressing a cylindrically polarized state, permits the definition of the degree of polarization that indicates the purity of the spatial symmetry of polarization of a light beam. In addition, the Pancharatnam–Berry phase related to the cylindrically polarized states is described by the new Stokes parameters.

We present the topological-charge-dispersion reduction scheme in optical vortex generation using axially symmetric half-wave plates (AHPs). The topological-charge dispersion caused by retardation errors of AHPs and other waveplates is decreased by eliminating unwanted circular-polarization components.

International audience; Structured light beams, such as optical vortices, vector beams, and non-diffracting beams, have been recently studied in a variety of fields, such as optical manipulations, optical telecommunications, nonlinear interactions, quantum physics, and 'super resolution' microscopy.. Their unique physical properties, such as annular intensity profile, helical wavefront and orbital angular momentum, give rise to a plethora of new, fundamental light-matter interactions and device applications. Recent progress in nanostructured materials, including metamaterials and metasurfaces, opened new opportunities for structured light generation on the microscale that exceed the capabilities of bulk-optics approaches such as computer generated holography and diffractive optics. Furthermore, structured optical fields may interact with matters on the subwavelength scale to yield new physical effects, such as spin-orbital momentum coupling. This special issue of Optics Express focuses on the state-of-the-art fundamental research and emerging technologies and applications enabled by the interplay of " structured light " and " structured materials " .

We reported on a plasmonic metal Au nano-needle by nanosecond optical vortex pulse illumination. The Au nano-needle with a tip-diameter of

A new method for the ultrafast rotation of ring-shaped optical lattices based on frequency-chirping of optical pulses was demonstrated in THz regime, which is three orders of magnitude faster than those by the conventional methods. Our optical lattice generator with a spatial light modulator is robust thanks to the 4-f configuration and enables us to flexibly control their rotational symmetry. The generated ultrafast-rotating ring-shaped optical lattices with a rotational frequency of 0.59 THz were successfully boosted from 5 μJ up to 125 μJ by using a home-built 4-pass Ti:sapphire amplifier without any limitation by optical damage to the spatial light modulator.

We reported on crystalline silicon structures formed on a silicon (111) substrate through picosecond optical vortex pulse illumination. A crystalline silicon needle with a height of 20 µm was structured through single vortex pulse illumination. Sixteen overlaid vortex pulses shaped the silicon into a crystalline pillar with a height of ~45 µm.

Nonlinear propagation of focused axisymmetrically-polarized ultrashort optical pulses along the optic axis in a uniaxial crystal is investigated experimentally and theoretically. The energy transfer between an azimuthally-polarized pulse and a radially-polarized pulse is observed. To analyze the nonlinear propagation, a general paraxial equation with a third-order nonlinearity for axisymmetrically-polarized pulses in a uniaxial crystal is derived and the extended Stokes parameters (ESPs) based on cylindrical coordinates are newly-introduced. The simulation results by using this equation, providing the calculated ESPs, well explain our experimental observations: 1) the energy transfer is attributed to the four-wave-mixing effect, reflecting the overlapping between the axisymmetrically polarized modes, 2) the variations of the polarization defined from the ESPs are clarified to be affected by the self- and the cross-phase modulations, which make the effective propagation length long or short.

The authors acknowledge support from the Japan Society for the Promotion of Science (JSPS) KAKENHI Grants (JP 16H06507, JP 17K19070, and JP 18H03884). The authors thank the UK Engineering and Physical Sciences Research Council for support through Grant No. EP/P030017/1.

The orbital angular momentum (OAM) resolved spectroscopy is being applied to various research fields associated with optical vortices or Laguerre–Gaussian (LG) beams, in which the key technique is to convert LG beams to a fundamental Gaussian ( HG ≡ HG 00 ) beam. In this work, we propose a method to realize efficient mode conversion by using spiral phase modulations. Numerical simulations and experiments are carried out to compare our proposal with the standard technique using rotational phase modulations. The results reveal that our proposed method improves the uniformity of the conversion efficiency across various OAM, allowing us to obtain precise OAM spectra.

The formation of a monocrystalline silicon needle by picosecond optical vortex pulse illumination was demonstrated for the first time in this study. The dynamics of this silicon needle formation was further revealed by employing an ultrahigh-speed camera. The melted silicon was collected through picosecond pulse deposition to the dark core of the optical vortex, forming the silicon needle on a submicrosecond time scale. The needle was composed of monocrystalline silicon with the same lattice index (100) as that of the silicon substrate and had a height of approximately 14 μm and a thickness of approximately 3 μm. Overlaid vortex pulses allowed the needle to be shaped with a height of approximately 40 μm without any changes to the crystalline properties. Such a monocrystalline silicon needle can be applied to devices in many fields, such as core–shell structures for silicon photonics and photovoltaic devices as well as nano- or microelectromechanical systems.

We derived the Berry connection of vector vortex states (VVSs) from the "true" Hamiltonian obtained through the Maxwell--Schr\"odinger equation for an inhomogeneous anisotropic (IA) medium, and we experimentally demonstrated measurement of the corresponding Pancharatnam--Berry (PB) geometrical phase of VVSs. The PB phase (PBP) of VVSs can be divided into two phases: homogeneous and inhomogeneous PBPs. Homogeneous and inhomogeneous PBPs are related to the conventional PBP and the spatially-dependent geometric phase given by an IA medium such as a polarization converter, respectively. We theoretically detected that inhomogeneous PBP accumulation originates from the gauge dependence of the index of the hybrid-order Poincar\'e sphere, which provides an alternate method for understanding optical spin--orbital angular momentum conversion. The homogeneous PBP, which is explicitly observed for the first time, has implications for quantum state manipulation and information processing.

Laser ablation of Ta plates using nanosecond optical vortex pulses was carried out, for the first time. It was suggested that owing to orbital angular momentum of optical vortex, clearer and smoother processed surfaces were obtained with less ablation threshold fluence, in comparison with the ablation by a nonvortex annular beam modified from a spatially Gaussian beam.

We directly produced for the first time a high-power 1.06 μm vortex mode from a diode-pumped Nd:GdVO4 bounce amplifier. A maximum output of 17.8 W was achieved for a pump power of 55 W. The corresponding optical efficiency from the diode to the output was above 30%.

The coherent dynamics of the exciton center-of-mass motion in bulk GaN are studied using degenerate four-wave-mixing (FWM) spectroscopy with Laguerre-Gaussian (LG) mode pulses. We evaluate the exciton orbital angular momentum (OAM) dynamics from the degree of OAM, which is derived from the distributions of OAM (topological charge) of the FWM signals. When excitons are excited with two single-mode LG pulses, the exciton OAM decay time significantly exceeds the exciton dephasing time, which can be attributed to high uniformity of the exciton dephasing in our bulk sample because the decoherence of the exciton OAM is governed by the angular variation in the exciton dephasing. We also analyze the topological charge $(\ensuremath{\ell})$ dependence of the OAM decay using a multiple-mode LG pump pulse, which allows us to simultaneously observe the dynamics of the exciton OAM for different $\ensuremath{\ell}$ values under the same excitation conditions. The OAM decay times of the $\ensuremath{\ell}=1$ component are usually longer than those of the $\ensuremath{\ell}=0$ component. The $\ensuremath{\ell}\text{-dependent}$ OAM decay is supported by a phenomenological model which takes into account the local nonuniformity of the exciton dephasing.

Cylindrically polarized (CP) modes are laser beam modes which have rotational symmetry of the polarization distribution around the beam axis. Considerable attention has been paid to CP modes for their various applications. In this paper, by using the extended Stokes parameters and the degree of polarization defined for the spatial distribution (DOP-SD), we fully-quantitatively characterize the spectrally-resolved polarization states of arbitrary CP (axisymmetrically polarized and higher-order cylindrically polarized) broadband pulses generated by coherent beam combining. All the generated pulse states were fully-quantitatively analyzed for the first time and proved to have high symmetry (DOP-SD ≳ 0.95) and low spectral dependence of polarization states. Moreover, we show the DOP-SD, which cannot be defined by the conventional higher-order and hybrid Stokes parameters, enables us to make a quantitative evaluation of small degradation of rotational symmetry of polarization distribution. This quantitative characterization with high precision is significant for applications of precise material processing, quantum information processing, magneto-optical storage and nonlinear spectroscopic polarimetry.

This paper introduces our self-recognition type of the computer-controlled spectral phase compensator (SRCSC), which consists of a greatly accurate phase manipulator with a spatial light modulator (SLM), a highly sensitive phase characterizer using a modified spectral phase interferometry for direct electric field reconstruction (M-SPIDER), and a computer for phase analysis and SLM control operating in the immediate feedback (FB) mode. The application of the SRCSC to adaptive compensation of various kinds of complicated spectral phases such as nonlinear chirped pulses with a weak intensity, induced-phase modulated pulses, photonic-crystal-fiber (PCF) output pulses, and nonlinear chirped pulses exceeding a 500-rad phase variation over-one-octave bandwidth demonstrated that the SRCSC is significantly useful for compensation of arbitrary nonlinear chirp and hence enables us to generate quasi-monocycle transform-limited (TL) pulses with a 2.8-fs duration. To the best of our knowledge, this 1.5-cycle pulse is the shortest single pulse with a clean temporal profile in the visible to near-infrared region.

We carried out optical selective excitation of individual self-assembled quantum dots by using phase-modulated pulses. Based on scattered photoluminescence excitation resonances in individual QDs, the excitation pulses modulated in the spectral region allows for addressing individual ground states emission. The photoluminescence spectra including several QDs showed intensity changes according to both the modulation energies and phases. The results also suggested the individual control of selective QDs even in collective excitation.

As a method of analyzing the nonlinear propagation of light, the Sellmeier equation for fused silica with three resonant frequencies is used and a finite-difference time-domain method taking the Raman response into account is proposed. The numerical results are compared with experimental results for optical pulses with a pulse width of 12 fs passing through a fused silica fiber. By this method of analysis, the numerical results are compared with those obtained by the conventional split-step Fourier method and it is found that these results are closer to the experimental results. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(5): 1–10, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10166

Transient transmission changes in the yellow luminescence (YL) band of GaN were investigated using excitation far smaller than the bandgap. At lower excitation power, time-resolved measurements revealed efficient transmission changes due to two-photon absorption (TPA), whose spectrum clearly indicates the contribution of the YL band. Upon increasing the excitation power, the transient signal showed an additional offset signal. The excitation power dependences of the offset suggested a two-step absorption process in conjunction with TPA in the YL band. The excitation energy dependence also supported this conclusion. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ultrabroadband optical pulses generated through self-phase and induced-phase modulation effects and ultrashort optical pulses whose phases were compensated for using a 4f pulse shaper with a spatial phase modulator were generated. Interferometric autocorrelation, frequency-resolved optical gating and spectral phase interferometry for direct electric-field reconstruction (SPIDER) measurements were made to characterize these pulses, and the results were compared. The generation of 5.0 fs (2.4 cycle) or shorter optical pulses was confirmed. For much shorter pulses, below-two-cycle or monocycle optical pulses, single-shot characterization excluding the errors due to the pulse-to-pulse fluctuation is essential. The sensitivity of SPIDER, which is the most advantageous characterization technique apart from its low sensitivity, was improved by a factor of about a hundred (~1 nJ/THz-bandwidth). Instead of a chirped reference pulse split from the pulse to be characterized, a powerful external pulse from a Ti:sapphire laser amplifier as a highly intensive chirped pulse was employed. By use of this modified SPIDER, the characterization of an over-one-octave ultrabroadband optical pulse was performed. This modified-SPIDER method is the most promising for characterization of monocycle optical pulses.

A promising design for achieving the ultimate spatial and temporal resolution is proposed. With modulation of the time delay between two femtosecond laser pulses repeatedly illuminating a scanning tunneling microscope junction, the induced component of the tunneling current is detected as a function of the delay time. With this method, a high signal-to-noise ratio, stable measurement free from fluctuation of laser intensity, and removal of the thermal expansion effect can be achieved. Using the photovoltage effect of GaAs, the high performance of the newly developed system is demonstrated in the femtosecond range.

The dynamics of a phase defect (P-defect) on the Si(100) surface was studied for the first time by scanning tunneling microscopy in pseudo-real time below 10K, using the repeated-line-scan technique in which single line scans are repeated on the same path along a dimer row. In addition to the pair creation and annihilation of the P-defect, the effect of a step on the motion of the P-defect was clearly demonstrated. Since the local barrier height for the migration of the P-defect depends on the local environment such as strain and electronic structure due to the existence of defects or dopants, the obtained results also indicate that analysis of the P-defect is promising for local probing of the Si(100) surface.

A modified-SPIDER (spectral phase interferometry for direct electric-field reconstruction) technique where external powerful optical pulses are employed as a light source of chirped reference pulses for sum-frequency generation is proposed and is demonstrated experimentally. It provides great improvements in sensitivity and signal-to-noise ratio, and will enable a single-shot measurement for a weak pulse, such as 1 nJ/THz-bandwidth. The technique demonstrates high accuracy for determining the delay-time, t, for weak pulse characterization, which greatly affects the group-delay dispersion of the reconstructed spectral phase.

An active chirp compensator consisting of a prism pair and a spatial-phase-modulating pulse shaper enables us to accurately measure the third-order dispersion (TOD) dependence of the interferometric autocorrelation trace while keeping the optimum group-delay dispersion constant. As a result, it is shown that even a small change in TOD (+60 fs3 and -100 fs3) greatly affects the temporal pulse profile in the sub-8-fs region, and 92-fs pulses at a 75-MHz repetition rate from a laser-oscillator glass-fiber system is transform-limitedly compressed to 7.1 fs.

The single orbital angular momentum mode emission from a commercially available broad-area vertical cavity surface emitting laser (VCSEL) is realized with an optical feedback technique using a spatial light modulator, where a computer generated hologram (CGH) is optimized by taking into account the mode properties of the external cavity VCSEL. The flexibility with which the chirality of the orbital angular momentum mode can be selected is also demonstrated simply by changing the chirality of the CGH. The technique is very simple and easily applicable to other VCSELs without processing.