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Negative Signal Refraction Has Not Been
Observed in Prism Experiment.
The strongly dispersed, rapidly decaying waves in NIM can tunnel through only finite, optically small NIM devices like those used in the UCSD experiment so far. Such tunnelling is not well represented by geometrical ray optics. A Laplace transform method can be used for the propagation of a finite pulse through a finite aperture. The results are qualitatively similar to those for infinite apertures, showing the large angle (84 degrees) between the output signal and the average phase velocities. The resulting inhomogeneous wave cannot be regarded as a ``negatively refracted beam'' because it disperses rapidly along the direction of supposed propagation. We therefore expect the intensity to decrease with distance, negating the interpretation of the data in in terms of a propagating output beam that was negatively refracted by the NIM prism. We interprete the angular intensity profile observed at the short distance of 15 cm (about 5 wavelengths) as near-field effects. In the NIM media used, the dispersive signal loss is further enhanced by the large impedance mismatch with vacuum and the direct loss due to the imaginary part of np. We also predict larger attenuation for the NIM case as compared to the teflon case. We cannot verify this because the data presented in Fig.3 of UCSD paper are without an absolute scale. |

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