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Opt Express. 2011 Jan 17;19(2):1378-84. doi: 10.1364/OE.19.001378.

High resolution cellular imaging with nonlinear optical infrared microscopy.

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Division of Convergence Technology, Korea Research Institute of Standards and Science, Yuseong-Gu, Daejeon, South Korea.


We developed a nonlinear optical infrared microscope exploiting a thermally induced refractive index change in the mid-infrared regime and imaged a single biological cell with high spatial resolution that was not possible in conventional infrared microscopes. A refractive index change of a sample induced by infrared (~3.5 μm) absorption was probed by a visible (633 nm) laser beam. Thus the chemical specificity stems from the spectral absorbance of specimen and the spatial resolution from the short wavelength visible radiation. A reflecting objective (NA0.5) was used to focus the infrared and visible beams on the sample plane, and the sample was raster-scanned for 2-D imaging. The high resolution beyond the infrared diffraction limit was demonstrated by imaging fine grating lines made up of epoxy grooves (830 lines/mm). The probe wavelength dependence of the spatial resolution was investigated by imaging polystyrene beads. We found that the resolution was as small as 0.7 μm with 633 nm probe wavelength.

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