Terahertz digital off-axis holography is demonstrated using a Mach-Zehnder interferometer with a highly coherent, frequency tunable, continuous wave terahertz source emitting around 0.7 THz and a single, spatially-scanned Schottky diode detector. The reconstruction of amplitude and phase objects is performed digitally using the angular spectrum method in conjunction with Fourier space filtering to reduce noise from the twin image and DC term. Phase unwrapping is achieved using the dual wavelength method, which offers an automated approach to overcome the 2π phase ambiguity. Potential applications for nondestructive test and evaluation of visually opaque dielectric and composite objects are discussed.

We examine and compare the diagonal magnetoresistance, R xx , and the photo-voltage induced by microwave (42 ≤ f < 300GHz) and terahertz (f ≥ 300GHz) photoexcitation in the high mobility quasi two-dimensional GaAs/AlGaAs system. The data demonstrate strong radiation-induced magneto-resistance oscillations in R xx to 360GHz. In addition, cyclotron resonance is observed in the photo-voltage to 725GHz. These results show that our high mobility GaAs/AlGaAs 2DES specimens remain photo-active in magnetotransport into the terahertz band.

Terahertz (THz) interferometric synthetic aperture tomography (TISAT) for confocal imaging within extended objects is demonstrated by combining attributes of synthetic aperture radar and optical coherence tomography. Algorithms recently devised for interferometric synthetic aperture microscopy are adapted to account for the diffraction-and defocusing-induced spatially varying THz beam width characteristic of narrow depth of focus, high-resolution confocal imaging. A frequency-swept two-dimensional TISAT confocal imaging instrument rapidly achieves in-focus, diffraction-limited resolution over a depth 12 times larger than the instrument's depth of focus in a manner that may be easily extended to three dimensions and greater depths.

Conventional, commercially available terahertz (THz) polarizers are made of uniformly and precisely spaced metallic wires. They are fragile and expensive, with performance characteristics highly reliant on wire diameters and spacings. Here, we report a simple and highly error-tolerant method for fabricating a freestanding THz polarizer with nearly ideal performance, reliant on the intrinsically one-dimensional character of conduction electrons in well-aligned carbon nanotubes (CNTs). The polarizer was constructed on a mechanical frame over which we manually wound acid-doped CNT fibers with ultrahigh electrical conductivity. We demonstrated that the polarizer has an extinction ratio of ∼−30 dB with a low insertion loss (<0.5 dB) throughout a frequency range of 0.2-1.1 THz. In addition, we used a THz ellipsometer to measure the Müller matrix of the CNT-fiber polarizer and found comparable attenuation to a commercial metallic wire-grid polarizer. Furthermore, based on the classical theory of light transmission through an array of metallic wires we demonstrated the most striking difference between the CNT-fiber and metallic wire-grid polarizers: the latter fails to work in the zero-spacing limit, where it acts as a simple mirror, while the former continues to work as an excellent polarizer even in that limit due to the one-dimensional conductivity of individual CNTs.

Mapping strain fields in visually opaque structural composites -for which failure is often sudden, irreparable, and even catastrophic -requires techniques to locate and record regions of stress, fatigue, and incipient failure. Many composite materials are transparent in the terahertz spectral region, but their strain history is often too subtle to recover. Here, terahertz metamaterials with strain-severable junctions are introduced that can identify structurally compromised regions of composite materials. Specifically, multi-layer arrays of aluminum meta-atoms were designed and fabricated as strip dipole antennas with a terahertz frequency resonance and a strong response to cross polarized radiation that disappears when local stress irreversibly breaks their bowtie-shaped junction. By spatially mapping the local polarimetric response of this metamaterial as a function of global strain, the regions of local stress extrema experienced by a visually opaque material may be visualized. This proof-of-concept demonstration heralds the opportunity for embedding metamaterial laminates within composites to record and recover their strain-dependent history of fatigue.The widespread proliferation of composite materials in civilian, industrial, and military sectors has created a need for tools to monitor their structural health and warn of incipient failure. Many techniques have been tried, including embedded sensors, laser surface mapping, acoustic transducers, x-ray imaging, and terahertz imaging concepts. [1][2][3][4][5][6] The opacity of most composites prevents the use of common optical polarimetric techniques for measuring photoelasticity, while stress-induced birefringence produces weak refractive index anisotropies at terahertz frequencies that are difficult to measure. [7,8] Many of these techniques can identify damaged regions, but none Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))