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Surface wave provides unique applications ranging from biological sensing, deep-subwavelength lasing to plasmonic circuits. Seeking new approaches for controlling surface wave is highly desired in future integrated photonic devices. Here, we develop a versatile platform based on metasurfaces for the launch and control of propagating surface wave in the terahertz frequency regime.
Density matrix model is developed for GaN-based two-well THz-QCLs. The optimized GaN/AlGaN two-well THz-QCL structure with a fixed aluminum composition is provided for a desired lasing frequency by calculations of all combinations of four layer thicknesses. The downhill simplex method is introduced when more parameters need to be optimized.
A conventional bull's eye antenna has a great potential to terahertz technologies, while its narrow band nature limits its ability for multi-frequency applications. Here we proposed an split-joint bull's eye (SJBE) structure with optimized aperture, which can achieve multi-frequency transmission and high concentration.
THz microscopic imaging is used to extract the Gouy phase shift of the transverse and longitudinal field components of a tightly focused, radially polarized beam. We demonstrate that the applied THz time domain approach allows to observe directly the evolution of the geometric phase as the wave propagates through the focus. Our method yields a Gouy phase shift of 2π for the transverse component and...
We compare two methods of wavefront analysis of THz pulses associated with a 2D electro-optic imaging system. The first one is the standard Hartmann sensor, and the second one is based on the well-known fact that EO sampling can record the phase variation of the THz electric field.
We demonstrate and compare the use of Mach-Zehnder and the fiber based interferometer schemes in improving the performance of terahertz electric field measurements based on spectral-domain interferometry. The new schemes enable unlimited temporal scanning window without significant loss in the signal-to-noise ratio, thus overcoming a major limitation in conventional spectral-domain interferometry...
Polar oxides are natural candidates for use in tunable mm-wave devices. Using different quasi-optical characterization setups, we present the complex dielectric constant of two ferroelectrics and the electrical tunability of one of them at 90GHz.
Terahertz (THz) streaking at individual sharp metallic tips allows for the control of photoelectron pulses in nanoscale volumes. The time-varying acceleration in the enhanced THz near-field facilitates a reshaping of electron energy spectra, corresponding to a manipulation of the phase space distribution. Here, we discuss our recent experimental and theoretical work on THz near-field streaking, with...
We report on a thickness dependence of the terahertz (THz) bull's eye antenna that uses surface plasmon. For the optimization of the device structure and the strong THz field enhancement, we investigate the thickness dependence of substrate for optimization. We achieved a high THz transmission through a sub-wavelength aperture and observed that the main peak has a weak dependence but the side peaks...
A conventional binary zone plate for terahertz focusing is compared with a proposed new configuration in which two zone plates are stacked, showing an increased focusing efficiency. The field intensity in the focal spot is enhanced by employing a low-loss cyclo-olefin polymer instead of more conventional materials.
We study the nonlinear ultrafast carrier dynamics in highly n-doped In0.53Ga0.47As using terahertz (THz) time-domain spectroscopy (THz-TDS). In addition to the bleaching effect, we further observe significant THz waveform modulations and high frequency generations.
We found the full analytical solution of the semiclassical model, described the stationary profile of the electric field in the miniband semiconductors, subjected to the DC voltage. The analysis of obtained solution shown the three different types of the field distribution, taken place in the semiconductor depending on the emitter current-field characteristics. Among the observed profiles we found...
Multistage depressed collectors can open up new possibilities for enhancement of the overall efficiency of gyrotrons. A new method of spatial separation of electrons in the collector region is based on application of azimuthal magnetic field in combination with axial electric field. In this paper, we describe main features of this method and present a design of the 4-stage depressed collector system...
We demonstrate electron tunneling-induced colossal nonlinear response of vertically oriented angstrom-metallic gaps by irradiation with intense terahertz pulses. We also investigate the sub-picosecond time evolution of the induced tunneling current extracted from the transmission measurement of light passing through the metallic gap. Our technology of angstrom gap lithography enlarges the boundary...
We demonstrate the generation of short terahertz pulses from spectrally broad metal-metal quantum cascade lasers at 77 K via active mode-locking, and show the limiting role of phase-matching between the terahertz pulse and the microwave modulation. Furthermore a new concept of THz pulse dispersion control is proposed to go beyond the limitation of the current modulation scheme.
Electromagnetically induced transmission (EIT) in THz domain is studied in Dolmen structures. The effect of dipole in exciting the otherwise dark quadrupole mode and the interaction of a 2nd dipole in controlling the EIT peak are studied. We show broad EIT peak in Dolmen as well as two EIT peaks and vanishing of EIT peak by varying the position of a 2nd dipole to form a ring like structure.
We present giant spectral broadening by cross phase modulation of a 60 fs nIR pulse in GaP by means of an intense Terahertz transient. The THz field induces up to 500% spectral broadening supporting sub-10 fs nIR pulses.
We measured the transient absorption changes of a near-infrared (NIR) pulse in GaAs quantum well under a multicycle THz wave driving. By changing the delay between the NIR probe and the THz wave, the absorption strength can be modulated on a sub-cycle timescale of THz wave, indicating the formation of THz-induced dressed states of excitons.
We demonstrate that single-cycle intense terahertz (THz) pulses manipulate the motion of electrons in a single tunnel junction. By tuning the carrier-envelope phase of the THz pulses, the direction of the electron tunneling through the junction was coherently controlled either from the nanotip to the sample or vice versa. By analyzing the experimental data based on the Simmons model, we found that...
We present here a novel design for a coupled split ring resonator antenna optimized for time-domain electric field enhancement in the 0.1 to 1 terahertz (THz) range. The antenna is designed to be sensitive to the incident field polarization and seeks to avoid metal damage due to electron bombardment.
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