Friday, December 2, 2016

Abstract-Extraction-controlled terahertz frequency quantum cascade lasers with a diagonal LO-phonon extraction and injection stage

Y. J. Han, L. H. Li, A. Grier, L. Chen, A. Valavanis, J. Zhu, J. R. Freeman, N. Isac, R. Colombelli, P. Dean, A. G. Davies, and E. H. Linfield
We report an extraction-controlled terahertz (THz)-frequency quantum cascade laser design in which a diagonal LO-phonon scattering process is used to achieve efficient current injection into the upper laser level of each period and simultaneously extract electrons from the adjacent period. The effects of the diagonality of the radiative transition are investigated, and a design with a scaled oscillator strength of 0.45 is shown experimentally to provide the highest temperature performance. A 3.3 THz device processed into a double-metal waveguide configuration operated up to 123 K in pulsed mode, with a threshold current density of 1.3 kA/cm2 at 10 K. The QCL structures are modeled using an extended density matrix approach, and the large threshold current is attributed to parasitic current paths associated with the upper laser levels. The simplicity of this design makes it an ideal platform to investigate the scattering injection process.
Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
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United States Patent 9508610-Inline measurement of molding material thickness using terahertz reflectance

United States Patent 9508610
Liu, Shuhong (Chandler, AZ, US) 
Ghosh, Nilanjan Z. (Chandler, AZ, US) 
Wang, Zhiyong (Chandler, AZ, US) 
Goyal, Deepak (Phoenix, AZ, US) 
Gokhale, Shripad (Gilbert, AZ, US) 
Zhang, Jieping (Chandler, AZ, US)

A method including emitting a terahertz beam from a light source at a layer of molding material; detecting a reflectance of the beam; and determining a thickness of the layer of molding material. A system including a panel supporter operable to support a panel including a plurality of substrates arranged in a planar array; a light source operable to emit a terahertz beam at a panel on the panel supporter; a detector operable to detect a reflection of a terahertz beam emitted at a panel; and a processor operable to determine a thickness of a material on the panel based on a time delay for an emitted terahertz beam to be detected by the detector.

Abstract-Measuring intensity correlations of a THz quantum cascade laser around its threshold at sub-cycle timescales

The quantum nature of photonic systems is reflected in the photon statistics of the light they emit. Therefore, the development of quantum optics tools with single photon sensitivity and excellent temporal resolution is paramount to the development of exotic sources, and is particularly challenging in the THz range where photon energies approach kbT at T=300 K. Here, we report on the first room temperature measurement of field g1({\tau}) and intensity correlations g2({\tau}) in the THz range with sub-cycle temporal resolution (146 fs) over the bandwidth 0.3-3 THz, based on electro-optic sampling. With this system, we are able to measure the photon statistics at threshold of a THz Quantum Cascade Laser.

Thursday, December 1, 2016

Abstract-Theoretical Insights into sub-Terahertz Acoustic Vibrations of Proteins Measured in Single Molecule Experiments

J. Phys. Chem. Lett., Just Accepted Manuscript
DOI: 10.1021/acs.jpclett.6b01812

Proteins are an important class of nanobioparticles with acoustical modes in the sub-THz frequency range. There is a considerable interest to measure and establish the role of these acoustical vibrations for the biological function. So far, the technique providing the most detailed information about the acoustical modes of proteins is the very recent Extraordinary Acoustic Raman (EAR) spectroscopy. In this technique, proteins are trapped in nanoholes and excited by two optical lasers of slightly different wavelengths producing an electric field at low frequency (< 100 GHz). We demonstrate that the acoustical modes of proteins studied by EAR spectroscopy are both infrared and Raman active modes and we provided the interpretation of the spectroscopic fingerprints measured at the single molecule level. Combination of the present calculations with techniques based on excitation of a single nanobioparticle by an electric field, as the EAR spectroscopy, should provide a wealth of information on the role of molecular dynamics for the biological function.

Abstract-A sub-terahertz broadband detector based on a GaN high-electron-mobility transistor with nanoantennas


We report a sub-terahertz (THz) detector based on a 0.25-µm-gate-length AlGaN/GaN high-electron-mobility transistor (HEMT) on a Si substrate with nanoantennas. The fabricated device shows excellent performance with a maximum responsivity (R v) of 15 kV/W and a minimal noise equivalent power (NEP) of 0.58 pW/Hz0.5 for 0.14 THz radiation at room temperature. We consider these excellent results as due to the design of asymmetric nanoantennas. From simulation, we show that indeed such nanoantennas can effectively enhance the local electric field induced by sub-THz radiation and thereby improve the detection response. The excellent results indicate that GaN HEMTs with nanoantennas are future competitive detectors for sub-THz and THz imaging applications.