Cryogenic Ultrafast Scattering-type Terahertz-probe Optical-pump Microscopy (CUSTOM) capability

The CUSTOM facility uses s-SNOM systems to perform near-field imaging and spectroscopy on nanometre length scales. These systems are not diffraction-limited, enabling us to image materials and characterise their properties on length scales significantly smaller than the wavelength of light. For example, when imaging with THz radiation that can have mm-wavelengths, we can image properties on nanometre length scales!

In an s-SNOM system, a light source is focused on to the apex of a nanoscale tip within an atomic force microscopes (AFMs). As the AFM tip is deeply sub-wavelength, the electric field of the light undergoes strong field confinement at the tip apex. The probing volume is on the same order of the radius of curvature of the tip, significantly below the diffraction limit.  In our systems, the AFM tips are approximately 30nm, so we achieve 30nm spatial resolution! When the light is coupled to the tip,  the near-fields at the apex of the tip interact with the sample, probing its local dielectric function. Information about the sample is then encoded onto the near-field of the source. This near-field can be scattered back into the far-field and detected. By tapping the tip up and down and modulating the measured signal at the tapping frequency, we can directly measure the near-field signal that has interacted with the sample and therefore measure its local properties on these nanometre length scales.

Further details can be found on allthingsterahertz.com 

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