Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session N5: Applications of THz Radiation |
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Sponsoring Units: FIAP Chair: Alan Todd, Advanced Energy Systems and Gwyn P. Williams, Jefferson Lab Room: LACC 502B |
Wednesday, March 23, 2005 8:00AM - 8:36AM |
N5.00001: Characteristics and Applications of High Intensity Coherent THz Pulses from Linear Accelerators Invited Speaker: G. Lawrence Carr Fifteen years have passed since coherent synchrotron radiation (CSR) from relativistic electrons was first observed[1,2]. Since then, CSR has served as a tool for characterizing electron bunch shapes[3] and has been proposed as a new type of millimeter wave source[4]. But until recently, the source characteristics (spectral range reaching 1 THz, waveform shape, energy per pulse, etc.) have not shown significant advantages over THz generators based on ultra-fast lasers. The present generation of photo-injected linear accelerators are now capable of producing sub-picosecond bunches with approximately 1nC of charge (or more), and the coherent radiation they emit has qualities that readily surpass what is available from other source types[5]. This presentation will describe characteristics of the coherent THz pulses produced as transition radiation from the Source Development Lab linac[6] at the National Synchrotron Light Source. Consistent with calculations, pulses can now be produced with energy approaching 100 microjoules (which is 2 orders of magnitude higher than from non-accelerator methods) and with spectral content reaching 2 THz. Other facilities (e.g., at Jefferson Lab) operate at multi-MHz repetition rates such that the average power is also very high. The E-field of a propagating THz pulse can be coherently detected and imaged using the electro-optic effect in ZnTe[7]. When focused, the transient E-field for such a pulse can exceed 1 MV/cm and should be sufficient for studying non-linear effects in solids, critical currents in superconductors, and ultra-fast magnetization in thin films. [1] T. Nakazato et al., \textit{Phys. Rev. Lett.} \textbf{63}, 1245 (1989). [2] H. Happek et al., \textit{Phys. Rev. Lett.} \textbf{67}, 2962 (1991). [3] R. Lai et al., \textit{Phys. Rev. }E\textbf{50}, R4294 (1994). [4] T. Takahashi et al., \textit{Rev. Sci. Instrum}., \textbf{69}, 3770 (1998). [5] G.L. Carr et al, \textit{Nature} \textbf{420}, 153 (2002). [6] X.J. Wang and X.Y. Chang, \textit{Nucl. Instr. {\&} Meth}. A \textbf{507}, 310 (2003). [7] Q. Wu et al., \textit{Appl. Phys. Lett.} \textbf{68}, 3224 (1996). [Preview Abstract] |
Wednesday, March 23, 2005 8:36AM - 9:12AM |
N5.00002: Submillimeter wave spectroscopy of biological macromolecules Invited Speaker: The recently emergence of submillimeter-wave or terahertz (THz) spectroscopy of biological molecules has demonstrated the capability to detect low-frequency internal molecular vibrations involving the weakest hydrogen bonds of the DNA base pairs and/or non-bonded interactions. These multiple bonds, although having only $\sim $ 5{\%} of the strength of covalent bonds, stabilize the structure of bio-polymers, by holding the two strands of the DNA double helix together, or polypeptides together in different secondary structure conformations. There will be a review of THz-frequency transmission (absorption) results for biological materials obtained from Fourier Transform Infrared (FTIR) spectroscopy during the last few years$^{1,2}$. Multiple resonances, due to low frequency vibrational modes within biological macromolecules, have been unambiguously demonstrated in qualitative agreement with theoretical prediction, thereby confirming the fundamental physical nature of observed resonance features. The discovery of resonance character of interaction between THz radiation and biological materials opens many possible applications for THz spectroscopy technique in biological sensing and biomedicine using multiple resonances as distinctive spectral fingerprints. However, many issues still require investigation. Kinetics of interactions with radiation at THz has not been studied and vibrational lifetimes have not been measured directly as a function of frequency. The strength of resonant modes of bio-molecules in aqueous environment and strong dependence of spectra on molecular orientation need explanation. Vibrational modes have not been assigned to specific motions within molecules. THz spectroscopy of bio-polymers makes it only in first steps. 1. T. Globus, D. Woolard, M. Bykhovskaia, B. Gelmont, L. Werbos, A. Samuels. International Journal of High Speed Electronics and Systems (IJHSES), \textbf{13}, No. 4, 903-936 (2003). 2. T. Globus, T. Khromova, D. Woolard and B. Gelmont. Proceedings of SPIE Vol. 5268-2, 10-18 (2004) [Preview Abstract] |
Wednesday, March 23, 2005 9:12AM - 9:48AM |
N5.00003: Homeland Security, Medical, Pharmaceutical and Non-destructive Testing Applications of Terahertz Radiation Invited Speaker: The terahertz region of the electromagnetic spectrum (300GHz-10THz) spans the region between radio and light. Recent advances in terahertz source, detector and systems technology are enabling new applications across a number of fields, based on both terahertz imaging and spectroscopy. This paper reviews our recent work on the development of practical systems and applications in security screening for the detection of explosives and non-metallic weapons; in medical imaging for cancer detection; as well as applications in non-destructive testing and the pharmaceutical industry. [Preview Abstract] |
Wednesday, March 23, 2005 9:48AM - 10:24AM |
N5.00004: Non-Destructive Evaluation (NDE) Applications of THz Radiation Invited Speaker: The technology and applications of time domain terahertz (THz) imaging to non-destructive evaluation (NDE) will be discussed. THz imaging has shown great promise in 2 and 3 dimensional non-contact inspection of non-conductive materials such as plastics, foam, composites, ceramics, paper, wood and glass. THz imaging employs safe low power non-ionizing electromagnetic pulses, with lateral resolution $<$ 200 um, and depth resolution $<$ 50 um. THz pulses can be analyzed spectroscopically to reveal chemical content. Recently, highly integrated turn-key THz imaging systems have been introduced commercially. We will demonstrate the detection of voids and disbonds intentionally incorporated within the sprayed on foam insulation of a space shuttle external tank mock-up segments. An industrially hardened THz scanning system which has been deployed to scan the space shuttle tank with small remote transceiver will be described. Additional terahertz security imaging applications for the detection of weapons and explosives will also be discussed, as well as the application of terahertz sensors for high speed industrial process monitoring and quality control. [Preview Abstract] |
Wednesday, March 23, 2005 10:24AM - 11:00AM |
N5.00005: Terahertz Imaging and Security Applications Invited Speaker: Imaging at millimeter-wave and terahertz frequencies could vastly improve the security of personnel checkpoints, because of the penetration through clothing and spatial resolution available in this spectral range. Since 9/11, the social need for improved checkpoint screening has been obvious and great. However, although efforts to develop such imagers had been underway for many years before that, practical low-cost systems, analogous to IR uncooled imagers, still don't exist. An emphasis on purely passive imaging places very stringent sensitivity requirements on such imagers. A number of long-term efforts, which I briefly mention, are underway to improve the sensitivity of such passive imagers. However, most of the emphasis in our program is on active imaging. With this approach, much simpler and lower-cost detectors, such as (uncooled) antenna-coupled microbolometers can be used, at the expense of incorporating slightly more complex optics and illumination components. I discuss several tradeoffs presented in the design of active imaging systems for the 100 to 1000 GHz frequency range, describe how we have addressed them in the design of a scanning, 95 GHz, bolometer-based imager for concealed weapons detection that is nearing completion, and describe how the system architecture can be modified to scale the operating frequency to the 650 GHz atmospheric window. \newline \newline Co-authors: Arttu Luukanen and Aaron Miller [Preview Abstract] |
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