Kotaro Nishimura

Ion Sensitive Transparent-Gate Transistor for Visible Cell Sensing

In this study, we developed an ion-sensitive transparent-gate transistor (IS-TGT) for visible cell sensing. The gate sensing surface of the IS-TGT is transparent in a solution because a transparent amorphous oxide semiconductor composed of amorphous In-Ga-Zn-oxide (a-IGZO) with a thin SiO2 film gate that includes an indium tin oxide (ITO) film as the source and drain electrodes is utilized. The pH response of the IS-TGT was found to be about 56 mV/pH, indicating approximately Nernstian response. Moreover, the potential signals of the IS-TGT for sodium and potassium ions, which are usually included in biological environments, were evaluated. The optical and electrical properties of the IS-TGT enable cell functions to be monitored simultaneously with microscopic observation and electrical measurement. A platform based on the IS-TGT can be used as a simple and cost-effective plate-cell-sensing system based on thin-film fabrication technology in the research field of life science.

Generation of TW-scale mid-IR femtosecond pulses using a dual-chirped optical parametric amplification

By using a dual-chirped optical parametric amplification (DC-OPA) scheme, we demonstrate high-energy infrared (IR) pulses with TW-scale peak power in the wavelength region of 1 ∼ 3.5 μm. In the central wavelengths between 1.2 ∼ 1.8 μm, we obtained over 100 mJ pulse energy. DC-OPA, which is an energy scalable method for an OPA process, can allow us to use a joule-class Ti:sapphire laser system for pumping an OPA. To the best of our knowledge, our DC-OPA laser is the first 100-mJ-class IR source with pulse duration of shorter than 100 fs. Additionally, to show the ability of our DC-OPA laser system, we demonstrate an energy-scaling strategy of high-order harmonic driven by a loosely focused 1.5 μm pulse. Using a 4-cm Ne gas cell with a 3.5-m laser focusing length, soft x-ray harmonics beyond 200 eV are clearly enhanced by a phase-matching effect.