J. Decker

Bio: J. Decker is an academic researcher from University of Michigan. The author has contributed to research in topics: Terahertz radiation & Waveform. The author has an hindex of 2, co-authored 5 publications receiving 99 citations.

Time reversal and object reconstruction with single-cycle pulses

Abstract: We demonstrate the reconstruction of one- and two-dimensional objects by numerically backpropagating measured scattered terahertz transients. The spatial resolution determined by the Sparrow criterion is found to correspond to approximately 30% of the peak wavelength and 85% of the mean wavelength of the power spectrum of the single-cycle waveform.

Time reversal terahertz imaging

Abstract: We describe a technique for imaging in the terahertz regime using time reversal of single-cycle pulses. Specifically, the time-reversal symmetry of Maxwell's wave equation is exploited to reconstruct the transmission function of a diffracting aperture by inverting the diffracted fields. After deriving a time-reversed form of the Huygens-Fresnel diffraction integral, we demonstrate through simulation and experiment the reconstruction of one-dimensional and two-dimensional (2-D) objects. A means to obtain data efficiently for reconstruction of 2-D apertures is described. The spatial resolution determined by the Sparrow criterion is found to correspond to approximately 30% of the peak wavelength and 85% of the mean wavelength of the power spectrum of the single-cycle waveform. Finally, the modulation transfer function for the imaging method is simulated and is shown to be nearly diffraction-limited when compared to an ideal imaging system.

Time-reversed image synthesis of dielectric objects

Abstract: Summary form only given. Typically, the inverse problem has employed frequency domain techniques to reconstruct an object from directly measured scattered fields. Recently, time-domain approaches to the inverse problem have been demonstrated using both electromagnetic and acoustic pulses. More recently, we developed another time-domain imaging technique in which diffracted transients from amplitude-contrast (metallic) objects were used to reconstruct their spatial transmission functions. In a similar vein, we now demonstrate the effectiveness and completeness of this technique using 1D and 2D dielectric objects, for which the image arises from both amplitude and (perhaps even more importantly) phase contrast.

Time reversal and object reconstruction using single-cycle terahertz pulses

Abstract: Developments in optoelectronics for the generation and detection of singleand few-cycle terahertz pulses over the past 10 years have resulted in a heightened understanding of the diffraction and propagation of ultrashort electromagnetic transients. Particularly, the spatiotemporal shaping of singleand few-cycle THz pulses, as investigated by Bromage et al. and Budiarto et al. (1998), has served to verify the effects that diffraction through conductive apertures impose on such pulses. These same developments in optoelectronics have also resulted in numerous inventive applications for this radiation, whereby THz imaging technology has opened new applications in medical and industrial settings. We present novel form of imaging using mathematically reversed scattered fields to reconstruct objects under test. Similar to the innovations pioneered by Cheville et al. (1995) in impulse ranging with single-cycle THz pulses, we have performed an experiment that can serve as a scaled model for the diffraction of single-cycle pulses in other systems. For the two-fold study presented, the reconstruction of the electric field amplitude at any position on an object in one dimension was achieved by measuring the diffracted fields at several off-axis positions (with one object orientation). For a two-dimensional object, the reconstruction was accomplished by rotating the object about its central normal and measuring the scattered radiation at one off-axis position; consequently in both case, we are able to ascertain the shape of the diffracting object.

Terahertz imaging via time reversal using single-cycle pulses

Abstract: We demonstrate for the first time the reconstruction of one-and two-dimensional objects by numerically back-propagating scattered terahertz transients.

Imaging with terahertz radiation

Abstract: Within the last several years, the field of terahertz science and technology has changed dramatically. Many new advances in the technology for generation, manipulation, and detection of terahertz radiation have revolutionized the field. Much of this interest has been inspired by the promise of valuable new applications for terahertz imaging and sensing. Among a long list of proposed uses, one finds compelling needs such as security screening and quality control, as well as whimsical notions such as counting the almonds in a bar of chocolate. This list has grown in parallel with the development of new technologies and new paradigms for imaging and sensing. Many of these proposed applications exploit the unique capabilities of terahertz radiation to penetrate common packaging materials and provide spectroscopic information about the materials within. Several of the techniques used for terahertz imaging have been borrowed from other, more well established fields such as x-ray computed tomography and synthetic aperture radar. Others have been developed exclusively for the terahertz field, and have no analogies in other portions of the spectrum. This review provides a comprehensive description of the various techniques which have been employed for terahertz image formation, as well as discussing numerous examples which illustrate the many exciting potential uses for these emerging technologies.

T-ray computed tomography.

Abstract: We demonstrate a tomographic imaging modality that uses pulsed terahertz (THz) radiation to probe the optical properties of three-dimensional (3D) structures in the far-infrared. This THz-wave computed tomography (T-ray CT) system provides sectional images of objects in a manner analogous to conventional CT techniques such as x-ray CT. The transmitted amplitude and phase of broadband pulses of THz radiation are measured at multiple projection angles. The filtered backprojection algorithm is then used to reconstruct the target object, including both its 3D structure and its frequency-dependent far-infrared optical properties.

Terahertz wave imaging: horizons and hurdles.

Abstract: Terahertz (THz) science will profoundly impact biotechnology It has tremendous potential for applications in imaging, medical diagnosis, health monitoring, environmental control and chemical and biological identification THz research will become one of the most promising research areas in the 21st century for transformational advances in imaging, as well as in other interdisciplinary fields However, terahertz wave (T-ray) imaging is still in its infancy This paper discusses the uniqueness and limitations of T-ray imaging, identifies the major challenges impeding T-ray imaging and proposes solutions and opportunities in this field It also concentrates on the generation, propagation and detection of T-rays by the use of femtosecond optics

Pulsed terahertz tomography

Abstract: Terahertz time-domain spectroscopy (THz-TDS) is a coherent measurement technology. Using THz-TDS, the phase and amplitude of the THz pulse at each frequency can be determined. Like radar, THz-TDS also provides time information that allows us to develop various three-dimensional THz tomographic imaging modalities. The three-dimensional THz tomographic imagings we investigated are: terahertz diffraction tomography (THz DT), terahertz computed tomography (THz CT), THz binary lens tomography and THz digital holography. THz DT uses the THz wave as a probe beam to interact with a target, and then reconstructs the three-dimensional image of the target using the THz waves scattered by the target. THz CT is based on geometrical optics and inspired by x-ray CT. THz binary lens tomography uses the frequency dependent focal length property of binary lenses to obtain tomographic images of an object. THz three-dimensional holography combines radar and conventional holography technology. By separating the multiple scattered THz waves of different scattering orders, we used a digital holography method to reconstruct the sparsely distributed scattering centres. Three-dimensional THz imaging has potential in such applications as non-destructive inspection. The interaction between a coherent THz pulse and an object provides rich information about the object under study; therefore, three-dimensional THz imaging is a very useful tool to inspect or characterize dielectric and semiconductor objects. For example, three-dimensional THz imaging can be used to detect and identify the defects inside a space shuttle insulation tile.

Review of Terahertz Tomography Techniques

Abstract: Terahertz and millimeter waves penetrate various dielectric materials, including plastics, ceramics, crystals, and concrete, allowing terahertz transmission and reflection images to be considered as a new imaging tool complementary to X-Ray or Infrared. Terahertz imaging is a well-established technique in various laboratory and industrial applications. However, these images are often two-dimensional. Three-dimensional, transmission-mode imaging is limited to thin samples, due to the absorption of the sample accumulated in the propagation direction. A tomographic imaging procedure can be used to acquire and to render three-dimensional images in the terahertz frequency range, as in the optical, infrared or X-ray regions of the electromagnetic spectrum. In this paper, after a brief introduction to two dimensional millimeter waves and terahertz imaging we establish the principles of tomography for Terahertz Computed tomography (CT), tomosynthesis (TS), synthetic aperture radar (SAR) and time-of-flight (TOF) terahertz tomography. For each technique, we present advantages, drawbacks and limitations for imaging the internal structure of an object.