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Emission of terahertz radiation is observed when semi-continuous ultrathin gold films near the percolation threshold are excited with femtosecond near-infrared laser pulses. Our experimental results suggest that the emission is through a percolation-enhanced second-order nonlinear optical rectification process.
Large area microbolometer detectors are very attractive for applications where high sensitivity is required. This is particularly important for long wavelength spectroscopy in the far-infrared and sub-millimeter region. This paper presents current progress in the development of large area uncooled microbolometer FPAs at INO.
We report on the room-temperature electrical rectification at 1.5 THz with novel non-linear asymmetric nanochannels. The planar layout facilitates the integration of microfabricated THz antennas without introducing parasitic elements, and enables ultra-high operation frequencies. This is the highest speed reported for nanorectifiers to date.
Fundamental and higher-order cooperative luminescence emitted from Yb-doped optical fiber (YDF) are observed. Each luminescence is well related to different transition between sublevels of YDF located in the infrared region. Detailed transition properties of YDF are discussed.
The measurement of complex dielectric permittivity of thin films are very difficult at millimeter and THz frequencies because the phase shift is not large enough to determine the real part of dielectric permittivity. To overcome this difficulty, dispersive Fourier transform spectroscopy is improved for the first time to have the mirror movement of 0.5 micrometer step size to characterize the permittivity...
Transmittance, Refractive Index, Absorption coefficient, Real and Imaginary part of complex dielectric permittivity data for several Silicon, Silicon Carbide, Gallium Arsenide, Cadmium Telluride and Copper Indium Selenide specimens were measured using Dispersive Fourier Transform Spectroscopy and Free Space Quasi-optical Spectrometer powered by several Backward Wave Oscillators for the characterization...
We present a new Terahertz imaging scheme based on total internal reflection that allows the study of aqueous samples while improving the longitudinal resolution. We were able to image a frog neuron using the spectral phase of the THz pulses using this technique.
A dual-band polarization-independent fishnet metamaterial for THz frequencies is proposed and investigated. Dual-band modes have two resonances in which the first one is fixed as a left-handed mode and the second one can be arranged as a left-handed or single-negative mode. We select the character of the second resonance by the choice of substrate properties.
GeTe is a conducting ferroelectric with a very simple crystal lattice. Since decades, its phase transition was deemed displacive; recent evidence suggested an order-disorder type. High-temperature THz spectra of thin films reveal a new sub-THz excitation but no critical phonon softening is observed.
We have measured the evolution of the THz spectrum of polymeric iron(II) spin crossover compounds within the Low-Spin/High-Spin thermal hysteresis loop in the ∼0.6–6 THz frequency range. This study enabled to evidence the large variations of both the refractive optical index and the absorption that occur during the spin state phase transition.
We report the complex refractive index, conductivity, and dielectric constants of GaN thin film in the terahertz frequency as a function of temperature using terahertz time-domain spectroscopy. Temperature dependent carrier dynamics and optical properties are observed in the frequency range from 0.3 to 2.0 THz. Temperature dependent complex conductivity is fitted by a Drude model to find changes in...
We measured gas content in smoke simultaneously with a continuous-wave sub-terahertz (THz) spectrometer and Fourier transform infrared spectrometer. The consistency of both measurements shows the validity of the THz spectroscopy for the analysis of gaseous substances in smoke.
Degeneration of the lasing mode in a Terahertz Quantum Cascade Laser due to interaction with parasitic ghost modes is demonstrated here through rigorous numerical analysis. We show that such interactions can adversely affect the performance of a QCL by causing abrupt rises in lasing threshold. We also show that such affects can be avoided by altering the width of the metal cladding layer.
Silicon nanofabrication technologies provide precise dimensional control and batch processing capability. These features have been exploited to enable novel active and passive components in the submillimeter-wave region. We report on silicon micromachined methodologies that will enable large format submillimeter-wave heterodyne arrays and 3-D integration of the whole receiver front-end.
Based on the Fabary-Parot cavity and subwavelength holes array, a 3-mirror quasi-optical cavity is presented and explored. The electron beam-wave interaction in this cavity is proposed and the results show that this interaction can reach an attractive value with reasonable current density of electron beam at THz regime.
The generation of a wide-range THz wave from a photoconductive antenna excited by a multimode semiconductor chaotic laser with an optical delayed feedback using an external mirror is investigated. The properties of the generated THz wave are compared with those of generated THz wave by using a CW steady state laser.
Designers are developing high power gyrotrons for the next generation of electron cyclotron heating systems. Testing of both the gyrotrons and the systems require loads to dissipate the RF power produced or transmitted. Designers are developing 2 MW gyrotrons for long pulse or CW operation. This presentation describes development of RF loads capable of safely dissipating 2 MW of RF power continuously.
Megawatt power level gyrotrons operate in high order cavity modes that face severe mode competition. During the voltage rise and start-up of the gyrotron, modes are excited in a sequence that determines the final operating state. We have completed a wide-ranging study of the modes excited during the start-up of a 1.5 MW, 110 GHz pulsed gyrotron operating at 96 kV and 42 A. We found that at the operating...
THz-Quantum Cascade Lasers (THz-QCLs) are expected as light sources for high-speed communication because their potential of high-speed modulation is predicted by theory. We have built THz-QCLs light-current characteristics measurement system, in which optical and current pulses were synchronized. And the reduction of output from THz-QCLs was observed with external optical pulse injection.
We demonstrate the operation of broadband heterogeneous terahertz quantum cascade lasers by carefully designing sub-stacks to align at the same field. Time domain spectroscopy measurements confirm that a flat gain spectrum is present and when incorporated into metal-metal waveguides we find broadband operation over 380 GHz when metal-metal ridges with non-vertical side-walls are used.
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