(a) Schematic of experimental arrangement for testing spatial resolution. PD denotes quadrant photodiode. (b) Detail of test sample and tip of probe (Si substrate shown transparent) showing coordinate system referred to in the text.
(a) Pulse width at output of 1.5 m length of HCPF measured by interferometric autocorrelation and assuming a sech 2 envelope. The zero dispersion wavelength is 765 nm and the input pulse bandwidth is 10 nm. (b) Typical throughput of a 1.2 m long fibre. The inset shows an electron micrograph of a cleaved fibre end.
(a) Examples of measured signals for the same source and geometry but different aperture sizes. The inset shows the case with no aperture on an extended time scale. (b) Measured (squares) variation of peak to peak signal amplitude with aperture size. The solid curves show the calculated variation for the antenna placed s = 2 μm (as in experiment) and, for comparison, s = 100 μm behind the aperture. The dashed line shows the expected trend in the far field. The horizontal bar shows the signal amplitude with no aperture.
(a) Examples of experimental spectra for the same source and geometry but different aperture sizes, using a common amplitude scale. (b) Calculated frequency dependence of aperture transmission relative to the response with no aperture for aperture sizes shown. The vertical arrows indicate the cut of frequencies for infinitely long square waveguides with the same lateral dimensions as the apertures.
Measured (points) and calculated (solid curve) peak electric field amplitude at a fixed delay corresponding to the peak THz signal at large negative x for incident THz polarisation (a) parallel and (b) perpendicular to test metal edge over which a 10 μm probe with 20 μm aperture is scanned at a constant gap of 20 μm or 50 μm. (c), (d) Evenly spaced, constant Fourier amplitude contours obtained from signal spectra at a gap of 20 μm. Parts (a) and (b) reprinted with permission from Appl. Phys. Lett. 100, 191109 (2012). Copyright 2012 American Institute of Physics.
Time average Ex (a) and Ez (b) field maps near the probe aperture and test metal edge for incident polarisation parallel to x and a 20 μm sample-probe separation.
(a) Measured (points) and calculated (solid curve) peak to peak amplitude of the receiver current for THz polarisation parallel (E//y) and perpendicular (E//x) to test metal edge over which a 10 μm probe with 20 μm aperture is scanned at a constant height of 20 μm. (b) Calculated fields 10 μm in front of the sample with (solid curves) and without (dashed curves) the probe which is treated as a uniform metal sheet. Reprinted with permission from Appl. Phys. Lett. 100, 191109 (2012). Copyright 2012 American Institute of Physics.
(a) and (b) show peak to peak signals versus probe position for a 10 μm apertureless probe and 20 μm probe-sample separation. In (a), experimental (points) and calculated (curves) signal amplitudes are shown for polarisations perpendicular (E//x) and parallel (E//y) to metal test edge. In (b), the calculated variation of fields in the middle of the gap is shown. (c) Measured peak signal amplitude at fixed delay for THz polarisation parallel to metal edge (E//y) at a probe-sample separation of 20 μm for the apertureless probe (points) and the probe with 20 μm aperture (dashed curve). The solid curve shows results for the 20 μm probe at a larger probe-sample separation of 50 μm.
(a) Electron micrograph of top surface of the metamaterial waveguide. (b) Cross section of the guide showing vertical side walls. (c) Schematic of end-fire coupling and near field probing arrangement and coordinate system
(a) Map showing out of plane electric field versus delay at different z positions above the metamaterial surface plane and x = 40 μm beyond the end of the guide. Red represents positive amplitude, blue negative and white zero. (b) Spectra versus z position. Blue is minimum and red is maximum amplitude. The plane of the sample surface is shown by the dashed lines.
(a) Comparison of calculated (solid curve) and measured (points) near field spectra for the metamaterial waveguide at a point z = 100 μm above the surface and x = 40 μm beyond the output end. (b) Measured and calculated peak to peak amplitude versus height above the surface at x = 40 μm.
(a) Spatial map at y = 0, showing time dependence of amplitudes versus probe position at the output end of the PPWG. The dashed lines show the limits of the waveguide air gap. Red colour indicates the positive field, blue negative and white zero. The two dashed lines indicate the air gap. (b) Sections through (a) at delays of 3.3 ps (blue curve) and 11.5 ps (red curve).
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