Toshiki Yamada

Following the achievement of inertial confinement fusion (ICF) ignition at the U.S. National Ignition Facility (NIF), the next grand challenge is the control of fusion burn, which requires diagnostic techniques with picosecond time resolution. Since the full width at half maximum (FWHM) of the typical ignition plasma has been estimated to be ~ 40 ps, diagnostics with sub-10-ps resolution are essential. In this study, we demonstrate an ultra–high-speed diagnostic for fusion reaction measurements using the Stark effect of an electro-optic (EO) polymer sensor with a chirped-pulse probe laser system at the GEKKO XII and LFEX facilities. The system response was characterized by using short-pulse electrons generated by the LFEX laser, resulting in a temporal resolution of 2 ± 0.5 ps. Using deuterium–deuterium (DD) fusion implosions driven by GEKKO XII, we have successfully measured a fusion burn duration of 16 ~ 20 ps. The detector sensitivity, evaluated theoretically and confirmed experimentally, shows good consistency, and is amply sufficient for applications to fusion burn history measurements at NIF-scale plasmas. These results establish the Stark-effect-based chirped-pulse probe as a next-generation diagnostic tool for various ultrafast phenomena in high-energy-density and fusion sciences.

High-speed active metasurfaces enable spatiotemporal light control within an ultrathin device layer, offering previously unexplored possibilities for optical communication, sensing, and computing. However, a trade-off between electrical conductivity and optical loss has hindered the realization of a high-speed, low-loss device. Here, we experimentally demonstrate an active metasurface operating at 1.5-μm wavelength range that achieves a record-high 17.5-GHz modulation bandwidth while maintaining a high quality ( Q ) factor of 102 and an ultralow optical loss of 0.56 dB. This is enabled by the indium phosphide (InP) membrane platform, where n-InP offers high electron mobility and low free-carrier absorption simultaneously. A high- Q Friedrich-Wintgen quasi-bound-state-in-the-continuum mode within the InP-membrane high-contrast grating (InP HCG) traps light in the organic electro-optic material for efficient modulation. The InP HCG also functions as an ultralow-resistance interdigitated electrode, enabling 50-fold faster modulation than silicon-based counterparts. Our work paves the way toward active metasurfaces for high-speed spatiotemporal light control beyond the GHz regime.

We present a new Mach-Zehnder (MZ) type ferroelectric-organic hybrid modulator (FOH) based on lead lanthanum zirconate titanate (PLZT) slot waveguides that are incorporating electro-optic (EO) polymers to enhance the EO performance of the PLZT modulator. The waveguide provides more efficient optical modulation; as a result, the half-wave voltage-length product (VπL) of the modulator is reduced to 0.52 Vcm.

A simple and reliable transmission measurement technique without an aperture was utilized to evaluate both the electro-optic (EO) effect and the Stark effect of EO polymers. For some EO polymers, both the EO effect and the Stark effect were evaluated using laser light sources with various wavelengths of 1550 nm, 1308 nm, 980 nm, and 640 nm and the analysis method was also described. We showed that both the magnitude and the phase of the modulated light signal in lock-in detection at both the π/2 and 3π/2 points are very important for appropriate analysis.

Free-space electro-optic (EO) modulators operating at gigahertz and beyond are attractive for a wide range of emerging applications, including high-speed imaging, free-space optical communication, microwave photonics, and diffractive computing. Here, we experimentally demonstrate a high-speed plasmonic metasurface EO modulator operating in a near-infrared wavelength range with a gigahertz modulation bandwidth. To achieve efficient intensity modulation of reflected light from an ultrathin metasurface layer, we utilize the bimodal plasmonic resonance inside a subwavelength metal–insulator–metal grating, which is precisely tuned to satisfy the critical coupling condition. As a result, perfect absorption of −27 dB (99.8%) and a high quality (Q) factor of 113 are obtained at a resonant wavelength of 1650 nm. By incorporating an EO polymer inside the grating, we achieve a modulation depth of up to 9.5 dB under an applied voltage of ±30 V. The 3-dB modulation bandwidth is confirmed to be 1.25 GHz, which is primarily limited by the undesired contact resistance and the output impedance of the driver. Owing to the high electrical conductivity of metallic gratings and a compact device structure with a minimal parasitic capacitance, the demonstrated device can potentially operate at several tens of gigahertz, which opens up exciting opportunities for ultrahigh-speed active metasurface devices in various applications.

Herein, lots of electro‐optic (EO) chromophores designed for applications at O‐band are synthesized, and the first hyperpolarizability β of EO chromophores is evaluated by the hyper‐Rayleigh scattering (HRS) technique. EO chromophores are constituted of various tricyanofuran (TCF) derivatives as the electron acceptor unit, thienyl‐di‐vinylene or thienyl‐di‐vinylene with ethylenedioxy as the π‐conjugation unit, and aminobenzene with a benzyloxy group as the donor unit. Halogen phenyl group or trifluoromethyl‐phenyl group in TCF acceptor unit leads to a relatively large improvement in β values. Furthermore, EO polymers with some promising EO chromophores that are suitable for the applications at O‐band (1260–1360 nm) are synthesized, and EO coefficient r₃₃ (or n³r₃₃) and absorption loss α are evaluated. Considering the trade‐off relationship between r₃₃ (or n³r₃₃) and α, EO polymers with excellent EO chromophores in the C‐band (1530–1565 nm) are not necessarily suitable EO polymers in the O‐band (1260–1360 nm). EO polymers with the O‐band chromophores have small α and moderate r₃₃ (or n³r₃₃) at the O‐band, while EO polymers with the C‐band chromophores have large α and slightly modified r₃₃ (or n³r₃₃) at the O‐band. The development of suitable EO chromophores and polymers for O‐band and C‐band respectively is very important.

D-band (110–170 GHz) antenna-coupled optical modulators with electro-optic (EO) polymer waveguides and non-coplanar patch antennas were fabricated using a poled EO polymer film transfer method. A carrier-to-sideband ratio (CSR) of 42.3 dB corresponding to an optical phase shift of 15.3 mrad was obtained by irradiating 150 GHz electromagnetic waves with an irradiation power density of 34.3 W/m². Our devices and fabrication method have great potential for achieving highly efficient wireless-to-optical signal conversion in radio-over-fiber (RoF) systems.

We performed terahertz time-domain spectroscopy and infrared spectroscopy of imidazolium-based, pyridinium-based, and tetraalkylammonium-based tetrafluoroborate ionic liquids to study their characteristic intermolecular and intramolecular vibrational modes to clarify interactions between various cations and the tetrafluoroborate anion. It was found that the central frequency of the intermolecular vibrational band for these ionic liquids has a relatively high frequency, ranging from 90 to 100 cm^-1. In the 900-1150 cm^-1 range, the intramolecular vibrational absorption band of the 3-fold degenerate mode of tetrafluoroborate anions in the ionic liquids was observed. Although the tetrafluoroborate anion is attributable to one of the weakly coordinated anions, the spectroscopic splitting behavior of the 3-fold degenerate mode differs depending on the cation species. It was revealed that the degenerate mode is very sensitive to local interactions between the tetrafluoroborate anion and each cation.