TST, Vol. 7, No. 1, PP. 1-9
(Invited paper) Development of terahertz gyrotrons for spectroscopy at MIT
Richard J. Temkin *
Plasma Science and Fusion Center, Massachusetts Institute of Technology
Cambridge, MA 02139 USA
* Email: temkin@mit.edu
(Received December 20, 2013 )
Abstract: Gyrotron oscillators are vacuum electron devices that have delivered megawatt average power levels at millimeter wavelengths. The lack of other sources that are able to match these power levels at high frequency, with the exception of much bulkier free-electron lasers, makes the gyrotron the oscillator of choice in many applications such as plasma heating, materials processing, and plasma diagnostics. Although the main attractiveness of the gyrotron resides in its high power capability, the ability to extend the frequency of operation into the terahertz frequency band is another attractive feature of the gyrotron. In addition, some applications would also benefit from having a frequency-tunable generator. For instance, the operation of a nuclear magnetic resonance (NMR) spectrometer enhanced by dynamic nuclear polarization (DNP) would be greatly simplified by utilizing a continuously tunable continuous-wave (CW) gyrotron. This paper describes the development and application of terahertz frequency gyrotron oscillators and sub-terahertz gyrotron amplifiers for the program of research on DNP/NMR. It will also describe the development of ancillary components such as low-loss waveguide for transmission of the terahertz radiation.
Keywords: Gyrotron, NMR, Terahertz spectroscopy, Terahertz waveguide
doi: 10.11906/TST.001-009.2014.03.01
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TST, Vol. 7, No. 1, PP. 10-22
(Invited paper) QCL based terahertz frequency metrology
L. Consolino 1, 2, P. De Natale 1*, 2, M. Ravaro 1, 2, M. S. Vitiello 1, 3 and S. Bartalini 1, 2
1 INO, Istituto Nazionale di Ottica – CNR, Largo E. Fermi 6, Firenze I-50125, Italy
2 LENS, European Laboratory for NonLinear Spectroscopy, Via N. Carrara 1, Sesto Fiorentino (FI) I-50019, Italy
3 NEST, Istituto Nanoscienze – CNR and Scuola Normale Superiore, Piazza San Silvestro 12, Pisa I-56127,
*1 Email: paolo.denatale@ino.it
(Received December 18, 2013)
Abstract: Quantum cascade lasers combine unique features in the framework of THz sources, namely compactness and mW output power. In addition, owing to an intrinsically low phase-noise level, they are suitable for frequency and phase stabilization, which makes them attractive sources for frequency metrology applications, and able to overcome the power limits of current microwave-traceable THz emitters. In this contribution, we address metrological grade THz quantum cascade lasers from their intrinsic spectral feature to the use of optical frequency combs as frequency reference.
Keywords: Terahertz generation, Coherent detection, Frequency metrology.
doi: 10.11906/TST.010-022.2014.03.02
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TST, Vol. 7, No. 1, PP. 23-38
(Invited paper) High-Power THz-Waves using gyrotrons: new physics results
Stefano Alberti *, Falk Braunmueller, Trach Minh Tran, Jean-Philippe Hogge, Jérémy Genoud, and Minh Quang Tran
Centre de Recherches en Physique des Plasmas (CRPP),
Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 13, 1015 Lausanne, Switzerland
* Email: stefano.alberti@epfl.ch
(Received December19, 2013)
Abstract: Gyrotrons are high-power coherent radiation sources based on the cyclotron maser instability. Since more than three decades the research and development of gyrotrons has been essentially driven from the need of high-power MW-level sources in the THz frequency range (0.1-1 THz) for electron cyclotron resonance heating of magnetically confined plasmas such as in ITER and DEMO. A more recent spin-off research activity has led to the development of lower power (1-100 W) gyrotrons with frequencies belonging to the THz domain. One of the main applications in the THz domain is in the field of Dynamic Nuclear Polarization Nuclear Magnetic Resonance spectroscopy (DNP/NMR).
With a THz gyrotron oscillator developped for DNP/NMR spectroscopy and operating at 260 GHz, novel operational regimes have been recently experimentally demonstrated in which the non-linear interaction excites a finite number of side-bands and eventually ends in a chaotic dynamics of the THz radiation field. The route to chaos via a period doubling cascade dynamics is experimentally observed and is supported by numerical simulations. In presence of phase-locked frequency-equidistant side-bands, a novel regime characterized by high-power nanosecond pulses is experimentally observed and is associated to a self-consistent Q-switch mechanism in which the cavity diffraction quality factor dynamically varies by nearly two orders of magnitude on a subnanosecond timescale. This novel regime is also well predicted with the self-consistent TWANG code and may open up new applications for gyrotrons.
Keywords: Terahertz Waves, Gyrotron Oscillator, Non-stationary regime (automodulation), Chaos, Nanosecond pulses, mode-locking, Q-switch.
doi: 10.11906/TST.023-038.2014.03.03
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TST, Vol. 7, No. 1, PP. 39-52
(Invited paper) Optical couplers for terahertz quantum well photodetectors
R. Zhang, X. G. Guo, and J. C. Cao *
Key Laboratory of Terahertz Solid-State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, 200050, China
* Email: jccao@mail.sim.ac.cn
(Received November 25, 2013)
Abstract: Constrained by the intersubband transition selection rule, terahertz (THz) quantum well photodetectors (QWPs) are insensitive to the normally incident light. On the other hand, the intersubband absorption efficiency of THz QWPs is relatively low due to the low doping concentrations in the quantum wells. To solve these issues, optical couplers including the metal-grating coupler, the micro-cavity coupler, and the surface-plasmon coupler, are introduced and investigated. Our findings show that, with these high efficient optical couplers, the performance of THz QWPs can be greatly improved.
Keywords: Coupler, Pphotodetector, Quantum well, Terahertz
doi: 10.11906/TST.039-052.2014.03.04
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