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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 combine sub-cycle, mid-infrared spectroscopy and near-field microscopy to achieve a spatial resolution of 25 nm and a temporal resolution of 50 fs. Using our nano-FTIR technology we can spatially, temporally and spectrally resolve the femtosecond carrier-dynamics in solid state materials like photo excited InAs nanowires.
We explore the nonlinear optical properties of plasmonic semiconductor antennas resonant in the mid infrared. The nanostructures are fabricated on silicon substrates from heavily doped germanium films with a plasma frequency of 30 THz, equivalent to a wavelength of 10 μm. Illumination with ultrashort pulses at 10.8 μm produces coherent emission at 3.6 μm via third-harmonic generation.
We report possible light-induced superconductivity in the organic molecular solid K3C60, a superconductor at equilibrium below Tc=20 K. In our experiment we excited this alkali-doped fulleride with strong femtosecond pulses, tuned to be resonant with local molecular vibrational modes. By means of THz time-domain spectroscopy, we detected the pump-induced changes in the conductivity spectrum as a function...
We report a technique for the single-shot measurement of single-cycle THz radiation without the need for ultrashort laser pulses. The nonlinear mixing between a narrow linewidth laser and a THz pulse encodes the THz temporal profile into the envelope of a new optical pulse. The preservation of temporal and spectral information in this process enables retrieval of the THz pulse from a standard FROG...
Quasi-continuous terahertz laser plasma discharge in inert gases on the Novosibirsk free-electron laser exists in form periodical self-oscillations at sound frequencies caused by plasma screening of its focal area. Full suppression of the self-oscillations has been obtained by a negative optical feedback.
Capturing the microscopic motion of an individual molecule on the femtosecond time scale with atomic spatial resolution has remained a key open challenge of modern nanoscience. Here, we bring the concept of lightwave-driven sub-cycle charge transport, the paradigm underlying high-harmonic generation, to a new arena of atomic spatial resolution. We enter an unprecedented regime of ultrafast lightwave-driven...
In this work we investigate and compare the features of the THz generation process caused by an optical breakdown of air both in a “filament” and “micro-plasma” regimes. We explore efficiency, a spatial and spectral distributions of terahertz radiation in each case.
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...
For frequency calibration of a Terahertz (THz) signal at a distant site we developed a THz frequency reference transfer system using an optical fiber link. Transmission of a 2.8THz frequency reference was demonstrated using 51km optical fiber including a 1km actually-laid fiber link, and used for evaluating a phase-locked THz quantum cascade laser. Depending on the condition of the fiber link, the...
The second-order nonlinear refractive index m (Kerr index) of cyclic olefin copolymer (TOPAS) and cyclic olefin polymers (ZEONEX, ZEONOR) is determined to be approximately 2 × 10−20 m2W−1 for all cases at the wavelength of 800 nm. The obtained values of n2 are subsequently used as input data to pulse propagation simulations based upon the generalized nonlinear Schrödinger equation.
The motion of spin-polarized carriers in the direction perpendicular to an electrical bias constitutes the anomalous velocity. So far, this phenomenon has been studied in time-integrated spin and anomalous Hall effect experiments. Here, we excite GaAs with optical and terahertz radiation to induce the anomalous velocity on an ultrafast time scale. Studying the shape of the terahertz radiation emitted...
We developed a dynamic terahertz time domain spectroscopy technique with single shot measurement of pulsed THz burst, which could be used to probe the irreversible ultrafast processes at multiple time points for dynamic information extraction.
Terahertz wave generation based on optical rectification in GaP waveguide emitters with a femtosecond zeroth-order Bessel beam was reported. The non-diffracting nature of the Bessel beam enabled an enhancement of the THz output power by factors of 3.46 and 3.34 from GaP waveguides of 6 and 10 mm, respectively, compared with a Gaussian beam having the same beam size and pump power as the central spot...
We investigate optical resonant cavities using metallic mirror in order to increase the absorption in low-temperature-grown GaAs (LT-GaAs) based photoconductors operating at telecom wavelength. Two different semi-transparent front mirrors are compared: the first one is a thin gold layer whereas the second one consists of a gold periodic array. We show that the generated photocurrent is 3 times higher...
We proposed a cylindrical lens telescope tilted pulse front pumping scheme for high energy terahertz pulse generation. The optimum pump laser spectral bandwidth and crystal cooling temperature for OR in LN crystal were researched systematically. Excitated by 800-nm laser, more than 0.19 mJ energy and 0.27% efficiency terahertz pulses generation was demonstrated with the optimum bandwidth pumping and...
Whether it is following electron ejection in water, probing hydrogen-bonding network dynamics of water or interactions of water-protein systems, time-resolved ultra-fast techniques in THz range are required. We present here our recent results from optical-pump THz-probe experiments [1], two-dimensional Raman-THz spectroscopy [2] as well as T-jump-THz experiments and discuss these advances also from...
We report on terahertz radiation from topological insulator (TI) Sb2Te3 thin film under ultrafast optical excitation with different helicity. Polarity-reversals of the emitted THz radiation were observed as the helicity of optical pulses reversed. The observed phenomena are coincident with the characteristics of the helicity-dependent photocurrent on TIs. Our work demonstrates the potential applications...
We experimentally and theoretically investigate the Gouy phase shift of the longitudinal terahertz (THz) wave in the entire focal region. By comparing the pulses shape and orientation before and after the focus, we find that the complete Gouy shift for the longitudinal field components is same to that of the transverse field components, with the value of π. The only different between them is their...
We present a simulation-based and experimental study propagating broadband terahertz vortex beams generated by a spiral phase plate. Numerical simulation based on scalar diffraction theory was used to obtain the spatial amplitude and phase distributions of the broadband (0.1 to 2.5 THz) vortex beam at different distances from the spiral phase plate. For experimental studies, THz pulse time-domain...
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