Browsing by Author "Johnson, Jon L."

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    Imaging with Terahertz Pulses
    (2000-07-01) Dorney, Timothy D.; Johnson, Jon L.; Mittleman, Daniel M.; Baraniuk, Richard G.; Center for Multimedia Communications (http://cmc.rice.edu/); Digital Signal Processing (http://dsp.rice.edu/)
    Recently, a real-time imaging system based on terahertz (THz) time-domain spectroscopy has been developed. This technique offers a range of unique imaging modalities due to the broad bandwidth, sub-picosecond duration, and phase-sensitive detection of the THz pulses. This paper provides a brief introduction of the state-of-the art in THz imaging. It also focuses on expanding the potential of this new and exciting field through two major efforts. The first concentrates on improving the experimental sensitivity of the system. We are exploring an interferometric arrangement to provide a background-free reflection imaging geometry. The second applies novel digital signal processing algorithms to extract useful information from the THz pulses. The possibility exists to combine spectroscopic characterization and/or identification with pixel-by-pixel imaging. We describe a new parameterization algorithm for both high and low refractive index materials.
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    Imaging with THz Pulses
    (2000-09-01) Dorney, Timothy D.; Johnson, Jon L.; Mittleman, Daniel M.; Baraniuk, Richard G.; Digital Signal Processing (http://dsp.rice.edu/)
    A real-time imaging system based on terahertz (THz) time-domain spectroscopy has been demonstrated. This technique offers a range of unique imaging modalities due to the broad bandwidth, sub-picosecond duration, and phase-sensitive detection of the THz pulses. This paper provides an introduction of the state-of-the art in THz imaging. It also focuses on expanding the potential of this new and exciting field through two major efforts. The first concentrates on improving the experimental sensitivity of the system. We are exploring an interferometric arrangement to provide a background-free reflection imaging geometry. The second applies novel digital signal processing algorithms to extract useful information from the THz pulses. The possibility exists to combine spectroscopic characterization and/or identification with pixel-by-pixel imaging.
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    Interferometric imaging system and method
    (2003-12-16) Mittleman, Daniel M.; Johnson, Jon L.; Rice University; United States Patent and Trademark Office
    A broadband imaging system is disclosed that provides greatly enhanced depth resolution through the use of phase shift interferometry. The system may comprise a transmitter, a splitter, a phase inverter, and a receiver. The transmitter transmits a signal pulse that is split into a measurement pulse and a reference pulse. The measurement pulse is applied to a sample, and a relative phase shift of approximately π radians is introduced between the measurement pulse and the reference pulse by the phase inverter. The measurement and reference pulses are then recombined to form a combined pulse that is detected by the receiver. The phase inverter may be a simple lens that introduces a Gouy phase shift by passing the measurement or reference pulse through a focal point. In this manner, a background-free measurement is provided, which provides a greatly enhanced sensitivity to small changes in the measurement waveform, regardless of origin.
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    Terahertz Reflection Imaging using Kirchhoff Migration
    (2001-10-01) Dorney, Timothy D.; Johnson, Jon L.; Rudd, J. Van; Baraniuk, Richard G.; Symes, William; Mittleman, Daniel M.; Digital Signal Processing (http://dsp.rice.edu/)
    We describe a new imaging method that uses single-cycle pulses of terahertz (THz) radiation. This technique emulates data-collection and image-processing procedures developed for geophysical prospecting and is made possible by the availability of fiber-coupled THz receiver antennas. We use a simple migration procedure to solve the inverse problem; this permits us to reconstruct the location and shape of targets. These results demonstrate the feasibility of the THz system as a test-bed for the exploration of new seismic processing methods involving complex model systems.