Xo-Cheng Zhang

University of Rochester, Optics, Faculty Member

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STANDOFF SENSING AND IMAGING OF EXPLOSIVE RELATED CHEMICAL AND BIO-CHEMICAL MATERIALS USING THz-TDS

International Journal of High Speed Electronics and Systems, 2007

We report the sensing and imaging of explosive related chemical and bio-chemical materials by usi... more We report the sensing and imaging of explosive related chemical and bio-chemical materials by using terahertz time domain spectroscopy (THz-TDS) at standoff distance. The 0.82 THz absorption peak of RDX is observed at a distance up to 30 m away from the emitter and receiver. Multiple absorption features of RDX, 2,4-DNT and Glutamic Acid are identified by using a large scale 2-D imaging system. These results support the feasibility of using THz-TDS technique in remote sensing and detection of chemical materials.

<title>Overview: MURI Center on spectroscopic and time domain detection of trace explosives in condensed and vapor phases</title>

Detection and Remediation Technologies for Mines and Minelike Targets VIII, 2003

The research center established by Army Research Office under the Multidisciplinary University Re... more The research center established by Army Research Office under the Multidisciplinary University Research Initiative program pursues a multidisciplinary approach to investigate and advance the use of complementary analytical techniques for sensing of explosives and/or explosive-related compounds as they occur in the environment. The techniques being investigated include Terahertz (THz) imaging and spectroscopy, Laser-Induced Breakdown Spectroscopy (LIBS), Cavity Ring Down Spectroscopy

Thin film characterization using terahertz differential time-domain spectroscopy and double modulation

Characterizing the optical and dielectric properties of thin films in the GHz to THz range is cri... more Characterizing the optical and dielectric properties of thin films in the GHz to THz range is critical for the development of new technologies in integrated circuitry, photonics systems and micro-opto-electro-mechanical systems (MOEMS). Terahertz differential time-domain spectroscopy (DTDS) is a new technique that uses pulsed terahertz (THz) radiation to detect phase changes of less than 0.6 femtoseconds (fs) and absorption changes

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Measurement of the dielectric constant of thin films using goniometric time-domain spectroscopy

Goniometric time-domain spectroscopy (GTDS), employing an ultrashort electromagnetic (EM) pulse t... more Goniometric time-domain spectroscopy (GTDS), employing an ultrashort electromagnetic (EM) pulse technique has been developed for measuring the dielectric constant of thin films in a broad band of gigahertz (GHz) to terahertz (THz). An ultrafast optoelectronic system, including an emitter and a detector unit, is constructed with a theta-2theta goniometer. A silicon wafer was analyzed as the reference substrate material. A

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Terahertz imaging of biological tissue using a chirped probe pulse

Electronics and Structures for MEMS II, 2001

There is increasing interest among research groups around the world in the terahertz portion of t... more There is increasing interest among research groups around the world in the terahertz portion of the electromagnetic spectrum. T-ray systems, driven by ultrafast THz pulses, offer a number of unique advantages over other techniques and are under investigation for a wide range of applications. Biomedical diagnostics is an area of particular emphasis. The sub-millimetre spectroscopic measurements obtained from T-ray systems contain a wealth of information about the sample under test. A number of hurdles, however, hinder the application of T-ray technology. One of the major hurdles to be overcome is the slow acquisition speed of modern THz systems. The chirped probe pulse technique offers a significant improvement in this context. We present results demonstrating the terahertz responses of biological samples measured using a chirped probe pulse, and discuss the problem of data processing and extracting sample characteristics. We show that different types of tissue can be classified based on their terahertz response measured with the chirped probe pulse technique. We consider chicken and beef samples and differentiate between bone and normal tissue. We demonstrate the performance of linear filter models for feature extraction and show that these models are significantly more accurate than a number of intuitive features.

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2-D Acoustic Phase Imaging With Millimeter-Wave Radiation

IEEE Transactions on Microwave Theory and Techniques, 2009

... Albert Redo-Sanchez, Gurpreet Kaur, Xi-Cheng Zhang, Fellow, IEEE, Federico Buersgens, and Rol... more

Terahertz Science and Technology Trends

IEEE Journal of Selected Topics in Quantum Electronics, 2008

Abstract The recent progress in terahertz science and technology (THz-S&amp;T) opens up a ran... more

Design and characterization of traveling-wave electrooptic terahertz sensors

IEEE Journal of Selected Topics in Quantum Electronics, 1996

We discuss the design considerations of travelingwave electrooptic terahertz sensors, wherein we ... more We discuss the design considerations of travelingwave electrooptic terahertz sensors, wherein we analyze limitations in frequency response due to velocity-mismatch in the sensor crystal. In zincblende electrooptic materials, optical group velocities are found to be able to match the phase velocity of low frequency terahertz wave at specific optical center frequencies. We observed excellent velocity-matching in ZnTe crystals within the tuning range of Ti : sapphire lasers. Terahertz pulses as short as 200 fs (full-width-at-half-maximum) have been measured using the ultra-broad-band radiation generated via terahertz optical rectification.

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Terahertz Biosensing Technology: Frontiers and Progress

ChemPhysChem, 2002

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Electro-optical and magneto-optical sensing apparatus and method for characterizing free-space electromagnetic radiation

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Terahertz time-domain spectroscopy of atmosphere with different humidity

SPIE Proceedings, 2003

Water, at both the liquid and gas phase, maintains a high absorption coefficient in the terahertz... more Water, at both the liquid and gas phase, maintains a high absorption coefficient in the terahertz (THz) frequency range. As a result, a major limitation of THz time-domain spectroscopy (THz-TDS) for real-world applications is water attenuation. The humidity in the atmosphere affects THz waves (T-ray) for long distance measurement and tracing materials, such as explosive materials. We measure air at

<title>Molecular and structural preservation of dehydrated bio-tissue for THz spectroscopy</title>

Biomedical Applications of Micro- and Nanoengineering III, 2006

Terahertz transmission through freshly excised biological tissue is limited by the tissue's high ... more Terahertz transmission through freshly excised biological tissue is limited by the tissue's high water content. Tissue fixation methods that remove water, such as fixation in Formalin, destroy the structural information of proteins hence are not suitable for THz applications. Dehydration is one possible method for revealing the tissue's underlying molecular structure and components. In this study, we measured the THz responses over time of dehydrating fresh, necrotic and lyophilized rat tissue. Our results show that as expected, THz absorption increases dramatically with drying and tissue freshness can be maintained through lyophilization. Dehydrated biological tissue with retained molecular structure can be useful for future laser-based THz wave molecular analysis.

Measurement of spatio-temporal terahertz field distribution by using chirped pulse technology

Mine field detection and identification using terahertz spectroscopic imaging

SPIE Proceedings, 2003

The spatial, temporal, and spectroscopic characteristics associated with pulsed THz (100 GHz -70 ... more The spatial, temporal, and spectroscopic characteristics associated with pulsed THz (100 GHz -70 THz) radiation provide this emerging technology with the potential for reliable identification of buried objects such as non-metallic landmines. With a suitable integration of these attributes, one can envision a THz detection platform that provides: (1) accurate identification of buried objects, and (2) a source-to-sample working distance that is sufficient for remote sensing applications. In our preliminary laboratory studies, we have demonstrated the detection capabilities of THz radiation by imaging a small rubber object embedded in a moist, sand-like soil. Despite the significant attenuation of the THz radiation via water absorption and particle scattering, the initial transmission results showed that pulsed THz imaging could identify the non-metallic object when buried in a few inches of soil. The sub-millimeter resolution observed in our THz images illustrates the potential to discriminate landmines from other buried objects. Finally, THz calculations and measurements determined that our current THz source and detector has sufficient SNR to detect a buried object to a depth of 6 inches in moist sand.

Recent Progresses in Terahertz Wave Air Photonics

IEEE Transactions on Terahertz Science and Technology, 2011

ABSTRACT Terahertz (THz) wave generation and detection using gaseous medium as both the THz wave ... more ABSTRACT Terahertz (THz) wave generation and detection using gaseous medium as both the THz wave emitter and sensor, also termed “THz wave air photonics”, has attracted much scientific attention. We report the most recent progresses in THz generation and detection in laser-induced gas plasma. The overall emphasis of this paper is on THz wave detection with gaseous medium, while in the generation part, emphasis will be on the case with two-color laser excitation.

Millimeter wave emission from GaN high electron mobility transistor

Applied Physics Letters, 2004

We report on millimeter wave electromagnetic radiation from a GaN high electron mobility transist... more We report on millimeter wave electromagnetic radiation from a GaN high electron mobility transistor with the gate length of 1.5 mum at 8 K. The emission takes place at gate and drain voltages in the linear regime of operation but close to the saturation voltage with the principal emission peak at approximately 75 GHz, which is much higher than the

Complex network demonstration: Topology of instant communication systems

2007 IEEE International Conference on Systems, Man and Cybernetics, 2007

ICS have become very popular communication tolls nowadays. They can provide instant, multi-direct... more ICS have become very popular communication tolls nowadays. They can provide instant, multi-directed and multi-types of communications which makes the message spreading in ICS different from those in WWW, Blog and email systems. Groups have great impacts on message spreading in ICS. The research demonstrates the power law distribution of groups in MSN with parameter Upsi ranging from 0.76 to

Terahertz Technology: Terahertz Tomographic Imaging With a Fresnel Lens

Optics and Photonics News, 2002

The promise of high-Tc superconduc-tors for technological applications such as loss-free electric... more

Terahertz radiation from a photoconducting antenna array

IEEE Journal of Quantum Electronics, 1992

An array of photoconducting antennas which generates electrically controllable millimeter-wave an... more An array of photoconducting antennas which generates electrically controllable millimeter-wave and submillimeter-wave radiation in free space is described. Under quasi-sinusoidal optical illumination, the emitted radiation is directional and electrically steerable, and can be scanned through an angle of over 40°. The center of the scanning range can be adjusted by changing the angle of incidence of the pump beam. The

Anti-reflection implementations for terahertz waves

Frontiers of Optoelectronics, 2013

Undesired reflection caused by impedance mismatch can lead to significant power loss and other un... more Undesired reflection caused by impedance mismatch can lead to significant power loss and other unwanted effects. In the terahertz regime, anti-reflection method has evolved from simple quarter-wave antireflection coating to sophisticated metamaterial device and photonic structures. In this paper, we examined and compared the theories and techniques of several antireflection implementations for terahertz waves, with emphasis on gradient index photonic structures. A comprehensive study is presented on the design, fabrication and evaluation of this new approach.

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