Nonlinear optical infrared microscopy with chemical specificity

We demonstrate a realization of nonlinear optical infrared microscopy that is capable of chemically specific imaging with high spatial resolution. It exploits the nonlinear refraction of the target material that is thermally induced by resonantly absorbed mid-infrared radiation and probed with a short wavelength near-infrared laser beam. The O–H and C–H2 vibrational modes in a water-oil mixture sample are selectively imaged at two different midinfrared wavelengths and the spatial resolution is measured to be 1.1 μm in the condition of numerical aperture 0.5, which is not attainable with conventional infrared microscopes.