Scanning near-field infrared microscope with a free electron laser illumination source

We have developed a Scanning Near-held Infrared Microscope (SNIM) that utilizes the Stanford Picosecond Free Electron Laser as its illumination source. Infrared spectroscopy is a sensitive technique for characterizing materials. However, the spatial resolution of conventional infrared microscopy is limited to a few micrometers due to diffraction. The SNIM overcomes this limitation by using infrared near-field optics to obtain sub-wavelength resolution. The system is built around a Near-field Scanning Optical Microscope (NSOM) head, in which a tapered infrared transmitting fiber is mounted as the scanning probe. The Stanford Picosecond Free Electron Laser, which provides high power infrared radiation with a wavelength that is continuously tunable from 3 to 15 micrometers, is then coupled to the fiber. In combination with the FEL, the SNIM can obtain infrared spectra of localized regions smaller than one micrometer and acquire images at a chosen wavelength with sub-micrometer resolution. The most promising aspect of SNIM is in the development of 'vibrational nanospectroscopy'. Images have been obtained of biological tissue such as kidney sections using the intrinsic amide absorption in the tissue proteins to provide contrast, instead of relying on an externally introduced stain or marker. Images of lithographically patterned semiconductor samples have also been obtained, revealing subsurface features in gallium arsenide.