Scanning nearfield optical microscopes (SNOM)

In scanning near-field optical microscopy (SNOM), the excitation laser light is focused through an aperture with a diameter smaller than the excitation wavelength, resulting in an evanescent field (or near-field) on the far side of the aperture.

When the sample is scanned at a small distance below the aperture the optical resolution of transmitted or fluorescent light is limited only by the diameter of the aperture. The surface of the sample is scanned under the aperture and the transmitted or reflected light is detected point by point and line by line in order to generate an optical image. The aperture itself is located at the apex of a hollow pyramid on the micro-fabricated WITec SNOM cantilever. The optical resolution attainable is in the range of 50 – 100 nm.

The scanning near-field optical microscope (SNOM)

Resolution in classical optical microscopy is limited by diffraction due to the wave nature of light. Therefore a resolution below approx. ?/2 is usually not possible. SNOM can easily overcome this diffraction limit and generate images with an optical resolution of typically between 60 and 100 nm. In addition, the technique requires only minimal sample preparation if any. With the featured WITec SNOM objective and the WITec cantilever SNOM sensors, imaging beyond the diffraction limit is accomplished quickly and effortlessly.

Typical applications are found in nanotechnology research and in particular the highly relevant fields of nano-photonics and nano-optics. In life science and materials research, SNOM allows the optical detection of the most miniscule surface structures of transparent as well as opaque samples. Using fluorescence techniques, even single-molecule detection can be easily achieved.

The alpha300 S is a user-friendly scanning nearfield optical microscope (SNOM) that combines the advantages of SNOM, confocal microscopy and atomic force microscopy (AFM) in a single instrument. Switching between the different modes can be easily done by rotating the objective turret. The alpha300 S uses unique micro-fabricated SNOM cantilever sensors for optical microscopy with spatial resolution beyond the diffraction limit.

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For the user with challenging experimental requirements, the alpha300 RS facilitates confocal Raman imaging in combination with scanning near-field optical microscopy (SNOM) for optical imaging with resolution beyond the diffraction limit. It combines all the features of the alpha300 S and alpha300 R and many AFM operation modes. Furthermore the combined Raman-SNOM microscope is ideally suited for combined high-resolution Raman imaging techniques such as nearfield-Raman imaging.

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