講演情報
[15p-S4_201-9]Supercontinuum-based 2-µm FTIR microscopy for spectroscopic analysis of water
〇(D)Senyu Wang1,2, Haruki Matsukura1, Makoto Shoshin1, Kazuki Hashimoto1, Takuro Ideguchi1 (1.IPST, Univ. of Tokyo, 2.UESTC)
キーワード：
Spectroscopy、FTIR、Balanced detection
Infrared spectroscopy in the 2-µm wavelength region visualizes absorption arising from the combination bands of the O–H vibrational modes of water molecules without spectral overlap with vibrational bands of other molecular species. By capturing subtle, localized changes in the water absorption spectrum, variations in solute in solutions can be sensitively detected [1, 2]. For example, changes in the spectrum of bound water inside cells can be exploited to analyze the structural dynamics of macromolecules. Such water microspectroscopy can be performed using a commercially available FTIR [3] microscope equipped with a lamp source. However, the pinhole used to improve spatial coherence of the lamp source for microspectroscopy inevitably reduces optical throughput, which in turn degrades the signal-to-noise ratio and imposes a severe limitation on the achievable measurement speed.In this study, we develop an FTIR microscope employing a 2-μm supercontinuum (SC) laser source combined with a custom-designed extended InGaAs balanced photodetector (Fig. 1(a)), specifically optimized for localized water-spectrum measurements. The enhanced brightness and mode-cleaned beam output of the SC source enable ~6 μm spatial resolution with high power delivery, while the balanced detection scheme mitigates the relative intensity noise of the source, resulting in 4-times better signal-to-noise ratio than the unbalanced case (exceeding 99 for a single-shot spectrum). Our FTIR microscope uses a high-speed voice-coil scanner in the Michelson interferometer, enabling interferogram acquisition at 6 Hz with a spectral resolution of 1 cm-1. Using the developed FTIR microscope, we measured the water absorption spectrum at various water thicknesses (Fig. 1(b)) and quantitatively evaluated the absorbed intensity at the peak absorption wavelength of water at ~1938 nm, as a function of thickness, which exhibits good agreement with the theoretical absorption model. (Fig. 1(c)).