This paper focuses on understanding the THz-phonon mediated transport of polarons in biomolecules, with particular attention on polaron transport in DNA. In order to exploit biology-based approaches to realizing new electronic systems, it is necessary to understand the electrical transport properties and THz-phonon interactions of biomolecules that portend applications both as electrically conductive wires and as structures that facilitate the chemically-directed assembly of massively integrated ensembles of nanoscale semiconducting elements into terascale integrated networks. Special attention is given to charge transport in biomolecules using indirect-bandgap colloidal nanocrystals linked with biomolecules.

The electro-optical properties of organic and bio-molecules have been previously investigated that have potential for selectively filtering and controlling the transmission of electromagnetic signals with carrier frequency in the THz band. Specifically, retinal isomers have been studied because they exhibit the type of THz characteristics needed for the design of molecular electronic devices. Here, the goal is to define bio-molecular filters that have utility in integrated platforms for sensing THz spectral signatures. According to our calculations, retinal isomers demonstrate the type of properties needed for the design of molecule-based optically-controllable filters in THz region. An initial challenge for this type of bio-architecture is the integration of the retinal-based components into conventional semiconductor devices. This paper presents a potential methodology for achieving such integrated sensor components. In particular, by modifying one end of retinal with a thiol linker, it is possible to chemically graft the retinal to gold surfaces. Therefore, since two-dimensional gold nanostructure arrays can be produced by depositing gold onto pit-patterned highly oriented pyrolytic graphite (HOPG) surface or semiconductor substrates, this approach could be applied to achieve large-scale integration of bio-molecular devices. This paper will report on simulations of ground state and metastable state energies, along with the associated THz spectra of the retinal isomeric molecule connected to a gold atom via the link of a cysteine molecule. In addition to the retinal isomers, this paper also investigates another isomer trans- and cis- stilbene and presents results suggesting that stilbene may also be a good candidate for molecular electronics. Hence, this paper provides results for the THz spectral characteristics and required optical excitations for a novel type of bio-device for sensing.

The convergence of terahertz spectroscopy and single molecule experimentation offer significant promise of enhancement in sensitivity and selectivity in molecular recognition, identification and quantitation germane to military and security applications. This presentation reports the results of experiments which address fundamental barriers to the integration of large, patterned bio-compatible molecular opto-electronic systems with silicon based microelectronic systems. The central thrust of this approach is sequential epitaxy on surface bound single stranded DNA one-dimensional substrates. The challenge of producing highly structured macromolecular substrates, which are necessary in order to implement molecular nanolithography, has been addressed by combining "designer" synthetic DNA with biosynthetically derived plasmid components. By design, these one dimensional templates are composed of domains which contain sites which are recognized, and therefore addressable by either complementary DNA sequences and/or selected enzymes. Such design is necessary in order to access the nominal 2 nm linewidth potential resolution of nanolithography on these one-dimensional substrates. The recognition and binding properties of DNA ensure that the lithographic process is intrinsically self-organizing, and therefore self-aligning, a necessity for assembly processes at the requisite resolution. Another requirement of this molecular epitaxy approach is that the substrate must be immobilized. The challenge of robust surface immobilization is being addressed via the production of the equivalent of molecular tube sockets. In this application, multi-valent core-shell fluorescent quantum dots provide a mechanism to prepare surface attachment sites with a pre-determined 1:1 attachment site : substrate (DNA) molecule ratio.

An implementation and review of our recently proposed scenarios [1-13] for processing and transfer of information is presented. We will show how computing using molecular potentials and vibronics communications can be adapted to upgrade present charge-current approaches, which are already in the limits of their technical and perhaps physical limits because their immense heat dissipation problems. It has long been recognized the many advantages and potential payoffs that the development of THz based applications could bring to the military and security areas. We focus our implementation in the development of THz sensing and imaging for a wide range of military and security applications as systems operating at these frequencies have shown to have high sensitivity and selectivity when applied to the analysis of molecules. These are properties that are highly desirable in the design of sensing tools for the detection, identification and characterization of chemical and biological agents; and in the design of monitoring tools for the detection of these substances, both in closed and, with less selectivity, in open environments. Many materials of interest for security applications including explosives, and chemical and biological agents have characteristic THz fingerprints which set them apart from non-hazardous materials, thus allowing their identification. As molecular electronics techniques become available [14], they could sharply improve our present detection and sensing techniques.

Spin dependent device transport, where the distinction between spin up and spin down carriers arises from the presence of local diluted magnetic semiconductor (DMS) regions, offers the possibility of magnetic field control of transport. This paper describes through the use of numerical solutions to the spin dependent Wigner distribution function, the means by which dilute magnetic semiconductors layers can lead to a magnetic field dependent break in the symmetry of superlattice structures. Specific examples area given in which all of the barriers are composed of DMS layers, and as a function of magnetic field there is an alteration in the relative population of spin up and spin down carriers. The symmetry breaking structure consists of a superlattice with a single DMS layer. As a function of magnetic field the barrier is higher for one spin state and lower of the other leading to a local region of charge accumulation that is not present in periodic lattice. The application of this broken symmetry to the creation of nucleation sites for high field domains, and in some cases alter the properties of the propagating domain is discussed.

A concept for a terahertz laser in vapor-phase-grown homoepitaxial GaAs with spatially periodic doping profile was theoretically explored. Monte Carlo simulation of hole transport in multilayer delta-doped p-GaAs/GaAs structures in crossed electric and magnetic fields was performed to investigate possibilities of the terahertz amplification on intervalence-band light-to-heavy hole transitions. The results are compared to those calculated for uniformly doped bulk p-GaAs and recently proposed p-Ge/Ge structures. The improvement in the gain for delta-doped p-GaAs structures is about ~2-3 times over bulk p-GaAs. Terahertz laser generation in the considered GaAs device concept appears feasible, as is growth of structures with active thicknesses sufficient to support quasioptical cavity solutions at 100 μm vacuum wavelengths. Potential applications for the considered laser device include sensing of chem/bio agents and explosives, biomedical imaging, non-destructive testing, and communications.

A novel optically-triggered (OT) interband resonant-tunneling-diode (I-RTD) device (based on AlGaSb/InAs/AlGaSb heterostructures) concept for generating terahertz (THz) frequency oscillations has been previously presented that shows promise for achieving enhanced output power levels under pulsed operation. The main concept is to utilize novel nanoscale mechanisms to achieve an externally driven relaxation oscillation that consists of two phases. Namely, the first phase is a valence band (VB) well hole-charging transient produced by a natural Zener (interband) tunneling process and the second is a discharging transient induced by optical annihilation of the VB well hole-charge by externally-injected photon flux. While the initial simulation results for a practical diode-laser implementation clearly show the superiority of this new oscillator concept (i.e., excellent output power capability, ~10mW, over broad portions of the THz regime, ~300-600GHz), the specific optical-triggering conditions required by the AlGaSb/InAs based material systems (i.e., photonic-energy ~4.7 μm, intensity level ~3.5x10⁷ W/cm² and a pulse repetition frequency (PRF) equal to the THz oscillation period) are technically too demanding to meet for continuous-wave (CW) mode operation. Hence, this paper will report on variations and extensions of the original OT-I-RTD oscillator concept. Specifically, modifications to the device structure will be considered to allow for OT operation at 1.55 μm where the optical technology is more robust. Here the specific focus will be in the introduction of In_1-xGa_xAs /GaSb_yAs_1-y hetero-systems and the application of band-engineering to assess the potential of a 1.55 μm based OT-I-RTD oscillator design.

A family of methods has been developed recently for generation, control, and visualization of terahertz (THz) phonon-polaritons in polar crystals¹. Phonon-Polaritons (below simply "polaritons") are admixture of polar lattice vibration and electromagnetic modes of similar frequency and wave vector. In this paper, we discuss the possible application of phonon-polariton spectroscopic imaging to the chemical sensing. Advantages of the polariton imaging for the use of sensor application include (1) No need for THz optics, (2) Compactness of the cell, and (3) Quick acquisition of time domain signal. In this paper, we present experimental results of solid and liquid samples, and show simultaneous measurement of multiple samples.

Novels diffractive element in the THz waveband offers the potential to realize novel types of devices for communications, sensing, integrated optics, networks, transmission lines, and so on. To this end, diffractive planar elements fabricated on non-flat surfaces make it possible to enrich the "pool of devices" for applications including integrated optics at different waveband, including THz, and to design elements with novel properties and potentials. This can be illustrated most clearly using as an example optical element such as that for optical polychromatic computers. For instance, the diffractive element discussed above can be used as a nonlinear device for polychromatic radiation or multiplexer or a focusing element with selectivity in the multimode regime. Frequency characteristics for such elements are determined by the extent of concavity (convexity) of the surface of the element and by the direction of incidence wave onto it. Therefore, when working on a wavelength λ is not equal to λ₀, the position of the focusing area in space (the amount of its displacement) and focusing properties should depend on the direction of incidence of the radiation. Hence, it is possible to distinguish between a signal incident on the "tip" of the element from that falling on its "base," simply by placing radiation receivers at the corresponding points in space. Thus, in this paper we will present detailed simulation results obtained using a parallel FDTD method and the application of the proposed device to focusing and frequency-selective properties of flat conical diffractive elements in THz waveband.

For imaging and remote sensing applications, the noise of the THz detector must be minimized. The quantum 1/f theory is introduced and used to obtain analytical expressions of noise in n⁺p diodes, Schottky diode THz detectors and mixers, a new type of suggested MEMS resonator based Thz detectors, QWIPs and bolometers. For the DAR and for THz communications we also consider phase noise in RTD and GaN/AlGaN HFET based THz generators.

As short range, ground based, surveillance systems operating at terahertz frequencies continue to evolve, increasing attention is being directed towards the behavior of dielectric materials at terahertz frequencies as well as the behavior of optical components used to control terahertz radiation. This work provides an overview of several terahertz optical components such as frequency selective filters, laser output couplers, artificial dielectrics, and electromagnetic absorbers. In addition, a database was established that contains terahertz properties of common materials that have been largely unexplored in this region of the spectrum. The database consists of transmittance and reflectance spectra of a variety of materials measured using Fourier transform infrared spectroscopy techniques from 175 GHz - 2 THz. In addition, ultra-stable, CO₂ optically pumped, far-infrared gas lasers were used to collect fixed-frequency transmittance data at 326 GHz, 584 GHz, and 1.04 THz. A Gunn oscillator was used for measurements at 94 GHz.

This paper focuses on the establishment of methodologies for the successful application of first principles theoretical analyses in the understanding of the terahertz spectroscopy of molecular solids, particularly high-energy materials. A solid-state density functional theoretical study has been performed on the high explosive pentaerythritol tetranitrate (PETN) in order to address the relationships between the choice of computational parameters and the predictions of molecular and solid-state properties, such as molecular geometries, intermolecular interactions within the crystal cell, charge distributions, and solid-state vibrations in the terahertz (3 to 200 cm^-1) region. This investigation has lead to the conclusion that the BP functional has the best overall performance and the choice of basis set is the most critical theoretical variable. Varying other parameters such as grid size, orbital cut-off, and convergence criteria lead to negligible differences among the calculations.

We apply THz imaging technology to evaluate fire damage to a variety of carbon fiber composite samples. The majority of carbon fiber materials have polarization-dependent reflectivities in the THz frequency range, and we show how the polarization dependence changes versus the burn damage level. Additionally, time domain information acquired through a THz time-domain spectroscopy (TDS) system provides further information with which to characterize the damage. The technology is discussed in terms of nondestructive testing applications to the defense and aerospace industries.

The development of an effective biological (bio) agent detection capability based upon terahertz (THz) frequency absorption spectra will require insight into how the constituent cellular components contribute to the overall THz signature. In this work, the specific contribution of ribonucleic acid (RNA) to THz spectra is analyzed in detail. Previously, it has only been possible to simulate partial fragments of the RNA (or DNA) structures due to the excessive computational demands. For the first time, the molecular structure of the entire transfer RNA (tRNA) molecule of E. coli was simulated and the associated THz signature was derived theoretically. The tRNA that binds amino acid tyrosine (tRNAtyr) was studied. Here, the molecular structure was optimized using the potential energy minimization and molecular dynamical (MD) simulations. Solvation effects (water molecules) were also included explicitly in the MD simulations. To verify that realistic molecular signatures were simulated, a parallel experimental study of tRNAs of E. coli was also conducted. Two very similar molecules, valine and tyrosine tRNA were investigated experimentally. Samples were prepared in the form of water solutions with the concentrations in the range 0.01-1 mg/ml. A strong correlation of the measured THz signatures associated with valine tRNA and tyrosine tRNA was observed. These findings are consistent with the structural similarity of the two tRNAs. The calculated THz signature of the tyrosine tRNA of E. coli reproduces many features of our measured spectra, and, therefore, provides valuable new insights into bio-agent detection.

Terahertz imaging sensors are being considered for providing a concealed weapon identification capability for military and security applications. In this paper the difficulty of this task is assessed in a systematic way. Using imaging systems operating at 640 GHz, high resolution imagery of possible concealed weapons has been collected. Information in this imagery is removed in a controlled and systematic way and then used in a human observer perception experiment. From the perception data, a calibration factor describing the overall difficulty of this task was derived. This calibration factor is used with a general model of human observer performance developed at the US Army Night Vision and Electronic Sensors Directorate to predict the task performance of observers using terahertz imaging sensors. Example performance calculations for a representative imaging sensor are shown.

This paper reports on the THz frequency characterization of highly diluted mixtures of Bacillus Subtilis (BG) cells and spores pressed into pellets with high densities of polyethylene (PE) micro-powders. This technique of forming matrices of sparsely distributed biological (bio) materials by mixing them into larger concentrations of PE is one that has been previously applied to study spectral signature phenomenology. In particular, previously results have suggested that isolating the microscopic bio-particles leads to an enhancement of the THz signatures - i.e., yielding sharper and stronger absorption resonances. However, it is important to minimize the influence of etalon effects because they can introduce sharp artificial fringes in the transmission spectra that obscure the underlying THz signatures. This paper will present results from optimally prepared PE matrices containing reduced concentrations of BG cells and spores. Here, the BG-PE matrices are of thickness of approximately 30 micrometers and contain BG concentrations from 0.1 to 0.3 %. As will be shown, these thinner layers allow for the more accurate characterization of smaller amounts of bio samples and reveal new information on the THz signatures of BG cells and spores. In particular these results show very close correlations between the spectra of BG cells and spores and suggest both contain common genetic components. These studies provide new information that will be useful in the future development of THz-based sensors.

We report the sensing of explosive materials by using terahertz (THz-TDS) time domain spectroscopy at standoff distance. The 0.82 THz absorption peak of RDX is observed at a distance up to 30 m away from the emitter and receiver. This result supports the application of THz-TDS technique in remote sensing and detection of explosives.

Using the widely-tunable monochromatic THz source developed by us recently, we have directly measured the transmission spectra of a few diatomic and triatomic molecules in the THz region. In addition, using the FTIR acquired from Bruker Optics, we have also measured the transmission spectra of the same molecules. As a result, we have observed distinct ro-vibrational and rotational transitions in two carbon monoxide isotopic variants, nitrogen dioxide, and carbon dioxide. After carefully analyzing these transmission spectra, we have identified a series of the transition peaks for each chemical species. The frequencies of the transition peaks measured by using two different methods agree with each other well. In order to determine the rotational constants for each chemical species, it is essential for us to accurately measure the transmission spectrum of the vapor of the chemical species in both of the mid-IR and THz regions.

We report the first systematic study of broadband THz wave generation by using the focused femtosecond laser beams in ambient air. Generations of pulsed THz waves using air as the nonlinear media have been previously demonstrated by Cook et al. and Hartmut et al. We measured dependence of generated THz wave on the polarization, amplitude and phase of the individually controlled fundamental and second harmonic beams. Our results confirms that four-wave-mixing rectification is the major mechanism of THz wave generation with mixing the fundamental and the SH beams in air. This work is significant by providing the feasibility of standoff distance detection greater than 50 meters.

We demonstrate a large area time domain terahertz (THz) imaging system capable of scanning 1 meter square area in less than 20-100 minutes for several security applications. The detection of concealed explosives; metallic and non-metallic weapons (such as ceramic, plastic or composite guns and knives); and flammables in luggage, packages and personnel has been demonstrated. Transmission mode images of luggage containing threat items are discussed. Reflection mode images of luggage and personnel are discussed. Time domain THz images can be analyzed for 3 dimensional and volumetric information. Time domain THz images have advantages over coherent narrow band imaging methods, with freedom from standing wave artifacts and with greater ability to discard irrelevant or intervening reflections through time discrimination.

Terahertz (THz) spectra of two TNT-related compounds (4-NT and 2,6-DNT) are investigated using Fourier transform infrared spectroscopy (FTIR) and THz time-domain spectroscopy (THz-TDS) between 0.1 to 20 THz. The Density Functional Theory (DFT) is applied to calculate the THz spectra of these two compounds. The transmission, diffuse reflection, and calculated spectra are in good agreement. The measured THz resonance lines from the transmission and diffuse reflectance spectra are assigned based on DFT simulation. The observed THz signatures imply that the THz spectrum has potential for standoff detection of explosive and related compounds (ERCs) in the THz range.

In response to the growing interest in developing terahertz imaging systems for concealed weapons detection, the Submillimeter-Wave Technology Laboratory (STL) at the University of Massachusetts Lowell has produced full-body terahertz imagery using coherent active radar measurement techniques. The proof-of-principle results were readily obtained utilizing the compact radar range resources at STL. Two contrasting techniques were used to collect the imagery. Both methods made use of in-house transceivers, consisting of two ultra-stable far-infrared lasers, terahertz heterodyne detection systems, and terahertz anechoic chambers. The first technique involved full beam subject illumination with precision azimuth and elevation control to produce high resolution images via two axis Fourier transforms. Imagery collected in this manner is presented at 1.56THz and 350GHz. The second method utilized a focused spot, moved across the target subject in a high speed two dimensional raster pattern created by a large two-axis positioning mirror. The existing 1.56THz compact radar range was modified to project a focused illumination spot on the target subject several meters away, and receive the back-reflected intensity. The process was repeated across two dimensions, and the resultant image was assembled and displayed utilizing minimal on-the-fly processing. Imagery at 1.56THz of human subjects with concealed weapons are presented and discussed for this scan type.

No Abstract.

We report experimental results for the optical responsivity and noise-equivalent power (NEP) of quasi-optically coupled, room-temperature ErAs-InGaAlAs rectifier diodes. Four-micron-diameter diodes were flip-chip coupled to self-complementary log-periodic and square-spiral antennas, and characterized with a 104-GHz Gunn diode oscillator coupled to the rectifiers through variable attenuators, a feedhorn, an aspherical polymeric lens, and a Si hyperhemisphere. The log-periodic mounted device displayed a responsivity and specific NEP' of 0.9x10³ V/W and 1.2x10^-12 W/Hz^1/2, respectively. The square-spiral mounted device displayed a responsivity and NEP' of 1.2x10³ V/W and 2.0x10^-12 W/Hz ^1/2, respectively. All values were measured at a post-detection center frequency of 33 Hz.

Terahertz radiation, which lies between microwave and infrared, has been shown to have the potential to use very low levels of this non-ionising radiation to detect and identify objects, such as weapons and explosives, hidden under clothing. This paper describes recent work on the development of prototype systems using terahertz to provide new capabilities in people screening. In particular, it explores how hyperspectral terahertz imaging and the use of both specularly reflected and scattered terahertz radiation can enhance the detection of threat objects.

To evaluate the potential of THz imaging systems for mail and luggage inspection we study a set of letters containing different hazardous items. The samples are investigated with three different THz systems available in our group: A microwave based system working around 100 GHz, a THz time-domain system and a THz gas laser. We provide a comparative discussion on our results and the advantages and disadvantages of each system.

The terahertz region of the electromagnetic spectrum has unique properties that make it especially useful for imaging and spectroscopic detection of concealed weapons, explosives and chemical and biological materials. However, terahertz energy is difficult to generate and detect, and this has led to a technology gap in this frequency band. Nonlinear diodes can be used to bridge this gap by translating the functionality achieved at microwave frequencies to the terahertz band. Basic building blocks include low-noise mixers, frequency multipliers, sideband generators and direct detectors. These terahertz components rely on planar Schottky diodes and recently developed integrated diode circuits make them easier to assemble and more robust. The new generation of terahertz sources and receivers requires no mechanical tuning, yet achieves high efficiency and broad bandwidth. This paper reviews the basic design of terahertz transmitters and receivers, with special emphasis on the recent development of systems that are compact, easy to use and have excellent performance.

From a commercial point of view the terahertz region from 100GHz to 10THz remains largely unexplored. The main reason for this has been the lack of readily available, rugged solid state detection technology that has sufficient sensitivity for applications such as passive imaging. This is particularly true when arrays of such detectors are considered. Until recently the main technology driver has been ground based Radio Astronomy. Here the drive for absolute noise performance has focused effort towards the development of cryogenically cooled detection techniques, primarily utilising liquid Helium cooled superconducting devices. Commercially, the use of such cryogens will usually rule out most potential high volume applications largely for practical reasons such as running cost, convenience and health and safety issues. In order to kick-start the commercial exploitation of the terahertz region an alternative detection technology is required. The detector technology reported here has its origins in remote sensing applications where the low noise performance requirements are not quite so stringent. Here, reliability, low power operation, low mass and volume are combined with rugged design. These so happen to be the main prerequisites for any commercial solution. For space borne technology, however, cost is not usually an issue and correspondingly until the application of manufacturing methodology the technology has been prohibitively expensive to adopt. This paper reports on the current state of the art in solid state detector array technology aimed at exploiting commercial applications in the terahertz region. An overview of the technology background is provided combined with a forward look outlining the areas where rapid technology advancement can be expected. The utilisation of this detector technology in the application of real time passive terahertz imaging will be shown.

Developments in terahertz sources include compacted electron beam systems, optical mixing techniques, and multiplication of microwave frequencies. Although significant advances in THz science have been achieved, efforts continue to obtain source technologies that are more mobile and suitable for field deployment. Strategies in source development have approached generation from either end of the THz spectrum, from up-conversion of high-frequency microwave to down-conversion of optical frequencies. In this paper, we present the design of a THz source which employs an up-conversion method in an assembly that integrates power supply, electronics, and radiative component into a man-portable unit for situations in which a lab system is not feasible. This unit will ultimately evolve into a ruggedized package suitable for use in extreme conditions, e.g. temporary security check points or emergency response teams, in conditions where THz diagnostics are needed with minimal planning or logistical support. In order to meet design goals of reduced size and complexity, the inner workings of the unit ideally would be condensed into a monolithic active element, with ancillary systems, e.g. user interface and power, coupled to the element. To attain these goals, the fundamental component of our design is a THz source and lens array that may be fabricated with either printed circuit board or wafer substrate. To reduce the volume occupied by the source array, the design employs a metamaterial composed of a periodic lattice of resonant elements. Each resonant element is an LC oscillator, or tank circuit, with inductance, capacitance, and center frequency determined by dimensioning and material parameters. The source array and supporting electronics are designed so that the radiative elements are driven in-phase to yield THz radiation with a high degree of partial coherence. Simulation indicates that the spectral width of operation may be controlled by detuning of critical dimensions. We discuss simulation results and frequency response for a single element and the source array, and the component density necessary to achieve target output intensities. After obtaining the primary objective of a designing a compact fieldable THz source, the secondary goal is developing a fabrication recipe which draws upon existing methods in PCB/integrated circuit manufacturing to obtain a device that may be produced at volume with high yield.

The temperature resolving power (NETD) of millimeter wave imagers based on InP HEMT MMIC radiometers is typically about 1 K (30 ms), but the MMIC technology is limited to operating frequencies below ~ 150 GHz. In this paper we report the first results from a pixel developed for an eight pixel sub-array of superconducting antenna-coupled microbolometers, a first step towards a real-time imaging system, with frequency coverage of 0.2 - 3.6 THz. These detectors have demonstrated video-rate NETDs in the millikelvin range, close to the fundamental photon noise limit, when operated at a bath temperature of ~ 4K. The detectors will be operated within a turn-key cryogen-free pulse tube refrigerator, which allows for continuous operation without the need for liquid cryogens. The outstanding frequency agility of bolometric detectors allows for multi-frequency imaging, which greatly enhances the discrimination of e.g. explosives against innoncuous items concealed underneath clothing.

Experimental results of homodyne terahertz interferometric 1-D and 2-D imaging are presented. Continuous waves at 0.25-0.3 THz are used to detect a metal object behind a barrier. The performance of an N element detector array is imitated by only one detector placed at N positions. The reconstructed images are in a good agreement with theoretical predictions. The terahertz interferometric imaging method can be used in defense and security applications to detect concealed weapons, explosives as well as chemical and biological agents.

Recent developments in active millimeter/THz waves high-quality 3D real-time imaging for security applications are discussed. Such type of imaging systems affords a compact, simple, fast and relatively low-cost system.

In the recent years, multifarious devices, systems and applications working in the THz frequency domain have been brought to life. Many of them are meant for security and military purposes, such as non-invasive detection of explosives, weapons, biological and chemical agents, etc. The problem, however, is not only with the detection and ever-increasing accuracy of measurements but often with understanding of what is seen; discriminating between the objects and the materials they are made of. It seems especially important to create an automatic or semi-automatic system and thus release the operator from constant watching. The proposed solution is an adaptive intelligent system based on usage of THz waves as the probing signal by means of mathematical statistics. Time series analysis is one of the forms that is employed in this research. The adaptivity of the system to various objects under investigation is based on the data base installed as well as on the possibility of changing of the detection system's parameters and modes of operation depending on the signal received from the identified objects. In other words, the suggested method allows for the detection system to switch from, say, the metal object mode to the pharmaceutical one and so forth.

We demonstrate the first long wave infrared (LWIR) transmission line design and characterization. Two of the widely used transmission-lines: coplanar striplines (CPS) and microstrip (MS) lines are characterized at IR frequency (28.3THz), in terms of transmission line parameters: characteristic impedance (Z_o), attenuation constant (α) and effective index of refraction (n_eff), through modeling, fabrication and measurement. These transmission-line parameters cannot be directly measured, what can be measured is the antenna response. So we compute, measure and compare the response of the dipole antenna connected to these transmission lines as a function of transmission-line length. The response depends on the transformation of antenna impedance along the transmission-line length according to the transmission-line parameters (Z_o, α and n_eff ) of the line. Comparison of measured and computed response validates extracted transmission-line parameters. This paper demonstrates excellent agreement between measured and computed response for both types of transmission-lines under study.