Large-aperture Photoconductive Antenna Research Articles

The calculation of terahertz wave power radiated from GaAs photoconductive antenna

Based on the Larmor formula, a mathematic model is established to calculate the power of THz wave radiated form the photoconductive antenna. The power of THz waves radiated by GaAs photoconductive antenna under different experimental conditions was calculated by Monte Carlo simulations. The results show that the power of THz radiation can be improved by increasing the bias electric field or the energy of triggering light pulse, and large-aperture photoconductive antenna can emit THz wave with higher power compared with photoconductive antennas with small apertures because the former can carry more photo-generated carriers.

Theoretical Study of Field Intensity of THz Radiation fromGaAs Large-Aperture Photoconductive Antennas

We simulate the THz radiation's time domain waveforms of both thenear field and the far field of a GaAs large aperture photoconductiveantenna based on the current surge model. Because the micro-kineticfactors, such as transient state changes of current carrier's mobility andlifetime of current carriers, are taken into account in the calculation,we find out the influences of these factors on the THz radiationintensity by changing the above parameters. The results are of guidingsignificance to design of high-power photoconductive THz radiationantenna materials.

Study of the surface and far fields of terahertz radiation generated by large-aperture photoconductive antennas

We have studied analytically the temporal characteristics of terahertz radiation emitted from a biased large-aperture photoconductive antenna triggered by an ultrashort optical pulse. We have included the effects of the finite lifetime and transient mobility dynamics of photogenerated carriers in the analysis. Succinct explicit expressions are obtained for the emitted radiation in the surface field and in the far field. The dependence of the waveforms of the radiated field on the fluence and duration of triggering optical pulse, carrier relaxation time and carrier lifetime are discussed in detail using the obtained expressions.

Phase-sensitive high-speed THz imaging

Phase-sensitive high-speed imaging of terahertz (THz) radiation was achieved by introducing the optical heterodyne detection method to high-speed electro-optic sampling of THz images. Intense THz pulses obtained from a large-aperture photoconductive antenna were used as the source. The electric field distribution on the focal plane of focused half-cycle THz pulses was observed using the apparatus. Annular spatial profiles were observed in the time-dependent images. The frequency-dependent distribution calculated by means of Fourier transformation showed almost diffraction-limited focusing.

Propagation of Focused Terahertz Pulses through Subcentimeter Conductive Apertures

Temporal waveforms of focused terahertz (THz) pulses, generated from a large-aperture photoconductive antenna, which were passed through conductive apertures were studied. The observed terahertz waveforms formed a large negative tail following the main peak, which was dependent on the aperture size. The observed features were reproduced by simulation using an analytic waveguide model which assumes a single cutoff frequency for the conductive aperture. This feature was observed using conductive apertures of subcentimeter (about 1 to 9 mm) diameter and thickness. Distortion of THz waveforms can be caused when using typical optics such as metal crystal holders that are unintentionally put in the path of THz propagation. Approximately half-cycle pulses without tails were generated by carefully avoiding this effect.

Ring formation of focused half-cycle terahertz pulses

Studies using a terahertz (THz) imaging system have shown that focused THz electromagnetic pulses exhibit a ring-like spatial intensity distribution. In the study, almost half-cycle THz pulses were generated from a large-aperture photoconductive antenna and focused by an off-axis parabolic mirror. Time-resolved spatial distribution of the THz electric field on the focal plane was found to form a ring before and after the time region where a single peak is formed around the time origin. On the other hand, with the delay time fixed at the origin, the field distribution was also found to exhibit a ring-like profile at positions away from the focal plane. Existence of relatively low-frequency components in the power spectrum of the THz field gives these observable phenomena. Numerical simulations using diffraction integral calculations reproduced the observed features. A simpler numerical analysis based on the Gaussian beam approximation was shown to yield the observed features and also predicted the dependence on the beam parameters.

Time-Resolved Study of Intense Terahertz Pulses Generated by a Large-Aperture Photoconductive Antenna

Saturation behavior of intense terahertz radiation pulses emitted by a large-aperture photoconductive antenna was studied by observing the waveforms of the generated terahertz pulse using the electrooptic sampling method. A peak terahertz field up to 5.7 kV/cm was observed. By increasing the pump pulse fluence, saturation of the peak terahertz field, shift of the peak appearance time and narrowing of the terahertz pulse were observed. These experimental results were found to be qualitatively consistent with the results of simulation based on the current surge model.

Optically Induced THz Electromagnetic Radiation From Planar Photoconducting Structures

We describe a novel optoelectronic technique to generate and detect THz electromagnetic waves by using large-aperture planar photoconductive antennas and antenna arrays. This approach is an effective method of producing directional and steerable sub-millimeter wave pulses in free space.