Abstract-Characteristics of the partially reflected terahertz wave: truncated beam propagation

J. W. Han, Y. G. Choi, and J. S. Lee

https://www.osapublishing.org/josab/abstract.cfm?uri=josab-36-6-1551

We investigate a free-space propagation of a truncated terahertz beam created as a result of a partial reflection from a small-sized metallic reflector. By using terahertz time-domain spectroscopy, we obtain both magnitude and phase spectra of a clipped terahertz beam after its propagation by about 15 cm. Compared to a fully reflected terahertz beam, the partially reflected beam exhibits large variations in both magnitude and phase spectra in the entire spectral range investigated, i.e., from 0.2 to 1.3 terahertz. To model the free-space propagation of the truncated Gaussian beam, we decompose it using a super-Gaussian beam and several other Gaussian beams with phase factors separately assigned to each component. From this, we could successfully reproduce the experimental results, i.e., the modulations observed in both magnitude and phase spectra.

© 2019 Optical Society of America

Abstract-Radiating pattern of surge-current-induced THz light in near-field and far-field zone

J. W. Han, Y. G. Choi ,  J. S. Lee

https://www.nature.com/articles/s41598-018-24673-9

We generate the THz wave on the surface of an unbiased GaAs crystal by illuminating femtosecond laser pulses with a 45° incidence angle, and investigate its propagation properties comprehensively both in a near-field and in a far-field zone by performing a knife-edge scan measurement. In the near-field zone, i.e. 540 μm away from the generation point, we found that the beam simply takes a Gaussian shape of which width follows well a behavior predicted by a paraxial wave equation. In the far-field zone, on the other hand, it takes a highly anisotropic shape; whereas the beam profile maintains a Gaussian shape along the normal to the plane of incidence, it takes satellite peak structures along the direction in parallel to the plane of incidence. From the comparison with simulation results obtained by using a dipole radiation model, we demonstrated that this irregular beam pattern is attributed to the combined effect of the position-dependent phase retardation of the THz waves and the diffraction-limited size of the initial beam which lead to the interference of the waves in the far-field zone. Also, we found that this consideration accounting for a crossover of THz beam profile to the anisotropic non-Gaussian beam in the far-field zone can be applied for a comprehensive understanding of several other THz beam profiles obtained previously in different configurations