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1

Terahertz pulsed imaging in vivo  

NASA Astrophysics Data System (ADS)

Terahertz (1012 Hz) pulsed imaging is a totally non-destructive and non-ionising imaging modality and thus potential applications in medicine are being investigated. In this paper we present results using our hand-held terahertz probe that has been designed for in vivo use. In particular, we use the terahertz probe to perform reflection geometry in vivo measurements of human skin. The hand-held terahertz probe gives more flexibility than a typical flat-bed imaging system, but it also results in noisier data and requires existing processing methods to be improved. We describe the requirements and limitations of system geometry, data acquisition rate, image resolution and penetration depth and explain how various factors are dependent on each other. We show how some of the physical limitations can be overcome using novel data processing methods.

Pickwell-MacPherson, E.

2011-03-01

2

Diffraction enhanced imaging with pulsed terahertz radiation  

Microsoft Academic Search

Terahertz radiation can penetrate through most non-conducting materials. Imaging with terahertz waves for these materials could provide an appropriate contrast compared with infrared, visible light and X-ray. Edge diffraction in terahertz pulsed imaging (TPI) enables the image contrast to be further enhanced, which exhibits considerable application potential to recognize shape features in the sample under test, especially for those weak

Yingxin Wang; Ziran Zhao; Zhiqiang Chen; Li Zhang; Kejun Kang; Jingkang Deng; Zhifeng Huang

2009-01-01

3

Optical properties of tissue measured using terahertz-pulsed imaging  

NASA Astrophysics Data System (ADS)

The first demonstrations of terahertz imaging in biomedicine were made several years ago, but few data are available on the optical properties of human tissue at terahertz frequencies. A catalogue of these properties has been established to estimate variability and determine the practicality of proposed medical applications in terms of penetration depth, image contrast and reflection at boundaries. A pulsed terahertz imaging system with a useful bandwidth 0.5-2.5 THz was used. Local ethical committee approval was obtained. Transmission measurements were made through tissue slices of thickness 0.08 to 1 mm, including tooth enamel and dentine, cortical bone, skin, adipose tissue and striated muscle. The mean and standard deviation for refractive index and linear attenuation coefficient, both broadband and as a function of frequency, were calculated. The measurements were used in simple models of the transmission, reflection and propagation of terahertz radiation in potential medical applications. Refractive indices ranged from 1.5 +/- 0.5 for adipose tissue to 3.06 +/- 0.09 for tooth enamel. Significant differences (P < 0.05) were found between the broadband refractive indices of a number of tissues. Terahertz radiation is strongly absorbed in tissue so reflection imaging, which has lower penetration requirements than transmission, shows promise for dental or dermatological applications.

Berry, Elizabeth; Fitzgerald, Anthony J.; Zinov'ev, Nickolay N.; Walker, Gillian C.; Homer-Vanniasinkam, Shervanthi; Sudworth, Caroline D.; Miles, Robert E.; Chamberlain, J. Martyn; Smith, Michael A.

2003-06-01

4

A promising diagnostic method: Terahertz pulsed imaging and spectroscopy  

PubMed Central

The terahertz band lies between the microwave and infrared regions of the electromagnetic spectrum. This radiation has very low photon energy and thus it does not pose any ionization hazard for biological tissues. It is strongly attenuated by water and very sensitive to water content. Unique absorption spectra due to intermolecular vibrations in this region have been found in different biological materials. These unique features make terahertz imaging very attractive for medical applications in order to provide complimentary information to existing imaging techniques. There has been an increasing interest in terahertz imaging and spectroscopy of biologically related applications within the last few years and more and more terahertz spectra are being reported. This paper introduces terahertz technology and provides a short review of recent advances in terahertz imaging and spectroscopy techniques, and a number of applications such as molecular spectroscopy, tissue characterization and skin imaging are discussed. PMID:21512652

Sun, Yiwen; Sy, Ming Yiu; Wang, Yi-Xiang J; Ahuja, Anil T; Zhang, Yuan-Ting; Pickwell-MacPherson, Emma

2011-01-01

5

Terahertz pulse imaging in reflection geometry of human skin cancer and skin tissue  

Microsoft Academic Search

We demonstrate the application of terahertz pulse imaging (TPI) in reflection geometry for the study of skin tissue and related cancers both in vitro and in vivo. The sensitivity of terahertz radiation to polar molecules, such as water, makes TPI suitable for studying the hydration levels in the skin and the determination of the lateral spread of skin cancer pre-operatively.

Ruth M Woodward; Bryan E Cole; Vincent P Wallace; Richard J Pye; Donald D Arnone; Edmund H Linfield; Michael Pepper

2002-01-01

6

Time-resolved pulsed-plasma characterization using broadband terahertz pulses correlated with fluorescence imaging  

E-print Network

Time-resolved pulsed-plasma characterization using broadband terahertz pulses correlated -bandwidth electromagnetic pulses have been used to probe pulsed-discharge argon plasmas at various pressures Lorentz model to the measured time-domain pulse with no plasma and comparing it to the measured pulse

Yoo, S. J. Ben

7

Hardness and Density Distributions of Pharmaceutical Tablets Measured by Terahertz Pulsed Imaging  

E-print Network

Hardness and Density Distributions of Pharmaceutical Tablets Measured by Terahertz Pulsed Imaging) as a novel tool to quantify the hard- ness and surface density distribution of pharmaceutical tablets. Good these relate to tablet hardness. Numerical simulations of tablet surface density distribu- tion by finite

Elliott, James

8

Terahertz pulsed imaging in vivo: measurements and processing methods.  

PubMed

This paper presents a number of data processing algorithms developed to improve the accuracy of results derived from datasets acquired by a recently designed terahertz handheld probe. These techniques include a baseline subtraction algorithm and a number of algorithms to extract the sample impulse response: double Gaussian inverse filtering, frequency-wavelet domain deconvolution, and sparse deconvolution. In vivo measurements of human skin are used as examples, and a comparison is made of the terahertz impulse response from a number of different skin positions. The algorithms presented enables both the spectroscopic and time domain properties of samples measured in reflection geometry to be better determined compared to previous calculation methods. PMID:22029357

Parrott, Edward P J; Sy, Stanley M Y; Blu, Thierry; Wallace, Vincent P; Pickwell-Macpherson, Emma

2011-10-01

9

Medical diagnostics using terahertz pulsed spectroscopy  

NASA Astrophysics Data System (ADS)

The paper contains recent results of studying the ability of human body disease diagnosis with terahertz time-domain spectroscopy. In vitro skin cancer samples (squamous cell carcinoma, epithelioid cell melanoma, infiltrating carcinoma) were studied experimentally with terahertz pulsed spectrometer. The parametrical in vitro images of skin cancers are presented. The ability to make early tooth cariosity diagnosis with terahertz time-domain spectroscopy was also shown experimentally. The results of studying the in vitro tooth samples are presented and discussed.

Zaytsev, Kirill I.; Kudrin, Konstantin G.; Koroleva, Svetlana A.; Fokina, Irina N.; Volodarskaya, Svetlana I.; Novitskaya, Ekaterina V.; Perov, Artem N.; Karasik, Valeriy E.; Yurchenko, Stanislav O.

2014-03-01

10

Terahertz Pulsed Imaging and Magnetic Resonance Imaging as Tools to Probe Formulation Stability  

PubMed Central

Dissolution stability over the entire shelf life duration is of critical importance to ensure the quality of solid dosage forms. Changes in the drug release profile during storage may affect the bioavailability of drug products. This study investigated the stability of a commercial tablet (Lescol® XL) when stored under accelerated conditions (40 °C/75% r.h.). Terahertz pulsed imaging (TPI) was used to investigate the structure of the tablet coating before and after the accelerated aging process. The results indicate that the coating was reduced in thickness and exhibited a higher density after being stored under accelerated conditions for four weeks. In situ magnetic resonance imaging (MRI) of the water penetration processes during tablet dissolution in a USP-IV dissolution cell equipped with an in-line UV-vis analyzer was carried out to study local differences in water uptake into the tablet matrix between the stressed and unstressed state. The drug release profiles of the Lescol® XL tablet before and after the accelerated storage stability testing were compared using a “difference” factor f1 and a “similarity” factor f2. The results reveal that even though the physical properties of the coating layers changed significantly during the stress testing, the coating protected the tablet matrix and the densification of the coating polymer had no adverse effect on the drug release performance. PMID:24300564

Zhang, Qilei; Gladden, Lynn F.; Avalle, Paolo; Zeitler, J. Axel; Mantle, Michael D.

2013-01-01

11

Terahertz pulsed imaging study to assess remineralization of artificial caries lesions  

NASA Astrophysics Data System (ADS)

We compare terahertz-pulsed imaging (TPI) with transverse microradiography (TMR) and microindentation to measure remineralization of artificial caries lesions. Lesions are formed in bovine enamel using a solution of 0.1 M lactic acid/0.2% Carbopol C907 and 50% saturated with hydroxyapatite adjusted to pH 5.0. The 20-day experimental protocol consists of four 1 min treatment periods with dentifrices containing 10, 675, 1385, and 2700 ppm fluoride, a 4-h/day acid challenge, and, for the remaining time, specimens are stored in a 50:50 pooled human/artificial saliva mixture. Each specimen is imaged at the focal point of the terahertz beam (data-point spacing = 50 ?m). The time-domain data are used to calculate the refractive index volume percent profile throughout the lesion, and the differences in the integrated areas between the baseline and post-treatment profiles are used to calculate ??Z(THz). In addition, the change from baseline in both the lesion depth and the intensity of the reflected pulse from the air/enamel interface is determined. Statistically significant Pearson correlation coefficients are observed between TPI and TMR/microindentation (P < 0.05). We demonstrate that TPI has potential as a research tool for hard tissue imaging.

Churchley, David; Lynch, Richard J. M.; Lippert, Frank; O'Bryan Eder, Jennifer Susan; Alton, Jesse; Gonzalez-Cabezas, Carlos

2011-02-01

12

Application of terahertz pulsed imaging to analyse film coating characteristics of sustained-release coated pellets.  

PubMed

Terahertz pulsed imaging (TPI) was employed to explore its suitability for detecting differences in the film coating thickness and drug layer uniformity of multilayered, sustained-release coated, standard size pellets (approximately 1mm in diameter). Pellets consisting of a sugar starter core and a metoprolol succinate layer were coated with a Kollicoat(®) SR:Kollicoat(®) IR polymer blend for different times giving three groups of pellets (batches I, II and III), each with a different coating thickness according to weight gain. Ten pellets from each batch were mapped individually to evaluate the coating thickness and drug layer thickness between batches, between pellets within each batch, and across individual pellets (uniformity). From the terahertz waveform the terahertz electric field peak strength (TEFPS) was used to define a circular area (approximately 0.13 mm(2)) in the TPI maps, where no signal distortion was found due to pellet curvature in the measurement set-up used. The average coating thicknesses were 46 ?m, 71 ?m and 114 ?m, for batches I, II and III respectively, whilst no drug layer thickness difference between batches was observed. No statistically significant differences in the average coating thickness and drug layer thickness within batches (between pellets) but high thickness variability across individual pellets was observed. These results were confirmed by scanning electron microscopy (SEM). The coating thickness results correlated with the subsequent drug release behaviour. The fastest drug release was obtained from batch I with the lowest coating thickness and the slowest from batch III with the highest coating thickness. In conclusion, TPI is suitable for detailed, non-destructive evaluation of film coating and drug layer thicknesses in multilayered standard size pellets. PMID:23721891

Haaser, M; Karrout, Y; Velghe, C; Cuppok, Y; Gordon, K C; Pepper, M; Siepmann, J; Rades, T; Taday, P F; Strachan, C J

2013-12-01

13

Terahertz pulse imaging of stratified architectural materials for cultural heritage studies  

NASA Astrophysics Data System (ADS)

Terahertz pulse imaging (TPI) is a novel noncontact, nondestructive technique for the examination of cultural heritage artifacts. It has the advantage of broadband spectral range, time-of-flight depth resolution, and penetration through optically opaque materials. Fiber-coupled, portable, time-domain terahertz systems have enabled this technique to move out of the laboratory and into the field. Much like the rings of a tree, stratified architectural materials give the chronology of their environmental and aesthetic history. This work concentrates on laboratory models of stratified mosaics and fresco paintings, specimens extracted from a neolithic excavation site in Catalhoyuk, Turkey, and specimens measured at the medieval Eglise de Saint Jean-Baptiste in Vif, France. Preparatory spectroscopic studies of various composite materials, including lime, gypsum and clay plasters are presented to enhance the interpretation of results and with the intent to aid future computer simulations of the TPI of stratified architectural material. The breadth of the sample range is a demonstration of the cultural demand and public interest in the life history of buildings. The results are an illustration of the potential role of TPI in providing both a chronological history of buildings and in the visualization of obscured wall paintings and mosaics.

Jackson, J. Bianca; Labaune, Julien; Mourou, Gérard; Duling, Irl N.; Walker, Gillian; Bowen, John; Menu, Michel

2011-06-01

14

Quantitative analysis of visible surface defect risk in tablets during film coating using terahertz pulsed imaging.  

PubMed

Tablets are the most common form of solid oral dosage produced by pharmaceutical industries. There are several challenges to successful and consistent tablet manufacturing. One well-known quality issue is visible surface defects, which generally occur due to insufficient physical strength, causing breakage or abrasion during processing, packaging, or shipping. Techniques that allow quantitative evaluation of surface strength and the risk of surface defect would greatly aid in quality control. Here terahertz pulsed imaging (TPI) was employed to evaluate the surface properties of core tablets with visible surface defects of varying severity after film coating. Other analytical methods, such as tensile strength measurements, friability testing, and scanning electron microscopy (SEM), were used to validate TPI results. Tensile strength and friability provided no information on visible surface defect risk, whereas the TPI-derived unique parameter terahertz electric field peak strength (TEFPS) provided spatial distribution of surface density/roughness information on core tablets, which helped in estimating tablet abrasion risk prior to film coating and predicting the location of the defects. TPI also revealed the relationship between surface strength and blending condition and is a nondestructive, quantitative approach to aid formulation development and quality control that can reduce visible surface defect risk in tablets. PMID:24300215

Niwa, Masahiro; Hiraishi, Yasuhiro

2014-01-30

15

Potential uses of terahertz pulse imaging in dentistry: caries and erosion detection  

NASA Astrophysics Data System (ADS)

TeraHertz Pulse Imaging (TPI) is a relatively new imaging modality for medical and dental imaging. The aim of the present study was to make a preliminary assessment of the potential uses of TPI in clinical dentistry, particularly in relation to caries detection and the detection and monitoring of erosion. Images were obtained in vitro using a new TPI system developed by TeraView Ltd. We present data showing that TPI in vitro images of approximal surfaces of whole teeth demonstrate a distinctive shadowing in the presence of natural carious lesions in enamel. The thickness of this enamel shadowing appears to be related to lesion depth. The use of non-ionizing radiation to image such lesions non-destructively in vitro represents a significant step towards such measurements in vivo. In addition, data is presented which indicates that TPI may have a potential role in the detection and monitoring of enamel erosion. In vitro experiments on whole incisor teeth show that TPI is capable of detecting relatively small artificially induced changes in the buccal or palatal surface of the enamel of these teeth. Imaging of enamel thickness at such a resolution without ionizing radiation would represent a significant breakthrough if applicable in vivo.

Longbottom, Christopher; Crawley, David A.; Cole, Bryan E.; Arnone, Donald D.; Wallace, Vincent P.; Pepper, Michael

2002-06-01

16

High-resolution reconstruction for terahertz imaging.  

PubMed

We present a high-resolution (HR) reconstruction model and algorithms for terahertz imaging, taking advantage of super-resolution methodology and algorithms. The algorithms used include projection onto a convex sets approach, iterative backprojection approach, Lucy-Richardson iteration, and 2D wavelet decomposition reconstruction. Using the first two HR reconstruction methods, we successfully obtain HR terahertz images with improved definition and lower noise from four low-resolution (LR) 22×24 terahertz images taken from our homemade THz-TDS system at the same experimental conditions with 1.0 mm pixel. Using the last two HR reconstruction methods, we transform one relatively LR terahertz image to a HR terahertz image with decreased noise. This indicates potential application of HR reconstruction methods in terahertz imaging with pulsed and continuous wave terahertz sources. PMID:25607865

Xu, Li-Min; Fan, Wen-Hui; Liu, Jia

2014-11-20

17

Critical factors in the measurement of tablet film coatings using terahertz pulsed imaging.  

PubMed

The present work gives an insight into some key measurement and signal processing considerations in terahertz pulsed imaging (TPI). TPI is increasingly used for the measurement of the spatial variation of coating thickness on coated solid dosage forms. The potential of TPI for the assessment of coating thickness distributions and the use in process development is described in recent literature. However, some critical factors need to be taken into account when working with this technique. These are (1) the signal processing of the raw data, (2) the influence of the composition of the sample matrix on the TPI signals and subsequent coating analysis, (3) signal distortions that can occur at tablet edges or areas with defects, and (4) the refractive index as a key parameter in the quantification of layer thickness. In this paper, we will highlight to what extent these factors impact on the qualitative and quantitative analysis of TPI data and how artifacts and misinterpretation of data can be avoided to ensure fully quantitative and robust measurements. PMID:23681565

Brock, Daniela; Zeitler, J Axel; Funke, Adrian; Knop, Klaus; Kleinebudde, Peter

2013-06-01

18

Imaging with terahertz radiation  

NASA Astrophysics Data System (ADS)

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.

Chan, Wai Lam; Deibel, Jason; Mittleman, Daniel M.

2007-08-01

19

Terahertz imaging with compressive sensing  

Microsoft Academic Search

Most existing terahertz imaging systems are generally limited by slow image acquisition due to mechanical raster scanning. Other systems using focal plane detector arrays can acquire images in real time, but are either too costly or limited by low sensitivity in the terahertz frequency range. To design faster and more cost-effective terahertz imaging systems, the first part of this thesis

Wai Lam Chan

2010-01-01

20

Investigating the use of terahertz pulsed time domain reflection imaging for the study of fabric layers of an Egyptian mummy  

NASA Astrophysics Data System (ADS)

This paper reports the first use of terahertz time domain reflection imaging involving textiles on part of a complete human mummy, still in original wrapping. X-ray technique has been used extensively to investigate anatomical features, since X-ray pass through the wrapping. Terahertz waves, on the other hand, can penetrate into non-metallic materials and its reflection depends on the refractive index of materials at the interface, such as textiles and the air. The mummy of Kharushere (ca. 945-712 B.C.) was examined by using Terahertz time domain reflection imaging in the Egyptian galleries of The Metropolitan Museum of Art. Experimental results suggest that the Terahetz imaging is a promising technique for probing the fabric layers surrounding Egyptian mummies, although it is still very limited in its current state. In the future it could become a useful complement to CT scanning when materials with low radiographic density and contrast are being investigated

Fukunaga, K.; Cortes, E.; Cosentino, A.; Stã¼nkel, I.; Leona, M.; Duling, N.; Mininberg, D. T.

2011-08-01

21

Identify paraffin-embedded brain glioma using terahertz pulsed spectroscopy  

NASA Astrophysics Data System (ADS)

The refractive indices, absorption coefficients and complex dielectric constants spectra of paraffin-embedded brain glioma and normal brain tissues have been measured by a terahertz time domain spectroscopy (THz-TDS) system in the range of 0.2 - 2.0 THz. The spectral differences between glioma and normal brain tissues were obtained. Our results indicate that, compared with normal tissue, glioma had higher refractive index, absorption coefficient, and dielectric constant. Based on these results, the suitable frequency components for different methods of glioma imaging (intensity imaging, coherent imaging and terahertz pulsed imaging) are analyzed.

Li, Ze-ren; Meng, Kun; Chen, Tu-nan; Chen, Tao; Zhu, Li-guo; Liu, Qiao; Li, Zhao; Li, Fei; Zhong, Sen-cheng; Feng, Hua; Zhao, Jian-heng

2015-01-01

22

Evaluation of critical process parameters for inter-tablet coating uniformity of active-coated GITS using Terahertz Pulsed Imaging.  

PubMed

The aim of this study was the evaluation of critical process parameters (CPP) for inter-tablet coating uniformity in an active pan coating process using nondestructive Terahertz Pulsed Imaging (TPI). Coating uniformity was assessed by calculating the coefficient of variation (CV) of coating thickness measured by TPI, and the CV of API content measured by high performance liquid chromatography (HPLC). A design of experiments (DoE) was performed at pilot scale with drum load, drum speed, spray rate, run duration and spray pressure as factors. Good agreement in the CV of both analytical techniques was shown. The DoE models both revealed the same CPP: a low drum load, high drum speed, low spray rate and high run duration were beneficial for coating uniformity. The spray pressure was only significant in one of the DoE models. It was further shown that the negative impact of a high drum load on the CV cannot only be compensated by high drum speed, but also be compensated by a low spray rate and long run duration. It was demonstrated that TPI is a feasible tool for the measurement of inter-tablet coating uniformity and for the evaluation of CPP in an active pan coating process. PMID:25034044

Brock, Daniela; Zeitler, J Axel; Funke, Adrian; Knop, Klaus; Kleinebudde, Peter

2014-10-01

23

Applications of terahertz-pulsed technology in the pharmaceutical industry  

NASA Astrophysics Data System (ADS)

Coatings are applied to pharmaceutical tablets (or pills) to for either cosmetic or release control reasons. Cosmetic coatings control the colour or to mask the taste of an active ingredient; the thickness of these coating is not critical to the performance of the product. On the other hand the thickness and uniformity of a controlled release coating has been found affect the release of the active ingredient. In this work we have obtained from a pharmacy single brand of pantoprazole tablet and mapped them using terahertz pulsed imaging (TPI) prior to additional dissolution testing. Three terahertz parameters were derived for univariate analysis for each layer: coating thickness, terahertz electric field peak strength and terahertz interface index. These parameters were then correlated dissolution tested. The best fit was found to be with combined coating layer thickness of the inert layer and enteric coating. The commercial tablets showed a large variation in coating thickness.

Taday, Philip F.

2010-02-01

24

Scanning Terahertz Heterodyne Imaging Systems  

NASA Technical Reports Server (NTRS)

Scanning terahertz heterodyne imaging systems are now at an early stage of development. In a basic scanning terahertz heterodyne imaging system, (see Figure 1) two far-infrared lasers generate beams denoted the local-oscillator (LO) and signal that differ in frequency by an amount, denoted the intermediate frequency (IF), chosen to suit the application. The LO beam is sent directly to a mixer as one of two inputs. The signal beam is focused to a spot on or in the specimen. After transmission through or reflection from the specimen, the beams are focused to a spot on a terahertz mixer, which extracts the IF outputs. The specimen is mounted on a translation stage, by means of which the focal spot is scanned across the specimen to build up an image.

Siegel, Peter; Dengler, Robert

2007-01-01

25

Analysis of terahertz pulse propagation through a dielectric edge  

Microsoft Academic Search

The wavelength of terahertz radiation is typically on the order of millimeters and submillimeters, and not negligible compared to the sizes of the optical components and the sample structure. Diffraction and scattering effects will be prominent in this situation, yielding spatiotemporal reshaping of terahertz pulse during its propagation. One representative example involves the propagation of a focused terahertz beam through

Yingxin Wang; Ziran Zhao; Zhiqiang Chen; Li Zhang; Kejun Kang

2008-01-01

26

Terahertz pulse propagation through small apertures  

SciTech Connect

Transmission of single-cycle terahertz pulses through subwavelength apertures is experimentally studied in the near-field zone. Measurements of throughput for aperture sizes d as small as {lambda}/300 show that the theoretical d{sup 3} law requires a correction term which takes into account the physical thickness of the aperture screen. Frequency dependent transmission of the broad band pulses explains changes in their spectral and temporal characteristics. Practical application of small apertures in near-field microscope probes allows achievement of spatial resolution of 7 {mu}m for pulses with a broad spectral content of {lambda}=120--1500{mu}m. {copyright} 2001 American Institute of Physics.

Mitrofanov, Oleg; Lee, M.; Hsu, J. W. P.; Pfeiffer, L. N.; West, K. W.; Wynn, J. D.; Federici, J. F.

2001-08-13

27

Whispering-gallery-mode cavity for terahertz pulses  

E-print Network

Whispering-gallery-mode cavity for terahertz pulses Jiangquan Zhang and D. Grischkowsky School an experimental and theoretical study of whispering-gallery-mode propagation of subpicosecond terahertz pulses fiber,7,10 microstrip transmission lines,11 or a dielectric waveguide.12 When the electro- magnetic wave

28

Lasers in Surgery and Medicine 43:457462 (2011) Continuous Wave Terahertz Transmission Imaging of  

E-print Network

Lasers in Surgery and Medicine 43:457­462 (2011) Continuous Wave Terahertz Transmission Imaging human skin cancers. Terahertz pulse imaging (TPI) has already shown that there is contrast between basal for delineating skin cancers by demonstra- ting contrast between cancerous and normal tissue in transmission mode

Massachusetts at Lowell, University of

2011-01-01

29

Terahertz technology for imaging and spectroscopy  

NASA Astrophysics Data System (ADS)

The terahertz region of the electromagnetic spectrum has unique properties that make it especially useful for imaging and spectroscopic detection of concealed weapons, explosives and chemical and biological materials. However, terahertz energy is difficult to generate and detect, and this has led to a technology gap in this frequency band. Nonlinear diodes can be used to bridge this gap by translating the functionality achieved at microwave frequencies to the terahertz band. Basic building blocks include low-noise mixers, frequency multipliers, sideband generators and direct detectors. These terahertz components rely on planar Schottky diodes and recently developed integrated diode circuits make them easier to assemble and more robust. The new generation of terahertz sources and receivers requires no mechanical tuning, yet achieves high efficiency and broad bandwidth. This paper reviews the basic design of terahertz transmitters and receivers, with special emphasis on the recent development of systems that are compact, easy to use and have excellent performance.

Crowe, T. W.; Porterfield, D. W.; Hesler, J. L.; Bishop, W. L.; Kurtz, D. S.; Hui, K.

2006-05-01

30

Transmission terahertz waveguide-based imaging below the diffraction limit  

E-print Network

Transmission terahertz waveguide-based imaging below the diffraction limit M. M. Awad and R. A 74078 Received 1 December 2004; accepted 5 May 2005; published online 26 May 2005 Using a terahertz line at terahertz frequencies with subwavelength image resolution. Terahertz radiation is coupled into a parallel

31

Terahertz Tools Advance Imaging for Security, Industry  

NASA Technical Reports Server (NTRS)

Picometrix, a wholly owned subsidiary of Advanced Photonix Inc. (API), of Ann Arbor, Michigan, invented the world s first commercial terahertz system. The company improved the portability and capabilities of their systems through Small Business Innovation Research (SBIR) agreements with Langley Research Center to provide terahertz imaging capabilities for inspecting the space shuttle external tanks and orbiters. Now API s systems make use of the unique imaging capacity of terahertz radiation on manufacturing floors, for thickness measurements of coatings, pharmaceutical tablet production, and even art conservation.

2010-01-01

32

Imaging of ex vivo nonmelanoma skin cancers in the optical and terahertz spectral regions optical and terahertz skin cancers imaging.  

PubMed

We tested the hypothesis that polarization sensitive optical and terahertz imaging may be combined for accurate nonmelanoma skin cancer (NMSC) delineation. Nine NMSC specimens were imaged. 513 ?m and 440 nm wavelengths were used for terahertz and optical imaging, respectively. Histopathology was processed for evaluation. Terahertz reflectance of NMSC was quantified. Our results demonstrate that cross-polarized terahertz images correctly identified location of the tumours, whereas cross-polarized and polarization difference optical images accurately presented morphological features. Cross-polarized terahertz images exhibited lower reflectivity values in cancer as compared to normal tissue. Combination of optical and terahertz imaging shows promise for intraoperative delineation of NMSC. PMID:22987857

Joseph, Cecil S; Patel, Rakesh; Neel, Victor A; Giles, Robert H; Yaroslavsky, Anna N

2014-05-01

33

Terahertz polarization pulse shaping with arbitrary field control  

NASA Astrophysics Data System (ADS)

Polarization shaping of terahertz pulses enables us to manipulate the temporal evolution of the amplitude and direction of electric-field vectors in a prescribed manner. Such arbitrary control of terahertz waves has great potential in expanding the scope of terahertz spectroscopy, the manipulation of terahertz nonlinear phenomena and coherent control. This is analogous to the use of pulse-shaping techniques for optical frequencies that involve light's polarization states as a controllable degree of freedom. Here, we propose and demonstrate a method for generating a prescribed terahertz polarization-shaped waveform by the optical rectification of a laser pulse whose instantaneous polarization state and intensity are controlled by an optical pulse shaper. We have developed a deterministic procedure to derive input parameters for the pulse shaper that are adequate to generate the desired terahertz polarization-shaped waveform, with the benefit of simple polarization selection rules for the rectification process of light waves propagating along the three-fold axis of a nonlinear optical crystal.

Sato, Masaaki; Higuchi, Takuya; Kanda, Natsuki; Konishi, Kuniaki; Yoshioka, Kosuke; Suzuki, Takayuki; Misawa, Kazuhiko; Kuwata-Gonokami, Makoto

2013-09-01

34

Processing and Probability Analysis of Pulsed Terahertz NDE of Corrosion under Shuttle Tile Data  

NASA Technical Reports Server (NTRS)

This paper examines data processing and probability analysis of pulsed terahertz NDE scans of corrosion defects under a Shuttle tile. Pulsed terahertz data collected from an aluminum plate with fabricated corrosion defects and covered with a Shuttle tile is presented. The corrosion defects imaged were fabricated by electrochemically etching areas of various diameter and depth in the plate. In this work, the aluminum plate echo signal is located in the terahertz time-of-flight data and a threshold is applied to produce a binary image of sample features. Feature location and area are examined and identified as corrosion through comparison with the known defect layout. The results are tabulated with hit, miss, or false call information for a probability of detection analysis that is used to identify an optimal processing threshold.

Anastasi, Robert F.; Madaras, Eric I.; Seebo, Jeffrey P.; Ely, Thomas M.

2009-01-01

35

Generation and manipulation of multi-cycle terahertz pulses via optical rectification in poled lithium niobate  

Microsoft Academic Search

We demonstrate control of terahertz (THz) waves developing novel devices in the THz regime: THz pulse shapers. THz technology is a relatively unexplored subject, yet the importance of THz wave manipulation cannot be emphasized enough considering its potential application to THz imaging systems, ultrafast optical signal processing, ultrahigh-speed computing, quantum information science, nanotechnology, and chemical reaction dynamics among other areas.

Yun-Shik Lee; N. Amer; W. C. Hurlbut; B. J. Norton; J. R. Danielson

2005-01-01

36

Terahertz polarization imaging for colon cancer detection  

NASA Astrophysics Data System (ADS)

Continuous wave terahertz (THz) imaging has the potential to offer a safe, noninvasive medical imaging modality for delineating colorectal cancer. The terahertz reflectance measurements of fresh 3 - 5 mm thick human colonic excisions were acquired using a continuous-wave polarization imaging technique. A CO2 optically pumped Far- Infrared molecular gas laser operating at 584 GHz was used to illuminate the colon tissue, while the reflected signals were detected using a liquid Helium cooled silicon bolometer. Both co-polarized and cross-polarized remittance from the samples was collected using wire grid polarizers in the experiment. The experimental analysis of 2D images obtained from THz reflection polarization imaging techniques showed intrinsic contrast between cancerous and normal regions based on increased reflection from the tumor. Also, the study demonstrates that the cross-polarized terahertz images not only correlates better with the histology, but also provide consistent relative reflectance difference values between normal and cancerous regions for all the measured specimens.

Doradla, Pallavi; Alavi, Karim; Joseph, Cecil S.; Giles, Robert H.

2014-03-01

37

Electromagnetic Pulse Technology: Biological and Terahertz Applications  

NASA Astrophysics Data System (ADS)

Since the mid-1970s, the field of Electromagnetic Pulse (EMP) technology has extended to include High-Power Electromagnetic (HPE) sources/antennas. Two such EMP/HPE antennas, designed to address unique applications, are presented in this dissertation. The first is the Prolate-Spheroidal Impulse-Radiating Antenna (PSIRA). Such an antenna uses a prolate-spheroidal reflector and has two foci. A fast (? 100 ps), high-voltage (> 100 kV) pulse launched from the first focal point is focused into a target located at the second focal point (near-field). It has been found that these pulses are useful for a variety of biological applications, such as accelerated wound healing and skin cancer (melanoma) treatment. Two lens designs for the PSIRA are explored. The first lens, called the focusing lens, is used at the second focal point of the PSIRA to better match the focused pulses into the (biological) target medium. Analytical calculations, numerical simulations and experimental results on a five-layer, hemispherical, dielectric focusing lens are detailed. The second lens, called the launching lens, is used at the first focal point of the PSIRA. For input voltages of 100 kV or more, a switch system, i.e., switch cones, pressure vessel, hydrogen chamber and launching lens, are required to effectively launch a spherical TEM wave from the first focal point. Various switch configurations are explored. It is shown that the pressure vessel can also serve as the launching lens, which considerably simplifies the design of the switch system. Spherical and cylindrical pressure vessel designs are investigated. The second is the Switched Oscillator (SwO) antenna. A SwO is essentially an electrical, shock-excited resonant structure. The SwO is adopted as a high-power antenna to radiate high-energy pulses in the terahertz frequency range. The primary focus is to use these pulses for secure communications. Analytical calculations for the SwO are detailed. Numerical simulations are used to optimize and more thoroughly study the antenna. Various characteristic relations obtained are used to provide a deeper insight into the working of the SwO radiator.

Kumar, Prashanth

2011-12-01

38

Creating Rydberg electron wave packets using terahertz pulses  

NASA Astrophysics Data System (ADS)

In this thesis I present experiments in which we excited classical-limit states of an atom using terahertz pulses. In a classical-limit state, an atom's outer electron is confined to a wave packet that orbits the core along a classical trajectory. Researchers have excited states with classical traits, but wave packets localized in all three dimensions have proved elusive. Theoretical studies have shown such states can be created using terahertz pulses. Using these techniques, we created a linear-orbit wave packet (LOWP), that is three-dimensionally localized and orbits along a line on one side of the atom's core. Terahertz pulses are sub-picosecond bursts of far- infrared radiation. Unlike ultrashort optical pulses, the electric field of terahertz pulses barely completes a single cycle. Our simulations of the atom-pulse interaction show that this electric field profile is critical in determining the quality of the wave packet. To characterize our terahertz pulses, we invented dithered-edge sampling which time- resolves the electric field using a photoconductive receiver and a triggered attenuator. We also studied how pulses are distorted after propagating through metallic structures, and used our findings to design our atomic experiments. We excited wave packets in atomic sodium using a two-step process. First, we used tunable, nanosecond dye lasers to excite an extreme Stark state. Next, we used a terahertz pump pulse to coherently redistribute population among extreme Stark states in neighboring manifolds. Interference between the final states produces a localized, dynamic LOWP. To analyze the LOWP, we ionized it with a stronger terahertz probe pulse, varying the pump-probe delay to map out its motion. We observed two strong LOWP signatures. Changing the static electric field produced small changes (2%) in the orbital period that agreed with our theoretical predictions. Secondly, because the LOWP scatters off the core, the pump-probe signal depended on the direction of the kick the LOWP received from the robe pulse. These observations, combined with our detailed simulations that used sodium parameters and the actual shape of the terahertz pulse, lead us to conclude that we excited a LOWP.

Bromage, Jake

1999-10-01

39

Far-Infrared Dielectric Properties of Polar Liquids Probed by Femtosecond Terahertz Pulse Spectroscopy  

E-print Network

. These spectra have been measured with femtosecond terahertz pulse transmission spectroscopy. These liquidsFar-Infrared Dielectric Properties of Polar Liquids Probed by Femtosecond Terahertz Pulse by femtosecond terahertz (fs THz) pulses.1 This paper reports the absorption and dispersion spectra of several

40

Direct acoustic phonon excitation by intense and ultrashort terahertz pulses  

SciTech Connect

We report on the direct and resonant excitation of acoustic phonons in an AlGaAs intrinsic semiconductor using intense coherent and single cycle terahertz pulses created by two-color femtosecond laser pulse filamentation in air. While the electrons are left unperturbed, we follow the lattice dynamics with time-delayed optical photons tuned to the interband transition.

Manceau, J.-M.; Loukakos, P. A.; Tzortzakis, S. [Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, Nikolaou Plastira 100, P.O. Box 1385, Vassilika Vouton, Heraklion 71110 (Greece)

2010-12-20

41

Metamaterial based devices for terahertz imaging  

Microsoft Academic Search

The terahertz (THz) region has been shown to have considerable application potential for spectroscopic imaging, nondestructive imaging through nonpolar, nonmetallic materials and imaging of biological materials. These applications have all been possible due to the recent progress in THz sources, detectors and measurement techniques. However, only moderate progress has been made in developing passive and active devices to control and

Xomalin G. Peralta; Michael C. Wanke; Igal Brener; Jerry Waldman; William D. Goodhue; J. Li; Abul K. Azad; Hou-Tong Chen; Antoinette J. Taylor; John F. O'Hara

2010-01-01

42

Array Technology for Terahertz Imaging  

NASA Technical Reports Server (NTRS)

Heterodyne terahertz (0.3 - 3THz) imaging systems are currently limited to single or a low number of pixels. Drastic improvements in imaging sensitivity and speed can be achieved by replacing single pixel systems with an array of detectors. This paper presents an array topology that is being developed at the Jet Propulsion Laboratory based on the micromachining of silicon. This technique fabricates the array's package and waveguide components by plasma etching of silicon, resulting in devices with precision surpassing that of current metal machining techniques. Using silicon increases the versatility of the packaging, enabling a variety of orientations of circuitry within the device which increases circuit density and design options. The design of a two-pixel transceiver utilizing a stacked architecture is presented that achieves a pixel spacing of 10mm. By only allowing coupling from the top and bottom of the package the design can readily be arrayed in two dimensions with a spacing of 10mm x 18mm.

Reck, Theodore; Siles, Jose; Jung, Cecile; Gill, John; Lee, Choonsup; Chattopadhyay, Goutam; Mehdi, Imran; Cooper, Ken

2012-01-01

43

Detection and Characterization of Flaws in Sprayed on Foam Insulation with Pulsed Terahertz Frequency Electromagnetic Waves  

NASA Technical Reports Server (NTRS)

The detection and repair of flaws such as voids and delaminations in the sprayed on foam insulation of the external tank reduces the probability of foam debris during shuttle ascent. The low density of sprayed on foam insulation along with it other physical properties makes detection of flaws difficult with conventional techniques. An emerging technology that has application for quantitative evaluation of flaws in the foam is pulsed electromagnetic waves at terahertz frequencies. The short wavelengths of these terahertz pulses make them ideal for imaging flaws in the foam. This paper examines the application of terahertz pulses for flaw detection in foam characteristic of the foam insulation of the external tank. Of particular interest is the detection of voids and delaminations, encapsulated in the foam or at the interface between the foam and a metal backing. The technique is shown to be capable of imaging small voids and delaminations through as much as 20 cm of foam. Methods for reducing the temporal responses of the terahertz pulses to improve flaw detection and yield quantitative characterizations of the size and location of the flaws are discussed.

Winfree, William P.; Madaras, Eric I.

2005-01-01

44

Nonlinear reshaping of terahertz pulses with graphene metamaterials  

NASA Astrophysics Data System (ADS)

We study the propagation of electromagnetic waves through a slab of graphene metamaterial composed of the layers of graphene separated by dielectric slabs. Starting from the kinetic expression for two-dimensional electric current in graphene, we derive a novel equation describing the nonlinear propagation of terahertz electromagnetic pulses through the layered graphene-dielectric structure in the presence of losses and non-linearities. We demonstrate strong nonlinearity-induced reshaping of transmitted and reflected terahertz pulses through the interaction with the thin multilayer graphene metamaterial structure.

Rapoport, Yu.; Grimalsky, V.; Iorsh, I.; Kalinich, N.; Koshevaya, S.; Castrejon-Martinez, Ch.; Kivshar, Yu. S.

2013-12-01

45

Terahertz transmission through nanogaps using both pulsed and CW sources  

Microsoft Academic Search

We measure field enhancement through nanogap by using both terahertz time domain spectroscopy (TDS) and terahertz imaging technique with continuous wave (CW) radiation source. Far-field amplitude is connected to the near-field enhancement through the Kirchhoff formalism. With TDS, we found that a field enhancement of 200 at 0.1 THz for the 500 nm slit. To confirm our TDS results, we

J. S. Kyoung; M. A. Seo; H. R. Park; O. Kwon; G. S. Park; O. K. Suwal; S. S. Choi; D. S. Kim

2009-01-01

46

Transmission properties of terahertz pulses through subwavelength double split-ring resonators  

E-print Network

Transmission properties of terahertz pulses through subwavelength double split-ring resonators Abul 1, 2005 We present a terahertz time-domain spectroscopy study of the transmission properties of the SRRs on the transmission properties of terahertz pulses in normal-incidence geometry. In one of the SRR

47

Generation and manipulation of multi-cycle terahertz pulses via optical rectification in poled lithium niobate  

NASA Astrophysics Data System (ADS)

We demonstrate control of terahertz (THz) waves developing novel devices in the THz regime: THz pulse shapers. THz technology is a relatively unexplored subject, yet the importance of THz wave manipulation cannot be emphasized enough considering its potential application to THz imaging systems, ultrafast optical signal processing, ultrahigh-speed computing, quantum information science, nanotechnology, and chemical reaction dynamics among other areas. THz time-domain spectroscopy (THz-TDS) can assess the performance of the THz pulse shapers monitoring time-dependent THz wave propagation. THz-TDS permits precise measurements not only of the amplitude but also of the phase of THz waves, thus a comprehensive assessment of the THz devices can be achieved. The phase sensitivity is also vital to many applications such as high-contrast THz imaging and quantum control of semiconductor nanostructures. We develop arbitrary THz pulse generators synthesizing THz waveforms via optical rectification in pre-engineered domain structures of poled nonlinear crystals using femtosecond lasers. The terahertz waveforms coincide with the crystal domain structures. The one dimensional nonlinear wave equation simulates the experimental results with a good qualitative agreement. The ratio of the domain length to the optical pulse length in the crystal turns out to be the crucial limiting factor to generating optimum terahertz fields and preventing waveform distortion. Optical pulse shaping techniques is integrated into the THz pulse generators to extend the scope of THz pulse shaping control. Continuously tunable narrow-band THz pulses are generated in a fanned-out periodically-poled lithium niobate crystal. We measure the free induction decay of rotational transitions in gas-phase HCl molecules using the narrow-band THz pulses. The shape of the multi-cycle THz pulses is controlled by adjusting the relative time delay and intensity between the two optical pulses.

Lee, Yun-Shik; Amer, N.; Hurlbut, W. C.; Norton, B. J.; Danielson, J. R.

2005-11-01

48

Focus free terahertz reflection imaging and tomography with Bessel beams  

NASA Astrophysics Data System (ADS)

A broadband terahertz (THz) reflection imaging system with high spatial resolution over a large depth of field is reported. A THz axicon lens producing a truncated THz Bessel beam with a linear focus exceeding 120 mm in length, and with the diameter of the central lobe less than 2 mm was used for imaging in a reflection geometry employing a pulsed THz time-domain spectrometer. With numerical post-processing, it was possible to reconstruct the three dimensional shape of the scanned object.

Busch, S. F.; Town, G. E.; Scheller, M.; Koch, M.

2015-03-01

49

Terahertz pulse transmission in plastic photonic crystal fibres  

Microsoft Academic Search

Guided-wave single-mode propagation of sub-ps terahertz (THz) pulses in a plastic photonic crystal fibre has been experimentally demonstrated. The plastic photonic crystal fibre (PPCF) is fabricated from high-density polyethylene tubes and filaments. The fibre exhibits low loss and relatively low dispersive propagation of THz pulses within the experimental bandwidth of 0.1-3 THz. Such PPCFs have the promise of low loss,

M. Cho; J. Kim; H. Han

2002-01-01

50

Polarization Reversal in Ferroelectric Nanowires using Terahertz Pulses  

NASA Astrophysics Data System (ADS)

Ferroelectric nanowires are very attractive for potential applications in nanodevices, nanosensors or ferroelectric computer memory, since they posses reversible polarization at the nanoscale. Here we report the possibility to remotely control the polarization direction in ferroelectric nanowires by the application of a small biased field in combination with a terahertz Gaussian-shaped pulse. Our study is carried out on Pb(Zr0.4Ti0.6)O3 nanowires using classical molecular dynamics with first-principle-based effective Hamiltonian[1]. The conditions for which the polarization reversal in the nanowire can be achieved by the coupled effect of a biased field with the application of a terahertz pulse are investigated. In particular, we will report computational data on the polarization reversal by application of THz pulses of different amplitude, frequency and width. Furthermore the dependence of the polarization reversal on the temperature is considered.

Herchig, Ryan; McCash, Kevin; Ponomareva, Inna

2013-03-01

51

Terahertz pulse induced intervalley scattering in photoexcited GaAs.  

PubMed

Nonlinear transient absorption bleaching of intense few-cycle terahertz (THz) pulses is observed in photoexcited GaAs using opticalpump--THz-probe techniques. A simple model of the electron transport dynamics shows that the observed nonlinear response is due to THz-electric- field-induced intervalley scattering over sub-picosecond time scales as well as an increase in the intravalley scattering rate attributed to carrier heating. Furthermore, the nonlinear nature of the THz pulse transmission at high peak fields leads to a measured terahertz conductivity in the photoexcited GaAs that deviates significantly from the Drude behavior observed at low THz fields, emphasizing the need to explore nonlinear THz pulse interactions with materials in the time domain. PMID:19506611

Su, F H; Blanchard, F; Sharma, G; Razzari, L; Ayesheshim, A; Cocker, T L; Titova, L V; Ozaki, T; Kieffer, J-C; Morandotti, R; Reid, M; Hegmann, F A

2009-06-01

52

Single-cycle megawatt terahertz pulse generation from a wavelength-scale plasma oscillator driven by ultrashort laser pulses  

E-print Network

The tremendous applications of terahertz (THz) spectroscopy and imaging require THz sources in different parameters. We propose a novel scheme to generate single-cycle powerful THz pulses by ultrashort intense laser pulses incident obliquely on a tenuous plasma slab of few THz wavelengths in thickness. This is made possible by driving a large amplitude electron plasma wave in the plasma slab, thus producing a net transient current at the plasma surfaces. Theory and simulations show that such a THz source is capable of providing megawatt power and field strength of MV/cm, which may open up new horizons for nonlinear THz science and applications.

Wu, H C; Zhang, J; Sheng, Zheng-Ming; Wu, Hui-Chun; Zhang, Jie

2007-01-01

53

Plasma wave resonant detection of femtosecond pulsed terahertz radiation by a nanometer field-effect transistor  

E-print Network

Plasma wave resonant detection of femtosecond pulsed terahertz radiation by a nanometer field detection of femtosecond pulsed terahertz radiation obtained by optical rectification in a ZnTe crystal show that physical mechanism of the detection is related to the plasma waves excited in the transistor

Levelut, Claire

54

May 1, 1997 / Vol. 22, No. 9 / OPTICS LETTERS 627 Spatiotemporal shaping of terahertz pulses  

E-print Network

May 1, 1997 / Vol. 22, No. 9 / OPTICS LETTERS 627 Spatiotemporal shaping of terahertz pulses Jake We report temporal shaping of few-cycle terahertz pulses, using a slit in a conductive screen of the cutoff transition was altered by changing the thickness of the screen. We measured the transmission

Stroud, Carlos R.

55

Enhancement of narrow-band terahertz radiation from photoconducting antennas by optical pulse shaping.  

PubMed

We report the use of optical pulse shaping to convert single femtosecond pulses into lower-intensity pulse sequences for excitation of photoconductive dipole antennas, which results in the generation of bursts of tunable narrow-band free-space terahertz radiation. Our experiments demonstrate that the use of such pulse sequences can significantly enhance the spectral amplitude of the narrow-band terahertz radiation by avoiding the saturation effects that occur with single-pulse excitation. Our technique also provides the capability for terahertz wave-form shaping. PMID:19881793

Liu, Y; Park, S G; Weiner, A M

1996-11-01

56

Generation of high power single-cycle and multiple-cycle terahertz pulses  

E-print Network

In this thesis, we present experimental methods and results of tabletop generation of high power single-cycle and frequency-tunable multiple-cycle terahertz (THz) pulses pumped with near-infrared ultrashort optical pulses ...

Chen, Zhao, S.M. Massachusetts Institute of Technology. Department of Chemistry

2013-01-01

57

Goya's artwork imaging with Terahertz waves.  

PubMed

In this paper we use a Terahertz (THz) time-domain system to image and analyze the structure of an artwork attributed to the Spanish artist Goya painted in 1771. The THz images show features that cannot be seen with optical inspection and complement data obtained with X-ray imaging that provide evidence of its authenticity, which is validated by other independent studies. For instance, a feature with a strong resemblance with one of Goya's known signatures is seen in the THz images. In particular, this paper demonstrates the potential of THz imaging as a complementary technique along with X-ray for the verification and authentication of artwork pieces through the detection of features that remain hidden to optical inspection. PMID:23938652

Seco-Martorell, C; López-Domínguez, V; Arauz-Garofalo, G; Redo-Sanchez, A; Palacios, J; Tejada, J

2013-07-29

58

Video-rate terahertz electric-field vector imaging  

NASA Astrophysics Data System (ADS)

We present an experimental setup to dramatically reduce a measurement time for obtaining spatial distributions of terahertz electric-field (E-field) vectors. The method utilizes the electro-optic sampling, and we use a charge-coupled device to detect a spatial distribution of the probe beam polarization rotation by the E-field-induced Pockels effect in a ?110?-oriented ZnTe crystal. A quick rotation of the ZnTe crystal allows analyzing the terahertz E-field direction at each image position, and the terahertz E-field vector mapping at a fixed position of an optical delay line is achieved within 21 ms. Video-rate mapping of terahertz E-field vectors is likely to be useful for achieving real-time sensing of terahertz vector beams, vector vortices, and surface topography. The method is also useful for a fast polarization analysis of terahertz beams.

Takai, Mayuko; Takeda, Masatoshi; Sasaki, Manabu; Tachizaki, Takehiro; Yasumatsu, Naoya; Watanabe, Shinichi

2014-10-01

59

Terahertz imaging employing graphene modulator arrays.  

PubMed

In this paper we propose and experimentally demonstrate arrays of graphene electro-absorption modulators as electrically reconfigurable patterns for terahertz cameras. The active element of these modulators consists of only single-atom-thick graphene, achieving a modulation of the THz wave reflectance > 50% with a potential modulation depth approaching 100%. Although the prototype presented here only contains 4x4 pixels, it reveals the possibility of developing reliable low-cost video-rate THz imaging systems employing single detector. PMID:23389211

Sensale-Rodriguez, Berardi; Rafique, Subrina; Yan, Rusen; Zhu, Mingda; Protasenko, Vladimir; Jena, Debdeep; Liu, Lei; Xing, Huili Grace

2013-01-28

60

Passive terahertz imaging for security application  

NASA Astrophysics Data System (ADS)

The passive detection is safe for passengers and operators as no radiation. Therefore, passive terahertz (THz) imaging can be applied to human body security check. Imaging in the THz band offers the unique property of being able to identify object through a range of materials. Therefore passive THz imaging is meaningful for security applications. This attribute has always been of interest to both the civil and military marks with applications. We took advantage of a single THz detector and a trihedral scanning mirror to propose another passive THz beam scanning imaging method. This method overcame the deficiencies of the serious decline in image quality due to the movement of the focused mirror. We exploited a THz scanning mirror with a trihedral scanning mirror and an ellipsoidal mirror to streamline the structure of the system and increase the scanning speed. Then the passive THz beam scanning imaging system was developed based on this method. The parameters were set as follows: the best imaging distance was 1.7m, the image height was 2m, the image width was 1m, the minimum imaging time of per frame was 8s, and the minimum resolution was 4cm. We imaged humans with different objects hidden under their clothes, such as fruit knife, belt buckle, mobile phone, screwdriver, bus cards, keys and other items. All the tested stuffs could be detected and recognized from the image.

Guo, Lan-tao; Deng, Chao; Zhao, Yuan-meng; Zhang, Cun-lin

2013-08-01

61

Laser pulse amplitude changes induced by terahertz waves under linear electro-optic effect  

SciTech Connect

Changes in the amplitude of femtosecond laser pulses and in the energy of terahertz wave radiation induced during their co-propagation in ZnTe and GaP crystals are studied theoretically and experimentally. The results show that variation of the optical field amplitude leads to changes in the laser pulse energy and spectrum shift. We investigate the quantitative correlations between variations of the optical pulse energy, spectrum, phase and terahertz radiation energy. The values of laser pulse energy change and spectrum shift are proportional to the first time derivative of the magnitude of terahertz electric field, which enables coherent electro-optic detection. A simple and convenient calibration technique for terahertz energy detectors based on the correlation between laser and terahertz energy changes is proposed and tested.

Ilyakov, I. E., E-mail: igor-ilyakov@mail.ru; Shishkin, B. V. [Institute of Applied Physics, RAS, Nizhny Novgorod 603950 (Russian Federation); Kitaeva, G. Kh. [Faculty of Physics, M.V. Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Akhmedzhanov, R. A. [Institute of Applied Physics, RAS, Nizhny Novgorod 603950 (Russian Federation); N.I. Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod 603950 (Russian Federation)

2014-04-14

62

Compact, high average power, fiber-pumped terahertz source for active real-time imaging of concealed objects  

NASA Astrophysics Data System (ADS)

We have modeled and demonstrated a scalable, compact, fiber-pumped terahertz source based on difference frequency mixing (DFM) in zinc germanium phosphide (ZGP) capable of producing high average and peak-power pulses. Currently, our terahertz source produces 2mW of average THz power and >40W of peak power with sub-nanosecond pulses at a repetition rate of 100kHz in the range of 2-3THz without cryogenic cooling or ultra-fast optics. This high average power laser-based terahertz output enables the real-time imaging of concealed objects using an off-the-shelf uncooled microbolometer focal-plane array. With this THz system, we have imaged objects obscured inside in a common shipping envelope, demonstrating the potential of compact laser-based terahertz sources for use in security screening applications.

Creeden, Daniel; McCarthy, John C.; Ketteridge, Peter A.; Schunemann, Peter G.; Southward, Timothy; Komiak, James J.; Chicklis, Evan P.

2007-05-01

63

Complex extreme learning machine applications in terahertz pulsed signals feature sets.  

PubMed

This paper presents a novel approach to the automatic classification of very large data sets composed of terahertz pulse transient signals, highlighting their potential use in biochemical, biomedical, pharmaceutical and security applications. Two different types of THz spectra are considered in the classification process. Firstly a binary classification study of poly-A and poly-C ribonucleic acid samples is performed. This is then contrasted with a difficult multi-class classification problem of spectra from six different powder samples that although have fairly indistinguishable features in the optical spectrum, they also possess a few discernable spectral features in the terahertz part of the spectrum. Classification is performed using a complex-valued extreme learning machine algorithm that takes into account features in both the amplitude as well as the phase of the recorded spectra. Classification speed and accuracy are contrasted with that achieved using a support vector machine classifier. The study systematically compares the classifier performance achieved after adopting different Gaussian kernels when separating amplitude and phase signatures. The two signatures are presented as feature vectors for both training and testing purposes. The study confirms the utility of complex-valued extreme learning machine algorithms for classification of the very large data sets generated with current terahertz imaging spectrometers. The classifier can take into consideration heterogeneous layers within an object as would be required within a tomographic setting and is sufficiently robust to detect patterns hidden inside noisy terahertz data sets. The proposed study opens up the opportunity for the establishment of complex-valued extreme learning machine algorithms as new chemometric tools that will assist the wider proliferation of terahertz sensing technology for chemical sensing, quality control, security screening and clinic diagnosis. Furthermore, the proposed algorithm should also be very useful in other applications requiring the classification of very large datasets. PMID:25037827

Yin, X-X; Hadjiloucas, S; Zhang, Y

2014-11-01

64

Image reconstruction and optimization using a terahertz scanned imaging system  

NASA Astrophysics Data System (ADS)

Due to the limited number of array detection architectures in the millimeter wave to terahertz region of the electromagnetic spectrum, imaging schemes with scan architectures are typically employed. In these configurations the interplay between the frequencies used to illuminate the scene and the optics used play an important role in the quality of the formed image. Using a multiplied Schottky-diode based terahertz transceiver operating at 340 GHz, in a stand-off detection scheme; the effect of image quality of a metal target was assessed based on the scanning speed of the galvanometer mirrors as well as the optical system that was constructed. Background effects such as leakage on the receiver were minimized by conditioning the signal at the output of the transceiver. Then, the image of the target was simulated based on known parameters of the optical system and the measured images were compared to the simulation. By using an image quality index based on ?2 algorithm the simulated and measured images were found to be in good agreement with a value of ?2 = 0 .14. The measurements as shown here will aid in the future development of larger stand-off imaging systems that work in the terahertz frequency range.

Y?ld?r?m, ?hsan Ozan; Özkan, Vedat A.; Idikut, F?rat; Takan, Taylan; ?ahin, Asaf B.; Altan, Hakan

2014-10-01

65

Terahertz imaging and spectroscopy of large-area single-layer graphene  

Microsoft Academic Search

We demonstrate terahertz (THz) imaging and spectroscopy of a 15x15-mm^2 single-layer graphene film on Si using broadband THz pulses. The THz images clearly map out the THz carrier dynamics of the graphene-on-Si sample, allowing us to measure sheet conductivity with sub-mm resolution without fabricating electrodes. The THz carrier dynamics are dominated by intraband transitions and the THz-induced electron motion is

J. L. Tomaino; A. D. Jameson; J. W. Kevek; M. J. Paul; A. M. van der Zande; R. A. Barton; P. L. McEuen; E. D. Minot; Yun-Shik Lee

2011-01-01

66

Terahertz imaging and quantum cascade laser based devices  

E-print Network

The terahertz (THz) frequency range (f=0.3-10 THz, [lambda]=30-1000 lam) is much less technologically developed that the adjacent microwave and infrared frequency ranges, but offers several advantages for imaging applications: ...

Lee, Alan Wei Min

2010-01-01

67

Terahertz Imaging System for Medical Applications and Related High Efficiency Terahertz Devices  

NASA Astrophysics Data System (ADS)

A terahertz (THz) imaging system and high efficient terahertz sources and detectors for medical applications were developed. A fiber laser based compact time domain terahertz tomography system was developed with a high depth resolution of less than 20 ?m. Three-dimensional images of porcine skin were obtained including some physical properties such as applied skin creams. The discrimination between healthy human tissue and tumor tissue has been achieved using reflection spectra. To improve the THz imaging system, a ridge waveguide LiNbO3 based nonlinear terahertz generator was studied to achieve high output power. A ridge waveguide with 5-7 ?m width was designed for high efficiency emission from the LiNbO3 crystal by the electro-optic Cherenkov effect. Terahertz electronic sources and detectors were also realized for future imaging systems. As electronic source devices, resonant tunneling diode (RTD) oscillators with a patch antenna were fabricated using an InGaAs/InAlAs/AlAs triple barrier structure. On the other side, Schottky barrier diode (SBD) detectors with a log-periodic antenna were fabricated by thin-film technology on a Si substrate. Both devices operate above 1 THz at room temperature. This electronic THz device set could provide a future high performance imaging system.

Ouchi, Toshihiko; Kajiki, Kousuke; Koizumi, Takayuki; Itsuji, Takeaki; Koyama, Yasushi; Sekiguchi, Ryota; Kubota, Oichi; Kawase, Kodo

2013-07-01

68

Super-resolution reconstruction of terahertz images  

NASA Astrophysics Data System (ADS)

A prototype of terahertz imaging system has been built in CSIRO. This imager uses a backward wave oscillator as the source and a Schottky diode as the detector. It has a bandwidth of 500-700 GHz and a source power 10 mW. The resolution at 610 GHz is about 0.85 mm. Even though this imaging system is a coherent system, only the signal power is measured at the detector and the phase information of the detected wave is lost. Some initial images of tree leaves, chocolate bars and pinholes have been acquired with this system. In this paper, we report experimental results of an attempt to improve the resolution of this imaging system beyond the limitation of diffraction (super-resolution). Due to the lack of phase information needed for applying any coherent super-resolution algorithms, the performance of the incoherent Richardson-Lucy super-resolution algorithm has been evaluated. Experimental results have demonstrated that the Richardson-Lucy algorithm can significantly improve the resolution of these images in some sample areas and produce some artifacts in other areas. These experimental results are analyzed and discussed.

Li, Yue; Li, Li; Hellicar, Andrew; Guo, Y. Jay

2008-04-01

69

Metamaterial based devices for terahertz imaging  

NASA Astrophysics Data System (ADS)

The terahertz (THz) region has been shown to have considerable application potential for spectroscopic imaging, nondestructive imaging through nonpolar, nonmetallic materials and imaging of biological materials. These applications have all been possible due to the recent progress in THz sources, detectors and measurement techniques. However, only moderate progress has been made in developing passive and active devices to control and manipulate THz radiation, which can enhance current imaging capabilities. One promising approach for implementing passive and active devices at THz frequencies are metamaterials - composite materials designed to have specific electromagnetic properties not found in naturally occurring materials. The most common implementation utilizes a metallic resonant particle periodically distributed in an insulator matrix where the periodicity is significantly smaller than the wavelength of operation. We have designed and implemented three metamaterial based devices with potential applications to THz imaging. We present an electrically-driven active metamaterial which operates as an external modulator for a ~2.8 THz CW quantum cascade laser. We obtained a modulation depth of ~60%. We also demonstrate a polarization sensitive metamaterial which can be used as a continuously variable attenuator or as a wave plate. The latter may be useful for the development of THz phase contrast imaging.

Peralta, Xomalin G.; Wanke, Michael C.; Brener, Igal; Waldman, Jerry; Goodhue, William D.; Li, J.; Azad, Abul K.; Chen, Hou-Tong; Taylor, Antoinette J.; O'Hara, John F.

2010-02-01

70

Investigation of Nonequilibrium Superconductivity Using Terahertz Pulse Spectroscopy  

NASA Astrophysics Data System (ADS)

The nonequilibrium response of both conventional and high-Tc superconductors is investigated using terahertz pulse spectroscopy. This technique has gained popularity in recent years and is now widely accepted as a useful spectroscopic tool for examining carrier dynamics of materials. A near single-cycle, picosecond width electromagnetic transient centered in the THz region is used as the probe in a typical pump-probe fashion along with an optical pump pulse. This THz pulse is ideal for the measurement of superconducting systems, being on the same energy scale as the gap. The time resolved response of various samples after optical excitation by a femtosecond laser pulse is reported as a function of pump fluence and temperature. Linear spectroscopy will also be used, where the ratio of the transmission coefficient in the superconducting state to that in the normal state Ts/Tn is used to monitor the superconducting gap in conventional samples. *We acknowledge financial support from NSERC, CFI, iCORE and CIPI.

Cooke, David; Hegmann, Frank A.

2003-03-01

71

Towards gigawatt terahertz emission by few-cycle laser pulses  

SciTech Connect

It is shown by analysis and simulations that an extremely powerful terahertz (THz) radiation can be produced by a few-cycle laser pulse in a tenuous plasma. The THz amplitude scales linearly with the laser amplitude as well as with the sine of the laser carrier-envelope phase, and in particular, it increases exponentially with the decrease of the laser duration. For example, the THz amplitude increases by near 2 orders of magnitude as the laser duration decreases from one and a half cycles to one cycle; a single-cycle laser of 200 TW can drive the THz radiation of 1 GW with the energy conversion efficiency higher than 10{sup -4}.

Wang Weimin [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190 (China); Graduate School of Engineering, Utsunomiya University, 7-1-2 Yohtoh, Utsunomiya 321-8585 (Japan); Kawata, Shigeo [Graduate School of Engineering, Utsunomiya University, 7-1-2 Yohtoh, Utsunomiya 321-8585 (Japan); Sheng Zhengming; Zhang Jie [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190 (China); Key Laboratory for Laser Plasmas of the Ministry of Education of China and Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China); Li Yutong [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190 (China)

2011-07-15

72

High-power terahertz pulse sensor with overmoded structure  

NASA Astrophysics Data System (ADS)

Based on the hot electron effect in a semiconductor, an overmoded resistive sensor for 0.3-0.4 THz band is investigated. The distribution of electromagnetic field components, voltage standing wave ratio (VSWR), and the average electric field in the silicon block are obtained by using the three-dimensional finite-difference time-domain (FDTD) method. By adjusting several factors (such as the length, width, height and specific resistance of the silicon block) a novel sensor with optimal structural parameters that can be used as a power measurement device for high power terahertz pulse directly is proposed. The results show that the sensor has a relative sensitivity of about 0.24 kW-1, with a fluctuation of relative sensitivity of no more than ±22%, and the maximum of VSWR is 2.74 for 0.3-0.4 THz band.

Wang, Xue-Feng; Wang, Jian-Guo; Wang, Guang-Qiang; Li, Shuang; Xiong, Zheng-Feng

2014-05-01

73

In vivo terahertz imaging of rat skin burns  

NASA Astrophysics Data System (ADS)

A reflective, pulsed terahertz (THz) imaging system was used to acquire high-resolution (d10-90/ ?~1.925) images of deep, partial thickness burns in a live rat. The rat's abdomen was burned with a brass brand heated to ~220°C and pressed against the skin with contact pressure for ~10 sec. The burn injury was imaged beneath a Mylar window every 15 to 30 min for up to 7 h. Initial images display an increase in local water concentration of the burned skin as evidenced by a marked increase in THz reflectivity, and this likely correlates to the post-injury inflammatory response. After ~1 h the area of increased reflectivity consolidated to the region of skin that had direct contact with the brand. Additionally, a low reflecting ring of tissue could be observed surrounding the highly reflective burned tissue. We hypothesize that these regions of increased and decreased reflectivity correlate to the zones of coagulation and stasis that are the classic foundation of burn wound histopathology. While further investigations are necessary to confirm this hypothesis, if true, it likely represents the first in vivo THz images of these pathologic zones and may represent a significant step forward in clinical application of THz technology.

Tewari, Priyamvada; Kealey, Colin P.; Bennett, David B.; Bajwa, Neha; Barnett, Kelli S.; Singh, Rahul S.; Culjat, Martin O.; Stojadinovic, Alexander; Grundfest, Warren S.; Taylor, Zachary D.

2012-04-01

74

Terahertz spectroscopic imaging of a rabbit VX2 hepatoma model  

NASA Astrophysics Data System (ADS)

Terahertz (THz) spectroscopic imaging technique was applied to classify the tumor region in the rabbit liver with VX2 hepatocellular carcinoma. Within the measurement range of 0.1-2 THz, the average reflectance values for all tumor samples were more than 4% higher than those for healthy cells, and the terahertz measurements correlated well with histological analysis results. This study on paraffin-embedded tissues showed the alteration of cell density and protein content in tumors, excluding the effect of water.

Park, Jae Yeon; Choi, Hyuck Jae; Cho, Kyoung-Sik; Kim, Kyu-Rae; Son, Joo-Hiuk

2011-03-01

75

Single-pixel terahertz imaging via compressed sensing  

NASA Astrophysics Data System (ADS)

With the development of terahertz related technologies, the terahertz imaging technology will show its greater practical value in more areas. In this paper, we describe a terahertz imaging system that uses a single pixel detector in combination with a series of random masks to enable high-speed image acquisition. The image formation is based on the theory of compressed sensing (CS). When the scene under view is compressible by an algorithm like JPEG or JPEG2000, the CS theory enables us to stably reconstruct an image of the scene from fewer measurements than the number of reconstructed pixels. In this manner, we achieve sub-Nyquist image acquisition. CS theory mainly includes signal sparse representation, encoding measurement and reconstruction algorithm. CS combines sampling and compression into a single non-adaptive linear measurement process. Rather than measuring pixel samples of the scene under view, we measure inner products between the scene and a set of test functions. CS permits the reconstruction of a N-by-N pixel image using much fewer than N2 measurements. This approach eliminates the need for raster scanning of the object or the terahertz beam, while maintaining the high sensitivity of a single-element detector. We demonstrate the concept using a backward wave oscillator (BWO) which is a continuous-wave terahertz source and get a preliminary test result.

Zhao, Ya-qin; Zhang, Liang-liang; Duan, Guo-teng; Liu, Xiao-hua; Zhang, Cun-lin

2011-08-01

76

Temporal and spectral shaping of broadband terahertz pulses in a photoexcited semiconductor  

NASA Astrophysics Data System (ADS)

Transmission through a photoexcited semiconductor is used to temporally and spectrally shape a terahertz (THz) pulse. By adjusting the optical pump-THz probe delay, we experimentally introduce a polar asymmetry in the pulse profile as large as 92%. To shape the spectrum, we apply the same technique after strongly chirping the terahertz pulse. This leads to significant reshaping of the spectrum resulting in a 52% upshift of its median value. The pulse shaping techniques introduced here are of particular importance for temporal and spectral shape-sensitive THz nonlinear experiments.

Shalaby, Mostafa; Peccianti, Marco; Cooke, David G.; Hauri, Christoph P.; Morandotti, Roberto

2015-02-01

77

Measurement of thickness and refractive index using femtosecond and terahertz pulses  

NASA Astrophysics Data System (ADS)

We report a simple method to measure the thickness and refractive index of parallel-plane samples simultaneously using femtosecond and terahertz pulses. The time-of-flight measurements of the pulses with and without a sample are exploited to determine the thickness and refractive index of the sample. The accuracy in thickness measurement using femtosecond pulses is 2–3 ?m where refractive index can be measured with an accuracy up to three decimal points. The accuracy and lower limit of thickness measurement using terahertz pulses is also improved.

Hussain, Babar; Nawaz, Muhammad; Ahmed, Mushtaq; Raja, M. Yasin Akhtar

2013-05-01

78

Real-time terahertz imaging for art conservation science  

NASA Astrophysics Data System (ADS)

A new real-time terahertz imaging system has been developed by using a quantum cascade laser source and a microbolometer focal plane detector array. The application to non-invasive analyses of cultural heritage is demonstrated with an oil paint specimen. The experimental results suggested that the terahertz imaging system can identify materials based on a spectral database with a spatial resolution of about 300 ?m. The transmission imaging indicated the difference between natural and artificial ultramarine pigments. Since the size of the system is similar to a common portable infrared camera, it can be used at the place where the object is located, such as museums, and can contribute to conservation activities, such as drying process monitoring. This real-time, small, non-invasive terahertz imaging system can be used in various fundamental research fields and practical industries.

Fukunaga, K.; Sekine, N.; Hosako, I.; Oda, N.; Yoneyama, H.; Sudou, T.

2008-08-01

79

Scattering and propagation of terahertz pulses in random soot aggregate systems  

NASA Astrophysics Data System (ADS)

Scattering and propagation of terahertz pulses in random soot aggregate systems are studied by using the generalized multi-particle Mie-solution (GMM) and the pulse propagation theory. Soot aggregates are obtained by the diffusion-limited aggregation (DLA) model. For a soot aggregate in soot aggregate systems, scattering characteristics are analyzed by using the GMM. Scattering intensities versus scattering angles are given. The effects of different positions of the aggregate on the scattering intensities, scattering cross sections, extinction cross sections, and absorption cross sections are computed and compared. Based on pulse propagation in random media, the transmission of terahertz pulses in random soot aggregate systems is determined by the two-frequency mutual coherence function. Numerical simulations and analysis are given for terahertz pulses (0.7956 THz).

Li, Hai-Ying; Wu, Zhen-Sen; Bai, Lu; Li, Zheng-Jun

2014-05-01

80

Pulsed Terahertz Transmission Spectroscopy of Liquid CHCl3, CCl4, and their Mixtures B. N. Flanders, R. A. Cheville, D. Grischkowsky, and N. F. Scherer*,  

E-print Network

Pulsed Terahertz Transmission Spectroscopy of Liquid CHCl3, CCl4, and their Mixtures B. N. Flanders are measured by pulsed terahertz time domain transmission spectroscopy. The absorbance spectrum for neat CHCl3

Scherer, Norbert F.

81

Imaging of terahertz fields and responses  

E-print Network

In recent years it has become possible to generate terahertz-frequency (THz) fields that are strong enough to induce nonlinear responses in ordinary molecules and materials. Part of the development of THz technology and ...

Sivarajah, Prasahnt

82

Ionic contrast terahertz time resolved imaging of frog auricular heart muscle electrical activity  

E-print Network

Ionic contrast terahertz time resolved imaging of frog auricular heart muscle electrical activity contrast terahertz time resolved imaging of frog auricular heart muscle electrical activity Jean of functional frog auricular fibers by ionic contrast terahertz ICT near field microscopy. This technique

Paris-Sud XI, Université de

83

Transient optical response of quantum well excitons to intense narrowband terahertz pulses  

NASA Astrophysics Data System (ADS)

Intense narrowband terahertz pulses are used to modify excitonic transitions in semiconductor quantum wells and to study the dephasing properties of the optically dark 2p states. Time-resolved terahertz-pump and optical-probe measurements exhibit strong nonlinear optical transients of the 1s heavy-hole and light-hole exciton resonances when the terahertz radiation is tuned near the 1s to 2p intraexciton transition. A microscopic theory attributes the observed nonlinearities to Rabi sidebands showing that the 2p-dephasing time is three times that of the 1s-state.

Jameson, A. D.; Tomaino, J. L.; Lee, Yun-Shik; Prineas, J. P.; Steiner, J. T.; Kira, M.; Koch, S. W.

2009-11-01

84

Detection and identification of illicit drugs using terahertz imaging  

NASA Astrophysics Data System (ADS)

We demonstrated an advanced terahertz imaging technique for detection and identification of illicit drugs by introducing the component spatial pattern analysis. As an explanation, the characteristic fingerprint spectra and refractive index of ketamine were first measured with terahertz time-domain spectroscopy both in the air and nitrogen. The results obtained in the ambient air indicated that some absorption peaks are not obvious or probably not dependable. It is necessary and important to present a more practical technique for the detection. The spatial distributions of several illicit drugs [3,4-methylenedioxymethamphetamine, methylenedioxyamphetamine, heroin, acetylcodeine, morphine, and ketamine], widely consumed in the world, were obtained from terahertz images using absorption spectra previously measured in the range from 0.2to2.6THz in the ambient air. The different kinds of pure illicit drugs hidden in mail envelopes were inspected and identified. It could be an effective method in the field of safety inspection.

Lu, Meihong; Shen, Jingling; Li, Ning; Zhang, Yan; Zhang, Cunlin; Liang, Laishun; Xu, Xiaoyu

2006-11-01

85

Technology and Applications of Terahertz Imaging Non-Destructive Examination: Inspection of Space Shuttle Sprayed On Foam Insulation  

Microsoft Academic Search

The implementation of terahertz (THz) imaging for non-destructive evaluation shows 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, which produce images with lateral resolution <200 microns, and depth resolution <50 microns. We demonstrate the detection of voids

David Zimdars; J. A. Valdmanis; Jeffrey S. White; G. Stuk; S. Williamson; William P. Winfree; Eric I. Madaras

2005-01-01

86

High-power femtosecond-terahertz pulse induces a wound response in mouse skin  

NASA Astrophysics Data System (ADS)

Terahertz (THz) technology has emerged for biomedical applications such as scanning, molecular spectroscopy, and medical imaging. Although a thorough assessment to predict potential concerns has to precede before practical utilization of THz source, the biological effect of THz radiation is not yet fully understood with scant related investigations. Here, we applied a femtosecond-terahertz (fs-THz) pulse to mouse skin to evaluate non-thermal effects of THz radiation. Analysis of the genome-wide expression profile in fs-THz-irradiated skin indicated that wound responses were predominantly mediated by transforming growth factor-beta (TGF-?) signaling pathways. We validated NF?B1- and Smad3/4-mediated transcriptional activation in fs-THz-irradiated skin by chromatin immunoprecipitation assay. Repeated fs-THz radiation delayed the closure of mouse skin punch wounds due to up-regulation of TGF-?. These findings suggest that fs-THz radiation initiate a wound-like signal in skin with increased expression of TGF-? and activation of its downstream target genes, which perturbs the wound healing process in vivo.

Kim, Kyu-Tae; Park, Jaehun; Jo, Sung Jin; Jung, Seonghoon; Kwon, Oh Sang; Gallerano, Gian Piero; Park, Woong-Yang; Park, Gun-Sik

2013-08-01

87

High-power femtosecond-terahertz pulse induces a wound response in mouse skin  

PubMed Central

Terahertz (THz) technology has emerged for biomedical applications such as scanning, molecular spectroscopy, and medical imaging. Although a thorough assessment to predict potential concerns has to precede before practical utilization of THz source, the biological effect of THz radiation is not yet fully understood with scant related investigations. Here, we applied a femtosecond-terahertz (fs-THz) pulse to mouse skin to evaluate non-thermal effects of THz radiation. Analysis of the genome-wide expression profile in fs-THz-irradiated skin indicated that wound responses were predominantly mediated by transforming growth factor-beta (TGF-?) signaling pathways. We validated NF?B1- and Smad3/4-mediated transcriptional activation in fs-THz-irradiated skin by chromatin immunoprecipitation assay. Repeated fs-THz radiation delayed the closure of mouse skin punch wounds due to up-regulation of TGF-?. These findings suggest that fs-THz radiation initiate a wound-like signal in skin with increased expression of TGF-? and activation of its downstream target genes, which perturbs the wound healing process in vivo. PMID:23907528

Kim, Kyu-Tae; Park, Jaehun; Jo, Sung Jin; Jung, Seonghoon; Kwon, Oh Sang; Gallerano, Gian Piero; Park, Woong-Yang; Park, Gun-Sik

2013-01-01

88

Efficient real-time detection of terahertz pulse radiation based on photoacoustic conversion by carbon nanotube nanocomposite  

NASA Astrophysics Data System (ADS)

Terahertz sensing plays an important role in industry, biology and material science. Most existing techniques for terahertz detection either require bulky optics or need cryogenic cooling, and the uncooled thermal detectors usually suffer from long integration times (1-1,000 ms). We propose, and experimentally demonstrate, a novel scheme based on photoacoustic detection of terahertz pulse radiation. The transient and localized heating in a carbon nanotube-polymer composite by the absorption of terahertz pulse energy produces ultrasound, which is subsequently detected by a highly sensitive acoustic sensor. In contrast to conventional thermal detectors utilizing continuous heat integration, this new method of terahertz detection responds to the energy of each individual terahertz pulse by a time-gated scheme, thus rejecting the continuous radiation from the ambient. In addition, this novel detector possesses advantages such as room-temperature operation, a fast response (~0.1 µs) allowing real-time detection, compact size (millimetre scale) and wide spectral response.

Chen, Sung-Liang; Chang, You-Chia; Zhang, Cheng; Ok, Jong G.; Ling, Tao; Mihnev, Momchil T.; Norris, Theodore B.; Guo, L. Jay

2014-07-01

89

Efficient Cherenkov emission of broadband terahertz radiation from an ultrashort laser pulse in a sandwich structure with nonlinear core  

SciTech Connect

A scheme for efficient generation of broadband terahertz radiation by a femtosecond laser pulse propagating in a planar sandwichlike structure is proposed. The structure consists of a thin nonlinear core cladded with prisms made of a material with low terahertz absorption. The focused into a line laser pulse propagates in the core as a leaky or waveguide mode and emits Cherenkov wedge of terahertz waves in the cladding. We developed a theory that describes terahertz generation in such a structure and calculated spatial distribution of the generated terahertz field, its energy spectrum and optical-to-terahertz conversion efficiency. The developed theory predicts the conversion efficiency of up to several percent in a 1 cm long and 1 cm wide Si-LiNbO{sub 3}-Si sandwich structure with a 20 {mu}m thick nonlinear layer pumped by 8.5 {mu}J Ti:sapphire laser with pulse duration of 100 fs.

Bodrov, S. B. [Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod 603950 (Russian Federation); University of Nizhny Novgorod, Nizhny Novgorod 603950 (Russian Federation); Bakunov, M. I. [University of Nizhny Novgorod, Nizhny Novgorod 603950 (Russian Federation); Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod 603950 (Russian Federation); Hangyo, M. [Laser Terahertz Division, Institute of Laser Engineering, Osaka University, Osaka (Japan)

2008-11-01

90

Terahertz wave two-dimensional transmission imaging with a backward wave oscillator  

NASA Astrophysics Data System (ADS)

We present a terahertz (THz) imaging system with a Backward Wave Oscillator (BWO). BWO Continuous-Wave THz imaging is a new approach to non-destructive testing. Many materials that are opaque to visible and infrared light are transparent to THz radiation. THz wave image provides a higher spatial resolution than microwave image by having much shorter wavelength. It also poses no known harm to living organisms, making it a safe and powerful imaging technology. Unlike pulsed THz imaging, BWO THz imaging only yields intensity data without providing any depth, frequency-domain or time-domain information about the subject. However, in most cases the energy plots are sufficient for identification of targets. In exchange for the loss of depth, time-domain and frequency-domain information, BWO imaging offers a simple, fast and relatively low-cost system. In this work we show a simple Terahertz (THz) 2-dimentional scanning imaging system utilizing a BWO source tunable from 0.52 to 0.71 THz and a pyroelectric sensor detector operated in THz range. The sample is placed on an X-Z two-dimensional stage controlled by a computer. The intensity information of the terahertz wave after passing sample is collected. Two-dimensional image of the sample is obtained by raster scanning the sample in X and Z directions. A number of potential imaging applications are demonstrated using the 0.71 THz radiation, including nondestructive real-time testing for campus debit card and various articles contained in an envelop. And we present the digital image processing based on the result of the imaging system. This work reveals that a BWO THz imaging system is very practical, effective and promising in nondestructive identification and security inspections applications in future.

Yuan, Hongyang; Ge, Xinhao; Zhang, Cunlin

2008-12-01

91

Terahertz imaging of subjects with concealed weapons Jason C. Dickinson*a  

E-print Network

Terahertz imaging of subjects with concealed weapons Jason C. Dickinson*a , Thomas M. Goyettea for concealed weapons detection, the Submillimeter-Wave Technology Laboratory (STL) at the University, consisting of two ultra-stable far-infrared lasers, terahertz heterodyne detection systems, and terahertz

Massachusetts at Lowell, University of

92

Applications of terahertz spectral imaging-diagnostics in dentistry  

NASA Astrophysics Data System (ADS)

We present a review on terahertz diagnostics in dentistry. Time domain and spectral domain imaging studies are compared. Imaging built on mapping time-domain dependencies delivers the information on mechanisms of light transport in tissue: ballistic, quasi-ballistic and diffusive photon transfer. Imaging utilizing transform in frequency-domain provides a wealth of data on specific characterization of object: spectral and chemical content, tissue structure and composition and various kind of tissue abnormalities.

Zinov'ev, N. N.; Nikoghosyan, A. S.; Chamberlain, J. M.

2006-03-01

93

592 IEEE JOURNAL ON SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 7, NO. 4, JULY/AUGUST 2001 Interferometric Imaging With Terahertz Pulses  

E-print Network

592 IEEE JOURNAL ON SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 7, NO. 4, JULY/AUGUST 2001-domain spectroscopy. IMAGING via time-of-flight tomography is common in many fields of research. Techniques as a temporal gate. We have recently described a time-of-flight reflection imaging technique using single

Mittleman, Daniel

94

Reflective terahertz (THz) imaging: system calibration using hydration phantoms  

NASA Astrophysics Data System (ADS)

Terahertz (THz) hydration sensing continues to gain traction in the medical imaging community due to its unparalleled sensitivity to tissue water content. Rapid and accurate detection of fluid shifts following induction of thermal skin burns as well as remote corneal hydration sensing have been previously demonstrated in vivo using reflective, pulsed THz imaging. The hydration contrast sensing capabilities of this technology were recently confirmed in a parallel 7 Tesla Magnetic Resonance (MR) imaging study, in which burn areas are associated with increases in local mobile water content. Successful clinical translation of THz sensing, however, still requires quantitative assessments of system performance measurements, specifically hydration concentration sensitivity, with tissue substitutes. This research aims to calibrate the sensitivity of a novel, reflective THz system to tissue water content through the use of hydration phantoms for quantitative comparisons of THz hydration imagery.Gelatin phantoms were identified as an appropriate tissue-mimicking model for reflective THz applications, and gel composition, comprising mixtures of water and protein, was varied between 83% to 95% hydration, a physiologically relevant range. A comparison of four series of gelatin phantom studies demonstrated a positive linear relationship between THz reflectivity and water concentration, with statistically significant hydration sensitivities (p < .01) ranging between 0.0209 - 0.038% (reflectivity: %hydration). The THz-phantom interaction is simulated with a three-layer model using the Transfer Matrix Method with agreement in hydration trends. Having demonstrated the ability to accurately and noninvasively measure water content in tissue equivalent targets with high sensitivity, reflective THz imaging is explored as a potential tool for early detection and intervention of corneal pathologies.

Bajwa, Neha; Garritano, James; Lee, Yoon Kyung; Tewari, Priyamvada; Sung, Shijun; Maccabi, Ashkan; Nowroozi, Bryan; Babakhanian, Meghedi; Sanghvi, Sajan; Singh, Rahul; Grundfest, Warren; Taylor, Zachary

2013-02-01

95

Terahertz imaging and spectroscopy of large-area single-layer graphene  

Microsoft Academic Search

We demonstrate terahertz (THz) imaging and spectroscopy of a 15x15-mm^2\\u000asingle-layer graphene film on Si using broadband THz pulses. The THz images\\u000aclearly map out the THz carrier dynamics of the graphene-on-Si sample, allowing\\u000aus to measure sheet conductivity with sub-mm resolution without fabricating\\u000aelectrodes. The THz carrier dynamics are dominated by intraband transitions and\\u000athe THz-induced electron motion is

J. L. Tomaino; A. D. Jameson; J. W. Kevek; M. J. Paul; A. M. van der Zande; R. A. Barton; P. L. McEuen; E. D. Minot; Yun-Shik Lee

2011-01-01

96

Proposal for real-time terahertz imaging system with palm-size terahertz camera and compact quantum cascade laser  

E-print Network

This paper describes a real-time terahertz (THz) imaging system, using the combination of a palm-size THz camera with a compact quantum cascade laser (QCL). The THz camera contains a 320x240 microbolometer focal plane array ...

Oda, Naoki

97

Terahertz compressive imaging with metamaterial spatial light modulators  

NASA Astrophysics Data System (ADS)

Imaging at long wavelengths, for example at terahertz and millimetre-wave frequencies, is a highly sought-after goal of researchers because of the great potential for applications ranging from security screening and skin cancer detection to all-weather navigation and biodetection. Here, we design, fabricate and demonstrate active metamaterials that function as real-time tunable, spectrally sensitive spatial masks for terahertz imaging with only a single-pixel detector. A modulation technique permits imaging with negative mask values, which is typically difficult to achieve with intensity-based components. We demonstrate compressive techniques allowing the acquisition of high-frame-rate, high-fidelity images. Our system is all solid-state with no moving parts, yields improved signal-to-noise ratios over standard raster-scanning techniques, and uses a source orders of magnitude lower in power than conventional set-ups. The demonstrated imaging system establishes a new path for terahertz imaging that is distinct from existing focal-plane-array-based cameras.

Watts, Claire M.; Shrekenhamer, David; Montoya, John; Lipworth, Guy; Hunt, John; Sleasman, Timothy; Krishna, Sanjay; Smith, David R.; Padilla, Willie J.

2014-08-01

98

Reflection type of terahertz imaging system using a high-T{sub c} superconducting oscillator  

SciTech Connect

A reflection type of imaging system is shown at sub-terahertz frequencies generated from high-T{sub c} superconducting intrinsic Josephson junction mesa structures fabricated by single crystalline Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+?} to demonstrate how the sub-terahertz imaging technique using monochromatic radiation is powerful and unique for the variety of practical applications. Several examples are discussed in detail and are compared to other terahertz imaging systems.

Kashiwagi, T.; Minami, H.; Kadowaki, K. [Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8571 (Japan); Division of Materials Science, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573 (Japan); Nakade, K.; Saiwai, Y.; Kitamura, T.; Watanabe, C.; Ishida, K.; Sekimoto, S.; Asanuma, K.; Yasui, T.; Shibano, Y. [Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8571 (Japan); Markovi?, B.; Mirkovi?, J. [Faculty of Sciences, University of Montenegro, George Washington Str., 81000 Podgorica (Montenegro); Tsujimoto, M. [Department of Electronic Science and Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan); Yamamoto, T. [National Institute for Materials Science, Wide Bandgap Materials Group, Optical and Electronic Materials Unit, Environment and Energy Materials Division, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan)

2014-01-13

99

Terahertz Radiation Source in Air Based on Bifilamentation of Femtosecond Laser Pulses  

SciTech Connect

A new terahertz (THz) source in air based on the bifilamentation of femtosecond laser pulses is reported. This THz radiation is 1 order of magnitude more intense than the transition-Cherenkov THz emission from femtosecond laser filaments reported recently and shows different angular and polarization properties. We attribute it to the emission from a bimodal transmission line created by two plasma filaments.

Liu, Y.; Houard, A.; Prade, B.; Akturk, S.; Mysyrowicz, A.; Tikhonchuk, V. T. [Laboratoire d'Optique Appliquee, ENSTA, Ecole Polytechnique, Teramobile project, CNRS UMR 7639, Palaiseau, 91761 (France) and Centre Lasers Intenses et Applications, Universite Bordeaux 1, CNRS, CEA, UMR 5107, Talence, 33405 (France)

2007-09-28

100

Transmission properties of terahertz pulses through an ultrathin subwavelength silicon hole array  

E-print Network

Transmission properties of terahertz pulses through an ultrathin subwavelength silicon hole array 30 March 2005 We demonstrate extraordinary THz transmission of an array of subwavelength apertures patterned on ultrathin highly doped silicon by reactive ion etching. The zero-order transmission spectra

101

A single-frame terahertz image super-resolution reconstruction method based on sparse representation theory  

NASA Astrophysics Data System (ADS)

Terrorist attacks make the public safety issue becoming the focus of national attention. Passive terahertz security instrument can help overcomesome shortcomings with current security instruments. Terahertz wave has a strong penetrating power which can pass through clothes without harming human bodies and detected objects. However, in the lab experiments, we found that original terahertz imagesobtained by passive terahertz technique were often too vague to detect the objects of interest. Prior studies suggest that learning-based image super-resolution reconstruction(SRR) method can solve this problem. To our knowledge, we applied the learning-based image SRR method for the first time in single-frame passive terahertz image processing. Experimental results showed that the processed passive terahertz images wereclearer and easier to identify suspicious objects than the original images. We also compare our method with three conventional methods and our method show greater advantage over the other methods.

Li, Yue; Zhao, Yuan-meng; Deng, Chao; Zhang, Cunlin

2014-11-01

102

Terahertz Lasers Reveal Information for 3D Images  

NASA Technical Reports Server (NTRS)

After taking off her shoes and jacket, she places them in a bin. She then takes her laptop out of its case and places it in a separate bin. As the items move through the x-ray machine, the woman waits for a sign from security personnel to pass through the metal detector. Today, she was lucky; she did not encounter any delays. The man behind her, however, was asked to step inside a large circular tube, raise his hands above his head, and have his whole body scanned. If you have ever witnessed a full-body scan at the airport, you may have witnessed terahertz imaging. Terahertz wavelengths are located between microwave and infrared on the electromagnetic spectrum. When exposed to these wavelengths, certain materials such as clothing, thin metal, sheet rock, and insulation become transparent. At airports, terahertz radiation can illuminate guns, knives, or explosives hidden underneath a passenger s clothing. At NASA s Kennedy Space Center, terahertz wavelengths have assisted in the inspection of materials like insulating foam on the external tanks of the now-retired space shuttle. "The foam we used on the external tank was a little denser than Styrofoam, but not much," says Robert Youngquist, a physicist at Kennedy. The problem, he explains, was that "we lost a space shuttle by having a chunk of foam fall off from the external fuel tank and hit the orbiter." To uncover any potential defects in the foam covering, such as voids or air pockets, that could keep the material from staying in place, NASA employed terahertz imaging to see through the foam. For many years, the technique ensured the integrity of the material on the external tanks.

2013-01-01

103

Intense terahertz pulses from SLAC electron beams using coherent transition radiation  

NASA Astrophysics Data System (ADS)

SLAC has two electron accelerators, the Linac Coherent Light Source (LCLS) and the Facility for Advanced Accelerator Experimental Tests (FACET), providing high-charge, high-peak-current, femtosecond electron bunches. These characteristics are ideal for generating intense broadband terahertz (THz) pulses via coherent transition radiation. For LCLS and FACET respectively, the THz pulse duration is typically 20 and 80 fs RMS and can be tuned via the electron bunch duration; emission spectra span 3-30 THz and 0.5 THz-5 THz; and the energy in a quasi-half-cycle THz pulse is 0.2 and 0.6 mJ. The peak electric field at a THz focus has reached 4.4 GV/m (0.44 V/Å) at LCLS. This paper presents measurements of the terahertz pulses and preliminary observations of nonlinear materials response.

Wu, Ziran; Fisher, Alan S.; Goodfellow, John; Fuchs, Matthias; Daranciang, Dan; Hogan, Mark; Loos, Henrik; Lindenberg, Aaron

2013-02-01

104

On the role of terahertz field acceleration and beaming of surface plasmon generated ultrashort electron pulses  

SciTech Connect

A mechanism for control of the energy and pitch angle of surface plasmon accelerated electron pulses is proposed. Electrons generated via multi-photon absorption in a silver film on a glass prism are ponderomotively accelerated in the surface plasmon field excited by a 30 fs, 800?nm optical pulse. Through introduction of a single-cycle terahertz (THz) pulse, the energy spectrum and trajectory of the generated electron pulse can be controlled via the THz field strength. Generated electron pulses achieve peak kinetic energies up to 1.56?keV, while utilizing an incident optical field strength five times less than comparable plasmon accelerated electron pulses. These results demonstrate that THz pulses can be utilized to achieve tunable, high energy, trajectory controlled electron pulses necessary for various applications that require ultrafast electron pulse manipulation.

Greig, S. R., E-mail: sgreig@ualberta.ca; Elezzabi, A. Y., E-mail: elezzabi@ece.ualberta.ca [Ultrafast Optics and Nanophotonics Laboratory, Department of Electrical and Computer Engineering, University of Alberta, Edmonton T6G 2V4 (Canada)

2014-07-28

105

Intense terahertz emission from atomic cluster plasma produced by intense femtosecond laser pulses  

SciTech Connect

Terahertz (THz) emission from argon cluster plasma, generated by intense femtosecond laser pulses in the energy range of 10-70 mJ, has been investigated. THz polarization, energy dependence, and angular distribution were measured to provide an initial discussion on the mechanisms of THz emission. THz pulses of much higher energy were generated from argon clusters than from argon gas, which indicates that plasma produced from atomic clusters holds considerable promise as an intense THz source.

Jahangiri, Fazel; Hashida, Masaki; Tokita, Shigeki; Sakabe, Shuji [Advanced Research Center for Beam Science, ICR, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan and Department of Physics, GSS, Kyoto University, Kitashirakawa, Sakyo, Kyoto 606-7501 (Japan); Nagashima, Takeshi; Hangyo, Masanori [Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka 565-0871 (Japan)

2011-12-26

106

Imaging with ultrashort shaped pulses  

Microsoft Academic Search

Ultrashort shaped pulses are becoming available and their use for biomedical imaging will permit signal enhancements, allow selective excitation, and reduced photobleaching. These pulses are also enabling new imaging modalities which provide greater chemical information.

Yair Andegeko; Dmitry Pestov; Yves Coello; Vadim V. Lozovoy; Marcos Dantus

2009-01-01

107

Advanced terahertz imaging system performance model for concealed weapon identification  

NASA Astrophysics Data System (ADS)

The U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) and the U.S. Army Research Laboratory (ARL) have developed a terahertz-band imaging system performance model for detection and identification of concealed weaponry. The details of this MATLAB-based model which accounts for the effects of all critical sensor and display components, and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination, were reported on at the 2005 SPIE Europe Security and Defence Symposium. The focus of this paper is to report on recent advances to the base model which have been designed to more realistically account for the dramatic impact that target and background orientation can have on target observability as related to specular and Lambertian reflections captured by an active-illumination-based imaging system. The advanced terahertz-band imaging system performance model now also accounts for target and background thermal emission, and has been recast into a user-friendly, Windows-executable tool. This advanced THz model has been developed in support of the Defense Advanced Research Project Agency's (DARPA) Terahertz Imaging Focal-Plane Technology (TIFT) program. This paper will describe the advanced THz model and its new radiometric sub-model in detail, and provide modeling and experimental results on target observability as a function of target and background orientation.

Murrill, Steven R.; Redman, Brian; Espinola, Richard L.; Franck, Charmaine C.; Petkie, Douglas T.; De Lucia, Frank C.; Jacobs, Eddie L.; Griffin, Steven T.; Halford, Carl E.; Reynolds, Joe

2007-04-01

108

Study of freshly excised brain tissues using terahertz imaging  

PubMed Central

We demonstrated that tumors in freshly excised whole brain tissue could be differentiated clearly from normal brain tissue using a reflection-type terahertz (THz) imaging system. THz binary images of brain tissues with tumors indicated that the tumor boundaries in the THz images corresponded well to those in visible images. Grey and white-matter regions were distinguishable owing to the different distribution of myelin in the brain tissue. THz images corresponded closely with magnetic resonance imaging (MRI) results. The MRI and hematoxylin and eosin-stained microscopic images were investigated to account for the intensity differences in the THz images for fresh and paraffin-embedded brain tissue. Our results indicated that the THz signals corresponded to the cell density when water was removed. Thus, THz imaging could be used as a tool for label-free and real-time imaging of brain tumors, which would be helpful for physicians to determine tumor margins during brain surgery. PMID:25136506

Oh, Seung Jae; Kim, Sang-Hoon; Ji, Young Bin; Jeong, Kiyoung; Park, Yeonji; Yang, Jaemoon; Park, Dong Woo; Noh, Sam Kyu; Kang, Seok-Gu; Huh, Yong-Min; Son, Joo-Hiuk; Suh, Jin-Suck

2014-01-01

109

Experimental imaging research on continuous-wave terahertz in-line digital holography  

NASA Astrophysics Data System (ADS)

The terahertz (THz) imaging is an advanced technique on the basis of the unique characteristics of terahertz radiation. Due to its noncontact, non-invasive and high-resolution capabilities, it has already shown great application prospects in biomedical observation, sample measurement, and quality control. The continuous-wave terahertz in-line digital holography is a combination of terahertz technology and in-line digital holography of which the source is a continuous-wave terahertz laser. Over the past decade, many researchers used different terahertz sources and detectors to undertake experiments. In this paper, the pre-process of the hologram is accomplished after the holograms' recording process because of the negative pixels in the pyroelectric detector and the air vibration caused by the chopper inside the camera. To improve the quality of images, the phase retrieval algorithm is applied to eliminate the twin images. In the experiment, the pin which terahertz wave can't penetrate and the TPX slice carved letters "THz" are chosen for the samples. The amplitude and phase images of samples are obtained and the twin image and noise in the reconstructed images are suppressed. The results validate the feasibility of the terahertz in-line digital holographic imaging technique. This work also shows the terahertz in-line digital holography technique's prospects in materials science and biological samples' detection.

Huang, Haochong; Wang, Dayong; Rong, Lu; Wang, Yunxin

2014-09-01

110

Terahertz imaging system performance model for concealed-weapon identification  

Microsoft Academic Search

The U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) and the U.S. Army Research Laboratory have developed a terahertz (THz) -band imaging system performance model for detection and identification of concealed weaponry. The MATLAB-based model accounts for the effects of all critical sensor and display components and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination.

Steven R. Murrill; Eddie L. Jacobs; Steven K. Moyer; Carl E. Halford; Steven T. Griffin; Frank C. De Lucia; Douglas T. Petkie; Charmaine C. Franck

2008-01-01

111

Advanced terahertz imaging system performance model for concealed weapon identification  

Microsoft Academic Search

The U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) and the U.S. Army Research Laboratory (ARL) have developed a terahertz-band imaging system performance model for detection and identification of concealed weaponry. The details of this MATLAB-based model which accounts for the effects of all critical sensor and display components, and for the effects of atmospheric attenuation, concealment material attenuation,

Steven R. Murrill; Brian Redman; Richard L. Espinola; Charmaine C. Franck; Douglas T. Petkie; Frank C. De Lucia; Eddie L. Jacobs; Steven T. Griffin; Carl E. Halford; Joe Reynolds

2007-01-01

112

Terahertz imaging system performance model for concealed weapon identification  

Microsoft Academic Search

The U.S. Army Night Vision and Electronic Sensors Directorate and the U.S. Army Research Laboratory have developed a terahertz-band imaging system performance model for detection and identification of concealed weaponry. The MATLAB-based model accounts for the effects of all critical sensor and display components, and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination. The model is

Steven R. Murrill; Eddie L. Jacobs; Steven K. Moyer; Carl E. Halford; Steven T. Griffin; Frank C. De Lucia; Douglas T. Petkie; Charmaine C. Franck

2005-01-01

113

Numerical studies of powerful terahertz pulse generation from a super-radiant surface wave oscillator  

SciTech Connect

The results of theoretical and numerical studies of coherent stimulated terahertz radiation from intense, subnanosecond electron beam are presented. The mechanism of terahertz pulse generation is associated with self-bunching of the beam and slippage of the wave over the whole electron flow. This so called Cherenkov super-radiance (SR) is used to propose a compact terahertz generator with high peak power. A large cross-section (overmoded), slow wave structure is designed to support the high power handling capability, and the mode competition is avoided by operating the device in the surface wave status. With 2.5 D particle-in-cell simulation, the 'hot' characteristics of the proposed super-radiant terahertz generator are investigated, and the numerical results show that the SR peak power could be further increased by optimizing the amplitude profile of electron pulse. Under the condition of 0.5 ns pulsewidth, 500 kV voltage, and 1.5 kA current, the 110 ps, 680 MW, and 0.14 THz SR pulse is achieved with a power efficiency of 90.67% in TM{sub 01} mode.

Zhang Hai [Key Laboratory of Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 (China); Wang Jianguo [Key Laboratory of Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 (China); Northwest Institute of Nuclear Technology, P.O. Box 69-12, Xi'an, Shaanxi 710024 (China); Tong Changjiang; Li Xiaoze [Northwest Institute of Nuclear Technology, P.O. Box 69-12, Xi'an, Shaanxi 710024 (China); Wang Guangqiang [Department of Engineering Physics, Tsinghua University, Beijing 100084 (China)

2009-12-15

114

EDITORIAL: Terahertz nanotechnology Terahertz nanotechnology  

NASA Astrophysics Data System (ADS)

A useful synergy is being established between terahertz research and nanotechnology. High power sources [1-3] and detectors [4] in what was once considered the terahertz 'frequency gap' [5] in the electromagnetic spectrum have stimulated research with huge potential benefits in a range of industries including food, medicine and security, as well as fundamental physics and astrophysics. This special section, with guest editors Masayoshi Tonouchi and John Reno, gives a glimpse of the new horizons nanotechnology is broaching in terahertz research. While the wavelengths relevant to the terahertz domain range from hundreds of micrometres to millimetres, structures at the nanoscale reveal interesting low energy dynamics in this region. As a result terahertz spectroscopy techniques are becoming increasingly important in nanomaterial characterization, as demonstrated in this special section by colleagues at the University of Oxford in the UK and the Australian National University. They use terahertz spectroscopy to identify the best nanostructure parameters for specific applications [6]. The low energy dynamics in nanostructures also makes them valuable tools for terahertz detection [7]. In addition the much sought after terahertz detection over broadband frequency ranges has been demonstrated, providing versatility that has been greatly in demand, particularly in spectroscopy applications [8, 9]. Also in this special section, researchers in Germany and China tackle some of the coupling issues in terahertz time domain spectroscopy with an emitter specifically well suited for systems operated with an amplified fibre [3]. 'In medical imaging, the advantage of THz radiation is safety, because its energy is much lower than the ionization energy of biological molecules, in contrast to hazardous x-ray radiation,' explains Joo-Hiuk Son from the University of Seoul in Korea in his review [10]. As he also points out, the rotational and vibrational energies of water molecules are within the THz spectral region providing an additional benefit. His review describes the principle, characteristics, and applications of terahertz molecular imaging, where the use of nanoparticle probes allows dramatically enhanced sensitivity. Jiaguang Han and Weili Zhang and colleagues in China, Saudi Arabia, Japan and the US report exciting developments for optoelectronics [11]. They describe work on plasmon-induced transparency (PIT), an analogue of electromagnetically induced transparency (EIT) where interference leads to a sharp transparency window that may be useful for nonlinear and slow-light devices, optical switching, pulse delay, and storage for optical information processing. While PIT has advantages over the cumbersome experimental systems required for EIT, it has so far been constrained to very narrow band operation. Now Zhang and colleagues present the simulation, implementation, and measurement of a broadband PIT metamaterial functioning across a frequency range greater than 0.40 THz in the terahertz regime. 'We can foresee a historic breakthrough for science and technology through terahertz research,' concluded Masayoshi Tonouchi in his review over five years ago as momentum in the field was mounting [12]. He added, 'It is also noteworthy that THz research is built on many areas of science and the coordination of a range of disciplines is giving birth to a new science.' With the inherently multidisciplinary nature of nanotechnology research it is not so strange to see the marriage of the two fields form such a fruitful partnership, as this special section highlights. References [1] Williams B S, Kumar S, Hu Q and Reno J L 2006 High-power terahertz quantum-cascade lasers Electron. Lett. 42 89-91 [2] Köhler R et al 2002 Terahertz semiconductor-heterostructure laser Nature 417 156-9 [3] Mittendorff M, Xu M, Dietz R J B, K¨unzel H, Sartorius B, Schneider H, Helm M and Winnerl S 2013 Large area photoconductive THz emitter for 1.55 ?m excitation based on an InGaAs heterostructure Nanotechnology 24 214007 [4] Chen H-T, Padilla W J, Zide J M O, Gossa

Demming, Anna; Tonouchi, Masayoshi; Reno, John L.

2013-05-01

115

Using Terahertz Pulses to Probe Transient Photoconductivity in Organic Molecular Crystals  

NASA Astrophysics Data System (ADS)

The nature of photoexcitations and charge carrier generation in conjugated polymers and organic molecular crystals is not completely understood. Are mobile charge carriers generated directly by the absorption of light in organic semiconductors, or are excitons initially formed which then take several picoseconds to dissociate by various mechanisms into separated charges? To address some of these issues, we have used for the first time terahertz pulse spectroscopy to measure transient photoconductivity in organic molecular crystals [Phys. Rev. Lett. 89, 227403 (2002)]. Functionalized pentacene single crystals were excited with 800 nm, 100 fs pump pulses and then probed with sub-picosecond terahertz pulses over a temperature range from 10 to 300 K. We find that mobile charge carriers are generated within 0.5 ps of the excitation pulse, limited by the time resolution of our setup. Larger photoconducting transients are observed at lower temperatures. The potential of terahertz pulse spectroscopy for probing ultrafast carrier dynamics in organic semiconductors is discussed. This work was supported by NSERC, CFI, IIPP, ASRA, CIPI, and ONR.

Hegmann, F. A.; Tykwinski, R. R.; Lui, K. P. H.; Bullock, J. E.; Anthony, J. E.

2003-03-01

116

The potential of terahertz imaging for cancer diagnosis: A review of investigations to date  

PubMed Central

The terahertz region lies between the microwave and infrared regions of the electromagnetic spectrum such that it is strongly attenuated by water and very sensitive to water content. Terahertz radiation has very low photon energy and thus it does not pose any ionization hazard for biological tissues. Because of these characteristic properties, there has been an increasing interest in terahertz imaging and spectroscopy for biological applications within the last few years and more and more terahertz spectra are being reported, including spectroscopic studies of cancer. The presence of cancer often causes increased blood supply to affected tissues and a local increase in tissue water content may be observed: this acts as a natural contrast mechanism for terahertz imaging of cancer. Furthermore the structural changes that occur in affected tissues have also been shown to contribute to terahertz image contrast. This paper introduces terahertz technology and provides a short review of recent advances in terahertz imaging and spectroscopy techniques. In particular investigations relating to the potential of terahertz imaging and spectroscopy for cancer diagnosis will be highlighted. PMID:23256057

Yu, Calvin; Fan, Shuting; Sun, Yiwen; Pickwell-MacPherson, Emma

2012-01-01

117

Target recognition in passive terahertz image of human body  

NASA Astrophysics Data System (ADS)

THz radiation can penetrate through many nonpolar dielectric materials and can be used for nondestructive/noninvasive sensing and imaging of targets under nonpolar, nonmetallic covers or containers. Thus using THz systems to "see through" concealing barriers (i.e. packaging, corrugated cardboard, clothing) has been proposed as a new security screening method. Objects that can be detected by THz include concealed weapons, explosives, and chemical agents under clothing. Passive THz imaging system can detect THz wave from human body without transmit any electromagnetic wave, and the suspicious objects will become visible because the THz wave is blocked by this items. We can find out whether or not someone is carrying dangerous objects through this image. In this paper, the THz image enhancement, segmentation and contour extraction algorithms were studied to achieve effective target image detection. First, the terahertz images are enhanced and their grayscales are stretched. Then we apply global threshold segmentation to extract the target, and finally the targets are marked on the image. Experimental results showed that the algorithm proposed in this paper can extract and mark targets effectively, so that people can identify suspicious objects under clothing quickly. The algorithm can significantly improve the usefulness of the terahertz security apparatus.

Zhao, Ran; Zhao, Yuan-meng; Deng, Chao; Zhang, Cun-lin; Li, Yue

2014-11-01

118

Development of Fiber-Coupled Compact Terahertz Time-Domain Spectroscopy Imaging Head  

E-print Network

Development of Fiber-Coupled Compact Terahertz Time-Domain Spectroscopy Imaging Head Ryotaro INOUE, 2006; published online October 6, 2006) The development of a fiber-coupled compact terahertz time-hemispherical lenses with no parabolic reflectors. The THz transmission image of an IC card clearly shows

Tonouchi, Masayoshi

119

Developments in time-resolved ultrafast imaging and spectroscopy at terahertz frequencies  

E-print Network

Prior to the advent of high energy pulsed femtosecond lasers, the field of terahertz (THz) spectroscopy was stagnated by the lack of both high power THz sources and sensitive THz detectors. Over the past few years, it has ...

Teo, Stephanie M

2014-01-01

120

Excitation of terahertz radiation by laser pulses in nonuniform plasma channels  

SciTech Connect

The excitation of terahertz radiation by laser pulses propagating in miniature plasma channels is considered. Generation of radiation by laser pulses in uniform plasmas is generally minimal. However, if one considers propagation in corrugated plasma channels, conditions for radiation generation can be met due to the inhomogeneity of the channel and the presence of guided waves with subluminal phase velocities. It is found that for channels and laser pulses with parameters that can be realized today, energy conversion rates of a fraction of a joule per centimeter can be achieved. Miniature corrugated channels can also be used for creation of THz radiation by bunched electron beams.

Antonsen, Thomas M. Jr.; Palastro, John; Milchberg, Howard M. [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States); Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States)

2007-03-15

121

Intense terahertz emission from relativistic circularly polarized laser pulses interaction with overdense plasmas  

SciTech Connect

During the interaction of a relativistic circularly polarized laser pulse with an overdense plasma target, the longitudinal motion of bunches of electrons under the action of light pressure and electrostatic restore force can emit intense terahertz (THz) pulses. This mechanism allows high pump laser intensity and large electron number participating in the emission. Two-dimensional particle-in-cell simulations are carried out to investigate the THz emission. The results suggest that such a source can produce remarkably intense THz pulses with energy of several mJ/sr and power of tens of gigawatts, which could find applications in nonlinear studies and relativistic laser-plasma interaction diagnostics.

Chen, Zi-Yu; Li, Xiao-Ya [National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900 (China)] [National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900 (China); Yu, Wei [Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China)] [Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China)

2013-10-15

122

Continuous wave terahertz reflection imaging of human colorectal tissue  

NASA Astrophysics Data System (ADS)

Continuous wave terahertz (THz) imaging has the potential to offer a safe, non-ionizing, and nondestructive medical imaging modality for delineating colorectal cancer. Fresh excisions of normal colon tissue were obtained from surgeries performed at the University of Massachusetts Medical School, Worcester. Reflection measurements of thick sections of colorectal tissues, mounted in an aluminum sample holder, were obtained for both fresh and formalin fixed tissues. The two-dimensional reflection images were acquired by using an optically pumped far-infrared molecular gas laser operating at 584 GHz with liquid Helium cooled silicon bolometer detector. Using polarizers in the experiment both co-polarized and cross-polarized remittance form the samples was collected. Analysis of the images showed the importance of understanding the effects of formalin fixation while determining reflectance level of tissue response. The resulting co- and cross-polarized images of both normal and formalin fixed tissues showed uniform terahertz response over the entire sample area. Initial measurements indicated a co-polarized reflectance of 16%, and a cross-polarized reflectance of 0.55% from fresh excisions of normal colonic tissues.

Doradla, Pallavi; Alavi, Karim; Joseph, Cecil S.; Giles, Robert H.

2013-03-01

123

Role of nonlinear refraction in the generation of terahertz field pulses by light fields  

NASA Astrophysics Data System (ADS)

The generation of microwave (terahertz) pulses without any envelope in a four-level quasi-resonant medium is considered. Two intense quasi-monochromatic laser fields lead to a partial upper-level population. Microwave field pulses cause the transition between these levels. For appropriately chosen scales, the evolution of the fields is shown to be described by the pseudo-spin evolution equations in a microwave field with the inclusion of nonlinear refraction caused by an adiabatic upper-level population. The evolution of terahertz field pulses is described outside the scope of the slow-envelope approximation. When a number of standard approximations are taken into account, this system of equations is shown to be equivalent to an integrable version of the generalized reduced Maxwell-Bloch equations or to the generalized three-wave mixing equations. The soliton solution found by the inverse scattering transform method is used as an example to show that nonlinear refraction leads to a strong compression of the microwave (terahertz) field soliton.

Zabolotskii, A. A.

2013-07-01

124

Role of nonlinear refraction in the generation of terahertz field pulses by light fields  

SciTech Connect

The generation of microwave (terahertz) pulses without any envelope in a four-level quasi-resonant medium is considered. Two intense quasi-monochromatic laser fields lead to a partial upper-level population. Microwave field pulses cause the transition between these levels. For appropriately chosen scales, the evolution of the fields is shown to be described by the pseudo-spin evolution equations in a microwave field with the inclusion of nonlinear refraction caused by an adiabatic upper-level population. The evolution of terahertz field pulses is described outside the scope of the slow-envelope approximation. When a number of standard approximations are taken into account, this system of equations is shown to be equivalent to an integrable version of the generalized reduced Maxwell-Bloch equations or to the generalized three-wave mixing equations. The soliton solution found by the inverse scattering transform method is used as an example to show that nonlinear refraction leads to a strong compression of the microwave (terahertz) field soliton.

Zabolotskii, A. A., E-mail: zabolotskii@iae.nsk.su [Russian Academy of Sciences, Institute of Automation and Electrometry, Siberian Branch (Russian Federation)

2013-07-15

125

Terahertz imaging system performance model for concealed-weapon identification  

NASA Astrophysics Data System (ADS)

The U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) and the U.S. Army Research Laboratory have developed a terahertz (THz) -band imaging system performance model for detection and identification of concealed weaponry. The MATLAB-based model accounts for the effects of all critical sensor and display components and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination. The model is based on recent U.S. Army NVESD sensor performance modeling technology that couples system design parameters to observer-sensor field performance by using the acquire methodology for weapon identification performance predictions. This THz model has been developed in support of the Defense Advanced Research Project Agencies' Terahertz Imaging Focal-Plane Technology (TIFT) program and is currently being used to guide the design and development of a 0.650 THz active-passive imaging system. This paper will describe the THz model in detail, provide and discuss initial modeling results for a prototype THz imaging system, and outline plans to calibrate and validate the model through human perception testing.

Murrill, Steven R.; Jacobs, Eddie L.; Moyer, Steven K.; Halford, Carl E.; Griffin, Steven T.; De Lucia, Frank C.; Petkie, Douglas T.; Franck, Charmaine C.

2008-03-01

126

Terahertz imaging system performance model for concealed-weapon identification.  

PubMed

The U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) and the U.S. Army Research Laboratory have developed a terahertz (THz) -band imaging system performance model for detection and identification of concealed weaponry. The MATLAB-based model accounts for the effects of all critical sensor and display components and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination. The model is based on recent U.S. Army NVESD sensor performance modeling technology that couples system design parameters to observer-sensor field performance by using the acquire methodology for weapon identification performance predictions. This THz model has been developed in support of the Defense Advanced Research Project Agencies' Terahertz Imaging Focal-Plane Technology (TIFT) program and is currently being used to guide the design and development of a 0.650 THz active-passive imaging system. This paper will describe the THz model in detail, provide and discuss initial modeling results for a prototype THz imaging system, and outline plans to calibrate and validate the model through human perception testing. PMID:18709076

Murrill, Steven R; Jacobs, Eddie L; Moyer, Steven K; Halford, Carl E; Griffin, Steven T; De Lucia, Frank C; Petkie, Douglas T; Franck, Charmaine C

2008-03-20

127

Terahertz imaging system performance model for concealed weapon identification  

NASA Astrophysics Data System (ADS)

The U.S. Army Night Vision and Electronic Sensors Directorate and the U.S. Army Research Laboratory have developed a terahertz-band imaging system performance model for detection and identification of concealed weaponry. The MATLAB-based model accounts for the effects of all critical sensor and display components, and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination. The model is based on recent U.S. Army NVESD sensor performance models that couple system design parameters to observer-sensor field performance using the acquire methodology for weapon identification performance predictions. This THz model has been developed in support of the Defense Advanced Research Project Agencies' Terahertz Imaging Focal-Plane-Array Technology (TIFT) program and is presently being used to guide the design and development of a 0.650 THz active/passive imaging system. This paper will describe the THz model in detail, provide and discuss initial modeling results for a prototype THz imaging system, and outline plans to validate and calibrate the model through human perception testing.

Murrill, Steven R.; Jacobs, Eddie L.; Moyer, Steven K.; Halford, Carl E.; Griffin, Steven T.; De Lucia, Frank C.; Petkie, Douglas T.; Franck, Charmaine C.

2005-11-01

128

Imaging at 0.2 and 2.5 terahertz  

NASA Astrophysics Data System (ADS)

We report the development and initial results of two Terahertz imaging systems based on monochromatic sources at 0.2 and 2.52 THz. The first is based on a microwave oscillator, whose frequency is multiplied to 0.2 THz, used in conjunction with a zero-bias detector. The sample is scanned across the beam, and transmission images are obtained after processing. The second system allows real-time images, and consists of a methanol gas laser emitting at 119 microns (2.52 THz) and a commercial camera based on a microbolometer array. We describe the construction and performance of the methanol laser and a tunable CO2 laser, which emits 20 W at the 9P(36) pump line. Due to the high coherence of the laser, this system is particularly suited for diffraction and interference imaging. We have measured the absorption coefficients of a few samples assuming the Beer law.

Melo, Arline M.; Toledo, Mauricio A. P.; Maia, Francisco C. B.; Rocha, Andre; Plotegher, Matheus B.; Pereira, Daniel; Cruz, Flavio C.

2013-03-01

129

Terahertz Polarization Imaging for Colon Cancer Detection Pallavi Doradlaa,b  

E-print Network

Terahertz Polarization Imaging for Colon Cancer Detection Pallavi Doradlaa,b , Karim Alavic , Cecil Division of Colon and Rectal Surgery, University of Massachusetts Medical School Worcester. ABSTRACT modality for delineating colorectal cancer. The terahertz reflectance measurements of fresh 3 ­ 5 mm thick

Massachusetts at Lowell, University of

130

Detection of colon cancer by continuous-wave terahertz polarization imaging  

E-print Network

Detection of colon cancer by continuous- wave terahertz polarization imaging technique Pallavi Doradla Karim Alavi Cecil Joseph Robert Giles #12;Detection of colon cancer by continuous-wave terahertz of registering reflectance differences between cancerous and normal colon. However, further investigations

Massachusetts at Lowell, University of

131

Cancer Diagnosis by Terahertz Molecular Imaging Technique  

NASA Astrophysics Data System (ADS)

We obtained the diagnostic images of cancerous tumors by employing the THz molecular imaging (TMI) technique which measured the THz response change by surface plasmon resonance induced on the surface of nanoparticles with a irradiation of near-infrared (NIR) beam. To demonstrate the principle of the TMI technique, THz images of tissues with nanoprobes were observed and compared with THz only images. The sensitivity of TMI was further enhanced by adopting a THz differential measurement technique, which was realized by modulating the NIR beams. By employing this differential TMI technique, the diagnostic images of cancerous tumors were obtained ex vivo and in vivo in the preclinical stage. These images indicated the feasibility of applying the differential TMI technique in the clinical stage.

Oh, Seung Jae; Huh, Yong-Min; Suh, Jin-Suck; Choi, Jihye; Haam, Seungjoo; Son, Joo-Hiuk

2012-01-01

132

Soliton regime of generation of terahertz radiation taking into account the phase of an optical pulse  

NASA Astrophysics Data System (ADS)

An integrable generalization of the Yajima-Oikawa system of equations has been obtained to describe the optical generation of broadband terahertz radiation in a quadratically nonlinear medium with allowance for the effect of the phase of an optical pulse on this process. The corresponding Lax pair has been found. A soliton solution has been constructed. The analysis has indicated, in particular, that the role of the phase of the optical pulse increases significantly in the vicinity of zero value of the second-order group dispersion parameter. This behavior can result in a significant increase in the efficiency of generation in the soliton regime.

Sazonov, S. V.; Sukhorukov, A. P.; Ustinov, N. V.

2015-01-01

133

Single-shot spatiotemporal measurements of high-field terahertz pulses  

SciTech Connect

The electric field profiles of broad-bandwidth coherent terahertz (THz) pulses, emitted by laser-wakefield-accelerated electron bunches, are studied. The near-single-cycle THz pulses are measured with two single-shot techniques in the temporal and spatial domains. Spectra of 0-6 THz and peak fields up to {approx_equal} 0.4 MV cm{sup -1} are observed. The measured field substructure demonstrates the manifestation of spatiotemporal coupling at focus, which affects the interpretation of THz radiation as a bunch diagnostic and in high-field pump-probe experiments.

van Tilborg, Jeroen; Schroeder, Carl; Toth, Csaba; Geddes, Cameron; Esarey, Eric; Leemans, Wim

2011-06-17

134

Terahertz Imaging and Spectroscopy of Carbon-Based and Semiconductor Nanostructures  

NASA Astrophysics Data System (ADS)

This thesis will cover work that I have completed relating to the field of terahertz (THz) science. My work has consisted of generating tunable, narrowband THz pulses in a table-top optical setup and using both narrow- and broadband THz pulses to study various material systems. Broadband THz pulses were used to study the transmission properties of a large-area graphene monolayer and vertically grown carbon nanotube forests. We performed raster scans to image our optically invisible graphene sample, which was clearly distinguished from its silicon substrate. From these studies, we were able to calculate the sheet conductivity/resistivity of the graphene using a contactless, non-damaging method that is immune to difficulties arising from local defects within the sample. It also opens up the possibility of studying the material properties of a sample enclosed within certain structures without having to remove the sample and/or damage the encasement. Further, we have discovered that vertically grown carbon nanotubes respond strongly to THz radiation. Preliminary simulations suggest that they respond in a very counterintuitive way and while much remains to be done before we can state with certainty exactly what is physically occurring, the prospect of uncovering such an unanticipated result is tantalizing on its own. I used difference frequency generation of orthogonal, temporally offset, chirped optical pulses to create our narrowband THz pulses. The variable time delay between these pulses was used to adjust the pulse's central frequency. THz time domain spectroscopy and calorimeter-based measurements were used to study the temporal and spectral composition and field strength of the THz pulses. These pulses, along with their broadband counterparts, were used to study electron dynamics within semiconductor nanostructures, both bare quantum wells and quantum wells grown inside of a microcavity. The dynamics of exciton and exciton-polariton polarizations were studied while intense THz pulses were used to modulate their resonances and coherently control their transitions.

Tomaino, Joseph L.

135

Terahertz imaging and spectroscopy of large-area single-layer graphene  

E-print Network

We demonstrate terahertz (THz) imaging and spectroscopy of a 15x15-mm^2 single-layer graphene film on Si using broadband THz pulses. The THz images clearly map out the THz carrier dynamics of the graphene-on-Si sample, allowing us to measure sheet conductivity with sub-mm resolution without fabricating electrodes. The THz carrier dynamics are dominated by intraband transitions and the THz-induced electron motion is characterized by a flat spectral response. A theoretical analysis based on the Fresnel coefficients for a metallic thin film shows that the local sheet conductivity varies across the sample from {\\sigma}s = 1.7x10^-3 to 2.4x10^-3 {\\Omega}^-1 (sheet resistance, {\\rho}s = 420 - 590 {\\Omega}/sq).

Tomaino, J L; Kevek, J W; Paul, M J; van der Zande, A M; Barton, R A; McEuen, P L; Minot, E D; Lee, Yun-Shik; 10.1364/OE.19.000141

2011-01-01

136

Single-cycle Terahertz Pulses with >0.2 V/A Field Amplitudes via Coherent Transition Radiation  

SciTech Connect

We demonstrate terahertz pulses with field amplitudes exceeding 0.2 V/{angstrom} generated by coherent transition radiation. Femtosecond, relativistic electron bunches generated at the Linac Coherent Light Source are passed through a beryllium foil, and the emitted radiation is characterized as a function of the bunch duration and charge. Broadband pulses centered at a frequency of 10 THz with energies of 140 {mu}J are measured. These far-below-bandgap pulses drive a nonlinear optical response in a silicon photodiode, with which we perform nonlinear autocorrelations that yield information regarding the terahertz temporal profile. Simulations of the spatiotemporal profile agree well with experimental results.

Daranciang, Dan; /Stanford U., Chem. Dept.; Goodfellow, John; /Stanford U. Materials Sci. Dept.; Fuchs, Matthias; /SIMES, Stanford /SLAC, PULSE; Wen, Haidan; /ANL, APS; Ghimire, Shambhu; /SLAC, PULSE; Reis, David A.; /SIMES, Sanford /SLAC, PULSE /Stanford U., Appl. Phys. Dept.; Loos, Henrik; Fisher, Alan S.; /SLAC, LCLS; Lindenberg, Aaron M.; /Stanford U. Materials Sci. Dept. /SIMES, Stanford /SLAC, PULSE

2012-02-15

137

Method for large and rapid terahertz imaging  

DOEpatents

A method of large-scale active THz imaging using a combination of a compact high power THz source (>1 watt), an optional optical system, and a camera for the detection of reflected or transmitted THz radiation, without the need for the burdensome power source or detector cooling systems required by similar prior art such devices. With such a system, one is able to image, for example, a whole person in seconds or less, whereas at present, using low power sources and scanning techniques, it takes several minutes or even hours to image even a 1 cm.times.1 cm area of skin.

Williams, Gwyn P.; Neil, George R.

2013-01-29

138

Compact fiber pumped terahertz source  

NASA Astrophysics Data System (ADS)

Converting near infrared signals in a nonlinear medium is an attractive way to generate terahertz radiation due to the availability of near-IR lasers and nonlinear materials. However, these terahertz generation schemes are typically inefficient and are often cumbersome, which may limit their use in certain applications. We have developed and demonstrated a compact, fiber pumped optical terahertz source based difference frequency mixing (DFM) of nanosecond pulses in zinc germanium phosphide (ZGP). With this setup, we have successfully generated 2mW of average power terahertz radiation at 2.45THz. This has enabled us to perform active, real-time terahertz imaging experiments using an uncooled microbolometer array. In performing these experiments, we have also developed a theoretical model for terahertz generation based on DFM of IR pump signals. In this paper, we discuss our compact fiber pumped terahertz source technology, imaging system, model, and how we intend to overcome some of the common issues associated with optical terahertz generation.

Creeden, Daniel; McCarthy, John C.; Ketteridge, Peter A.; Southward, Timothy; Schunemann, Peter G.; Kmoiak, James J.; Dove, Webster; Chicklis, Evan P.

2007-04-01

139

Terahertz standoff imaging testbed design and performance for concealed weapon and device identification model development  

Microsoft Academic Search

This paper describes the design and performance of the U.S. Army RDECOM CERDEC Night Vision and Electronic Sensors Directorate's (NVESD), active 0.640-THz imaging testbed, developed in support of the Defense Advanced Research Project Agency's (DARPA) Terahertz Imaging Focal-Plane Technology (TIFT) program. The laboratory measurements and standoff images were acquired during the development of a NVESD and Army Research Laboratory terahertz

Charmaine C. Franck; Dave Lee; Richard L. Espinola; Steven R. Murrill; Eddie L. Jacobs; Steve T. Griffin; Douglas T. Petkie; Joe Reynolds

2007-01-01

140

Temperature dependent narrow-band terahertz pulse generation in periodically poled crystals via difference frequency generation  

NASA Astrophysics Data System (ADS)

Femtosecond optical pulse is used to generate narrow-band terahertz pulses depending on a quasi-phase-matched condition in periodically poled lithium niobate (PPLN) and stoichiometric lithium tantalate (PPSLT) crystals by difference frequency generation. The origin of narrow-band THz generation proved that the two frequency components of the fs pulse contribute to the frequency mixing. By cryogenic cooling, the absorption of THz waves in the crystal is significantly reduced which results in efficient THz generation. Simultaneously generated forward and backward THz pulses were 1.38 and 0.65 THz with as narrow as the bandwidth of 32 GHz in the PPSLT sample. Temperature dependence of the generated THz waveforms had good agreement with the simulation result using one dimensional plane-wave propagation model.

Yu, N. E.; Lee, K. S.; Ko, D.-K.; Kang, C.; Takekawa, S.; Kitamura, K.

2011-03-01

141

Terahertz bandwidth RF spectrum analysis of femtosecond pulses using a chalcogenide chip.  

PubMed

We report the first demonstration of the use of an RF spectrum analyser with multi-terahertz bandwidth to measure the properties of femtosecond optical pulses. A low distortion and broad measurement bandwidth of 2.78 THz (nearly two orders of magnitude greater than conventional opto-electronic analyzers) was achieved by using a 6 cm long As(2)S(3) chalcogenide waveguide designed for high Kerr nonlinearity and near zero dispersion. Measurements of pulses as short as 260 fs produced from a soliton-effect compressor reveal features not evident from the pulse's optical spectrum. We also applied an inverse Fourier transform numerically to the captured data to re-construct a time-domain waveform that resembled pulse measurement obtained from intensity autocorrelation. PMID:19466183

Pelusi, M D; Vo, T D; Luan, F; Madden, S J; Choi, D-Y; Bulla, D A P; Luther-Davies, B; Eggleton, B J

2009-05-25

142

Broadband terahertz modulators based on reconfigurable metamaterials and their potential application in terahertz imaging  

Microsoft Academic Search

A new scheme for broadband terahertz modulation based on periodic arrays of subwavelength metallic slits is presented. By using this scheme, we demonstrate low loss terahertz modulation with 100% modulation index over a broad modulation bandwidth of more than 0.2THz.

Mona Jarrahi

2010-01-01

143

Non-destructive terahertz imaging of illicit drugs using spectral fingerprints  

NASA Astrophysics Data System (ADS)

The absence of non-destructive inspection techniques for illicit drugs hidden in mail envelopes has resulted in such drugs being smuggled across international borders freely. We have developed a novel basic technology for terahertz imaging, which allows detection and identification of drugs concealed in envelopes, by introducing the component spatial pattern analysis. The spatial distributions of the targets are obtained from terahertz multispectral transillumination images, using absorption spectra measured with a tunable terahertz-wave source. The samples we used were methamphetamine and MDMA, two of the most widely consumed illegal drugs in Japan, and aspirin as a reference.

Kawase, Kodo; Ogawa, Yuichi; Watanabe, Yuuki; Inoue, Hiroyuki

2003-10-01

144

JTC based concealed object detection in terahertz imaging  

NASA Astrophysics Data System (ADS)

Detection of concealed objects under cloth or inside paper/lather/plastic box is a challenge for security applications. With terahertz (THz) imaging technology, it is possible to spot concealed objects inside plastic box, underneath cloths paper or similar scenarios. THz frequency domain (~100 GHz - 10 THz) shows a unique feature in the under-used domain of the electromagnetic spectrum which helps to acquire image of concealed objects. This property of THz wave makes it useful in a variety of applications. Previously millimeter wave imaging and infrared imaging were used for detection of concealed features in an image with limited success rate. THz imaging helps solving the problem to a great extent because it can transmit through substances like cloths, paper, plastic, dried food etc. THz images have poor quality and low signal-to-noise-ratio. Noises and related artifacts must be reduced for proper detection of concealed objects. In this paper, a new technique for artifact reduction and detection of concealed object is proposed by utilizing nonzero-order fringe adjusted joint transform correlation (NFJTC) technique. In the proposed NFJTC technique, the joint power spectrum (JPS) is modified to obtain the nonzero-order fringe-adjusted joint power spectrum. NFJTC is already been used for object detection but never been used to detect concealed objects in THz imagery. Test results using real life THz imagery confirm the effectiveness of the proposed technique.

Habib, M. U.; Alam, M. S.; Al-Assadi, W. K.

2013-03-01

145

Numerical and simulation study of terahertz radiation generation by laser pulses propagating in the extraordinary mode in magnetized plasma  

SciTech Connect

A one-dimensional numerical model for studying terahertz radiation generation by intense laser pulses propagating, in the extraordinary mode, through magnetized plasma has been presented. The direction of the static external magnetic field is perpendicular to the polarization as well as propagation direction of the laser pulse. A transverse electromagnetic wave with frequency in the terahertz range is generated due to the presence of the magnetic field. Further, two-dimensional simulations using XOOPIC code show that the THz fields generated in plasma are transmitted into vacuum. The fields obtained via simulation study are found to be compatible with those obtained from the numerical model.

Jha, Pallavi; Kumar Verma, Nirmal [Department of Physics, University of Lucknow, Lucknow-226007 (India)

2014-06-15

146

A Real-Time Terahertz Time-Domain Polarization Analyzer with 80-MHz Repetition-Rate Femtosecond Laser Pulses  

PubMed Central

We have developed a real-time terahertz time-domain polarization analyzer by using 80-MHz repetition-rate femtosecond laser pulses. Our technique is based on the spinning electro-optic sensor method, which we recently proposed and demonstrated by using a regenerative amplifier laser system; here we improve the detection scheme in order to be able to use it with a femtosecond laser oscillator with laser pulses of a much higher repetition rate. This improvement brings great advantages for realizing broadband, compact and stable real-time terahertz time-domain polarization measurement systems for scientific and industrial applications. PMID:23478599

Watanabe, Shinichi; Yasumatsu, Naoya; Oguchi, Kenichi; Takeda, Masatoshi; Suzuki, Takeshi; Tachizaki, Takehiro

2013-01-01

147

Generation of megawatt-power terahertz pulses by noncollinear difference-frequency mixing in GaAs  

NASA Astrophysics Data System (ADS)

Terahertz pulses with a peak power of ˜2MW were generated in a noncollinear phase-matched GaAs crystal at room temperature. Efficient difference-frequency generation was achieved using 250-ps CO2 laser pulses for which the surface damage threshold increased in comparison with standard 200-ns pulses. Tunable CO2 lasers in combination with this technique should yield a source in the 0.1-3.0-THz range.

Tochitsky, S. Ya.; Ralph, J. E.; Sung, C.; Joshi, C.

2005-07-01

148

Gelatin embedding: a novel way to preserve biological samples for terahertz imaging and spectroscopy  

NASA Astrophysics Data System (ADS)

Sample dehydration has traditionally been a challenging problem in ex vivo terahertz biomedical experiments as water content changes significantly affect the terahertz properties and can diminish important contrast features. In this paper, we propose a novel method to prevent sample dehydration using gelatin embedding. By looking at terahertz image data and calculating the optical properties of the gelatin-embedded sample, we find that our method successfully preserves the sample for at least 35?h, both for imaging and spectroscopy. Our novel preservation method demonstrates for the first time the capability to simultaneously maintain sample structural integrity and prevent dehydration at room temperature. This is particularly relevant for terahertz studies of freshly excised tissues but could be beneficial for other imaging and spectroscopy techniques.

Fan, Shuting; Ung, Benjamin; Parrott, Edward P. J.; Pickwell-MacPherson, Emma

2015-04-01

149

Gelatin embedding: a novel way to preserve biological samples for terahertz imaging and spectroscopy.  

PubMed

Sample dehydration has traditionally been a challenging problem in ex vivo terahertz biomedical experiments as water content changes significantly affect the terahertz properties and can diminish important contrast features. In this paper, we propose a novel method to prevent sample dehydration using gelatin embedding. By looking at terahertz image data and calculating the optical properties of the gelatin-embedded sample, we find that our method successfully preserves the sample for at least 35?h, both for imaging and spectroscopy. Our novel preservation method demonstrates for the first time the capability to simultaneously maintain sample structural integrity and prevent dehydration at room temperature. This is particularly relevant for terahertz studies of freshly excised tissues but could be beneficial for other imaging and spectroscopy techniques. PMID:25768394

Fan, Shuting; Ung, Benjamin; Parrott, Edward P J; Pickwell-MacPherson, Emma

2015-04-01

150

Resonant-Phonon Terahertz Quantum-Cascade Lasers and Video-Rate Terahertz Imaging  

Microsoft Academic Search

We review the development of terahertz quantum-cascade lasers (QCLs) that can be uniquely qualified based on a resonant-phonon depopulation scheme. Record performances in terms of operating temperature and optical power output are reported. The best temperature performance is achieved in the metal-metal (MM) waveguides, which provide near-unity mode confinement and low waveguiding loss at terahertz (THz) frequencies even for cavities

Sushil Kumar; Alan W. M. Lee

2008-01-01

151

Generation of high power pulsed terahertz radiation using a plasmonic photoconductive emitter array with logarithmic spiral antennas  

NASA Astrophysics Data System (ADS)

An array of 3 × 3 plasmonic photoconductive terahertz emitters with logarithmic spiral antennas is fabricated on a low temperature (LT) grown GaAs substrate and characterized in response to a 200 fs optical pump from a Ti:sapphire mode-locked laser at 800 nm wavelength. A microlens array is used to split and focus the optical pump beam onto the active area of each plasmonic photoconductive emitter element. Pulsed terahertz radiation with record high power levels up to 1.9 mW in the 0.1-2 THz frequency range is measured at an optical pump power of 320 mW. The record high power pulsed terahertz radiation is enabled by the use of plasmonic contact electrodes, enhancing the photoconductor quantum efficiencies, and by increasing the overall device active area, mitigating the carrier screening effect and thermal breakdown at high optical pump power levels.

Berry, Christopher W.; Hashemi, Mohammad R.; Jarrahi, Mona

2014-02-01

152

Generation of high power pulsed terahertz radiation using a plasmonic photoconductive emitter array with logarithmic spiral antennas  

SciTech Connect

An array of 3?×?3 plasmonic photoconductive terahertz emitters with logarithmic spiral antennas is fabricated on a low temperature (LT) grown GaAs substrate and characterized in response to a 200 fs optical pump from a Ti:sapphire mode-locked laser at 800?nm wavelength. A microlens array is used to split and focus the optical pump beam onto the active area of each plasmonic photoconductive emitter element. Pulsed terahertz radiation with record high power levels up to 1.9 mW in the 0.1–2 THz frequency range is measured at an optical pump power of 320 mW. The record high power pulsed terahertz radiation is enabled by the use of plasmonic contact electrodes, enhancing the photoconductor quantum efficiencies, and by increasing the overall device active area, mitigating the carrier screening effect and thermal breakdown at high optical pump power levels.

Berry, Christopher W. [Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109 (United States); Hashemi, Mohammad R.; Jarrahi, Mona [Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109 (United States); Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States)

2014-02-24

153

Terahertz Imaging of cyclotron emission from quantum Hall conductors  

NASA Astrophysics Data System (ADS)

Microscopy of extremely weak terahertz (THz) waves via photon-counting method is reported. A quantum-dot photon detector [1] is incorporated into a scanning terahertz microscope [2]. By using a quantum Hall detector [3] as well, measurements cover the intensity dynamic range more than five orders of magnitude. The minimum intensity reaches as lo as 10?-21^ watt (one photon per one second). Applying the measurement system to the study of semiconductor quantum Hall (QH) devices, we image cyclotron radiation emitted by non-equilibrium electrons generated in QH electron systems. Owing to the unprecedented sensitivity, a variety of new features of electron kinetics are unveiled [4]. It is stressed that the present approach is in marked contrast to the THz- wave applications recently discussed extensively in a wide variety of fields including clinic, security, and environment. In the vast majority of those applications, room-temperature operation is implicit. The intensity of treated THz radiation is hence well beyond the level of 300K black body radiation (roughly 10?-7 watts or 10?14 photons/s per square centimeter in a 1/10 relative band width). From the scientific viewpoint, however, detecting extremely weak THz waves from an object without external illumination such as applied in the present work is of strong importance, because the microscopic kinetics of an object can be probed only in such a passive method. Besides semiconductor electric devices studied here, we will also discuss possible applications of the present method for molecular dynamics, micro thermography, and cell activities.. [1] S. Komiyama et al., Nature 403, 405 (2000). [2] K. Ikushima et al.,. Rev. Sci. Instrum. 74, 4209 (2003). [3] Y.Kawano et al., J. Appl. Phys. 89, 4037 (2001). [4] K.Ikushima et al., Phys. Rev. Lett. 93, 146804 (2004).

Komiyama, Susumu

2006-03-01

154

Dual-frequency continuous-wave terahertz transmission imaging of nonmelanoma skin cancers  

Microsoft Academic Search

Continuous wave terahertz imaging has the potential for diagnosing and delineating skin cancers. While contrast has been observed between cancerous and normal tissue at terahertz frequencies, the source mechanism behind this contrast is not clearly understood.1Transmission measurements of 240mum thick sections of nonmelanoma skin cancer were taken at two frequencies of 1.39 THz and 1.63 THz that lie within and

Cecil S. Joseph; Anna N. Yaroslavsky; Julie L. Lagraves; Thomas M. Goyette; Robert H. Giles

2010-01-01

155

264 IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY, VOL. 1, NO. 1, SEPTEMBER 2011 Broadband THz Pulse Transmission  

E-print Network

264 IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY, VOL. 1, NO. 1, SEPTEMBER 2011 Broadband THz Pulse Transmission Through the Atmosphere Yihong Yang, Student Member, IEEE, Mahboubeh Mandehgar that experienced negligible attenuation and group velocity dispersion due to transmission through water vapor

Oklahoma State University

156

1.56 Terahertz 2-frames per second standoff imaging  

NASA Astrophysics Data System (ADS)

A Terahertz imaging system intended to demonstrate identification of objects concealed under clothing was designed, assembled, and tested. The system design was based on a 2.5 m standoff distance, with a capability of visualizing a 0.5 m by 0.5 m scene at an image rate of 2 frames per second. The system optical design consisted of a 1.56 THz laser beam, which was raster swept by a dual torsion mirror scanner. The beam was focused onto the scan subject by a stationary 50 cm-diameter focusing mirror. A heterodyne detection technique was used to down convert the backscattered signal. The system demonstrated a 1.5 cm spot resolution. Human subjects were scanned at a frame rate of 2 frames per second. Hidden metal objects were detected under a jacket worn by the human subject. A movie including data and video images was produced in 1.5 minutes scanning a human through 180° of azimuth angle at 0.7° increment.

Goyette, Thomas M.; Dickinson, Jason C.; Linden, Kurt J.; Neal, William R.; Joseph, Cecil S.; Gorveatt, William J.; Waldman, Jerry; Giles, Robert; Nixon, William E.

2008-02-01

157

Terahertz imaging of excised oral cancer at frozen temperature  

PubMed Central

The feasibility of terahertz (THz) imaging at frozen temperature for the clinical application of oral cancer detection was investigated by analyzing seven oral tissues resected from four patients. The size, shape, and internal position of the oral cancers were mapped by THz radiation in the frequency range of 0.2–1.2 THz at ?20 °C and 20 °C, and compared with those identified in the histological examination. THz imaging of frozen tissue was found to offer greater sensitivity in distinguishing cancerous areas from surrounding tissue and a larger THz-frequency spectral difference between the oral cancer and normal mucosa than room-temperature THz imaging. A cancerous tumor hidden inside tissue was also detected using this method by observing the THz temporal domain waveform. The histological analysis showed that these findings resulted from cell structure deformations involving the invasion of oral tumor and neoplastic transformations of mucous cells. Therefore, a cytological approach using THz radiation at a frozen temperature might be applied to detect oral cancer. PMID:24010003

Sim, Yookyeong Carolyn; Park, Jae Yeon; Ahn, Kang-Min; Park, Chansik; Son, Joo-Hiuk

2013-01-01

158

Restoration of distorted images, terahertz generation and terahertz interference based on multiple-coupled optical parametric oscillators  

NASA Astrophysics Data System (ADS)

We review our progress made on applications of coupled optical parametric oscillators based on a composite consisting of adhesive-free-bonded KTiOPO4 stacks. By using the phase- conjugate output generated by the composite, we have demonstrated that the spatial profile after the beam propagates through the phase-distorted medium can be restored to the profile before the distortion. In addition, we have restored the images being blurred by the phase distortion. We have efficiently generated terahertz outputs by mixing the idler twins from the coupled optical parametric oscillators. By using the alternatively-rotated GaP plates as an output coupler for the coupled optical parametric oscillators, we have efficiently generated terahertz waves based on an intracavity configuration. By placing both the composite and a bulk KTiOPO4 crystal in the same cavity, we have demonstrated the interference effect of the THz waves generated by using different pairs of the optical beams.

Ding, Yujie J.

2015-03-01

159

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Intraband dynamics and terahertz emission in biased semiconductor superlattices coupled to double far-infrared pulses  

NASA Astrophysics Data System (ADS)

This paper studies both the intraband polarization and terahertz emission of a semiconductor superlattice in combined dc and ac electric fields by using the superposition of two identical time delayed and phase shifted optical pulses. By adjusting the delay between these two optical pulses, our results show that the intraband polarization is sensitive to the time delay. The peak values appear again for the terahertz emission intensity due to the superposition of two optical pulses. The emission lines of terahertz blueshift and redshift in different ac electric fields and dynamic localization appears. The emission lines of THz only appear to blueshift when the biased superlattice is driven by a single optical pulse. Due to excitonic dynamic localization, the terahertz emission intensity decays with time in different dc and ac electric fields. These are features of this superlattice which distinguish it from a superlattice generated by a single optical pulse to drive it.

Li, Min; Mi, Xian-Wu

2009-12-01

160

Strong sub-terahertz surface waves generated on a metal wire by high-intensity laser pulses  

NASA Astrophysics Data System (ADS)

Terahertz pulses trapped as surface waves on a wire waveguide can be flexibly transmitted and focused to sub-wavelength dimensions by using, for example, a tapered tip. This is particularly useful for applications that require high-field pulses. However, the generation of strong terahertz surface waves on a wire waveguide remains a challenge. Here, ultrafast field propagation along a metal wire driven by a femtosecond laser pulse with an intensity of 1018 W/cm2 is characterized by femtosecond electron deflectometry. From experimental and numerical results, we conclude that the field propagating at the speed of light is a half-cycle transverse-magnetic surface wave excited on the wire and a considerable portion of the kinetic energy of laser-produced fast electrons can be transferred to the sub-surface wave. The peak electric field strength of the surface wave and the pulse duration are estimated to be 200 MV/m and 7 ps, respectively.

Tokita, Shigeki; Sakabe, Shuji; Nagashima, Takeshi; Hashida, Masaki; Inoue, Shunsuke

2015-02-01

161

Terahertz spectroscopy of liver cirrhosis: investigating the origin of contrast  

NASA Astrophysics Data System (ADS)

We have previously demonstrated that terahertz pulsed imaging is able to distinguish between rat tissues from different healthy organs. In this paper we report our measurements of healthy and cirrhotic liver tissues using terahertz reflection spectroscopy. The water content of the fresh tissue samples was also measured in order to investigate the correlations between the terahertz properties, water content, structural changes and cirrhosis. Finally, the samples were fixed in formalin to determine whether water was the sole source of image contrast in this study. We found that the cirrhotic tissue had a higher water content and absorption coefficient than the normal tissue and that even after formalin fixing there were significant differences between the normal and cirrhotic tissues' terahertz properties. Our results show that terahertz pulsed imaging can distinguish between healthy and diseased tissue due to differences in absorption originating from both water content and tissue structure.

Sy, Stanley; Huang, Shengyang; Wang, Yi-Xiang J.; Yu, Jun; Ahuja, Anil T.; Zhang, Yuan-ting; Pickwell-MacPherson, Emma

2010-12-01

162

High-speed terahertz reflection three-dimensional imaging for nondestructive  

E-print Network

.4290) Nondestructive testing. References and links 1. W. Withayachumnankul, G. M. Png, X. Yin, S. Atakaramians, IHigh-speed terahertz reflection three- dimensional imaging for nondestructive evaluation Kyong Hwan of the imaging system to nondestructive evaluation, a THz reflection 3D image of an artificially made sample

163

Pulsed magneto-acoustic imaging.  

PubMed

Nanoparticles are attracting considerable interest as contrast agents for many different imaging modalities. Moreover, imaging the events at the cellular and molecular level is possible by using nanoparticles that have the desired targeting moiety. Unfortunately, ultrasound imaging cannot visualize the nano-structures directly due to its limited spatial resolution and contrast. We present a new technique, pulsed magneto-acoustic imaging, capable of imaging magnetic nanoparticles indirectly. In this method, a high-strength pulsed magnetic field is used to induce motion within the magnetically labeled tissue and ultrasound is used to detect internal tissue motion. Experiments on tissue-mimicking phantoms and ex-vivo animal tissues demonstrated a clear contrast between normal and iron-laden samples labeled with 5 nm magnetic nanoparticles. In addition, the sensitivity of this new imaging technique was investigated for different concentrations of magnetic agents. The results of the study suggest that magnetic nanoparticles can be used as contrast agents in pulsed magneto-acoustic imaging. Furthermore, PMA imaging could become an imaging tool capable of visualizing the cellular and molecular composition of deep-lying structures. PMID:19964848

Mehrmohammadi, Mohammad; Oh, Junghwan; Aglyamov, Salavat R; Karpiouk, Andrei B; Emelianov, Stanislav Y

2009-01-01

164

Non-destructive imaging with compact and portable terahertz systems  

NASA Astrophysics Data System (ADS)

This paper illustrates the non-destructive application of a compact and portable Terahertz (THz) system to analyze the structure of an old painting and to measure the layers of composite plastic samples. THz images from the painting reveal features that resemble the signature of the artist that is not visible in the optical or X-ray channels, which support the authenticity of the painting. On the other hand, data from a composite plastic sample is analyzed to measure the thickness of each layer and determine the presence or absence of adhesive bonding between them. The presence and position of the adhesive is clearly visible in the THz images and the measured thickness shows an excellent agreement with nominal thickness. These applications demonstrate the capabilities of THz technology for unique non-destructive inspection applications. Furthermore, available compact and portable THz systems enable to perform these inspections onsite without the need to bring the sample to the laboratory, increasing the utility and convenience of THz technology.

Redo-Sanchez, Albert; Laman, Norman; Schulkin, Brian; Tongue, Thomas

2014-02-01

165

Single-shot measurement of the spectral envelope of broad-bandwidth terahertz pulses from femtosecond electron bunches  

SciTech Connect

We present a new approach (demonstrated experimentally and through modeling) to characterize the spectral envelope of a terahertz (THz) pulse in a single shot. The coherent THz pulse is produced by a femtosecond electron bunch and contains information on the bunch duration. The technique, involving a single low-power laser probe pulse, is an extension of the conventional spectral encoding method (limited in time resolution to hundreds of femtoseconds) into a regime only limited in resolution by the laser pulse length (tens of femtoseconds). While only the bunch duration is retrieved (and not the exact charge profile), such a measurement provides a useful and critical parameter for optimization of the electron accelerator.

van Tilborg, Jeroen; Toth, Csaba; Matlis, Nicholas; Plateau, Guillaume; Leemans, Wim

2011-06-17

166

Terahertz Imaging of cyclotron emission from quantum Hall conductors  

Microsoft Academic Search

Microscopy of extremely weak terahertz (THz) waves via photon-counting method is reported. A quantum-dot photon detector [1] is incorporated into a scanning terahertz microscope [2]. By using a quantum Hall detector [3] as well, measurements cover the intensity dynamic range more than five orders of magnitude. The minimum intensity reaches as lo as 10ˆ-21^ watt (one photon per one second).

Susumu Komiyama

2006-01-01

167

The intrinsic coupling of polarization with terahertz pulses in a ferroelectric nanowire  

NASA Astrophysics Data System (ADS)

We use first-principles-based molecular dynamics simulations to study the interaction of a terahertz (THz) radiation with polarization in a ferroelectric ultrathin nanowire made of a lead zirconate titanate alloy. In our computational experiment, a 12 nm thick nanowire is first annealed down to temperature of 300 K and then subjected to a wide variety of THz pulses which differ in width, strength and frequency. Such nanowire develops an electrical polarization along the nanowire axial direction which couples strongly with incoming THz radiation. The atomistic resolution of our computational experiments allows us to trace the intrinsic polarization response and energy propagation/dissipation mechanisms that occur at the scale of femtoseconds. Our simulations were carried out under MVE and MVT conditions and the results did not vary significantly between the two ensembles. We further explore how the unique features of such response could be utilized in an ultrafast THz nanoswitches.

Schultz, Kimberly; Herchig, Ryan; McCash, Kevin; Ponomareva, Inna

2012-02-01

168

Efficient terahertz wave generation from GaP crystals pumped by chirp-controlled pulses from femtosecond photonic crystal fiber amplifier  

SciTech Connect

A chirp-tunable femtosecond 10?W, 42?MHz photonic-crystal-fiber oscillator-amplifier system that is capable of delivering sub-60 fs light pulses at 1040?nm is used to demonstrate high-efficiency terahertz radiation generation via optical rectification in GaP crystals only a few millimeters in length. The optimization of the chirp of the fiber-laser pulses is shown to radically enhance the terahertz output, indicating one possible way to more efficiently use these extended nonlinear crystals in compact fiber-pumped terahertz radiation sources.

Li, Jiang; Shi, Junkai; Xu, Baozhong; Xing, Qirong; Wang, Chingyue [Ultrafast Laser Laboratory, College of Precision Instrument and Optoelectronics Engineering, Key Laboratory of Optoelectronic Information Technology (Ministry of Education), Tianjin University, Tianjin 300072 (China); Chai, Lu, E-mail: lu-chai@tju.edu.cn, E-mail: yanfengli@tju.edu.cn; Liu, Bowen; Hu, Minglie; Li, Yanfeng, E-mail: lu-chai@tju.edu.cn, E-mail: yanfengli@tju.edu.cn [Ultrafast Laser Laboratory, College of Precision Instrument and Optoelectronics Engineering, Key Laboratory of Optoelectronic Information Technology (Ministry of Education), Tianjin University, Tianjin 300072 (China); MOEMS Key Laboratory (Ministry of Education), Tianjin University, Tianjin 300072 (China); Fedotov, Andrey B. [Physics Department, Russian Quantum Center, International Laser Center, M.V. Lomonosov Moscow State University, Moscow 119992 (Russian Federation); Zheltikov, Aleksei M. [Physics Department, Russian Quantum Center, International Laser Center, M.V. Lomonosov Moscow State University, Moscow 119992 (Russian Federation); Department of Physics and Astronomy, Texas A and M University, College Station, Texas 77843 (United States)

2014-01-20

169

Diffraction mode terahertz tomography  

SciTech Connect

A method of obtaining a series of images of a three-dimensional object. The method includes the steps of transmitting pulsed terahertz (THz) radiation through the entire object from a plurality of angles, optically detecting changes in the transmitted THz radiation using pulsed laser radiation, and constructing a plurality of imaged slices of the three-dimensional object using the detected changes in the transmitted THz radiation. The THz radiation is transmitted through the object as a two-dimensional array of parallel rays. The optical detection is an array of detectors such as a CCD sensor.

Ferguson, Bradley; Wang, Shaohong; Zhang, Xi-Cheng

2006-10-31

170

Combined terahertz spectral imaging and NIR Raman microscopy for the analysis of chromoprotein and chromophore films  

Microsoft Academic Search

A tunable frequency terahertz (THz) wave source provides spectral images of chromoprotein and chromophore films on quartz plates. A near-infrared (NIR) Raman microprobe mapping technique is used to measure the same regions in the films in order to detect the molecular structure and to understand THz spectral images. The fact that there is little fluorescence interference in NIR Raman microscopy

K. Ajito; R. Rungsawang; Y. Ueno; I. Tomita; H. Takenouchi

2005-01-01

171

Coherent detection of multicycle terahertz pulses generated in periodically inverted GaAs structures  

NASA Astrophysics Data System (ADS)

Narrow-band, multi-cycle terahertz (THz) pulses have been generated in the pre-engineered domain structure of periodically-poled lithium niobate (PPLN) crystals. The mechanism for THz generation is quasi-phase-matching (QPM) optical rectification. Recently, THz generation of high conversion efficiency in a new material, QPM GaAs, were demonstrated using mid-IR femtosecond pulses. GaAs has several advantages for QPM THz wave generation, as compared to PPLN. First, it is highly transparent at THz frequencies (absorption coefficient below 1.5 THz < 1 cm -1). Second, the mismatch between the optical group velocity and THz phase velocity is much smaller: the corresponding group (ng) and refractive (n) indices are ng=3.431 at 2?m and n=3.61 at 1 THz. In this work, we report on generation of THz wave packets in three different types of QPM GaAs, combined with their coherent detection using two-color THz time-domain spectroscopy. The QPM GaAs structures are optically-contacted GaAs, diffusion-bonded GaAs, and all-epitaxially-grown orientation patterned GaAs. The QPM optical rectification in GaAs is a nonresonant mechanism, as opposed to widely used photoconductive antenna technique in GaAs, where THz radiation is produced via ultrafast charge transport caused by photoexcitation with femtosecond laser pulses of the near-IR range. In order to avoid linear and two-photon absorption in GaAs, we use 2?m femtosecond pulses to generate THz pulses. We measure the THz waveforms via electro-optic sampling in ZnTe using 0.8?m probe pulses. The corresponding power spectra are also measured by a THz Michelson interferometer. Frequency tunability in the range 0.8-3 THz is achieved with several structure periods.

Lee, Yun-Shik; Hurlbut, W. C.; Vodopyanov, K. L.; Fejer, M. M.; Kozlov, V. G.

2007-02-01

172

Proposal for real-time terahertz imaging system with palm-size terahertz camera and compact quantum cascade laser  

NASA Astrophysics Data System (ADS)

This paper describes a real-time terahertz (THz) imaging system, using the combination of a palm-size THz camera with a compact quantum cascade laser (QCL). The THz camera contains a 320x240 microbolometer focal plane array which has nearly flat spectral response over a frequency range of ca. 1.5 to 100 THz, and operates at 30 Hz frame rate. The QCL is installed in compact cryogen-free cooler. A variety of QCLs are prepared which can cover frequency range from ca. 1.5 to 5 THz. THz images of biochemical samples will be presented, using the combined imaging system. Performance of the imaging system, such as signal-to-noise ratio of transmission-type THz microscope, is predicted.

Oda, Naoki; Lee, Alan W. M.; Ishi, Tsutomu; Hosako, Iwao; Hu, Qing

2012-05-01

173

High-Power Terahertz Source Opens the Door for Full-Field Video-Rate Terahertz Imaging  

SciTech Connect

Terahertz (THz) light, at wavelengths between electronics and photonics, promises novel imaging applications such as revealing epithelial carcinomas 1 or identifying objects hidden in clothing and packages 2. But THz imaging has been little exploited because generating source power high enough for adequate signal detection is difficult -- and because even more power is needed for most applications that require detecting scattered light rather than light transmitted straight through the target 3. The ability to image movement in real time would aid medicine by allowing the rapid viewing of multiple perspectives and larger areas for detecting skin cancer. Real-time imaging is also essential for the efficient detection, with sufficient resolution, of hidden, and possibly moving, objects. Here, in work building on our earlier demonstration that relativistic electrons can yield tens of watts of broadband THz light 4, 5, we report the first video-rate THz movies of objects observed in real t

Klopf, John; Coppinger, Matthew; Sustersic, Nathan; Kolodzey, James; Williams, Gwyn

2008-07-01

174

Development and Testing of a Single Frequency Terahertz Imaging System for Breast Cancer Detection  

PubMed Central

The ability to discern malignant from benign tissue in excised human breast specimens in Breast Conservation Surgery (BCS) was evaluated using single frequency terahertz radiation. Terahertz (THz) images of the specimens in reflection mode were obtained by employing a gas laser source and mechanical scanning. The images were correlated with optical histological micrographs of the same specimens, and a mean discrimination of 73% was found for five out of six samples using Receiver Operating Characteristic (ROC) analysis. The system design and characterization is discussed in detail. The initial results are encouraging but further development of the technology and clinical evaluation is needed to evaluate its feasibility in the clinical environment. PMID:25055306

St. Peter, Benjamin; Yngvesson, Sigfrid; Siqueira, Paul; Kelly, Patrick; Khan, Ashraf; Glick, Stephen; Karellas, Andrew

2013-01-01

175

Terahertz technology: a boon to tablet analysis.  

PubMed

The terahertz gap has a frequency ranges from approximately 0.3 THz to approximately 10 THz in the electromagnetic spectrum which is in between microwave and infrared. The terahertz radiations are invisible to naked eye. In comparison with x-ray they are intrinsically safe, non-destructive and non-invasive. Terahertz spectroscopy enables 3D imaging of structures and materials, and the measurement of the unique spectral fingerprints of chemical and physical forms. Terahertz radiations are produced by a dendrimer based high power terahertz source and spectroscopy technologies. It resolves many of the questions left unanswered by complementary techniques, such as optical imaging, Raman and infrared spectra. In the pharmaceutical industries it enables nondestructive, internal, chemical analysis of tablets, capsules, and other dosage forms. Tablet coatings are a major factor in drug bioavailability. Therefore tablet coatings integrity and uniformity are of crucial importance to quality. Terahertz imaging gives an unparalleled certainty about the integrity of tablet coatings and the matrix performance of tablet cores. This article demonstrates the potential of terahertz pulse imaging for the analysis of tablet coating thickness by illustrating the technique on tablets. PMID:20490288

Wagh, M P; Sonawane, Y H; Joshi, O U

2009-05-01

176

Room temperature terahertz wave imaging at 60 fps by frequency up-conversion in DAST crystal  

NASA Astrophysics Data System (ADS)

Terahertz imaging has attracted a lot of interests for more than 10 years. But real time, high sensitive, low cost THz imaging in room temperature, which is widely needed by fields such as biology, biomedicine and homeland security, has not been fully developed yet. A lot of approaches have been reported on electro-optic (E-O) imaging and THz focal plane arrays with photoconductive antenna or micro-bolometer integrated. In this paper, we report high sensitive realtime THz image at 60 frames per second (fps) employing a commercial infrared camera, using nonlinear optical frequency up-conversion technology. In this system, a flash-lamp pumped nanosecond pulse green laser is used to pump two optical parametric oscillator systems with potassium titanyl phosphate crystals (KTP-OPO). One system with dual KTP crystals is used to generate infrared laser for the pumping of THz difference frequency generation (DFG) in a 4- Dimethylamino-N-Methyl-4-Stilbazolium Tosylate (DAST) crystal. The other one is for generation of pumping laser for THz frequency up-conversion in a second DAST crystal. The THz frequency can be tuned continuously from a few THz to less than 30 THz by controlling the angle of KTP crystals. The frequency up-converted image in infrared region is recorded by a commercial infrared camera working at 60 Hz. Images and videos are presented to show the feasibility of this technique and the real-time ability. Comparison with a general micro-bolometer THz camera shows the high sensitivity of this technique.

Fan, Shuzhen; Qi, Feng; Notake, Takashi; Nawata, Kouji; Matsukawa, Takeshi; Takida, Yuma; Minamide, Hiroaki

2014-02-01

177

Terahertz standoff imaging testbed design and performance for concealed weapon and device identification model development  

NASA Astrophysics Data System (ADS)

This paper describes the design and performance of the U.S. Army RDECOM CERDEC Night Vision and Electronic Sensors Directorate's (NVESD), active 0.640-THz imaging testbed, developed in support of the Defense Advanced Research Project Agency's (DARPA) Terahertz Imaging Focal-Plane Technology (TIFT) program. The laboratory measurements and standoff images were acquired during the development of a NVESD and Army Research Laboratory terahertz imaging performance model. The imaging testbed is based on a 12-inch-diameter Off-Axis Elliptical (OAE) mirror designed with one focal length at 1 m and the other at 10 m. This paper will describe the design considerations of the OAE-mirror, dual-capability, active imaging testbed, as well as measurement/imaging results used to further develop the model.

Franck, Charmaine C.; Lee, Dave; Espinola, Richard L.; Murrill, Steven R.; Jacobs, Eddie L.; Griffin, Steve T.; Petkie, Douglas T.; Reynolds, Joe

2007-04-01

178

High power pulsed fiber laser sources and their use in terahertz generation  

NASA Astrophysics Data System (ADS)

In this dissertation I report the development of high power pulsed fiber laser systems. These systems utilize phosphate glass fiber for active elements, instead of the industry-standard silica fiber. Because the phosphate glass allows for much higher doping of rare-earth ions than silica fibers, much shorter phosphate fibers can be used to achieve the same gain as longer silica fibers. This single-frequency laser technology was used to develop an all-fiber actively Q-switched fiber lasers. A short cavity is used to create large spacing between longitudinal modes. Using this method, we demonstrated the first all-fiber Q-switched fiber laser in the 1 micron region. In addition to creating high peak powers with Q-switched lasers, created even higher powers using fiber amplifier systems. High power fiber lasers typically produce spectral broadening through the nonlinear effects of stimulated Raman scattering, stimulated Brullion scattering, and self-phase modulation. The thresholds for these nonlinearities scale inversely with intensity and length. Thus, we used a short phosphate fiber gain stage to reduce the length, and a large core fiber final stage to reduce intensity. In this way we were able to generate high peak power pulses while avoiding visible nonlinearities, and keeping a narrow bandwidth. The immediate goal of developing these high power fiber laser systems was to generate narrowband terahertz radiation. Two different wavelengths were combined into the final amplifier stage at orthogonal polarizations. These were collimated and directed into a GaSe crystal, which has a very high figure of merit for THz generation. The two wavelengths combined in the crystal through the process of nonlinear difference frequency generation. This produced a narrowband beam of THz pulses, at higher powers than previous narrowband THz pulses produced by eyesafe fiber lasers.

Leigh, Matthew A.

179

Bi-directional terahertz emission from gold-coated nanogratings by excitation via femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

We report on the investigation of terahertz (THz) emission from gold-coated nanogratings (500 nm grating constant) upon femtosecond laser irradiation (785 nm, 150 fs, 1 kHz, ?1 mJ/pulse). Unlike common assumptions, THz emission is not only observed in case of rear side irradiation (through substrate (Welsh et al. in Phys. Rev. Lett. 98:026803, 2007; Welsh and Wynne in Opt. Express 17:2470-2480, 2009)) of the nanograting, but also in case of front side excitation (through air). Furthermore in both cases, THz emission propagates in the direction of laser beam propagation and reverse. Based on these findings, we suggest a new approach to describe the newly observed phenomena. Using a highly sensitive and fast superconducting transition edge sensor (TES) as calorimeter, it was possible to directly measure the absolute energy of the emitted THz pulses in a defined spectral and spatial range, enabling for the first time a quantitative analysis of the THz emission process.

Garwe, F.; Schmidt, A.; Zieger, G.; May, T.; Wynne, K.; Hübner, U.; Zeisberger, M.; Paa, W.; Stafast, H.; Meyer, H.-G.

2011-03-01

180

Non-destructive terahertz imaging of illicit drugs using spectral fingerprints  

Microsoft Academic Search

The absence of non-destructive inspection techniques for illicit drugs hidden in mail envelopes has resulted in such drugs being smuggled across international borders freely. We have developed a novel basic technology for terahertz imaging, which allows detection and identification of drugs concealed in envelopes, by introducing the component spatial pattern analysis. The spatial distributions of the targets are obtained from

Kodo Kawase; Yuichi Ogawa; Yuuki Watanabe; Hiroyuki Inoue

2003-01-01

181

Application of Terahertz Imaging and Backscatter Radiography to Space Shuttle Foam Inspection  

NASA Technical Reports Server (NTRS)

Two state of the art technologies have been developed for External Fuel Tank foam inspections. Results of POD tests have shown Backscatter Radiography and Terahertz imaging detect critical defects with no false positive issue. These techniques are currently in use on the External Tank program as one component in the foam quality assurance program.

Ussery, Warren

2008-01-01

182

Continuous wave terahertz transmission imaging through near-field aperture funnels  

Microsoft Academic Search

We report high throughput, continuous wave terahertz imaging using a near-field funnel aperture with adjustable output diameter. The frequency dependence of the output power and resolution immediately following the aperture are reported, as are the propagation and resolution characteristics as a function of distance from the aperture.

Martin S. Heimbeck; Dennis G. Wilson; Amy E. Frees; Henry O. Everitt

2011-01-01

183

Terahertz Laser Based Standoff Imaging System Kurt J. Linden, William R. Neal  

E-print Network

_gatesman@uml.edu, andriy_danylov@student.uml.edu Abstract Definition and design of a terahertz standoff imag- ing system materials such as clothing, paper, metals, or a human body. Beyond the far-infrared spectral region however explosive materials), but materials such as clothing, paper, and most packaging materials are relatively

Massachusetts at Lowell, University of

184

Nonlinear imaging with femtosecond laser pulses  

Microsoft Academic Search

The high peak powers delivered by femtosecond laser pulses easily induce nonlinear optical processes which are useful for a variety of applications, including biological imaging. This dissertation presents various contributions to the development of nonlinear imaging with femtosecond laser pulses. The spectral phase distortions that femtosecond laser pulses suffer due to dispersion as they transmit through microscope objectives have hindered

Yves Coello

2010-01-01

185

Numerical and experimental studies of mechanisms underlying the effect of pulsed broadband terahertz radiation on nerve cells  

NASA Astrophysics Data System (ADS)

We have studied the mechanisms underlying the effect of pulsed broadband terahertz radiation on the growth of neurites of sensory ganglia using a comparative analysis of measured reflection spectra of ganglion neurites (in the frequency range 0.1 – 2.0 THz) and spectra obtained by numerical simulation with CST Microwave Studio. The observed changes are shown to be mainly due to pulse energy absorption in the ganglion neurites. Of particular interest are the observed single resonance frequencies related to resonance size effects, which can be used to irradiate ganglia in order to activate their growth.

Duka, M. V.; Dvoretskaya, L. N.; Babelkin, N. S.; Khodzitskii, M. K.; Chivilikhin, S. A.; Smolyanskaya, O. A.

2014-08-01

186

Dielectric Covered Planar Antennas at Submillimeter Wavelengths for Terahertz Imaging  

NASA Technical Reports Server (NTRS)

Most optical systems require antennas with directive patterns. This means that the physical area of the antenna will be large in terms of the wavelength. When non-cooled systems are used, the losses of microstrip or coplanar waveguide lines impede the use of standard patch or slot antennas for a large number of elements in a phased array format. Traditionally, this problem has been solved by using silicon lenses. However, if an array of such highly directive antennas is to be used for imaging applications, the fabrication of many closely spaced lenses becomes a problem. Moreover, planar antennas are usually fed by microstrip or coplanar waveguides while the mixer or the detector elements (usually Schottky diodes) are coupled in a waveguide environment. The coupling between the antenna and the detector/ mixer can be a fabrication challenge in an imaging array at submillimeter wavelengths. Antennas excited by a waveguide (TE10) mode makes use of dielectric superlayers to increase the directivity. These antennas create a kind of Fabry- Perot cavity between the ground plane and the first layer of dielectric. In reality, the antenna operates as a leaky wave mode where a leaky wave pole propagates along the cavity while it radiates. Thanks to this pole, the directivity of a small antenna is considerably enhanced. The antenna consists of a waveguide feed, which can be coupled to a mixer or detector such as a Schottky diode via a standard probe design. The waveguide is loaded with a double-slot iris to perform an impedance match and to suppress undesired modes that can propagate on the cavity. On top of the slot there is an air cavity and on top, a small portion of a hemispherical lens. The fractional bandwidth of such antennas is around 10 percent, which is good enough for heterodyne imaging applications.The new geometry makes use of a silicon lens instead of dielectric quarter wavelength substrates. This design presents several advantages when used in the submillimeter-wave and terahertz bands: a) Antenna fabrication compatible with lithographic techniques. b) Much simpler fabrication of the lens. c) A simple quarter-wavelength matching layer of the lens will be more efficient if a smaller portion of the lens is used. d) The directivity is given by the lens diameter instead of the leaky pole (the bandwidth will not depend anymore on the directivity but just on the initial cavity). The feed is a standard waveguide, which is compatible with proven Schottky diode mixer/detector technologies. The development of such technology will benefit applications where submillimeter- wave heterodyne array designs are required. The main fields are national security, planetary exploration, and biomedicine. For national security, wideband submillimeter radars could be an effective tool for the standoff detection of hidden weapons or bombs concealed by clothing or packaging. In the field of planetary exploration, wideband submillimeter radars can be used as a spectrometer to detect trace concentrations of chemicals in atmospheres that are too cold to rely on thermal imaging techniques. In biomedicine, an imaging heterodyne system could be helpful in detecting skin diseases.

Chattopadhyay, Goutam; Gill, John J.; Skalare, Anders; Lee, Choonsup; Llombart, Nuria; Siegel, Peter H.

2011-01-01

187

Terahertz imaging technique and application in large scale integrated circuit failure inspection  

NASA Astrophysics Data System (ADS)

Terahertz ray, as a new style optic source, usually means the electromagnetic whose frequencies lies in between 0.1THz~10THz, the waveband region of the electromagnetic spectrum lies in the gap between microwaves and infrared ray. With the development of laser techniques, quantum trap techniques and compound semiconductor techniques, many new terahertz techniques have been pioneered, motivated in part by the vast range of possible applications for terahertz imaging, sensing, and spectroscopy. THz imaging technique was introduced, and THz imaging can give us not only the density picture but also the phase information within frequency domain. Consequently, images of suspicious objects such as concealed metallic or metal weapons are much sharper and more readily identified when imaged with THz imaging scanners. On the base of these, the application of THz imaging in nondestructive examination, more concretely in large scale circuit failure inspection was illuminated, and the important techniques of this application were introduced, also future prospects were discussed. With the development of correlative technology of THz, we can draw a conclusion that THz imaging technology will have nice application foreground.

Di, Zhi-gang; Yao, Jian-quan; Jia, Chun-rong; Xu, De-gang; Bing, Pi-bin; Yang, Peng-fei; Zheng, Yi-bo

2010-11-01

188

21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.  

Code of Federal Regulations, 2013 CFR

... false Ultrasonic pulsed echo imaging system. 892.1560...892.1560 Ultrasonic pulsed echo imaging system. (a) Identification. An ultrasonic pulsed echo imaging system is a device intended to project a pulsed sound beam into body...

2013-04-01

189

21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.  

Code of Federal Regulations, 2012 CFR

... false Ultrasonic pulsed echo imaging system. 892.1560...892.1560 Ultrasonic pulsed echo imaging system. (a) Identification. An ultrasonic pulsed echo imaging system is a device intended to project a pulsed sound beam into body...

2012-04-01

190

21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.  

Code of Federal Regulations, 2010 CFR

... false Ultrasonic pulsed echo imaging system. 892.1560...892.1560 Ultrasonic pulsed echo imaging system. (a) Identification. An ultrasonic pulsed echo imaging system is a device intended to project a pulsed sound beam into body...

2010-04-01

191

21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.  

Code of Federal Regulations, 2014 CFR

... false Ultrasonic pulsed echo imaging system. 892.1560...892.1560 Ultrasonic pulsed echo imaging system. (a) Identification. An ultrasonic pulsed echo imaging system is a device intended to project a pulsed sound beam into body...

2014-04-01

192

21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.  

Code of Federal Regulations, 2011 CFR

... false Ultrasonic pulsed echo imaging system. 892.1560...892.1560 Ultrasonic pulsed echo imaging system. (a) Identification. An ultrasonic pulsed echo imaging system is a device intended to project a pulsed sound beam into body...

2011-04-01

193

IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 14, NO. 2, MARCH/APRIL 2008 505 Plasma Characterization With Terahertz Pulses  

E-print Network

PULSES In ionized gases, the plasma frequency is defined as p nee2 0m (1) where ne is the free electronIEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 14, NO. 2, MARCH/APRIL 2008 505 Plasma Characterization With Terahertz Pulses B. H. Kolner, Senior Member, IEEE, R. A. Buckles, Member, IEEE, P. M

Yoo, S. J. Ben

194

Thickness-tunable terahertz plasma oscillations in a semiconductor slab excited by femtosecond optical pulses  

NASA Astrophysics Data System (ADS)

We report on the observation of terahertz oscillations in an electron-hole plasma optically excited by a femtosecond pulse in the ?m -sized slab of low-temperature-grown-GaAs (LT-GaAs) grown on the GaAs substrate. The frequency of oscillations is shown to be inversely proportional to the slab thickness. It is suggested that the LT-GaAs slab serves as a resonant cavity for traveling plasma waves, which have been generated as a consequence of the shock interaction of photoexcited electron plasma with the GaAs/LT-GaAs interface. The instantaneous diffusion of photoexcited plasma inward the material is driven by the density gradient over the Beer’s law distributed carrier population and is evidenced to be a main reason of the shock interaction in the localized plasma. The frequencies of oscillations observed are 3.5 times larger that the inverse electron transit time in the LT-GaAs slab, suggesting the “ballistic” regime for plasma wave propagation to occur. The oscillations have been observed in the photocurrent autocorrelation measurements. The dynamical electric field at the GaAs/LT-GaAs interface arising due to the instantaneous diffusion of photoexcited electrons inward the material was studied through the transient reflectivity change responses, which have been measured simultaneously with photocurrent.

Glinka, Y. D.; Maryenko, D.; Smet, J. H.

2008-07-01

195

Remote generation of high-energy terahertz pulses from two-color femtosecond laser filamentation in air  

SciTech Connect

We experimentally investigated the dynamic behavior of remote terahertz (THz) generation from two-color femtosecond laser-induced filamentation in air. A record-high THz pulse energy of 570 nJ at frequency below 5.5 THz was measured by optimizing the pump parameters at a controllable remote distance of 16 m, while super-broadband THz (<300 THz) pulse energy was up to 2.8 {mu}J. A further energy-scaling possibility was proposed. By analyzing simultaneously the fluorescence from both neutral N{sub 2} and N{sub 2}{sup +} in the filament, we found that the enhancement of THz radiation was due principally to guiding of the weak second-harmonic pulse inside the filament of the first strong fundamental pulse.

Wang, T.-J.; Daigle, J.-F.; Yuan, S.; Chin, S. L. [Centre d'Optique, Photonique et Laser (COPL) and Departement de physique, de genie physique et d'optique, Universite Laval, Quebec, Quebec G1V 0A6 (Canada); Theberge, F.; Chateauneuf, M.; Dubois, J.; Roy, G. [Defence Research and Development Canada-Valcartier, 2459 Pie-XI Boulevard North, Quebec, Quebec G3J 1X5 (Canada); Zeng, H. [State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062 (China)

2011-05-15

196

Strong sub-terahertz surface waves generated on a metal wire by high-intensity laser pulses  

PubMed Central

Terahertz pulses trapped as surface waves on a wire waveguide can be flexibly transmitted and focused to sub-wavelength dimensions by using, for example, a tapered tip. This is particularly useful for applications that require high-field pulses. However, the generation of strong terahertz surface waves on a wire waveguide remains a challenge. Here, ultrafast field propagation along a metal wire driven by a femtosecond laser pulse with an intensity of 1018?W/cm2 is characterized by femtosecond electron deflectometry. From experimental and numerical results, we conclude that the field propagating at the speed of light is a half-cycle transverse-magnetic surface wave excited on the wire and a considerable portion of the kinetic energy of laser-produced fast electrons can be transferred to the sub-surface wave. The peak electric field strength of the surface wave and the pulse duration are estimated to be 200?MV/m and 7?ps, respectively. PMID:25652694

Tokita, Shigeki; Sakabe, Shuji; Nagashima, Takeshi; Hashida, Masaki; Inoue, Shunsuke

2015-01-01

197

Strong sub-terahertz surface waves generated on a metal wire by high-intensity laser pulses.  

PubMed

Terahertz pulses trapped as surface waves on a wire waveguide can be flexibly transmitted and focused to sub-wavelength dimensions by using, for example, a tapered tip. This is particularly useful for applications that require high-field pulses. However, the generation of strong terahertz surface waves on a wire waveguide remains a challenge. Here, ultrafast field propagation along a metal wire driven by a femtosecond laser pulse with an intensity of 10(18)?W/cm(2) is characterized by femtosecond electron deflectometry. From experimental and numerical results, we conclude that the field propagating at the speed of light is a half-cycle transverse-magnetic surface wave excited on the wire and a considerable portion of the kinetic energy of laser-produced fast electrons can be transferred to the sub-surface wave. The peak electric field strength of the surface wave and the pulse duration are estimated to be 200?MV/m and 7?ps, respectively. PMID:25652694

Tokita, Shigeki; Sakabe, Shuji; Nagashima, Takeshi; Hashida, Masaki; Inoue, Shunsuke

2015-01-01

198

Metamaterial fibres for subdiffraction imaging and focusing at terahertz frequencies over optically long distances  

PubMed Central

Using conventional materials, the resolution of focusing and imaging devices is limited by diffraction to about half the wavelength of light, as high spatial frequencies do not propagate in isotropic materials. Wire array metamaterials, because of their extreme anisotropy, can beat this limit; however, focusing with these has only been demonstrated up to microwave frequencies and using propagation over a few wavelengths only. Here we show that the principle can be scaled to frequencies orders of magnitudes higher and to considerably longer propagation lengths. We demonstrate imaging through straight and tapered wire arrays operating in the terahertz spectrum, with unprecedented propagation of near field information over hundreds of wavelengths and focusing down to 1/28 of the wavelength with a net increase in power density. Applications could include in vivo terahertz-endoscopes with resolution compatible with imaging individual cells. PMID:24162458

Tuniz, Alessandro; Kaltenecker, Korbinian J.; Fischer, Bernd M.; Walther, Markus; Fleming, Simon C.; Argyros, Alexander; Kuhlmey, Boris T.

2013-01-01

199

Metamaterial fibres for subdiffraction imaging and focusing at terahertz frequencies over optically long distances.  

PubMed

Using conventional materials, the resolution of focusing and imaging devices is limited by diffraction to about half the wavelength of light, as high spatial frequencies do not propagate in isotropic materials. Wire array metamaterials, because of their extreme anisotropy, can beat this limit; however, focusing with these has only been demonstrated up to microwave frequencies and using propagation over a few wavelengths only. Here we show that the principle can be scaled to frequencies orders of magnitudes higher and to considerably longer propagation lengths. We demonstrate imaging through straight and tapered wire arrays operating in the terahertz spectrum, with unprecedented propagation of near field information over hundreds of wavelengths and focusing down to 1/28 of the wavelength with a net increase in power density. Applications could include in vivo terahertz-endoscopes with resolution compatible with imaging individual cells. PMID:24162458

Tuniz, Alessandro; Kaltenecker, Korbinian J; Fischer, Bernd M; Walther, Markus; Fleming, Simon C; Argyros, Alexander; Kuhlmey, Boris T

2013-01-01

200

Metamaterial fibres for subdiffraction imaging and focusing at terahertz frequencies over optically long distances  

NASA Astrophysics Data System (ADS)

Using conventional materials, the resolution of focusing and imaging devices is limited by diffraction to about half the wavelength of light, as high spatial frequencies do not propagate in isotropic materials. Wire array metamaterials, because of their extreme anisotropy, can beat this limit; however, focusing with these has only been demonstrated up to microwave frequencies and using propagation over a few wavelengths only. Here we show that the principle can be scaled to frequencies orders of magnitudes higher and to considerably longer propagation lengths. We demonstrate imaging through straight and tapered wire arrays operating in the terahertz spectrum, with unprecedented propagation of near field information over hundreds of wavelengths and focusing down to 1/28 of the wavelength with a net increase in power density. Applications could include in vivo terahertz-endoscopes with resolution compatible with imaging individual cells.

Tuniz, Alessandro; Kaltenecker, Korbinian J.; Fischer, Bernd M.; Walther, Markus; Fleming, Simon C.; Argyros, Alexander; Kuhlmey, Boris T.

2013-10-01

201

An ultrafast terahertz scanning tunnelling microscope  

NASA Astrophysics Data System (ADS)

Ultrafast studies of excitations on the nanometre scale are essential for guiding applications in nanotechnology. Efforts to integrate femtosecond lasers with scanning tunnelling microscopes (STMs) have yielded a number of ultrafast STM techniques, but the basic ability to directly modulate the STM junction bias while maintaining nanometre spatial resolution has been limited to ~10 ps (refs 7,8) and has required specialized probe or sample structures. Here, without any modification to the STM design, we modulate the STM junction bias by coupling terahertz pulses to the scanning probe tip of an STM and demonstrate terahertz-pulse-induced tunnelling in an STM. The terahertz STM (THz-STM) provides simultaneous subpicosecond (<500 fs) time resolution and nanometre (2 nm) imaging resolution under ambient laboratory conditions, and can directly image ultrafast carrier capture into a single InAs nanodot. The THz-STM accesses an ultrafast tunnelling regime that opens the door to subpicosecond scanning probe microscopy of materials with atomic resolution.

Cocker, Tyler L.; Jelic, Vedran; Gupta, Manisha; Molesky, Sean J.; Burgess, Jacob A. J.; Reyes, Glenda De Los; Titova, Lyubov V.; Tsui, Ying Y.; Freeman, Mark R.; Hegmann, Frank A.

2013-08-01

202

Effect of dielectric properties of metals on terahertz transmission in subwavelength hole arrays  

E-print Network

Effect of dielectric properties of metals on terahertz transmission in subwavelength hole arrays of dielectric function of metals on the transmission properties of terahertz pulses through periodically metals become highly conductive at terahertz frequencies. Extraordinary terahertz trans- mission

203

Imaging molecular adsorption and desorption dynamics on graphene using terahertz emission spectroscopy  

PubMed Central

Being an atomically thin material, graphene is known to be extremely susceptible to its environment, including defects and phonons in the substrate on which it is placed as well as gas molecules that surround it. Thus, any device design using graphene has to take into consideration all surrounding components, and device performance needs to be evaluated in terms of environmental influence. However, no methods have been established to date to readily measure the density and distribution of external perturbations in a quantitative and non-destructive manner. Here, we present a rapid and non-contact method for visualizing the distribution of molecular adsorbates on graphene semi-quantitatively using terahertz time-domain spectroscopy and imaging. We found that the waveform of terahertz bursts emitted from graphene-coated InP sensitively changes with the type of atmospheric gas, laser irradiation time, and ultraviolet light illumination. The terahertz waveform change is explained through band structure modifications in the InP surface depletion layer due to the presence of localized electric dipoles induced by adsorbed oxygen. These results demonstrate that terahertz emission serves as a local probe for monitoring adsorption and desorption processes on graphene films and devices, suggesting a novel two-dimensional sensor for detecting local chemical reactions. PMID:25116593

Sano, Y.; Kawayama, I.; Tabata, M.; Salek, K. A.; Murakami, H.; Wang, M.; Vajtai, R.; Ajayan, P. M.; Kono, J.; Tonouchi, M.

2014-01-01

204

Imaging molecular adsorption and desorption dynamics on graphene using terahertz emission spectroscopy.  

PubMed

Being an atomically thin material, graphene is known to be extremely susceptible to its environment, including defects and phonons in the substrate on which it is placed as well as gas molecules that surround it. Thus, any device design using graphene has to take into consideration all surrounding components, and device performance needs to be evaluated in terms of environmental influence. However, no methods have been established to date to readily measure the density and distribution of external perturbations in a quantitative and non-destructive manner. Here, we present a rapid and non-contact method for visualizing the distribution of molecular adsorbates on graphene semi-quantitatively using terahertz time-domain spectroscopy and imaging. We found that the waveform of terahertz bursts emitted from graphene-coated InP sensitively changes with the type of atmospheric gas, laser irradiation time, and ultraviolet light illumination. The terahertz waveform change is explained through band structure modifications in the InP surface depletion layer due to the presence of localized electric dipoles induced by adsorbed oxygen. These results demonstrate that terahertz emission serves as a local probe for monitoring adsorption and desorption processes on graphene films and devices, suggesting a novel two-dimensional sensor for detecting local chemical reactions. PMID:25116593

Sano, Y; Kawayama, I; Tabata, M; Salek, K A; Murakami, H; Wang, M; Vajtai, R; Ajayan, P M; Kono, J; Tonouchi, M

2014-01-01

205

Character research on 2.52 terahertz coaxial reflection-mode confocal scanning microscopic imaging  

NASA Astrophysics Data System (ADS)

The technology of terahertz (THz) is a major research area in the 21st century. THz imaging is an important research direction. The single-frequency continuous-wave THz technology is combined with coaxial reflection-mode confocal scanning microscopic imaging in this article. Under the given system parameters, the transverse response character of 2.52THz (118.83?m) coaxial reflection-mode confocal scanning microscopic imaging is emulated and analyzed. The results of emulation show that coaxial reflection-mode confocal scanning microscopic imaging is feasible in THz region.

Yang, Yong-fa; Li, Qi; Hu, Jia-qi

2014-12-01

206

Nonlinear response of superconducting NbN thin film and NbN metamaterial induced by intense terahertz pulses  

NASA Astrophysics Data System (ADS)

We present the nonlinear response of superconducting niobium nitride (NbN) thin film and NbN metamaterial with different thicknesses under intense terahertz pulses. For NbN thin film, nonlinearity emerges and superconductivity is suppressed with increasing incident terahertz electric field, and the suppression extent weakens as the film thickness increases from 15 to 50 nm. As the variation in intense terahertz fields alters the intrinsic conductivity in NbN, a consequent remarkable amplitude modulation in NbN metamaterial is observed due to the strong nonlinearity. Absorbed photo density in either NbN film or NbN metamaterial is estimated and used to understand the mechanism of nonlinear response. With a thicker NbN film element of 200 nm, the resonance of the metamaterial shows similar nonlinear modulation accompanied by a lower loss and a higher quality factor compared with a thinner NbN film element of 50 nm, which demonstrates the innovative implementation of strongly enhanced nonlinearity with thick superconducting film elements and the potential for novel applications using nonlinear metamaterial.

Zhang, Caihong; Jin, Biaobing; Han, Jiaguang; Kawayama, Iwao; Murakami, Hironaru; Jia, Xiaoqing; Liang, Lanju; Kang, Lin; Chen, Jian; Wu, Peiheng; Tonouchi, Masayoshi

2013-05-01

207

406 IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY, VOL. 2, NO. 4, JULY 2012 Understanding THz Pulse Propagation in the  

E-print Network

. Index Terms--Absorption, atmospheric transmission, spectroscopy, terahertz (THz), THz communication. I406 IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY, VOL. 2, NO. 4, JULY 2012 Understanding

Oklahoma State University

208

Generation of Widely Tunable Fourier-Transform Pulsed Terahertz Radiation Using Narrowband Near-Infrared Laser Radiation  

NASA Astrophysics Data System (ADS)

Widely tunable, Fourier-transform-limited pulses of terahertz (THz) radiation have been generated by optical frequency deference using (i) crystals of the highly nonlinear organic salt 4-N,N-dimethylamino-4^'-N^'-methyl stilbazolium tosylate (DAST), (ii) zinc telluride (ZnTe) crystals, and (iii) gallium phosphide (GaP) crystals. Outputs from two narrowband (??<1 MHz, ?˜800 nm) cw titanium-doped sapphire (Ti:Sa) ring lasers with a well-controlled frequency difference were shaped into pulses using acousto-optic modulators, coupled into an optical fiber, pulse amplified in Nd:YAG-pumped Ti:Sa crystals and used as optical sources to pump the THz nonlinear crystals. The THz radiation was detected over a broad frequency range and its bandwidth was determined to be ˜10 MHz. Absorption spectra of gas phase molecules including HF and OCS using the THz source will be presented.

Liu, Jinjun; Haase, Christa; Merkt, Frédéric

2009-06-01

209

Terahertz Imaging and Backscatter Radiography Probability of Detection Study for Space Shuttle Foam Inspections  

NASA Technical Reports Server (NTRS)

This slide presentation reviews the use of terahertz imaging and Backscatter Radiography in a probability of detection study of the foam on the external tank (ET) shedding and damaging the shuttle orbiter. Non-destructive Examination (NDE) is performed as one method of preventing critical foam debris during the launch. Conventional NDE methods for inspection of the foam are assessed and the deficiencies are reviewed. Two methods for NDE inspection are reviewed: Backscatter Radiography (BSX) and Terahertz (THZ) Imaging. The purpose of the Probability of Detection (POD) study was to assess performance and reliability of the use of BSX and or THZ as an appropriate NDE method. The study used a test article with inserted defects, and a sample of blanks included to test for false positives. The results of the POD study are reported.

Ussery, Warren; Johnson, Kenneth; Walker, James; Rummel, Ward

2008-01-01

210

Terahertz Antenna System for a Near-Video-Rate Radar Imager [Antenna Applications  

Microsoft Academic Search

In this contribution. we present simulations and measurements of a reflector system that can rapidly scan a terahertz beam for a high-resolution standoff-imaging application, without compromising the beam quality. The antenna system utilizes a Gregorian confocal-reflector geometry, with a small mechanical rotating mirror. The system has been successfully fabricated and tested, with THz imagery of targets at a 25 m

N. Llombart; R. J. Dengler; K. B. Cooper

2010-01-01

211

Passive imaging with pulsed ultrasound insonations  

PubMed Central

Previously, passive cavitation imaging has been described in the context of continuous-wave high-intensity focused ultrasound thermal ablation. However, the technique has potential use as a feedback mechanism for pulsed-wave therapies, such as ultrasound-mediated drug delivery. In this paper, results of experiments and simulations are reported to demonstrate the feasibility of passive cavitation imaging using pulsed ultrasound insonations and how the images depend on pulsed ultrasound parameters. The passive cavitation images were formed from channel data that was beamformed in the frequency domain. Experiments were performed in an invitro flow phantom with an experimental echo contrast agent, echogenic liposomes, as cavitation nuclei. It was found that the pulse duration and envelope have minimal impact on the image resolution achieved. The passive cavitation image amplitude scales linearly with the cavitation emission energy. Cavitation images for both stable and inertial cavitation can be obtained from the same received data set. PMID:22779500

Haworth, Kevin J.; Mast, T. Douglas; Radhakrishnan, Kirthi; Burgess, Mark T.; Kopechek, Jonathan A.; Huang, Shao-Ling; McPherson, David D.; Holland, Christy K.

2012-01-01

212

Real-time, continuous-wave terahertz imaging using a microbolometer focal-plane array  

NASA Technical Reports Server (NTRS)

The present invention generally provides a terahertz (THz) imaging system that includes a source for generating radiation (e.g., a quantum cascade laser) having one or more frequencies in a range of about 0.1 THz to about 10 THz, and a two-dimensional detector array comprising a plurality of radiation detecting elements that are capable of detecting radiation in that frequency range. An optical system directs radiation from the source to an object to be imaged. The detector array detects at least a portion of the radiation transmitted through the object (or reflected by the object) so as to form a THz image of that object.

Hu, Qing (Inventor); Min Lee, Alan W. (Inventor)

2010-01-01

213

Terahertz imaging through self-mixing in a quantum cascade laser.  

PubMed

We demonstrate terahertz (THz) frequency imaging using a single quantum cascade laser (QCL) device for both generation and sensing of THz radiation. Detection is achieved by utilizing the effect of self-mixing in the THz QCL, and, specifically, by monitoring perturbations to the voltage across the QCL, induced by light reflected from an external object back into the laser cavity. Self-mixing imaging offers high sensitivity, a potentially fast response, and a simple, compact optical design, and we show that it can be used to obtain high-resolution reflection images of exemplar structures. PMID:21725488

Dean, Paul; Lim, Yah Leng; Valavanis, Alex; Kliese, Russell; Nikoli?, Milan; Khanna, Suraj P; Lachab, Mohammad; Indjin, Dragan; Ikoni?, Zoran; Harrison, Paul; Raki?, Aleksandar D; Linfield, Edmund H; Davies, A Giles

2011-07-01

214

High Frequency Methods for Simulation of High Resolution Imaging in Terahertz Regime  

NASA Astrophysics Data System (ADS)

High resolution imaging in the terahertz (THz) frequency range is investigated theoretically in this paper through the use of the high frequency methods in computational electromagnetics (CEM). Physical optics (PO), shooting and bouncing ray (SBR) and truncated-wedge incremental length diffraction coefficients (TW-ILDCs) methods are combined together to compute the scattered fields, which are then used to construct the inverse synthetic aperture radar (ISAR) images through two dimensional fast Fourier transform (2D-FFT). The corresponding ISAR images clearly show that high range and bearing resolution can be easily realized for THz carrier waves with broad bandwidth.

Li, Zhuo; Cui, Tie Jun

2010-03-01

215

Terahertz imaging system based on bessel beams via 3D printed axicons at 100GHz  

NASA Astrophysics Data System (ADS)

Terahertz (THz) imaging technology shows great advantage in nondestructive detection (NDT), since many optical opaque materials are transparent to THz waves. In this paper, we design and fabricate dielectric axicons to generate zeroth order-Bessel beams by 3D printing technology. We further present an all-electric THz imaging system using the generated Bessel beams in 100GHz. Resolution targets made of printed circuit board are imaged, and the results clearly show the extended depth of focus of Bessel beam, indicating the promise of Bessel beam for the THz NDT.

Liu, Changming; Wei, Xuli; Zhang, Zhongqi; Wang, Kejia; Yang, Zhenggang; Liu, Jinsong

2014-11-01

216

Processing sequence for non-destructive inspection based on 3D terahertz images  

NASA Astrophysics Data System (ADS)

In this paper we present an innovative data and image processing sequence to perform non-destructive inspection from 3D terahertz (THz) images. We develop all the steps starting from a 3D tomographic reconstruction of a sample from its radiographs acquired with a monochromatic millimetre wave imaging system. Thus an automated segmentation provides the different volumes of interest (VOI) composing the sample. Then a 3D visualization and dimensional measurements are performed on these VOI, separately, in order to provide an accurate nondestructive testing (NDT) of the studied sample. This sequence is implemented onto an unique software and validated through the analysis of different objects

Balacey, H.; Perraud, Jean-Baptiste; Bou Sleiman, J.; Guillet, Jean-Paul; Recur, B.; Mounaix, P.

2014-11-01

217

Enhanced terahertz imaging system performance analysis and design tool for concealed weapon identification  

NASA Astrophysics Data System (ADS)

The U.S. Army Research Laboratory (ARL) and the U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) have developed a terahertz-band imaging system performance model/tool for detection and identification of concealed weaponry. The details of the MATLAB-based model which accounts for the effects of all critical sensor and display components, and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination, were reported on at the 2005 SPIE Europe Security & Defence Symposium (Brugge). An advanced version of the base model that accounts for both the dramatic impact that target and background orientation can have on target observability as related to specular and Lambertian reflections captured by an active-illumination-based imaging system, and for the impact of target and background thermal emission, was reported on at the 2007 SPIE Defense and Security Symposium (Orlando). This paper will provide a comprehensive review of an enhanced, user-friendly, Windows-executable, terahertz-band imaging system performance analysis and design tool that now includes additional features such as a MODTRAN-based atmospheric attenuation calculator and advanced system architecture configuration inputs that allow for straightforward performance analysis of active or passive systems based on scanning (single- or line-array detector element(s)) or staring (focal-plane-array detector elements) imaging architectures. This newly enhanced THz imaging system design tool is an extension of the advanced THz imaging system performance model that was developed under the Defense Advanced Research Project Agency's (DARPA) Terahertz Imaging Focal-Plane Technology (TIFT) program. This paper will also provide example system component (active-illumination source and detector) trade-study analyses using the new features of this user-friendly THz imaging system performance analysis and design tool.

Murrill, Steven R.; Franck, Charmaine C.; Espinola, Richard L.; Petkie, Douglas T.; De Lucia, Frank C.; Jacobs, Eddie L.

2011-11-01

218

Spectroscopic Imaging using Terahertz Time-Domain Signals Timothy D. Dorney, Richard G. Baraniuk, Daniel M. Mittleman, and Robert D. Nowak  

E-print Network

Spectroscopic Imaging using Terahertz Time-Domain Signals Timothy D. Dorney, Richard G. Baraniuk Imaging systems based on terahertz time-domain spectroscopy offer a range of unique modalities due spectroscopic transmission measurements require accurate knowledge of the sample's thickness to determine

219

Terahertz imaging using quantum cascade lasers—a review of systems and applications  

NASA Astrophysics Data System (ADS)

The terahertz (THz) frequency quantum cascade laser (QCL) is a compact source of THz radiation offering high power, high spectral purity and moderate tunability. As such, these sources are particularly suited to the application of THz frequency imaging across a range of disciplines, and have motivated significant research interest in this area over the past decade. In this paper we review the technological approaches to THz QCL-based imaging and the key advancements within this field. We discuss in detail a number of imaging approaches targeted to application areas including multiple-frequency transmission and diffuse reflection imaging for the spectral mapping of targets; as well as coherent approaches based on the self-mixing phenomenon in THz QCLs for long-range imaging, three-dimensional imaging, materials analysis, and high-resolution inverse synthetic aperture radar imaging.

Dean, P.; Valavanis, A.; Keeley, J.; Bertling, K.; Lim, Y. L.; Alhathlool, R.; Burnett, A. D.; Li, L. H.; Khanna, S. P.; Indjin, D.; Taimre, T.; Raki?, A. D.; Linfield, E. H.; Davies, A. G.

2014-09-01

220

Competition between linear and nonlinear processes during generation of pulsed terahertz radiation in a ZnTe crystal  

SciTech Connect

The generation of terahertz (THz) pulses by the optical rectification of femtosecond laser pulses in a ZnTe crystal is studied. A substantial decrease in the THz radiation power was observed upon tight focusing of laser radiation into the crystal. It is shown that the consideration of competing two-photon absorption and second-harmonic generation processes proceeding simultaneously with optical rectification cannot explain this effect even qualitatively. It is assumed that the observed decrease in the THz radiation power is caused by a decrease in the size of a source of nonlinear polarisation. The conditions are found for the most efficient generation of THz radiation in the ZnTe crystal. (nonlinear optical phenomena)

Gaivoronsky, Vladimir Ya; Shepelyavyi, Yevgenii V [Institute of Physics, National Academy of Sciences of Ukraine, Kiev (Ukraine); Nazarov, Maksim M; Sapozhnikov, Dmitrii A [International Laser Center, M. V. Lomonosov Moscow State University, Moscow (Russian Federation); Shkel'nyuk, Svetlana A; Shkurinov, A P; Shuvaev, Aleksandr V [Department of Physics, M.V. Lomonosov Moscow State University, Moscow (Russian Federation)

2005-05-31

221

Propagation of broadband terahertz pulses through a dense-magnetized-collisional-bounded plasma layer  

SciTech Connect

The terahertz characteristics of a dense-magnetized-collisional-bounded plasma under normal incident are analyzed in this study, which is of practical significance in plasma diagnostics with electromagnetic waves. We theoretically calculate the reflection, absorption, and transmission coefficients for right- and left-handed polarized terahertz waves through a uniform, magnetized, and collisional plasma slab bounded by lossless transparent walls. The power absorption spectra in the frequency range of 0.1-2 THz are given with strong external magnetic fields and different plasma parameters such as plasma density and collisional frequency. Our numerical result is consistent with Jamison's experimental result. It is found that plasma absorption is mainly caused by the collisional absorption and electron cyclotron resonance. Furthermore, the absorption heavily depends on the polarization mode of the terahertz waves when the external magnetic field B is high enough that the election gyrofrequency is near the incident wave frequency. The relationships between the corresponding parameters of the problem are studied numerically.

Yuan Chengxun; Zhou Zhongxiang; Sun Hongguo; Pu Shaozhi [Department of Physics, Harbin Institute of Technology, Harbin, Heilongjiang 150001 (China); Xiang Xiaoli [Shanghai Academy of Spaceflight Technology, Shanghai 201108 (China)

2010-11-15

222

Spatial pattern separation of chemicals and frequency-independent components by terahertz spectroscopic imaging  

NASA Astrophysics Data System (ADS)

We separated the component spatial patterns of frequency-dependent absorption in chemicals and frequency-independent components such as plastic, paper, and measurement noise in terahertz (THz) spectroscopic images, using known spectral curves. Our measurement system, which uses a widely tunable coherent THz-wave parametric oscillator source, can image at a specific frequency in the range 1-2 THz. The component patterns of chemicals can easily be extracted by use of the frequency-independent components. This method could be successfully used for nondestructive inspection for the detection of illegal drugs and devices of bioterrorism concealed, e.g., inside mail and packages.

Watanabe, Yuuki; Kawase, Kodo; Ikari, Tomofumi; Ito, Hiromasa; Ishikawa, Youichi; Minamide, Hiroaki

2003-10-01

223

Ionic contrast terahertz time resolved imaging of frog auricular heart muscle electrical activity  

NASA Astrophysics Data System (ADS)

The authors demonstrate the direct, noninvasive and time resolved imaging of functional frog auricular fibers by ionic contrast terahertz (ICT) near field microscopy. This technique provides quantitative, time-dependent measurement of ionic flow during auricular muscle electrical activity, and opens the way of direct noninvasive imaging of cardiac activity under stimulation. ICT microscopy technique was associated with full three-dimensional simulation enabling to measure precisely the fiber sizes. This technique coupled to waveguide technology should provide the grounds to development of advanced in vivo ion flux measurement in mammalian hearts, allowing the prediction of heart attack from change in K+ fluxes.

Masson, Jean-Baptiste; Sauviat, Martin-Pierre; Gallot, Guilhem

2006-10-01

224

Terahertz imaging system for stand-off detection of threats  

NASA Astrophysics Data System (ADS)

Suicide bombers and hidden bombs or explosives have become serious threats especially for mass transportation. Until now there exists no established system which can be used against these threats. Therefore new technologies especially for stand-off detection of threats are required. Terahertz (THz) rays offer an alternative inspection method, which can cope with these new challenges. Major advantages of THz radiation as compared to other spectral regions are the possibility to penetrate through clothes and that THz radiation is not harmful for human health. In this report the design and results of a THz stand-off detection system will be presented. The sensor is based on active illumination of the object and sensitive heterodyne detection of reflected and backscattered radiation. The system operates at about 0.8 THz. A THz laser is used for illumination and a superconducting hot-electron bolometric mixer for detection. The local oscillator required for heterodyne detection is a multiplied microwave source. The optical system is designed to allow for stand-off detection at 20 m with a spatial resolution less than 2 cm.

Hübers, H.-W.; Semenov, A. D.; Richter, H.; Böttger, U.

2007-04-01

225

Feasibility demonstration of frequency domain terahertz imaging in breast cancer margin determination  

NASA Astrophysics Data System (ADS)

In breast conservation surgery, surgeons attempt to remove malignant tissue along with a surrounding margin of healthy tissue. Subsequent pathological analysis determines if those margins are clear of malignant tissue, a process that typically requires at least one day. Only then can it be determined whether a follow-up surgery is necessary. This possibility of re-excision is undesirable in terms of reducing patient morbidity, emotional stress and healthcare. It has been shown that terahertz (THz) images of breast specimens can accurately differentiate between breast carcinoma, normal fibroglandular tissue, and adipose tissue. That study employed the Time-Domain Spectroscopy (TDS) technique. We are instead developing a new technique, Frequency-Domain Terahertz Imaging (FDTI). In this joint project between UMass/Amherst and UMass Medical School/Worcester (UMMS), we are investigating the feasibility of the FDTI technique for THz reflection imaging of breast cancer margins. Our system, which produces mechanically scanned images of size 2cm x 2cm, uses a THz gas laser. The system is calibrated with mixtures of water and ethanol and reflection coefficients as low as 1% have been measured. Images from phantoms and specimens cut from breast cancer lumpectomies at UMMS will be presented. Finally, there will be a discussion of a possible transition of this FDTI setup to a compact and inexpensive CMOS THz camera for use in the operating room.

Yngvesson, Sigfrid K.; St. Peter, Benjamin; Siqueira, Paul; Kelly, Patrick; Glick, Stephen; Karellas, Andrew; Khan, Ashraf

2012-03-01

226

Feasibility demonstration of frequency domain terahertz imaging in breast cancer margin determination  

PubMed Central

In breast conservation surgery, surgeons attempt to remove malignant tissue along with a surrounding margin of healthy tissue. Subsequent pathological analysis determines if those margins are clear of malignant tissue, a process that typically requires at least one day. Only then can it be determined whether a follow-up surgery is necessary. This possibility of re-excision is undesirable in terms of reducing patient morbidity, emotional stress and healthcare. It has been shown that terahertz (THz) images of breast specimens can accurately differentiate between breast carcinoma, normal fibroglandular tissue, and adipose tissue. That study employed the Time-Domain Spectroscopy (TDS) technique. We are instead developing a new technique, Frequency-Domain Terahertz Imaging (FDTI). In this joint project between UMass/Amherst and UMass Medical School/Worcester (UMMS), we are investigating the feasibility of the FDTI technique for THz reflection imaging of breast cancer margins. Our system, which produces mechanically scanned images of size 2cm × 2cm, uses a THz gas laser. The system is calibrated with mixtures of water and ethanol and reflection coefficients as low as 1% have been measured. Images from phantoms and specimens cut from breast cancer lumpectomies at UMMS will be presented. Finally, there will be a discussion of a possible transition of this FDTI setup to a compact and inexpensive CMOS THz camera for use in the operating room. PMID:24353380

Yngvesson, Sigfrid K.; St. Peter, Benjamin; Siqueira, Paul; Kelly, Patrick; Glick, Stephen; Karellas, Andrew; Khan, Ashraf

2013-01-01

227

An ultrafast carbon nanotube terahertz polarisation modulator  

SciTech Connect

We demonstrate ultrafast modulation of terahertz radiation by unaligned optically pumped single-walled carbon nanotubes. Photoexcitation by an ultrafast optical pump pulse induces transient terahertz absorption in nanowires aligned parallel to the optical pump. By controlling the polarisation of the optical pump, we show that terahertz polarisation and modulation can be tuned, allowing sub-picosecond modulation of terahertz radiation. Such speeds suggest potential for semiconductor nanowire devices in terahertz communication technologies.

Docherty, Callum J.; Stranks, Samuel D.; Habisreutinger, Severin N.; Joyce, Hannah J.; Herz, Laura M.; Nicholas, Robin J.; Johnston, Michael B., E-mail: m.johnston@physics.ox.ac.uk [Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU (United Kingdom)

2014-05-28

228

Propagation through terahertz waveguides with photonic crystal boundaries  

Microsoft Academic Search

Scope and method of study. The research presented in this dissertation investigates the integration of photonic crystal lattices into parallel plate waveguides at terahertz frequencies. The experimental data was obtained by measuring the terahertz pulses through the photonic crystal waveguides in a standard terahertz time-domain spectroscopy system. The terahertz pulses were generated and detected via optoelectronic means utilizing lithographically fabricated

Adam L. Bingham

2007-01-01

229

Fringe removal for continuous-wave terahertz imaging based on cartoon-texture decomposition  

NASA Astrophysics Data System (ADS)

Continuous-wave (CW) terahertz (THz) imaging system has advantages of high power, compact structure and low cost, thus having been investigated for widespread applications. In typical reflection mode of CW imaging, the obtained image is usually degraded by repeated fringes, which is caused by interference phenomenon. The undesired interference signal originates from the reflection of surfaces of samples and lenses. When the samples are titled placed or their surfaces are uneven, the detected signal intensity is fluctuant even if the same sample lies in different positions. Therefore, small-sized or weekly absorbing objects are hard to be distinguished. Based on cartoon-texture decomposition, we propose a practical method to restore CW THz reflection images. After decomposition, the fringes and the objects are separated. In order to preserve edges, sharpening and fusion steps are employed respectively. The object in the final image is obvious with little loss of information.

Qiao, Lingbo; Wang, Yingxin; Zhao, Ziran; Chen, Zhiqiang

2013-08-01

230

Personnel screening with terahertz opto-mechanical scanning imaging  

NASA Astrophysics Data System (ADS)

We presented a passive THz opto-mechnical scanning imaging method using a single detector and a trihedral scanning mirror. The system improved the imaging speed through employing two flapping mirrors. Also the trihedral scanning mirror and an ellipsoidal mirror were adopted. The parameters were set as follows: the best imaging distance was 2.2m with the image range of 1.6m (W) ×1.6m (H), the imaging time was 2s, and the resolution was 3cm. We imaged human body with different objects concealed under their clothes, such as buckle, ceramic chip, etc.

Guo, Lan-tao; Liu, Xin; Deng, Chao; Zhao, Yuan-meng; Zhang, Cun-lin

2014-11-01

231

Non-contact weight measurement of flat-faced pharmaceutical tablets using terahertz transmission pulse delay measurements.  

PubMed

By measuring the time delay of a terahertz pulse traversing a tablet, and hence its effective refractive index, it is possible to non-invasively and non-destructively detect the weight of tablets made of microcrystalline cellulose (MCC). Two sets of MCC tablets were used in the study: Set A (training set) consisted of 13 tablets with nominally constant height but varying porosities, whereas Set B (test set) comprised of 21 tablets with nominally constant porosity but different heights. A linear correlation between the estimated absolute weight based on the terahertz measurement and the measured weight of both sets of MCC tablets was found. In addition, it was possible to estimate the height of the tablets by utilizing the estimated absolute weight and calculating the relative change of height of each tablet with respect to an ideal tablet. A good agreement between the experimental and the calculated results was found highlighting the potential of this technique for in-line sensing of the weight, porosity and the relative change in height of the tablets compared to a reference/ideal tablet. In this context, we propose a quantitative quality control method to assess the deviations in porosity of tablets immediately after compaction. PMID:25245546

Bawuah, Prince; Silfsten, Pertti; Ervasti, Tuomas; Ketolainen, Jarkko; Zeitler, J Axel; Peiponen, Kai-Erik

2014-12-10

232

Identification of tissue interaction of terahertz radiation toward functional tissue imaging  

NASA Astrophysics Data System (ADS)

In recent years, many applications have been recognized for biomedical imaging techniques utilizing terahertz frequency radiation. This is largely due to the capability of unique tissue identification resulting from the nature of the interaction between THz radiation and the molecular structure of the cells. By THz identification methods, tissue changes in tooth enamel, cartilage, and malignant cancer cells have already been demonstrated. Terahertz Time-Domain Spectroscopy (THz-TDS) remains one of the most versatile methods for spectroscopic image acquisition for its ability to simultaneously determine amplitude and phase over a broad spectral range. In this study we investigate the use of THz imaging techniques to uniquely identify damage types in tissue samples for both forensic and treatment applications. Using THz-TDS imaging in both transmission and reflection schemes, we examine tissue samples which have been damaged using a variety of acids. Each method of damage causes structural deterioration to the tissue by a different mechanism, thus leaving the remaining tissue uniquely changed based on the damage type. We correlate the change in frequency spectra, phase shift for each damage type to the mechanisms and severity of injury.

Yokus, Hamdullah; Baughman, William; Balci, Soner; Bolus, Michael; Wilbert, David; Kung, Patrick; Kim, Seongsin M.

2013-02-01

233

The ethical dimension of terahertz and millimeter-wave imaging technologies: security, privacy, and acceptability  

NASA Astrophysics Data System (ADS)

Terahertz and millimeter-wave imaging technologies, wherever they are applied to human beings, generate problems with the "naked" body. Security issues thus inevitably lead to ethical questions of privacy and intimacy. Less apparent but no less important are other issues such as discrimination and the question of reducing this problem through post processing of data; scalability; questions of controlling the controllers; questions of proliferation. Ethical research alone can not provide acceptability. However, ultimately innovative technologies will not achieve widespread and sustainable acceptance without a fundamental clarification of the ethically relevant issues.

Ammicht Quinn, R.; Rampp, B.

2009-05-01

234

Imaging of free carriers in semiconductors via optical feedback in terahertz quantum cascade lasers  

SciTech Connect

To monitor the density of photo-generated charge carriers on a semiconductor surface, we demonstrate a detectorless imaging system based on the analysis of the optical feedback in terahertz quantum cascade lasers. Photo-excited free electron carriers are created in high resistivity n-type silicon wafers via low power (?40 mW/cm{sup 2}) continuous wave pump laser in the near infrared spectral range. A spatial light modulator allows to directly reconfigure and control the photo-patterned intensity and the associated free-carrier density distribution. The experimental results are in good agreement with the numerical simulations.

Mezzapesa, F. P., E-mail: francesco.mezzapesa@uniba.it; Brambilla, M.; Dabbicco, M.; Scamarcio, G. [Dipartimento Interateneo di Fisica, Università degli Studi e Politecnico di Bari, via Amendola 173, 70126 Bari (Italy); CNR-IFN UOS Bari, via Amendola 173, 70126 Bari (Italy); Columbo, L. L. [Dipartimento Interateneo di Fisica, Università degli Studi e Politecnico di Bari, via Amendola 173, 70126 Bari (Italy); CNR-IFN UOS Bari, via Amendola 173, 70126 Bari (Italy); Dipartimento di Scienza ed Alta Tecnologia, Università dell'Insubria, via Valleggio 11, 22100 Como (Italy); Vitiello, M. S. [NEST, CNR - Istituto Nanoscienze and Scuola Normale Superiore, piazza San Silvestro 12, 56127 Pisa (Italy)

2014-01-27

235

Terahertz imaging of sub-wavelength particles with Zenneck surface waves  

SciTech Connect

Impact of sub-wavelength-size dielectric particles on Zenneck surface waves on planar metallic antennas is investigated at terahertz (THz) frequencies with THz near-field probe microscopy. Perturbations of the surface waves show the particle presence, despite its sub-wavelength size. The experimental configuration, which utilizes excitation of surface waves at metallic edges, is suitable for THz imaging of dielectric sub-wavelength size objects. As a proof of concept, the effects of a small strontium titanate rectangular particle and a titanium dioxide sphere on the surface field of a bow-tie antenna are experimentally detected and verified using full-wave simulations.

Navarro-Cía, M., E-mail: m.navarro@imperial.ac.uk [Optical and Semiconductor Devices Group, Department of Electrical and Electronic Engineering, Imperial College London, London SW7 2BT (United Kingdom); Centre for Plasmonics and Metamaterials, Imperial College London, London SW7 2AZ (United Kingdom); Centre for Terahertz Science and Engineering, Imperial College London, London SW7 2AZ (United Kingdom); Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE (United Kingdom); Natrella, M.; Graham, C.; Renaud, C. C.; Seeds, A. J.; Mitrofanov, O., E-mail: o.mitrofanov@ucl.ac.uk [Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE (United Kingdom); Dominec, F.; Kužel, P., E-mail: kuzelp@fzu.cz [Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8 (Czech Republic); Delagnes, J. C.; Mounaix, P., E-mail: p.mounaix@loma.u-bordeaux1.fr [LOMA, Bordeaux 1 University, CNRS UMR 4798, 351 cours de la Libération, 33405 Talence (France)

2013-11-25

236

Swept-frequency feedback interferometry using terahertz frequency QCLs: a method for imaging and materials analysis.  

PubMed

The terahertz (THz) frequency quantum cascade laser (QCL) is a compact source of high-power radiation with a narrow intrinsic linewidth. As such, THz QCLs are extremely promising sources for applications including high-resolution spectroscopy, heterodyne detection, and coherent imaging. We exploit the remarkable phase-stability of THz QCLs to create a coherent swept-frequency delayed self-homodyning method for both imaging and materials analysis, using laser feedback interferometry. Using our scheme we obtain amplitude-like and phase-like images with minimal signal processing. We determine the physical relationship between the operating parameters of the laser under feedback and the complex refractive index of the target and demonstrate that this coherent detection method enables extraction of complex refractive indices with high accuracy. This establishes an ultimately compact and easy-to-implement THz imaging and materials analysis system, in which the local oscillator, mixer, and detector are all combined into a single laser. PMID:24104111

Raki?, Aleksandar D; Taimre, Thomas; Bertling, Karl; Lim, Yah Leng; Dean, Paul; Indjin, Dragan; Ikoni?, Zoran; Harrison, Paul; Valavanis, Alexander; Khanna, Suraj P; Lachab, Mohammad; Wilson, Stephen J; Linfield, Edmund H; Davies, A Giles

2013-09-23

237

Terahertz Emission from Narrow Gap Semiconductors Photoexcited by Femtosecond Laser Pulses  

NASA Astrophysics Data System (ADS)

Large increase in the emitted terahertz power was observed for p-InAs samples with the p-doping levels of approximately 1016-1017 cm-3. This increase was explained by a large surface depletion layer and an electric-field-induced optical rectification effect in the layer. Terahertz fields radiated by the samples of all three investigated CdxHg1-xTe layers was of the same order of magnitude. No azimuthal angle dependence of the radiated signal was detected, which evidences that linear current surge effect is dominating over nonlinear optical rectification. Azimuthal angle and magnetic fields emission witness that it is caused by linear photo-Dember type processes.

Adomavicius, R.; Urbanowicz, A.; Molis, G.; Krotkus, A.

2005-01-01

238

Screening mail for powders using terahertz technology  

NASA Astrophysics Data System (ADS)

Following the 2001 Anthrax letter attacks in the USA, there has been a continuing interest in techniques that can detect or identify so-called 'white powder' concealed in envelopes. Electromagnetic waves (wavelengths 100-500 ?m) in the terahertz frequency range penetrate paper and have short enough wavelengths to provide good resolution images; some materials also have spectroscopic signatures in the terahertz region. We report on an experimental study into the use of terahertz imaging and spectroscopy for mail screening. Spectroscopic signatures of target powders were measured and, using a specially designed test rig, a number of imaging methods based on reflection, transmission and scattering were investigated. It was found that, contrary to some previous reports, bacterial spores do not appear to have any strong spectroscopic signatures which would enable them to be identified. Imaging techniques based on reflection imaging and scattering are ineffective in this application, due to the similarities in optical properties between powders of interest and paper. However, transmission imaging using time-of-flight of terahertz pulses was found to be a very simple and sensitive method of detecting small quantities (25 mg) of powder, even in quite thick envelopes. An initial feasibility study indicates that this method could be used as the basis of a practical mail screening system.

Kemp, Mike

2011-11-01

239

Materials for terahertz science and technology  

Microsoft Academic Search

Terahertz spectroscopy systems use far-infrared radiation to extract molecular spectral information in an otherwise inaccessible portion of the electromagnetic spectrum. Materials research is an essential component of modern terahertz systems: novel, higher-power terahertz sources rely heavily on new materials such as quantum cascade structures. At the same time, terahertz spectroscopy and imaging provide a powerful tool for the characterization of

Bradley Ferguson; Xi-Cheng Zhang

2002-01-01

240

Generation of widely tunable Fourier-transform-limited terahertz pulses using narrowband near-infrared laser radiation  

NASA Astrophysics Data System (ADS)

Widely tunable, Fourier-transform-limited pulses of terahertz (THz) radiation have been generated using (i) crystals of the highly nonlinear organic salt 4- N, N-dimethylamino-4'- N'-methyl stilbazolium tosylate (DAST), (ii) zinc telluride (ZnTe) crystals, (iii) gallium phosphide (GaP) crystals, and (iv) low-temperature-grown gallium arsenide (LTG-GaAs) photomixers with THz spiral antennas. Outputs from two narrowband (? ? < 1 MHz, ? ˜ 800 nm) cw titanium-doped sapphire (Ti:Sa) ring lasers with a well-controlled frequency difference were shaped into pulses using acousto-optic modulators (AOM), coupled into an optical fiber, pulse amplified in Nd:YAG-pumped Ti:Sa crystals and used as optical sources to pump the THz emitters. The THz radiation was detected over a broad frequency range and its bandwidth was determined to be ˜10 MHz. The spectroscopic potential of the THz source is illustrated by the absorption spectrum of a pure rotational transition of OCS.

Liu, Jinjun; Schmutz, Hansjürg; Merkt, Frédéric

2009-07-01

241

Terahertz single pixel imaging with an optically controlled dynamic spatial light modulator.  

PubMed

We present a single pixel terahertz (THz) imaging technique using optical photoexcitation of semiconductors to dynamically and spatially control the electromagnetic properties of a semiconductor mask to collectively form a THz spatial light modulator (SLM). By co-propagating a THz and collimated optical laser beam through a high-resistivity silicon wafer, we are able to modify the THz transmission in real-time. By further encoding a spatial pattern on the optical beam with a digital micro-mirror device (DMD), we may write masks for THz radiation. We use masks of varying complexities ranging from 63 to 1023 pixels and are able to acquire images at speeds up to 1/2 Hz. Our results demonstrate the viability of obtaining real-time and high-fidelity THz images using an optically controlled SLM with a single pixel detector. PMID:23736469

Shrekenhamer, David; Watts, Claire M; Padilla, Willie J

2013-05-20

242

Underwater modulated pulse laser imaging system  

NASA Astrophysics Data System (ADS)

The detection and identification of underwater threats in coastal areas are of interest to the Navy. When identifying a potential target, both two-dimensional (amplitude versus position) and three-dimensional (amplitude and range versus position) information are important. Laser imaging in turbid coastal waters makes this task challenging due to absorption and scattering in both the forward and backward directions. Conventional imaging approaches to suppress scatter rely on a pulsed laser and a range-gated receiver or an intensity-modulated continuous wave laser and a coherent RF receiver. The modulated pulsed laser imaging system is a hybrid of these two approaches and uses RF intensity modulation on a short optical pulse. The result is an imaging system capable of simultaneously acquiring high-contrast images along with high-precision unambiguous ranges. A working modulated pulsed laser line scanner was constructed and tested with a custom-built transmitter, a large-bandwidth optical receiver, and a high-speed digitizing oscilloscope. The effectiveness of the modulation to suppress both backscatter and forward scatter, as applied to both magnitude and range images, is discussed.

O'Connor, Shawn; Mullen, Linda J.; Cochenour, Brandon

2014-05-01

243

Development of an electro-optic resonator probe for Terahertz imaging R. Mueckstein, Huiyun Liu, and O. Mitrofanov  

E-print Network

] is presented. The idea of a Fabry-Perot cavity is introduced and its design parameters are discussedDevelopment of an electro-optic resonator probe for Terahertz imaging R. Mueckstein, Huiyun Liu, Abstract: We introduce the concept of an electro-optic resonator to improve resolution and enhance

Haddadi, Hamed

244

Single nanowire photoconductive terahertz detectors.  

PubMed

Spectroscopy and imaging in the terahertz (THz) region of the electromagnetic spectrum has proven to provide important insights in fields as diverse as chemical analysis, materials characterization, security screening, and nondestructive testing. However, compact optoelectronics suited to the most powerful terahertz technique, time-domain spectroscopy, are lacking. Here, we implement single GaAs nanowires as microscopic coherent THz sensors and for the first time incorporated them into the pulsed time-domain technique. We also demonstrate the functionality of the single nanowire THz detector as a spectrometer by using it to measure the transmission spectrum of a 290 GHz low pass filter. Thus, nanowires are shown to be well suited for THz device applications and hold particular promise as near-field THz sensors. PMID:25490548

Peng, Kun; Parkinson, Patrick; Fu, Lan; Gao, Qiang; Jiang, Nian; Guo, Ya-Nan; Wang, Fan; Joyce, Hannah J; Boland, Jessica L; Tan, Hark Hoe; Jagadish, Chennupati; Johnston, Michael B

2015-01-14

245

Terahertz holography for imaging amplitude and phase objects.  

PubMed

A non-monochromatic THz Quantum Cascade Laser and an uncooled micro-bolometer array detector with VGA resolution are used in a beam-splitter free holographic set-up to measure amplitude and phase objects in transmission. Phase maps of the diffraction pattern are retrieved using the Fourier transform carrier fringe method; while a Fresnel-Kirchhoff back propagation algorithm is used to reconstruct the complex object image. A lateral resolution of 280 µm and a relative phase sensitivity of about 0.5 rad are estimated from reconstructed images of a metallic Siemens star and a polypropylene test structure, respectively. Simulations corroborate the experimental results. PMID:24977861

Hack, Erwin; Zolliker, Peter

2014-06-30

246

Adaptive terahertz imaging using a virtual transceiver and coherence weighting  

E-print Network

.-C. Li, and M.-L. Li, "Adaptive imaging using the generalized coherence factor," IEEE Trans. Ultrason factor of speckle from a multi-row probe," in Proceedings of the 1999 IEEE Ultrasonics Symposium (IEEE-speed inhomogeneities: The van Cittert Zernike approach and focusing criterion," J. Acoust. Soc. Am. 96(6), 3721

Buma, Takashi

247

The generation of high field terahertz radiation and its application in terahertz nonlinear spectroscopy  

E-print Network

In this thesis research, I implemented a terahertz generation scheme that enables high-field near-single-cycle terahertz (THz) pulse generation via optical rectification in a LiNbO3 (LN) crystal. I also developed a method ...

Yeh, Ka-Lo

2009-01-01

248

A Nipkow disk integrated with Fresnel lenses for terahertz single pixel imaging.  

PubMed

We present a novel Nipkow disk design for terahertz (THz) single pixel imaging applications. A 100 mm high resistivity (??3k-10k ??cm) silicon wafer was used for the disk on which a spiral array of twelve 16-level binary Fresnel lenses were fabricated using photolithography and a dry-etch process. The implementation of Fresnel lenses on the Nipkow disk increases the THz signal transmission compared to the conventional pinhole-based Nipkow disk by more than 12 times thus a THz source with lower power or a THz detector with lower detectivity can be used. Due to the focusing capability of the lenses, a pixel resolution better than 0.5 mm is in principle achievable. To demonstrate the concept, a single pixel imaging system operating at 2.52 THz is described. PMID:24150289

Li, Chong; Grant, James; Wang, Jue; Cumming, David R S

2013-10-21

249

Terahertz spectroscopic imaging and properties of gastrointestinal tract in a rat model  

PubMed Central

We have investigated basic properties of normal gastrointestinal (GI) tract tissues, including glandular stomach (GS), fore stomach (FS), large intestine (LI), small intestine (SI), and esophagus (ESO), from a rat model using terahertz (THz) reflection imaging and spectroscopy. The THz images collected from stratified squamous epithelia (SSE) of FS and ESO show a lower peak-to-peak value compared to those from columnar epithelia (CE) of GS, LI, or SI because the SSE contains less water than CE. The refractive index and absorption coefficient of FS were less than those of GS or LI, both having values similar to those of water. Additionally, we report internal reflection THz signals from ESO, although we were unable to determine the exact interface for this internal reflection. PMID:25574429

Ji, Young Bin; Kim, Sang-Hoon; Jeong, Kiyoung; Choi, Yuna; Son, Joo-Hiuk; Park, Dong Woo; Noh, Sam Kyu; Jeon, Tae-In; Huh, Yong-Min; Haam, Seungjoo; Lee, Sang Kil; Oh, Seung Jae; Suh, Jin-Suck

2014-01-01

250

Characterization of temperature-induced phase transitions in five polymorphic forms of sulfathiazole by terahertz pulsed spectroscopy and differential scanning calorimetry.  

PubMed

The far-infrared properties of all five known polymorphic forms of the drug sulfathiazole have been studied by terahertz pulsed spectroscopy and low-frequency Raman spectroscopy. The observed spectra of the different polymorphs are distinctly different. Terahertz pulsed spectroscopy proves to be a rapid and complementary alternative to other physical characterization techniques reported in the literature for distinguishing between the five forms. Variable-temperature measurements (293-473 K) of all polymorphic forms have been performed. The phase transitions observed have been related to thermal analysis data. Form I is the form stable at high temperature of sulfathiazole with a melting point of about 475 K. Form II melts at around 470 K and recrystallizes at higher temperatures to form I. Forms III, IV, and V all convert to form I via a solid-solid phase transition at temperatures below 450 K. The phase transitions can be monitored by terahertz pulsed spectroscopy. Polymorphic impurities of the samples can be detected in the room temperature spectra and their effect on the phase transition behavior can be studied. PMID:16892211

Zeitler, J Axel; Newnham, David A; Taday, Philip F; Threlfall, Terry L; Lancaster, Robert W; Berg, Rolf W; Strachan, Clare J; Pepper, Michael; Gordon, Keith C; Rades, Thomas

2006-11-01

251

Applications of pulse radiolysis to imaging sciences  

SciTech Connect

Pulse radiolysis has been used over the last 3 decades to study a variety of physical and chemical systems, including those relevant to imaging processes. This review outlines the similarities between photolysis and radiolysis and highlight the differences. It focuses on time-resolved variants of the two disciplines, flash photolysis vs pulse radiolysis. The strength (and weakness) of the radiolytic techniques is their nonspecificity; the energy is always absorbed by the solvent and not the solute. Radiation chemistry principles that were developed for one discipline are easily transportable to another. The pulse radiolysis technique with a wide arsenal of detection techniques is currently used to identify short-lived intermediates and to determine their kinetic and thermodynamic properties. Together, these studies provide mechanistic insight into the behavior of physical systems. We demonstrate the utility of the approach in several areas of interest to imaging sciences: clustering of silver atoms, growth of silver halides, and medium effects on these systems.

Meisel, D.

1996-05-01

252

Imaging embryonic development with ultrashort pulse microscopy  

NASA Astrophysics Data System (ADS)

We report the application of ultrashort pulse microscopy (UPM) for integrated imaging of embryonic development at the tissue, cell, and molecular length scales. The UPM is a multimodal imaging platform that utilizes the broad-power spectrum and high-peak power of 10-fs pulses to render two-photon excited signals and the short coherence gate of such pulses to render optical coherence signals. We show that ultrashort pulses efficiently excite cellular autofluorescence in developing zebrafish embryos such that tissues are readily visualized and individual cells can be monitored, providing a potential method for label-free cell tracking. We also show the ability of ultrashort pulses, without tuning, to excite a broad spectrum of fluorescent protein variants for tracking genetically labeled cell lineages in live embryos, with no apparent damage to the embryos. Molecular information at the mRNA transcript level can also be obtained from embryos that have been stained to reveal the localization of the expression of a gene using NBT/BCIP, which we show can be detected with three-dimensional resolution using a combination of two-photon and optical coherence signals. From this demonstration, we conclude that UPM is an efficient and a powerful tool for elucidating the dynamic multiparameter and multiscale mechanisms of embryonic development.

Gibbs, Holly C.; Bai, Yuqiang; Lekven, Arne C.; Yeh, Alvin T.

2014-05-01

253

21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.  

Code of Federal Regulations, 2012 CFR

...892.1550 Ultrasonic pulsed doppler imaging system. (a) Identification. An ultrasonic pulsed doppler imaging system is a device that...the features of continuous wave doppler-effect technology with...

2012-04-01

254

21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.  

Code of Federal Regulations, 2010 CFR

...892.1550 Ultrasonic pulsed doppler imaging system. (a) Identification. An ultrasonic pulsed doppler imaging system is a device that...the features of continuous wave doppler-effect technology with...

2010-04-01

255

21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.  

Code of Federal Regulations, 2014 CFR

...892.1550 Ultrasonic pulsed doppler imaging system. (a) Identification. An ultrasonic pulsed doppler imaging system is a device that...the features of continuous wave doppler-effect technology with...

2014-04-01

256

21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.  

Code of Federal Regulations, 2011 CFR

...892.1550 Ultrasonic pulsed doppler imaging system. (a) Identification. An ultrasonic pulsed doppler imaging system is a device that...the features of continuous wave doppler-effect technology with...

2011-04-01

257

21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.  

Code of Federal Regulations, 2013 CFR

...892.1550 Ultrasonic pulsed doppler imaging system. (a) Identification. An ultrasonic pulsed doppler imaging system is a device that...the features of continuous wave doppler-effect technology with...

2013-04-01

258

TIME-RESOLVED TERAHERTZ TRANSMISSION SPECTROSCOPY OF DIELECTRICS  

E-print Network

TIME-RESOLVED TERAHERTZ TRANSMISSION SPECTROSCOPY OF DIELECTRICS PETR KUZEL AND JAN PETZELT Republic. Using the method of time-domain terahertz-transmission spectroscopy we measured the far Terahertz pulses; far infrared; time-resolved spectroscopy INTRODUCTION The time-domain terahertz-transmission

Ku?el, Petr

259

Coupling between surface plasmons and nonresonant transmission in subwavelength holes at terahertz frequencies  

E-print Network

Coupling between surface plasmons and nonresonant transmission in subwavelength holes at terahertz 23 July 2007; published online 17 August 2007 Transmission spectra of terahertz pulses through transmission characteristics of periodic sub- wavelength structures.6­14 Extraordinary terahertz transmis- sion

260

Transmission mode terahertz computed tomography  

DOEpatents

A method of obtaining a series of images of a three-dimensional object by transmitting pulsed terahertz (THz) radiation through the entire object from a plurality of angles, optically detecting changes in the transmitted THz radiation using pulsed laser radiation, and constructing a plurality of imaged slices of the three-dimensional object using the detected changes in the transmitted THz radiation. The THz radiation is transmitted through the object as a scanning spot. The object is placed within the Rayleigh range of the focused THz beam and a focusing system is used to transfer the imaging plane from adjacent the object to a desired distance away from the object. A related system is also disclosed.

Ferguson, Bradley Stuart; Wang, Shaohong; Zhang, Xi-Cheng

2006-10-10

261

Controlling and Streaking Nanotip Photoemission by Enhanced Single-cycle Terahertz Pulses  

E-print Network

The active control of matter by strong electromagnetic fields is of growing importance, with applications all across the optical spectrum from the extreme-ultraviolet to the far-infrared. In recent years, phase-stable terahertz (THz) fields have shown tremendous potential in the observation and manipulation of elementary excitations in complex systems. The combination of concepts from attosecond science with advanced THz technology facilitates novel spectroscopic schemes, such as THz streaking. In general, driving charges at lower frequency enhances interaction energies and can promote drastically different dynamics. For example, mid-infrared excitation induces field-driven sub-cycle electron dynamics in nanostructure nearfields. Such frequency scalings will also impact nanostructure-based streaking, which has been theoretically proposed. Here, we experimentally demonstrate extensive control over nanostructure photoelectron emission using single-cycle THz transients. The locally enhanced THz near-field at a n...

Wimmer, L; Solli, D R; Yalunin, S V; Echternkamp, K; Ropers, C

2013-01-01

262

Pulse-Modulation Imaging—Review and Performance Analysis  

Microsoft Academic Search

In time-domain or pulse-modulation (PM) imaging, the incident light intensity is not encoded in amounts of charge, voltage, or current as it is in conventional image sensors. Instead, the image data are represented by the timing of pulses or pulse edges. This method of visual information encoding optimizes the phototransduction individually for each pixel by abstaining from imposing a fixed

Denis Guangyin Chen; Daniel Matolin; Amine Bermak; Christoph Posch

2011-01-01

263

Coded pulse excitation for ultrasonic strain imaging.  

PubMed

Decorrelation strain noise can be significantly reduced in low echo-signal-to-noise (eSNR) conditions using coded excitation. Large time-bandwidth-product (>30) pulses are transmitted into tissue mimicking phantoms with 2.5-mm diameter inclusions that mimic the elastic properties of breast lesions. We observed a 5-10 dB improvement in eSNR that led to a doubling of the depth of focus for strain images with no reduction of spatial resolution. In high eSNR conditions, coded excitation permits the use of higher carrier frequencies and shorter correlation windows to improve the attainable spatial resolution for strain relative to that obtained with conventional short pulses. This paper summarizes comparative studies of strain imaging in noise-limited conditions obtained by short pulses and four common aperiodic codes (chirp, Barker, suboptimal, and Golay) as a function of attenuation, eSNR and applied strain. Imaging performance is quantified using SNR for displacement (SNRd), local modulation transfer function (LMTF), and contrast-to-noise ratio for strain (CNRepsilon). We found that chirp and Golay codes are the most robust for imaging soft tissue deformation using matched filter decoding. Their superior performance is obtained by balancing the need for low-range lobes, large eSNR improvement, and short-code duration. PMID:15801311

Liu, Jie; Insana, Michael F

2005-02-01

264

Coded Pulse Excitation for Ultrasonic Strain Imaging  

PubMed Central

Decorrelation strain noise can be significantly reduced in low echo-signal-to-noise (eSNR) conditions using coded excitation. Large time-bandwidth-product (>30) pulses are transmitted into tissue mimicking phantoms with 2.5-mm diameter inclusions that mimic the elastic properties of breast lesions. We observed a 5–10 dB improvement in eSNR that led to a doubling of the depth of focus for strain images with no reduction of spatial resolution. In high eSNR conditions, coded excitation permits the use of higher carrier frequencies and shorter correlation windows to improve the attainable spatial resolution for strain relative to that obtained with conventional short pulses. This paper summarizes comparative studies of strain imaging in noise-limited conditions obtained by short pulses and four common aperiodic codes (chirp, Barker, suboptimal, and Golay) as a function of attenuation, eSNR and applied strain. Imaging performance is quantified using SNR for displacement (SNRd), local modulation transfer function (LMTF), and contrast-to-noise ratio for strain (CNR?). We found that chirp and Golay codes are the most robust for imaging soft tissue deformation using matched filter decoding. Their superior performance is obtained by balancing the need for low-range lobes, large eSNR improvement, and short-code duration. PMID:15801311

Liu, Jie; Insana, Michael F.

2009-01-01

265

Terahertz NDE for Metallic Surface Roughness Evaluation  

NASA Technical Reports Server (NTRS)

Metallic surface roughness in a nominally smooth surface is a potential indication of material degradation or damage. When the surface is coated or covered with an opaque dielectric material, such as paint or insulation, then inspecting for surface changes becomes almost impossible. Terahertz NDE is a method capable of penetrating the coating and inspecting the metallic surface. The terahertz frequency regime is between 100 GHz and 10 THz and has a free space wavelength of 300 micrometers at 1 THz. Pulsed terahertz radiation, can be generated and detected using optical excitation of biased semiconductors with femtosecond laser pulses. The resulting time domain signal is 320 picoseconds in duration. In this application, samples are inspected with a commercial terahertz NDE system that scans the sample and generates a set of time-domain signals that are a function of the backscatter from the metallic surface. Post processing is then performed in the time and frequency domains to generate C-scan type images that show scattering effects due to surface non-uniformity.

Madaras, Eric I.; Anastasi, Robert F.

2006-01-01

266

CARS imaging with a single laser pulse  

NASA Astrophysics Data System (ADS)

We report coherent anti-Stokes Raman scattering (CARS) microscopy with ns-pulses. The chosen wide-field geometry allows imaging of the whole field of view at once, without scanning of the sample. Tuning the difference of the two incident laser frequencies overlapping at the sample to a specific vibrational level, one can map the spatial distribution of selected Raman active molecules. Both the CARS signal of the surrounding solvent can be excited (negative contrast) as well as the signal of the structure embedded by the solvent (positive contrast). As a biological sample we used slices of a sunflower seed and tuned to the vibrational transition of its ingredient - linoleic acid - at 2870 cm-1 which corresponds to the strongest C-H stretching vibration. Even with a single pair of laser pulses of 3 ns duration it was possible to acquire a rough, but still meaningful image.

Heinrich, Christoph; Bernet, Stefan; Ritsch-Marte, Monika

2005-09-01

267

Two-pulse structured illumination imaging.  

PubMed

Structured illumination (SI), which is an imaging technique that is employed in a variety of fields, permits unique possibilities to suppress unwanted signal contributions that carry misguiding information such as out-of-focus light or multiply scattered light. So far SI has been applied mostly for averaged imaging or for imaging of slowly occurring events because it requires three acquisitions (subimages) to construct the final SI image. This prerequisite puts technological constraints on SI that make "instantaneous" imaging of fast transient processes (occurring on submicrosecond time scales) very challenging and expensive. Operating SI with fewer subimages generates errors in the form of residual lines that stretch across the image. Here, a new approach that circumvents this limiting factor is presented and experimentally demonstrated. By judiciously choosing the intensity modulation, it is possible to extract an SI image from two subimages only. This development will allow standard double-pulsed lasers and interline transfer CCD or scientific CMOS cameras to be used to acquire temporally frozen SI images of rapidly occurring processes as well as to boost the frame-rate of current SI video systems; a technical advancement that will benefit both macro- and microscopic imaging applications. PMID:24784051

Kristensson, Elias; Berrocal, Edouard; Aldén, Marcus

2014-05-01

268

Standoff Detection of Hidden Explosives and Cold and Fire Arms by Terahertz Time-Domain Spectroscopy and Active Spectral Imaging (Review)  

NASA Astrophysics Data System (ADS)

Terahertz time-domain spectroscopy and standoff spectral imaging for detection of explosives and cold and fire arms hidden, for example, under clothing, were reviewed. Special attention was paid to different schemes for practical implementation of these methods. Progress in this direction and existing problems and the prospects for their solution were discussed. Issues related to sources and receivers of terahertz radiation were briefly discussed. It was noted that interest in quantum-cascade lasers as compact sources of terahertz radiation and the potential of using them at room temperature were increasing.

Skvortsov, L. A.

2014-11-01

269

Temperature-dependent terahertz radiation from the surfaces of narrow-gap semiconductors illuminated by femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

Temperature-dependent increase of the terahertz (THz) electric field emitted from the surfaces of optically pumped narrow-gap semiconductors InAs, InSb, and Cd xHg 1-xTe is presented. In the case of Cd 0.2Hg 0.8Te increase up to 15-17 times has been observed, when cooling the sample from the room temperature to close to liquid-helium temperatures, and THz emission from this material becomes comparable to that of p-InAs emitter. This effect was explained in terms of the increased photoexcited electron excess energy due to the positive temperature coefficient for energy bandgap of Cd xHg 1-xTe, as well as by weaker surface field screening and carrier-carrier scattering. Temperature-dependent modification of the shape of THz pulses emitted from InSb surfaces has been observed and attributed to plasma oscillation of the cold electrons.

Molis, G.; Adomavi?ius, R.; Krotkus, A.

2008-10-01

270

High-contrast coherent terahertz imaging of porcine tissue via swept-frequency feedback interferometry.  

PubMed

There is considerable interest in the interrogation of biological tissue at terahertz (THz) frequencies, largely due to the contrast in the optical properties of different biological tissues which occur in this electro-magnetic radiation band. Of particular interest are THz biomedical images, which have the potential to highlight different information than those acquired in other frequency bands, thereby providing an augmented picture of biological structures. In this work, we demonstrate the feasibility of an interferometric biological imaging technique using a THz quantum cascade laser (QCL) operating at 2.59 THz to perform coherent imaging of porcine tissue samples. We show the potential of this new THz biomedical imaging technique for in vivo studies, by virtue of its reflection geometry and useful tissue penetration depth enabled by the large THz powers emitted by the quantum cascade laser used in this work. The observed clustering of interferometric tissue signatures opens a pathway towards automatic techniques for the discrimination of healthy tissue types for the study of normal physiology and possible therapeutic approaches. PMID:25426324

Lim, Yah Leng; Taimre, Thomas; Bertling, Karl; Dean, Paul; Indjin, Dragan; Valavanis, Alexander; Khanna, Suraj P; Lachab, Mohammad; Schaider, Helmut; Prow, Tarl W; Peter Soyer, H; Wilson, Stephen J; Linfield, Edmund H; Giles Davies, A; Raki?, Aleksandar D

2014-11-01

271

In vivo confirmation of hydration based contrast mechanisms for terahertz medical imaging using MRI  

NASA Astrophysics Data System (ADS)

Terahertz (THz) detection has been proposed and applied to a variety of medical imaging applications in view of its unrivaled hydration profiling capabilities. Variations in tissue dielectric function have been demonstrated at THz frequencies to generate high contrast imagery of tissue, however, the source of image contrast remains to be verified using a modality with a comparable sensing scheme. To investigate the primary contrast mechanism, a pilot comparison study was performed in a burn wound rat model, widely known to create detectable gradients in tissue hydration through both injured and surrounding tissue. Parallel T2 weighted multi slice multi echo (T2w MSME) 7T Magnetic Resonance (MR) scans and THz surface reflectance maps were acquired of a full thickness skin burn in a rat model over a 5 hour time period. A comparison of uninjured and injured regions in the full thickness burn demonstrates a 3-fold increase in average T2 relaxation times and a 15% increase in average THz reflectivity, respectively. These results support the sensitivity and specificity of MRI for measuring in vivo burn tissue water content and the use of this modality to verify and understand the hydration sensing capabilities of THz imaging for acute assessments of the onset and evolution of diseases that affect the skin. A starting point for more sophisticated in vivo studies, this preliminary analysis may be used in the future to explore how and to what extent the release of unbound water affects imaging contrast in THz burn sensing.

Bajwa, Neha; Sung, Shijun; Garritano, James; Nowroozi, Bryan; Tewari, Priyamvada; Ennis, Daniel B.; Alger, Jeffery; Grundfest, Warren; Taylor, Zachary

2014-09-01

272

High-contrast coherent terahertz imaging of porcine tissue via swept-frequency feedback interferometry  

PubMed Central

There is considerable interest in the interrogation of biological tissue at terahertz (THz) frequencies, largely due to the contrast in the optical properties of different biological tissues which occur in this electro-magnetic radiation band. Of particular interest are THz biomedical images, which have the potential to highlight different information than those acquired in other frequency bands, thereby providing an augmented picture of biological structures. In this work, we demonstrate the feasibility of an interferometric biological imaging technique using a THz quantum cascade laser (QCL) operating at 2.59 THz to perform coherent imaging of porcine tissue samples. We show the potential of this new THz biomedical imaging technique for in vivo studies, by virtue of its reflection geometry and useful tissue penetration depth enabled by the large THz powers emitted by the quantum cascade laser used in this work. The observed clustering of interferometric tissue signatures opens a pathway towards automatic techniques for the discrimination of healthy tissue types for the study of normal physiology and possible therapeutic approaches. PMID:25426324

Lim, Yah Leng; Taimre, Thomas; Bertling, Karl; Dean, Paul; Indjin, Dragan; Valavanis, Alexander; Khanna, Suraj P.; Lachab, Mohammad; Schaider, Helmut; Prow, Tarl W.; Peter Soyer, H.; Wilson, Stephen J.; Linfield, Edmund H.; Giles Davies, A.; Raki?, Aleksandar D.

2014-01-01

273

Crack imaging by pulsed laser spot thermography  

NASA Astrophysics Data System (ADS)

A surface crack close to a spot heated by a laser beam impedes lateral heat flow and produces alterations to the shape of the thermal image of the spot that can be monitored by thermography. A full 3D simulation has been developed to simulate heat flow from a laser heated spot in the proximity of a crack. The modelling provided an understanding of the ways that different parameters affect the thermal images of laser heated spots. It also assisted in the development of an efficient image processing strategy for extracting the scanned cracks. Experimental results show that scanning pulsed laser spot thermography has considerable potential as a remote, non-contact crack imaging technique.

Li, T.; Almond, D. P.; Rees, D. A. S.; Weekes, B.

2010-03-01

274

Image enhancement for underwater pulsed laser line scan imaging system  

NASA Astrophysics Data System (ADS)

Recent progress in system hardware such as laser, photon detectors and other electronic and optical components resulted in significant improvement for the underwater serial laser imaging system. Nevertheless, during normal system operation, system issues such as laser instability, electronic noise, and environmental conditions such as imaging in highly turbid water can still put constraint on the performance of imager. In this work, post-processing to take advantage of the improvement hardware to further reduce image noise and enhance the image quality as a critical aspect of the overall system design is studied. A novel realization of the bilateral principle based image/pulse noise reduction and image deconvolution using point spread function (PSF) predicted with EODES radiative transfer model is used to implement the processing chain. The concept is further extended to a multichannel deconvolution to exploit the benefit offered by the new multi element PMT configuration developed in HBOI. Two datasets were used to test the developed techniques respectively.

Ouyang, B.; Dalgleish, F. R.; Caimi, F. M.; Vuorenkoski, A. K.; Giddings, T. E.; Shirron, J. J.

2012-06-01

275

Tunable terahertz radiation from an ultrashort-laser-pulse-induced discharge in biased air  

Microsoft Academic Search

Strong beams of coherent radiation are essential to induce nonlinear excitation phenomena in biology and material sciences. Optical-field-induced ionization by an ultrashort laser pulse produces ultrabroadband bursts of radiation with photon energies ranging from radio-wave at the microsecond timescale to x-ray at the attosecond timescale. As the laser pulse drives an ultrafast-discharge with high current it induces nonlinear spectral conversion

Fuminori Suzuki; Hiroaki Anno-Kashiwazaki; Jun Miyazawa; Shohei Ono; Takeshi Higashiguchi; Noboru Yugami; Yasuhiko Sentoku; Ryosuke Kodama; Patric Muggli

2011-01-01

276

Terahertz spectroscopy and imaging for cultural heritage management: state of art and perspectives  

NASA Astrophysics Data System (ADS)

Non-invasive diagnostic tools able to provide information on the materials and preservation state of artworks are crucial to help conservators, archaeologists and anthropologists to plan and carry out their tasks properly. In this frame, technological solutions exploiting Terahertz (THz) radiation, i.e., working at frequencies ranging from 0.1 to 10 THz, are currently deserving huge attention as complementary techniques to classical analysis methodologies based on electromagnetic radiations from X-rays to mid infrared [1]. The main advantage offered by THz spectroscopy and imaging systems is referred to their capability of providing information useful to determine the construction modality, the history life and the conservation state of artworks as well as to identify previous restoration actions [1,2]. In particular, unlike mid- and near-infrared spectroscopy, which provides fingerprint absorption spectra depending on the intramolecular behavior, THz spectroscopy is related to the structure of the molecules of the investigated object. Hence, it can discriminate, for instance, the different materials mixed in a paint [1,2]. Moreover, THz radiation is able to penetrate several materials which are opaque to both visible and infrared materials, such as varnish, paint, plaster, paper, wood, plastic, and so on. Accordingly, it is useful to detect hidden objects and characterize the inner structure of the artwork under test even in the direction of the depth, while avoiding core drillings. In this frame, THz systems allow us to discriminate different layers of materials present in artworks like paints, to obtain images providing information on the construction technique as well as to discover risk factors affecting the preservation state, such as non-visible cracks, hidden molds and air gaps between the paint layer and underlying structure. Furthermore, adopting a no-ionizing radiation, THz systems offer the not trivial benefit of negligible long term risks to the molecular stability of the exposed objects and humans. Recently, the interest on THz technology is also growing up thanks to the development of flexible and compact commercial systems having source and detector probes coupled by means of optical fiber cables and that do not require complex optical alignments. These features allow us to reconfigure the measurement configuration easily; thus transmission, normal reflection and oblique reflection data can be collected according to the constrains and objective of the survey to be performed. Moreover, they open the way to on field applications. An example of last generation THz systems is the Fiber-Coupled Terahertz Time Domain System (FICO) marketed by Z-Omega and available at the Institute of Electromagnetic Sensing of the Environment. Such a system is designed to perform both transmission and reflection spectroscopy and imaging measurements in the range from 60GHz to 3THz; with a waveform acquisition speed up to 500Hz. A review of the literature assessing potentialities and open challenges of THz spectroscopy and imaging in the frame of cultural heritage preservation will be provided at the conferences, with a specific focus on the diagnostic capabilities of last generation systems. REFERENCES [1] K. Fukunaga, I. Hosako, Innovative non-invasive analysis techniques for cultural heritage using terahertz technology, C. R. Physique, vol. 11, pp.519-526, 2010. [2] G.Fillippidis, M. Massaouti, A. Selimis, E.J. Gualda, J.M. Manceau, S. Tzortzakis, Nonlinear imaging and THz diagnostic tools in the service of Cultural Heritage, Appl. Phys. A, vol.106, pp.257-263, 2012.

Catapano, Ilaria; Soldovieri, Francesco

2014-05-01

277

2microm pulsed fiber laser sources and their application in terahertz generation  

NASA Astrophysics Data System (ADS)

In this dissertation, an all-fiber-based single frequency nanosecond pulsed laser system at ˜ 1918.4 nm in master-oscillator-power-amplifier (MOPA) configuration is present. The nanosecond pulse seed is achieved by directly modulating a continuous wave (CW) single frequency fiber laser using a fast electro-optical modulator (EOM) driven by an arbitrary waveform generator (AWG). One piece of single mode, large core, polarization-maintaining (PM) highly thulium-doped (Tm-doped) germanate glass fiber (LC-TGF) is used to boost the pulse power and pulse energy of these modulated pulses in the final power amplifier. This laser system can work in both high power and high energy regime: in high power regime, to the best of our knowledge, the highest average power 16 W and peak power 78.1 kW are achieved for single frequency transform-limited ˜2.0 ns pulses at 500 kHz and 100 kHz repetition rate, respectively: In high energy regime, nearly 1 mJ and half mJ pulse energy is obtained for ˜15 ns pulses at 1 kHz repetition rate and 5 kHz repetition rate, respectively. Theoretical modeling of the large-core highly Tm-doped germanate glass double-cladding fiber amplifier (LC-TG-DC-FA) is also present for 2 microm nanosecond pulse amplification. A good agreement between the theoretical and experimental results is achieved. The model can simulate the evolution of pump power, signal energy, pulse shape and the amplified stimulated emission (ASE) in the amplifier. It can also be utilized to investigate the dependence of the stored energy in the LC-TGF on the pump power, seed energy and repetition rate, which can be used to design and optimize the LC-TG-DC-FA to achieve higher pulse energy and average power. Two channel of high energy nanosecond pulses (at 1918.4 nm and 1938 nm) are utilized to generate THz wave in a quasi-phase-matched (QPM) gallium arsenide (GaAs) based on difference frequency generation. THz wave with ˜ 5.4 microW average power and ˜18 mW peak power has been achieved. Besides, one model is built to simulate a singly resonated THz parametric oscillator. The threshold, the dependence of output THz energy on pump energy has been investigated through this model. One pump enhanced THz parametric oscillator has been proposed. The enhancement factor of the nanosecond pulses in a bow-tie ring cavity has been calculated for different pulse duration, cavity length and the transmission of the coupler. And the laser resonances in the ring cavity have been observed by using a piezo to periodically adjust the cavity length. We also build an all-fiber thulium-doped wavelength tunable mode-locked laser operating near 2 microm. Reliable self-starting mode locking over a large tuning range (> 50 nm) using fiber taper based carbon nanotube (FTCNT) saturable absorber (SA) is observed. Spectral tuning is achieved by stretching another fiber taper. To the best of our knowledge, this is the first demonstration of an all-fiber wavelength tunable mode-locked laser near 2 microm.

Fang, Qiang

278

Terahertz macrospin dynamics in insulating ferrimagnets  

NASA Astrophysics Data System (ADS)

We investigate numerically the excitation of nonlinear magnetic interactions in a ferrite material by an energetic pump pulse of terahertz (THz) radiation. The calculations are performed by solving the coupled Maxwell and Landau-Lifshitz-Gilbert differential equations. In a time-resolved THz pump/THz probe scheme, it is demonstrated that Faraday rotation of a delayed THz probe pulse can be used to map these interactions. Our study is motivated by the ability of soft x-ray free electron lasers to perform time-resolved imaging of the magnetization process at the submicrometer and subpicosecond length and time scales.

Shalaby, Mostafa; Vidal, Francois; Peccianti, Marco; Morandotti, Roberto; Enderli, Florian; Feurer, Thomas; Patterson, Bruce D.

2013-10-01

279

Imaging with a 90 frames/s microbolometer focal plane array and high-power terahertz free electron laser  

SciTech Connect

An uncooled microbolometer focal plane array (FPA) has been developed and used for imaging of objects illuminated by monochromatic coherent radiation of a free electron laser tunable in the range of 1.25-2.5 THz. A sensitivity threshold of 1.3x10{sup -3} W/cm{sup 2} was obtained for the FPA with a homemade absolute interferometric power meter. Videos up to 90 frames/s were recorded in both transmission and reflection/scattering modes. When objects were illuminated by laser radiation scattered by a rough metal surface, speckled images were observed. Good quality terahertz images were achieved through the fast rotation of the scatterer.

Dem'yanenko, M. A.; Esaev, D. G. [Rzhanov Institute of Semiconductor Physics SB RAS, 630090 Novosibirsk (Russian Federation); Knyazev, B. A.; Vinokurov, N. A. [Budker Institute of Nuclear Physics SB RAS, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, 630090 Novosibirsk (Russian Federation); Kulipanov, G. N. [Budker Institute of Nuclear Physics SB RAS, 630090 Novosibirsk (Russian Federation)

2008-03-31

280

Computed tomography image using sub-terahertz waves generated from a high-Tc superconducting intrinsic Josephson junction oscillator  

NASA Astrophysics Data System (ADS)

A computed tomography (CT) imaging system using monochromatic sub-terahertz coherent electromagnetic waves generated from a device constructed from the intrinsic Josephson junctions in a single crystalline mesa structure of the high-Tc superconductor Bi2Sr2CaCu2O8+? was developed and tested on three samples: Standing metallic rods supported by styrofoam, a dried plant (heart pea) containing seeds, and a plastic doll inside an egg shell. The images obtained strongly suggest that this CT imaging system may be useful for a variety of practical applications.

Kashiwagi, T.; Nakade, K.; Saiwai, Y.; Minami, H.; Kitamura, T.; Watanabe, C.; Ishida, K.; Sekimoto, S.; Asanuma, K.; Yasui, T.; Shibano, Y.; Tsujimoto, M.; Yamamoto, T.; Markovi?, B.; Mirkovi?, J.; Klemm, R. A.; Kadowaki, K.

2014-02-01

281

Theoretical analysis of conditions for observation of plasma oscillations in semiconductors from pulsed terahertz emission  

SciTech Connect

Oscillations of electron-hole plasma generated by femtosecond optical pulse in freestanding semiconductor are studied using hydrodynamic model and Monte Carlo simulations. The conditions required for the observation of coherent plasma oscillations in THz emission from semiconductor are determined. It is shown that several conditions have to be fulfilled in order to observe coherent plasma oscillations. First, the intensity of the optical pulse must exceed some threshold value. Second, the optical absorption depth must exceed the thickness of the built-in electric field region. Third, the generation of electron-hole pairs with uniform illumination is required, i.e., the laser beam with the flattop intensity profile has to be used. It is found that the duration of the optical pulse does not play a vital role in the development of plasma oscillations.

Reklaitis, Antanas, E-mail: reklaitis@pfi.lt [Semiconductor Physics Institute, Center for Physical Sciences and Technology, A. Goshtauto 11, Vilnius 01108 (Lithuania)

2014-08-28

282

Operation of Terahertz Quantum-cascade Lasers at 164 K in Pulsed Mode and at 117 K in Continuous-wave Mode  

NASA Technical Reports Server (NTRS)

We report the demonstration of a terahertz quantum-cascade laser that operates up to 164 K in pulsed mode and 117 K in continuous-wave mod e at approximately 3.0 THz. The active region was based on a resonant -phonon depopulation scheme and a metal-metal waveguide was used for modal confinement. Copper to copper thermocompression wafer bonding w as used to fabricate the waveguide, which displayed improved thermal properties compared to a previous indium-gold bonding method.

Williams, Benjamin S.; Kumar, Sushil; Hu, Qing; Reno, John L.

2005-01-01

283

Transient increase of the energy gap of superconducting NbN thin films excited by resonant narrow-band terahertz pulses.  

PubMed

Observations of radiation-enhanced superconductivity have thus far been limited to a few type-I superconductors (Al, Sn) excited at frequencies between the inelastic scattering rate and the superconducting gap frequency 2?/h. Utilizing intense, narrow-band, picosecond, terahertz pulses, tuned to just below and above 2?/h of a BCS superconductor NbN, we demonstrate that the superconducting gap can be transiently increased also in a type-II dirty-limit superconductor. The effect is particularly pronounced at higher temperatures and is attributed to radiation induced nonthermal electron distribution persisting on a 100 ps time scale. PMID:23848912

Beck, M; Rousseau, I; Klammer, M; Leiderer, P; Mittendorff, M; Winnerl, S; Helm, M; Gol'tsman, G N; Demsar, J

2013-06-28

284

Investigation of microelectromechanical systems bimaterial sensors with metamaterial absorbers for terahertz imaging  

NASA Astrophysics Data System (ADS)

One attractive option to achieve real-time terahertz (THz) imaging is a microelectromechanical systems (MEMS) bimaterial sensor with embedded metamaterial absorbers. We have demonstrated that metamaterial films can be designed using standard MEMS materials such as silicon oxide (SiOx), silicon oxinitrate (SiOxNy), and aluminum (Al) to achieve nearly 100% resonant absorption matched to the illumination source, providing structural support, desired thermomechanical properties and access to external optical readout. The metamaterial structure absorbs the incident THz radiation and transfers the heat to bimaterial microcantilevers that are connected to the substrate, which acts as a heat sink via thermal insulating legs, allowing the overall structure to deform proportionally to the absorbed power. The amount of deformation can be probed by measuring the displacement of a laser beam reflected from the sensor's metallic ground plane. Several sensor configurations have been designed, fabricated, and characterized to optimize responsivity and speed of operation and to minimize structural residual stress. Measured responsivity values as high as 1.2 deg/?W and time constants as low as 20 ms with detectable power on the order of 10 nW were obtained, indicating that the THz MEMS sensors have a great potential for real-time imaging.

Alves, Fabio; Grbovic, Dragoslav; Karunasiri, Gamani

2014-09-01

285

Terahertz real-time imaging uncooled array based on antenna- and cavity-coupled bolometers.  

PubMed

The development of terahertz (THz) applications is slowed down by the availability of affordable, easy-to-use and highly sensitive detectors. CEA-Leti took up this challenge by tailoring the mature infrared (IR) bolometer technology for optimized THz sensing. The key feature of these detectors relies on the separation between electromagnetic absorption and the thermometer. For each pixel, specific structures of antennas and a resonant quarter-wavelength cavity couple efficiently the THz radiation on a broadband range, while a central silicon microbridge bolometer resistance is read out by a complementary metal oxide semiconductor circuit. 320×240 pixel arrays have been designed and manufactured: a better than 30?pW power direct detection threshold per pixel has been demonstrated in the 2-4?THz range. Such performance is expected on the whole THz range by proper tailoring of the antennas while keeping the technological stack largely unchanged. This paper gives an overview of the developed bolometer-based technology. First, it describes the technology and reports the latest performance characterizations. Then imaging demonstrations are presented, such as real-time reflectance imaging of a large surface of hidden objects and THz time-domain spectroscopy beam two-dimensional profiling. Finally, perspectives of camera integration for scientific and industrial applications are discussed. PMID:24567477

Simoens, François; Meilhan, Jérôme

2014-03-28

286

Hot electron bolometer for detection of fast terahertz pulses from optical parametric oscillator  

NASA Astrophysics Data System (ADS)

Detection of nanosecond pulses by fast and sensitive Hot Electron Bolometer (HEB) is reported. Pulses were generated by an Optical Parametric Oscillator (OPO)-based source. The laser can be tuned in the range 0.7-2.5 THz; its repetition rate equals to 53Hz, duration of the pulse is about 10-20ns, energy is 10nJ and spectral width 50GHz. HEB operates at temperature of about 8.8K in a cryogenic refrigeration system. A sensitive element is a bridge from a 4-mm thick NbN film integrated with a planar logarithmic spiral antenna on a high-resistive silicon. HEB works in 0.3-3THz range with NEP ~3x10-13 W/Hz1/2 and dynamic range 0.1 uW. Thanks to exploitation of hot electrons in superconducting state, the detector is very fast with minimum response time equals to 50ps. The THz radiation is focused with a silicon lens, and then is coupled to a sensitive bolometer using the planar antenna. THz radiation from the OPO, through a set of mirrors and attenuators, was coupled to the detector. The distance between the source and detector was about 3m. Full Width at Half Maximum of the recorded pulses was about 20 ns. Moreover, we measured linearity of the detector in the range 0.7- 2.0 THz by rotation of the polarizer axis. The pulses were averaged and integrated for better stability. We obtained a good similarity to the theoretical curve of the polarizer.

Palka, Norbert; Zagrajek, Przemyslaw; Czerwinski, Adam; Trzcinski, Tomasz; Rurka, Elzbieta; Szustakowski, Mieczyslaw; Sypek, Maciej

2012-10-01

287

A study of background signals in terahertz apertureless near-field microscopy and their use for scattering-probe imaging  

NASA Astrophysics Data System (ADS)

Apertureless near-field microscopy is an imaging technique in which a small metal tip is held close to a surface, converting evanescent waves to propagating waves and permitting extreme subwavelength spatial resolution. This technique has recently been adapted for use in the terahertz region of the spectrum. Here, the interpretation of the measured signals and the suppression of background scattering can be complicated by the extremely broad bandwidth of the terahertz source and by the coherent (i.e., phase-sensitive) detection of the scattered radiation. We have analyzed the use of tip-sample distance modulation for the removal of background signals. We find that significant background signals, originating from scattering off the probe tip, can be observed even after modulation. These background signals result from path-length difference modulation, and thus are relevant when phase-sensitive detection is used. We use a dipole antenna model to explain the spatial variation in the scattered signal. Since this signal originates from the tip only, it can be used to characterize free-space terahertz wave fronts with subwavelength resolution.

Astley, Victoria; Zhan, Hui; Mendis, Rajind; Mittleman, Daniel M.

2009-06-01

288

Readout system for the terahertz superconducting imaging array (TeSIA)  

NASA Astrophysics Data System (ADS)

Terahertz Superconducting Imaging Array (TeSIA) is a project for the development of a large THz direct-detection array for mapping observations. The prototype of TeSIA is an 8×8 pixel direct-detection array operating at the 850 ?m band, incorporating THz superconducting detectors such as kinetic inductance detectors (KIDs) and transition edge sensors (TES). KIDs have the advantage that only a broadband low noise cryogenic amplifier is needed at low temperature for the readout system, and hundreds of pixels could be readout simultaneously by the frequency-division multiplexing (FDM) technique. The readout system for a KIDs array is composed of several parts like excitation signal generating, intermediate frequency (IF) circuit, baseband signal acquisition and processing. Excitation signal is a kind of comb signal carrying various frequencies corresponding simply to resonant frequencies of the detectors. It is generated in baseband with a bandwidth covering all KIDs and up-converted to microwave frequency (about several gigahertz) to feed the detectors. With THz radiation, the forward transmission coefficient (S21) of all KIDs varies and the variation can be measured through the comb signal. Fast Fourier transform (FFT) with pipeline structure will be used to process the baseband excitation signal in real time. Consequently, the radiation intensity can be estimated by monitoring the signal amplitude and phase of the corresponding frequency channels. In this paper we will present mainly the design ofan electronic readout system for the 8×8 pixel array.

Li, Sheng; Yang, Jin-Ping; Duan, Wen-Ying; Lin, Zhen-Hui; Li, Jing; Shi, Sheng-Cai

2012-12-01

289

Nanowire-based field effect transistors for terahertz detection and imaging systems  

NASA Astrophysics Data System (ADS)

The development of self-assembled nanostructure technologies has recently opened the way towards a wide class of semiconductor integrated devices, with progressively optimized performances and the potential for a widespread range of electronic and photonic applications. Here we report on the development of field effect transistors (FETs) based on semiconductor nanowires (NWs) as highly-sensitive room-temperature plasma-wave broadband terahertz (THz) detectors. The electromagnetic radiation at 0.3?THz is funneled onto a broadband bow-tie antenna, whose lobes are connected to the source and gate FET electrodes. The oscillating electric field experienced by the channel electrons, combined with the charge density modulation by the gate electrode, results in a source-drain signal rectification, which can be read as a DC signal output. We investigated the influence of Se-doping concentration of InAs NWs on the detection performances, reaching responsivity values higher than 100 V W-1, with noise-equivalent-power of ˜10-9 W Hz-1/2. Transmission imaging experiments at 0.3 THz show the good reliability and sensitivity of the devices in a real practical application.

Romeo, L.; Coquillat, D.; Pea, M.; Ercolani, D.; Beltram, F.; Sorba, L.; Knap, W.; Tredicucci, A.; Vitiello, M. S.

2013-05-01

290

Research of room-temperature continuous-wave terahertz imaging array based on microbolometer  

NASA Astrophysics Data System (ADS)

We have designed a novel uncooled Terahertz (THz) imaging array based microbolometer. The Micro Electro Mechanical System (MEMS) technology is used to fabricate the imaging array which comprise bolometer layer, THz absorption layer, supporting layer (silicon nitride (SiNx)), resonant optical cavity and electrode. The vanadium oxide thin films is selected for the bolometer temperature sensing material because it has a high temperature coefficient of resistance (TCR) in the range 2%/K and 3%/K at room temperature and suitable square resistance 18.40k?/?, a small 1/f noise constant and can be integrated with signal read-out electronics in a cost efficient way. In order to provide a high absorption of the radiation in the bolometer membrane, a resonant optical cavity structure which has a reflection layer formed at the bottom of air gap is adopted for the targeted wavelength. The best air gap of the optical cavity structure is quarter of wavelength of interest, for example, 25?m for 3 THz radiation. The absorption mechanism is that the two reflected THz radiations coming from the absorption layer and reflection layer interfere destructively at THz absorption layer and free carriers in THz absorption layer absorb THz radiation, the absorbed THz radiation heats the imaging array so that the resistance values of bolometer change. The microbolometer need to be packaged in vacuum for best performance, so a cylindrical vacuum chamber which is sealed with polyethylene lamina for the THz radiation is fabricated. In order to maintain the vacuum performance of the chamber (conventional bolometers operate with vacuum levels <0.01mbar), the vacuum pump and molecular pump are adopted; furthermore the packaging technique of vacuum chamber is introduced in detail. Finally, because of its uncooled property of the microbolometer, it will have a low cost and be easy for fabrication of large array.

Su, Bo; Duan, Guoteng; Cui, Hai-lin; Zhang, Cun-lin

2013-08-01

291

Carbon irradiated semi insulating GaAs for photoconductive terahertz pulse detection  

NASA Astrophysics Data System (ADS)

We report here a photoconductive material for THz generation and detection with sub-picosecond carrier lifetime made by C12 (Carbon) irradiation on commercially available semi-insulating (SI) GaAs. We are able to reduce the carrier lifetime of SI-GaAs down to sub-picosecond by irradiating it with various irradiation dosages of Carbon (C12) ions. With an increase of the irradiation dose from ~1012 /cm2 to ~1015 /cm2 the carrier lifetime of SI-GaAs monotonously decreases to 0.55 picosecond, resulting in strongly improved THz pulse detection compared with normal SI-GaAs.

Singh, Abhishek; Pal, Sanjoy; Surdi, Harshad; Prabhu, S. S.; Mathimalar, S.; Nanal, Vandana; Pillay, R. G.; Döhler, G. H.

2015-03-01

292

Terahertz spectroscopic investigations of leather in terahertz wave range  

NASA Astrophysics Data System (ADS)

Pulsed THz time-domain spectroscopy is a coherent technique, in which both the amplitude and the phase of a THz pulse are measured. Recently, material characterization using THz spectroscopy has been applied to biochemicals, pharmaceuticals, polymers and semiconductors and has given us important information. Moreover, THz imaging has progressed and is expected to be applicable for the identification of narcotics and explosives. The most important and characteristic point of THz spectroscopy is said to be its ability to observe intermolecular vibrations in contrast to infrared spectroscopy (IR), which observes intramolecular vibrations. Coherent detection enables direct calculations of both the imaginary and the real parts of the refractive index without using the Kramers-Kronig relations. Terahertz wave spectroscopy has been used to study the properties and absorption spectra characteristic of materials. In this paper, the spectral characteristics of cow skin, pig skin sheep skin, horse skin and deer skin have been measured with terahertz time-domain spectroscopy in the range of 0.1~2.0THz. The results show that THz-TDS technology provides an important tool for quality analysis and detection of leathers.

Song, Mei-jing; Li, Jiu-sheng

2011-11-01

293

Terahertz spectroscopic investigations of leather in terahertz wave range  

NASA Astrophysics Data System (ADS)

Pulsed THz time-domain spectroscopy is a coherent technique, in which both the amplitude and the phase of a THz pulse are measured. Recently, material characterization using THz spectroscopy has been applied to biochemicals, pharmaceuticals, polymers and semiconductors and has given us important information. Moreover, THz imaging has progressed and is expected to be applicable for the identification of narcotics and explosives. The most important and characteristic point of THz spectroscopy is said to be its ability to observe intermolecular vibrations in contrast to infrared spectroscopy (IR), which observes intramolecular vibrations. Coherent detection enables direct calculations of both the imaginary and the real parts of the refractive index without using the Kramers-Kronig relations. Terahertz wave spectroscopy has been used to study the properties and absorption spectra characteristic of materials. In this paper, the spectral characteristics of cow skin, pig skin sheep skin, horse skin and deer skin have been measured with terahertz time-domain spectroscopy in the range of 0.1~2.0THz. The results show that THz-TDS technology provides an important tool for quality analysis and detection of leathers.

Song, Mei-jing; Li, Jiu-sheng

2012-03-01

294

FDTD-based quantitative analysis of terahertz wave detection for multilayered structures.  

PubMed

Experimental investigations have shown that terahertz pulsed imaging (TPI) is able to quantitatively characterize a range of multilayered media (e.g., biological issues, pharmaceutical tablet coatings, layered polymer composites, etc.). Advanced modeling of the interaction of terahertz radiation with a multilayered medium is required to enable the wide application of terahertz technology in a number of emerging fields, including nondestructive testing. Indeed, there have already been many theoretical analyses performed on the propagation of terahertz radiation in various multilayered media. However, to date, most of these studies used 1D or 2D models, and the dispersive nature of the dielectric layers was not considered or was simplified. In the present work, the theoretical framework of using terahertz waves for the quantitative characterization of multilayered media was established. A 3D model based on the finite difference time domain (FDTD) method is proposed. A batch of pharmaceutical tablets with a single coating layer of different coating thicknesses and different refractive indices was modeled. The reflected terahertz wave from such a sample was computed using the FDTD method, assuming that the incident terahertz wave is broadband, covering a frequency range up to 3.5 THz. The simulated results for all of the pharmaceutical-coated tablets considered were found to be in good agreement with the experimental results obtained using a commercial TPI system. In addition, we studied a three-layered medium to mimic the occurrence of defects in the sample. PMID:25401257

Tu, Wanli; Zhong, Shuncong; Shen, Yaochun; Zhou, Qing; Yao, Ligang

2014-10-01

295

High-peak-power terahertz sources pumped by high power laser and single-shot measurement of terahertz temporal waveform  

NASA Astrophysics Data System (ADS)

Optical rectification of laser pulses in LiNbO3 crystal pumped by high power laser is one of the most powerful way to generate this high-peak-power terahertz pulses. It enhances the laser-terahertz transform efficiency by tilted-pulse-front pumping(TPFP) to fulfill phase match in the LiNbO3 crystal. However, comprehensive theoretical analysis is still lack. In this work, a detailed theoretical model to investigate the THz generation efficiency by using nonlinear susceptibility tensor of LiNbO3 crystal was presented. Based on femtosecond laser system, a setup to generate high-peak-power terahertz pulses and a time domain spectroscopy system are established. The property of generated terahertz pulses was analyzed by using terahertz camera and THz time domain system. We also realized the single-shot measurement of terahertz temporal waveform by using this terahertz source.

Zhong, Sen-Cheng; Zhai, Zhao-Hui; Zhu, Li-Guo; Meng, Kun; Liu, Qiao; Peng, Qi-Xian; Li, Ze-Ren

2015-02-01

296

Diffraction-limited real-time terahertz imaging by optical frequency up-conversion in a DAST crystal.  

PubMed

Real-time terahertz (THz) wave imaging has wide applications in areas such as security, industry, biology, medicine, pharmacy, and the arts. This report describes real-time room-temperature THz imaging by nonlinear optical frequency up-conversion in an organic 4-dimethylamino-N'-methyl-4'-stilbazolium tosylate (DAST) crystal, with high resolution reaching the diffraction limit. THz-wave images were converted to the near infrared region and then captured using an InGaAs camera in a tandem imaging system. The resolution of the imaging system was analyzed. Diffraction and interference of THz wave were observed in the experiments. Videos are supplied to show the interference pattern variation that occurs with sample moving and tilting. PMID:25837099

Fan, Shuzhen; Qi, Feng; Notake, Takashi; Nawata, Kouji; Takida, Yuma; Matsukawa, Takeshi; Minamide, Hiroaki

2015-03-23

297

Pulsed-Source Interferometry in Acoustic Imaging  

NASA Technical Reports Server (NTRS)

A combination of pulsed-source interferometry and acoustic diffraction has been proposed for use in imaging subsurface microscopic defects and other features in such diverse objects as integrated-circuit chips, specimens of materials, and mechanical parts. A specimen to be inspected by this technique would be mounted with its bottom side in contact with an acoustic transducer driven by a continuous-wave acoustic signal at a suitable frequency, which could be as low as a megahertz or as high as a few hundred gigahertz. The top side of the specimen would be coupled to an object that would have a flat (when not vibrating) top surface and that would serve as the acoustical analog of an optical medium (in effect, an acoustical "optic").

Shcheglov, Kirill; Gutierrez, Roman; Tang, Tony K.

2003-01-01

298

Terahertz time-domain imaging of hidden defects in wooden artworks: application to a Russian icon painting.  

PubMed

We use terahertz time-domain imaging and time-of-flight tomography to examine subsurface defects in an early-19th-century Russian icon painting. In the transmission geometry, we distinguish between native wood and higher-absorption knotted wood. In reflection, we identify a void in the wood filled with foreign filler material. By using time-of-flight tomographic analysis, we ascertain the depth of burial of the defects. This information helps us to identify the cause of surface faults in the painting, thus allowing the conservators to choose an adequate restoration strategy. PMID:24663298

Skryl, Anton S; Jackson, J Bianca; Bakunov, Michael I; Menu, Michel; Mourou, Gerard A

2014-02-20

299

Nondestructive evaluation of aircraft composites using transmissive terahertz time domain spectroscopy.  

PubMed

Terahertz time domain spectroscopy (TDS) was assessed as a nondestructive evaluation technique for aircraft composites. Damage to glass fiber was studied including voids, delaminations, mechanical damage, and heat damage. Measurement of the material properties on samples with localized heat damage showed that burning did not change the refractive index or absorption coefficient noticeably; however, material blistering was detected. Voids were located by TDS transmissive imaging using amplitude and phase techniques. The depth of delaminations was measured via the timing of Fabry-Perot reflections after the main pulse. Evidence of bending stress damage and simulated hidden cracks was also detected with terahertz imaging. PMID:18852814

Stoik, Christopher D; Bohn, Matthew J; Blackshire, James L

2008-10-13

300

Simultaneous Noncontact Precision Imaging of Microstructural and Thickness Variation in Dielectric Materials Using Terahertz Energy  

NASA Technical Reports Server (NTRS)

A process for simultaneously measuring the velocity of terahertz electromagnetic radiation in a dielectric material sample without prior knowledge of the thickness of the sample and for measuring the thickness of a material sample using terahertz electromagnetic radiation in a material sample without prior knowledge of the velocity of the terahertz electromagnetic radiation in the sample is disclosed and claimed. The process evaluates, in a plurality of locations, the sample for microstructural variations and for thickness variations and maps the microstructural and thickness variations by location. A thin sheet of dielectric material may be used on top of the sample to create a dielectric mismatch. The approximate focal point of the radiation source (transceiver) is initially determined for good measurements.

Roth, Donald J (Inventor)

2011-01-01

301

Precise real-time polarization measurement of terahertz electromagnetic waves by a spinning electro-optic sensor.  

PubMed

We propose and develop a method to quickly and precisely determine the polarization direction of coherent terahertz electromagnetic waves generated by femtosecond laser pulses. The measurement system consists of a conventional terahertz time-domain spectroscopy system with the electro-optic (EO) sampling method, but we add a new functionality in the EO crystal which is continuously rotating with the angular frequency ?. We find a simple yet useful formulation of the EO signal as a function of the crystal orientation, which enables a lock-in-like detection of both the electric-field amplitude and the absolute polarization direction of the terahertz waves with respect to the probe laser pulse polarization direction at the same time. The single measurement finishes around two periods of the crystal rotations (?21 ms), and we experimentally prove that the accuracy of the polarization measurement does not suffer from the long-term amplitude fluctuation of the terahertz pulses. Distribution of the measured polarization directions by repeating the measurements is excellently fitted by a gaussian distribution function with a standard deviation of ? = 0.56°. The developed technique is useful for the fast direct determination of the polarization state of the terahertz electromagnetic waves for polarization imaging applications as well as the precise terahertz Faraday or Kerr rotation spectroscopy. PMID:22380076

Yasumatsu, Naoya; Watanabe, Shinichi

2012-02-01

302

How to take your pulse (image)  

MedlinePLUS

... the blood pulsing beneath your fingers. Use a watch or clock with a second hand. Count the beats you ... the blood pulsing beneath your fingers. Use a watch or clock with a second hand. Count the beats you ...

303

Pulsed Magneto-motive Ultrasound Imaging Using Ultrasmall Magnetic Nanoprobes  

PubMed Central

Nano-sized particles are widely regarded as a tool to study biologic events at the cellular and molecular levels. However, only some imaging modalities can visualize interaction between nanoparticles and living cells. We present a new technique, pulsed magneto-motive ultrasound imaging, which is capable of in vivo imaging of magnetic nanoparticles in real time and at sufficient depth. In pulsed magneto-motive ultrasound imaging, an external high-strength pulsed magnetic field is applied to induce the motion within the magnetically labeled tissue and ultrasound is used to detect the induced internal tissue motion. Our experiments demonstrated a sufficient contrast between normal and iron-laden cells labeled with ultrasmall magnetic nanoparticles. Therefore, pulsed magneto-motive ultrasound imaging could become an imaging tool capable of detecting magnetic nanoparticles and characterizing the cellular and molecular composition of deep-lying structures. PMID:21439255

Mehrmohammadi, Mohammad; Oh, Junghwan; Mallidi, Srivalleesha; Emelianov, Stanislav Y.

2011-01-01

304

Continuous-wave terahertz field imaging based on photonics-based self-heterodyne electro-optic detection.  

PubMed

We demonstrate a photonics-based self-heterodyne electro-optic field imaging technique at terahertz (THz) frequency. An optical intensity beat generated by mixing two frequency-detuned free-running lasers is used for both the generation and the detection. The frequency of the beat for detection is shifted by an optical frequency shifter to realize coherent heterodyne measurement with free-running lasers. Neither mechanical delay lines nor phase-locked synthesizers are required for the amplitude and the phase imaging of the THz field, and the system simplicity is thus improved. The amplitude and phase of the THz field (125 GHz) radiated from a horn antenna are simultaneously imaged, and the standard deviation of the phase measurement is found to be 0.18 rad. PMID:23811911

Hisatake, Shintaro; Nagatsuma, Tadao

2013-07-01

305

Imaging of broadband terahertz beams using an array of antenna-coupled microbolometers operating at room temperature.  

PubMed

We present results of 2D real-time imaging of terahertz (THz) beam generated by a photoconductive antenna driven by a femtosecond oscillator. The detector, operating at room temperature, is a 320 x 240 array of antenna-coupled microbolometers with integrated CMOS read-out electronics delivering 25 images per second. High quality images of broadband THz beams covering the 0.1-2 THz range are recorded while maintaining a signal-to-noise ratio of 10 for detected THz power as low as 25 nW. The compactness of the easy-to-use uncooled camera makes it very useful for the alignment of systems such as THz time-domain spectrometers and for the characterization of emitters, optics and other components. PMID:23482016

Oden, Jonathan; Meilhan, Jérome; Lalanne-Dera, Jérémy; Roux, Jean-François; Garet, Frédéric; Coutaz, Jean-Louis; Simoens, François

2013-02-25

306

Terahertz Mapping of Microstructure and Thickness Variations  

NASA Technical Reports Server (NTRS)

A noncontact method has been devised for mapping or imaging spatial variations in the thickness and microstructure of a layer of a dielectric material. The method involves (1) placement of the dielectric material on a metal substrate, (2) through-the-thickness pulse-echo measurements by use of electromagnetic waves in the terahertz frequency range with a raster scan in a plane parallel to the substrate surface that do not require coupling of any kind, and (3) appropriate processing of the digitized measurement data.

Roth, Donald J.; Seebo, Jeffrey P.; Winfree, William P.

2010-01-01

307

Terahertz sources and detectors  

NASA Astrophysics Data System (ADS)

Through the support of the US Army Research Office we are developing terahertz sources and detectors suitable for use in the spectroscopy of chemical and biological materials as well as for use in imaging systems to detect concealed weapons. Our technology relies on nonlinear diodes to translate the functionality achieved at microwave frequencies to the terahertz band. Basic building blocks that have been developed for this application include low-noise mixers, frequency multipliers, sideband generators and direct detectors. These components rely on planar Schottky diodes and integrated diode circuits and are therefore easy to assemble and robust. They require no mechanical tuners to achieve high efficiency and broad bandwidth. This paper will review the range of performance that has been achieved with these terahertz components and briefly discuss preliminary results achieved with a spectroscopy system and the development of sources for imaging systems.

Crowe, Thomas W.; Porterfield, David W.; Hesler, Jeffrey L.; Bishop, William L.; Kurtz, David S.; Hui, Kai

2005-05-01

308

Pulse frequency modulation based CMOS image sensor for subretinal stimulation  

Microsoft Academic Search

We have developed a CMOS image sensor based on pulse frequency modulation for subretinal implantation. The sensor chip forms part of the proposed intraocular retinal prosthesis system where data and power transmission are provided wirelessly from an extraocular unit. Image sensing and electrical stimulus are integrated onto the same chip. Image of sufficient resolution has been demonstrated using 16times16 pixels.

David C. Ng; Tetsuo Furumiya; Koutaro Yasuoka; Akihiro Uehara; Keiichiro Kagawa; Takashi Tokuda; Masahiro Nunoshita; Jun Ohta

2006-01-01

309

Femtosecond pulse imaging by nonlinear optical three-wave mixing  

Microsoft Academic Search

We have introduced and experimentally demonstrated a nonlinear optical processor that performs pulse imaging of l-D femtosecond optical pulses. The processor operates at femtosecond rates and can be useful for optical network time-to-space demultiplexing applications. The demultiplexer is based on nonlinear three-wave mixing in a LBO crystal

Pang-Chen Sun; Y. T. Mazurenko; Y. Fainman

1996-01-01

310

Antenna-coupled field-effect transistors for multi-spectral terahertz imaging up to 4.25 THz.  

PubMed

We demonstrate for the first time the applicability of antenna-coupled field-effect transistors for the detection of terahertz radiation (TeraFETs) for multi-spectral imaging from 0.76 to 4.25 THz. TeraFETs were fabricated in a commercial 90-nm CMOS process and noise-equivalent powers of 59, 20, 63, 85 and 110?pW/?(Hz) at 0.216, 0.59, 2,52, 3.11 and 4.25 THz, respectively, have been achieved. A set of TeraFETs has been applied in raster-scan transmission and reflection imaging of pellets of sucrose and tartaric acid simulating common plastic explosives. Transmittance values are in good agreement with Fourier-transform infrared spectroscopy data. The spatial distribution of the components in the samples has been determined from the transmission data using principal component analysis. PMID:25321008

Bauer, M; Venckevi?ius, R; Kašalynas, I; Boppel, S; Mundt, M; Minkevi?ius, L; Lisauskas, A; Valušis, G; Krozer, V; Roskos, H G

2014-08-11

311

Improvements in magnetic resonance imaging excitation pulse design  

E-print Network

This thesis focuses on the design of magnetic resonance imaging (MRI) radio-frequency (RF) excitation pulses, and its primary contributions are made through connections with the novel multiple-system single-output (MSSO) ...

Zelinski, Adam Charles

2008-01-01

312

High-speed, low-photodamage nonlinear imaging using passive pulse splitters  

E-print Network

+ imaging of hippocampal slices. RESULTS Pulse splitter design Several methods of passive pulse splittingHigh-speed, low-photodamage nonlinear imaging using passive pulse splitters Na Ji, Jeffrey C Magee a passive pulse splitter that converts each laser pulse into a fixed number of sub-pulses of equal energy

Eddy, Sean

313

Terahertz in-line sensor for direct coating thickness measurement of individual tablets during film coating in real-time.  

PubMed

We present a new in-line measurement technique to determine the coating thickness of individual pharmaceutical tablets during film coating in a pan coating unit using pulsed terahertz technology. Results of these real-time terahertz measurements acquired during a production scale coating run are validated using both off-line high-resolution terahertz pulsed imaging of the whole dosage form as well as weight-gain measurements made on sample tablets removed at discrete time intervals during the process run. The terahertz measurements provide a direct method of determining the coating thickness, and no chemometric calibration models are required for the quantification. The results, and their repeatability, demonstrate that real-time monitoring of pharmaceutical tablet coating is not only possible but also provides substantially more information of the coating quality than the standard quality control method. Rather than providing the average coating thickness of a large number of tablets, the terahertz sensor provides the thickness of up to 100 individual tablet coatings per minute. Using this information, the operator can get additional information about the thickness distribution in the coating pan and adjust the process accordingly. At present, a minimum coating thickness of 40 ?m is required to determine the coating thickness. The technique is applicable for coatings up to 1 mm in thickness. Within that range, it provides thickness measurements of sub-micron resolution. Terahertz in-line coating process measurements show considerable potential for applications in real-time release, process analytical technology and quality by design. PMID:20957746

May, Robert K; Evans, Michael J; Zhong, Shuncong; Warr, Ian; Gladden, Lynn F; Shen, Yaochun; Zeitler, J Axel

2011-04-01

314

SAR image quality using advanced pulse compression noise (APCN)  

NASA Astrophysics Data System (ADS)

This work demonstrates the feasibility of using the advanced pulse compression noise (APCN) radar waveform for synthetic aperture radar (SAR). Using a simple image formation process (IFP), we not only show that we can successfully form images using the APCN waveform, but we grow our understanding of how different combinations of APCN waveforms and side lobe weighting functions impact SAR image quality. In this paper, an analysis is presented that compares the target range point spread function (PSF) for several simulated SAR images.

Govoni, Mark A.; Elwell, Ryan A.

2014-05-01

315

Tunable Terahertz Metamaterials  

Microsoft Academic Search

In recent years terahertz (1 THz = 10^12 Hz) technology has become an optimistic candidate for numerous sensing, imaging, and diagnostic applications. Nevertheless, THz technology still suffers from a deficiency in high-power sources, efficient detectors, and other functional devices ubiquitous in neighboring microwave and infrared frequency bands, such as amplifiers, modulators, and switches. One of the greatest obstacles in this

Antoinette J. Taylor

2009-01-01

316

Active Terahertz Metamaterials  

Microsoft Academic Search

In recent years terahertz technology has become an optimistic candidate for numerous sensing, imaging, and diagnostic applications. Nevertheless, THz technology still suffers from a deficiency in high-power sources, efficient detectors, and other functional devices ubiquitous in neighboring microwave and infrared frequency bands, such as amplifiers, modulators, and switches. One of the greatest obstacles in this progress is the lack of

Antoinette Taylor; Abul K. Azad; John F. O'Hara; Ranjan Singh; Jiangfeng Zhou; Matthew T. Reiten; Dibakar Roy Chowdhury; Quanxi Jia; Stuart A. Trugman

2011-01-01

317

A spatial light modulator for terahertz radiation  

Microsoft Academic Search

We characterize the operation of a 4times4 electrically-driven terahertz metamaterial spatial modulator, and demonstrate high modulation uniformly at each pixel with minimal cross-talk. This modulator will enable high-speed terahertz imaging in a single-pixel imaging system.

Wai Lam Chan; Hou-Tong Chen; A. J. Taylor; I. Brener; M. Cich; D. M. Mittleman

2009-01-01

318

The SPARC linear accelerator based terahertz source  

SciTech Connect

Ultra-short electron beams, produced through the velocity bunching compression technique, are used to drive the SPARC linear accelerator based source, which relies on the emission of coherent transition radiation in the terahertz range. This paper reports on the main features of this radiation, as terahertz source, with spectral coverage up to 5 THz and pulse duration down to 200 fs, with an energy per pulse of the order of several micro-joule, and as electron beam longitudinal diagnostics.

Chiadroni, E.; Bacci, A.; Bellaveglia, M.; Boscolo, M.; Castellano, M.; Cultrera, L.; Di Pirro, G.; Ferrario, M.; Ficcadenti, L.; Filippetto, D.; Gatti, G.; Pace, E.; Rossi, A. R.; Vaccarezza, C. [INFN-LNF, Frascati (Italy)] [INFN-LNF, Frascati (Italy); Catani, L.; Cianchi, A.; Marchetti, B. [INFN and University of Rome 'Tor Vergata,' Rome (Italy)] [INFN and University of Rome 'Tor Vergata,' Rome (Italy); Mostacci, A.; Palumbo, L. [INFN and SBAI Department, Sapienza University of Rome, Rome (Italy)] [INFN and SBAI Department, Sapienza University of Rome, Rome (Italy); Ronsivalle, C. [ENEA C.R. Frascati (Italy)] [ENEA C.R. Frascati (Italy); and others

2013-03-04

319

Terahertz metamaterials  

DOEpatents

Terahertz metamaterials comprise a periodic array of resonator elements disposed on a dielectric substrate or thin membrane, wherein the resonator elements have a structure that provides a tunable magnetic permeability or a tunable electric permittivity for incident electromagnetic radiation at a frequency greater than about 100 GHz and the periodic array has a lattice constant that is smaller than the wavelength of the incident electromagnetic radiation. Microfabricated metamaterials exhibit lower losses and can be assembled into three-dimensional structures that enable full coupling of incident electromagnetic terahertz radiation in two or three orthogonal directions. Furthermore, polarization sensitive and insensitive metamaterials at terahertz frequencies can enable new devices and applications.

Peralta, Xomalin Guaiuli; Brener, Igal; O'Hara, John; Azad, Abul; Smirnova, Evgenya; Williams, John D.; Averitt, Richard D.

2014-08-12

320

Investigation on reconstruction methods applied to 3D terahertz computed  

E-print Network

. Cheville, "Transmission terahertz waveguide-based imaging below the diffraction limit," Appl. Phys. LettInvestigation on reconstruction methods applied to 3D terahertz computed tomography B. Recur,3 A *em.abraham@loma.u-bordeaux1.fr Abstract: 3D terahertz computed tomography has been performed using

Boyer, Edmond

321

Terahertz Quantum-Cascade Transmission-Line Metamaterials  

NASA Astrophysics Data System (ADS)

Terahertz quantum-cascade (QC) lasers operating at 0.6 - 5 THz (? ˜ 60 - 500 µm) are poised to become the dominant solid-state sources of continuous-wave (cw) far-infrared radiation enabling applications in terahertz spectroscopy, imaging, and sensing. QC-lasers are the longest wavelength semiconductor laser sources in which terahertz gain is obtained from electronic intersubband radiative transitions in GaAs/AlGaAs heterostructure quantum wells. Since their invention in 2001, rapid development has enabled demonstration of cw powers greater than 100 mW. However, challenges still remain in the areas of operating temperature, laser efficiency and power, and beam quality to name a few. The highest-temperature operation of terahertz quantum-cascade lasers (200 K pulsed, 117 K cw) depends on the use of a low-loss "metal-metal" waveguide where the active gain material is sandwiched between two metal cladding layers; a technique similar, in concept, to microstrip transmission line technology at microwave frequencies. Due to the subwavelength transverse dimensions of the metal-metal waveguide, however, obtaining a directive beam pattern and efficient out-coupling of THz power is non-trivial. This thesis reports the demonstration of a one-dimensional waveguide for terahertz quantum-cascade lasers that acts as a leaky-wave antenna and tailors laser radiation in one dimension to a directional beam. This scheme adapts microwave transmission-line metamaterial concepts to a planar structure realized in terahertz metal-metal waveguide technology and is fundamentally different from distributed feedback/photonic crystal structures that work based on Bragg scattering of propagating modes. The leaky-wave metamaterial antenna operates based on a propagating mode with an effective phase index smaller than unity such that it radiates in the surface direction via a leaky-wave mechanism. Surface emission (˜ 40° from broadside) with a single directive beam (FWHM ˜ 15°) at 2.74 THz was demonstrated from terahertz QC-lasers with leaky-wave coupler antennas which exhibited slope efficiencies ˜ 4 times greater than conventional Fabry-Perot metal-metal waveguides. Using this technique the first demonstration of beam scanning for a terahertz QC-laser was reported (from 35° - 60°) as the emission frequency varied from 2.65 - 2.81 THz. Towards the bigger goal of realizing an active terahertz metamaterial to ultimately develop "zero-index" terahertz quantum-cascade lasers immune to spatial hole burning, or "negative-index" metamaterials for superresolution terahertz imaging, a composite right-/left-handed transmission-line metamaterial based upon subwavelength metal waveguide loaded with terahertz QC material was demonstrated. Due to the addition of distributed series capacitors (realized by introducing gaps in top metallization) and shunt inductors (realized by operating in the higher-order lateral mode of the waveguide), the transmission-line metamaterial exhibits left-handed (backward waves or negative index) leaky-wave propagation from 2.3 - 2.45 THz in addition to the conventional right-handed leaky-wave behavior (from 2.6 - 3.0 THz).

Tavallaee, Amir Ali

322

Pulsed laser linescanner for a backscatter absorption gas imaging system  

DOEpatents

An active (laser-illuminated) imaging system is described that is suitable for use in backscatter absorption gas imaging (BAGI). A BAGI imager operates by imaging a scene as it is illuminated with radiation that is absorbed by the gas to be detected. Gases become "visible" in the image when they attenuate the illumination creating a shadow in the image. This disclosure describes a BAGI imager that operates in a linescanned manner using a high repetition rate pulsed laser as its illumination source. The format of this system allows differential imaging, in which the scene is illuminated with light at least 2 wavelengths--one or more absorbed by the gas and one or more not absorbed. The system is designed to accomplish imaging in a manner that is insensitive to motion of the camera, so that it can be held in the hand of an operator or operated from a moving vehicle.

Kulp, Thomas J.; Reichardt, Thomas A.; Schmitt, Randal L.; Bambha, Ray P.

2004-02-10

323

PUPA: a pulse programming assistant for NMR imaging  

SciTech Connect

The design of pulse programs for magnetic resonance imaging (MRI) experiments is tedious and complex, requiring a deep understanding of the interactions that exist between magnetic fields generated during an MRI experiment. This paper describes an intelligent system that understands how to construct the multichannel temporal sequences of pulses needed to control an MRI experiment. PUPA, the PUlse Programmers Assistant, provides assistance to a relatively naive user of MRI systems. Knowledge is coded in the form of rules and semantic networks. A natural language facility and menu system are provided for communication with the user.

Foxvog, D.; Li, X.; Vargas, J.E.; Bourne, J.R.; Sztipanovits, J.; Mushlin, R.; Harrison, C.G.

1987-12-01

324

Pulse Processing System for the RADMAP Radiation Modulation Aperture Imager  

SciTech Connect

We are currently developing a portable radiation imager for emergency responders. The instrument contains a position-sensitive photomultiplier tube with a thin CsI(Na) scintillator and a tungsten radiation modulation aperture. As part of this project, we have designed a novel pulse processing system to record the amplitude and position of incident events. This system consists of four charge-to-pulse-width converters that transfer time-modulated digital pulses to a field-programmable gate array. The design can process data at count rates exceeding 40,000 events per second and transmit data over an Ethernet link at 1 Gb/sec.

Myjak, Mitchell J.; Rohrer, John S.; Morris, Scott J.; Woodring, Mitchell L.; Ely, James H.

2007-12-31

325

Photo-designed terahertz devices  

PubMed Central

Technologies are being developed to manipulate electromagnetic waves using artificially structured materials such as photonic crystals and metamaterials, with the goal of creating primary optical devices. For example, artificial metallic periodic structures show potential for the construction of devices operating in the terahertz frequency regime. Here we demonstrate the fabrication of photo-designed terahertz devices that enable the real-time, wide-range frequency modulation of terahertz electromagnetic waves. These devices are comprised of a photo-induced, planar periodic-conductive structure formed by the irradiation of a silicon surface using a spatially modulated, femtosecond optical pulsed laser. We also show that the modulation frequency can be tuned by the structural periodicity, but is hardly affected by the excitation power of the optical pump pulse. We expect that our findings will pave the way for the construction of all-optical compact operating devices, such as optical integrated circuits, thereby eliminating the need for materials fabrication processes. PMID:22355638

Okada, Takanori; Tanaka, Koichiro

2011-01-01

326

Ladar range image interpolation exploiting pulse width expansion  

NASA Astrophysics Data System (ADS)

Laser radar (LADAR) systems produce both a range image and an intensity image. When the transmitted LADAR pulse strikes a sloped surface, the returned pulse is expanded temporally. This makes it possible to estimate the gradient of a surface, pixel by pixel. This paper seeks to find the gradient of the surface of an object from a realistic LADAR return pulse that includes probabilistic noise models. Additionally, optimal and computationally simple interpolation filters are each derived to recover Nyquist-sampled data from data spatially sampled below the Nyquist rate. The filters will then be applied to the embedded information in the gradient to allow the sampling density in the spatial domain to be taken at below the Nyquist criterion while still facilitating an effective 3D reconstruction of an image.

Martin, Richard K.; Mathews, Kirk A.; Motes, Jeramy W.

2011-09-01

327

Applications of Ultrafast Terahertz Pulses for Intra-ExcitonicSpectroscopy of Quasi-2D Electron-Hole Gases  

SciTech Connect

Excitons are of fundamental interest and of importance foropto-electronic applications of bulk and nano-structured semiconductors.This paper discusses the utilization of ultrafast terahertz (THz) pulsesfor the study of characteristic low-energy excitations of photoexcitedquasi 2D electron-hole (e-h) gases. Optical-pump THz-probe spectroscopyat 250-kHz repetition rate is employed to detect characteristic THzsignatures of excitons and unbound e-h pairs in GaAs quantum wells.Exciton and free-carrier densities are extracted from the data using atwo-component model. We report the detailed THz response and pairdensities for different photoexcitation energies resonant to heavy-holeexcitons, light-hole excitons, or the continuum of unbound pairs. Suchexperiments can provide quantitative insights into wavelength, time, andtemperature dependence of the low-energy response and composition ofoptically excited e-h gases in low-dimensionalsemiconductors.

Kaindl, Robert A.; Carnahan, Marc A.; Hagele, Daniel; Chemla, D.S.

2006-09-02

328

Research on time-resolved terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

We have built a set of terahertz time-domain spectroscopy system using electro-optic crystals. Conventional terahertz time-domain spectroscopy based on Fourier-transform for spectra analysis, which mixes the frequency components of the entire temporal terahertz waveform in one frequency domain; therefore, it yields different terahertz spectra from a same terahertz pulse with different scanning lengths. We introduce a new technique for the joint time-frequency analysis of terahertz time-domain spectroscopy based on wavelet-transform technique. With this technique, the frequency components in different time locations are clearly exhibited on a two-dimensional plane; therefore, the noise in the pulse tail cannot affect the frequency in the main pulse. This technique clearly separates the frequency of terahertz from that of its echo in the time domain; therefore, the interference spectrum occur in Fourier-transform is naturally removed. By varying the shape of analysis wavelet, high time resolution and high frequency resolution are easily obtained. The absorption coefficients of envelope, plastic, foam and cotton have been measured with the wavelet technique.

Deng, Yuqiang; Sun, Qing; Liu, Feng; Wang, Changlei; Xing, Qirong

2010-10-01

329

Computed tomography image using sub-terahertz waves generated from a high-T{sub c} superconducting intrinsic Josephson junction oscillator  

SciTech Connect

A computed tomography (CT) imaging system using monochromatic sub-terahertz coherent electromagnetic waves generated from a device constructed from the intrinsic Josephson junctions in a single crystalline mesa structure of the high-T{sub c} superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+?} was developed and tested on three samples: Standing metallic rods supported by styrofoam, a dried plant (heart pea) containing seeds, and a plastic doll inside an egg shell. The images obtained strongly suggest that this CT imaging system may be useful for a variety of practical applications.

Kashiwagi, T., E-mail: kashiwagi@ims.tsukuba.ac.jp; Minami, H.; Kadowaki, K. [Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba (Japan); Division of Materials Science, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573 (Japan); Nakade, K.; Saiwai, Y.; Kitamura, T.; Watanabe, C.; Ishida, K.; Sekimoto, S.; Asanuma, K.; Yasui, T.; Shibano, Y. [Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba (Japan); Tsujimoto, M. [Department of Electronic Science and Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan); Yamamoto, T. [Wide Bandgap Materials Group, Optical and Electronic Materials Unit, Environment and Energy Materials Division, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Markovi?, B. [Faculty of Sciences, University of Montenegro, George Washington Str., 81000 Podgorica (Montenegro); Mirkovi?, J. [Faculty of Science, University of Montenegro, and CETI, Put Radomira Ivanovica, 81000 Podgorica (Montenegro); Klemm, R. A. [Department of Physics, University of Central Florida, 4000 Central Florida Blvd., Orlando, Florida 32816-2385 (United States)

2014-02-24

330

Characteristic responses of biological and nanoscale systems in the terahertz frequency range  

NASA Astrophysics Data System (ADS)

This paper briefly examines methods for the generation of pulsed terahertz radiation and principles of pulsed terahertz spectroscopy, an advanced informative method for studies of complex biological and nanostructured systems. Some of its practical applications are described. Using a number of steroid hormones as examples, we demonstrate that terahertz spectroscopy in combination with molecular dynamics methods and computer simulation allows one to gain information about the structure of molecules in crystals. A 'terahertz colour vision' method is proposed for analysis of pulsed terahertz signals reflected from biological tissues and it is shown that this method can be effectively used to analyse the properties of biological tissues and for early skin cancer diagnosis.

Angeluts, A. A.; Balakin, A. V.; Evdokimov, M. G.; Esaulkov, M. N.; Nazarov, M. M.; Ozheredov, I. A.; Sapozhnikov, D. A.; Solyankin, P. M.; Cherkasova, O. P.; Shkurinov, A. P.

2014-07-01

331

Nonresonant ionization of oxygen molecules by femtosecond pulses: Plasma dynamics studied by time-resolved terahertz spectroscopy  

E-print Network

Nonresonant ionization of oxygen molecules by femtosecond pulses: Plasma dynamics studied by time for exploring laser-induced ionization and plasma formation in gases. Plasma was produced in gaseous oxygen by focused amplified femtosecond pulses. The ionization mechanisms at 400- and 800-nm excitation wavelengths

Apkarian, V. Ara

332

Study on conversion efficiency of optical-to-terahertz in optical rectification  

NASA Astrophysics Data System (ADS)

Optical rectification of ultra-short laser pulses is an attractive technique for efficient generation of terahertz pulses. An analytical expression of the optical-to-terahertz conversion efficiency in optical rectification by the use of the method of tilted-pulse-front pumping has been derived and used to simulate the maximum optical-to-terahertz conversion efficiency. The variations of the conversion efficiency of optical-to-terahertz with the length of crystal, the intensity and the pulse duration of the pumping ultra-short laser have been investigated, both in numerical and analytical solutions. In addition, the absorption of terahertz wave in LiNbO3 has also been taken into account. The results show that, the optical-to-terahertz conversion efficiency increases with the intensity of pump pulse and the length of crystal, whereas decreases with the increasing of the pulse duration for the case of the relatively large pulses duration.

Meng, Qinglong; Ye, Rong; Zeng, Bing; Zhong, Zheqiang; Zhang, Bin

2015-02-01

333

Image reconstruction with sub-diffraction resolution in radio vision devices of millimeter and terahertz range using receiving arrays and image scanning  

NASA Astrophysics Data System (ADS)

The method of image reconstruction with sub-diffraction resolution in radio vision devices (RVD) of shortwave millimeter and terahertz frequency range is proposed. The method is based on image scanning using two-dimensional receiving element array of RVD when array and image move circularly in common plane relatively each to other (rotating or not rotating) with small eccentricity between their centers. The results of scanning are signals reading out by detectors of array receiving elements. Each signal is proportional to the integral of two functions product. One function is a perfect image field distribution of the observed object received by RVD without diffraction distortion. Another one is RVD optical (quasioptical) transfer function comprising beams delivering incident radiation to detectors of array. The second function takes into account whole received radiation beam paths from RVD input to each detector including the effect of diffraction and reciprocal circular scanning of array and image. The image of observed object itself can be found solving inverse ill-posed problem determined by mentioned above integral relations. The estimation using computer simulation has shown that proposed method permits to increase resolution up to ten times in comparison with the case of diffraction restriction. The method is aimed at radioastronomy telescopes and RVD's for the security, medical diagnostics and other systems.

Vystavkin, Alexander N.; Pestryakov, Andrey V.; Bankov, Sergey E.; Chebotarev, Vladimir M.

2009-09-01

334

Lossless Image Compression Using Modular Differential Pulse Code Modulation  

Microsoft Academic Search

This paper presents a new lossless image compression technique called modular differential pulse code modulation (MDPCM). The proposed technique consists of a VQ classifier and several neural network class predictors. The classifier uses the four previously encoded pixels to identify the class of the current pixel (the pixel to be predicted). The current pixel is then predicted by the corresponding

Syed A. Rizvi; Nasser M. Nasrabadit

1999-01-01

335

Differential pulse code modulation image compression using artifical neural networks  

Microsoft Academic Search

Differential pulse code modulation (DPCM) is a widely used technique for both lossy and lossless compression of images. In this paper, the effect of using a nonlinear predictor based on artificial neural networks (ANN) for a DPCM encoder is investigated. The ANN predictor uses a 3-layer perceptron model with 3 input nodes, 30 hidden nodes, and 1 output node. The

Majid Rabbani; Soheil A. Dianat

1993-01-01

336

Lossless image compression using modular differential pulse code modulation  

Microsoft Academic Search

This paper presents a new lossless image compression technique called modular differential pulse code modulation. The proposed technique consists of a VQ classifier and several neural network class predictors. The classifier uses the four previously encoded pixels to identify the class of the current pixel (the pixel to be predicted). The current pixel is then predicted by the corresponding class

Syed A. Rizvi; Richard Toussaint; George Awad

2000-01-01

337

Methods for MRI RF Pulse Design and Image Reconstruction  

E-print Network

involved in the 7T scanner operations. I really apprecMethods for MRI RF Pulse Design and Image Reconstruction by Feng Zhao A dissertation submitted and MRI scanner operations was from him. It is so nice of him that he always warmly welcomes me

Fessler, Jeffrey A.

338

Finite amplitude distortion-based inhomogeneous pulse echo ultrasonic imaging  

Microsoft Academic Search

Ultrasonic pulse echo imaging in inhomogeneous media suffers from significant lateral and contrast resolution losses due to the defocusing effects of the inhomogeneities. The losses in lateral and contrast resolution are associated with increases in the width of the mainbeam and increases in sidelobe levels, respectively. These two forms of resolution loss represent significant hurdles to improving the clinical utility

Ted Christopher

1997-01-01

339

Direct imaging of hot spot in Bi2Sr2CaCu2O8+? mesa terahertz sources  

NASA Astrophysics Data System (ADS)

Stacks of intrinsic Josephson junctions (IJJs) made from high-temperature superconductors such as Bi2Sr2CaCu2O8+? (Bi-2212) are a promising source of coherent continuous-wave terahertz radiation. When electrical power is applied to these devices, it is thought that hot spots may form due to resistive self-heating, and that these spots may be highly beneficial for the generation of high levels of THz power from Bi-2212 stacks. In order to better understand these hot spots, we have performed a thermal imaging study of BSCCO stacks which generate approximately 50 microwatts of radiation power at 0.59 THz. Utilizing the temperature-dependent 612nm fluorescence line of Eu^3+, we are able to directly measure the temperature distribution at the top surface of these stacks with a resolution of +/- 1K. The images reveal a highly non-uniform temperature distribution in which the temperature in the middle of the stack can exceed the superconducting transition temperature by tens of Kelvin under biasing conditions typical for THz-emission.

Benseman, Timothy; Gray, Ken; Koshelev, Alexei; Kwok, Wai-Kwong; Welp, Ulrich; Vlasko-Vlasov, Vitalii; Kadowaki, Kazuo; Minami, Hidetoshi

2013-03-01

340

Submicrosecond Imaging Under A Pulsed-Laser Fluorescence Microscope  

NASA Astrophysics Data System (ADS)

A microscope system has been constructed that enables digital imaging of a fluorescent cell under pulsed illumination. Each image is produced by a single laser pulse of duration less than 0.3 11 s. With this system, microsecond responses of a single cell to an externally applied electric field have been resolved temporally and spatially. The cell membrane was stained with a voltage-sensitive fluorescent dye. The induction of transsmembrane potential by the applied field, and the perforation (electroporation) of the cell membrane under an intense field, were seen as successive images. The major finding was a transient increase, at the moment of perforation, in the membrane permeability to an enormous level in localized regions of the cell membrane. Possible roles in cell technology, as well as other applications of the microscope system, are discussed.

Kinosita, Kazuhiko; Ashikawa, Ikuo; Hibino, Masahiro; Shigemori, Masaya; Yoshim ura, Hideyuki; Itoh, Hiroyasu; Nagayama, Kuniaki; lkegami, Akira

1988-06-01

341

Band structure of terahertz metallic photonic crystals with high metal filling factor  

E-print Network

that terahertz transmission through structures composed of metallic objects can be enhanced by surface plasmonBand structure of terahertz metallic photonic crystals with high metal filling factor Benjamin The excitation of resonant eigenmodes in two-dimensional metallic photonic crystals by incident terahertz pulses

342

Terahertz conductivity of thin metal films N. Laman and D. Grischkowskya  

E-print Network

measured via their transmission at terahertz frequencies. The conductivities of all the films, particularly and confirmed these results by measuring the terahertz transmission of a number of thin films comprised- troscopy THz-TDS apparatus.2,3 Their transmission was measured at both 295 and 77 K. The terahertz pulses

Oklahoma State University

343

896 OPTICS LETTERS / Vol. 29, No. 8 / April 15, 2004 Terahertz transmission properties of thin, subwavelength  

E-print Network

896 OPTICS LETTERS / Vol. 29, No. 8 / April 15, 2004 Terahertz transmission properties of thin present experimental results of the transmission magnitude and phase change of terahertz pulses through-selective components in the development of terahertz optoelectronics. High transmission or reflection at selective

344

Terahertz metamaterials  

Microsoft Academic Search

In this paper we present our recent developments in terahertz (THz) metamaterials and devices. Planar THz metamaterials and their complementary structures fabricated on suitable substrates have shown electric resonant response, which causes the band-pass or band-stop property in THz transmission and reflection. The operational frequency can be further tuned up to 20% upon photoexcitation of an integrated semiconductor region in

Hou-Tong Chen; John F. O'Hara; Abul K. Azad; Willie J. Padilla; Richard D. Averitt; Antoinette J. Taylor

2009-01-01

345

Diffusion and Swelling Measurements in Pharmaceutical Powder Compacts Using Terahertz Pulsed Imaging  

E-print Network

-faced pharmaceutical compacts exposed to dissolution medium from one face of the tablet. The technique was demonstrated on three tableting excipients: hydroxypropylmethyl cellulose (HPMC), Eudragit RSPO, and lactose. Upon contact with water, HPMC initially shrinks...

Yassin, Samy; Su, Ke; Lin, Hungyen; Gladden, Lynn F.; Zeitler, J. Axel

2015-02-02

346

A spatial light modulator for terahertz beams  

SciTech Connect

Spatial light modulators that control the spatial transmission of a terahertz beam either electrically or optically, have been difficult to build due to the lack of suitable materials. Here we propose the use of active terahertz metamaterials for the construction of a multi-pixel spatial modulator for terahertz beams. Our first-generation device consists of a 4 x 4 pixel array, where each pixel is an array of sub-wavelength-sized split-ring resonator elements fabricated on a semiconductor substrate, and is independently controlled by applying an external voltage. Through terahertz transmission experiments, we show that the spatial modulator has a uniform modulation depth of around 40 percent across all pixels at the resonant frequency. Around this operating frequency, the crosstalk between pixels is negligible. This device can operate under small voltage levels, at room temperature, with low power consumption and reasonably high switching speed, and can therefore benefit future applications in terahertz imaging and communications.

Chen, Hou-tong [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory

2009-01-01

347

Plasma characterization with terahertz timedomain measurements S. P. Jamisona)  

E-print Network

Plasma characterization with terahertz time­domain measurements S. P. Jamisona) Department­domain spectral techniques are applied to the characterization of a He discharge plasma. Electro-optically sampling of the electric field of a quasi-unipolar terahertz pulse transmitted through the plasma has

Strathclyde, University of

348

Terahertz transmission properties of thin, subwavelength metallic hole arrays  

Microsoft Academic Search

We present experimental results of the transmission magnitude and phase change of terahertz pulses through thin metallic films patterned with subwavelength hole arrays on silicon wafers. Terahertz time-domain spectroscopy measurements reveal a sharp phase peak centered on the surface plasmon resonance. Corre- spondingly, and consistent with the Kramers -Kronig relations, the measured transmission magnitude has the shape of the derivative

Dongxia Qu; D. Grischkowsky; Weili Zhang

349

Terahertz transmission properties of thin, subwavelength metallic hole arrays  

Microsoft Academic Search

We present experimental results of the transmission magnitude and phase change of terahertz pulses through thin metallic films patterned with subwavelength hole arrays on silicon wafers. Terahertz time-domain spectroscopy measurements reveal a sharp phase peak centered on the surface plasmon resonance. Correspondingly, and consistent with the Kramers-Kronig relations, the measured transmission magnitude has the shape of the derivative of this

Dongxia Qu; D. Grischkowsky; Weili Zhang

2004-01-01

350

Asymmetric planar terahertz metamaterials Ranjan Singh,1,2,*  

E-print Network

Asymmetric planar terahertz metamaterials Ranjan Singh,1,2,* Ibraheem A. I. Al-Naib,3 Martin Koch,3). 6. A. K. Azad, J. M. Dai, and W. Zhang, "Transmission properties of terahertz pulses through. H. T. Chen, J. F. O'Hara, A. K. Azad, A. J. Taylor, R. D. Averitt, D. B. Shrekenhamer, and W. J

Oklahoma State University

351

Characteristics of nonlinear imaging of broadband laser stacked by chirped pulses  

NASA Astrophysics Data System (ADS)

Nanosecond-level pulses of specific shape is usually generated by stacking chirped pulses for high-power inertial confinement fusion driver, in which nonlinear imaging of scatterers may damage precious optical elements. We present a numerical study of the characteristics of nonlinear imaging of scatterers in broadband laser stacked by chirped pulses to disclose the dependence of location and intensity of images on the parameters of the stacked pulse. It is shown that, for sub-nanosecond long sub-pulses with chirp or transform-limited sub-pulses, the time-mean intensity and location of images through normally dispersive and anomalously dispersive self-focusing medium slab are almost identical; While for picosecond-level short sub-pulses with chirp, the time-mean intensity of images for weak normal dispersion is slightly higher than that for weak anomalous dispersion through a thin nonlinear slab; the result is opposite to that for strong dispersion in a thick nonlinear slab; Furthermore, for given time delay between neighboring sub-pulses, the time-mean intensity of images varies periodically with chirp of the sub-pulse increasing; for a given pulse width of sub-pulse, the time-mean intensity of images decreases with the time delay between neighboring sub-pulses increasing; additionally, there is a little difference in the time-mean intensity of images of the laser stacked by different numbers of sub-pulses. Finally, the obtained results are also given physical explanations.

Wang, Youwen; You, Kaiming; Chen, Liezun; Lu, Shizhuan; Dai, Zhiping; Ling, Xiaohui

2014-11-01

352

Review of Terahertz Tomography Techniques J. P. Guillet & B. Recur & L. Frederique & B. Bousquet & L. Canioni &  

E-print Network

terahertz transmission and reflection images to be considered as a new imaging tool complementary to XReview of Terahertz Tomography Techniques J. P. Guillet & B. Recur & L. Frederique & B. Bousquet & L. Canioni & I Manek-Hönninger & P. Desbarats & P. Mounaix Abstract Terahertz and millimeter waves

Paris-Sud XI, Université de

353

Terahertz sensing using ferroelectric nanowires.  

PubMed

Molecular dynamics simulations are used to study the interaction of ferroelectric nanowires with terahertz (THz) Gaussian-shaped pulses of electric field. The computational data indicate the existence of two interaction scenarios that are associated with 'lossless' and dissipative, or 'lossy', interaction mechanisms. A thermodynamical approach is used to analyze the computational data for a wide range of THz pulses. The analysis establishes the foundation for understanding the nanowires' response to the THz pulses and reveals the potential of ferroelectric nanowires to function as nanoscale sensors of THz radiation. Various aspects of this THz nanosensing are analyzed and discussed. PMID:23299283

Herchig, R; Schultz, Kimberly; McCash, Kevin; Ponomareva, I

2013-02-01

354

Single pulse frequency compounding protocol for superharmonic imaging  

NASA Astrophysics Data System (ADS)

Second harmonic imaging is currently accepted as the standard in commercial echographic systems. A new imaging technique, coined as superharmonic imaging (SHI), combines the third till the fifth harmonics, arising during nonlinear sound propagation. It could further enhance the resolution and quality of echographic images. To meet the bandwidth requirement for SHI a dedicated phased array has been developed: a low frequency subarray, intended for transmission, interleaved with a high frequency subarray, used in reception. As the bandwidth of the elements is limited, the spectral gaps in between the harmonics cause multiple (ghost) reflection artifacts. A dual-pulse frequency compounding method aims at suppressing those artifacts at a price of a reduced frame rate. In this study we explore a possibility of performing frequency compounding within a single transmission. The traditional frequency compounding method suppresses the ripples by consecutively emitting two short Gaussian bursts with a slightly different center frequency. In the newly proposed method, the transmit aperture is divided into two parts: the first half is used to send a pulse at the lower center frequency, while the other half simultaneously transmits at a slightly higher center frequency. The suitability of the protocol for medical imaging applications in terms of the steering capabilities was performed in a simulation study with INCS and the hydrophone measurements. Moreover, an experimental study was carried out to find the optimal parameters for the clinical imaging protocol. The latter was subsequently used to obtain the images of a tissue mimicking phantom containing strongly reflecting wires. Additionally, the images of a human heart in the parasternal projection were acquired. The scanning aperture with the developed protocol amounts to approximately 90°, which is sufficient to capture the cardiac structures in the standard anatomical projections. The theoretically estimated and experimentally measured grating lobe levels are equal to -28.3 dB and -35.9 dB, respectively. A considerable improvement in the axial resolution of the SHI component (0.73 mm) at -6 dB in comparison with the third harmonic (2.23 mm) was observed. A similar comparison in terms of the lateral resolution slightly favored the superharmonic component by 0.2 mm. Additionally, the images of the tissue mimicking phantom exhibited the absence of the multiple reflection artifacts. The in-vivo acquisition allows one to clearly observe the dynamic of the mitral valve leaflets. The new method is equally effective in eliminating the ripple artifacts associated with SHI as the dual-pulse technique, while the full frame rate is maintained.

Danilouchkine, M. G.; van Neer, P. L. M. J.; Verweij, M. D.; Matte, G. M.; Vletter, W. B.; van der Steen, A. F. W.; de Jong, N.

2013-07-01

355

Nonlinear terahertz superconducting plasmonics  

NASA Astrophysics Data System (ADS)

Nonlinear terahertz (THz) transmission through subwavelength hole array in superconducting niobium nitride (NbN) film is experimentally investigated using intense THz pulses. The good agreement between the measurement and numerical simulations indicates that the field strength dependent transmission mainly arises from the nonlinear properties of the superconducting film. Under weak THz pulses, the transmission peak can be tuned over a frequency range of 145 GHz which is attributed to the high kinetic inductance of 50 nm-thick NbN film. Utilizing the THz pump-THz probe spectroscopy, we study the dynamic process of transmission spectra and demonstrate that the transition time of such superconducting plasmonic device is within 5 ps.

Wu, Jingbo; Zhang, Caihong; Liang, Lanju; Jin, Biaobing; Kawayama, Iwao; Murakami, Hironaru; Kang, Lin; Xu, Weiwei; Wang, Huabing; Chen, Jian; Tonouchi, Masayoshi; Wu, Peiheng

2014-10-01

356

Terahertz detection and carbon nanotubes  

ScienceCinema

Researchers at Sandia National Laboratories, along with collaborators from Rice University and the Tokyo Institute of Technology, are developing new terahertz detectors based on carbon nanotubes that could lead to significant improvements in medical imaging, airport passenger screening, food inspection and other applications.

Leonard, Francois

2014-06-13

357

Terahertz detection and carbon nanotubes  

SciTech Connect

Researchers at Sandia National Laboratories, along with collaborators from Rice University and the Tokyo Institute of Technology, are developing new terahertz detectors based on carbon nanotubes that could lead to significant improvements in medical imaging, airport passenger screening, food inspection and other applications.

Leonard, Francois

2014-06-11

358

Optical pump-terahertz probe spectroscopy utilizing a cavity-dumped oscillator-driven terahertz spectrometer  

Microsoft Academic Search

A terahertz spectrometer capable of steady-state and time-resolved measurements over the 0.1-3.5-THz spectral region has been built. This spectrometer routinely produces and detects terahertz pulses that exhibit signal-to-noise ratios (SNRs) greater than 6000 in the time domain and a spectral noise door of magnitude 2.7×10-4. Hence, the spectrometer achieves nearly four decades of dynamic range in the frequency domain. Two

Bret N. Flanders; David C. Arnett; Norbert F. Scherer

1998-01-01

359

High-resolution broadband terahertz spectroscopy via electronic heterodyne detection of photonically generated terahertz frequency comb.  

PubMed

We report an alternative approach to the terahertz frequency-comb spectroscopy (TFCS) based on nonlinear mixing of a photonically generated terahertz pulse train with a continuous wave signal from an electronic synthesizer. A superlattice is used as a nonlinear mixer. Unlike the standard TFCS technique, this approach does not require a complex double-laser system but retains the advantages of TFCS-high spectral resolution and wide bandwidth. PMID:25360955

Pavelyev, D G; Skryl, A S; Bakunov, M I

2014-10-01

360

Greatly enhanced continuous-wave terahertz emission by nano-electrodes in a photoconductive photomixer  

NASA Astrophysics Data System (ADS)

An efficient, room-temperature-operation continuous-wave terahertz source will greatly benefit compact terahertz system development for high-resolution terahertz spectroscopy and imaging applications. Here, we report highly efficient continuous-wave terahertz emission using nanogap electrodes in a photoconductive antenna-based photomixer. The tip-to-tip nanogap electrode structure provides strong terahertz field enhancement and acts as a nano-antenna to radiate the terahertz wave generated in the active region of the photomixer. In addition, it provides good impedance-matching to the terahertz planar antenna and exhibits a lower RC time constant, allowing more efficient radiation, especially at the higher part of the terahertz spectrum. As a result, the output power of the photomixer with the new nanogap electrode structure in the active region is two orders of magnitude higher than for a photomixer with typical interdigitated electrodes. The terahertz emission bandwidth also increases by a factor of more than two.

Tanoto, H.; Teng, J. H.; Wu, Q. Y.; Sun, M.; Chen, Z. N.; Maier, S. A.; Wang, B.; Chum, C. C.; Si, G. Y.; Danner, A. J.; Chua, S. J.

2012-02-01

361

Approaching real-time terahertz imaging using photo-induced reconfigurable aperture arrays  

NASA Astrophysics Data System (ADS)

We report a technique using photo-induced coded-aperture arrays for potential real-time THz imaging at roomtemperature. The coded apertures (based on Hadamard coding) were implemented using programmable illumination on semi-insulating Silicon wafer by a commercial digital-light processing (DLP) projector. Initial imaging experiments were performed in the 500-750 GHz band using a WR-1.5 vector network analyzer (VNA) as the source and receiver. Over the entire band, each array pixel can be optically turned on and off with an average modulation depth of ~20 dB and ~35 dB, for ~4 cm2 and ~0.5 cm2 imaging areas respectively. The modulation speed is ~1.3 kHz using the current DLP system and data acquisition software. Prototype imaging demonstrations have shown that a 256-pixel image can be obtained in the order of 10 seconds using compressed sensing (CS), and this speed can be improved greatly for potential real-time or video-rate THz imaging. This photo-induced coded-aperture imaging (PI-CAI) technique has been successfully applied to characterize THz beams in quasi-optical systems and THz horn antennas.

Shams, Md. Itrat Bin; Jiang, Zhenguo; Rahman, Syed; Qayyum, Jubaid; Hesler, Jeffrey L.; Cheng, Li-Jing; Xing, Huili Grace; Fay, Patrick; Liu, Lei

2014-05-01

362

A Concealed Barcode Identification System Using Terahertz Time-domain Spectroscopy  

NASA Astrophysics Data System (ADS)

We present a concealed terahertz barcode/chipless tag to achieve remote identification through an obstructing material using terahertz radiation. We show scanned terahertz reflection spectral images of barcodes concealed by a thick obstacle. A concealed and double- side printed terahertz barcode structure is proposed, and we demonstrate that our design has better performance in definition than a single-side printed barcode using terahertz time-domain spectroscopy. This technique combines the benefits of a chipless tag to read encoded information covered by an optically opaque material with low cost and a simple fabrication process. Simulations are also described, along with an explanation of the principle of the terahertz barcode identification system.

Guan, Yu; Yamamoto, Manabu; Kitazawa, Toshiyuki; Tripathi, Saroj R.; Takeya, Kei; Kawase, Kodo

2015-03-01

363

Simulation of terahertz generation in corrugated plasma waveguides  

SciTech Connect

We simulate the response of a corrugated plasma channel to an ultrashort laser pulse in two dimensions with the goal of demonstrating the production of terahertz frequency electromagnetic modes. Corrugated channels support electromagnetic modes that have a Floquet-type dispersion relation and thus consist of a sum of spatial harmonics with subluminal phase velocities. This allows the possibility of phase matching between the ponderomotive potential associated with the laser pulse and the electromagnetic modes of the channel. Since the bandwidth of an ultrashort pulse includes terahertz frequencies, significant excitation of terahertz radiation is possible. Here we consider realistic density profiles to obtain predictions of the terahertz power output and mode structure for a channel with periodic boundary conditions. We then estimate pulse depletion effects from our simulation results. The fraction of laser energy converted to terahertz is independent of laser pulse energy in the linear regime, and we find it to be around 1%. Extrapolating to a pulse energy of 0.5 J gives a terahertz power output of 6 mJ with a pulse depletion length of less than 20 cm.

Pearson, Andrew J.; Palastro, John; Antonsen, Thomas M. [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States)

2011-05-15

364

Active terahertz metamaterials  

SciTech Connect

In this paper we present an overview of research in our group in terahertz (THz) metamaterials and their applications. We have developed a series of planar metamaterials operating at THz frequencies, all of which exhibit a strong resonant response. By incorporating natural materials, e.g. semiconductors, as the substrates or as critical regions of metamaterial elements, we are able to effectively control the metamaterial resonance by the application of external stimuli, e.g., photoexcitation and electrical bias. Such actively controllable metamaterials provide novel functionalities for solid-state device applications with unprecedented performance, such as THz spectroscopy, imaging, and many others.

Chen, Hou-tong [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory

2009-01-01

365

Features of plasma glow in low pressure terahertz gas discharge  

SciTech Connect

Investigations of the low pressure (1–100 Torr) gas discharge in the powerful (1 kW) quasi-optical terahertz (0.55 THz) wave beams were made. An intense afterglow was observed after the end of gyrotron terahertz radiation pulse. Afterglow duration significantly exceeded radiation pulse length (8 ?s). This phenomenon could be explained by the strong dependence of the collisional-radiative recombination rate (that is supposed to be the most likely mechanism of electron losses from the low pressure terahertz gas discharge) on electron temperature.

Bratman, V. L.; Golubev, S. V.; Izotov, I. V.; Kalynov, Yu. K.; Koldanov, V. A.; Razin, S. V. [Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod 603950 (Russian Federation)] [Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod 603950 (Russian Federation); Litvak, A. G.; Sidorov, A. V.; Skalyga, V. A.; Zorin, V. G. [Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod 603950 (Russian Federation) [Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod 603950 (Russian Federation); Lobachevsky State University of Nizhny Novgorod (UNN), 23 Gagarina st., 603950 Nizhny Novgorod (Russian Federation)

2013-12-15

366

Strong Enhancement of Terahertz Radiation from Laser Filaments in Air by a Static Electric Field  

Microsoft Academic Search

We observe a 3 order of magnitude enhancement of the terahertz energy radiated by a femtosecond pulse undergoing filamentation in air in the presence of a static electric field. Measurements of terahertz pulse duration, spectrum, polarization, and radiation pattern elucidate the physical processes responsible for this radiation. A theoretical model explains the results and predicts another 3 orders of magnitude

Aurélien Houard; Yi Liu; Bernard Prade; Vladimir T. Tikhonchuk; André Mysyrowicz

2008-01-01

367

Time-Delay Multiplexing of Two Beams in a Terahertz Imaging Radar  

Microsoft Academic Search

We demonstrate a time-delay multiplexing technique that doubles the frame rate of a 660-690-GHz imaging radar with minimal additional instrument complexity. This is done by simultaneously projecting two offset, orthogonally polarized radar beams generated and detected by a common source and receiver. Beam splitting and polarization rotation is accomplished with a custom designed waveguide hybrid coupler and twist. A relative

Nuria Llombart; Ken B. Cooper; Robert J. Dengler; Tomas Bryllert; Goutam Chattopadhyay; Peter H. Siegel

2010-01-01

368

Multichannel terahertz time-domain spectroscopy system at 1030 nm excitation wavelength.  

PubMed

We present Terahertz (THz) imaging with a 1D multichannel time-domain spectroscopy (TDS) system which operates with a photoconductive array of 15 detection channels excited by a 1030 nm femtosecond fiber laser. The emitter and detector are photoconductive antennas based on InGaAs/InAlAs multi-layer heterostructures (MLHS). We characterized the THz optics and the resolution of the system. The performance is demonstrated by the multichannel imaging of two samples. A simultaneous measurement of 15 THz pulses with a pixel pitch of 1 mm increases the measurement speed of the TDS system by factor 15. PMID:24921495

Brahm, Anika; Wilms, Annika; Dietz, Roman J B; Göbel, Thorsten; Schell, Martin; Notni, Gunther; Tünnermann, Andreas

2014-06-01

369

A new technology for terahertz imaging in breast cancer margin determination  

NASA Astrophysics Data System (ADS)

In this paper we describe a project for designing, developing and translating a THz imaging device for monitoring margins from extracted tissue during surgical breast cancer conservation procedures. In this application, the reflective and transmission properties of extracted tissue are monitored, in near real-time using a fine-beam THz signal which is sensitive to the presence of liquid and bound water content. In this way, it is intended that the extracted tissue will be studied in the operating theatre to determine during surgery, whether or not the region of malignant tissue has been fully excised from the patient. In the early stages of this project, we are determining to what degree an existing THz system at the University of Massachusetts (UMass) in Amherst is able to differentiate between breast carcinoma, normal fibroglandular and adipose tissues. This is achieved through close collaboration with a surgical and radiological team at the UMass-Worcester medical school and involves post-surgical recovered tissues. As part of this work, we are describing the system, measurement methodology, and first results that were obtained to calibrate the imaging system.

Yngvesson, Sigfrid; St. Peter, Benjamin; Siqueira, Paul; Kelly, Patrick; Glick, Stephen; Karellas, Andrew

2011-03-01

370

Application of laser pulse stretching scheme for efficiently delivering laser energy in photoacoustic imaging.  

PubMed

High-energy and short-duration laser pulses are desirable to improve the photoacoustic image quality when imaging deeply seated lesions. In many clinical applications, the high-energy pulses are coupled to tissue using optical fibers. These pulses can damage fibers if the damage threshold is exceeded. While keeping the total energy under the Food and Drug Administration limit for avoiding tissue damage, it is necessary to reduce the peak intensity and increase the pulse duration for minimizing fiber damage and delivering sufficient light for imaging. We use laser-pulse-stretching to address this problem. An initial 17-ns pulse was stretched to 27 and 37 ns by a ring-cavity laser-pulse-stretching system. The peak power of the 37-ns stretched pulse reduced to 42% of the original, while the fiber damage threshold was increased by 1.5-fold. Three ultrasound transducers centered at 1.3-, 3.5-, and 6-MHz frequencies were simulated, and the results showed that the photoacoustic signal of a 0.5-mm-diameter target obtained with 37-ns pulse was about 98, 91, and 80%, respectively, using the same energy as the 17-ns pulse. Simulations were validated using a broadband hydrophone. Quantitative comparisons of photoacoustic images obtained with three corresponding transducers showed that the image quality was not affected by stretching the pulse. PMID:22734748

Wang, Tianheng; Kumavor, Patrick D; Zhu, Quing

2012-06-01

371

Application of laser pulse stretching scheme for efficiently delivering laser energy in photoacoustic imaging  

NASA Astrophysics Data System (ADS)

High-energy and short-duration laser pulses are desirable to improve the photoacoustic image quality when imaging deeply seated lesions. In many clinical applications, the high-energy pulses are coupled to tissue using optical fibers. These pulses can damage fibers if the damage threshold is exceeded. While keeping the total energy under the Food and Drug Administration limit for avoiding tissue damage, it is necessary to reduce the peak intensity and increase the pulse duration for minimizing fiber damage and delivering sufficient light for imaging. We use laser-pulse-stretching to address this problem. An initial 17-ns pulse was stretched to 27 and 37 ns by a ring-cavity laser-pulse-stretching system. The peak power of the 37-ns stretched pulse reduced to 42% of the original, while the fiber damage threshold was increased by 1.5-fold. Three ultrasound transducers centered at 1.3-, 3.5-, and 6-MHz frequencies were simulated, and the results showed that the photoacoustic signal of a 0.5-mm-diameter target obtained with 37-ns pulse was about 98, 91, and 80%, respectively, using the same energy as the 17-ns pulse. Simulations were validated using a broadband hydrophone. Quantitative comparisons of photoacoustic images obtained with three corresponding transducers showed that the image quality was not affected by stretching the pulse.

Wang, Tianheng; Kumavor, Patrick D.; Zhu, Quing

2012-06-01

372

Real-time terahertz wave imaging by nonlinear optical frequency up-conversion in a 4-dimethylamino-N'-methyl-4'-stilbazolium tosylate crystal  

NASA Astrophysics Data System (ADS)

Real-time terahertz (THz) wave imaging has wide applications in areas such as security, industry, biology, medicine, pharmacy, and arts. In this letter, we report on real-time room-temperature THz imaging by nonlinear optical frequency up-conversion in organic 4-dimethylamino-N'-methyl-4'-stilbazolium tosylate crystal. The active projection-imaging system consisted of (1) THz wave generation, (2) THz-near-infrared hybrid optics, (3) THz wave up-conversion, and (4) an InGaAs camera working at 60 frames per second. The pumping laser system consisted of two optical parametric oscillators pumped by a nano-second frequency-doubled Nd:YAG laser. THz-wave images of handmade samples at 19.3 THz were taken, and videos of a sample moving and a ruler stuck with a black polyethylene film moving were supplied online to show real-time ability. Thanks to the high speed and high responsivity of this technology, real-time THz imaging with a higher signal-to-noise ratio than a commercially available THz micro-bolometer camera was proven to be feasible. By changing the phase-matching condition, i.e., by changing the wavelength of the pumping laser, we suggest THz imaging with a narrow THz frequency band of interest in a wide range from approximately 2 to 30 THz is possible.

Fan, Shuzhen; Qi, Feng; Notake, Takashi; Nawata, Kouji; Matsukawa, Takeshi; Takida, Yuma; Minamide, Hiroaki

2014-03-01

373

A Framework to Simulate and Improve Terahertz Quantum Well  

E-print Network

for terahertz radiations. In fact, medical imaging, homeland security screening, very high-speed wireless of the photocurrent is depending on the intensity of the radiation received by the device. The device active region of terahertz radiations to ensure market penetration with practicable civil applications. In that regard, we

Anderson, Charles H.

374

Plasma Imaging and Spectroscopy Diagnostics Developed on 100500-kA Pulsed Power Devices  

E-print Network

Plasma Imaging and Spectroscopy Diagnostics Developed on 100­500-kA Pulsed Power Devices DANIEL B discuss the development of high-resolution plasma imaging and spectroscopy diagnostics for the soft X-ray and ultraviolet en- ergy ranges developed and used on 100­500 kA pulsed power facil- ities. Requiring just a few

375

Pulse  

MedlinePLUS

... the pulse rate can help determine if the patient's heart is pumping. Pulse measurement has other uses as well. During or immediately after exercise, the pulse rate gives information about your fitness ...

376

Applying laser pulse stretching technique on photoacoustic imaging for efficiently delivering laser energy  

NASA Astrophysics Data System (ADS)

High-energy and short-duration outputs from lasers are desirable to improve the photoacoustic image quality when imaging deeply-seated lesions. In many clinical applications, optical fibers are used to couple the high-energy laser pulse to tissue. These high peak intensity pulses can damage an optical fiber input face if the damage threshold is exceeded. It is necessary to reduce the peak intensity to minimize the fiber damage and to delivery sufficient light for imaging. In this paper, a laser-pulse-stretching technique is introduced to reduce the peak intensity of laser pulses. To demonstrate the technique, an initial 17ns pulse was stretched to 37ns by a ring-cavity laser-pulse-stretching system, and the laser peak power reduced to 42%. The stretched pulse increased the fiber damage threshold by 1.5-fold. Three ultrasound transducers centered at 1.3MHz, 3.5MHz, 6MHz frequencies were simulated and the results showed that the photoacoustic signal of 0.5mm-diameter target obtained with 37ns pulse was about 98%, 91% and 80% respectively using the same energy as with the 17ns pulse. Simulations were validated using a broadband hydrophone. Quantitative comparisons of photoacoustic images obtained with three corresponding ultrasound transducers showed that the image quality was not affected by stretching the pulse.

Wang, Tianheng; Kumavor, Patrick D.; Zhu, Quing

2012-02-01

377

Characterization of burn injuries using terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

The accuracy rates of the clinical assessment techniques used in grading burn injuries remain significantly low for partial thickness burns. In this paper, we present experimental results from terahertz characterization of 2nd and 3rd degree burn wounds induced on a rat model. Reflection measurements were obtained from the surface of both burned and normal skin using pulsed terahertz spectroscopy. Signal processing techniques are described for interpretation of the acquired terahertz waveform and differentiation of burn wounds. Furthermore, the progression of burn injuries is shown by comparison between acute characterization and 72-hours survival studies. While the water content of healthy and desiccated skin has been considered as a source of terahertz signal contrast, it is demonstrated that other biological effects such as formation of post-burn interstitial edema as well as the density of the discrete scattering structures in the skin (such as hair follicles, sweat glands, etc.) play a significant role in the terahertz response of the burn wounds.

Arbab, M. Hassan; Dickey, Trevor C.; Winebrenner, Dale P.; Chen, Antao; Mourad, Pierre D.

2011-03-01

378

Polarization dependent terahertz generation efficiency by optical rectification in LiNbO3  

NASA Astrophysics Data System (ADS)

Optical rectification of laser pulses in LiNbO3 by tilted-pulse-front pumping (TPFP) is a powerful way to generate terahertz(THz) pulses. However, comprehensive theoretical analysis is still lack. In this work, we first established and presented a detailed theoretical model for TPFP scheme, which then was used to analyze the pump beam polarization dependent terahertz pulses generated by this scheme. The results indicate that one can change the polarization state of the terahertz pulse by changing the pump beam polarization. A scheme using tilted-pulse-front pumping was also set up, and the generated terahertz pulses have maximal conversion efficiency when the pump beam electric field vector is parallel to the crystal axis, which is consistent with theoretical model.

Meng, Kun; Zhong, Sen-Cheng; Zhu, Li-Guo; Liu, Qiao; Li, Ze-Ren

2015-01-01

379

Terahertz metamaterials  

NASA Astrophysics Data System (ADS)

In this paper we present our recent developments in terahertz (THz) metamaterials and devices. Planar THz metamaterials and their complementary structures fabricated on suitable substrates have shown electric resonant response, which causes the band-pass or band-stop property in THz transmission and reflection. The operational frequency can be further tuned up to 20% upon photoexcitation of an integrated semiconductor region in the split-ring resonators as the metamaterial elements. On the other hand, the use of semiconductors as metamaterial substrates enables dynamical control of metamaterial resonances through photoexcitation, and reducing the substrate carrier lifetime further enables an ultrafast switching recovery. The metamaterial resonances can also be actively controlled by application of a voltage bias when they are fabricated on semiconductor substrates with appropriate doping concentration and thickness. Using this electrically driven approach, THz modulation depth up to 80% and modulation speed of 2 MHz at room temperature have been demonstrated, which suggests practical THz applications.

Chen, Hou-Tong; O'Hara, John F.; Azad, Abul K.; Padilla, Willie J.; Averitt, Richard D.; Taylor, Antoinette J.

2009-02-01

380

Terahertz metamaterials  

SciTech Connect

In this paper we present our recent developments in terahertz (THz) metamaterials and devices. Planar THz metamaterials and their complementary structures fabricated on suitable substrates have shown electric resonant response, which causes the band-pass or band-stop property in THz transmission and reflection. The operational frequency can be further tuned up to 20% upon photoexcitation of an integrated semiconductor region in the splitring resonators as the metamaterial elements. On the other hand, the use of semiconductors as metamaterial substrates enables dynamical control of metamaterial resonances through photoexcitation, and reducing the substrate carrier lifetime further enables an ultrafast switching recovery. The metamaterial resonances can also be actively controlled by application of a voltage bias when they are fabricated on semiconductor substrates with appropriate doping concentration and thickness. Using this electrically driven approach, THz modulation depth up to 80% and modulation speed of 2 MHz at room temperature have been demonstrated, which suggests practical THz applications.

Chen, Hou-tong [Los Alamos National Laboratory; Taylor, Antoineete J [Los Alamos National Laboratory; Azad, Abul K [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory

2009-01-01

381

Noncontact imaging photoplethysmography to effectively access pulse rate variability  

NASA Astrophysics Data System (ADS)

Noncontact imaging photoplethysmography (PPG) can provide physiological assessment at various anatomical locations with no discomfort to the patient. However, most previous imaging PPG (iPPG) systems have been limited by a low sample frequency, which restricts their use clinically, for instance, in the assessment of pulse rate variability (PRV). In the present study, plethysmographic signals are remotely captured via an iPPG system at a rate of 200 fps. The physiological parameters (i.e., heart and respiration rate and PRV) derived from the iPPG datasets yield statistically comparable results to those acquired using a contact PPG sensor, the gold standard. More importantly, we present evidence that the negative influence of initial low sample frequency could be compensated via interpolation to improve the time domain resolution. We thereby provide further strong support for the low-cost webcam-based iPPG technique and, importantly, open up a new avenue for effective noncontact assessment of multiple physiological parameters, with potential applications in the evaluation of cardiac autonomic activity and remote sensing of vital physiological signs.

Sun, Yu; Hu, Sijung; Azorin-Peris, Vicente; Kalawsky, Roy; Greenwald, Stephen

2013-06-01

382

Incoherent optical differential pulse code modulation (ODPCM) technique for image information compression  

Microsoft Academic Search

The basic principle of using an incoherent optical system to simulate the digital optical differential pulse code modulation (ODPCM) for image compression and the calculation of image compression ratio. The design and development of the optical sampler and the optical interpolator are demonstrated. Some preliminary experimental results on the transmitted, compressed image and the received, restored image of a binary

Ning Lin; Changfa Wu; Jianxiang Ye

1988-01-01

383

Place Pulse : measuring the collaborative image of the city  

E-print Network

This thesis presents Place Pulse, a tool capable of conducting large crowdsourced visual preference surveys. The data collected with Place Pulse was used to create quantitative measures of the perceptions people hold of ...

Salesses, Mark Philip

2012-01-01

384

Imaging the Cardiovascular Pulse Dept. of Computer Sc.  

E-print Network

's cardiac pulse. The golden standard for pulse measurement is Electro-Cardio- Graphy (ECG) [1]. ECG records present a brief introduction to the pulse physiology in section 2. In section 3, we describe how to select and track the line-shaped region of interest on the tissue imagery. In section 4, we describe a novel method

385

Quantitative real-time pulsed Schlieren imaging of ultrasonic waves  

Microsoft Academic Search

A pulsed Schlieren system based on Raman-Nath scattering by ultrasonic waves in water is described. High powered, monochromatic infrared pulsed light is used in conjunction with axial optics and a video camera to visualize the acoustic field. Projection beam profiles in any plane parallel or orthogonal to the direction of acoustic propagation are demonstrated. Controlled delay between acoustic pulse and

A. Hanafy; C. I. Zanelli

1991-01-01

386

Communication: SHG-detected circular dichroism imaging using orthogonal phase-locked laser pulses.  

PubMed

We demonstrate a novel method for second harmonic generation-detected circular dichroism (CD) imaging based on the use of phase-locked, temporally delayed femtosecond laser pulses. The polarization state of the fundamental wave was controllably changed over 2? rad by using a birefringent delay line, which provided attosecond inter-pulse delays for orthogonal phase-locked replicas; the achievable phase stability was 14 as. By introducing either a positive or negative delay of ?667 as, we induced a ±?/2 phase shift between the orthogonally polarized pulses, resulting in left circularly polarized or right circularly polarized light. CD imaging performance using the pulse sequence was compared to results obtained for plasmonic nanoantennas using a rotating quarter-wave plate. The pulse sequence is expected to simplify polarization-resolved optical imaging by reducing experimental artifacts and decreasing image acquisition times. This method can be easily extended to other CD spectroscopy measurements. PMID:25903859

Jarrett, Jeremy W; Liu, Xiaoying; Nealey, Paul F; Vaia, Richard A; Cerullo, Giulio; Knappenberger, Kenneth L

2015-04-21

387

Passive Euro-American terahertz camera (PEAT-CAM): passive indoor THz imaging at video rates for security applications  

NASA Astrophysics Data System (ADS)

The objective of this program is to demonstrate a system capable of passive indoors detection and identification of concealed threat items hidden underneath the clothing of non-cooperative subjects from a stand-off distance of several meters. To meet this difficult task, we are constructing an imaging system utilising superconducting ultrawideband antenna-coupled microbolometers, coupled to innovative room temperature read-out electronics, and operated within a cryogen-free pulse tube refrigerator. Previously, we have demonstrated that these devices are capable of a Noise Equivalent Temperature Difference (NETD) of 125 mK over a pre-detection bandwidth from 0.2-1 THz using a post-detection integration time of 30 ms. Further improvements on our devices are reducing this number to a few tens of mK. Such an exquisite sensitivity is necessary in order to achieve the undoubtedly stringent requirements for low false positive alarm rate combined with high probability of detection dictated by the application. Our technological approach allows for excellent per frame NETD (objective 0.5 K or below at 30 Hz frame rate), and is also amenable to multispectral (colour) imagery that enhances the discrimination of innocuous objects against real threats. In the paper we present results obtained with an 8-pixel subarray from our linear array of 128 pixels constructed using a modular approach. Two-dimensional imaging will be achieved by the use of conical scanning.

Luukanen, Arttu; Grönberg, Leif; Helistö, Panu; Penttilä, Jari S.; Seppä, Heikki; Sipola, Hannu; Dietlein, Charles R.; Grossman, Erich N.

2007-04-01

388

Propagation through terahertz waveguides with photonic crystal boundaries  

NASA Astrophysics Data System (ADS)

Scope and method of study. The research presented in this dissertation investigates the integration of photonic crystal lattices into parallel plate waveguides at terahertz frequencies. The experimental data was obtained by measuring the terahertz pulses through the photonic crystal waveguides in a standard terahertz time-domain spectroscopy system. The terahertz pulses were generated and detected via optoelectronic means utilizing lithographically fabricated transmitting and receiving antennas and a femtosecond laser. Findings and conclusions. The main findings of this research are that metallic photonic crystal waveguides are a potential two-dimensional interconnect, and photonic waveguides act as an excellent guided-wave filter. The photonic crystal waveguides demonstrate attenuation approximating that of a comparable metallic waveguide, and demonstrate the capability to integrate guided-wave components with a high level of performance. The photonic waveguides act as a powerful filter, and the mode-matching theory allows complete design control over the waveguides.

Bingham, Adam L.

389

High Dynamic Velocity Range Particle Image Velocimetry Using Multiple Pulse Separation Imaging  

PubMed Central

The dynamic velocity range of particle image velocimetry (PIV) is determined by the maximum and minimum resolvable particle displacement. Various techniques have extended the dynamic range, however flows with a wide velocity range (e.g., impinging jets) still challenge PIV algorithms. A new technique is presented to increase the dynamic velocity range by over an order of magnitude. The multiple pulse separation (MPS) technique (i) records series of double-frame exposures with different pulse separations, (ii) processes the fields using conventional multi-grid algorithms, and (iii) yields a composite velocity field with a locally optimized pulse separation. A robust criterion determines the local optimum pulse separation, accounting for correlation strength and measurement uncertainty. Validation experiments are performed in an impinging jet flow, using laser-Doppler velocimetry as reference measurement. The precision of mean flow and turbulence quantities is significantly improved compared to conventional PIV, due to the increase in dynamic range. In a wide range of applications, MPS PIV is a robust approach to increase the dynamic velocity range without restricting the vector evaluation methods. PMID:22346564

Persoons, Tim; O’Donovan, Tadhg S.

2011-01-01

390

Resonant terahertz transmission in subwavelength metallic hole arrays of sub-skin-depth thickness  

Microsoft Academic Search

We study surface-plasmon-enhanced terahertz transmission through subwavelength metallic hole arrays of sub-skin-depth thickness. Dynamic evolution of surface-plasmon resonance in terms of array thickness is characterized by use of terahertz time-domain spectroscopy in the frequency range 0.1 4.5 THz. A critical thickness of lead array film is observed, above which surface-plasmon coupling of terahertz pulses begins and is enhanced rapidly as

Abul K. Azad; Weili Zhang

2005-01-01

391

64 ?W pulsed terahertz emission from growth optimized InGaAs/InAlAs heterostructures with separated photoconductive and trapping regions  

SciTech Connect

We present results on optimized growth temperatures and layer structure design of high mobility photoconductive Terahertz (THz) emitters based on molecular beam epitaxy grown In{sub 0.53}Ga{sub 0.47}As/In{sub 0.52}Al{sub 0.48}As multilayer heterostructures (MLHS). The photoconductive antennas made of these MLHS are evaluated as THz emitters in a THz time domain spectrometer and with a Golay cell. We measured a THz bandwidth in excess of 4 THz and average THz powers of up to 64 ?W corresponding to an optical power-to-THz power conversion efficiency of up to 2 × 10{sup ?3}.

Dietz, Roman J. B.; Globisch, Björn; Stanze, Dennis; Roehle, Helmut; Göbel, Thorsten; Schell, Martin [Fraunhofer Institute for Telecommunications, Heinrich-Hertz-Institute, Einsteinufer 37, 10587 Berlin (Germany)] [Fraunhofer Institute for Telecommunications, Heinrich-Hertz-Institute, Einsteinufer 37, 10587 Berlin (Germany); Gerhard, Marina; Velauthapillai, Ajanthkrishna; Koch, Martin [Department of Physics, Philipps-Universität Marburg, Renthof 5, 35032 Marburg (Germany)] [Department of Physics, Philipps-Universität Marburg, Renthof 5, 35032 Marburg (Germany)

2013-08-05

392

Terahertz emission from a two-color plasma filament in a slot waveguide  

SciTech Connect

Terahertz emission in forward direction from a long two-color filament placed in the center of a slot waveguide is reported. The waveguide improves the collection and imaging of the generated THz radiation. By tuning the plate separation and position of the waveguide along the filament axis, the emitted mode can be matched to the collection optics. We achieved an increase of the detected electric field by 40% and of the THz pulse energy by four times compared to the case without waveguide.

Dietze, D.; Unterrainer, K.; Darmo, J. [Photonics Institute, Vienna University of Technology, Gusshausstr. 27-29/E387, A-1040 Vienna (Austria)

2012-02-27

393

MREIT conductivity imaging of canine head using multi-echo pulse sequence  

NASA Astrophysics Data System (ADS)

In magnetic resonance electrical impedance tomography (MREIT), we measure induced magnetic flux densities subject to multiple injection currents to reconstruct cross-sectional conductivity images. Spin echo pulse sequence has been widely used in MREIT and produce postmortem and in vivo conductivity images of animal and human subjects. The image quality depends on the SNR of the measured magnetic flux density image. In order to reduce the scan time and current amplitude while keeping the image quality, we have developed a multi-echo pulse sequence for MREIT. In this study, we show results of canine head MREIT imaging experiments using the multi-echo pulse sequence. Compared to the injection current nonlinear encoding (ICNE) pulse sequence, it provides a higher SNR of MR magnitude images by combining multiple echo signals. Noise in measured magnetic flux density data is significantly reduced due to an increased current injection time over multiple echo signals. These allow us to significantly decrease the total scan time. Reconstructed conductivity images of a canine head show enhanced conductivity contrast between gray and white matter using the multi-echo pulse sequence. In our future work, we will focus on in vivo human and disease model animal experiments using the new MREIT pulse sequence.

Han, Y. Q.; Meng, Z. J.; Jeong, W. C.; Kim, Y. T.; Minhas, A. S.; Kim, H. J.; Nam, H. S.; Kwon, O.; Woo, E. J.

2010-04-01

394

Double predictor differential pulse code modulation algorithm for image data compression  

Microsoft Academic Search

A new algorithm for designing differential pulse code modulation (DPCM) systems is presented for image data compression. When transmitting images over noiseless channels, the distortion between the original and reconstructed images results primarily from quantization noise. This is true when optimal predictor structures are employed. The quantization error becomes severe at low bit rates. This is because of the large

David G. Daut; Dongming Zhao; Jia-Chyi Wu

1993-01-01

395

All optical histology : Serial ablation and multiphoton imaging of neuronal tissue with femtosecond laser pulses  

E-print Network

All optical histology : Serial ablation and multiphoton imaging of neuronal tissue with femtosecond pulses to serially image and ablate neuronal tissue. This allows histological imaging throughout techniques in histology involve the manual slicing of frozen or embedded tissue, which is labor intensive

Kleinfeld, David

396

Image Fusion Based on Nonsubsampled Contourlet Transform and Pulse Coupled Neural Networks  

Microsoft Academic Search

In order to overcome the lacking of Shift- invariance in Contourlet Transform, enable the image fusion to be in accord with human vision properties, Nonsubsampled Contourlet Transform (NSCT) and Pulse Coupled Neural Networks(PCNN) were used jointly in image fusion algorithms. Original images were decomposed to get the coefficients of low frequency subbands and high frequency subbands. The coefficients of low

Liu Fu; Liao Yifan; Liang Xin

2011-01-01

397

Design, fabrication, and experimental characterization of plasmonic photoconductive terahertz emitters.  

PubMed

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on photoconduction, which has been one of the most commonly used techniques for terahertz generation (1-8). Terahertz generation in a photoconductive emitter is achieved by pumping an ultrafast photoconductor with a pulsed or heterodyned laser illumination. The induced photocurrent, which follows the envelope of the pump laser, is routed to a terahertz radiating antenna connected to the photoconductor contact electrodes to generate terahertz radiation. Although the quantum efficiency of a photoconductive emitter can theoretically reach 100%, the relatively long transport path lengths of photo-generated carriers to the contact electrodes of conventional photoconductors have severely limited their quantum efficiency. Additionally, the carrier screening effect and thermal breakdown strictly limit the maximum output power of conventional photoconductive terahertz sources. To address the quantum efficiency limitations of conventional photoconductive terahertz emitters, we have developed a new photoconductive emitter concept which incorporates a plasmonic contact electrode configuration to offer high quantum-efficiency and ultrafast operation simultaneously. By using nano-scale plasmonic contact electrodes, we significantly reduce the average photo-generated carrier transport path to photoconductor contact electrodes compared to conventional photoconductors (9). Our method also allows increasing photoconductor active area without a considerable increase in the capacitive loading to the antenna, boosting the maximum terahertz radiation power by preventing the carrier screening effect and thermal breakdown at high optical pump powers. By incorporating plasmonic contact electrodes, we demonstrate enhancing the optical-to-terahertz power conversion efficiency of a conventional photoconductive terahertz emitter by a factor of 50 (10). PMID:23892574

Berry, Christopher; Hashemi, Mohammad Reza; Unlu, Mehmet; Jarrahi, Mona

2013-01-01

398

CMOS Architecture of Synchronous Pulse-Coupled Neural Network and Its Application to Image Processing  

E-print Network

first, then its application to image processing and the synchronization effect between neighboring-propagation velocity, (iv) pulse-shaping action during its propagation through the neuristor line, and (v) annihilation reactions, with a given external stimulus, by generating a stream of electrical pulse waves. In this case

Wilamowski, Bogdan Maciej

399

Development of tunable terahertz quantum cascade wire lasers  

E-print Network

For a long time, terahertz (THz) radiation has been of great interest to scientific community because of its spectroscopic and imaging applications based on its unique properties, such as the capabilities to penetrate many ...

Qin, Qi, Ph. D. Massachusetts Institute of Technology

2012-01-01

400

FLASH imaging. Rapid NMR imaging using low flip-angle pulses  

NASA Astrophysics Data System (ADS)

A new method for rapid NMR imaging dubbed FLASH ( fast low-angle shot) imaging is described which, for example, allows measuring times of the order of 1 s (64 × 128 pixel resolution) or 6 s (256 × 256 pixels). The technique takes advantage of excitation pulses with small flip angles eliminating the need of waiting periods in between successive experiments. It is based on the acquisition of the free induction decay in the form of a gradient echo generated by reversal of the read gradient. The entire imaging time is only given by the number of projections desired times the duration of slice selection and data acquisition. The method results in about a 100-fold reduction in measuring time without sacrificing spatial resolution. Further advantages are an optimized signal-to-noise ratio, the applicability of commercial gradient systems, and the deposition of extremely low rf power. FLASH imaging is demonstrated on phantoms, animals, and human extremities using a 2.3 T 40 cm bore magnet system. 1H NMR images are obtained with variable relaxation time contrasts and without motional artifacts.

Haase, A.; Frahm, J.; Matthaei, D.; Hanicke, W.; Merboldt, K.-D.

401

Correlation chemical shift imaging with low-power adiabatic pulses and constant-density spiral trajectories  

E-print Network

In this work we introduce the concept of correlation chemical shift imaging (CCSI). Novel CCSI pulse sequences are demonstrated on clinical scanners for two-dimensional Correlation Spectroscopy (COSY) and Total Correlation ...

Andronesi, Ovidiu C.

402

Pulse Wave Imaging of Human Abdominal Aortas Jianwen Luo1  

E-print Network

, NY, USA JL2767@columbia.edu Abstract-- Vascular diseases (e.g., abdominal aortic aneurysm or, AAA on the mechanical properties of the aortic wall in vivo. Keywords-abdominal aortic aneurysm; pulse wave; pulse wave. Various vascular diseases including abdominal aortic aneurysms (AAAs) are known to change the tissue

Konofagou, Elisa E.

403

Broadband graphene terahertz modulators enabled by intraband transitions  

NASA Astrophysics Data System (ADS)

Terahertz technology promises myriad applications including imaging, spectroscopy and communications. However, one major bottleneck at present for advancing this field is the lack of efficient devices to manipulate the terahertz electromagnetic waves. Here we demonstrate that exceptionally efficient broadband modulation of terahertz waves at room temperature can be realized using graphene with extremely low intrinsic signal attenuation. We experimentally achieved more than 2.5 times superior modulation than prior broadband intensity modulators, which is also the first demonstrated graphene-based device enabled solely by intraband transitions. The unique advantages of graphene in comparison to conventional semiconductors are the ease of integration and the extraordinary transport properties of holes, which are as good as those of electrons owing to the symmetric conical band structure of graphene. Given recent progress in graphene-based terahertz emitters and detectors, graphene may offer some interesting solutions for terahertz technologies.

Sensale-Rodriguez, Berardi; Yan, Rusen; Kelly, Michelle M.; Fang, Tian; Tahy, Kristof; Hwang, Wan Sik; Jena, Debdeep; Liu, Lei; Xing, Huili Grace

2012-04-01

404

Broadband Terahertz Modulators based on MEMS-Reconfigurable Mesh Filters  

E-print Network

Despite the extensive progress in terahertz technology, existing terahertz modulators have not yet offered the modulation specifications required for high-performance terahertz imaging, spectroscopy, and communication systems. Here, we present a novel terahertz intensity modulation technique based on MEMS-reconfigurable double-layered mesh filters, which offers record-high modulation depths and modulation bandwidths, without a considerable compromise in modulation speed or modulation voltage through a fully integrated device configuration. The unique advantage of the presented modulation technique compared with the previously demonstrated terahertz modulation schemes based on tunable metamaterials is reconfiguring the device geometry, which enables radical changes in the device scattering parameters over a broad range of frequencies. Device geometry reconfiguration is made possible through integration of a double-layered mesh filter with an array of electrostatically-actuated MEMS switches. We experimentally ...

Unlu, Mehmet; Li, Shenglin; Yang, Shang-Hua; Hashemi, Mohammad R; Jarrahi, Mona

2013-01-01

405

Integrated heterodyne terahertz transceiver  

SciTech Connect

A heterodyne terahertz transceiver comprises a quantum cascade laser that is integrated on-chip with a Schottky diode mixer. A terahertz signal can be received by an antenna connected to the mixer, an end facet or sidewall of the laser, or through a separate active section that can amplify the incident signal. The quantum cascade laser couples terahertz local oscillator power to the Schottky diode to mix with the received terahertz signal to provide an intermediate frequency output signal. The fully integrated transceiver optimizes power efficiency, sensitivity, compactness, and reliability. The transceiver can be used in compact, fieldable systems covering a wide variety of deployable applications not possible with existing technology.

Wanke, Michael C. (Albuquerque, NM); Lee, Mark (Albuquerque, NM); Nordquist, Christopher D. (Albuquerque, NM); Cich, Michael J. (Albuquerque, NM)

2012-09-25

406

Integrated heterodyne terahertz transceiver  

DOEpatents

A heterodyne terahertz transceiver comprises a quantum cascade laser that is integrated on-chip with a Schottky diode mixer. An antenna connected to the Schottky diode receives a terahertz signal. The quantum cascade laser couples terahertz local oscillator power to the Schottky diode to mix with the received terahertz signal to provide an intermediate frequency output signal. The fully integrated transceiver optimizes power efficiency, sensitivity, compactness, and reliability. The transceiver can be used in compact, fieldable systems covering a wide variety of deployable applications not possible with existing technology.

Lee, Mark (Albuquerque, NM); Wanke, Michael C. (Albuquerque, NM)

2009-06-23

407

Development of a new pulsed source for photoacoustic imaging based on aperiodically poled lithium niobate.  

PubMed

We present the development of a source of deep-red radiation for photoacoustic imaging. This source, which is based on two cascaded wavelength conversion processes in aperiodically poled lithium niobate, emits 10 nanosecond pulses of over 500 µJ at 710 nm. Photoacoustic images were obtained from phantoms designed to mimic the optical and acoustic properties of oral tissue. Results indicate this device is a viable source of optical pulses for photoacoustic applications. PMID:24575341

Yankelevich, Diego; González, J E; Cudney, Roger S; Ríos, Luis A; Marcu, Laura

2014-02-01

408

GaSb homojunctions for far-infrared ,,terahertz... detection P. V. V. Jayaweera, S. G. Matsik, and A. G. U. Pereraa  

E-print Network

for the surging demand of high performance terahertz detectors in recent years. Charge transport properties3 terahertz imaging as a method of screening passengers for explosives at air- ports. For military

Perera, A. G. Unil

409

Techniques for introscopy of condense matter in terahertz spectral region  

Microsoft Academic Search

Feasibility study of the introscopy of solids and biological objects using high-power terahertz-free-electron laser radiation was performed. A complete set of quasi-optical elements (beam-splitters, windows, mirrors, zone plates and kinoform lens), detectors (bolometers, piroelectric detectors) and imagers (thermograph, luminescence quenching thermal image plate and thermosensitive visible-light interferometer) for the terahertz spectral region have been developed. Detection of hidden amino acids

V. S. Cherkassky; V. V. Gerasimov; G. M. Ivanov; B. A. Knyazev; G. N. Kulipanov; L. A. Lukyanchikov; L. A. Merzhievsky; N. A. Vinokurov

2007-01-01

410

Dynamic control of metamaterials at terahertz frequencies  

NASA Astrophysics Data System (ADS)

Progress in the field of metamaterials has started coming to a point where the field may finally begin to emerge as a viable solution to many electromagnetic challenges facing the community. No where is that more true then at terahertz frequencies where there lies an immense opportunity for growth. The development of mature technologies within this region of the electromagnetic spectrum would provide a valuable resource to become available for a multitude of applications. In order to achieve this, the necessary first steps of identifying viable materials and paths to integrate these with metamaterials will need to be completed. In this dissertation, we examine several different paths to achieve dynamic metamaterial electromagnetic response at terahertz frequencies, and demonstrate several paths to package these devices into imaging systems. In Chapter 1, we introduce the basic theory and design principles of metamaterials. We also describe the experimental techniques involved in the study of terahertz metamaterials. Chapter 2 presents a computational and experimental study investigating the integration of high electron mobility transistors with metamaterials allowing for high speed modulation of incident terahertz radiation. In Chapters 3 and 4, we investigate several different paths to create tunable terahertz metamaterial absorbers. Chapter 3 presents an investigation where we encapsulate a metametarial absorber unit cell with liquid crystals. We study both computationally and experimentally the tuning mechanism of the absorber as the liquid crystal refractive index is controlled as a function of the applied electric field strength and modulation frequency. In Chapter 4, we form a doped semiconducting metamaterial spatial light modulator with multi-color super-pixels composed of arrays of electronically controlled terahertz metamaterial absorbers. We computationally and experimentally study the independent tunability of each pixel in the spatial array and demonstrate high speed modulation. Chapter 5 introduces a multiplex imaging approach by using a terahertz spatial light modulator to enable terahertz imaging with a single pixel detector. We demonstrate the capability for high speed image acquisition, currently only limited by the commerical software used to reconfigure the spatial masks. We also configure the system to capture high fidelity images of varying complexity. In Chapter 6, we show how a metamaterial absorber can be implemented into a detector focal plane array for high sensitivity, low mutual coupling, and broad angle performance. Finally, we summarize in Chapter 7 the achievments of the research presented and highlight the direction of future work.

Shrekenhamer, David

411

A modulated pulse laser for underwater detection, ranging, imaging, and communications  

NASA Astrophysics Data System (ADS)

A new, modulated-pulse, technique is currently being investigated for underwater laser detection, ranging, imag- ing, and communications. This technique represents a unique marriage of pulsed and intensity modulated sources. For detection, ranging, and imaging, the source can be congured to transmit a variety of intensity modulated waveforms, from single-tone to pseudorandom code. The utility of such waveforms in turbid underwater envi- ronments in the presence of backscatter is investigated in this work. The modulated pulse laser may also nd utility in underwater laser communication links. In addition to exibility in modulation format additional variable parameters, such as macro-pulse width and macro-pulse repetition rate, provide a link designer with additional methods of optimizing links based on the bandwidth, power, range, etc. needed for the application. Initial laboratory experiments in simulated ocean waters are presented.

Cochenour, Brandon; Mullen, Linda; Muth, John

2012-06-01

412

Terahertz semiconductor-heterostructure laser  

NASA Astrophysics Data System (ADS)

Semiconductor devices have become indispensable for generating electromagnetic radiation in everyday applications. Visible and infrared diode lasers are at the core of information technology, and at the other end of the spectrum, microwave and radio-frequency emitters enable wireless communications. But the terahertz region (1-10THz 1THz = 1012Hz) between these ranges has remained largely underdeveloped, despite the identification of various possible applications-for example, chemical detection, astronomy and medical imaging. Progress in this area has been hampered by the lack of compact, low-consumption, solid-state terahertz sources. Here we report a monolithic terahertz injection laser that is based on interminiband transitions in the conduction band of a semiconductor (GaAs/AlGaAs) heterostructure. The prototype demonstrated emits a single mode at 4.4THz, and already shows high output powers of more than 2mW with low threshold current densities of about a few hundred Acm-2 up to 50K. These results are very promising for extending the present laser concept to continuous-wave and high-temperature operation, which would lead to implementation in practical photonic systems.

Köhler, Rüdeger; Tredicucci, Alessandro; Beltram, Fabio; Beere, Harvey E.; Linfield, Edmund H.; Davies, A. Giles; Ritchie, David A.; Iotti, Rita C.; Rossi, Fausto

2002-05-01

413

Application of Hilbert-Huang Transform for Improved Defect Detection in Terahertz NDE of Shuttle Tiles  

NASA Technical Reports Server (NTRS)

Terahertz NDE is being examined as a method to inspect the adhesive bond-line of Space Shuttle tiles for defects. Terahertz signals are generated and detected, using optical excitation of biased semiconductors with femtosecond laser pulses. Shuttle tile samples were manufactured with defects that included repair regions unbond regions, and other conditions that occur in Shuttle structures. These samples were inspected with a commercial terahertz NDE system that scanned a tile and generated a data set of RF signals. The signals were post processed to generate C-scan type images that are typically seen in ultrasonic NDE. To improve defect visualization the Hilbert-Huang Transform, a transform that decomposes a signal into oscillating components called intrinsic mode functions, was applied to test signals identified as being in and out of the defect regions and then on a complete data set. As expected with this transform, the results showed that the decomposed low-order modes correspond to signal noise while the high-order modes correspond to low frequency oscillations in the signal and mid-order modes correspond to local signal oscillations. The local oscillations compare well with various reflection interfaces and the defect locations in the original signal.

Anastasi, Robert F.; Madaras, Eric I.

2005-01-01

414

Terahertz Array Receivers with Integrated Antennas  

NASA Technical Reports Server (NTRS)

Highly sensitive terahertz heterodyne receivers have been mostly single-pixel. However, now there is a real need of multi-pixel array receivers at these frequencies driven by the science and instrument requirements. In this paper we explore various receiver font-end and antenna architectures for use in multi-pixel integrated arrays at terahertz frequencies. Development of wafer-level integrated terahertz receiver front-end by using advanced semiconductor fabrication technologies has progressed very well over the past few years. Novel stacking of micro-machined silicon wafers which allows for the 3-dimensional integration of various terahertz receiver components in extremely small packages has made it possible to design multi-pixel heterodyne arrays. One of the critical technologies to achieve fully integrated system is the antenna arrays compatible with the receiver array architecture. In this paper we explore different receiver and antenna architectures for multi-pixel heterodyne and direct detector arrays for various applications such as multi-pixel high resolution spectrometer and imaging radar at terahertz frequencies.

Chattopadhyay, Goutam; Llombart, Nuria; Lee, Choonsup; Jung, Cecile; Lin, Robert; Cooper, Ken B.; Reck, Theodore; Siles, Jose; Schlecht, Erich; Peralta, Alessandro; Thomas, Bertrand; Mehdi, Imran

2011-01-01

415

Perfect terahertz absorber using fishnet based metafilm  

SciTech Connect

We present a perfect terahertz (THz) absorber working for a broad-angle of incidence. The two fold symmetry of rectangular fishnet structure allows either complete absorption or mirror like reflection depending on the polarization of incident the THz beam. Metamaterials enable the ability to control the electromagnetic wave in a unique fashion by designing the permittivity or permeability of composite materials with desired values. Although the initial idea of metamaterials was to obtain a negative index medium, however, the evolution of metamaterials (MMs) offers a variety of practically applicable devices for controlling electromagnetic wave such as tunable filters, modulators, phase shifters, compact antenna, absorbers, etc. Terahertz regime, a crucial domain of the electromagnetic wave, is suffering from the scarcity of the efficient devices and might take the advantage of metamaterials. Here, we demonstrate design, fabrication, and characterization of a terahertz absorber based on a simple fishnet metallic film separated from a ground mirror plane by a dielectric spacer. Such absorbers are in particular important for bolometric terahertz detectors, high sensitivity imaging, and terahertz anechoic chambers. Recently, split-ring-resonators (SRR) have been employed for metamaterial-based absorbers at microwave and THz frequencies. The experimental demonstration reveals that such absorbers have absorptivity close to unity at resonance frequencies. However, the downside of these designs is that they all employ resonators of rather complicated shape with many fine parts and so they are not easy to fabricate and are sensitive to distortions.

Azad, Abul Kalam [Los Alamos National Laboratory; Shchegolkov, Dmitry Yu [Los Alamos National Laboratory; Chen, Houtong [Los Alamos National Laboratory; Taylor, Antoinette [Los Alamos National Laboratory; Smirnova, E I [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory

2009-01-01

416

Terahertz metamaterial devices  

Microsoft Academic Search

Compared to the neighboring infrared and microwave regions, the terahertz regime is still in need of fundamental technological advances. This derives, in part, from a paucity of naturally occurring materials with useful electronic or photonic properties at terahertz frequencies. This results in formidable challenges for creating the components needed for generating, detecting, and manipulating THz waves. Considering the promising applications

R. D. Averitt; W. J. Padilla; H. T. Chen; J. F. O'Hara; A. J. Taylor; C. Highstrete; M. Lee; J. M. O. Zide; S. R. Bank; A. C. Gossard

2007-01-01

417

Terahertz reflectarray as a polarizing beam splitter.  

PubMed

A reflectarray is designed and demonstrated experimentally for polarization-dependent beam splitting at 1 THz. This reflective component is composed of two sets of orthogonal strip dipoles arranged into interlaced triangular lattices over a ground plane. By varying the length and width of the dipoles a polarization-dependent localized phase change is achieved on reflection, allowing periodic subarrays with a desired progressive phase distribution. Both the simulated field distributions and the measurement results from a fabricated sample verify the validity of the proposed concept. The designed terahertz reflectarray can efficiently separate the two polarization components of a normally incident wave towards different predesigned directions of ±30°. Furthermore, the measured radiation patterns show excellent polarization purity, with a cross-polarization level below -27 dB. The designed reflectarray could be applied as a polarizing beam splitter for polarization-sensitive terahertz imaging or for emerging terahertz communications. PMID:24977867

Niu, Tiaoming; Withayachumnankul, Withawat; Upadhyay, Aditi; Gutruf, Philipp; Abbott, Derek; Bhaskaran, Madhu; Sriram, Sharath; Fumeaux, Christophe

2014-06-30

418

Resolution-enhanced polarization imaging with focused thermal pulses  

NASA Astrophysics Data System (ADS)

The non-destructive measurement of electrical polarization and space charge densities is a key technique in electret research. The principal idea behind these methods is a non-uniform deformation or heating, which gives rise to a short-circuit current that can be recorded in the time or frequency domain, and which carries information about the polarization depth profile. In recent years, thermal pulses and thermal waves have been used successfully to obtain three-dimensional polarization maps in polymeric electrets by scanning the beam of a pulsed or intensity-modulated cw laser across the sample surface. However, the polarization maps in these experiments were reconstructed using a relatively simplistic one-dimensional heat diffusion model that does not take into account lateral heat diffusion in the metal electrode. A two-dimensional "coupled neighbors" model was developed, where the current signal from several adjacent beam pointings along a scan line is coupled together, and a Monte Carlo method is used for the deconvolution. Simulations show that the new approach enhances the lateral resolution by a factor of 2-3×, since it avoids the information loss occurring when three-dimensional polarization measurements are processed with a one-dimensional thermal model. We also present an augmented, low-noise thermal-pulse instrument where thermal pulses are initiated by a pulse-modulated diode laser.

Aryal, Saurav; Mellinger, Axel

2013-10-01

419

Image coding by differential pulse code modulation and transform coding techniques, a comparative survey  

Microsoft Academic Search

Differential pulse code modulation (DPCM) and transform coding techniques for digital image transmission are described, and their relative advantages are compared. For high-quality video transmission, both DCPM and transform coding were found to need sufficient data protection. Initial experiments showed that in transform coding the decomposition of the image into blocks results in residual errors that do not impair picture

H.-J. Grallert; W. Tengler

1984-01-01

420

Laser-induced fluorescence images of NO distribution after needle-plane pulsed negative corona discharge  

Microsoft Academic Search

Images showing the spatial distribution of nitric oxide (NO) following propagation of a 30 ns pulsed, negative streamer between needle-plane electrodes, in 25 parts per million (ppm) NO seeded air, are reported. The images were generated using laser-induced fluorescence, and show uniform destruction of 10 ppm NO between the cathode and anode. This evidence shows that processes associated with the

Gregory J. Roth; Martin A. Gundersen

1999-01-01

421

All optical histology of brain tissue: Serial ablation and multiphoton imaging with femtosecond laser pulses  

E-print Network

All optical histology of brain tissue: Serial ablation and multiphoton imaging with femtosecond pulses for serial histology. Successive iterations of multiphoton imaging and ablation provide techniques in histology involve the manual slicing of frozen or embedded tissue, which is both labor

Kleinfeld, David

422

Imaging carrier and phonon transport in Si using ultrashort optical pulses  

SciTech Connect

A series of experiments have been conducted that microscopically image thermal diffusion and surface acoustic phonon propagation within a single crystallite of a polycrystalline Si sample. The experimental approach employs ultrashort optical pulses to generate an electron-hole plasma and a second probe pulse is used to image the evolution of the plasma. By decomposing the signal into a component that varies with delay time and a steady state component that varies with pump modulation frequency, the respective influence of carrier recombination and thermal diffusion are identified. Additionally, the coherent surface acoustic phonon component to the signal is imaged using a Sagnac interferometer to monitor optical phase.

David H. Hurley; O. B. Wright; O. Matsuda; B. E. McCandless; S. Shinde

2009-01-01

423

Terahertz transmission properties of metamaterials composed of split ring resonators and wires  

Microsoft Academic Search

We present the transmission properties of terahertz pulses through metamaterials composed of an array of split ring resonators and strip wires. We also present 3-D simulation results to support the experimentally observed transmission behavior.

A. K. Agrawal; Wenqi Zhu; Xiang Shou; Ajay Nahata

2006-01-01

424

Nonlinear terahertz spectroscopy of electronic and vibrational responses in condensed matter systems  

E-print Network

In this work, I describe experiments utilizing high-field terahertz (THz) pulses to initiate nonlinear responses in several classes of materials. We have developed several methods for interrogating the nonlinear THz response ...

Hwang, Harold Young

2012-01-01

425

Subsurface imaging for panel paintings inspection: A comparative study of the ultraviolet, the visible, the infrared and the terahertz spectra  

NASA Astrophysics Data System (ADS)

Infrared (IR) reflectography has been used for many years for the detection of underdrawings on panel paintings. Advances in the fields of IR sensors and optics have impelled the wide spread use of IR reflectography by several recognized Art Museums and specialized laboratories around the World. The transparency or opacity of a painting is the result of a complex combination of the optical properties of the painting pigments and the underdrawing material, as well as the type of illumination source and the sensor characteristics. For this reason, recent researches have been directed towards the study of multispectral approaches that could provide simultaneous and complementary information of an artwork. The present work relies on non-simultaneous multispectral inspection using a set of detectors covering from the ultraviolet to the terahertz spectra. It is observed that underdrawings contrast increases with wavelength up to 1700 nm and, then, gradually decreases. In addition, it is shown that IR thermography, i.e., temperature maps or thermograms, could be used simultaneously as an alternative technique for the detection of underdrawings besides the detection of subsurface defects.

Bendada, A.; Sfarra, S.; Ibarra-Castanedo, C.; Akhloufi, M.; Caumes, J.-P.; Pradere, C.; Batsale, J.-C.; Maldague, X.

2015-03-01

426

Acoustic investigation of microbubble response to medical imaging ultrasound pulses   

E-print Network

Ultrasound contrast agents have the ability to provide locally increased echogenicity, improving the sensitivity and specificity of images. Due to the unique interaction of microbubbles with the imaging ultrasound field, ...

Thomas, David H.

2010-01-01

427

Conversion of laser radiation to terahertz frequency waves in plasma  

SciTech Connect

A new scheme of terahertz radiation (T-ray) amplification based on four-wave coupling in plasma is proposed. Three stages of the amplification, namely, linear, initial nonlinear, and advanced nonlinear are analyzed. It is shown that (1) during the advanced nonlinear stage, a series of T-ray pulses with fixed energies is generated, and (2) the duration of each pulse decreases during the amplification, while the pulse amplitude grows. Possible parameters of the actual experimental apparatus are also suggested.

Yampolsky, N. A.; Fraiman, G. M. [Institute of Applied Physics, RAS, Nizhniy Novgorod, 603950 (Russian Federation)

2006-11-15

428

Terahertz Physics  

NASA Astrophysics Data System (ADS)

1. Introduction; Part I. Basics: 2. Oscillations; 3. Combining oscillations; 4. Light; 5. Matter; 6. Interaction of light and matter; Part II. Components: 7. Sources; 8. Optics; 9. Detectors; Part III. Applications: 10. Spectroscopy; 11. Imaging; Glossary; Appendices; Index.

Lewis, R. A.

2013-01-01

429

3D current source density imaging based on acoustoelectric effect: a simulation study using unipolar pulses  

PubMed Central

It is of importance to image electrical activity and properties of biological tissues. Recently hybrid imaging modality combing ultrasound scanning and source imaging through the acousto-electric (AE) effect has generated considerable interest. Such modality has the potential to provide high spatial resolution current density imaging by utilizing the pressure induced AE resistivity change confined at the ultrasound focus. In this study, we investigate a novel 3-dimensional (3D) ultrasound current source density imaging (UCSDI) approach using unipolar ultrasound pulses. Utilizing specially designed unipolar ultrasound pulses and by combining AE signals associated to the local resistivity changes at the focusing point, we are able to reconstruct the 3D current density distribution with the boundary voltage measurements obtained while performing a 3D ultrasound scan. We have shown in computer simulation that using the present method, it is feasible to image with high spatial resolution an arbitrary 3D current density distribution in an inhomogeneous conductive media. PMID:21628774

Yang, Renhuan; Li, Xu; Liu, Jun; He, Bin

2011-01-01

430

Spatial Terahertz Modulator  

NASA Astrophysics Data System (ADS)

Terahertz (THz) technology is a developing and promising candidate for biological imaging, security inspection and communications, due to the low photon energy, the high transparency and the broad band properties of the THz radiation. However, a major encountered bottleneck is lack of efficient devices to manipulate the THz wave, especially to modulate the THz wave front. A wave front modulator should allow the optical or electrical control of the spatial transmission (or reflection) of an input THz wave and hence the ability to encode the information in a wave front. Here we propose a spatial THz modulator (STM) to dynamically control the THz wave front with photo-generated carriers. A computer generated THz hologram is projected onto a silicon wafer by a conventional spatial light modulator (SLM). The corresponding photo-generated carrier spatial distribution will be induced, which forms an amplitude hologram to modulate the wave front of the input THz beam. Some special intensity patterns and vortex beams are generated by using this method. This all-optical controllable STM is structure free, high resolution and broadband. It is expected to be widely used in future THz imaging and communication systems.

Xie, Zhenwei; Wang, Xinke; Ye, Jiasheng; Feng, Shengfei; Sun, Wenfeng; Akalin, Tahsin; Zhang, Yan

2013-11-01

431

Terahertz remote sensing  

NASA Astrophysics Data System (ADS)

The subject of this article is implementation of terahertz remote sensing for detection and imaging of concealed objects from distances of several metres. Many materials used for packaging and clothing are partially transparent in the spectral range 0.1 - 10 THz. The transparency property can be utilised to detect objects concealed by the materials, which are often opaque in other spectral regions. This can be achieved by detecting the radiation from these objects through the use of an appropriate detector, which is sensitive at THz frequencies. The radiation from the concealed objects can be either self-emitted or reflected. The use of THz remote sensing is being pursued in IARD by both theoretical and practical approaches. The article contains a short review on the detectors, sources and components, which can be used for remote sensing systems operating at THz frequencies, and describes energy calculations and system design considerations. Characteristic and exemplar performance of the components, which are being used in IARD, is presented. The article then describes prototypes of a passive THz radiometer and an active THz system, which were built in IARD. Performance characteristics of both systems are described. The measurement results of the optical properties of various materials are presented as well as examples of images obtained by the active THz system.

Kellarev, Alexander; Sheffer, Dan

2011-05-01

432

Optimized Saturation Pulse Train for Human First-Pass Myocardial Perfusion Imaging at 7T  

PubMed Central

Purpose To investigate whether saturation using existing methods developed for 3T imaging is feasible for clinical perfusion imaging at 7T, and to propose a new design of saturation pulse train for first-pass myocardial perfusion imaging at 7T. Methods The new design of saturation pulse train consists of four hyperbolic-secant (HS8) radiofrequency pulses, whose peak amplitudes are optimized for a target range of static and transmit field variations and radiofrequency power deposition restrictions measured in the myocardium at 7T. The proposed method and existing methods were compared in simulation, phantom, and in vivo experiments. Results In healthy volunteer experiments without contrast agent, average saturation efficiency with the proposed method was 97.8%. This is superior to results from the three previously published methods at 86/95/90.8%. The first series of human first-pass myocardial perfusion images at 7T have been successfully acquired with the proposed method. Conclusion Existing saturation methods developed for 3T imaging are not optimal for perfusion imaging at 7T. The proposed new design of saturation pulse train can saturate effectively, and with this method first-pass myocardial perfusion imaging is feasible in humans at 7T. Magn Reson Med 73:1450–1456, 2015. © 2014 The Authors. Magnetic Resonance in Medicine Published by Wiley Periodicals, Inc. on behalf of International Society of Medicine in Resonance. PMID:24753130

Tao, Yuehui; Hess, Aaron T; Keith, Graeme A; Rodgers, Christopher T; Liu, Alexander; Francis, Jane M; Neubauer, Stefan; Robson, Matthew D

2015-01-01

433

Sub-harmonic periodic pulse train recovery from aperiodic optical pulse sequences through dispersion-induced temporal self-imaging.  

PubMed

Temporal self-imaging effects (TSIs) are observed when a periodic pulse train propagates through a first-order dispersive medium. Under specific dispersion conditions, either an exact, rate multiplied or rate divided image of the input signal is reproduced at the output. TSI possesses an interesting self-restoration capability even when acting over an aperiodic train of pulses. In this work, we investigate and demonstrate, for the first time to our knowledge, the capability of TSI to produce periodic sub-harmonic (rate-divided) pulse trains from aperiodic sequences. We use this inherent property of the TSI to implement a novel, simple and reconfigurable sub-harmonic optical clock recovery technique from RZ-OOK data signals. The proposed technique features a very simple realization, involving only temporal phase modulation and first-order dispersion and it allows one to set the repetition rate of the reconstructed clock signal in integer fractions (sub-harmonics) of the input bit rate. Proof-of-concept experiments are reported to validate the proposed technique and guidelines for optimization of the clock-recovery process are also outlined. PMID:25836212

Maram, Reza; Cortés, Luis Romero; Azaña, José

2015-02-01

434

Terahertz Computed Tomography of NASA Thermal Protection System Materials  

NASA Technical Reports Server (NTRS)

A terahertz axial computed tomography system has been developed that uses time domain measurements in order to form cross-sectional image slices and three-dimensional volume renderings of terahertz-transparent materials. The system can inspect samples as large as 0.0283 cubic meters (1 cubic foot) with no safety concerns as for x-ray computed tomography. In this study, the system is evaluated for its ability to detect and characterize flat bottom holes, drilled holes, and embedded voids in foam materials utilized as thermal protection on the external fuel tanks for the Space Shuttle. X-ray micro-computed tomography was also performed on the samples to compare against the terahertz computed tomography results and better define embedded voids. Limits of detectability based on depth and size for the samples used in this study are loosely defined. Image sharpness and morphology characterization ability for terahertz computed tomography are qualitatively described.

Roth, D. J.; Reyes-Rodriguez, S.; Zimdars, D. A.; Rauser, R. W.; Ussery, W. W.

2011-01-01

435

A New Algorithm of Multimodality Medical Image Fusion Based on Pulse-Coupled Neural Networks  

Microsoft Academic Search

\\u000a In this paper, a new multi-modality medical image fusion algorithm based on pulse-coupled neural networks (PCNN) is presented.\\u000a Firstly a multi-scale decomposition on each source image is performed, and then the PCNN is used to combine these decomposition\\u000a coefficients. Finally an inverse multi-scale transform is taken upon the new fused coefficients to reconstruct fusion image.\\u000a The new algorithm utilizes the

Wei Li; Xue-feng Zhu

2005-01-01

436

Suppression of tissue harmonics for pulse-inversion contrast imaging using time reversal.  

PubMed

Pulse-inversion (PI) sequences are sensitive to the nonlinear echoes from microbubbles allowing an improvement in the blood-to-tissue contrast. However, at larger mechanical indices, this contrast is reduced by harmonics produced during nonlinear propagation. A method for tissue harmonics cancellation exploiting time reversal is experimentally implemented using a 128-channel 12-bit emitter receiver. The probe calibration is performed by acquiring the nonlinear echo of a wire in water. These distorted pulses are time-reversed, optimized and used for the PI imaging of a tissue phantom. Compared to normal (straight) pulses, the time-reversed distorted pulses reduced the tissue signal in PI by 11 dB. The second harmonic signals from microbubbles flowing in a wall-less vessel were unaffected by the correction. This technique can thus increase the blood-to-tissue contrast ratio while keeping the pressure and the number of pulses constant. PMID:18765888

Couture, Olivier; Aubry, Jean-François; Montaldo, Gabriel; Tanter, Mickael; Fink, Mathias

2008-10-01

437

Ultrasound Biomicroscopy Glaucoma Images Analysis Based on Rough Set and Pulse Coupled Neural Network  

Microsoft Academic Search

The objective of this book chapter is to present the rough sets and pulse coupled neural network scheme for Ultrasound Biomicroscopy\\u000a glaucoma images analysis. To increase the efficiency of the introduced scheme, an intensity adjustment process is applied\\u000a first using the Pulse Coupled Neural Network (PCNN) with a median filter. This is followed by applying the PCNN-based segmentation\\u000a algorithm to

El-Sayed A. El-Dahshan; Aboul Ella Hassanien; Amr Radi; Soumya Banerjee

2009-01-01

438

Metamaterials for terahertz polarimetric devices  

SciTech Connect

We present experimental and numerical investigations of planar terahertz metamaterial structures designed to interact with the state of polarization. The dependence of metamaterial resonances on polarization results in unique amplitude and phase characteristics of the terahertz transmission, providing the basis for polarimetric terahertz devices. We highlight some potential applications for polarimetric devices and present simulations of a terahertz quarter-wave plate and a polarizing terahertz beam splitter. Although this work was performed at terahertz frequencies, it may find applications in other frequency ranges as well.

O'hara, John F [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory; Smirnova, Evgenya [Los Alamos National Laboratory; Azad, Abul [Los Alamos National Laboratory

2008-01-01

439

Freely tunable broadband polarization rotator for terahertz waves.  

PubMed

A freely tunable polarization rotator for broadband terahertz waves is demonstrated using a three-rotating-layer metallic grating structure, which can conveniently rotate the polarization of a linearly polarized terahertz wave to any desired direction with nearly perfect conversion efficiency. This low-cost, high-efficiency, and freely tunable device has potential applications as material analysis, wireless communication, and THz imaging. PMID:25545177

Fan, Ren-Hao; Zhou, Yu; Ren, Xiao-Ping; Peng, Ru-Wen; Jiang, Shang-Chi; Xu, Di-Hu; Xiong, Xiang; Huang, Xian-Rong; Wang, Mu

2015-02-18

440

Heat Induced Damage Detection by Terahertz (THz) Radiation  

Microsoft Academic Search

Terahertz (THz) and sub-terahertz imaging and spectroscopy are becoming increasingly popular nondestructive evaluation techniques\\u000a for damage detection and characterization of materials. THz radiation is being used for inspecting ceramic foam tiles used\\u000a in TPS (Thermal Protection System), thick polymer composites and polymer tiles that are not good conductors of ultrasonic\\u000a waves. Capability of THz electromagnetic waves in detecting heat induced

Ehsan Kabiri Rahani; Tribikram Kundu; Ziran Wu; Hao Xin

2011-01-01

441

Terahertz NDE for Under Paint Corrosion Detection and Evaluation  

NASA Technical Reports Server (NTRS)

Corrosion under paint is not visible until it has caused paint to blister, crack, or chip. If corrosion is allowed to continue then structural problems may develop. Identifying corrosion before it becomes visible would minimize repairs and costs and potential structural problems. Terahertz NDE imaging under paint for corrosion is being examined as a method to inspect for corrosion by examining the terahertz response to paint thickness and to surface roughness.

Anastasi, Robert F.; Madaras, Eric I.

2005-01-01

442

Fiber-based ultrashort pulse delivery for nonlinear imaging using high-energy solitons.  

PubMed

We present an approach for fiber delivery of femtosecond pulses relying on pulse breakup and soliton self-frequency shift in a custom-made solid-core photonic bandgap fiber. In this scheme, the fiber properties themselves ensure that a powerful Fourier-transform-limited pulse is emitted at the fiber output, hence doing away with the need for complex precompensation and enabling tunability of the excitation. We report high-energy soliton excitation for two-photon fluorescence microspectroscopy over a 100-nm range and multimodal nonlinear imaging on biological samples. PMID:25157612

Saint-Jalm, Sarah; Andresen, Esben R; Ferrand, Patrick; Bendahmane, Abdelkrim; Mussot, Arnaud; Vanvincq, Olivier; Bouwmans, Géraud; Kudlinski, Alexandre; Rigneault, Hervé

2014-08-01

443

Multiresolution Approach for Noncontact Measurements of Arterial Pulse Using Thermal Imaging  

NASA Astrophysics Data System (ADS)

This chapter presents a novel computer vision methodology for noncontact and nonintrusive measurements of arterial pulse. This is the only investigation that links the knowledge of human physiology and anatomy, advances in thermal infrared (IR) imaging and computer vision to produce noncontact and nonintrusive measurements of the arterial pulse in both time and frequency domains. The proposed approach has a physical and physiological basis and as such is of a fundamental nature. A thermal IR camera was used to capture the heat pattern from superficial arteries, and a blood vessel model was proposed to describe the pulsatile nature of the blood flow. A multiresolution wavelet-based signal analysis approach was applied to extract the arterial pulse waveform, which lends itself to various physiological measurements. We validated our results using a traditional contact vital signs monitor as a ground truth. Eight people of different age, race and gender have been tested in our study consistent with Health Insurance Portability and Accountability Act (HIPAA) regulations and internal review board approval. The resultant arterial pulse waveforms exactly matched the ground truth oximetry readings. The essence of our approach is the automatic detection of region of measurement (ROM) of the arterial pulse, from which the arterial pulse waveform is extracted. To the best of our knowledge, the correspondence between noncontact thermal IR imaging-based measurements of the arterial pulse in the time domain and traditional contact approaches has never been reported in the literature.

Chekmenev, Sergey Y.; Farag, Aly A.; Miller, William M.; Essock, Edward A.; Bhatnagar, Aruni

444

Terahertz plasmonic Bessel beamformer  

NASA Astrophysics Data System (ADS)

We experimentally demonstrate terahertz Bessel beamforming based on the concept of plasmonics. The proposed planar structure is made of concentric metallic grooves with a subwavelength spacing that couple to a point source to create tightly confined surface waves or spoof surface plasmon polaritons. Concentric scatterers periodically incorporated at a wavelength scale allow for launching the surface waves into free space to define a Bessel beam. The Bessel beam defined at 0.29 THz has been characterized through terahertz time-domain spectroscopy. This approach is capable of generating Bessel beams with planar structures as opposed to bulky axicon lenses and can be readily integrated with solid-state terahertz sources.

Monnai, Yasuaki; Jahn, David; Withayachumnankul, Withawat; Koch, Martin; Shinoda, Hiroyuki

2015-01-01

445

Terahertz spectroscopy of two-dimensional subwavelength plasmonic structures  

SciTech Connect

The fascinating properties of plasmonic structures have had significant impact on the development of next generation ultracompact photonic and optoelectronic components. We study two-dimensional plasmonic structures functioning at terahertz frequencies. Resonant terahertz response due to surface plasmons and dipole localized surface plasmons were investigated by the state-of-the-art terahertz time domain spectroscopy (THz-TDS) using both transmission and reflection configurations. Extraordinary terahertz transmission was demonstrated through the subwavelength metallic hole arrays made from good conducting metals as well as poor metals. Metallic arrays m!lde from Pb, generally a poor metal, and having optically thin thicknesses less than one-third of a skin depth also contributed in enhanced THz transmission. A direct transition of a surface plasmon resonance from a photonic crystal minimum was observed in a photo-doped semiconductor array. Electrical controls of the surface plasmon resonances by hybridization of the Schottkey diode between the metallic grating and the semiconductor substrate are investigated as a function of the applied reverse bias. In addition, we have demonstrated photo-induced creation and annihilation of surface plasmons with appropriate semiconductors at room temperature. According to the Fano model, the transmission properties are characterized by two essential contributions: resonant excitation of surface plasmons and nonresonant direct transmission. Such plasmonic structures may find fascinating applications in terahertz imaging, biomedical sensing, subwavelength terahertz spectroscopy, tunable filters, and integrated terahertz devices.

Azad, Abul K [Los Alamos National Laboratory; Chen, Houtong [Los Alamos National Laboratory; Taylor, Antoinette [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory; Han, Jiaguang [OSU; Lu, Xinchao [OSU; Zhang, Weili [OSU

2009-01-01

446

Terahertz spectroscopy of two-dimensional subwavelength plasmonic structures  

NASA Astrophysics Data System (ADS)

The fascinating properties of plasmonic structures have had significant impact on the development of next generation ultracompact photonic and optoelectronic components. We study two-dimensional plasmonic structures functioning at terahertz frequencies. Resonant terahertz response due to surface plasmons and dipole localized surface plasmons were investigated by the state-of-the-art terahertz time domain spectroscopy (THz-TDS) using both transmission and reflection configurations. Extraordinary terahertz transmission was demonstrated through the subwavelength metallic hole arrays made from good conducting metals as well as poor metals. Metallic arrays made from Pb, generally a poor metal, and having optically thin thicknesses less than one-third of a skin depth also contributed in enhanced THz transmission. A direct transition of a surface plasmon resonance from a photonic crystal minimum was observed in a photo-doped semiconductor array. Electrical controls of the surface plasmon resonances by hybridization of the Schottky diode between the metallic grating and the semiconductor substrate are investigated as a function of the applied reverse bias. In addition, we have demonstrated photo-induced creation and annihilation of surface plasmons with appropriate semiconductors at room temperature. According to the Fano model, the transmission properties are characterized by two essential contributions: resonant excitation of surface plasmons and nonresonant direct transmission. Such plasmonic structures may find fascinating applications in terahertz imaging, biomedical sensing, subwavelength terahertz spectroscopy, tunable filters, and integrated terahertz devices.

Azad, Abul K.; Chen, Hou-Tong; Taylor, Antoinette J.; O'Hara, John F.; Han, Jiaguang; Lu, Xinchao; Zhang, Weili

2009-02-01

447

Imaging focused ultrasound pulses in superfluid helium 4  

NASA Astrophysics Data System (ADS)

Focusing of sound pulses emitted by a hemispherical piezo-electric transducer in liquid helium 4 at 1.1 K and 24 bar is studied in detail. Time variations of the density map are recorded by using an optical interferometric method. Numerical integration of elastic wave equations by a finite difference scheme is used for comparison. A good agreement is found between both density maps. The amplification factor from the transducer surface to the focus is deduced.

Souris, F.; Grucker, J.; Dupont-Roc, J.; Jacquier, Ph

2012-12-01

448

Sub-wavelength terahertz beam profiling of a THz source via an all-optical knife-edge technique  

NASA Astrophysics Data System (ADS)

Terahertz technologies recently emerged as outstanding candidates for a variety of applications in such sectors as security, biomedical, pharmaceutical, aero spatial, etc. Imaging the terahertz field, however, still remains a challenge, particularly when sub-wavelength resolutions are involved. Here we demonstrate an all-optical technique for the terahertz near-field imaging directly at the source plane. A thin layer (<100 nm-thickness) of photo carriers is induced on the surface of the terahertz generation crystal, which acts as an all-optical, virtual blade for terahertz near-field imaging via a knife-edge technique. Remarkably, and in spite of the fact that the proposed approach does not require any mechanical probe, such as tips or apertures, we are able to demonstrate the i