Locally resolved infrared spectroscopy

In this paper, we show that spectroscopic studies in the mid-infrared range may be achieved in the near-field regime. First of all, we describe the experimental conditions that must be implemented in order to satisfactorily record the sub-wavelength information with a fiber tip of ≈ 1 μm diameter. Second, we report the first vibrational infrared spectrum which has been acquired in the near-field regime: the characteristic doublet of a photosensitive resin deposited on a Si substrate is clearly observed with a spectral resolution of about 5 cm^-1. Finally, we discuss the possibility of developing an instrument which combines a lateral resolution better than 1 μm with the spectroscopic capability. This should be obtained by making use of a new infrared source which can deliver continuous light with a high intensity per area unit over a wide spectral range.