Keisaku Yamane

Electric field applications and surface boundary conditions play important roles in controlling the molecular orientation of nematic liquid crystals. Spatially periodic director modulation in a microscopic area is useful for optical applications, such as polarization conversion. In this study, we demonstrate an efficient method to control the pattern formation of a nematic liquid crystal by varying the thickness of the electrode using a pulsed laser. Laser-processed spots preferentially induce defects owing to nanoscale topographical effects. This approach can be used not only to expand uniform patterns but also to stabilize various structures that are useful for optical studies.

We demonstrate high-definition, direct-printing of micron-scale metallic dots, comprised of close-packed gold nanoparticles, by utilizing the optical vortex laser-induced forward transfer technique. We observe that the spin angular momentum of the optical vortex, associated with circular polarization, assists in the close-packing of the gold nanoparticles within the printed dots. The printed dots exhibit excellent electrical conductivity without any additional sintering processes. This technique of applying optical vortex laser-induced forward transfer to metallic dots is an innovative approach to metal printing, which does not require additional sintering. It also serves to highlight new insights into light–matter interactions.

We report an experimental approach to produce spatially localized photoinduced superconducting (SC) state in a cuprate superconductor using optical vortices (OVs) with ultrafast pulses. The measurements were carried out using coaxially aligned three-pulse time-resolved spectroscopy, in which an intense OV pulse was used for coherent quenching of SC and the resulting spatially modulated metastable states were analyzed by the pump-probe spectroscopy. The transient response after quenching by the OV pulse shows a spatially localized SC that remains unquenched at the dark core of the OV for a few picoseconds. Because the SC quenching is instantaneously driven by photoexcited quasiparticles, the OV beam profile can be transferred directly to the electron system. By using the OV-induced SC, we demonstrate spatially resolved imaging of the SC response and show that the spatial resolution can be improved using the same principle as that of super-resolution microscopy for fluorescent molecules. The demonstration of spatially controlled photoinduced SC is significant for establishing a new method for exploring novel photoinduced phenomena and applications in ultrafast optical devices.

Wavefront shaping of structured light beams is attracting considerable attention in optics and related technologies. Due to the potential benefits, it is crucial to develop versatile methods for controlling the wavefront in a compact space with the capacity for high‐throughput parallel processing. Herein, a unique concept is introduced for converting the wavefront of multiple structured light beams, which are periodically packed in a microscopic area. An experimental demonstration is provided by using transmissive planar optical elements consisting of a microarray of geometric phase based on nematic liquid crystals. The periodic microstructure is fabricated by the directed self‐organization of topological defects present in a nanoscale relief obtained by area‐selective surface modification. The conversion of multiple wavefronts is realized by using the Talbot self‐imaging effect of the microarray. The integrated geometric phase microarray has potential applications in vortex beam emitters to harness structured light, such as for optical manipulation and lithography.

We successfully demonstrated ultrafast snapshot imaging based on time-to-frequency mapping method with four frames and ~ 5.5 ns time interval (i.e. sub-GHz framerate) by using our newly-developed recirculation system without ultrafast image sensor.

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 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.

Spectroscopic polarization measurement and control using channeled spectrum has several unique features and is useful for various spectroscopic instruments. It utilizes the strong dispersion characteristics in polarization retardation of high-order retarders so that the polarization modulation can be made without using mechanical or active elements for polarization modulation. In this presentation, we describe its principle, basic features, and several applications including a spectroscopic ellipsometer and ultrafast rotations of beam profile and polarization.