(a) Transient of a few-cycle terahertz pulse transmitted through the microscope. (b) Normalized near field spectra for different needle surface separations and a reference spectrum of the incident radiation.
Schematic of the near field microscope head (top) and experimental data on the transmitted terahertz signal in dependence on the tip-sample separation (bottom).
(a) Quartz tuning fork, (b) aluminum tuning fork, and (c) block diagram of the control loop. The tuning forks are loaded with tungsten wires having thicknesses of 200 and for the quartz fork and the aluminum fork, respectively.
Frequency dependence of the drive current at the first resonance of a commercial quartz tuning fork. The fork was loaded with a tungsten tip having a diameter of and a length of about .
Normalized amplitude of the piezoelectric current of the aluminum tuning fork in dependence on the tip-surface distance.
Topographic profile of a chromium structure on glass recorded by shear force microscopy. The chromium line has a width of and a nominal height of .
(Color online) Terahertz image of a grating made of cresol resin. The grating lines have a width of and a height of . The integration time per data point was .
Absolute change of the image contrast depending on the thickness of the layer (dots) and least mean squares fit based on Eq. (1) (solid line).
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