Characterization of apparent superluminal effects in terahertz Bessel beams

Summary form only given. We describe the apparent superluminal behavior of the interference pattern in front of an axicon lens using terahertz spectroscopy. The ability to coherently detect the electric field permits a more complete characterization of this Bessel beam than has been previously reported. We report direct observations of superluminal phase and group velocities, both of which are only weak functions of frequency. As a result, it is possible to discount pulse reshaping effects in the consideration of experiments of this type. We also expect that the extended Rayleigh range of these Bessel beams should be useful for enhanced depth-of-field terahertz imaging.