Thursday, February 21, 2019

Abstract-Design and analysis of optical micro-two-ring resonator temperature sensor with graphene

Sina Javanshir, Ali Pourziad, Saeed Nikmehr,

Micrometer-sized optical temperature sensors with graphene have been designed and analyzed in order to reach the highest temperature sensitivity. The main idea is to control the temperature of any system by surface graphene material in a micro-two-ring resonator path. By rising the temperature of the system, graphene with 5000  W  /  mK temperature conductivity senses the increase and applies it in the sensor resonance peaks. The prominent features of these sensors are small dimensions, high finesse and sensitivity, safe from electromagnetic interference, high bandwidth, low weight, and low cost. Electronic sensors suffer from electrical disturbances and electromagnetic interference, and sometimes do not function properly. Therefore, this micrometer optical temperature sensor with 44  ×  40  μm dimensions and high sensitivity and finesse in all industrial and medical fields is necessary. The materials used in this sensor are graphene, Si, and SiO2, which are natural elements and have very high temperature stability. Free-spectral range reaches to 820 GHz and full width at half maximum to 21 GHz, and this quantity increases the finesse and sensitivity of the system, the time delay of sensor is 1.21 ps, which shows the low light dispersion and fast performance time.

© 2019 Society of Photo-Optical Instrumentation Engineers (SPIE) 0091-3286/2019/$25.00 © 2019 SPIE

Abstract-Wideband, high-resolution terahertz spectroscopy by light-induced frequency tuning of quantum-cascade lasers

T. Alam, M. Wienold, X. Lü, K. Biermann, L. Schrottke, H. T. Grahn, and H.-W. Hübers

Fig. 1 (a) Schematics of the experimental setup. The QCL (yellow box) is mounted in a He-flow cryostat. BS - dichroic beamsplitter; OL - objective lens; Ge:Ga - photoconductive Ge:Ga detector. (b) Microscope image of the illuminated QCL facet. The excitation spot with a diameter of approximately 90 μm originates from a multimode diode laser emitting at 809 nm and exhibits essentially a flat-top profile. (c) Calculated profile of the waveguide mode in the vertical (epitaxial-growth) direction for different frequencies (the mode propagates perpendicular to y along the waveguide ridge). The active region (a. r.) has a height of 10 μm and corresponds to the QCL ridge structure in (b).

Near-infrared optical excitation enables wideband frequency tuning of terahertz quantum-cascade lasers. In this work, we demonstrate the feasibility of the approach for molecular laser absorption spectroscopy. We present a physical model which explains the observed frequency tuning characteristics by the optical excitation of an electron-hole plasma. Due to an improved excitation configuration as compared to previous work, we observe a single-mode continuous-wave frequency coverage of as much as 40 GHz for a laser at 3.1 THz. This represents, for the same device, a ten-fold improvement over the usually employed tuning by current. The method can be readily applied to a large class of devices.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz spectroscopy of diglycidylether of bisphenol A: Experimental investigations and density functional theory based simulations

P. Suma Sindhua, Dipak Prasada, Simone Pelib, Nilanjan Mitraa, P.K. Dattaa

Fig.1. Molecular structure of DGEBA (black: Carbon; grey: Hydrogen; red: Oxygen)
A combined methodology of Terahertz spectroscopy and Density functional theory based simulations is presented for a molecule to determine its molecular vibration frequency and associated configuration. A case study of diglycidylether of bisphenol A, which is an important ingredient of epoxy resin, has been presented in this manuscript. Apart from determination of absorbtion peaks in the THz regime both through experiment and simulation, the vibration configuration corresponding to each of the peaks are also presented. Within 3 THz, the refractive index of the material is determined to be within 1.15–1.3 and the dielectric constant is estimated as 1.5.

Wednesday, February 20, 2019

Abstract-Terahertz Compression of Electron Pulses at a Planar Mirror Membrane

Dominik Ehberger, Kathrin J. Mohler, Thomas Vasileiadis, Ralph Ernstorfer, Lutz Waldecker, and Peter Baum

Compression of electron pulses with terahertz radiation offers short pulse durations and intrinsic subcycle stability in time. We report the generation of 12-fs (rms), 28-fs (FWHM) electron pulses at a kinetic energy of 75 keV by using single-cycle terahertz radiation and a simple planar mirror. The mirror interface provides transverse velocity matching and spatially uniform compression in time with purely longitudinal field-electron interaction. The measured short-term and long-term temporal drifts are substantially below the pulse duration without any active synchronization. A simple phase-space model explains the measured temporal focusing dynamics for different compressor strengths and shows a path toward generating isolated attosecond electron pulses from beams of almost arbitrary transverse emittance.
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Abstract-Coherent Transition Radiation from Relativistic Beam-Foil Interaction in the Terahertz and Optical Range

Coherent transition radiation (CTR) from relativistic electron beam interaction with an overdense plasma foil is investigated by making use of two-dimensional particle-in-cell simulations. Well-defined single electron beam either of uniform profile or having substructures is considered for various beam-plasma parameters. The main purpose is to mimic the complicated beam-plasma conditions that is often found, for example, in intense laser plasma interactions. Key properties of the CTR concerning their temporal, angular and spectral profiles are identified. Several saturation effects due to the beam energy, size and foil density are found for the CTR energy, and the dependences vary for different spectral components such as in the Terahertz (THz) and optical range. The detailed substructure of the beam also affects greatly the radiation generation, leading to distinctive high harmonic components. Electrons with kinetic energy from sub MeV to tens of GeV are explored. For few MeV electron beams, the effects of the foil plasma on the beam dynamics and associated CTR generation, resembles closely the CTR from hot electrons produced in intense laser-plasma interactions. These results may find important applications in beam diagnostics either in laser-plasma based acceleration or conventional accelerators. They may also be employed to design novel THz radiation sources using tunable electron beams.

Abstract-Terahertz plasmonic detector controlled by phase asymmetry

I. V. Gorbenko, V. Y. Kachorovskii, and Michael Shur

Fig. 1 TeraFET Spectrometer principle of operation: (a) phase shift induced by asymmetric antennas and circularly polarized radiation (b) nonzero incident angle of incoming radiation

We demonstrate that a phase difference between terahertz signals coupled to the gate and source and gate and drain terminals of a field effect transistor (a TeraFET) induces a plasmon-assisted DC current, which is dramatically enhanced in the vicinity of plasmonic resonances. We describe a TeraFET operation with identical radiation amplitudes at the source and drain antennas but with a phase-shift-induced asymmetry. In this regime, the TeraFET operates as a tunable resonant polarization-sensitive plasmonic spectrometer, operating in the sub-terahertz and terahertz ranges of frequencies. We also propose an effective scheme of a phase-sensitive homodyne detector operating in this phase-asymmetry mode, which allows for a dramatic enhancement of the response. These regimes can be implemented in different materials systems, including silicon. The p-diamond TeraFETs could support operation in the 200 to 600 GHz atmospheric windows, which is especially important for beyond 5G communication systems.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement