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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.
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.
Here the cyclotron electron beam (CEB) excitation of surface plasmon polaritons (SPPs) on the circular cylindrical structures is used to replace the linearly moving electron beam excitations. We have found that this change leads to essential consequence in physics for that there is natural periodicity of 2π in both circular cylindrical structure and CEB, and the combination of this dual natural periodicity...
Graphene's plasmons are extremely confined, with velocities as low as c/200, yet with long lifetimes exceeding 200 fs at room temperature. I will discuss recent experimental results in graphene plasmons in the frequency range 2–50 THz: how to engineer and understand their spatiotemporal dispersion, how to improve the lifetimes, and how plasmons may be optoelectronically detected using the graphene...
We report ultra-broadband, easily tuned, and highly efficient metamaterial terahertz wave retarders that are able to convert linear polarization into circular and elliptical polarization states. The broadband nature arises from the combination of the plasmonic effect and the property of polarization conversion. The dielectric response of the metamaterial microstructure and the angular phase dispersion...
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...
Terahertz grapheme surface plasmon polaritons (GSPPs) radiation source excited by electron beam has been presented. Here we show the theoretical analysis and initial experimental results on this kind of terahertz source. The theoretical calculations of greatly enhancement due to GSPPs and wide tunability indicate that this mechanism has huge potential. THz TDS is utilized to obtain conductance of...
Pumping a quadratic nonlinear crystal in the mid-IR we observe octave-spanning mid-IR supercontinua. A self-acting cascaded process leads to the formation of a self-defocusing nonlinearity, allowing formation of filament-free octave-spanning supercontinua in the 2.0–7.0 μm range with 10s of μJ pulse energies, much higher than filament-based techniques. This allows to use the supercontinuum as ultra-broadband...
We demonstrate and validate Geometric Algebra (GA) based terahertz (THz) signal classification of various powders in tablet form of various thicknesses, and compare the results with a conventional Support Vector Machine (SVM) approach. By using geometric algebra we can perform classification independently of dispersion and hence independently of the transmission path length through the sample. In...
In this work, we present on-wafer near-field scanning of a CMOS nonlinear transmission line with external electrooptic sampling. From Fourier transformation of the scanned voltage on the line, transmission line parameters such as dispersion and varactor capacitance as a function of frequency in the mm-wave range are characterized.
A novel physical mechanism is reported which can generate coherent and tunable terahertz (THz) radiation. Due to the natural periodicity of 2π of circular cylindrical graphene structure, the surface plasmon polaritions (SPPs), excited by a cyclotron electron beam (CEB), can be transformed into radiation. The radiation density is strongly enhanced over two orders, up to 105 W/cm2. The radiation frequency...
By introducing side-absorbers to metal-metal waveguides of broadband terahertz quantum cascade lasers, we are able to control and completely suppress higher-order lateral waveguide modes. This change leads to an octave spanning laser spectrum with a 600 GHz wide flat top. In addition, the absence of higher order lateral modes has a strong effect on the pulse generation of injection seeded QCLs. We...
We have proposed a novel design for a contact grating setup with an incorporated Fabry-Perot resonator for intense terahertz (THz) light generation. This setup is scalable and extremely compact as compared with the conventional LiNbO3 prism setup. We evaluated the THz generation process in the device by experimental and calculated studies, and optimized the device to obtain maximum THz output.
A system where a graphene sheet is placed above a topologically insulating material is investigated when hopping is allowed between the two surfaces. The optical conductivity of such a system presents interesting features that do not occur in the two constituent surfaces separately.
We report on the implementation of a metal ridge spoof plasmon waveguide of micro pillars in a hexagonal lattice for guidance of Terahertz (THz) radiation. Finite-difference time-domain (FDTD) simulations demonstrate broadband, low-loss and low dispersion guidance between 0.30 THz to 0.65 THz. A very high 2D coupling efficiency can be achieved with a common linearly polarized Gaussian beam source...
We couple magneto-plasmons ultra-strongly to subwavelength split-ring resonator cavities, probed with THz time domain spectroscopy (TDS). In contrast to cyclotron-polaritons, the ultrastrong coupling regime is reached already at zero magnetic field. Further, the plasmon frequency ωρ is widely tunable using a gate and by changing the sample geometry. This thus allows to observe the transition from...
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