Special Issue "THz: Research Frontiers for New Sources, Imaging and Other Advanced Technologies"

A special issue of Condensed Matter (ISSN 2410-3896).

Deadline for manuscript submissions: closed (29 February 2020).

Special Issue Editors

Prof. Stefano Lupi
Website
Guest Editor
TeraLab Laboratory and SISSI and [email protected], Department of Physics, Sapienza University of Rome, Italy
Interests: THz radiation; Pump-Probe spectroscopy; plasmonics; metal-insulator transition; optical spectroscopy; nanoMicroscopy
Prof. Akinori Irizawa
Website
Guest Editor
ISIR, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan
Interests: solid state physics; nonlinear phenomena; synchrotron radiation; free electron laser; IR and THz radiation; optical spectroscopy; photoemission spectroscopy
Prof. Augusto Marcelli
Website
Guest Editor
INFN – LNF, Via Enrico Fermi 40, 00044 Frascati, Italy
Interests: synchrotron radiation research; synchrotron radiation instrumentation: IR and x-ray optics; x-ray absorption spectroscopy; circular magnetic x-ray dichroism; time resolved concurrent experiments; high Tc superconductors and quantum materials; multiple scattering theory applied to core level x-ray absorption spectra; dust and aerosol characterization and ultra-trace detection; FTIR spectromicroscopy and imaging applied to protein, cells and tissues
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Special Issue Information

Dear Colleagues,

The region of the electromagnetic spectrum from 0.1 to 20 terahertz (THz, 3–600 cm−1, 3 mm–15 μm wavelength) is a frontier area for research in Physics, Chemistry, Biology, Materials science, Biosafety and Medicine. THz sources showing high stability, high-intensity and covering a broad spectral range have been scarce, but this gap has been filled by a wide range of new technologies ranging from Quantum-Cascade-Lasers (QCL), to THz emission from high-intensity sub-ps lasers, from THz production from new synchrotrons and Free-Electron-Lasers. Terahertz radiation is now available in both cw and pulsed form, down to single-cycles or less, with time duration down to hundreds of fs, and a peak powers up to 1 GW. New sources have led to new applications in many scientific areas, as researchers are aware of the opportunities for research progress in their fields using THz radiation. In this book, different scientific applications in THz science will be discussed, ranging from new sources non linear optics, pump-probe spectroscopy, imaging in biomedicine, THz spectroscopy of gases and liquid, THz detectors and much more.

Prof. Stefano Lupi
Prof. Akinori Irizawa
Prof. Augusto Marcelli
Guest Editors

Manuscript Submission Information

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Keywords

  • THz
  • spectroscopy
  • Pump-Probe spectroscopy
  • plasmonics
  • optical spectroscopy
  • microscopy
  • imaging
  • non-linear phenomena
  • synchrotron radiation
  • free electron laser

Published Papers (13 papers)

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Research

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Open AccessArticle
Broadband Anisotropic Optical Properties of the Terahertz Generator HMQ-TMS Organic Crystal
Condens. Matter 2020, 5(3), 47; https://doi.org/10.3390/condmat5030047 - 14 Jul 2020
Cited by 2
Abstract
HMQ-TMS (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 2,4,6-trimethylbenzenesulfonate) is a recently discovered anisotropic organic crystal that can be exploited for the production of broadband high-intensity terahertz (THz) radiation through the optical rectification (OR) technique. HMQ-TMS plays a central role in THz technology due to its broad transparency range, [...] Read more.
HMQ-TMS (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 2,4,6-trimethylbenzenesulfonate) is a recently discovered anisotropic organic crystal that can be exploited for the production of broadband high-intensity terahertz (THz) radiation through the optical rectification (OR) technique. HMQ-TMS plays a central role in THz technology due to its broad transparency range, large electro-optic coefficient and coherence length, and excellent crystal properties. However, its anisotropic optical properties have not been deeply researched yet. Here, from polarized reflectance and transmittance measurements along the x 1 and x 3 axes of a HMQ-TMS single-crystal, we extract both the refraction index n and the extinction coefficient k between 50 and 35,000 cm 1 . We further measure the THz radiation generated by optical rectification at different infrared (IR) wavelengths and along the two x 1 and x 3 axes. These data highlight the remarkable anisotropic linear and nonlinear optical behavior of HMQ-TMS crystals, expanding the knowledge of its properties and applications from the THz to the UV region. Full article
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Open AccessArticle
Spatially Resolved Spectral Imaging by A THz-FEL
Condens. Matter 2020, 5(2), 38; https://doi.org/10.3390/condmat5020038 - 04 Jun 2020
Cited by 1
Abstract
Using the unique characteristics of the free-electron-laser (FEL), we successfully performed high-sensitivity spectral imaging of different materials in the terahertz (THz) and far-infrared (FIR) domain. THz imaging at various wavelengths was achieved using in situ spectroscopy by means of this wavelength tunable and [...] Read more.
Using the unique characteristics of the free-electron-laser (FEL), we successfully performed high-sensitivity spectral imaging of different materials in the terahertz (THz) and far-infrared (FIR) domain. THz imaging at various wavelengths was achieved using in situ spectroscopy by means of this wavelength tunable and monochromatic source. In particular, owing to its large intensity and directionality, we could collect high-sensitivity transmission imaging of extremely low-transparency materials and three-dimensional objects in the 3–6 THz range. By accurately identifying the intrinsic absorption wavelength of organic and inorganic materials, we succeeded in the mapping of spatial distribution of individual components. This simple imaging technique using a focusing optics and a raster scan modality has made it possible to set up and carry out fast spectral imaging experiments on different materials in this radiation facility. Full article
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Open AccessArticle
Evaluation of Bunch Length by Measuring Coherent Synchrotron Radiation with a Narrow-Band Detector at LEBRA
Condens. Matter 2020, 5(2), 34; https://doi.org/10.3390/condmat5020034 - 09 May 2020
Abstract
This study presents a novel technology to measure electron bunch length with a high time resolution by measuring coherent synchrotron radiation using a narrow-band detector at Laboratory for Electron Beam Research and Application (LEBRA)—an S-band linear accelerator facility for free-electron lasers. The form [...] Read more.
This study presents a novel technology to measure electron bunch length with a high time resolution by measuring coherent synchrotron radiation using a narrow-band detector at Laboratory for Electron Beam Research and Application (LEBRA)—an S-band linear accelerator facility for free-electron lasers. The form factor was observed to decrease exponentially with charge—in concordance with the relationship between the intensity of the coherent synchrotron radiation and the magnitude of electron bunch charge—in the region in which the effect of electron bunch charge on bunch length is negligible. The calculated root-mean-square bunch length was observed to agree well with the value determined from the spectral shape obtained. The aforementioned results are expected to be useful in real-time observation of small changes in electron bunches in advanced accelerators. Full article
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Open AccessArticle
Proximity Array Device: A Novel Photon Detector Working in Long Wavelengths
Condens. Matter 2020, 5(2), 33; https://doi.org/10.3390/condmat5020033 - 01 May 2020
Cited by 3
Abstract
We present here an innovative photon detector based on the proximity junction array device (PAD) working at long wavelengths. We show that the vortex dynamics in PAD undergoes a transition from a Mott insulator to a vortex metal state by application of an [...] Read more.
We present here an innovative photon detector based on the proximity junction array device (PAD) working at long wavelengths. We show that the vortex dynamics in PAD undergoes a transition from a Mott insulator to a vortex metal state by application of an external magnetic field. The PAD also evidences a Josephson I-V characteristic with the external field dependent tunneling current. At high applied currents, we observe a dissipative regime in which the vortex dynamics is dominated by the quasi-particle contribution from the normal metal. The PAD has a relatively high photo-response even at frequencies below the expected characteristic frequency while, its superconducting properties such as the order parameter and the Josephson characteristic frequency can be modulated via external fields to widen the detection band. This device represents a promising and reliable candidate for new high-sensitivity long-wavelength detectors. Full article
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Open AccessArticle
Infrared Synchrotron Radiation and Its Application to the Analysis of Cultural Heritage
Condens. Matter 2020, 5(2), 28; https://doi.org/10.3390/condmat5020028 - 09 Apr 2020
Abstract
Infrared synchrotron radiation (IR-SR) is a broad-band light source. Its brilliance is the main advantage for microspectroscopy experiments, when the limited size of the sample often prevents the use of conventional thermal radiation sources. Cultural heritage materials are delicate and valuable; therefore, nondestructive [...] Read more.
Infrared synchrotron radiation (IR-SR) is a broad-band light source. Its brilliance is the main advantage for microspectroscopy experiments, when the limited size of the sample often prevents the use of conventional thermal radiation sources. Cultural heritage materials are delicate and valuable; therefore, nondestructive experiments are usually preferred. Nevertheless, sometimes, small pieces can be acquired in the process of preservation and conservation. These samples are analyzed by various experimental techniques and give information about the original material and current condition. In this paper, four attempts to analyze cultural heritage materials are introduced. All these experiments are performed at the microspectroscopy station of IR beamline BL43IR in SPring-8. Full article
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Open AccessArticle
Cross-Correlation of THz Pulses from the Electron Storage Ring BESSY II
Condens. Matter 2020, 5(2), 24; https://doi.org/10.3390/condmat5020024 - 27 Mar 2020
Abstract
Coherent synchrotron radiation from an electron storage ring is observed in the THz spectral range when the bunch length is shortened down to the sub-mm-range. With increasing stored current, the bunch becomes longitudinally unstable and modulates the THz emission in the time domain. [...] Read more.
Coherent synchrotron radiation from an electron storage ring is observed in the THz spectral range when the bunch length is shortened down to the sub-mm-range. With increasing stored current, the bunch becomes longitudinally unstable and modulates the THz emission in the time domain. These micro-instabilities are investigated at the electron storage ring BESSY II by means of cross-correlation of the THz fields from successive bunches. The investigations allow deriving the longitudinal length scale of the micro bunch fluctuations and show that it grows faster than the current-dependent bunch length. Our findings will help to set the limits for the possible time resolution for pump-probe experiments achieved with coherent THz synchrotron radiation from a storage ring. Full article
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Open AccessArticle
Angular Dependence of Copper Surface Damage Induced by an Intense Coherent THz Radiation Beam
Condens. Matter 2020, 5(1), 16; https://doi.org/10.3390/condmat5010016 - 10 Mar 2020
Cited by 1
Abstract
In this work, we show the damage induced by an intense coherent terahertz (THz) beam on copper surfaces. The metallic surface was irradiated by multiple picosecond THz pulses generated by the Free Electron Laser (FEL) at the ISIR facility of the Osaka University, [...] Read more.
In this work, we show the damage induced by an intense coherent terahertz (THz) beam on copper surfaces. The metallic surface was irradiated by multiple picosecond THz pulses generated by the Free Electron Laser (FEL) at the ISIR facility of the Osaka University, reaching an electric field on the sample surface up to ~4 GV/m. No damage occurs at normal incidence, while images and spectroscopic analysis of the surface point out a clear dependence of the damage on the incidence angle, the electric field intensity, and polarization of the pulsed THz radiation. Ab initio analysis shows that the damage at high incidence angles could be related to the increase of the absorbance, i.e., to the increase of the temperature around or above 1000 °C. The experimental approach we introduced with multiple fast irradiations represents a new powerful technique useful to test, in a reproducible way, the damage induced by an intense electric gradient on copper and other metallic surfaces in view of future THz-based compact particle accelerators. Full article
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Open AccessArticle
Sub-THz Waveguide Spectroscopy of Coating Materials for Particle Accelerators
Condens. Matter 2020, 5(1), 9; https://doi.org/10.3390/condmat5010009 - 20 Jan 2020
Abstract
The electromagnetic characterisation of different materials for the inner wall coating of beam pipes is a long-standing problem in accelerator physics, regardless the purpose they are used for, since their presence may affect in an unpredictable way the beam coupling impedance and therefore [...] Read more.
The electromagnetic characterisation of different materials for the inner wall coating of beam pipes is a long-standing problem in accelerator physics, regardless the purpose they are used for, since their presence may affect in an unpredictable way the beam coupling impedance and therefore the machine performance. Moreover, in particle accelerators and storage rings of new generation very short bunches might be required, extending far in frequency the exploration of the beam spectrum and rendering therefore more and more important to assess the coating material response up to hundreds of GHz. This paper describes a time domain method based on THz waveguide spectroscopy to infer the coating properties at very high frequencies. The technique has been tested on Non Evaporable Getter thick films deposited by DC magnetron sputtering on copper plates. Full article
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Open AccessArticle
The TeraFERMI Electro-Optic Sampling Set-Up for Fluence-Dependent Spectroscopic Measurements
Condens. Matter 2020, 5(1), 8; https://doi.org/10.3390/condmat5010008 - 20 Jan 2020
Cited by 2
Abstract
TeraFERMI is the THz beamline at the FERMI free-electron-laser facility in Trieste (Italy). It uses superradiant Coherent Transition Radiation emission to produce THz pulses of 10 to 100 μ J intensity over a spectral range which can extend up to 12 THz. TeraFERMI [...] Read more.
TeraFERMI is the THz beamline at the FERMI free-electron-laser facility in Trieste (Italy). It uses superradiant Coherent Transition Radiation emission to produce THz pulses of 10 to 100 μ J intensity over a spectral range which can extend up to 12 THz. TeraFERMI can be used to perform non-linear, fluence-dependent THz spectroscopy and THz-pump/IR-probe measurements. We describe in this paper the optical set-up based on electro-optic-sampling, which is presently in use in our facility and discuss the properties of a representative THz electric field profile measured from our source. The measured electric field profile can be understood as the superimposed emission from two electron bunches of different length, as predicted by electron beam dynamics simulations. Full article
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Open AccessArticle
Novel Schemes for Compact FELs in the THz Region
Condens. Matter 2019, 4(4), 90; https://doi.org/10.3390/condmat4040090 - 19 Nov 2019
Abstract
The rapid advance of terahertz technologies in terms of radiation generators, systems, and scientific or industrial applications has put a particular focus on compact sources with challenging performances in terms of generated power (peak and/or average), radiation time structure, and frequency band tunability. [...] Read more.
The rapid advance of terahertz technologies in terms of radiation generators, systems, and scientific or industrial applications has put a particular focus on compact sources with challenging performances in terms of generated power (peak and/or average), radiation time structure, and frequency band tunability. Free electron laser (FEL)-based sources are probably the best candidates to express such a versatility; there are a number of schemes that have been investigated over the years to generate coherent radiation from free electrons in the mm-wave and terahertz regions of the spectrum, covering a wide frequency range from approximately 100 GHz to 10 THz. This paper proposes novel schemes for exploring the limits in the performance of radio frequency-driven free-electron devices in terms of ultrashort pulse duration, wide bandwidth operation, and energy recovery for near continuous wave (CW) operation. The aim of the present work is to demonstrate the feasibility of an FEL achieving performance comparable to a conventional photoconductive THz source, which is commonly used for time-domain spectroscopy (TDS), in terms of bandwidth and pulse duration. We will also demonstrate that a THz FEL could be very powerful and flexible in terms of tailoring its spectral features. Full article
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Review

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Open AccessReview
A Versatile THz Source from High-Brightness Electron Beams: Generation and Characterization
Condens. Matter 2020, 5(2), 40; https://doi.org/10.3390/condmat5020040 - 08 Jun 2020
Abstract
Ultra-short electron bunches, such as those delivered by a high-brightness photo-injector, are suitable to produce high peak power THz radiation, both broad and narrow band, with sub-picosecond down to femtosecond pulse shaping. The features of this kind of source in the THz range [...] Read more.
Ultra-short electron bunches, such as those delivered by a high-brightness photo-injector, are suitable to produce high peak power THz radiation, both broad and narrow band, with sub-picosecond down to femtosecond pulse shaping. The features of this kind of source in the THz range of the electromagnetic spectrum are extremely appealing for frequency- and time-domain experiments in a wide variety of fields. The present manuscript will overview the method of generation and characterization of THz radiation produced by high-brightness electron beams, as those available at the SPARC_LAB test facility. Full article
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Open AccessReview
THz Pulsed Imaging in Biomedical Applications
Condens. Matter 2020, 5(2), 25; https://doi.org/10.3390/condmat5020025 - 01 Apr 2020
Cited by 7
Abstract
Recent advances in technology have allowed the production and the coherent detection of sub-ps pulses of terahertz (THz) radiation. Therefore, the potentialities of this technique have been readily recognized for THz spectroscopy and imaging in biomedicine. In particular, THz pulsed imaging (TPI) has [...] Read more.
Recent advances in technology have allowed the production and the coherent detection of sub-ps pulses of terahertz (THz) radiation. Therefore, the potentialities of this technique have been readily recognized for THz spectroscopy and imaging in biomedicine. In particular, THz pulsed imaging (TPI) has rapidly increased its applications in the last decade. In this paper, we present a short review of TPI, discussing its basic principles and performances, and its state-of-the-art applications on biomedical systems. Full article
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Open AccessFeature PaperReview
Fabry-Perot Cavity Leaky Wave Antennas with Tunable Features for Terahertz Applications
Condens. Matter 2020, 5(1), 11; https://doi.org/10.3390/condmat5010011 - 25 Jan 2020
Cited by 2
Abstract
Terahertz (THz) radiation is a very appealing band of the electromagnetic spectrum due to its practical applications. In this context, the THz generation and manipulation is an essential part of the technological development. The demand of THz antennas is still high because it [...] Read more.
Terahertz (THz) radiation is a very appealing band of the electromagnetic spectrum due to its practical applications. In this context, the THz generation and manipulation is an essential part of the technological development. The demand of THz antennas is still high because it is already difficult to obtain directive, efficient, planar, low-cost, and easy-to-fabricate THz radiating systems. In this regard, Fabry-Perot cavity leaky-wave antennas are gaining increasing attention at THz, due to their very interesting radiating features: the combination of planar designs with metamaterials and metasurfaces could offer a promising platform for future THz manipulation technologies. In this short review, we focus on different classes of leaky-wave antennas, based on materials with tunable quasi-optical parameters. The possibility of producing directive patterns with particularly good efficiencies, as well as the capability of dynamically reconfiguring their radiating features, are discussed by taking into account the risk of increasing costs and fabrication complexity. Full article
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