Raman effect occurs when a sample is illuminated by a laser, which tells us what kinds of chemical bonds exist, and how they vibrate in the sample. In addition, by scanning the laser, we can visualize its spatial distribution through Raman microscopic imaging. I observe and analyze various samples through Raman microscopy to reveal their novel characteristics. Furthermore, I have been developing my own unique Raman techniques such as low-frequency Raman spectroscopy to analyze weak van deer Waals forces between molecules, not covalent bonds between atoms, cryo-Raman spectroscopy by building a lab-made cryo-chamber, and so on. Recently, I also work on infrared absorption spectroscopy. 

T. Umakoshi*, et al., J. Phys. Chem. A, 127, 1849−1856 (2023).

T. Moriyama, T. Umakoshi*, et al., ACS Omega, 6, 9520-9527 (2021).

T. Sugiyama, T. Umakoshi, et al., Analyst, 146, 1268 (2021).

R. T. Sam, T. Umakoshi, et a., Sci. Rep., 10, 21227 (2020).

T. Umakoshi, et al., J. Phys. Chem. C, 124(12), 6922-6928 (2020).

B. S. Bhardwaj, T. Umakoshi, et al., Sci. Rep., 9, 15149 (2019).

The spatial resolution of optical microscopy is limited to half of the optical wavelength (~500 nm) due to the diffraction limit. By coupling light with plasmons, a quantum of free electron groups in metals, light can be localized at nanoscale (near-field light). "Near-field scanning optical microscopy" enables high-resolution optical imaging over the diffraction limit by creating the near-field light at a metallic tip apex. It even enables super-resolution Raman imaging with a typical spatial resolution of ~10 nm. I am developing near-field optical microscopy to further improve detection sensitivity, measurement reproducibility, and imaging speed to bring it up to the next level.

T. Umakoshi* et al., Sci. Rep., 12, 12776 (2022).

R. Kato, T. Umakoshi*, et al., Sci. Adv., 8, eabo4021 (2022).

R. Kato, T. Umakoshi*, et al., Nanotechnology, 31, 335207 (2020).

R. Kato, T. Umakoshi*, et al., Appl. Phys. Lett., 114, 073105 (2019).

T. Umakoshi, et al., Appl. Phys. Express, 5, 052001 (2012).

"Plasmon nanofocusing" is one of the useful ways to create near-field light, where plasmons propagate on a tapered metallic structure and eventually create near-field light at its apex with compressing their energy. A unique and powerful characteristic of plasmon nanofocusing is that it is  extremely broadband. As it works at an arbitrary wavelength, we can create white near-field light over a wide frequency range, or we can make various wavelengths of light coexist at the nanoscale. Focusing on this feature, I have been developing novel optical technologies such as super-resolution imaging techniques, optical sensors, and so on.

T. Umakoshi*, et al., arXiv, 2207.12839.

K. Taguchi, T. Umakoshi*, et al., J. Phys. Chem. C, 125, 6378-6386 (2021).

T. Umakoshi*, et al., Sci. Adv., 6(23), eaba4179 (2020).

T. Umakoshi, et al., Nanoscale, 8, 5634-5640, (2016).

By scanning a tip over the samples in two dimensions, the shape of the samples can be observed as an image with nanoscale spatial resolution. This technique is known as atomic force microscopy (AFM), which is the basis for near-field scanning optical microscopy. Scanning the tip to capture one image typically takes several minutes; however, "high-speed AFM" has recently been developed by significantly increasing the scanning speed, which now allows the real-time observation of moving biomolecules. By combining high-speed AFM with optical techniques, it is possible to film the nanoscale world in real time with high-speed AFM, while investigating the details with optical techniques, realizing unique and powerful measurements. I have been developing various integrated techniques of high-speed AFM and optical technologies, including high-speed scanning near-field optical microscopy and high-speed AFM combined with an optical illumination system.

K. Yang, T. Umakoshi*, et al., Nano Lett., 24, 2805-2811 (2024).

T. Umakoshi, et al., BBA Gen. Sub., 1864, 129325 (2020).

T. Umakoshi et al., Colloids Surf. B, 167, 267-274 (2018).