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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.
We demonstrate cascaded optical parametric amplification (COPA) as a promising pathway for efficient generation of THz-waves beyond the Manley-Rowe limit. The spectro-temporal characterization of this novel regime of parametric amplification is reported.
A family of approaches employing sequences of optical pump pulses, yielding energy conversion efficiencies in the 5–10% range, is introduced. A method to generate these sequences by cascaded optical parametric amplification of narrowband pulses is discussed.
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...
A new approach for precise complex optical parameter of highly absorptive liquid is proposed for transmission THz time-domain spectroscopy. Due to the nature of liquid, indirect measurement of sample thickness increases inaccuracy in optical parameter. Here, we reduced uncertainty in optical parameter through an algorithm optimizing sample thickness by Kramers-Kronig relations. Less than 2% error...
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...
For the first time, we demonstrate heterodyne EO sampling of terahertz pulses in a DAST crystal. Compared with lithium niobate, which was used in our previous heterodyne EO sampling studies, organic DAST crystal has a 1.5 times larger EO coefficient. Our experimental results demonstrate that DAST is a very promising material for highly sensitive terahertz EO sampling.
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.
This paper presents a novel scheme for generation of high power short THz pulses using optical rectification. The procedure consists of two main steps. In the first step, generation of a chirped broadband THz pulse is proposed using a chirped aperiodically poled lithium niobate (APLN) crystal. In order to design a crystal with optimum generation efficiency, we take advantage of binary optimization...
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.
We measure THz-induced change in refractive index of ∼5×10−3 in high resistivity silicon at 800 nm which indicates generation of high density of free carriers. The change in refractive index increases by more than 30 times with high initial carrier density set by optical excitation compared to optically unexcited sample showing strong dependence of carrier generation on initial carrier density. The...
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.
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 demonstrate the generation of single-cycle 0.1-THz radiation in a lithium niobate crystal using optical rectification and obtain THz output energy of 65 μJ with 31.6 MV/m peak field. This amounts to an optical-to-THz energy conversion efficiency of 0.3% at 85 K, which is in agreement with theory.
We investigate the THz-field induced orientation of molecules in the liquid state by means of the Kerr effect. In contrast to an optical or near-infrared excitation, THz photons have frequencies below the intramolecular vibrations and therefore leave the internal structure of the molecule mostly unaffected. We find experimental evidence for a THz-induced optical birefringence, which provides evidence...
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 present a novel large-area photoconductive terahertz emitter based on a 2D plasmonic nano-antenna array and compatible with telecommunication optical wavelengths. We experimentally demonstrate a record-high terahertz radiation power level of 300μW over 0.1–5 THz frequency range.
We report a significant signal enhancement on the periphery of the probe optical beam in the “heterodyne EO sampling” of pulsed terahertz radiation. Our experimental results coincide with the theoretical prediction. By using this enhancement effect, it is possible to increase the heterodyne EO sampling signal ΔI/I by several folds with optimized detection optics.
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