Mid-infrared (longwave infrared) passive spectroscopic imaging with an uncooled microbolometer array sensor (second report): palm-sized two-dimensional spectroscopic imager with reflective optics for high sensitivity and visibility (Withdrawal Notice)

Abstract

We aim to measure the glucose concentration in the body through passive mid-infrared spectroscopy using a palm-sized imaging two-dimensional Fourier spectrometer. Radiation in the mid-infrared region (at a wavelength of approximately 10 µm) is emitted from the object surface, with the intensity of the radiated light corresponding to the object temperature. Passive spectroscopy acquires component information from the spectral intensity of the radiated light emitted from the object without a light source. Intrinsic vibrations of molecules in the object itself are detected, and the spectral characteristics are thus the emission spectrum of intrinsic vibration peaks. In contrast, conventional active spectroscopy irradiates the measurement target with light and acquires spectral characteristics from the reflected light. Molecular vibrations excited by the light source are measured, and the spectral characteristics are thus absorption spectra of the energy absorbed at the eigenfrequency of the molecule. The wavelengths that are confirmed as absorption wavelengths in active spectroscopy are confirmed as emission wavelengths in passive spectroscopy. Active spectroscopy and passive spectroscopy thus have a negative–positive relationship. The imaging-type two-dimensional Fourier spectrometer (7 to 14 µm) used in past measurement has transmission optics. Using three Ge lenses for the front lens, objective lens, and imaging lens, we constructed reflective optics using reflective mirrors for the objective and imaging lenses. The reflective mirror guarantees flatness and high spectral reflectance over a wide bandwidth (3 to 20 µm), and the measurement bandwidth is thus extended.