Optical sectioning robotic microscopy for everyone: the structured illumination microscope with the OpenFlexure stages.

We report on the 3D-printed structured illumination microscope (SIM) with optical sectioning capability. Optically sectioned images are obtained by projecting a single-spatial-frequency grid pattern onto the specimen and recording three images with the grid pattern at different spatial phases, and then post-processing with simple mathematics. For the precise actuation of the grid for the structured illumination and the positioning of the sample, stages of the open-sourced, 3D-printable OpenFlexure families, which are capable of highly precise positioning control of tens of nanometers based on the flexure mechanism of the flexible plastics, are utilized.

Direct imaging of tunable photonic nanojets from a self-assembled liquid crystal microdroplet.

We report the direct experimental observation of electrically tunable photonic nanojets (PNJs) generated from self-assembled liquid crystal (LC) microdroplets formed by dispersing nematic LCs in polymer matrix. Optical measurements were performed with a home-built laser-scanning confocal microscope system. PNJs with subwavelength beam waists were successfully obtained from LC microdroplets of 5 μm diameter, similar to those from SiO microspheres of the same size.

Electron-beam induced terahertz radiation from graded metallic grating.

We have numerically analyzed, based on a simplified particle-in-cell finite-difference time-domain (PIC-FDTD) method, an electron-beam (e-beam) induced terahertz (THz) radiation from metallic grating structures with graded depths (graded grating). Upon exciting with e-beam, directional THz radiations with wide-band spectrum containing several sharp peaks are obtained only from the one of the edge of the grating, which cannot be expected from the conventional theory of Smith-Purcell radiation. It was clarified that each modes originate from different locations on the graded grating reflecting different dispersion characteristics of spoof surface plasmon polariton (spoof SPP) at each locations, and they can propagate toward only the shallower groove as a surface wave due to the cutoff at each locations, and all of these modes eventually emitted from the one of the edge of the graded grating.

Mechanism of optical terahertz-transmission modulation in an organic/inorganic semiconductor interface and its application to active metamaterials.

Terahertz (THz) transmission modulation through copper phthalocyanine (CuPc)-coated Si under various laser light irradiation conditions was investigated using THz time-domain spectroscopy. The charge carrier transfer from Si to CuPc is crucial for photo-induced metallization, and the thickness of the CuPc layer is a critical parameter for achieving high charge carrier density for metallization. Transmission through a split-ring resonator array metamaterial, fabricated on CuPc-coated Si, can be efficiently modulated by laser light irradiation.

Extraordinary optical transmission through metallic films perforated with aperture arrays having short-range order.

Using terahertz time-domain spectroscopy, we have measured the optical properties of metallic films perforated with arrays of subwavelength apertures that possess short-range order (SRO), but lack long-range orientational order (LRO). We demonstrate that extraordinary transmission enhancement still occurs through the SRO aperture structures, despite the absence of LRO. The dielectric response of these arrays is characterized by a superposition of a broad principal resonance that is due to the random rotations of the building block (BB) units, and discrete resonances arising from well-defined reciprocal vectors in the structure factor that result from a virtual lattice associated with the BB units.

Transmission resonances through aperiodic arrays of subwavelength apertures.

Resonantly enhanced light transmission through periodic subwavelength aperture arrays perforated in metallic films has generated significant interest because of potential applications in near-field microscopy, photolithography, displays, and thermal emission. The enhanced transmission was originally explained by a mechanism where surface plasmon polaritons (collective electronic excitations in the metal surface) mediate light transmission through the grating. In this picture, structural periodicity is perceived to be crucial in forming the transmission resonances.

Tunable photonic defect modes in a cholesteric liquid crystal induced by optical deformation of helix.

We have demonstrated, based on numerical analyses, that the introduction and tuning of photonic defect modes in a cholesteric liquid crystal (CLC) can be realized by the local deformation of its one-dimensional periodic helical structure. The defect modes appear in transmission spectra only when incident circularly polarized light has the same handedness as CLC's. The tuning of defect modes position can be performed upon both local elongation and shortening of the helix; however, the direction of the shift of the defect mode wavelength is opposite.