Terahertz pulse propagation in the near field and the far field.

We present a detailed investigation of the propagation properties of beams of ultrashort terahertz (THz) pulses emitted from large-aperture (LA) antennas. The large area of the emitter is demonstrated to have substantial influence on the temporal pulse profile in both the near field and the far field. We perform a numerical analysis based on scalar and vectorial broadband diffraction theory and are able to distinguish between near-field and far-field contributions to the total THz signal. We find that the THz beam from a LA antenna propagates like a Gaussian beam and that the temporal profile of the THz pulse, measured in the near field, contains information about the temporal and spatial field distribution on the emitter surface, which is intrinsically connected to the carrier dynamics of the antenna substrate. As a result of pulse reshaping, focusing of the THz beam leads to a reduced relative pulse momentum, with implications in THz field-ionization experiments.

[1]  P. Bucksbaum,et al.  Propagation of half-cycle far infrared pulses , 1997 .

[2]  Jepsen,et al.  Detection of THz pulses by phase retardation in lithium tantalate. , 1996, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics.

[3]  Jones.  Creating and probing electronic wave packets using half-cycle pulses. , 1996, Physical review letters.

[4]  P. Jepsen,et al.  Radiation patterns from lens-coupled terahertz antennas. , 1995, Optics letters.

[5]  Capasso,et al.  Direct subpicosecond measurement of carrier mobility of photoexcited electrons in gallium arsenide. , 1987, Physical review letters.

[6]  Xiang Zhang,et al.  Saturation properties of large-aperture photoconducting antennas , 1991 .

[7]  C. Winnewisser,et al.  Transmission characteristics of dichroic filters measured by THz time-domain spectroscopy , 1998 .

[8]  Raman,et al.  Ionization of Rydberg wave packets by subpicosecond, half-cycle electromagnetic pulses. , 1996, Physical review letters.

[9]  H. Winful,et al.  Gouy shift and temporal reshaping of focused single-cycle electromagnetic pulses: errata. , 1998, Optics letters.

[10]  C. Winnewisser,et al.  Electro-optic detection of THz radiation in LiTaO3, LiNbO3 and ZnTe , 1997 .

[11]  Morkoç,et al.  Subpicosecond time-resolved Raman spectroscopy of LO phonons in GaAs-AlxGa1-xAs multiple-quantum-well structures. , 1988, Physical review. B, Condensed matter.

[12]  Spatiotemporal shaping of half-cycle terahertz pulses by diffraction through conductive apertures of finite thickness , 1998 .

[13]  M. Brereton.  Classical Electrodynamics (2nd edn) , 1976 .

[14]  J. Goodman.  Introduction to Fourier optics , 1969 .

[15]  X. Zhang,et al.  Free‐space electro‐optic sampling of terahertz beams , 1995 .

[16]  S. Radic,et al.  Spatiotemporal shaping of terahertz pulses. , 1997, Optics letters.

[17]  J. Bokor,et al.  Near-field propagation of terahertz pulses from a large-aperture antenna. , 1998, Optics letters.

[18]  R. Jacobsen,et al.  Generation and detection of terahertz pulses from biased semiconductor antennas , 1996 .