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Scheme (top view) of the grating with curved grooves showing the wave vectors (incoming, grating and SP). (b) Calculated curved shape for five grooves of a grating with , , , and . The dashed line shows the circle tangent in to the first groove.
Sketch of the experimental setup. An incident and then reflected terahertz beams superimposed on an actual photography of the device. The period of the grating is 1.04 mm and its groove depth is .
Upper curve: Spectrum of the grating reflection coefficient. Bottom curve: Spectrum of the SP signal diffracted by the second grating. The inset corresponds to the measured temporal waveform of the SP signal.
Upper curves: Transmitted signal amplitude vs the position of the blade in the beam. Open circles are data recorded with the blade in , while the dashed line is a fit. Full circles and continuous line are related to the blade located in . Bottom curves: Derivatives of the upper fits, which correspond to the transverse shapes of the terahertz beam (continuous line: blade in , dashed line: blade in ).
Transmitted signal amplitude vs the position of the blade at the focus. The full circles are data recorded with the blade in , while the dashed line is a fit. Continuous line is the derivative of the fit, which corresponds to the vertical spatial extension of the SP field in air.
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