Ryohei Morita

We examined the state of sodium electrochemically inserted in HC prepared at 700–2000 °C using solid state Na magic angle spinning (MAS) NMR and multiple quantum (MQ) MAS NMR.

Photonic crystal surface-emitting lasers (PCSELs), which use a two-dimensional photonic crystal as the laser cavity, can achieve both high output powers and narrow beam divergence angles owing to single-mode lasing over a large area. High-speed, high-power, direct modulation of PCSELs is expected to realize compact and power-saving optical transmitters without bulky lens systems and fiber amplifiers for free-space optical communications. In this paper, we realize high-speed, high-power, free-spa

Photonic-crystal surface-emitting lasers (PCSELs) are capable of single-mode, high-power lasing over a large resonator area owing to two-dimensional resonance at a singularity point of the photonic band structure. Since the number of photons in the lasing mode in PCSELs are much larger than those in conventional semiconductor lasers, PCSELs are in principle suitable for coherent operation with a narrow spectral linewidth. In this paper, we numerically and experimentally investigate intrinsic spe

Short-pulse high-peak-power lasers are crucial laser sources for various applications such as non-thermal ultrafine material processing and eye-safe high-resolution remote sensing. Realizing such operation in a single semiconductor laser chip without amplifiers or external resonators is expected to contribute to the development of compact, affordable laser sources for such applications. In this paper, we demonstrate short-pulse high-peak-power photonic-crystal surface-emitting lasers based on si

We demonstrate self-pulsation with a pulse width of 100 ps and a beam divergence angle of 0.35° in a photonic-crystal surface-emitting laser by introducing a saturable absorber section and employing a new double-hole photonic crystal.

We propose photonic-crystal surface-emitting lasers based on photon-photon resonance to extend the direct modulation bandwidth. We experimentally demonstrate over 10-GHz direct modulation with over 1-W high output power under continuous-wave operation.

We develop time-dependent three-dimensional coupled-wave theory for photonic-crystal surface-emitting lasers (PCSELs), which enables comprehensive analyses of lasing characteristics of high-power PCSELs under high current injection including relaxation oscillation, spatial hole-burning, and lasing spectra.

Photonic-crystal surface-emitting lasers (PCSELs) are capable of single-mode, high-power lasing over a large resonator area owing to two-dimensional resonance at a singularity point of the photonic band structure. Since the number of photons in the lasing mode in PCSELs are much larger than those in conventional semiconductor lasers, PCSELs are in principle suitable for coherent operation with a narrow spectral linewidth. In this paper, we numerically and experimentally investigate intrinsic spe

We report theoretical and experimental results on intrinsic spectral linewidths of 1-mm-diameter PCSELs under continuous-wave operation, and we demonstrate 1-kHz-class intrinsic spectral linewidths with 5-W-class output power.

環境・エネルギー問題の解決に向け，リチウムイオン電池(LIB)などの蓄電池に注目が集まっている。LIBにはリチウムやコバルトなどの希少な元素が使われているが，今後も電池需要の増加が見込まれるなか，こうした元素を用いない新型蓄電デバイスの実現に向けた研究開発が進められている。リチウムをナトリウムに置き換えたナトリウムイオン電池(NIB)はLIBに匹敵する性能を持つ新規蓄電池の一つとして注目されており，膨大な物質が電極物質として研究されている。なかでも難黒鉛化性炭素（ハードカーボン；HC）はNIBの負極活物質として期待されている。また，リンはほかの材料に比べてとりわけ多くのナトリウムを吸蔵できるためNIB高容量化に寄与する材料として研究が進められている。しかし，HCは非晶質炭素であり，リンも電気化学的にNaを導入した場合非晶質となることが多いため，X線回折(XRD)などの回折法によるナトリウムの吸蔵状態や充放電機構の解明は難しかった。本研究ではHCおよびリンを対象とし，物質の状態によらず測定核種を直接観測できる核磁気共鳴(NMR)や第一原理計算を活用してナトリウム吸蔵状態や充放電機構の解明