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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 propose a novel reference-acquisition method that provides precise phase alignment for terahertz imaging. The method significantly improves the accuracy of the extracted sample optical properties and greatly improves the experimental efficiency compared to traditional reference methods.
We demonstrated the gapless THz comb by combination of dual THz comb spectroscopy and spectrally interleaving technique. This method enhanced the spectral resolution to the comb-mode linewidth rather than its interval.
We have experimentally realized a broadband THz modulator in a total internal reflection geometry using SiO2/Si gated monolayer graphene. The modulation depth in our device is up to 83% over the range of 0.2–0.6 THz, and can be further improved by extending the size of our modulator and using multiple reflections.
A model is constructed for extrinsic photoconductivity in GaAs heavily doped with Er and driven around 1550 nm. The model is based on internal photoionization of ErAs nanoparticles in the diameter range 2.0 to 2.5 nm, which occurs via a resonant, bound-to-continuum electron transition between the Γ-point in the atomic-like ErAs and the Γ-valley in the GaAs. The model is consistent with all experimental...
The electro-optic sampling system (EOS) at Beijing Institute of Radio Metrology and Measurement (BIRMM) in China is introduced in this paper. Traceable measurement of ultrafast electrical pulse waveforms can be offered by BIRMM based on the EOS that can be used to establish a traceable chain between ultrafast electrical pulse waveforms and the SI.
We present a current study of mid-IR isolator using nonreciprocal (NR) magnetoplasmonic InSb mirror. The reflectivity of n-type InSb surface was calculated using Rigorous Coupled Wave Algorithm (RCWA) method. We report magnetooptical (MO) effect for low external magnetic field (B=0.1T), which can be enhanced by a plasmonic grating.
A combination of circular polarizer and polarization rotator at 170 GHz were designed and constructed by General Atomics (GA) and tested at MIT for Electron Cyclotron Heating in ITER. Cold test measurements were performed using a Vector Network Analyzer to determine the relative amplitudes and phase shifts between two orthogonal components of the reflected field. Measured polarization parameters,...
By controlling the polarization of two-color 10-fs pulses, we enhanced the intensity of ultrabroadband coherent infrared pulses from two-color excited air plasma and achieved the time domain measurements in a spectral range up to 200 THz. This result without a time plate for two-color pulses implies the contribution of negative group velocity dispersion in plasma.
We report on the enhancement of the terahertz magnetic near-field which is realized by a tapered waveguide. A Tb3Ga5O12 crystal coupled with a double split-ring resonator was pumped by this tightly confined terahertz field, and the magnetic near-field was measured via the magneto-optic sampling. With the use of the tapered waveguide, the amplitude of the magnetic near-field is enhanced by about 2...
In this paper, a novel and small sub-terahertz (THz) sheet beam extended interaction klystron (EIK) has been designed. With the help of a three-dimensional(3D) particle-in-cell(PIC) simulation, design and optimizing geometry of THz sheet beam EIK is performed. The interaction system consists of two dumbbell five-gap cavities, one is used for input cavity, the other is output cavity. The operating...
Enhanced terahertz-to-infrared(THz-to-IR)emission from gas-surrounded nanostructured metal films as a result of femtosecond laser irradiation is systematically investigated using selected gases. The dependencies of the THz-to-IR power on the gas species, gas pressure, and pump optical power are studied for Ar, N2, Ne, and He. The experimental results reveal that the power of the THz-to-IR emission...
A carrier-envelope phase (CEP) shifter for broadband terahertz (THz) pulses was demonstrated. The CEP, the phase of the carrier frequency with respect to the peak of the THz pulses, is a key element in light-matter interactions in high fields, especially when few-cycle pulses are used. The CEP shifter was constructed by suitably arranging several prism wave plates. By rotating the wave plates, we...
Over the past decades, advances in ultrafast technologies led to the generation of intense ultrashort THz to optical pulses with single-cycle pulse duration. Using such ultrashort pulses for electron acceleration offers advantages in terms of higher thresholds for material breakdown which opens up a promising path towards increased acceleration gradients. In this contribution, we present the first...
Collector of worked-out electron beam and RF cavity resonator are the most-heat-stressed units of 1MW CW gyrotron. To withstand near 1MW power of a worked-out electron beam it is swept along the collector surface exposing it to cycling loading. In the cavity, at over 40 kW dissipated power cycling loading appears only when a modulation of output power is used. Cycling aggravates work of heat-stressed...
The conductivity of graphene and its change induced by electromagnetic waves is crucial for many applications. Here we show that both the photoconductivity and high-field conductivity of highly doped graphene can be described by a simple thermodynamic balance maintained within the free carrier population of graphene.
In this paper, we have demonstrated a viable microstrip array patch antenna technology for the first time on GaN-on-low resistivity silicon (LR-Si) substrates (ρ < 40 Ω.cm) at H-band frequencies (220–325 GHz). The developed technology is compatible with standard MMIC technology with no requirement for high temperature processes. To mitigate the losses presented by the substrate and to enhance the...
A circularly polarized horn antenna was calibrated by the generalized three-antenna method in the frequency range from 220 to 330 GHz. We show the validity of the calibration method by experimentally determining the actual gain, the polarization, and the axial ratio of the circularly polarized horn antenna.
Antenna calibration requires the exact knowledge of the phase center position. In addition, the accuracy of calibration is often affected by multi-path propagation. We present an approach to reliably estimate the phase center position and to correct for multi-path propagation effects and demonstrate the performance of this approach with horn antennas in the W-band between 75 GHz and 110 GHz.
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