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 have discovered that a novel chiral structured surface relief (termed 'conch'-shaped surface relief) with a height of over 1 mm can be formed in an azo-polymer film merely by employing circularly polarized optical vortex irradiation with a total angular momentum of j 5 62. The temporal evolution of the conch-shaped surface relief in the azo-polymer film was also observed. The results provide physical insight into how the angular momentum of light is transferred to a material through mass transport by cis-trans photo-isomerization. Such conch-shaped surface reliefs with chirality, in which functional chemical composites can be doped, enable new applications, such as planar chiral metamaterials, plasmonic holograms, and identification of chiral chemical composites.S urface relief holograms 1-3 on azo-polymer films have been widely investigated through mass transport owing to a driving force based on an optical gradient force, anisotropic photo-fluidity, and cis-trans photoisomerization 4-6 . They allow for unique optical devices, such as active waveguides 7 and photonic circuits, by the doping of functional chemical composites, such as laser dyes and metal (or semiconductor, magnetic) nanoparticles into the films.In general, the mass transport driving force acts to direct the azo-polymer from a bright fringe toward a dark fringe along the polarization direction of the light. Thus, a spiral surface relief formation in the azo-polymer film is mostly inhibited by the irradiation of linearly polarized light.An optical vortex, i.e. light with a helical wavefront due to an azimuthal phase singularity, exp(imw) (where m is an integer known as the topological charge), has been widely studied in a variety of fields, such as optical trapping and guiding [8][9][10] , optical telecommunications 11 , and a super resolution microscope 12,13 , because of its unique characteristics, such as its annular intensity profile and orbital angular momentum, mh 14-17 .Recently, Ambrosio et.al. demonstrated spiral surface relief (termed ''spiral relief'' in their work) formation produced through linearly polarized higher-order optical vortex irradiation 18 . Tightly focused higher-order optical vortices can create a spiral surface relief with a shallow depth (10 , 20 nm) through slight mass-transport along an azimuthal direction owing to interference between longitudinal and transverse optical fields. However, there are still no reports on a single-arm chiral surface relief with depth and height on the micro-scale formed in azo polymer films, so far.Circularly polarized light with a helical electric field exhibits spin angular momentum, sh. Thus, the circularly polarized optical vortex has a total angular momentum (the sum vector of the orbital and spin angular momenta), jh, associated with its helicities of both the wavefront and the polarization [19][20][21] . These angular momenta of light are evidenced by the orbital and spinning motions of trapped particles in optical tweezers.Recently, together with another co-worker, we first dem...

The unique properties of optical vortex beams, in particular their spiral wavefront, have resulted in the emergence of a wide range of unique applications for this type of laser output. These applications include optical tweezing, free space optical communications, microfabrication, environmental optics, and astrophysics. However, much like the laser in its infancy, the adaptation of this type of laser output requires a diversity of wavelengths. We report on recent progress on development of optical vortex laser sources and in particular, focus on their wavelength extension, where nonlinear optical processes have been used to generate vortex laser beams with wavelengths which span the ultraviolet to infrared. We show that nonlinear optical conversion can be used to not only diversify the output wavelength of these sources, but can be used to uniquely engineer the wavefront and spatial properties of the laser output.

A terahertz (THz) spiral phase plate with high transmission (>90% after Fresnel correction) and low dispersion has been developed based on the Tsurupica olefin polymer. Direct observations of the topological charge (both magnitude and sign) of a THz vortex beam are performed by using a THz camera with tilted lens focusing and radial defect introduction. The vortex outputs with a topological charge of ±1 (or ±2) are obtained at a frequency of 2 (or 4) THz.