Showing papers in "Journal of Infrared, Millimeter, and Terahertz Waves in 2012"
TL;DR: A review of pioneering and recent studies of the conductivity of solid state systems at terahertz frequencies can be found in this article, where a variety of theoretical formalisms that describe the tera-hertz conductivities of bulk, mesoscopic and nanoscale materials are outlined, and their validity and limitations are given.
Abstract: We review pioneering and recent studies of the conductivity of solid state systems at terahertz frequencies. A variety of theoretical formalisms that describe the terahertz conductivity of bulk, mesoscopic and nanoscale materials are outlined, and their validity and limitations are given. Experimental highlights are discussed from studies of inorganic semiconductors, organic materials (such as graphene, carbon nanotubes and polymers), metallic films and strongly correlated electron systems including superconductors.
400 citations
TL;DR: Terahertz thin-film sensing is reviewed, summarizing the motivation, challenges, and state-of-the-art approaches based predominately on terahertz time-domain spectroscopy.
Abstract: In the past two decades, the development and steady improvement of terahertz technology has motivated a wide range of scientific studies designed to discover and develop terahertz applications. Terahertz sensing is one such application, and its continued maturation is virtually guaranteed by the unique properties that materials exhibit in the terahertz frequency range. Thin-film sensing is one branch of this effort that has enjoyed diverse development in the last decade. Deeply subwavelength sample thicknesses impose great difficulties to conventional terahertz spectroscopy, yet sensing those samples is essential for a large number of applications. In this article we review terahertz thin-film sensing, summarizing the motivation, challenges, and state-of-the-art approaches based predominately on terahertz time-domain spectroscopy.
191 citations
TL;DR: In this article, the Terahertz frequencies between 0.1-15 THz (3-500 cm−1) have been used for the analysis of protein structures.
Abstract: Spectroscopic analysis using the Terahertz frequencies between 0.1-15 THz (3–500 cm−1) has been underutilised by the biochemistry community but is starting to yield some scientifically interesting information. Analysis of structures from simple molecules like N-methylacetamide, to polyamides, peptides and relatively complex proteins provides different types of information dependant on the molecular size. The absorbance spectrum of small molecules is dominated by individual modes and specific hydrogen bonds, peptide spectra have peaks associated with secondary structure, while protein spectra are dominated by ensembles of hydrogen bonds and/or collective modes. Protein dynamics has been studied using Terahertz spectroscopy using proteins like bacteriorhodopsin, illustrating a potential application where this approach can provide complementary global dynamics information to the current nuclear magnetic resonance and fluorescence-based techniques. Analysis of higher-order protein structures like polyomavirus virus-like particles generate quite different spectra compared to their constituent parts. The presence of an extended hydration layer around proteins, first postulated to explain data generated using p-germanium spectroscopy may present a particularly interesting opportunity to better understand protein’s complex interaction with water and small solutes in an aqueous environment. The practical aspects of Terahertz spectroscopy including sample handling, the use of molecular dynamics simulation and orthogonal experiment design are also discussed.
149 citations
TL;DR: In this article, spatial mapping of moisture and liquid detection by terahertz (THz) imaging is reviewed, and analysis of the moisture content is discussed in terms of a double Debye model for liquid water and effective medium models for the permittivity of the dry and "wet" materials of interest.
Abstract: The relatively high permittivity of liquid water compared to other materials in the Terahertz (THz) range enables a contrast mechanism for the detection and imaging of moisture. In this paper, spatial mapping of moisture and liquid detection by THz imaging is reviewed. Analysis of the moisture content is discussed in terms of a double Debye model for liquid water and effective medium models for the permittivity of the dry and ‘wet’ materials of interest. Examples from medical applications, forestry products, agriculture/ food products, and polymers are reviewed. Extraction of diffusion rates and diffusion maps from THz images are discussed.
130 citations
TL;DR: In this article, a review of terahertz time domain spectroscopy (THz TDS) and related measurements of graphene is presented, with a focus on the inter and intraband response of excited carriers.
Abstract: Graphene has proved itself as being unique in terms of fundamental physics, and of particular importance for post–silicon electronics. Research into graphene has divided into two branches, one probing the remarkable electronic and optical properties of graphene, and the other pursuing technologically viable forms of the material. Terahertz time domain spectroscopy (THz TDS) is a powerful tool for both, able to characterise the free carrier response of graphene and probe the inter and intraband response of excited carriers with sub-ps time resolution. We review THz TDS and related THz measurements of graphene.
86 citations
TL;DR: In this article, a coherent mid-infrared continuum source with 700 cm-1 usable bandwidth, readily tuned within 600-2500 cm-2 (4-17μm) and covering much of the infrared fingerprint molecular vibration region is described.
Abstract: We describe a coherent mid-infrared continuum source with 700 cm-1 usable bandwidth, readily tuned within 600–2500 cm-1 (4–17 μm) and thus covering much of the infrared "fingerprint" molecular vibration region. It is based on nonlinear frequency conversion in GaSe using a compact commercial 100-fs-pulsed Er fiber laser system providing two amplified near-infrared beams, one of them broadened by a nonlinear optical fiber. The resulting collimated mid-infrared continuum beam of 1 mW quasi-cw power represents a coherent infrared frequency comb with zero carrier-envelope phase, containing about 500,000 modes that are exact multiples of the pulse repetition rate of 40 MHz. The beam's diffraction-limited performance enables long-distance spectroscopic probing as well as maximal focusability for classical and ultraresolving near-field microscopies. Applications are foreseen also in studies of transient chemical phenomena even at ultrafast pump-probe scale, and in high-resolution gas spectroscopy for e.g. breath analysis.
81 citations
TL;DR: In this paper, the authors outline two series of gyro-devices, namely pulsed gyrotrons and gyrotron FU CW Series, which consist of tubes operated in a continuous wave or long pulse mode, both developed at the FIR FU Center.
Abstract: Powerful sources of coherent radiation in the sub-terahertz and in the terahertz frequency range of the electromagnetic spectrum are necessary for a great and continuously expanding number of applications in the physical research and in various advanced technological processes as well as in radars, communication systems, for remote sensing and inspection etc.. In recent years, a spectacular progress in the development of various gyro-devices and in particular of the powerful high frequency (sub-terahertz and terahertz) gyrotron oscillators has demonstrated a remarkable potential for bridging the so-called terahertz power gap and stimulated many novel and prospective applications. In this review paper we outline two series of such devices, namely the Gyrotron FU Series which includes pulsed gyrotrons and Gyrotron FU CW Series which consist of tubes operated in a CW (continuous wave) or long pulse mode, both developed at the FIR FU Center. We present the most remarkable achievements of these devices and illustrate their applications by some characteristic examples. An outlook for the further extension of the Gyrotron FU CW Series is also provided.
71 citations
TL;DR: In this paper, the principles of impedance matching in photoconductive antennas in comparison with conventional antennas are described, and the photoconductor impedance optimization criteria are evaluated according to the antenna structure and operational settings.
Abstract: The principles of impedance matching in photoconductive antennas in comparison with conventional antennas are described. Because of the optical nature of the input signal in photoconductive antennas and the dependence of photoconductor conductance on the optical pump power, the optimum photoconductor impedance is not necessarily determined by the complex conjugate of antenna impedance. Using the equivalent circuit model of photoconductive antennas, the photoconductor impedance optimization criteria are evaluated according to the photoconductive antenna structure and operational settings.
68 citations
TL;DR: The development of scalable emitters for pulsed broadband terahertz (THz) radiation is reviewed in this article, where the authors demonstrate that the scalable concept provides freedom for designing optimized antenna patterns for different polarization modes.
Abstract: The development of scalable emitters for pulsed broadband terahertz (THz) radiation is reviewed. Their large active area in the 1 – 100 mm2 range allows for using the full power of state-of-the-art femtosecond lasers for excitation of charge carriers. Large fields for acceleration of the photogenerated carriers are achieved at moderate voltages by interdigitated electrodes. This results in efficient emission of single-cycle THz waves. THz field amplitudes in the range of 300 V/cm and 17 kV/cm are reached for excitation with 10 nJ pulses from Ti:sapphire oscillators and for excitation with 5 μJ pulses from amplified lasers, respectively. The corresponding efficiencies for conversion of near-infrared to THz radiation are 2.5 × 10-4 (oscillator excitation) and 2 × 10-3 (amplifier excitation). In this article the principle of operation of scalable emitters is explained and different technical realizations are described. We demonstrate that the scalable concept provides freedom for designing optimized antenna patterns for different polarization modes. In particular emitters for linearly, radially and azimuthally polarized radiation are discussed. The success story of photoconductive THz emitters is closely linked to the development of mode-locked Ti:sapphire lasers. GaAs is an ideal photoconductive material for THz emitters excited with Ti:sapphire lasers, which are widely used in research laboratories. For many applications, especially in industrial environments, however, fiber-based lasers are strongly preferred due to their lower cost, compactness and extremely stable operation. Designing photoconductive emitters on InGaAs materials, which have a low enough energy gap for excitation with fiber lasers, is challenging due to the electrical properties of the materials. We discuss why the challenges are even larger for microstructured THz emitters as compared to conventional photoconductive antennas and present first results of emitters suitable for excitation with ytterbium-based fiber lasers. Furthermore an alternative concept, namely the lateral photo-Dember emitter, is presented. Due to the strong THz output scalable emitters are well suited for THz systems with fast data acquisition. Here the application of scalable emitters in THz spectrometers without mechanical delay stages, providing THz spectra with 1 GHz spectral resolution and a signal-to-noise ratio of 37 dB within 1 s, is presented. Finally a few highlight experiments with radiation from scalable THz emitters are reviewed. This includes a brief discussion of near-field microscopy experiments as well as an overview over gain studies of quantum-cascade lasers.
68 citations
TL;DR: Applications of high-power Terahertz (THz) sources require low-loss transmission lines to minimize loss, prevent overheating and preserve the purity of the transmission mode, and concepts for THz transmission lines are reviewed with special emphasis on overmoded, metallic, corrugated transmission lines.
Abstract: Applications of high-power Terahertz (THz) sources require low-loss transmission lines to minimize loss, prevent overheating and preserve the purity of the transmission mode. Concepts for THz transmission lines are reviewed with special emphasis on overmoded, metallic, corrugated transmission lines. Using the fundamental HE11 mode, these transmission lines have been successfully implemented with very low-loss at high average power levels on plasma heating experiments and THz dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) experiments. Loss in these lines occurs directly, due to ohmic loss in the fundamental mode, and indirectly, due to mode conversion into high order modes whose ohmic loss increases as the square of the mode index. An analytic expression is derived for ohmic loss in the modes of a corrugated, metallic waveguide, including loss on both the waveguide inner surfaces and grooves. Simulations of loss with the numerical code HFSS are in good agreement with the analytic expression. Experimental tests were conducted to determine the loss of the HE11 mode in a 19 mm diameter, helically-tapped, three meter long brass waveguide with a design frequency of 330 GHz. The measured loss at 250 GHz was 0.029 ± 0.009 dB/m using a vector network analyzer approach and 0.047 ± 0.01 dB/m using a radiometer. The experimental results are in reasonable agreement with theory. These values of loss, amounting to about 1% or less per meter, are acceptable for the DNP NMR application. Loss in a practical transmission line may be much higher than the loss calculated for the HE11 mode due to mode conversion to higher order modes caused by waveguide imperfections or miter bends.
63 citations
TL;DR: In this paper, a switchable THz notch filter with liquid crystal layer that acts as a half wave retarder in one state and as an isotropic layer in the other state is presented.
Abstract: In this letter we present a switchable THz notch filter. The filter contains a liquid crystal layer that acts as a half wave retarder in one state and as an isotropic layer in the other state. The device combines three unique properties: it can be switched electrically, it provides a filter depth of 35 dB at 350 GHz and it can be tuned over wide frequency range from 350 GHz to 700 GHz.
TL;DR: Polarized resolved terahertz spectroscopy has been used to study a number of complex dielectric anisotropic properties of materials that could not be easily measured before as discussed by the authors.
Abstract: Measuring the full polarization state of radiation in terahertz time-domain spectroscopy has allowed scientists to study a number of complex dielectric anisotropic properties of materials that could not be easily measured before. Novel polarization sensitive photoconductive detectors have simplified this task and their development has been a significant challenge. In this review I will present some of these devices and will also discuss some of the most recent studies that involve the use of polarization resolved terahertz spectroscopy.
TL;DR: In this paper, an electronic beam switching/steering device for operation at THz frequencies is presented, where the propagation direction of the THz beam is switched via electronic manipulation of the refractive index of a liquid crystal.
Abstract: We present an electronic beam switching/steering device for operation at THz frequencies. The propagation direction of the THz beam is switched via electronic manipulation of the refractive index of a liquid crystal. The design of the steering device and the parameters of the liquid crystal are described and angle-dependent THz-TDS measurements of the beam steering are reported. This device is able to deflect the propagation direction of the THz beam by 6.3 °. This particular device approach offers a viable option for beam steering/switching in various THz applications including fiber switches, scanning imagers, and free-space communication systems in which the detector or emitter is in motion.
TL;DR: In this paper, a review summarizes recent experimental results in the field of THz gyrotrons developed for various applications, and a powerful pulsed 0.67-THz/200-kW gyrotron is under development for remote detection of ionization sources.
Abstract: The review summarizes recent experimental results in the field of THz gyrotrons developed for various applications. A CW gyrotron with the operation frequency of 0.26 THz has been successfully used for DNP spectroscopy A pulsed high-harmonic Large Orbit Gyrotron (LOG) with the frequency of 0.55 THz and kW level of output power has been used for THz breakdown and obtaining dense plasma in gases. A powerful pulsed 0.67 THz/200 kW gyrotron is under development for remote detection of ionization sources.
TL;DR: In this paper, the authors demonstrate the utility of a continuously frequency-tunable 0.4 THz gyrotron in a dynamic nuclear polarization (DNP)-enhanced solid-state NMR (SSNMR) spectroscopy at one of the highest magnetic fields, B0 = 14.1 T (600 MHz for 1H Larmor frequency).
Abstract: In this paper we present results that demonstrate the utility of a continuously frequency-tunable 0.4 THz-gyrotron in a dynamic nuclear polarization (DNP)-enhanced solid-state NMR (SSNMR) spectroscopy at one of the highest magnetic fields, B0 = 14.1 T (600 MHz for 1H Larmor frequency). Our gyrotron called FU CW VI generates sub-mm wave at a frequency near 0.4 THz with an output power of 4–25 W and a tunability over a range of more than 1 GHz by sweeping the magnetic field at the gyrotron cavity. We observed overall down shifting of the central frequency by up to ~1 GHz at high radiation duty factors and beam current, presumably due to the cavity thermal expansion by a heating, but the tunable range was not significantly changed. The frequency tunability facilitated the optimization of the DNP resonance condition without time-consuming field-sweep of the high-resolution NMR magnet, and enabled us to observe substantial enhancement of the SSNMR signal (eDNP = 12 at 90 K).
TL;DR: In this article, the authors presented a high precise high precise THz technique (frequency synthesizers and spectrometer) and its applications for noninvasive medical diagnostics and security systems.
Abstract: In the paper we present a high precise THz technique (frequency synthesizers and spectrometer) and its applications for noninvasive medical diagnostics and security systems. The cornerstone of the presented devices is multipliers and mixers based on quantum superlattice structures. The multipliers based on superlattice structures are shown to be more effective than Schottky diodes and provide THz radiation up to 8.1 THz.
TL;DR: In this article, the authors obtained the diagnostic images of cancerous tumors by employing the THz molecular imaging (TMI) technique which measured the response change by surface plasmon resonance induced on the surface of nanoparticles with a irradiation of near-infrared (NIR) beam.
Abstract: We obtained the diagnostic images of cancerous tumors by employing the THz molecular imaging (TMI) technique which measured the THz response change by surface plasmon resonance induced on the surface of nanoparticles with a irradiation of near-infrared (NIR) beam. To demonstrate the principle of the TMI technique, THz images of tissues with nanoprobes were observed and compared with THz only images. The sensitivity of TMI was further enhanced by adopting a THz differential measurement technique, which was realized by modulating the NIR beams. By employing this differential TMI technique, the diagnostic images of cancerous tumors were obtained ex vivo and in vivo in the preclinical stage. These images indicated the feasibility of applying the differential TMI technique in the clinical stage.
TL;DR: In this article, the phase unwrapping method was used to recover the constitutive parameters of a metamaterial slab showing negative refractive index over the 9-12 GHz frequency range.
Abstract: The constitutive parameters of a metamaterial slab showing negative refractive index over the 9-12 GHz frequency range are unambiguously retrieved from complex scattering parameters upon using the phase unwrapping method. Such a technique relies on properly adding to the phase of the complex transmission coefficient a stepwise function constructed from critical frequencies at which the phase of the transmission coefficient reaches ∓ π.
TL;DR: Transmission spectra of wet human teeth and dentin slices, together with blood of different flow rates, make it possible to find the optimum light frequency for an all-optical determination of pulpal blood flow and, consequently, for clinically diagnosis of tooth vitality.
Abstract: Transmission spectra of wet human teeth and dentin slices, together with blood of different flow rates were investigated. The measurements carried out over a wide spectral range, from visible light down to terahertz radiation. The results make it possible to find the optimum light frequency for an all-optical determination of pulpal blood flow and, consequently, for clinically diagnosis of tooth vitality.
TL;DR: In this article, the first gyrotron with an internal mode convertor has been developed in Research Center for Development of Far-Infrared Region, University of Fukui (FIR FU).
Abstract: Development of gyrotrons with an internal mode convertor has started in Research Center for Development of Far-Infrared Region, University of Fukui (FIR FU). As the first gyrotron of such a kind, we have designed and manufactured Gyrotron FU CW GI. It operates at 203 GHz at fundamental cyclotron resonance. We have designed a cavity and a mode convertor under some constraints such as reuse of an electron gun and small diameter of a magnet bore. Designed output power is about 1 kW. We have succeeded in observation of a circular radiation pattern. The maximum observed output power is 0.5 kW for the setting cathode voltage of 20 kV and the beam current of 0.5 A. This success makes gyrotron development in FIR FU to proceed to a new stage.
TL;DR: Terahertz systems can profit from technologies developed originally for telecom applications as discussed by the authors, and ways towards CW systems with highest flexibility and excellent performance at reasonable costs are sketched. But they do not consider how to use CW for wireless communications.
Abstract: Terahertz systems can profit from technologies developed originally for telecom applications. Recent developments on telecom-based key devices are summarized and ways towards CW systems with highest flexibility and excellent performance at reasonable costs are sketched.
TL;DR: In this paper, a numerical study of self-complementary antennas on substrate lenses made of high-permittivity dielectric material was performed in the terahertz band at frequencies up to 5.0 THz.
Abstract: This paper presents a numerical study of self-complementary antennas on substrate lenses made of high-permittivity dielectric material. Bowtie, logarithmically periodic, and logarithmic spiral antennas with the same outer and inner dimensions were selected for study, and their overall performances were compared in the terahertz band at frequencies up to 5.0 THz. The resonance and radiation characteristics of the three antennas were investigated in terms of input impedance, directivity, and radiation efficiency, using a full electromagnetic simulator. This study provides useful guidelines and partially solves the difficult problems of choosing the proper feed and optimizing the lens structure for a THz broadband integrated lens antenna.
TL;DR: In this article, a photoconductive (PC) antenna design for efficient generation and detection of terahertz (THz) pulsed radiation is discussed, and the results reveal valuable insights on the design of an efficient, compact, and cost-effective THz time-domain spectroscopy system based on 1.55-μm fs laser sources.
Abstract: Recent studies on the techniques and development of photoconductive (PC) semiconductor devices for efficient generation and detection of terahertz (THz) pulsed radiation are reported. Firstly, the optimization of PC antenna design is discussed. The PC detection of THz pulsed radiation using low-temperature grown GaAs with 1.55-μm wavelength probe is then described. Finally, the enhancement of THz radiation from InSb by using a coupling lens and magnetic field is investigated. These results reveal valuable insights on the design of an efficient, compact, and cost-effective THz time-domain spectroscopy system based on 1.55-μm fs laser sources.
TL;DR: In this article, a continuous-wave (CW) terahertz (THz) imaging with a horn antenna is proposed to enhance the spatial resolution of a THz imaging system.
Abstract: Continuous-wave (CW) terahertz (THz) imaging with a horn antenna is proposed to enhance the spatial resolution of a THz imaging system. The attached waveguide that is smaller than the wavelength can easily increase the spatial resolution, and the optimized horn flare can significantly increase the transmission power. Consequentially, transmission THz images of a phantom obtained by the amplitude signal using a 0.2 THz wave reveal that the spatial resolution is achieved up to 500 μm. Also, the transmitted power is increased up to 6 times higher compared to the pinhole aperture. The feasibility of CW THz imaging with a horn antenna is demonstrated by the inspection of the organic samples inside food resulting in a relatively high sensitivity for soft organic samples compared with the sensitivity of X-ray imaging to this kind of samples.
TL;DR: In this article, a ground-based synthetic aperture radar (GB-SAR) was used to detect foreign object debris (FOD)-type objects on the ground using millimeter-wave imaging.
Abstract: In this paper, millimeter-wave imaging of foreign object debris (FOD)-type objects on the ground is studied with the help of ground-based synthetic aperture radar (GB-SAR) technique To test the feasibility of detecting runway FODs with this technique, some preliminary experiments are conducted within short antenna-to-target ranges of small imaging patches An automated stripmap GB-SAR system with stepped-frequency transmission is constructed together with a quasi-monostatic data collection operation The imaging experiments for various braces and screws are then carried out by using 32–36 GHz and 90–95 GHz frequency bands of the millimeter-wave Images reconstructed by a matched-filter based algorithm are analyzed to determine the proper system parameters for an efficient imaging and to comprehend the factors against a successful detection Results demonstrate the capability of GB-SAR imaging in accurately locating these FOD-like targets under near-range operating conditions
TL;DR: In this article, the authors used terahertz time-domain spectroscopy and Fourier transform infrared spectrograms to investigate the conductivities of one-dimensional and two-dimensional electrons in films of highly aligned SWCNTs and gated large-area graphene.
Abstract: Low-dimensional carbon nanostructures, such as single-wall carbon nanotubes (SWCNTs) and graphene, offer new opportunities for terahertz science and technology. Being zero-gap systems with a linear, photon-like energy dispersion, metallic SWCNTs and graphene exhibit a variety of extraordinary properties. Their DC and linear electrical properties have been extensively studied in the last decade, but their unusual finite-frequency, nonlinear, and/or non-equilibrium properties are largely unexplored, although they are predicted to be useful for new terahertz device applications. Terahertz dynamic conductivity measurements allow us to probe the dynamics of such photon-like electrons, or massless Dirac fermions. Here, we use terahertz time-domain spectroscopy and Fourier transform infrared spectroscopy to investigate terahertz conductivities of one-dimensional and two-dimensional electrons, respectively, in films of highly aligned SWCNTs and gated large-area graphene. In SWCNTs, we observe extremely anisotropic terahertz conductivities, promising for terahertz polarizer applications. In graphene, we demonstrate that terahertz and infrared properties sensitively change with the Fermi energy, which can be controlled by electrical gating and thermal annealing.
TL;DR: In this article, the authors used Terahertz time-domain spectroscopy (THz-TDS) to investigate the complex dielectric function of water solutions containing different ions.
Abstract: We have used Terahertz time-domain spectroscopy (THz-TDS) to investigate the complex dielectric function of water solutions containing different ions. Using HCl and NaCl solutions with different concentrations we study the changes of the dielectric response introduced by the ions. We find a linear increase of the real and imaginary part of the dielectric function compared with pure water with increasing ion concentrations. We use an expanded model for fitting the dielectric function based on a combination of a Debye relation and damped harmonic oscillators for the anions and cations. A good agreement between the model and the experimental results is obtained.
TL;DR: By using intense terahertz (THz) monocycle pulses, nonlinear light-matter interaction in aligned semiconducting single-walled carbon nanotubes (SWNTs) embedded in a polymer film was investigated in this article.
Abstract: By using intense terahertz(THz) monocycle pulses, nonlinear light-matter interaction in aligned semiconducting single-walled carbon nanotubes(SWNTs) embedded in a polymer film was investigated. THz electric-field-induced ultrafast Stark effect of one-dimensional excitons in SWNTs was observed at room temperature, suggesting the potential functionality of SWNTs for high speed electro-optic devices operating at telecom wavelength with a THz bandwidth. When the peak electric field amplitude exceeds 200 kV/cm, the generation of excitons by the THz pump becomes prominent. The mechanism is described by the above-gap excitation of electrons and holes in SWNTs due to the impact excitation process induced by the intense THz electric field.
TL;DR: In this article, the most important developments in the technology of THz photoconductive antennas made from ion-bombarded semiconductors are reviewed and the structural, optical and electrical properties of various ion-battered semiconductor materials are discussed.
Abstract: We review the most important developments in the technology of THz photoconductive antennas made from ion-bombarded semiconductors. We describe the structural, optical and electrical properties of various ion-bombarded semiconductors and discuss the nature of the defects introduced by the ion bombardment technique and their impact on the characteristics of THz photoconductive antennas. Finally, we present the performances achieved by photoconductive antennas based on ion-bombarded semiconductors for optical excitation at various wavelength.