Asymmetric phase anomaly of terajet generated from dielectric cube under oblique illumination

The terajet, a jet in the terahertz (THz, 0.1-10 THz) region, has attracted considerable research interest owing to its capability to compress beams to subwavelength hotspots. Here, we report a finding of an abnormal asymmetric Gouy phase anomaly in a terajet generated from a Teflon (n = 1.46) cube illuminated by the TM-mode oblique incidences. This asymmetric Gouy phase anomaly causes an interesting deviation angle between the normal of the phase distribution of the Gouy phase anomaly and the propagation direction of the incident beam at the position where the terajet is generated. This deviation angle exponentially decreases as THz waves propagate over several wavelengths. The output angle of the generated terajet, which is evaluated based on the experimental peak values of the amplitude distribution, shows linearity and is identical to the input angle of the incident beam. The full width at half maximum is also maintained within a wavelength for wide angles (45°) of oblique illuminations.