J.V. Rudd

Bio: J.V. Rudd is an academic researcher from University of Michigan. The author has contributed to research in topics: Terahertz radiation & Amplifier. The author has an hindex of 3, co-authored 7 publications receiving 137 citations.

Electronic holography and speckle methods for imaging through tissue using femtosecond gated pulses.

Abstract: Electronic holography and speckle interferometry are combined with femtosecond gating techniques to form images of absorbing structures embedded in organic tissue. The method takes advantage of the inherent instability of living tissue.

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.

Photoconductive sampling with an integrated source follower/amplifier

Abstract: A hybrid, optoelectronic sampling circuit based on a photoconductive switch and a junction‐field‐effect‐transistor (JFET) source follower/amplifier has been demonstrated to have picosecond response, high‐sensitivity, absolute‐voltage capability, and a very high impedance. The distributed capacitance of the electrical measurement system is reduced to the gate input capacitance of the JFET, and the conventional photoconductive current measurement is transferred into an absolute voltage measurement. Gating measurements with an improvement of 150 times in output voltage over unamplified photoconductive gates have been made using only 10 μW of average optical power. The effective on‐state resistance of the photogate has also been increased by more than 150 times, indicating that a photoconductive probe with very low invasiveness may be produced.

An ultrafast photoconductive sampling gate integrated with a JFET amplifier

Abstract: Ultrafast photoconductive (PC) sampling techniques have been used in the measurement of electrical waveforms with picosecond resolution and high sensitivity. In this work, an integrated JFET source follower/amplifier, with its high input impedance and low input capacitance (3 pF), has been found to sense absolute signal voltages noninvasively, with as much as 150 times larger output signal levels than those of unamplified PC gates.

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.

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.

Speckle in Optical Coherence Tomography

Abstract: Speckle arises as a natural consequence of the limited spatial-frequency bandwidth of the interference signals measured in optical coherence tomography (OCT). In images of highly scattering biological tissues, speckle has a dual role as a source of noise and as a carrier of information about tissue microstructure. The first half of this paper provides an overview of the origin, statistical properties, and classification of speckle in OCT. The concepts of signal-carrying and signal-degrading speckle are defined in terms of the phase and amplitude disturbances of the sample beam. In the remaining half of the paper, four speckle-reduction methods-polarization diversity, spatial compounding, frequency compounding, and digital signal processing-are discussed and the potential effectiveness of each method is analyzed briefly with the aid of examples. Finally, remaining problems that merit further research are suggested. © 1999 Society of Photo-Optical Instrumentation Engineers.

Optical imaging in medicine: I. Experimental techniques.

Abstract: The overwhelming scatter which occurs when optical radiation propagates through tissue severely limits the ability to image internal structure using measurements of transmitted intensity. A broad range of methods has been proposed during the past decade or so in order to improve imaging performance. Direct methods involve isolating an unscattered or least-scattered component of transmitted scattered light. Indirect methods generally involve measuring some characteristic of the temporal distribution of transmitted light, or an equivalent in the frequency domain, and obtaining a computational solution to the inverse problem. In this paper, we review the experimental techniques which have been proposed in order to explore both direct and indirect imaging. The relative merits and limitations of the various experimental methods are discussed, and we consider the future directions and likelihood of success of optical imaging in medicine.

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