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We report on the development of a high-resolution (< 1 GHz at 1.0 THz), broadly-tunable (∼0.5 – 3.0 THz) fiber MOPA-based terahertz spectrometer system. The flexibility and performance of this system will be demonstrated with gaseous (water vapor) and aqueous (water and solvated protein) samples with a view towards selectively and non-destructively probing functionally significant large-scale protein...
We demonstrated a reciprocal planar chiral metamaterials in the THz spectral regime exhibiting asymmetric electromagnetic transmission in opposite propagation directions for circular polarization. We also measured dichroism for counter propagating linear polarized light, which is identical with measured dichroism from its mirror image.
We report optical coherent control of the emission direction of THz radiation by excitation of bulk GaAs with femtosecond laser pulses. Changing the phase of the optical excitation, steering angles of ∼8 degrees are realized. A simple model is introduced to analyze the underlying parameters.
The photoconductive properties of graphene nanoribbons and carbon nanotubes were studied using optical pump-THz probe spectroscopy. A reduction in conductivity of GNRs compared to CNTs was observed.
We measure the duty cycle impact of pulsed signals at 1.5 µm wavelength used for optical THz generation. Our results suggest pulse coding for wireless transmitters can maximize emitted THz power.
A terahertz (THz) wire-grid polarizer is designed and demonstrated using an effective fill-factor (EFF) approach. Full-wave numerical simulations are performed to compare the performance of the EFF device with that of a baseline design wire-grid polarizer at two fill-factors (FF). The simulation results predict that the physical effects seen in the baseline design can be realized in the EFF device...
We combine spectrally and spatially resolved measurements of the ultra-broadband THz-mid-infrared (IR) emission from a two-color-excited gas plasma, which provides a more detailed picture of the emission process and allows one to simulate the predicted spatio-temporal propagation through a subsequent focal region.
A circular dichroism polarimeter (CDP) with an attenuated total reflection element for study of strongly absorbing substances and NovoFEL as a monochromatic source of THz radiation has been developed. Polarimetric characteristics of polysaccharide enantiomers have been studied for the device performance testing.
We demonstrate all-optically induced real-space charge transfer in semiconductors, which reverses its direction upon a change of the temporal order of two excitation fields. Such charge transfer leads to a new type of photocurrent and only appears for certain polarization-shaped optical pulses while it ceases for continuous-wave excitation.
We report on the observation of the giant photocurrent in HgTe/HgCdTe quantum wells (QW) of critical thickness at which a Dirac spectrum emerges1,2. Exciting QW of 6.6 nm width by terahertz (THz) radiation and sweeping the magnetic field we detected a resonant photocurrent. Remarkably, the position of the resonance can be tuned from negative (−0.4 T) to positive (up to 1.2 T) magnetic fields by means...
Terahertz induced Kerr effect in a (100) GaP crystal is reported. The measured dependence of the optical birefringence with respect to the azimuthal orientation of the crystal agrees with theoretical calculations. Additional electro-optic contribution to the detected signal is observed and attributed to crystal abnormity.
We report on the implementation of a continuous-wave terahertz spectrometer into a magneto-cryostat. The integrated setup for THz investigations down to 3 K and in magnetic fields up to 8 T overcomes the drawbacks of windows or additional focusing components and allows for a stable determination of transmittance and phase.
Laser driven terahertz radiation sources have been developed to enable energy modulation of relativistic electron bunches on a sub-picosecond timescale. Photoconductive and nonlinear optical generation schemes capable of providing the required > 1MV cm−1 field strengths, and longitudinal polarisation components, are discussed.
We present the results of theoretical and experimental investigations for different types of chiral and achiral frequency selective polarization converters designed for sub-THz band. The converters are implemented as planar bilayer metastructures and exhibit good performance versus alternative polarization converting devices.
Using optical pump - THz probe spectroscopy we reveal complex ultrafast photoconductivity dynamics in InGaN/GaN quantum wells under dynamical screening conditions, where, at sufficiently high excitation densities, the photo-generated carriers fully screen the initial internal field of 3 MV/cm. The THz photoconductivity spectra contain features of both localized and free charges.
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