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1

Detection and identification of explosives using terahertz pulsed spectroscopic imaging  

NASA Astrophysics Data System (ADS)

The absorption spectrum of the explosive 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) has been measured using a conventional Fourier transform infrared spectroscopy and by terahertz pulsed spectroscopy. Seven absorption features in the spectral range of 5-120cm-1 have been observed and identified as the fingerprint of RDX. Furthermore, the spatial distribution of individual chemical substances including RDX, has been mapped out using reflection terahertz spectroscopic imaging in combination with component spatial pattern analysis. This is the terahertz spectroscopy and chemical mapping of explosives obtained using reflection terahertz measurement, and represents a significant advance toward developing a terahertz pulsed imaging system for security screening of explosives.

Shen, Y. C.; Lo, T.; Taday, P. F.; Cole, B. E.; Tribe, W. R.; Kemp, M. C.

2005-06-01

2

Time-Frequency Analysis in Terahertz-Pulsed Imaging  

Microsoft Academic Search

Recent advances in laser and electro-optical technologies have made the previously underutilized terahertz frequency band\\u000a of the electromagnetic spectrum accessible for practical imaging. Applications are emerging, notably in the biomedical domain.\\u000a In this chapter the technique of terahertz-pulsed imaging is introduced in some detail. The need for special computer vision\\u000a methods, which arises from the use of pulses of radiation

Elizabeth Berry; Roger D Boyle; Anthony J Fitzgerald; James Handley

3

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

4

TOPICAL REVIEW: Pulsed terahertz tomography  

Microsoft Academic Search

Terahertz time-domain spectroscopy (THz-TDS) is a coherent measurement technology. Using THz-TDS, the phase and amplitude of the THz pulse at each frequency can be determined. Like radar, THz-TDS also provides time information that allows us to develop various three-dimensional THz tomographic imaging modalities. The three-dimensional THz tomographic imagings we investigated are: terahertz diffraction tomography (THz DT), terahertz computed tomography (THz

S. Wang; X.-C. Zhang

2004-01-01

5

Detection of tulobuterol crystal in transdermal patches using terahertz pulsed spectroscopy and imaging.  

PubMed

Applicability of a Terahertz Pulsed Spectroscopy (TPS) and a Terahertz Pulsed Imaging (TPI) for detection of tulobuterol (TBR) crystals in transdermal patches was investigated. Because TBR has high permeability in dermis, crystalline TBR in patch matrices contributes to controlling the release rate of TBR from a matrix. Therefore, crystalline TBR is one of the important factors for quality control of TBR transdermal tapes. A model tape that includes 5 w/w%, 10 w/w%, 20 w/w% or 30 w/w% of TBR was measured by TPS/TPI. TBR crystals in the matrices were successfully detected by TPI. Identification of TBR in an image of a crystal-like mass was done by comparison between the spectra of tapes and a TBR standard substance. These results indicate that TPS and TPI are applicable to identifying crystalline lumps of an active drug in tapes for quality control. PMID:19618670

Sakamoto, T; Portieri, A; Taday, P F; Takada, Y; Sasakura, D; Aida, K; Matsubara, T; Miura, T; Terahara, T; Arnone, D D; Kawanishi, T; Hiyama, Y

2009-06-01

6

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

7

Characterisation of historic plastics using terahertz time-domain spectroscopy and pulsed imaging.  

PubMed

Terahertz (THz) time-domain spectroscopy and 3D THz pulsed imaging have been explored with regard to polymer materials, both commodity and historic polymers. A systematic spectroscopic study of a wide range of different polymer materials showed significant differences in their spectra. Polyolefins and polystyrenes generally exhibit lower absorption than other examined polymers, various cellulose derivates, poly(vinyl chloride), poly(methyl methacrylate), polyamide, hard rubber and phenol formaldehyde resin, the last of these exhibiting the most intense absorption over the entire range, 0.15-4.2 THz. It was also examined how the presence of plasticisers in poly(vinyl chloride), the presence of fillers in polypropylene, and the degree of branching in polyethylene and polystyrene affect the spectra; inorganic fillers in polypropylene affected the absorption most. With 3D THz pulsed imaging, features in polymer objects were explored, appearing either as integral parts of the material (coatings and pores in foams) or as a consequence of physical deterioration (cracks, delamination). All of these features of various complexities can be successfully imaged in 3D. Terahertz technology is thus shown to have significant potential for both chemical and structural characterisation of polymers, which will be of interest to heritage science, but also to the polymer industry and development of analytical technologies in general. PMID:22447218

Pastorelli, Gianluca; Trafela, Tanja; Taday, Phillip F; Portieri, Alessia; Lowe, David; Fukunaga, Kaori; Strli?, Matija

2012-05-01

8

Classification of terahertz-pulsed imaging data from excised breast tissue  

NASA Astrophysics Data System (ADS)

We investigate the efficacy of using data reduction techniques to aid classification of terahertz (THz) pulse data obtained from tumor and normal breast tissue. Fifty-one samples were studied from patients undergoing breast surgery at Addenbrooke's Hospital in Cambridge and Guy's Hospital in London. Three methods of data reduction were used: ten heuristic parameters, principal components of the pulses, and principal components of the ten parameter space. Classification was performed using the support vector machine approach with a radial basis function. The best classification accuracy, when using all ten components, came from using the principal components on the pulses and principal components on the parameter, with an accuracy of 92%. When less than ten components were used, the principal components on the parameter space outperformed the other methods. As a visual demonstration of the classification technique, we apply the data reduction/classification to several example images and demonstrate that, aside from some interpatient variability and edge effects, the algorithm gives good classification on terahertz data from breast tissue. The results indicate that under controlled conditions data reduction and SVM classification can be used with good accuracy to classify tumor and normal breast tissue.

Fitzgerald, Anthony J.; Pinder, Sarah; Purushotham, Anand D.; O'Kelly, Padraig; Ashworth, Philip C.; Wallace, Vincent P.

2012-01-01

9

Terahertz pulsed imaging as an advanced characterisation tool for film coatings--a review.  

PubMed

Solid dosage forms are the pharmaceutical drug delivery systems of choice for oral drug delivery. These solid dosage forms are often coated to modify the physico-chemical properties of the active pharmaceutical ingredients (APIs), in particular to alter release kinetics. Since the product performance of coated dosage forms is a function of their critical coating attributes, including coating thickness, uniformity, and density, more advanced quality control techniques than weight gain are required. A recently introduced non-destructive method to quantitatively characterise coating quality is terahertz pulsed imaging (TPI). The ability of terahertz radiation to penetrate many pharmaceutical materials enables structural features of coated solid dosage forms to be probed at depth, which is not readily achievable with other established imaging techniques, e.g. near-infrared (NIR) and Raman spectroscopy. In this review TPI is introduced and various applications of the technique in pharmaceutical coating analysis are discussed. These include evaluation of coating thickness, uniformity, surface morphology, density, defects and buried structures as well as correlation between TPI measurements and drug release performance, coating process monitoring and scale up. Furthermore, challenges and limitations of the technique are discussed. PMID:23570960

Haaser, Miriam; Gordon, Keith C; Strachan, Clare J; Rades, Thomas

2013-12-01

10

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

11

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

12

Terahertz phase contrast imaging  

NASA Astrophysics Data System (ADS)

Terahertz imaging is presently in its exploratory stage. Although plots of time versus terahertz amplitude, and frequency versus terahertz magnitude are some of the most common ways of analyzing terahertz data, no standard rendering technique has been established. While existing methods are indispensable, improvements to how terahertz data is rendered and analyzed should be explored so that new techniques can complement existing ones and/or provide a means of displaying new information that existing methods cannot. This paper reports on one solution to terahertz imaging: an implementation of a new form of phase contrast imaging, which is based on a well-established technique for optical microscopy. This will provide us with a further way of interpreting information from terahertz imaging systems.

Png, Gretel M.; Mickan, Samuel P.; Rainsford, Tamath J.; Abbott, Derek

2005-02-01

13

Hardness and density distributions of pharmaceutical tablets measured by terahertz pulsed imaging.  

PubMed

We present terahertz pulsed imaging (TPI) as a novel tool to quantify the hardness and surface density distribution of pharmaceutical tablets. Good agreement between the surface refractive index (SRI) measured by TPI and the crushing force measured from diametral compression tests was found using a set of tablets that were compacted at various compression forces. We also found a strong correlation between TPI results and tablet bulk density, and how these relate to tablet hardness. Numerical simulations of tablet surface density distribution by finite element analysis exhibit excellent agreement with the TPI measured SRI maps. These results show that TPI has an advantage over traditional diametral compression and is more suitable for nondestructive hardness and density distribution monitoring and control of pharmaceutical manufacturing processes. PMID:23609052

May, Robert K; Su, Ke; Han, Lianghao; Zhong, Shuncong; Elliott, James A; Gladden, Lynn F; Evans, Mike; Shen, Yaochun; Zeitler, J Axel

2013-07-01

14

Spatiotemporal transformations of ultrashort terahertz pulses  

E-print Network

Spatiotemporal transformations of ultrashort terahertz pulses Petr Kuzel, Maxim A. Khazan, and Jan-cycle terahertz pulses emitted by large-aperture emitters. The spatial transformations of the beams are connected the temporal waveform and the spectrum of the pulses are altered as a result of these spa- tial transformations

KuÂ?el, Petr

15

Spectroscopy by pulsed terahertz radiation  

NASA Astrophysics Data System (ADS)

Spectroscopies using terahertz (THz) radiation excited by ultrashort laser pulses have been rapidly developing recently. In this paper, the principles of various types of THz time domain spectroscopies (THz TDSs), i.e. transmission-, reflection-and ellipsometry-type THz TDSs, and their applications to the characterization of semiconductors are described. In addition to the THz TDS using a femtosecond laser, a sub-THz TDS system using a cheap and compact continuous multimode laser diode is also described.

Hangyo, M.; Nagashima, T.; Nashima, S.

2002-11-01

16

Pulsed Terahertz Spectroscopy of Biomolecules  

NASA Astrophysics Data System (ADS)

Measurements of the collective vibrational modes associated with the 3D tertiary structure of biomolecules were undertaken using pulse terahertz spectroscopy. Transmission measurements of calf thymus DNA (CT-DNA), bovine serum albumin (BSA), and collagen were made for 2 cm-1 to 45 cm-1. For all three biomolecules, low frequency absorption bands could be distinguished from a broadband absorption increasing with frequency. For lyophilized powder samples, features appear at 15 cm-1 and 22 cm-1 for CT-DNA, 10 cm-1 for BSA, and 8 cm-1 and 12 cm-1 for collagen. Measurements were performed as a function of hydration and conformation.

Markelz, A. G.; Heilweil, E. J.

1998-03-01

17

Polarization information for terahertz imaging.  

PubMed

A method to analyze the change in the polarization state of a terahertz (THz) wave by using a typical electro-optic sampling setup with a ?110? zinc-blende crystal as a sensor is presented. To illustrate knowledge of the polarization of the THz pulse, the THz detection function in a ZnTe crystal is presented. Two kinds of Jones matrix for the birefringence device and the polarizer device are used to analyze the polarization change in the THz electric field caused by the sample. It is found that THz polarization imaging is sensitive to the edge of the sample. PMID:19037370

Zhang, Ranxi; Cui, Ye; Sun, Wenfeng; Zhang, Yan

2008-12-01

18

Continuous-wave terahertz imaging of nonmelanoma skin cancers  

NASA Astrophysics Data System (ADS)

Continuous wave terahertz imaging has the potential to offer a safe, non-invasive medical imaging modality for detecting different types of human skin cancers. Terahertz pulse imaging (TPI) has already shown that there is contrast between basal cell carcinoma and normal skin. Continuous-wave imaging offers a simpler, lower cost alternative to terahertz pulse imaging. This project aims to isolate the optimal contrast frequency for a continuous wave terahertz imaging system and demonstrate transmission based, in-vitro , imaging of thin sections of non-melanoma skin cancers and correlate the images to sample histology. The aim of this project is to conduct a proof-of-principle experiment that establishes whether continuous-wave terahertz imaging can detect differences between cancerous and normal tissue while outlining the basic requirements for building a system capable of performing in vivo tests.

Joseph, Cecil Sudhir

19

Applications of terahertz (THz) technology to medical imaging  

Microsoft Academic Search

An imaging system has been developed based on pulses of Terahertz (THz) radiation generated and detected using all- optical effects accessed by irradiating semiconductors with ultrafast pulses of visible laser light. This technique, commonly referred to as T-Ray Imaging or THz Pulse Imaging (TPI), holds enormous promise for certain aspects of medical imaging. We have conducted an initial survey of

Don D. Arnone; Craig M. Ciesla; Alessandra Corchia; S. Egusa; M. Pepper; J. Martyn Chamberlain; C. Bezant; E. H. Linfield; R. Clothier; N. Khammo

1999-01-01

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

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

22

Imaging with Terahertz Pulses Timothy Dorney, Jon Johnson, Daniel Mittleman, Richard Baraniuk  

E-print Network

. The images, created from 'T-rays', included moisture analysis in a leaf, thermal analysis of a flame received power or arrival time shifts were often used to determine a false color image. This paper focuses

23

Principle and applications of terahertz molecular imaging  

NASA Astrophysics Data System (ADS)

The principle, characteristics and applications of molecular imaging with terahertz electromagnetic waves are reviewed herein. The terahertz molecular imaging (TMI) technique uses nanoparticle probes to achieve dramatically enhanced sensitivity compared with that of conventional terahertz imaging. Surface plasmons, induced around the nanoparticles, raise the temperature of water in biological cells, and the temperature-dependent changes in the optical properties of water, which are large in the terahertz range, are measured differentially by terahertz waves. TMI has been applied to cancer diagnosis and nanoparticle drug delivery imaging. The technique is also compared with magnetic resonance imaging by using a dual-modality nanoparticle probe.

Son, Joo-Hiuk

2013-05-01

24

Components and Metrology for Terahertz Imaging  

E-print Network

Components and Metrology for Terahertz Imaging by Charles Robert Dietlein B.S., Seattle Pacific, Charles Robert All rights reserved #12;This thesis entitled: Components and Metrology for Terahertz Engineering) Components and Metrology for Terahertz Imaging Thesis directed by Professor Zoya Popovi

Popovic, Zoya

25

Time reversal three-dimensional imaging using single-cycle terahertz pulses  

E-print Network

reversal imaging is similar to Kirch- hoff migration5 and inverse synthetic aperture radar6 ISAR . All, and receiv- ers. Time reversal and Kirchhoff migration process the sig- nals in the time domain, while ISAR processes signals in the frequency domain. ISAR assumes the object lies in the far field of the synthetic

Buma, Takashi

26

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

E-print Network

diametral compression tests was found using a set of tablets that were compacted at various compression has an advantage over traditional diametral compression and is more suitable for nondestructive imaging (TPI); tablet hardness testing; density distribution; finite element analysis (FEA); diametral

Elliott, James

27

Terahertz pulsed spectroscopy of paraffin-embedded brain glioma.  

PubMed

The refractive indices, absorption coefficients, and complex dielectric constants of paraffin-embedded brain glioma and normal brain tissues have been measured by a terahertz time-domain spectroscopy (THz-TDS) system in the 0.2- to 2.0-THz range. The spectral differences between gliomas and normal brain tissues were obtained. Compared with normal brain tissue, our results indicate that paraffin-embedded brain gliomas have a higher refractive index, absorption coefficient, and dielectric constant. Based on these results, the best THz frequencies for different methods of paraffin-embedded brain glioma imaging, such as intensity imaging, coherent imaging with continuum THz sources, and THz pulsed imaging with short-pulsed THz sources, are analyzed. PMID:25003757

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

2014-07-01

28

Terahertz imaging using strained-Si MODFETs as sensors  

NASA Astrophysics Data System (ADS)

We report on non-resonant (broadband) and resonant detection of terahertz radiation using strained-Si modulation doped field effect transistors. The devices were excited at room temperature by two types of terahertz sources (an electronic source based on frequency multipliers at 0.292 THz and a pulsed parametric laser at 1.5 THz). In both cases, a non-resonant response with maxima around the threshold voltage was observed. Shubnikov-de Haas and photoresponse measurements were performed simultaneously and showed a phase-shift of ?/2 in good agreement with the theory, which demonstrates that the observed response is related to the plasma waves oscillation in the channel. The non-resonant features were used to demonstrate the capabilities of such devices in terahertz imaging. We also cooled our device down to 4.2 K to increase the quality factor and resonant detection was observed by using a tunable source of terahertz radiation.

Meziani, Y. M.; Garcìa-Garcìa, E.; Velázquez-Pérez, J. E.; Coquillat, D.; Dyakonova, N.; Knap, W.; Grigelionis, I.; Fobelets, K.

2013-05-01

29

Terahertz Medical Imaging  

NASA Astrophysics Data System (ADS)

The past 30 years have witnessed the evolution of medical imaging. Imaging technology has drastically improved medical care and, as a result, everyday life. Since the discovery of X-rays by William Roentgen in 1895, doctors have used radiography to diagnose many diseases of the internal organs for several decades. The development of X-rays brought about a revolution in the field of medical diagnostics. The peak of this revolution would begin in the 1970s when computed tomography, magnetic resonance imaging, and ultrasonography were developed. Enormous progress in the field of computer technology has been boosting the evolution of imaging technology since the 1990s. To date, medical imaging innovations have focused on achieving excellent anatomic resolution and contrast.

Han, Joon Koo

30

Terahertz Imaging and Security Applications  

NASA Astrophysics Data System (ADS)

Imaging at millimeter-wave and terahertz frequencies could vastly improve the security of personnel checkpoints, because of the penetration through clothing and spatial resolution available in this spectral range. Since 9/11, the social need for improved checkpoint screening has been obvious and great. However, although efforts to develop such imagers had been underway for many years before that, practical low-cost systems, analogous to IR uncooled imagers, still don't exist. An emphasis on purely passive imaging places very stringent sensitivity requirements on such imagers. A number of long-term efforts, which I briefly mention, are underway to improve the sensitivity of such passive imagers. However, most of the emphasis in our program is on active imaging. With this approach, much simpler and lower-cost detectors, such as (uncooled) antenna-coupled microbolometers can be used, at the expense of incorporating slightly more complex optics and illumination components. I discuss several tradeoffs presented in the design of active imaging systems for the 100 to 1000 GHz frequency range, describe how we have addressed them in the design of a scanning, 95 GHz, bolometer-based imager for concealed weapons detection that is nearing completion, and describe how the system architecture can be modified to scale the operating frequency to the 650 GHz atmospheric window. Co-authors: Arttu Luukanen and Aaron Miller

Grossman, Erich

2005-03-01

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

Nondestructive terahertz imaging for aerospace applications  

NASA Astrophysics Data System (ADS)

The full potential of terahertz imaging systems for nondestructive aerospace imaging applications has not been realized due to the lack of data linking damage and defects to terahertz signatures coupled with the complexity of modeling the signatures. Terahertz systems (0.1 - 2.0 THz) may be ideally suited for NDI applications because of the ability of THz radiation to penetrate through substances commonly found on the surfaces of aircraft structures while maintaining the optical resolution required to detect defects. We will discuss several systems that we have used to study the signatures of a set of target samples with known defects.

Petkie, Douglas T.; Kemp, Izaak V.; Benton, Carla; Boyer, Christopher; Owens, Lindsay; Deibel, Jason A.; Stoik, Christopher D.; Bohn, Matthew J.

2009-09-01

33

Using terahertz pulsed spectroscopy to study crystallinity of pharmaceutical materials  

NASA Astrophysics Data System (ADS)

The application of terahertz pulsed spectroscopy to polymorphic, liquid crystalline and amorphous forms of pharmaceutical compounds has been investigated. The different polymorphic forms of carbamazepine and enalapril maleate exhibit distinct terahertz absorbance spectra. In contrast to crystalline indomethacin and fenoprofen calcium, amorphous indomethacin and liquid crystalline fenoprofen calcium show no absorption modes, which is likely to be due to a lack of order. These findings suggest that the modes observed are due to crystalline phonon and possibly hydrogen-bonding vibrations. The large spectral differences between different forms of the compounds studied is evidence that terahertz pulsed spectroscopy is well-suited to distinguishing crystallinity differences in pharmaceutical compounds.

Strachan, Clare J.; Rades, Thomas; Newnham, David A.; Gordon, Keith C.; Pepper, Michael; Taday, Philip F.

2004-05-01

34

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

35

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

36

Sub-surface terahertz imaging through uneven surfaces: visualizing Neolithic wall paintings in Çatalhöyük.  

PubMed

Pulsed terahertz imaging is being developed as a technique to image obscured mural paintings. Due to significant advances in terahertz technology, portable systems are now capable of operating in unregulated environments and this has prompted their use on archaeological excavations. August 2011 saw the first use of pulsed terahertz imaging at the archaeological site of Çatalhöyük, Turkey, where mural paintings dating from the Neolithic period are continuously being uncovered by archaeologists. In these particular paintings the paint is applied onto an uneven surface, and then covered by an equally uneven surface. Traditional terahertz data analysis has proven unsuccessful at sub-surface imaging of these paintings due to the effect of these uneven surfaces. For the first time, an image processing technique is presented, based around Gaussian beam-mode coupling, which enables the visualization of the obscured painting. PMID:23571902

Walker, Gillian C; Bowen, John W; Matthews, Wendy; Roychowdhury, Soumali; Labaune, Julien; Mourou, Gerard; Menu, Michel; Hodder, Ian; Jackson, J Bianca

2013-04-01

37

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

38

Terahertz spin current pulses controlled by magnetic heterostructures.  

PubMed

In spin-based electronics, information is encoded by the spin state of electron bunches. Processing this information requires the controlled transport of spin angular momentum through a solid, preferably at frequencies reaching the so far unexplored terahertz regime. Here, we demonstrate, by experiment and theory, that the temporal shape of femtosecond spin current bursts can be manipulated by using specifically designed magnetic heterostructures. A laser pulse is used to drive spins from a ferromagnetic iron thin film into a non-magnetic cap layer that has either low (ruthenium) or high (gold) electron mobility. The resulting transient spin current is detected by means of an ultrafast, contactless amperemeter based on the inverse spin Hall effect, which converts the spin flow into a terahertz electromagnetic pulse. We find that the ruthenium cap layer yields a considerably longer spin current pulse because electrons are injected into ruthenium d states, which have a much lower mobility than gold sp states. Thus, spin current pulses and the resulting terahertz transients can be shaped by tailoring magnetic heterostructures, which opens the door to engineering high-speed spintronic devices and, potentially, broadband terahertz emitters. PMID:23542903

Kampfrath, T; Battiato, M; Maldonado, P; Eilers, G; Nötzold, J; Mährlein, S; Zbarsky, V; Freimuth, F; Mokrousov, Y; Blügel, S; Wolf, M; Radu, I; Oppeneer, P M; Münzenberg, M

2013-04-01

39

Terahertz-pulse emission through excitation of surface  

E-print Network

Terahertz-pulse emission through excitation of surface plasmons in metallic nanostructures Gregor H ­ gratings ­ prisms ­ rough films · Rectification in a metallic grating ­ surface plasmons (SPs), electron;Introduction · Rectification on metal surfaces · Multiphoton photoelectric effect (MPPE) on metal surfaces

Strathclyde, University of

40

Terahertz imaging of subjects with concealed weapons  

NASA Astrophysics Data System (ADS)

In response to the growing interest in developing terahertz imaging systems for concealed weapons detection, the Submillimeter-Wave Technology Laboratory (STL) at the University of Massachusetts Lowell has produced full-body terahertz imagery using coherent active radar measurement techniques. The proof-of-principle results were readily obtained utilizing the compact radar range resources at STL. Two contrasting techniques were used to collect the imagery. Both methods made use of in-house transceivers, consisting of two ultra-stable far-infrared lasers, terahertz heterodyne detection systems, and terahertz anechoic chambers. The first technique involved full beam subject illumination with precision azimuth and elevation control to produce high resolution images via two axis Fourier transforms. Imagery collected in this manner is presented at 1.56THz and 350GHz. The second method utilized a focused spot, moved across the target subject in a high speed two dimensional raster pattern created by a large two-axis positioning mirror. The existing 1.56THz compact radar range was modified to project a focused illumination spot on the target subject several meters away, and receive the back-reflected intensity. The process was repeated across two dimensions, and the resultant image was assembled and displayed utilizing minimal on-the-fly processing. Imagery at 1.56THz of human subjects with concealed weapons are presented and discussed for this scan type.

Dickinson, Jason C.; Goyette, Thomas M.; Gatesman, Andrew J.; Joseph, Cecil S.; Root, Zachary G.; Giles, Robert H.; Waldman, Jerry; Nixon, William E.

2006-05-01

41

Highly sensitive surface plasmon terahertz imaging with planar plasmonic crystals.  

PubMed

We report on the operation of a highly sensitive terahertz imaging system relying on a planar metallic plasmonic crystal as a terahertz surface plasmon resonant (THz-SPR) sensor. The terahertz imaging is based on the resonantly enhanced transmission phenomenon of a periodically perforated metal film. The detection sensitivity and the imaging contrast for small amounts of substance are considerably better than those of the conventional terahertz transmission imaging without a THz-SPR sensor. As a demonstration, a high contrast image of a fingerprint recorded on a thin film can be achieved by using this system. PMID:19550760

Miyamaru, F; Takeda, M W; Suzuki, T; Otani, C

2007-10-29

42

High-speed time domain terahertz security imaging  

Microsoft Academic Search

Terahertz imaging has the potential to reveal concealed explosives; metallic and non-metallic weapons (such as ceramic, plastic or composite guns and knives); flammables; biological agents; chemical weapons and other threats hidden in packages or on personnel. Time domain terahertz imaging can be employed in reflection mode to image with sub millimeter resolution. Previously, single pixel acquisition times for THz waveforms

David Zimdars; Jeffrey White; Steven Williamson; G. Stuk

2005-01-01

43

Ultrashort pulse characterization with a terahertz streak camera.  

PubMed

A phase-locked terahertz transient is exploited as an ultrafast phase gate for femtosecond optical pulses. We directly map out the group delay dispersion of a low-power near-infrared pulse by measuring the electro-optically induced polarization rotation as a function of wavelength. Our experiment covers the spectral window from 1.0 to 1.4 ?m and reaches a temporal precision better than 1 fs. A quantitative analysis of the detector response confirms that this streaking technique requires no reconstruction algorithm and is also well suited for the characterization of pulses spanning more than one optical octave. PMID:22089596

Schubert, O; Riek, C; Junginger, F; Sell, A; Leitenstorfer, A; Huber, R

2011-11-15

44

Terahertz ISAR imaging in noise backgroud  

NASA Astrophysics Data System (ADS)

We investigate the ISAR imaging in background noises by using the analytical solutions and physical optics within the terahertz region. When increasing the frequency band wide, the scattering signals of the metal sphere are enhanced by the coherent measurement technique, and the background noises are effectively canceled. Furthermore, the resolution of SAR imaging is improved to precisely locate the scattering centers of objects. However, the increased band wide seemly decreases the contrast of imaging due to the discrete grids of filtered back projection algorithm.

Li, Liang-Sheng; Li, Sheng; Yin, Hong-cheng

2013-08-01

45

Comprehensive imaging of terahertz surface plasmon polaritons.  

PubMed

A comprehensive system with a high speed is built for imaging the terahertz (THz) surface plasmon polaritons (SPPs). Both the amplitude and the phase information of the focusing THz-SPPs excited by a semicircular plasmonic lens are achieved by using this system. The amplitude images present the focusing profiles of the THz-SPPs with different frequencies and the phase images reveal the Gouy phase shift as the THz-SPPs evolving through the focus. The simulations are also performed and a good agreement between the experimental and simulated results has been found. PMID:25090508

Wang, Sen; Zhao, Feng; Wang, Xinke; Qu, Shiliang; Zhang, Yan

2014-07-14

46

Chirped-pulse terahertz spectroscopy for broadband trace gas sensing.  

PubMed

We report the first demonstration of a broadband trace gas sensor based on chirp-pulse terahertz spectroscopy. The advent of newly developed solid state sources and sensitive heterodyne detectors for the terahertz frequency range have made it possible to generate and detect precise arbitrary waveforms at THz frequencies with ultra-low phase noise. In order to maximize sensitivity, the sample gas is first polarized using sub-?s chirped THz pulses and the free inductive decays (FIDs) are then detected using a heterodyne receiver. This approach allows for a rapid broadband multi-component sensing with low parts in 10(9) (ppb) sensitivities and spectral frequency accuracy of <20 kHz in real-time. Such a system can be configured into a portable, easy to use, and relatively inexpensive sensing platform. PMID:21643150

Gerecht, Eyal; Douglass, Kevin O; Plusquellic, David F

2011-04-25

47

Selecting rotational two-level coherence in polar molecules by double terahertz pulses  

NASA Astrophysics Data System (ADS)

We demonstrate experimentally a method for controlling two-level coherence in jet-cooled rotating polar molecules by using a pair of intense terahertz pulses. The broad spectra of the terahertz pulses can induce resonant population transfer between four rotational states J =0 ,1 ,2 ,3 to establish two-level coherence. This coherence is controlled by the delay between the two terahertz pulses, resulting in selection of a single two-level coherence. This scheme can be extended to select a specific two-level coherence in a thermally distributed molecular ensemble by applying a train of terahertz pulses.

Kitano, Kenta; Ishii, Nobuhisa; Kanai, Teruto; Itatani, Jiro

2014-10-01

48

Possibility of direct estimation of terahertz pulse electric field.  

PubMed

In this Letter, we introduce a new method of estimation of the terahertz (THz) field amplitude. This method uses second-harmonic generation (SHG) in the presence of THz and DC fields in gaseous media. We take into account contributions from both nonionized molecules and free plasma electrons to the nonlinear process of SHG. We analyze the applicability of this method of detection to obtaining correct information on the waveform and amplitude of broadband THz pulses. PMID:25121659

Borodin, Alexander V; Esaulkov, Mikhail N; Frolov, Alexander A; Shkurinov, Alexander P; Panchenko, Vladislav Ya

2014-07-15

49

Tunable and collimated terahertz radiation generation by femtosecond laser pulses  

SciTech Connect

A mechanism is proposed for the generation of tunable terahertz (THz) radiation under the application of two femtosecond laser pulses and an external magnetic field, where quick tunnel ionization is achieved that leads to higher plasma density evolution and large residual current for the efficient THz radiation generation. With the optimization of magnetic field, phase difference, and amplitudes of lasers' fields, a THz source can be obtained with tunable frequency and power along with a control on the direction of radiation emission.

Malik, Hitendra K.; Malik, Anil K.

2011-12-19

50

Distinguishing different parts of objects by terahertz imaging  

NASA Astrophysics Data System (ADS)

Since every matter has its distinctive absorption and transmission capacity of terahertz, Terahertz time domain spectroscopy provides a powerful means to distinguish the different parts of objects. The transmittance of terahertz under different frequency can reflect the absorption distribution of the different parts of the samples. The phase shift of the terahertz wave indicates the change of optical thickness of the sample. Tree leaves, plastic ring, plastic convex lens and plastic piece with a small hole have been imaged by terahertz. As widespread samples, leaves are proved to be well imaged by terahertz wave. For the moisture content at different parts of leaves, such as mesophyll and vein, is not the same, the absorption of terahertz at these parts are quite different. At 1.4THz, the leaf's image is of good quality and the vein grids are well shown. The hole and defects in the plastic ring are also clearly shown in the THz image because the phase shifts of terahertz in different parts, such as air, defects or plastic region are not the same. It is also shown that objects with large radius of curvature are suitable for THz imagining and the scattering of THz does not affect THz phase information too much. In short, Terahertz imaging is a powerful technique to distinguish the different parts of most objects as long as the absorption of THz is not very strong.

Ge, Jin; Wang, Reng; Hu, Shuhong; Dai, Ning; Li, Dong; Ma, Hong; Ma, Guohong

2010-10-01

51

Imaging of terahertz fields and responses  

NASA Astrophysics Data System (ADS)

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 nonlinear spectroscopy has relied on optical imaging of THz field profiles and their time and position-dependent evolution. A THz "polaritonics" platform enables extensive control over THz fields that are generated; integration of functional elements such as bandgap structures and metamaterial devices; optical imaging of the THz near and far fields with subcycle temporal and subwavelength spatial resolution; and exploitation of the results for nonlinear spectroscopy.

Ofori-Okai, Benjamin K.; Sivarajah, Prasahnt; Teo, Stephanie M.; Werley, Christopher A.; Nelson, Keith A.

2014-09-01

52

Terahertz real-time imaging for nondestructive detection  

NASA Astrophysics Data System (ADS)

We present a real time imaging measurement in the terahertz (THz) frequency region. The dynamic subtraction technique is used to reduce long-term optical background drift. The reflective images of two targets, a Nikon camera's lens cap and a plastic toy gun, are obtained. For the lens cap, the image data were processed to be false color images. For the toy gun, we show that even under an optically opaque canvas bag, a clear terahertz image is obtained. It is shown that terahertz real time imaging can be used to nondestructively detect concealed objects.

Zhang, LiangLiang; Karpowicz, Nick; Zhang, CunLin; Zhao, YueJin; Zhang, XiCheng

2008-03-01

53

Applications of terahertz (THz) technology to medical imaging  

NASA Astrophysics Data System (ADS)

An imaging system has been developed based on pulses of Terahertz (THz) radiation generated and detected using all- optical effects accessed by irradiating semiconductors with ultrafast pulses of visible laser light. This technique, commonly referred to as T-Ray Imaging or THz Pulse Imaging (TPI), holds enormous promise for certain aspects of medical imaging. We have conducted an initial survey of possible medical applications of TPI and demonstrated that TPI images show good contrast between different animal tissue types. Moreover, the diagnostic power of TPI has been elicidated by the spectra available at each pixel in the image, which are markedly different for the different tissue types. This suggests that the spectral information inherent in TPI might be used to identify the type of soft and hard tissue at each pixel in an image and provide other diagnostic information not afforded by conventional imagin techniques. Preliminary TPI studies of pork skin show that 3D tomographic imaging of the skin surface and thickness is possible, and data from experiments on models of the human dermis are presented which demonstrate that different constituents of skin have different refractive indices. Lastly, we present the first THz image of human tissue, namely an extracted tooth. The time of flight of THz pulses through the tooth allows the thickness of the enamel to be determined, and is used to create an image showing the enamel and dentine regions. Absorption of THz pulses in the tooth allows the pulp cavity region to be identified. Initial evidence strongly suggests that TPI my be used to provide valuable diagnostic information pertaining to the enamel, dentine, and the pump cavity.

Arnone, Donald D.; Ciesla, Craig M.; Corchia, Alessandra; Egusa, S.; Pepper, Michael; Chamberlain, J. Martyn; Bezant, C.; Linfield, Edmund H.; Clothier, R.; Khammo, N.

1999-09-01

54

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

55

Characteristics of terahertz pulses from antireflective GaAs surfaces with nanopillars  

NASA Astrophysics Data System (ADS)

We investigated the characteristics of terahertz pulses generated from antireflective GaAs surfaces with nanopillars under femtosecond laser excitation. Although the antireflective nanostructures contribute to the enhancement of free photocarrier excitation in GaAs, they could reduce the transient photocurrent density and advance the start time of the photocurrent decay. Thus, the relative amplitudes of the high-frequency spectral components of terahertz pulses increased, whereas the energies of the pulses decreased. However, we showed that thinly distributed nanopillar structures could generate a short terahertz pulse without a reduction in the pulse energy.

Kang, Chul; Woo Leem, Jung; Wook Lee, Joong; Su Yu, Jae; Kee, Chul-Sik

2013-05-01

56

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

57

A real-time terahertz imaging system consisting of terahertz quantum cascade laser and uncooled microbolometer array detector  

NASA Astrophysics Data System (ADS)

Terahertz imaging has attracted much attention in recent years, because the technique can be applied to many application fields such as nondestructive analysis and imaging method through opaque materials. A terahertz real-time imaging technique (Terahertz Camera) considered increasingly important in the future has been developed. The terahertz camera consists of a light source (Terahertz quantum cascade laser) and an un-cooled micro-bolometer array, which can easily get real-time terahertz-image. As an application of the terahertz camera, a stand-off imaging system that could be useful in a fire disaster relief and a label-free bio-materials detection system have developed and demonstrated.

Hosako, Iwao; Sekine, Norihiko; Oda, Naoki; Sano, Masahiko; Kurashina, Seiji; Miyoshi, Masaru; Sonoda, Ken'ichi; Yoneyama, Hajime; Sasaki, Tokuhito

2011-05-01

58

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

59

A terahertz pulse emitter monolithically integrated with a quantum cascade laser  

E-print Network

A terahertz pulse emitter monolithically integrated with a quantum cascade laser(QCL) is demonstrated. The emitter facet is excited by near-infrared pulses from a mode-locked Ti:sapphire laser, and the resulting current ...

Kao, Tsung-Yu

60

3-D Terahertz Synthetic-Aperture Imaging and Spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz (THz) wavelengths have attracted recent interest in multiple disciplines within engineering and science. Situated between the infrared and the microwave region of the electromagnetic spectrum, THz energy can propagate through non-polar materials such as clothing or packaging layers. Moreover, many chemical compounds, including explosives and many drugs, reveal strong absorption signatures in the THz range. For these reasons, THz wavelengths have great potential for non-destructive evaluation and explosive detection. Three-dimensional (3-D) reflection imaging with considerable depth resolution is also possible using pulsed THz systems. While THz imaging (especially 3-D) systems typically operate in transmission mode, reflection offers the most practical configuration for standoff detection, especially for objects with high water content (like human tissue) which are opaque at THz frequencies. In this research, reflection-based THz synthetic-aperture (SA) imaging is investigated as a potential imaging solution. THz SA imaging results presented in this dissertation are unique in that a 2-D planar synthetic array was used to generate a 3-D image without relying on a narrow time-window for depth isolation cite [Shen 2005]. Novel THz chemical detection techniques are developed and combined with broadband THz SA capabilities to provide concurrent 3-D spectral imaging. All algorithms are tested with various objects and pressed pellets using a pulsed THz time-domain system in the Northwest Electromagnetics and Acoustics Research Laboratory (NEAR-Lab).

Henry, Samuel C.

61

Terahertz Radiation from Graphite Excited by Femtosecond Laser Pulses  

NASA Astrophysics Data System (ADS)

We experimentally investigate the terahertz (THz) generation from a graphite surface induced by femtosecond laser pulses, and systematically study the dependence on the excitation power, the crystal orientation of graphite, polarization state and incident angle of optical beam. New evidence related to excitation and detection geometry is found and presented, which supports the THz generation mechanism of transient photocarrier transporting along the basal plane normal. Our observation also suggests other probable contributions by in-plane charge oscillations. The results may be helpful to explore and understand the photoelectric properties of graphite and other allotropes of carbon.

Wu, Zhong-An; Wu, Xiao-Jun; Wang, Li

2014-01-01

62

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

63

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

64

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

65

High-bandwidth terahertz radiation from ponderomotively accelerated carriers using Bessel-Gauss femtosecond pulses  

Microsoft Academic Search

Terahertz generation from high intensity excitation of a semiconductor plasma by a radially polarized Bessel-Gauss femtosecond pulse is modeled. The results are compared with Gaussian pulses of equivalent fluence. Due to carrier confinement, a radially polarized Bessel-Gauss pulse exerts a significantly stronger ponderomotive force on photocarriers than a Gaussian pulse, resulting in an order of magnitude increase in the THz

K. J. Chau; A. L. Dechant; A. Y. Elezzabi

2005-01-01

66

High-bandwidth terahertz radiation from ponderomotively accelerated carriers using Bessel–Gauss femtosecond pulses  

Microsoft Academic Search

Terahertz generation from high intensity excitation of a semiconductor plasma by a radially polarized Bessel–Gauss femtosecond pulse is modeled. The results are compared with Gaussian pulses of equivalent fluence. Due to carrier confinement, a radially polarized Bessel–Gauss pulse exerts a significantly stronger ponderomotive force on photocarriers than a Gaussian pulse, resulting in an order of magnitude increase in the THz

K. J. Chau; A. L. Dechant; A. Y. Elezzabi

2005-01-01

67

Terahertz imaging system using high-Tc superconducting oscillation devices  

NASA Astrophysics Data System (ADS)

Microwatt power oscillation devices at sub-terahertz frequency region between 0.3 and 1.0 terahertz (THz) were fabricated from high-Tc superconducting single crystalline Bi2Sr2CaCu2O8+? and used as a source of the transmission terahertz imaging system. As test examples, terahertz images of coins and a razor blade placed inside the brownish paper envelopes with the spatial resolution of 1 mm are presented. The signal-to-noise ratio exceeds 130 in these images. Using a simple wedge-shaped interferometer and analysing the interference fringe pattern, the wavelength of the terahertz wave is calibrated within 0.1% accuracy. This interferometer also provides a simple method to measure the absorption coefficient of the liquid sample. Two test measurements for distilled water and ethanol are demonstrated and their absorption coefficients are obtained with 99.2% accuracy. This suggests that our terahertz imaging system can be applied to many practical applications, such as biological and biomedical imaging, environmental monitoring, microanalysis of impurities, structure and dynamical analyses of large molecules and ions in solution.

Tsujimoto, M.; Minami, H.; Delfanazari, K.; Sawamura, M.; Nakayama, R.; Kitamura, T.; Yamamoto, T.; Kashiwagi, T.; Hattori, T.; Kadowaki, K.

2012-06-01

68

Terahertz real-time imaging for nondestructive detection  

Microsoft Academic Search

We present a real time imaging measurement in the terahertz (THz) frequency region. The dynamic subtraction technique is used to reduce long-term optical background drift. The reflective images of two targets, a Nikon camera's lens cap and a plastic toy gun, are obtained. For the lens cap, the image data were processed to be false color images. For the toy

LiangLiang Zhang; Nick Karpowicz; CunLin Zhang; YueJin Zhao; XiCheng Zhang

2008-01-01

69

Amplification of terahertz pulses in gases beyond thermodynamic equilibrium  

SciTech Connect

In Ebbinghaus et al. [Plasma Sources Sci. Technol. 15, 72 (2006)] we reported terahertz time-domain spectroscopy in a plasma at low pressure, we observed a simultaneous absorption and amplification process within each single rotational transition. Here we show that this observation is a direct consequence of the short interaction time of the pulsed terahertz radiation with the plasma, which is shorter than the average collision time between the molecules. Thus, during the measurement time the molecular states may be considered entangled. Solution of the time-dependent Schroedinger equation yields a linear term that may be neglected for long observation times, large frequencies, or nonentangled states. We determine the restrictions for the observation of this effect and calculate the spectrum of a simple diatomic molecule. Using this model we are able to explain the spectral features showing a change from emission to absorption as observed previously. In addition we find that the amplification and absorption do not follow the typical Lambert-Beer exponential law but an approximate square law.

Schwaab, G. W.; Schroeck, K.; Havenith, M. [Physical Chemistry II, Ruhr-University Bochum, D-44780 Bochum (Germany)

2007-03-15

70

Terahertz time-lapse imaging of hydration in physiological tissues  

NASA Astrophysics Data System (ADS)

This study describes terahertz (THz) imaging of hydration changes in physiological tissues with high water concentration sensitivity. A fast-scanning, pulsed THz imaging system (centered at 525 GHz; 125 GHz bandwidth) was utilized to acquire a 35 mm x 35 mm field-of-view with 0.5 mm x 0.5 mm pixels in less than two minutes. THz time-lapsed images were taken on three sample systems: (1) a simple binary system of water evaporating from a polypropylene towel, (2) the accumulation of fluid at the site of a sulfuric acid burn on ex vivo porcine skin, and (3) the evaporative dehydration of an ex vivo porcine cornea. The diffusion-regulating behavior of corneal tissue is elucidated, and the correlation of THz reflectivity with tissue hydration is measured using THz spectroscopy on four ex vivo corneas. We conclude that THz imaging can discern small differences in the distribution of water in physiological tissues and is a good candidate for burn and corneal imaging.

Bennett, David B.; Taylor, Zachary D.; Bajwa, Neha; Tewari, Priyamvada; Maccabi, Ashkan; Sung, Shijun; Singh, Rahul S.; Culjat, Martin O.; Grundfest, Warren S.; Brown, Elliott R.

2011-02-01

71

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

72

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

73

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

74

Percolation-enhanced generation of terahertz pulses by optical rectification on ultrathin gold films.  

PubMed

Emission of pulses of electromagnetic radiation in the terahertz range is observed when ultrathin gold films on glass are illuminated with femtosecond near-IR laser pulses. A distinct maximum is observed in the emitted terahertz amplitude from films of average thickness just above the percolation threshold. Our measurements suggest that the emission is through a second-order nonlinear optical rectification process, enhanced by the excitation of localized surface plasmon hot spots on the percolated metal film. PMID:21725483

Ramakrishnan, Gopakumar; Planken, Paul C M

2011-07-01

75

Ray-Rracing Model for Terahertz Imaging of SOFI Inspection  

NASA Astrophysics Data System (ADS)

Significant advances made in the field of Terahertz Imaging have captured the attention of many applications including industrial NDE, biomedical imaging and homeland security. The NASA spray on foam insulation (SOFI) inspection is one such critical application were Terahertz imaging is used to detect disbonds and delamination between SOFI and the substrate metal (external tank). This paper discusses modeling aspects of the high frequency inspection system. The feasibility of using a simple ray-tracing model is studied. The efficiency of the model is demonstrated by comparing the model prediction with experimental measurements and further using it in an iterative inverse problem scheme for defect reconstruction.

Melapudi, Vikram R.; Udpa, Lalita; Udpa, Satish S.; Winfree, William P.

2006-03-01

76

Imaging and Modeling Techniques for Terahertz Inspection of NASA-SOFI  

NASA Astrophysics Data System (ADS)

Short-pulsed terahertz imaging techniques have found application in recent years especially in the areas of nondestructive evaluation, homeland security and biomedical imaging. One such application involves the inspection of bonding between spray on foam insulation (SOFI) and the external tank in the NASA space shuttle. This work discusses a suite of image enhancement techniques that was developed to improve the probability of detection of voids and disbands SOFI. Physics based defect detection and profiling methods are detailed along with initial results. In addition a ray-tracing model was developed to simulate the inspection process. Results comparing the model and experimental images will also be presented.

Melapudi, Vikram R.; Nair, Naveen V.; Udpa, Lalita; Udpa, Satish S.; Winfree, William P.

2007-03-01

77

TERAHERTZ RADIATION: Speckle pattern of the images of objects exposed to monochromatic coherent terahertz radiation  

NASA Astrophysics Data System (ADS)

By using a free electron laser and a microbolometer array, real-time images are recorded for the first time in the terahertz range at the rate of up to 90 frames per second. In the case of diffusive illumination of objects by coherent monochromatic radiation, the images consist of speckles. The study of the statistical properties of speckle patterns shows that they are quite accurately described by the theory developed for speckles in the visible range. By averaging a set of images with the help of a rotating scatterer during the exposure time of a frame (20 ms) and by summing statistically independent speckle patterns of many frames, images of the acceptable quality are obtained. The possibilities of terahertz speckle photography and speckle interferometry are discussed.

Vinokurov, Nikolai A.; Dem'yanenko, M. A.; Esaev, D. G.; Knyazev, Boris A.; Kulipanov, Gennadii N.; Chashchina, O. I.; Cherkasskii, Valerii S.

2009-05-01

78

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

79

IMAGING WITH THZ PULSES Timothy Dorney, Jon Johnson, Daniel Mittleman, Richard Baraniuk  

E-print Network

IMAGING WITH THZ PULSES Timothy Dorney, Jon Johnson, Daniel Mittleman, Richard Baraniuk Department-time imaging system based on terahertz (THz) time-domain spectroscopy has been demonstrated. This technique-sensitive detection of the THz pulses. This paper provides a brief introduction of the state-of-the art in THz imaging

80

Rapid Scanning Terahertz Time-Domain Magnetospectroscopy with a Table-Top Repetitive Pulsed Magnet  

E-print Network

We have performed terahertz time-domain magnetospectroscopy by combining a rapid scanning terahertz time-domain spectrometer based on the electronically coupled optical sampling method with a table-top mini-coil pulsed magnet capable of producing magnetic fields up to 30 T. We demonstrate the capability of this system by measuring coherent cyclotron resonance oscillations in a high-mobility two-dimensional electron gas in GaAs and interference-induced terahertz transmittance modifications in a magnetoplasma in lightly doped n-InSb.

Noe, G T; Lee, J; Kato, E; Woods, G L; Nojiri, H; Kono, J

2014-01-01

81

Rapid scanning terahertz time-domain magnetospectroscopy with a table-top repetitive pulsed magnet.  

PubMed

We have performed terahertz time-domain magnetospectroscopy by combining a rapid scanning terahertz time-domain spectrometer based on the electronically controlled optical sampling method with a table-top minicoil pulsed magnet capable of producing magnetic fields up to 30 T. We demonstrate the capability of this system by measuring coherent cyclotron resonance oscillations in a high-mobility two-dimensional electron gas in GaAs and interference-induced terahertz transmittance modifications in a magnetoplasma in lightly doped n-InSb. PMID:25321662

Noe, G Timothy; Zhang, Qi; Lee, Joseph; Kato, Eiji; Woods, Gary L; Nojiri, Hiroyuki; Kono, Junichiro

2014-09-10

82

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

83

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

84

Identification of tooth decay using terahertz imaging and spectroscopy  

Microsoft Academic Search

Terahertz (THz) frequency spectroscopic imaging studies of teeth are reported. The aim is to establish the characteristic properties of the enamel and dentine at these high frequencies. Changes to the THz characteristics as a result of various types of tooth decay are reported showing the potential of this technique for dental diagnosis.

N. N. Zinov'ev; A. F. Fitzgerald; S. M. Strafford; D. J. Wood; F. A. Carmichael; R. E. Miles; M. A. Smith; J. M. Chamberlain

2002-01-01

85

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

86

High field, high efficiency terahertz pulse generation by optical rectification  

E-print Network

The great difficulty of producing high intensity radiation in the terahertz (THz) spectral region by conventional electronics has stimulated interest in development of sources based on photonics. Optical rectification in ...

Huang, Wenqian Ronny

2014-01-01

87

Efficient flat metasurface lens for terahertz imaging.  

PubMed

Metamaterials offer exciting opportunities that enable precise control of amplitude, polarization and phase of the light beam at a subwavelength scale. A gradient metasurface consists of a class of anisotropic subwavelength metamaterial resonators that offer abrupt amplitude and phase changes, thus enabling new applications in optical device design such as ultrathin flat lenses. We propose a highly efficient gradient metasurface lens based on a metal-dielectric-metal structure that operates in the terahertz regime. The proposed structure consists of slotted metallic resonator arrays on two sides of a thin dielectric spacer. By varying the geometrical parameters, the metasurface lens efficiently manipulates the spatial distribution of the terahertz field and focuses the beam to a spot size on the order of a wavelength. The proposed flat metasurface lens design is polarization insensitive and works efficiently even at wide angles of incidence. PMID:25401626

Yang, Quanlong; Gu, Jianqiang; Wang, Dongyang; Zhang, Xueqian; Tian, Zhen; Ouyang, Chunmei; Singh, Ranjan; Han, Jiaguang; Zhang, Weili

2014-10-20

88

Terahertz radiation from antiferromagnetic MnO excited by optical laser pulses  

NASA Astrophysics Data System (ADS)

Terahertz (THz) radiation from antiferromagnetic (AFM) MnO excited by femtosecond laser pulses has been investigated. The radiated THz pulse consists of a single-cycle broadband pulse and an oscillating component with a frequency of 0.83 THz at 10 K. The oscillations are magnetic dipole radiation from optically excited AFM magnons. We found that the peak amplitude of the broadband pulse from MnO increases as the temperature decreases and is significantly enhanced below AFM order temperature. The origin of the broadband pulse radiation observed below AFM order temperature can be attributed to second-order nonlinear optical effects depending on the AFM order.

Nishitani, Junichi; Nagashima, Takeshi; Hangyo, Masanori

2013-08-01

89

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

90

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

91

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

E-print Network

to study gases,2 semiconductors,3 super- conductors,4 dielectrics,5 nonpolar liquids,6 and water.7 WeFar-Infrared Dielectric Properties of Polar Liquids Probed by Femtosecond Terahertz Pulse (), over the frequency range from 2 to 50 cm-1 for water, methanol, ethanol, 1-propanol, and liquid ammonia

92

High-bandwidth terahertz radiation from ponderomotively accelerated carriers using BesselGauss femtosecond pulses  

E-print Network

High-bandwidth terahertz radiation from ponderomotively accelerated carriers using Bessel­Gauss generation from high intensity excitation of a semiconductor plasma by a radially polarized Bessel­Gauss to carrier confinement, a radially polarized Bessel­Gauss pulse exerts a significantly stronger ponderomotive

Chau, Kenneth

93

Terahertz-pulse emission through excitation of surface plasmons in metallic nanostructures  

Microsoft Academic Search

The second-order processes of optical rectification and photoconduction are well known and widely used to produce ultrafast electromagnetic pulses in the terahertz frequency domain. We present a new form of rectification relying on the excitation of surface plasmons (SPs) in metallic nanostructures. Multiphoton ionization and ponderomotive acceleration of electrons in the enhanced evanescent field of the SPs, results in a

Gregor H. Welsh; Klaas Wynne

2008-01-01

94

Plasmon-enhanced terahertz emission in self-assembled quantum dots by femtosecond pulses  

NASA Astrophysics Data System (ADS)

A scheme for terahertz (THz) generation from intraband transition in a self-assembled quantum dot (QD) molecule coupled to a metallic nanoparticle (MNP) is analyzed. The QD structure is described as a three-level atom-like system using the density matrix formalism. The MNP with spherical geometry is considered in the quasistatic approximation. A femtosecond laser pulse creates a coherent superposition of two subbands in the quantum dots and produces localized surface plasmons in the nanoparticle which act back upon the QD molecule via dipole-dipole interaction. As a result, coherent THz radiation with a frequency corresponding to the interlevel spacing can be obtained, which is strongly modified by the presence of the MNP. The peak value of the terahertz signal is analyzed as a function of nanoparticle's size, the MNP to QD distance, and the area of the applied laser field. In addition, we theoretically demonstrate that the terahertz pulse generation can be effectively controlled by making use of a train of femtosecond laser pulses. We show that by a proper choice of the parameters characterizing the pulse train a huge enhancement of the terahertz signal is obtained.

Carreño, F.; Antón, M. A.; Melle, Sonia; Calderón, Oscar G.; Cabrera-Granado, E.; Cox, Joel; Singh, Mahi R.; Egatz-Gómez, A.

2014-02-01

95

Study of freshly excised brain tissues using terahertz imaging.  

PubMed

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

2014-08-01

96

Micromachined antenna-coupled uncooled microbolometers for terahertz imaging arrays  

NASA Astrophysics Data System (ADS)

In recent years our group has made significant progress toward the goal of a scalable, inexpensive terahertz imaging system for the detection of weapons concealed under clothing. By actively illuminating the subject under examination with only moderate source power (few milliwatts) the sensitivity constraints on the detector technology are significantly lessened compared to purely passive millimeter-wave detection. Last year, we demonstrated a fully planar, optically lithographed, uncooled terahertz imaging array with 120 pixels on a silicon substrate 75 mm in diameter. In this paper we present the recent progress on improving the responsivity of the individual microbolometers by a simple technique of surface micromachining to reduce the substrate thermal conduction. We describe the microbolometer array fabrication and present results on devices with a measured electrical responsivity of over 85 V/W (electrical NEP ~25 pW/rtHz), an improvement by a factor of two over current substrate-supported bolometers.

Miller, Aaron J.; Luukanen, Arttu; Grossman, Erich N.

2004-09-01

97

Excitation of terahertz radiation by laser pulses in nonuniform plasma Thomas M. Antonsen, Jr. and John Palastro  

E-print Network

Institute of Physics. DOI: 10.1063/1.2715864 I. INTRODUCTION Electromagnetic terahertz radiation spansExcitation of terahertz radiation by laser pulses in nonuniform plasma channels Thomas M. Antonsen, Jr. and John Palastro Institute for Research in Electronics and Applied Physics, University

Milchberg, Howard

98

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

99

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

100

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

101

Large area terahertz imaging and non-destructive evaluation applications  

Microsoft Academic Search

Abstract: Terahertz (THz) imaging,is being adopted for non-destructive evaluation (NDE) applications in aerospace and other government,and industrial settings [1-3]. NASA is currently employing ,THz reflection NDE to examine ,the space shuttle external tank sprayed on foam insulation (SOFI) for voids and disbonds. Homeland security applications such as the inspection of personnel[2], the detection of concealed explosives[2], biological agents, chemical weapons,

David Zimdars; Jeffrey S. White; G. stuk; A. chernovsky; G. Fichter; S. Williamson

2006-01-01

102

Cost-efficient delay generator for fast terahertz imaging.  

PubMed

We present a fast and low-cost delay generator for terahertz (THz) waves that transfers a rotational motion of a transparent dielectric cube into an effective THz delay. The device is easily implemented in the THz beam path and allows for coherent sampling over 40 ps with a scan rate of hundreds of hertz. Furthermore, we show that our approach is particularly suitable for fast THz imaging. PMID:25121894

Probst, T; Rehn, A; Busch, S F; Chatterjee, S; Koch, M; Scheller, M

2014-08-15

103

Intense terahertz pulses from SLAC electron beams using coherent transition radiation  

SciTech Connect

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/A) at LCLS. This paper presents measurements of the terahertz pulses and preliminary observations of nonlinear materials response.

Wu Ziran; Fisher, Alan S.; Hogan, Mark; Loos, Henrik [Accelerator Directorate, SLAC National Accelerator Laboratory, Stanford University, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Goodfellow, John [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Fuchs, Matthias [Stanford Institute for Materials and Energy Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); PULSE Institute for Ultrafast Energy Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Daranciang, Dan [Department of Chemistry, Stanford University, Stanford, California 94305 (United States); Lindenberg, Aaron [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); PULSE Institute for Ultrafast Energy Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States)

2013-02-15

104

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

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

Excitation of terahertz surface polaritons in a cylindrical waveguide by femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

Generation of terahertz surface polaritons in homogeneous round cross-section plasma waveguides upon nonlinear optical rectification of femtosecond laser pulses is analyzed theoretically. It is assumed that nonlinear polarization inducing a surface electromagnetic wave is formed at the waveguide boundary in a thin layer of the nonlinear dielectric that surrounds the waveguide. The efficiency of the femtosecond radiation conversion into surface polaritons is studied as a function of the waveguide radius and duration of the exciting laser pulse.

Malevich, V. L.; Sinitsyn, G. V.; Rosanov, N. N.

2014-08-01

107

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

NASA Astrophysics Data System (ADS)

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.; Elezzabi, A. Y.

2014-07-01

108

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

109

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

110

Relativistic Doppler frequency upconversion of terahertz pulses reflecting from a photoinduced plasma front in silicon  

NASA Astrophysics Data System (ADS)

We demonstrate experimentally the frequency upconversion of a terahertz (THz) pulse by the relativistic Doppler reflection from a counterpropagating charge-carrier plasma front in high-resistivity Si. The plasma front is generated via interband excitation with an ultrashort optical pump pulse. Spectral components extending to ˜28 THz are observed, using an input THz pulse with a bandwidth of ˜20 THz obtained from a two-color gas plasma emitter. We model the experiment using one-dimensional finite-difference time-domain simulations with realistic values of the Drude parameters for the plasma front, including effects due to excitation from a weak prepulse structure on the pump pulse.

Meng, Fanqi; Thomson, Mark D.; Roskos, Hartmut G.

2014-10-01

111

Terahertz quasi-near-field real-time imaging  

NASA Astrophysics Data System (ADS)

A terahertz (THz) quasi-near-field real-time imaging system is presented. Not only the consumption of experimental time is dramatically reduced, but also the resolution of the imaging system is improved to the magnitude of sub-wavelength of THz waves. THz images of a razor blade edge are obtained and the spatial resolution of the imaging system is discussed in detail. For checking the imaging capability of this system, three metallic plates with different sub-wavelength air hole arrays are imaged and the microstructure of these samples can be clearly observed in their THz images. It is believed that the THz quasi-near-field real-time imaging system should have tremendous applications in the THz microscopic field.

Wang, Xinke; Cui, Ye; Hu, Dan; Sun, Wenfeng; Ye, JiaSheng; Zhang, Yan

2009-12-01

112

High-speed time domain terahertz security imaging  

NASA Astrophysics Data System (ADS)

Terahertz imaging has the potential to reveal concealed explosives; metallic and non-metallic weapons (such as ceramic, plastic or composite guns and knives); flammables; biological agents; chemical weapons and other threats hidden in packages or on personnel. Time domain terahertz imaging can be employed in reflection mode to image with sub millimeter resolution. Previously, single pixel acquisition times for THz waveforms was typically 20 Hz with time records of approx 80 picoseconds, which typically restricted imaging time to hours for areas on the order of 1 square foot, limiting the field practicality of the equipment. We describe and demonstrate advanced imagers with 100 Hz --> 320 picosecond, and 4000 Hz -- 20 picosecond waveform records. These systems have been demonstrated to image >600 pixels/second from a single channel. Such a system, combined with a 32 channel linear THz array, could image a 1 square foot area with 1 mm resolution in <5 seconds, performing a shoe explosives detection image in a short period of time.

Zimdars, David; White, Jeffrey; Williamson, Steven; Stuk, G.

2005-05-01

113

Terahertz generation by nonlinear mixing of laser pulses in a clustered gas  

SciTech Connect

A scheme of terahertz (THz) generation by two collinear laser pulses of finite spot size in a clustered gas is investigated theoretically. The lasers quickly ionize the atoms of the clusters, converting them into plasma balls, and exert a ponderomotive force on the cluster electrons, producing a beat frequency longitudinal current of limited transverse extent. The current acts as an antenna to produce beat frequency terahertz radiation. As the cluster expands under the hydrodynamic pressure, plasma frequency of cluster electrons {omega}{sub pe} decreases and approaches {radical}(3) times the frequency of laser, resonant heating and expansion of clusters occurs. On further expansion of clusters as {omega}{sub pe} approaches {radical}(3) times the terahertz frequency, resonant enhancement in THz radiated power occurs.

Kumar, Manoj; Tripathi, V. K. [Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016 (India)

2011-05-15

114

Inspection of plastic weld joints with terahertz imaging  

NASA Astrophysics Data System (ADS)

Polymers cover the whole range from commodities to high-tech applications. Plastic products have also gained in importance for construction purposes. This draws the attention to joining techniques like welding. Common evaluation of the weld quality is mostly mechanical and destructive. Existing non-destructive techniques are mostly not entirely reliable or economically inefficient. Here, we demonstrate the potential of terahertz time-domain spectroscopy imaging as a non-destructive testing tool for the inspection of plastic weld joints. High-density polyethylene sheets welded in a lap joint with varying quality serve as samples for terahertz transmission measurements. Imperfections within the weld contact area can clearly be detected by displaying the transmitted intensity in a limited frequency range. Contaminations such as metal or sand are identified since they differ significantly from the polymer in the terahertz image. Furthermore, this new and promising technique is capable of detecting the boundaries of a weld contact area. Aside from revealing a contrast between a proper weld joint and no material connection, the size of an air gap between two plastic sheets can be determined by considering the characteristic frequency-dependent transmission through the structure: The spectral positions of the maxima and minima allow for the calculation of the air layer thickness.

Wietzke, S.; Krumbholz, N.; Jördens, C.; Baudrit, B.; Bastian, M.; Koch, M.

2007-06-01

115

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

116

UWB Antennas for CW Terahertz Imaging: Cross Talk Issues  

NASA Astrophysics Data System (ADS)

There is a strong need for wideband and sensitive receivers in the terahertz (THz) region. When considering imaging issues, cross talk between neighbor pixels is of key importance. The case of continuous wave imaging with superconducting hot-electron bolometers as heterodyne mixing sensors is considered, when the coupling to the incident THz radiation is accomplished by means of planar multi-octave self-complementary log-periodic antennas. The minimum distance between two antennas is considered in terms of resolution, diffraction, and electromagnetic coupling criteria. Back-end cross talk between the output lines at the intermediate frequency is briefly addressed.

Kreisler, A. J.; Türer, I.; Gaztelu, X.; Dégardin, A. F.

117

Terahertz imaging with missing data analysis for metamaterials characterization  

NASA Astrophysics Data System (ADS)

Terahertz imaging proves advantageous for metamaterials characterization since the interaction of THz radiation with the metamaterials produces clear patterns of the material. Characteristic "finger prints" of the crystal structure help locating defects, dislocations, contamination, etc. TDS-THz spectroscopy is one of the tools to control metamaterials design and manufacturing. A computational technique is suggested that provides a reliable way of calculation of the metamaterials structure parameters, spotting defects. Based on missing data analysis, the applied signal processing facilitates a better quality image while compensating for partially absent information. Results are provided.

Sokolnikov, Andre

2012-05-01

118

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

119

Physical mechanisms of terahertz pulse emission from photoexcited surfaces of tellurium crystals  

NASA Astrophysics Data System (ADS)

We report on terahertz (THz) emission from tellurium crystal surfaces excited by femtosecond optical pulses. Measurements were performed on three differently cut Te samples and with different wavelength optical excitation pulses. THz pulse amplitude dependences on the azimuthal angle measured at various excitation wavelengths have evidenced that three different mechanisms are responsible for THz generation in tellurium: second order nonlinear optical rectification effect, dominating at lower excitation photon energies, as well as transverse and ordinary photo-Dember effects, which emerge at energies larger than 0.9 eV. The shapes of the azimuthal angle dependences were also explained by theoretical model.

Bi?iÅ«nas, A.; Arlauskas, A.; Adamonis, J.; CicÄ--nas, P.; Krotkus, A.

2014-09-01

120

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

121

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

NASA Astrophysics Data System (ADS)

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; Yu, Wei

2013-10-01

122

Measurement of coherent terahertz radiation for time-domain spectroscopy and imaging  

NASA Astrophysics Data System (ADS)

A high-power terahertz (THz) source for THz time-domain spectroscopy (THz-TDS) and THz imaging has been developed based on an S-band compact electron linac at the National Institute of Advanced Industrial Science and Technology (AIST). A THz pulse was generated as coherent synchrotron radiation (CSR) from an ultra-short electron bunch and expected to have peak power of kW-order with frequency range of 0.1-2 THz. The electro-optic (EO) sampling method with a ZnTe crystal for the THz pulse measurement has been prepared for THz-TDS system. The timing measurement between the THz pulse and a probe laser was carried out. A preliminary experiment of THz transmission imaging of an integrated circuit (IC) card has been successfully demonstrated using the THz CSR pulse and a W-band rf detector. The imaging result was experimentally compared with a result of X-ray imaging. It is confirmed that its intensity and stability are enough to perform for the THz applications.

Kuroda, R.; Yasumoto, M.; Sei, N.; Toyokawa, H.; Ikeura-Sekiguchi, H.; Ogawa, H.; Koike, M.; Yamada, K.

2009-12-01

123

Terahertz imaging in dielectric media with quasi-Bessel beams  

NASA Astrophysics Data System (ADS)

Terahertz (THz) imaging is promising for nondestructive evaluation, since many optically opaque dielectrics are transparent to THz waves. Conventional THz imaging systems employ focusing elements such as spherical lenses and off-axis parabolas, but their fixed focal length produces an inherent trade-off between lateral resolution and depth of focus. Furthermore, image quality suffers when imaging objects located inside a dielectric medium. The air-dielectric interface introduces significant spherical aberration that degrades spatial resolution. Bessel beams are known to produce a small spot size over a large depth of focus. The contribution of our work is two-fold: (1) We demonstrate THz imaging with a significantly improved depth of focus using a zero-th order Bessel beam produced by an axicon lens. (2) We also demonstrate, for the first time to our knowledge, that Bessel beams experience reduced spherical aberration when imaging objects embedded in a dielectric medium. Imaging experiments are performed with a time-domain THz system, where a zero-th order quasi-Bessel beam is formed with an axicon lens made from high density polyethylene (HDPE). The HDPE axicon has a 50 mm diameter and an apex angle of 120 degrees. Point spread function (PSF) measurements confirm that lateral resolution is maintained over a 25 mm depth of field in air. The same lateral resolution is achieved over a 35 mm range inside a HDPE substrate. Needle objects embedded inside a thick HDPE substrate are imaged with high spatial resolution. Image contrast is significantly improved by digital filtering to reduce sidelobe levels. These promising results suggest that Bessel beams are well suited for terahertz nondestructive imaging of thick dielectric objects.

Zhang, Zhuopeng; Buma, Takashi

2011-02-01

124

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

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 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

126

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

127

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

128

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

129

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

130

The excitation and emission of terahertz surface plasmon polaritons on metal wire waveguides  

Microsoft Academic Search

The development of effective techniques for guiding pulsed terahertz radiation is essential for the continued development of terahertz spectroscopy and imaging applications based on the technique of time-domain spectroscopy. Terahertz surface plasmon polaritons (SPPs) can be excited and guided on cylindrical metal wires with low loss and dispersion. This propagating surface wave, known as a Sommerfeld wave, possesses radial polarization,

Jason A. Deibel; Kanglin Wang; Matthew Escarra; Nicholas Berndsen; Daniel M. Mittleman

2008-01-01

131

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

132

Terahertz Generation in Lithium Niobate Driven by Ti:Sapphire Laser Pulses and its Limitations  

E-print Network

We experimentally investigate the limits to 800 nm-to-terahertz (THz) energy conversion in lithium niobate at room temperature driven by amplified Ti:Sapphire laser pulses with tilted-pulse-front. The influence of the pump central wavelength, pulse duration, and fluence on THz generation is studied. We achieved a high peak efficiency of 0.12% using transform limited 150 fs pulses and observed saturation of the optical to THz conversion efficiency at a fluence of 15 mJ/cm2. We experimentally identify two main limitations for the scaling of optical-to-THz conversion efficiencies: (i) the large spectral broadening of the optical pump spectrum in combination with large angular dispersion of the tilted-pulse-front and (ii) free-carrier absorption of THz radiation due to multi-photon absorption of the 800 nm radiation.

Wu, Xiaojun; Ravi, Koustuban; Ahr, Frederike; Cirmi, Giovanni; Zhou, Yue; Mücke, Oliver D; Kärtner, Franz X

2014-01-01

133

Enhancing the energy of terahertz radiation from plasma produced by intense femtosecond laser pulses  

SciTech Connect

Terahertz (THz) radiation from atomic clusters illuminated by intense femtosecond laser pulses is investigated. By studying the angular distribution, polarization properties and energy dependence of THz waves, we aim to obtain a proper understanding of the mechanism of THz generation. The properties of THz waves measured in this study differ from those predicted by previously proposed mechanisms. To interpret these properties qualitatively, we propose that the radiation is generated by time-varying quadrupoles, which are produced by the ponderomotive force of the laser pulse.

Jahangiri, Fazel [Advanced Research Center for Beam Science, ICR, Kyoto University, Kyoto (Japan) [Advanced Research Center for Beam Science, ICR, Kyoto University, Kyoto (Japan); Laser and Plasma Research Institute, Shahid Beheshti University, Tehran (Iran, Islamic Republic of); Hashida, Masaki; Tokita, Shigeki; Sakabe, Shuji [Advanced Research Center for Beam Science, ICR, Kyoto University, Kyoto (Japan) [Advanced Research Center for Beam Science, ICR, Kyoto University, Kyoto (Japan); Department of Physics, GSS, Kyoto University, Kyoto (Japan); Nagashima, Takeshi; Hangyo, Masanori [Department of Physics, GSS, Kyoto University, Kyoto (Japan) [Department of Physics, GSS, Kyoto University, Kyoto (Japan); Institute of Laser Engineering, Osaka University, Osaka (Japan)

2013-05-13

134

A Comparison of Terahertz Pulsed Spectroscopy and Backward-Wave Oscillator Spectroscopy  

NASA Astrophysics Data System (ADS)

This paper presents new experimental and theoretical results for the material parameter reconstruction utilizing the terahertz (THz) pulsed spectroscopy (TPS). The material parameter reconstruction algorithm was realized and experimentally implemented to study the test sample. The algorithm takes into account multiple reflections of THz pulse within the flat sample during the transmission mode measurements. Therefore the samples with small thickness or low refractive index could be studied utilizing the proposed method. In order to estimate the reconstruction accuracy, test sample material parameters, obtained with the TPS, were compared with the results of the same sample studying by the use of the backward-wave oscillator (BWO) spectroscopy. Thus, high reconstruction accuracy was demonstrated.

Zaytsev, Kirill I.; Gavdush, Arseniy A.; Chernomyrdin, Nikita V.; Kruchkov, Nikita P.; Kudrin, Konstantin G.; Nosov, Pavel A.; Karasik, Valeriy E.; Yurchenko, Stanislav O.

2014-09-01

135

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

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

Fiber-pigtailed terahertz time domain spectroscopy instrumentation for package inspection and security imaging  

NASA Astrophysics Data System (ADS)

Terahertz imaging has the potential to reveal concealed explosives; metallic and non-metallic weapons (such as ceramic, plastic or composite guns and knives); flammables; biological agents; chemical weapons and other threats hidden in packages or on personnel. Because terahertz imaging employs safe non-ionizing radiation that penetrates clothing, people may be routinely scanned as well as packages. Images can have sub-millimeter resolution, superior to longer wavelength techniques. Explosives, chemical weapons, and biological agents may posses a spectral fingerprint in the terahertz regime. The application of commercially available time domain terahertz spectroscopy equipment to imaging of concealed threats within packages is shown to penetrate common packing materials and clearly image common plastic and metal threat objects.

Zimdars, David A.

2003-08-01

138

Nonlinear imaging and 3D-mapping of terahertz fields with Kerr media  

E-print Network

We investigate the spatially and temporally resolved four-wave mixing of terahertz fields and optical pulses in large band-gap dielectrics, such as diamond. We show that it is possible to perform beam profiling and space-time resolved mapping of terahertz fields with sub-wavelength THz resolution by encoding the spatial information into an optical signal, which can then be recorded by a standard CCD camera.

Clerici, Matteo; Caspani, Lucia; Peccianti, Marco; Rubino, Eleonora; Razzari, Luca; Légaré, François; Ozaki, Tsuneyuki; Morandotti, Roberto

2013-01-01

139

Terahertz detectors for long wavelength multi-spectral imaging.  

SciTech Connect

The purpose of this work was to develop a wavelength tunable detector for Terahertz spectroscopy and imaging. Our approach was to utilize plasmons in the channel of a specially designed field-effect transistor called the grating-gate detector. Grating-gate detectors exhibit narrow-linewidth, broad spectral tunability through application of a gate bias, and no angular dependence in their photoresponse. As such, if suitable sensitivity can be attained, they are viable candidates for Terahertz multi-spectral focal plane arrays. When this work began, grating-gate gate detectors, while having many promising characteristics, had a noise-equivalent power (NEP) of only 10{sup -5} W/{radical}Hz. Over the duration of this project, we have obtained a true NEP of 10{sup -8} W/{radical}Hz and a scaled NEP of 10{sup -9}W/{radical}Hz. The ultimate goal for these detectors is to reach a NEP in the 10{sup -9{yields}-10}W/{radical}Hz range; we have not yet seen a roadblock to continued improvement.

Lyo, Sungkwun Kenneth; Wanke, Michael Clement; Reno, John Louis; Shaner, Eric Arthur; Grine, Albert D.

2007-10-01

140

Terahertz-Pulse Emission Through Laser Excitation of Surface Plasmons in a Metal Grating Gregor H. Welsh, Neil T. Hunt, and Klaas Wynne*  

E-print Network

Terahertz-Pulse Emission Through Laser Excitation of Surface Plasmons in a Metal Grating Gregor H excitation on terahertz-pulse generation on a gold surface. Surface plasmons can facilitate multi- photon present a new form of rectification that relies on the excitation of surface plasmons in metal films

Strathclyde, University of

141

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

142

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

143

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

E-print Network

. The sam- ples were processed and imaged within 24 hours after surgery. During the imaging experimentLasers in Surgery and Medicine 43:457­462 (2011) Continuous Wave Terahertz Transmission Imaging- hertz imaging has the potential to offer a safe, noninva- sive medical imaging modality for delineating

Massachusetts at Lowell, University of

144

Terahertz transceiver concept.  

PubMed

We present a photoconductive terahertz transceiver based on a modulation of the optical pulses used for generation and detection at different rates. External modulation of the THz pulses is not required as opposed to previously reported approaches. Devices from fiber-optic technology are used, providing flexibility and stability to the system. Imaging and thickness measurement experiments are carried out to demonstrate the performance of the transceiver. PMID:25090501

Busch, Stefan; Probst, Thorsten; Schwerdtfeger, Michael; Dietz, Roman; Palací, Jesús; Koch, Martin

2014-07-14

145

Discrete Pulse Transform of Images  

Microsoft Academic Search

\\u000a The Discrete Pulse Transform (DPT) of images is defined by using a new class of LULU operators on multidimensional arrays.\\u000a This transform generalizes the DPT of sequences and replicates its essential properties, e.g. total variation preservation.\\u000a Furthermore, the discrete pulses in the transform capture the contrast in the original image on the boundary of their supports.\\u000a Since images are perceived

Roumen Anguelov; Inger Fabris-rotelli

2008-01-01

146

Distributed Bragg pulse shapers for terahertz modulation and ultrafast communications  

NASA Astrophysics Data System (ADS)

This work centers around the distributed Bragg pulse shaper (DBPS) and its use in ultrafast communications systems. The DBPS uses parallel electrical inputs to encode serial optical packets. It consists of an array of switchable Bragg mirrors in series along a semiconductor waveguide that encode ultrafast packets through multiple partial reflections of a broadband source pulse. Switching of individual bits in the output packet is achieved by switching the reflectivity of the Bragg mirrors. This is accomplished by electrically inducing a change in the refractive index within a Bragg mirror, moving it in or out of resonance with the source pulse. In this thesis, the coherence domain multiplexed (CDM) communications system is introduced, in which the DBPS acts as a coherence domain encoding source for an ultrafast point-to-point link which uses interferometric detection to compensate for linear dispersion. Compensation of linear dispersion in fiber transmission is demonstrated in a simple optical system. The principles of operation and factors in the design of the DBPS are discussed. The first proof-of-principle demonstrations of the DBPS are presented. A pulse from a Ti:sapphire laser is shaped into a terabit-per-second pulse train, and electrical inputs are used to switch on and off one bit in a 350 Gbit/s packet. Switching is demonstrated first by moving a reflecting Bragg grating out of resonance with the optical source pulse thereby ceasing reflection, and again by moving a nonreflecting Bragg grating into resonance with the source pulse, thereby causing reflection. The operation of the DBPS is modeled using coupled-mode theory, and a simulation of the device is presented that accurately reproduces observed data. The simulation is used to model pulse shapers with ideal characteristics. The magnitude and speed of the electrically induced refractive index change, which is the mechanism responsible for switching in the DBPS, are discussed. Several problems and technical challenges with the current generation of experimental devices are presented, and solutions are proposed which may in the future make the DBPS and CDM system a viable alternative for ultrafast communications.

Purchase, Kenneth Graham

1998-11-01

147

UWB Antennas for CW Terahertz Imaging: Geometry Choice Criteria  

NASA Astrophysics Data System (ADS)

There is a strong need for wideband and sensitive receivers in the terahertz (THz) region. This chapter focuses on the detection of continuous waves (CW) in the THz, using innovative bolometric sensors working as mixers for heterodyne reception with down conversion to the GHz range, as needed for radio astronomy, remote sensing, or passive imaging. In this case, the coupling to the incident THz radiation is accomplished by means of multi-octave planar micro-antennas. After selecting the antenna shape as angular, self-complementary, and/or self-similar, various antenna geometries are studied, namely, bow tie, Sierpinski fractal, sinuous, and log-periodic. Delivered power, directivity, and radiation pattern are discussed. According to seven criteria, the log-periodic antenna is preferred.

Türer, I.; Dégardin, A. F.; Kreisler, A. J.

148

Directional elliptically polarized terahertz emission from air plasma produced by circularly polarized intense femtosecond laser pulses  

SciTech Connect

We have observed directional elliptically polarized terahertz (THz) waves emitted from air plasma produced by circularly polarized femtosecond laser pulses. The spatial distribution of the THz waves shows that the radiation is strongly directed forward with a peak around the laser propagation direction. Measured THz power shows a square dependence on laser energy. We consider the parametric decay of laser light to R-waves in plasma in the presence of a spontaneous magnetic field as a possible explanation for the polarization, power dependence, and direction of the THz beam.

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)

2011-10-17

149

Sensitivity of a vanadium oxide uncooled microbolometer array for terahertz imaging  

NASA Astrophysics Data System (ADS)

The broadband imaging capabilities of a vanadium oxide microbolometer camera were investigated in the far-infrared for applications in real-time terahertz imaging and analysis. To accomplish this, we used an optical configuration consisting of a broadband terahertz source, terahertz filtering optics, and a modified commercial broadband microbolometer camera. A blackbody radiator was employed as the broadband terahertz source to illuminate the microbolometer array with all components in a nitrogen purged enclosure. Data was taken using several different levels of radiant flux intensity. Optical filtering were necessary to isolate incident radiation frequencies into a band from 1.5 to 7.5 THz. Fourier transform infrared spectroscopy was used to characterize the transmission properties of each optical component. The noise equivalent differential temperature (NEDT) and the noise equivalent power (NEP) were recorded over a range of blackbody intensities. We discuss the relative utility of these two figures of merit for terahertz imaging. For example, at a blackbody temperature of 925°C the NEDT was recorded below 800 mK, and the NEP was calculated to be 136 pW/?Hz. This study provides a complete analysis of a microbolometer as the detector component of a terahertz imaging system in a broadband imaging configuration.

Coppinger, Matthew J.; Sustersic, Nathan A.; Kolodzey, James; Allik, Toomas H.

2011-05-01

150

Terahertz imaging systems: a non-invasive technique for the analysis of paintings  

NASA Astrophysics Data System (ADS)

Terahertz (THz) imaging is an emerging technique for non-invasive analysis. Since THz waves can penetrate opaque materials, various imaging systems that use THz waves have been developed to detect, for instance, concealed weapons, illegal drugs, and defects in polymer products. The absorption of THz waves by water is extremely strong, and hence, THz waves can be used to monitor the water content in various objects. THz imaging can be performed either by transmission or by reflection of THz waves. In particular, time domain reflection imaging uses THz pulses that propagate in specimens, and in this technique, pulses reflected from the surface and from the internal boundaries of the specimen are detected. In general, the internal structure is observed in crosssectional images obtained using micro-specimens taken from the work that is being analysed. On the other hand, in THz time-domain imaging, a map of the layer of interest can be easily obtained without collecting any samples. When realtime imaging is required, for example, in the investigation of the effect of a solvent or during the monitoring of water content, a THz camera can be used. The first application of THz time-domain imaging in the analysis of a historical tempera masterpiece was performed on the panel painting Polittico di Badia by Giotto, of the permanent collection of the Uffizi Gallery. The results of that analysis revealed that the work is composed of two layers of gypsum, with a canvas between these layers. In the paint layer, gold foils covered by paint were clearly observed, and the consumption or ageing of gold could be estimated by noting the amount of reflection. These results prove that THz imaging can yield useful information for conservation and restoration purposes.

Fukunaga, K.; Hosako, I.; Duling, I. N., III; Picollo, M.

2009-07-01

151

Emission of terahertz pulses from nanostructured metal surfaces  

NASA Astrophysics Data System (ADS)

When (nanostructured) metals, such as gold and silver, are illuminated with laser pulses having a duration in the femtosecond range, they can emit pulses of THz light. Most of these experiments have been performed using amplified lasers, giving rise to energy densities on the sample on the order of mJ cm-2. The results of the different experiments are surprisingly inconsistent in both the measurements of the THz fluence as a function of laser fluence and in the interpretation of the results. This paper reviews the current state of affairs of this interesting topic and discusses some effects related to surface preparation that may influence the emission THz light on metals, particularly silver and copper. We also show results of measurements on nanostructured metals using unamplified laser pulses, which emphasize the role played by plasmons in the generation of THz light. When increasing the optical energy density on a specially nanostructured sample, we observe a transition from a ‘classical’ second-order non-linear optical process to a higher-order process as the source of the THz radiation. This supports recent results on a differently structured metal by Polyushkin et al (2014 Phys. Rev. B 89 125426), who also observe two different power regimes when decreasing the intensity coming from the high energy density side.

Ramanandan, G. K. P.; Ramakrishnan, G.; Kumar, N.; Adam, A. J. L.; Planken, P. C. M.

2014-09-01

152

Photonic Crystal Fano Laser: Terahertz Modulation and Ultrashort Pulse Generation  

NASA Astrophysics Data System (ADS)

We suggest and analyze a laser with a mirror realized by Fano interference between a waveguide and a nanocavity. For small-amplitude modulation of the nanocavity resonance, the laser can be modulated at frequencies exceeding 1 THz, not being limited by carrier dynamics as for conventional lasers. For larger modulation, a transition from pure frequency modulation to the generation of ultrashort pulses is observed. The laser dynamics is analyzed by generalizing the field equation for conventional lasers to account for a dynamical mirror, described by coupled mode theory.

Mork, J.; Chen, Y.; Heuck, M.

2014-10-01

153

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

154

Substance Detection for Security Screening Using Terahertz Imaging Technology  

Microsoft Academic Search

The ability of terahertz radiation to render many non-metallic and non-polar substances transparent provides for many security applications. In this paper we will focus on the possible application of terahertz radiation scanning the contents for illicit substances in common use suitcases in secure areas. Suitcases and contents were simulated by sandwiching a cotton sheet between nylon or plastic, with the

B. Ung; J. Balakrishnan; B. Fischer; B. W.-H. Ng; D. Abbott

2006-01-01

155

Terahertz generation by dynamical photon drag effect in graphene excited by femtosecond optical pulses.  

PubMed

Graphene has been proposed as a particularly attractive material for the achievement of strong optical nonlinearities, in particular generation of terahertz radiation. However, owing to the particular symmetries of the C-lattice, second-order nonlinear effects such as difference-frequency or rectification processes are predicted to vanish in a graphene layer for optical excitations (?? ? 2EF) involving the two relativistic dispersion bands. Here we experimentally demonstrate that graphene excited by femtosecond optical pulses generate a coherent THz radiation ranging from 0.1 to 4 THz via a second-order nonlinear effect. We fully interpret its characteristics with a model describing the electron and hole states beyond the usual massless relativistic scheme. This second-order nonlinear effect is dynamical photon drag, which relies on the transfer of light momentum to the carriers by the ponderomotive electric and magnetic forces. The model highlights the key roles of next-C-neighbor couplings and of unequal electron and hole lifetimes in the observed second-order response. Finally, our results indicate that dynamical photon drag effect in graphene can provide emission up to 60 THz, opening new routes for the generation of ultrabroadband terahertz pulses. PMID:25226076

Maysonnave, J; Huppert, S; Wang, F; Maero, S; Berger, C; de Heer, W; Norris, T B; De Vaulchier, L A; Dhillon, S; Tignon, J; Ferreira, R; Mangeney, J

2014-10-01

156

Operation of a Wideband Terahertz Superconducting Bolometer Responding to Quantum Cascade Laser Pulses  

NASA Astrophysics Data System (ADS)

We make use of a niobium film to produce a micrometric vacuum-bridge superconducting bolometer responding to THz frequency. The bolometer works anywhere in the temperature range 2-7 K, which can be easily reached in helium bath cryostats or closed-cycle cryocoolers. In this work the bolometer is mounted on a pulse tube refrigerator and operated to measure the equivalent noise power (NEP) and the response to fast (?s) terahertz pulses. The NEP above 100 Hz equals that measured in a liquid helium cryostat showing that potential drawbacks related to the use of a pulse tube refrigerator (like mechanical and thermal oscillations, electromagnetic interference, noise) are irrelevant. At low frequency, instead, the pulse tube expansion-compression cycles originate lines at 1 Hz and harmonics in the noise spectrum. The bolometer was illuminated with THz single pulses coming either from a Quantum Cascade Laser operating at liquid nitrogen temperature or from a frequency-multiplied electronic oscillator. The response of the bolometer to the single pulses show that the device can track signals with a rise time as fast as about 450 ns.

Cibella, S.; Beck, M.; Carelli, P.; Castellano, M. G.; Chiarello, F.; Faist, J.; Leoni, R.; Ortolani, M.; Sabbatini, L.; Scalari, G.; Torrioli, G.; Turcinkova, D.

2012-06-01

157

Generation, transport, and detection of linear accelerator based femtosecond-terahertz pulses  

SciTech Connect

The generation and detection of intense terahertz (THz) radiation has drawn a great attention recently. The dramatically enhanced energy and peak electric field of the coherent THz radiation can be generated by coherent superposition of radiated fields emitted by ultrafast electron bunches. The femtosecond (fs)-THz beamline construction at the Pohang Accelerator Laboratory (PAL) was completed in the end of 2009. The fs-THz beamline at PAL can supply ultrafast and intense fs-THz radiation from a 75 MeV linear accelerator. The radiation is expected to have frequency up to 3 THz ({approx}100 cm{sup -1}) and the pulse width of <200 fs with pulse energy up to 10 {mu}J. This intense THz source has great potential for applications in nonlinear optical phenomena and fields such asmaterial science, biomedical science, chemistry, and physics, etc.

Park, Jaehun; Kim, Changbum; Jung, Seonghoon; Kang, Heung-Sik [Pohang Accelerator Laboratory, POSTECH, Pohang 790-784 (Korea, Republic of); Lee, Jongseok [Department of Applied Physics and QPEC, University of Tokyo, Tokyo 113-8656 (Japan); Yim, Changmook [Department of Physics, POSTECH, Pohang 790-784 (Korea, Republic of); Kim, Chul Hoon; Lee, Junghwa; Ryu, Jaehyun; Joo, Taiha [Department of Chemistry, POSTECH, Pohang 790-784 (Korea, Republic of)

2011-01-15

158

Continuous-wave terahertz reflection imaging of ex vivo nonmelanoma skin cancers  

NASA Astrophysics Data System (ADS)

Nonmelanoma skin cancers are the most common form of cancer. Continuous wave terahertz imaging has the potential to differentiate between nonmelanoma skin cancers and normal skin. Terahertz imaging is non-ionizing and offers a high sensitivity to water content. Contrast between cancerous and normal tissue in transmission mode has already been demonstrated using a continuous wave terahertz system. The aim of this experiment was to implement a system that is capable of reflection modality imaging of nonmelanoma skin cancers. Fresh excisions of skin cancer specimens were obtained from Mohs surgeries for this study. A CO2 optically pumped far-infrared molecular gas laser was used for illuminating the tissue at 584 GHz. The reflected signal was detected using a liquid Helium cooled Silicon bolometer. The terahertz images were compared with sample histology. The terahertz reflection images exhibit some artifacts that can hamper the specificity. The beam waist at the sample plane was measured to be 0.57 mm, and the system's signal-to-noise ratio was measured to be 65 dB.

Joseph, Cecil S.; Yaroslavsky, Anna N.; Neel, Victor A.; Goyette, Thomas M.; Giles, Robert H.

2012-02-01

159

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

E-print Network

since molecular and atomic vibrations as well as surface plasmons can be observed in this energy rangeDevelopment of an electro-optic resonator probe for Terahertz imaging R. Mueckstein, Huiyun Liu sensitivity in Terahertz near-field imaging. Different design parameters are considered and discussed

Haddadi, Hamed

160

Terahertz polariton propagation in patterned materials.  

PubMed

Generation and control of pulsed terahertz-frequency radiation have received extensive attention, with applications in terahertz spectroscopy, imaging and ultrahigh-bandwidth electro-optic signal processing. Terahertz 'polaritonics', in which terahertz lattice waves called phonon-polaritons are generated, manipulated and visualized with femtosecond optical pulses, offers prospects for an integrated solid-state platform for terahertz signal generation and guidance. Here, we extend terahertz polaritonics methods to patterned structures. We demonstrate femtosecond laser fabrication of polaritonic waveguide structures in lithium tantalate and lithium niobate crystals, and illustrate polariton focusing into, and propagation within, the fabricated waveguide structures. We also demonstrate a 90 degrees turn within a structure consisting of two waveguides and a reflecting face, as well as a structure consisting of splitting and recombining elements that can be used as a terahertz Mach-Zehnder interferometer. The structures permit integrated terahertz signal generation, propagation through waveguide-based devices, and readout within a single solid-state platform. PMID:12618821

Stoyanov, Nikolay S; Ward, David W; Feurer, Thomas; Nelson, Keith A

2002-10-01

161

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

162

DEVELOPMENT OF A 4 K STIRLING-TYPE PULSE TUBE CRYOCOOLER FOR A MOBILE TERAHERTZ DETECTION SYSTEM  

SciTech Connect

We discuss in this paper the design and development of a 4 K Stirling-type pulse tube cryocooler for a mobile terahertz detection system. This system integrates new heterodyne detector technology at terahertz frequencies with advancements of Stirling-type pulse tube technology that brings the advent of cooled detector sensitivities in a mobile, compact, and long duration operation system without degradation of sensitivity. To achieve this goal we reduced overall system size, input power, and temperature fluctuations and mechanical vibrations in order to maintain the detector sensitivity. The Stirling-type pulse tube cryocooler developed for this system is a hybrid design employing a He-4 pulse-tube cryocooler operating at 60 Hz and 2.5 MPa average pressure that precools a He-3 pulse tube cryocooler operating at 30 Hz and 1.0 MPa average pressure to achieve 4 K cooling for the terahertz receiver. The He-4 cryocooler employs stainless steel mesh regenerators for the first stage and ErPr spheres for the second stage, while the He-3 cryocooler employs stainless mesh for the first stage and ErPr spheres for the second stage with a layered rare-earth third stage regenerator. Design details and cooler performance goals are discussed.

Bradley, P. E.; Gerecht, E.; Radebaugh, R. [National Institute of Standards and Technology, Boulder, Colorado, 80305 (United States); Garaway, I. [National Institute of Standards and Technology, Boulder, Colorado, 80305 (United States); Technion-Israel Institute of Technology, Haifa (Israel)

2010-04-09

163

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

164

Improved terahertz imaging with a sparse synthetic aperture array  

NASA Astrophysics Data System (ADS)

Sparse arrays are highly attractive for implementing two-dimensional arrays, but come at the cost of degraded image quality. We demonstrate significantly improved performance by exploiting the coherent ultrawideband nature of singlecycle THz pulses. We compute two weighting factors to each time-delayed signal before final summation to form the reconstructed image. The first factor employs cross-correlation analysis to measure the degree of walk-off between timedelayed signals of neighboring elements. The second factor measures the spatial coherence of the time-delayed delayed signals. Synthetic aperture imaging experiments are performed with a THz time-domain system employing a mechanically scanned single transceiver element. Cross-sectional imaging of wire targets is performed with a onedimensional sparse array with an inter-element spacing of 1.36 mm (over four ? at 1 THz). The proposed image reconstruction technique improves image contrast by 15 dB, which is impressive considering the relatively few elements in the array. En-face imaging of a razor blade is also demonstrated with a 56 x 56 element two-dimensional array, showing reduced image artifacts with adaptive reconstruction. These encouraging results suggest that the proposed image reconstruction technique can be highly beneficial to the development of large area two-dimensional THz arrays.

Zhang, Zhuopeng; Buma, Takashi

2010-02-01

165

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

166

Log-periodic antennas for pulsed terahertz radiatioin D, R. Dykaar, B. I. Greene, J. F. Federici, A. F. J. Levi, L. N. Pfeiffer, and R. F. Kopf  

E-print Network

Log-periodic antennas for pulsed terahertz radiatioin D, R. Dykaar, B. I. Greene, J. F. Federici, A of log-periodic antenna, the wire log-spiral, has been designed and implemented on GaAs substrates designs (log-periodic and dipole) used for the detection of pulsed THz radiation. Microwave pulses

Levi, Anthony F. J.

167

Toward remote sensing with broadband terahertz waves  

NASA Astrophysics Data System (ADS)

Terahertz electromagnetic waves, defined as the frequency region between 0.1 and 10 terahertz on the electromagnetic spectrum, have demonstrated remarkable usefulness for imaging and chemical identification with the ability to penetrate many optically opaque barriers. Photon energies at these frequencies are relatively small (meV), which means the radiation is non-ionizing and therefore considered biologically innocuous. With the growing list of applications and demand for terahertz technology, there is a need to develop innovative terahertz sources and detectors that can overcome existing limitations in power, bandwidth, and operating range. Although terahertz radiation has demonstrated unique and exceptional abilities, it has also presented several fundamental challenges. Most notably, the water vapor absorption of terahertz waves in air at habitable altitudes is greater than 100 dB/km. There is an immediate push to utilize the material and vapor identification abilities of terahertz radiation, while extending the effective distances over which the technology can be used. Remote terahertz detection, until recently, was thought to be impossible due to the high water content in the atmosphere, limited signal collection geometries, and solid state materials necessary for generation and detection. This dissertation focuses on laser air-photonics used for sensing short pulses of electromagnetic radiation. Through the ionization process, the very air that we breathe is capable of generating terahertz field strengths greater than 1 MV/cm, useful bandwidths over 100 terahertz, and highly directional emission patterns. Following ionization and plasma formation, the emitted plasma acoustics or fluorescence can be modulated by an external field to serve as omnidirectional, broadband, electromagnetic sensor. A deeper understanding of terahertz wave-plasma interaction is used to develop methods for retrieving coherent terahertz wave information that can be encoded into plasma acoustic and fluorescence wave emission; the ultimate goal aimed at overcoming fundamental limitations of the current terahertz technology. A synthesized bichromatic field-induced laser plasma is used to study effects of electron velocity redistribution inside the plasma filament, and a technique for obtaining a direct correlation between the terahertz field and the plasma acoustic or fluorescence emission is engineered. This dissertation presents significant advances in terahertz air photonics that help to close the "THz gap" once existing between electronic and optical frequencies, and the acoustic and fluorescence detection methodologies developed provide promising new avenues for extending the useful range of terahertz wave technology.

Clough, Benjamin W.

168

Effects of laser-plasma interactions on terahertz radiation from solid targets irradiated by ultrashort intense laser pulses  

Microsoft Academic Search

Interactions of 100-fs laser pulses with solid targets at intensities of 1018 W\\/cm2 and resultant terahertz (THz) radiation are studied under different laser contrast ratio conditions. THz emission is measured in the specular reflection direction, which appears to decrease as the laser contrast ratio varies from 10-8 to 10-6. Correspondingly, the frequency spectra of the reflected light are observed changing

Chun Li; Mu-Lin Zhou; Wen-Jun Ding; Fei Du; Feng Liu; Yu-Tong Li; Wei-Min Wang; Zheng-Ming Sheng; Jing-Long Ma; Li-Ming Chen; Xin Lu; Quan-Li Dong; Zhao-Hua Wang; Zheng Lou; Sheng-Cai Shi; Zhi-Yi Wei; Jie Zhang

2011-01-01

169

Pulsed terahertz spectroscopy of DNA, bovine serum albumin and collagen between 0.1 and 2.0 THz  

Microsoft Academic Search

We report the first use of pulsed terahertz spectroscopy to examine low-frequency collective vibrational modes of biomolecules. Broadband absorption increasing with frequency was observed for lyophilized powder samples of calf thymus DNA, bovine serum albumin and collagen in the 0.06–2.00 THz (2–67 cm?1) frequency range, suggesting that a large number of the low-frequency collective modes for these systems are IR

A. G. Markelz; A. Roitberg; E. J. Heilweil

2000-01-01

170

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

171

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

172

Terahertz near-field probe incorporating a ?/100 aperture for time-domain spectroscopy and imaging  

NASA Astrophysics Data System (ADS)

Achieving high spatial resolutions for imaging with terahertz (THz) waves requires near-field probes, such as a sub-wavelength aperture probe. Bethe's theory of transmission through a sub-wavelength aperture of size a predicts that the transmitted electric field scales as E?a3. This strong dependence limits the size of apertures that can be employed and hence the spatial resolution. This dependence however changes for the evanescent field components in very close proximity (~1?m for THz waves) to the aperture, as shown by electromagnetic simulations. To exploit this effect in a THz near-field probe, we developed a photoconductive THz near-field detector structure, which incorporates a thinned photo-conductive detector region and a distributed Bragg reflector between the detector and the aperture plane. Near-field probes are manufactured with different aperture sizes to investigate transmission of THz pulses through apertures as small as 3?m. The experimental results confirm that the transmitted field amplitude, and therefore the sensitivity, increases by about one order of magnitude for the new probes. A 3?m aperture probe with a spatial resolution of ?/100 at 1THz is demonstrated.

Macfaden, Alexander J.; Reno, John L.; Brener, Igal; Mitrofanov, Oleg

2013-12-01

173

Effect of preformed plasma on terahertz-wave emission from the plasma generated by two-color laser pulses  

SciTech Connect

We introduced a weak prepulse 0-2 ns before the main pulse in the formation of a terahertz (THz) wave in air plasma by laser pulses composed of fundamental and second-harmonic waves. The prepulse suppressed the THz wave generated by the main pulse. We analyzed the suppression factor as a function of the time interval between the prepulse and the main pulse and found that the THz wave from the main pulse decreases immediately after the prepulse, recovers partially within several hundred picoseconds, and then recovers slowly. This suppression is attributed to the dense plasma, which absorbs and screens the generated THz wave, since the relaxation time is close to the lifetime of the fluorescence from the plasma. The results support the idea that the major mechanism of THz wave generation is explained by the plasma current model.

Minami, Yasuo; Nakajima, Makoto; Suemoto, Tohru [Institute for Solid State Physics, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa-shi, Chiba, 277-8581 (Japan)

2011-02-15

174

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

175

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

NASA Astrophysics Data System (ADS)

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 240?m thick sections of nonmelanoma skin cancer were taken at two frequencies of 1.39 THz and 1.63 THz that lie within and outside the tryptophan absorption band, respectively. Two CO2 pumped Far-Infrared molecular gas lasers were used for illuminating the tissue while the transmitted signals were detected using a liquid Helium cooled Silicon bolometer. At both THz frequencies 2-dimensional THz transmission images of nonmelanoma skin cancers were acquired with better than 0.5mm spatial resolution. The resulting images were compared to the sample histology and showed a correlation between cancerous tissue and decreased transmission. The results of the imaging experiments will be presented and discussed.

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

2010-02-01

176

Femtosecond pulse imaging: ultrafast optical oscilloscope  

E-print Network

waves of a shaped femtosecond pulse are mixed with those of a transform-limited pulse to generateFemtosecond pulse imaging: ultrafast optical oscilloscope P. C. Sun, Y. T. Mazurenko,* and Y 12, 1996 A nonlinear optical processor that is capable of real-time conversion of a femtosecond pulse

Fainman, Yeshaiahu

177

Metal wires for terahertz wave guiding.  

PubMed

Sources and systems for far-infrared or terahertz (1 THz = 10(12) Hz) radiation have received extensive attention in recent years, with applications in sensing, imaging and spectroscopy. Terahertz radiation bridges the gap between the microwave and optical regimes, and offers significant scientific and technological potential in many fields. However, waveguiding in this intermediate spectral region still remains a challenge. Neither conventional metal waveguides for microwave radiation, nor dielectric fibres for visible and near-infrared radiation can be used to guide terahertz waves over a long distance, owing to the high loss from the finite conductivity of metals or the high absorption coefficient of dielectric materials in this spectral range. Furthermore, the extensive use of broadband pulses in the terahertz regime imposes an additional constraint of low dispersion, which is necessary for compatibility with spectroscopic applications. Here we show how a simple waveguide, namely a bare metal wire, can be used to transport terahertz pulses with virtually no dispersion, low attenuation, and with remarkable structural simplicity. As an example of this new waveguiding structure, we demonstrate an endoscope for terahertz pulses. PMID:15549101

Wang, Kanglin; Mittleman, Daniel M

2004-11-18

178

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

SciTech Connect

We report on the observation of terahertz oscillations in an electron-hole plasma optically excited by a femtosecond pulse in the {mu}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. [Max-Planck-Institut fur Festkoerperforschung, Heisenberg Str. 1, 70569 Stuttgart (Germany)

2008-07-15

179

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

180

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

181

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

182

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

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

183

High-speed terahertz spectroscopic imaging using noncollinear electro-optic sampling and a multistep mirror.  

PubMed

We propose a method for high-speed terahertz spectroscopic imaging that is based on electro-optic sampling with a noncollinear geometry of the THz beam and probe laser beam and has a multistep mirror in the path of the probe beam. We made an imaging system that operates in the over 2.0-THz range and enables the sample region corresponding to a (28 × 28)-pixel area on the sensor to be imaged with a spatial resolution of 1.07 mm and a frequency resolution of 0.079 THz. We also show how the proposed method might be extended for faster THz spectroscopic imaging. PMID:21935141

Maruyama, Kazunori; Itani, Norihiko; Hasegawa, Shin-ya; Wakana, Shinichi

2011-08-29

184

Kilowatt-peak Terahertz-wave Generation and Sub-femtojoule Terahertz-wave Pulse Detection Based on Nonlinear Optical Wavelength-conversion at Room Temperature  

NASA Astrophysics Data System (ADS)

Intense Terahertz (THz)-wave generation and highly sensitive THz-wave detection were obtained by wavelength conversion with nonlinear optical susceptibility ?(2) of LiNbO3 crystals. Maximum peak output of about 50 kW (5 ?J/pulse) was demonstrated in an injection-seeded THz-wave parametric generator pumped by post-amplified emission from a microchip Nd:YAG laser. Using the sub-nanosecond pulse duration of the laser proposed herein provides effective mitigation of stimulated Brillouin scattering in LiNbO3, producing higher gain for wavelength conversion between near-infrared (near-IR) pump light and THz waves. Monochromatic THz radiation was obtained in the continuous tuning range of 0.7-2.9 THz. Additionally, highly sensitive THz-wave detection was demonstrated based on up-conversion from THz waves to near-IR light as well as efficient THz-wave generation. The signal generated with non-collinear phase-matching condition showed spectroscopic detection on the screen apart from the LiNbO3 crystal. Highly sensitive detection with minimum energy of about 80 aJ/pulse (0.8 ?W at peak) and a large dynamic range of more than 100 dB were achieved in this experiment.

Minamide, Hiroaki; Hayashi, Shin'ichiro; Nawata, Koji; Taira, Takunori; Shikata, Jun-ichi; Kawase, Kodo

2013-12-01

185

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

Microsoft Academic Search

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,

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

2011-01-01

186

Effect of extreme pump pulse reshaping on intense terahertz emission in lithium niobate at multimilliJoule pump energies.  

PubMed

We report on terahertz (THz) generation via optical rectification in a room-temperature lithium niobate crystal under variable pump pulse durations, ranging from 100 to 300 fs, at 800 nm center wavelength. The efficiency for the process is predicted to have an order of magnitude increase when longer duration Fourier-limited pump pulses are used. Our results confirm this increase in efficiency, and we report a record 800 nm pump energy conversion efficiency of 0.35% with a saturation at >240??fs pulse duration. While promising, our findings show a series of key problems that must be overcome before the theoretical limit can be achieved, including the influence of the pump bandwidth broadening due to the cascaded nonlinearity taking place within the crystal. PMID:25078170

Blanchard, F; Ropagnol, X; Hafez, H; Razavipour, H; Bolduc, M; Morandotti, R; Ozaki, T; Cooke, D G

2014-08-01

187

Terahertz heterodyne receiver with quantum cascade laser and hot electron bolometer mixer in a pulse tube cooler  

NASA Astrophysics Data System (ADS)

A liquid cryogen-free terahertz heterodyne receiver in a pulse tube cooler has been realized. The receiver operates at 2.5 THz. It is based on a quantum cascade laser (QCL) as local oscillator and a hot electron bolometric mixer. A detailed study of the QCL beam quality yielded a beam propagation factor of 1.1-1.2. The double sideband noise temperature of the system is 2000 K and when corrected for optical losses in the signal path it is ˜800 K.

Richter, H.; Semenov, A. D.; Pavlov, S. G.; Mahler, L.; Tredicucci, A.; Beere, H. E.; Ritchie, D. A.; Il'in, K. S.; Siegel, M.; Hübers, H.-W.

2008-10-01

188

Terahertz emission from coherent phonons in lithium ternary chalcopyrite crystals illuminated by 1560 nm femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

We have investigated terahertz (THz) emission from lithium ternary chalcopyrite crystals LiInSe2, LiGaSe2, LiInS2, and LiGaS2 that were illuminated by 1560 nm femtosecond pump laser pulses. Monocyclic THz emission caused by nonlinear optical effects was initially observed in all the illuminated crystals. Narrow-band THz emission from the coherent phonons were observed in LiInSe2 (2.87 THz) and LiGaSe2 (2.60 and 3.45 THz). These phonon modes were most likely caused by impulsive stimulated Raman scattering.

Takeya, K.; Takemoto, Y.; Kawayama, I.; Murakami, H.; Matsukawa, T.; Yoshimura, M.; Mori, Y.; Tonouchi, M.

2010-07-01

189

Pulsed terahertz spectroscopy of DNA, bovine serum albumin and collagen between 0.1 and 2.0 THz  

NASA Astrophysics Data System (ADS)

We report the first use of pulsed terahertz spectroscopy to examine low-frequency collective vibrational modes of biomolecules. Broadband absorption increasing with frequency was observed for lyophilized powder samples of calf thymus DNA, bovine serum albumin and collagen in the 0.06-2.00 THz (2-67 cm -1) frequency range, suggesting that a large number of the low-frequency collective modes for these systems are IR active. Transmission measurements at room temperature showed increasing FIR absorption with hydration and denaturing.

Markelz, A. G.; Roitberg, A.; Heilweil, E. J.

2000-03-01

190

Terahertz laser frequency combs  

NASA Astrophysics Data System (ADS)

Terahertz light can be used to identify numerous complex molecules, but has traditionally remained unexploited due to the lack of powerful broadband sources. Pulsed lasers can be used to generate broadband radiation, but such sources are bulky and produce only microwatts of average power. Conversely, although terahertz quantum cascade lasers are compact semiconductor sources of high-power terahertz radiation, their narrowband emission makes them unsuitable for complex spectroscopy. In this work, we demonstrate frequency combs based on terahertz quantum cascade lasers, which combine the high power of lasers with the broadband capabilities of pulsed sources. By fully exploiting the quantum-mechanically broadened gain spectrum available to these lasers, we can generate 5 mW of terahertz power spread across 70 laser lines. This radiation is sufficiently powerful to be detected by Schottky-diode mixers, and will lead to compact terahertz spectrometers.

Burghoff, David; Kao, Tsung-Yu; Han, Ningren; Chan, Chun Wang Ivan; Cai, Xiaowei; Yang, Yang; Hayton, Darren J.; Gao, Jian-Rong; Reno, John L.; Hu, Qing

2014-06-01

191

Review of Moisture and Liquid Detection and Mapping using Terahertz Imaging  

NASA Astrophysics Data System (ADS)

The relatively high permittivity of liquid water compared to other materials in the Terahertz (THz) range enables a contrast mechanism for the detection and imaging of moisture. In this paper, spatial mapping of moisture and liquid detection by THz imaging is reviewed. Analysis of the moisture content is discussed in terms of a double Debye model for liquid water and effective medium models for the permittivity of the dry and `wet' materials of interest. Examples from medical applications, forestry products, agriculture/ food products, and polymers are reviewed. Extraction of diffusion rates and diffusion maps from THz images are discussed.

Federici, John F.

2012-02-01

192

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

193

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

194

Highly precise and accurate terahertz polarization measurements based on electro-optic sampling with polarization modulation of probe pulses.  

PubMed

We have developed an electro-optic (EO) sampling method with polarization modulation of probe pulses; this method allows us to measure the direction of a terahertz (THz) electric-field vector with a precision of 0.1 mrad in a data acquisition time of 660 ms using a 14.0-kHz repetition rate pulsed light source. Through combination with a THz time-domain spectroscopy technique, a time-dependent two-dimensional THz electric field was obtained. We used a photoelastic modulator for probe-polarization modulation and a (111)-oriented zincblende crystal as the EO crystal. Using the tilted pulse front excitation method with stable regeneratively amplified pulses, we prepared stable and intense THz pulses and performed pulse-by-pulse analog-to-digital conversion of the signals. These techniques significantly reduced statistical errors and enabled sub-mrad THz polarization measurements. We examined the performance of this method by measuring a wire-grid polarizer as a sample. The present method will open a new frontier of high-precision THz polarization sensitive measurements. PMID:25089412

Nemoto, Natsuki; Higuchi, Takuya; Kanda, Natsuki; Konishi, Kuniaki; Kuwata-Gonokami, Makoto

2014-07-28

195

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

196

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

197

Real-time terahertz imaging over a standoff distance (>25 meters)  

NASA Astrophysics Data System (ADS)

The authors demonstrate the use of a terahertz quantum cascade laser (QCL) for real-time imaging in transmission mode at a standoff distance of 25meters. Lasing frequency was selected for optimum transmission within an atmospheric window at ˜4.9THz. Coarse frequency selection was made by design of the QCL gain medium. Finer selection (to within 0.1THz) was made by judicious choice of laser cavity length to adjust facet losses and therefore lasing threshold bias, in order to overlap the peak frequency of the Stark-shifted gain spectrum with the atmospheric window. Images are shown using an uncooled 320×240 microbolometer camera.

Lee, Alan W. M.; Qin, Qi; Kumar, Sushil; Williams, Benjamin S.; Hu, Qing; Reno, John L.

2006-10-01

198

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

199

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

200

Using terahertz pulse spectroscopy to study the crystalline structure of a drug: A case study of the polymorphs of ranitidine hydrochloride  

Microsoft Academic Search

We describe the application of Terahertz pulse spectroscopy to polymorph identification. The particular compounds investigated were the different crystalline Forms 1 and 2 of ranitidine hydrochloride, both in the pure form and also obtained as a marketed pharmaceutical product. Identification was clear. The technique has advant- ages that excitation is not via a powerful laser source, as used in Raman

P. F. Taday; I. V. Bradley; D. D. Arnone; M. Pepper

2003-01-01

201

Transmission properties of terahertz pulses through semiconductor split-ring resonators  

NASA Astrophysics Data System (ADS)

In this paper, two novel planar terahertz semiconductor split-ring resonators are successfully constructed and measured using the commercial software CST Microwave Studio. They exhibit a duel-band and a triple-band transmission property within the frequencies ranging from 0.1THz to 3THz. We have simulated the dual-band planar metamaterial with two distinct electric resonances at 0.81THz and 1.818THz, and triple-band planar metamaterial with three distinct electric resonances at 0.543THz, 1.044THz, and 1.506THz. These developments are further steps towards the development of broadband terahertz devices.

yun-hong, He; Jiu-sheng, Li

2011-02-01

202

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

203

Analysis of terahertz spectral images of explosives and bioagents using trained neural networks  

NASA Astrophysics Data System (ADS)

A non-invasive means to detect and characterize concealed agents of mass destruction in near real-time with a wide field-of-view is under development. The method employs spatial interferometric imaging of the characteristic transmission or reflection frequency spectrum in the Terahertz range. However, the successful (i.e. low false alarm rate) analysis of such images will depend on correct distinction of the true agent from non-lethal background signals. Neural networks are being trained to successfully distinguish images of explosives and bioagents from images of harmless items. Artificial neural networks are mathematical devices for modeling complex, non-linear relationships. Both multilayer perceptron and radial basis function neural network architectures are used to analyze these spectral images. Positive identifications are generally made, though, neural network performance does deteriorate with reduction in frequency information. Internal tolerances within the identification process can affect the outcome.

Oliveira, Filipe; Barat, Robert; Schulkin, Brian; Huang, Feng; Federici, John F.; Gary, Dale; Zimdars, David

2004-09-01

204

Terahertz imaging with sub-wavelength resolution by femtosecond laser filament in air.  

PubMed

Terahertz (THz) imaging provides cutting edge technique in biology, medical sciences and non-destructive evaluation. However, due to the long wavelength of the THz wave, the obtained resolution of THz imaging is normally a few hundred microns and is much lower than that of the traditional optical imaging. We introduce a sub-wavelength resolution THz imaging technique which uses the THz radiation generated by a femtosecond laser filament in air as the probe. This method is based on the fact that the femtosecond laser filament forms a waveguide for the THz wave in air. The diameter of the THz beam, which propagates inside the filament, varies from 20??m to 50??m, which is significantly smaller than the wavelength of the THz wave. Using this highly spatially confined THz beam as the probe, THz imaging with resolution as high as 20??m (~?/38 at 0.4?THz) can be realized. PMID:24457525

Zhao, Jiayu; Chu, Wei; Guo, Lanjun; Wang, Zhi; Yang, Jing; Liu, Weiwei; Cheng, Ya; Xu, Zhizhan

2014-01-01

205

Terahertz polarization real-time imaging based on balanced electro-optic detection.  

PubMed

A terahertz (THz) polarization real-time imaging system that can effectively reduce experimental time consumption for acquiring a sample's polarization information is achieved. An alternative THz polarization measurement method is proposed. In this method, a <110> zinc-blende crystal is used as the sensor, and the probe polarization is adjusted to detect THz electric fields on the two orthogonal polarization components. The relative sensitivity of the imaging system to the THz polarization angle is estimated to be less than 0.5°. To illustrate the ability of the system, two samples are designed and measured by using the system. From their THz polarization real-time images, each region of these samples can be precisely presented. Experimental results clearly show the special influences of different materials on the THz polarization. This work effectively extends the information content obtained by THz real-time imaging and improves the feasibility of the imaging technique. PMID:21045903

Wang, Xinke; Cui, Ye; Sun, Wenfeng; Ye, JiaSheng; Zhang, Yan

2010-11-01

206

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

207

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

Microsoft Academic Search

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

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

2009-01-01

208

Millimeter-Wave and Terahertz Imaging in Security Applications  

NASA Astrophysics Data System (ADS)

The relatively short wavelength of mm-wave and THz radiation coupled with good transmission through many dielectric materials allows images to be formed of concealed objects. This chapter gives an overview of the detectors, their associated circuitry, and system developments over the past 10 years, focussing on personnel security screening. We will discuss the phenomenology of imaging at these wavelengths, introduce the reader to the basic architectures being used and developed for image forming instruments, show examples of systems, and also discuss the feasibility of spectroscopic THz imaging for security screening applications.

Luukanen, Arttu; Appleby, Roger; Kemp, Mike; Salmon, Neil

209

Passive stand-off terahertz imaging with 1 hertz frame rate  

NASA Astrophysics Data System (ADS)

Terahertz (THz) cameras are expected to be a powerful tool for future security applications. If such a technology shall be useful for typical security scenarios (e.g. airport check-in) it has to meet some minimum standards. A THz camera should record images with video rate from a safe distance (stand-off). Although active cameras are conceivable, a passive system has the benefit of concealed operation. Additionally, from an ethic perspective, the lack of exposure to a radiation source is a considerable advantage in public acceptance. Taking all these requirements into account, only cooled detectors are able to achieve the needed sensitivity. A big leap forward in the detector performance and scalability was driven by the astrophysics community. Superconducting bolometers and midsized arrays of them have been developed and are in routine use. Although devices with many pixels are foreseeable nowadays a device with an additional scanning optic is the straightest way to an imaging system with a useful resolution. We demonstrate the capabilities of a concept for a passive Terahertz video camera based on superconducting technology. The actual prototype utilizes a small Cassegrain telescope with a gyrating secondary mirror to record 2 kilopixel THz images with 1 second frame rate.

May, T.; Zieger, G.; Anders, S.; Zakosarenko, V.; Starkloff, M.; Meyer, H.-G.; Thorwirth, G.; Kreysa, E.

2008-04-01

210

Mine field detection and identification using terahertz spectroscopic imaging  

Microsoft Academic Search

The spatial, temporal, and spectroscopic characteristics associated with pulsed THz (100 GHz 70 THz) radiation provide this emerging technology with the potential for reliable identification of buried objects such as non-metallic landmines. With a suitable integration of these attributes, one can envision a THz detection platform that provides: (1) accurate identification of buried objects, and (2) a source-to-sample working distance

Robert Osiander; Joseph A. Miragliotta; Zhiping Jiang; Jingzhou Xu; Xi-Cheng Zhang

2003-01-01

211

Diffuse reflection imaging at terahertz frequencies for security applications  

NASA Astrophysics Data System (ADS)

We report diffuse reflection imaging of concealed powdered samples in atmospheric air using a quantum cascade laser operating at 2.83 THz. The imaging system uses a helium-cooled silicon bolometer for mapping radiation diffusely reflected and scattered from samples, and a room-temperature pyroelectric sensor for simultaneously acquiring a specular image. A range of powders concealed within plastic packaging and standard FedEx envelopes was imaged with a resolution of better than 0.5 mm, and it was possible to detect powdered samples concealed within packaging from which there was a strong component of surface reflection. The feasibility of performing dual-wavelength diffuse reflection imaging for identification of illicit drugs and explosives is discussed.

Dean, P.; Khanna, S.; Chakraborty, S.; Lachab, M.; Davies, A. G.; Linfield, E. H.

2007-10-01

212

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

SciTech Connect

We show that optical pump-terahertz probe spectroscopy is a direct experimental tool 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 differ significantly being primarily of a multiphoton character in the former case and a strong-field process in the latter case. The generation of the plasma in the focal volume of the laser and its expansion on subnanosecond time scale is directly monitored through its density-dependent susceptibility. A Drude model used to evaluate the plasma densities and electron-scattering rates successfully captures the observations for a wide range of pump intensities. In addition, rotational fingerprints of molecular and ionic species were also observed in the spectra.

Mics, Zoltan; Kadlec, Filip; Kuzel, Petr; Jungwirth, Pavel; Bradforth, Stephen E.; Apkarian, V. Ara [Institute of Physics, Academy of Sciences of the Czech Republic, and Center for Biomolecules and Complex Molecular Systems, Na Slovance 2, 182 21 Prague 8 (Czech Republic); Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic (Czech Republic); Center for Biomolecules and Complex Molecular Systems, Flemingovo nam. 2, 166 10 Prague 6 (Czech Republic); Department of Chemistry, University of Southern California, Los Angeles, California 90089 (United States); Department of Chemistry, University of California, Irvine, California 92697 (United States)

2005-09-08

213

Terahertz and Millimetre Wave Imaging with a Broadband Josephson Detector Working above 77 K  

NASA Astrophysics Data System (ADS)

A high-Tc superconducting (HTS) broadband Josephson detector has been developed and applied to millimetre wave (mm-wave) and terahertz (THz) imaging. The detector is based on a YBa2Cu3O7-x (YBCO) step-edge Josephson junction, which is coupled to a thin-film log-periodic antenna, designed for operation at 200-600 GHz, and a hemispheric silicon lens. The junction parameters have been optimised to achieve a high IcRn value so that the detector responds well to the specified frequencies at liquid nitrogen temperature (77 K). Images at ˜200 GHz and ˜600 GHz were acquired with the same detector; each demonstrated their unique properties. The results demonstrate the potential of achieving a cheaper, compact and portable multi-spectral imager based on a HTS detector.

Du, Jia; Hellicar, A. D.; Hanham, S. M.; Li, L.; Macfarlane, J. C.; Leslie, K. E.; Foley, C. P.

2011-05-01

214

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

215

Uncooled bolometer-type Terahertz focal plane array and camera for real-time imaging  

NASA Astrophysics Data System (ADS)

Real-time Terahertz (THz) imaging technologies which make use of uncooled bolometer-type infrared focal plane arrays (FPAs) and quantum cascade lasers (QCLs) will be reviewed. A description of how THz focal plane array and THz imagers have been developed on the basis of infrared technologies, especially the improvement in both THz sensitivity of bolometer-type FPA and THz transmittance of materials for lens and vacuum package window will be given. Characteristics of 320×240 THz-FPA, such as relation of noise equivalent power (NEP) to wavelength and real-time THz imageries will be presented. One of the imageries indicates that THz technology is promising for label-free detection of reaction of small molecules with proteins.

Oda, Naoki

2010-08-01

216

Ultrafast far-infrared dynamics probed by terahertz pulses: a frequency-domain approach. II. Applications.  

PubMed

We present data obtained by time-resolved terahertz spectroscopy in selected semiconducting and molecular systems exhibiting subpicosecond far-infrared dynamics. We use a frequency-domain method which eliminates the influence of instrumental functions and artifacts due to frequency mixing and yields a two-dimensional transient conductivity of the photoexcited sample. This technique enables improving the attainable experimental time resolution and allows a simple qualitative interpretation of the results without a priori modeling. The quantitative interpretation is based on the time-dependent Drude and damped harmonic oscillator models. PMID:15836329

N?mec, H; Kadlec, F; Kadlec, C; Kuzel, P; Jungwirth, P

2005-03-01

217

FDTD-based computed terahertz wave propagation in multilayer medium structures  

NASA Astrophysics Data System (ADS)

The terahertz region of the electromagnetic spectrum spans the frequency range of 0.1THz~10THz, which means it sandwiches between the mid-infrared (IR) and the millimeter/ microwave. With the development and commercialization of terahertz pulsed spectroscopy (TPS) and terahertz pulsed imaging (TPI) systems, terahertz technologies have been widely used in the sensing and imaging fields. It allows high quality cross-sectional images from within scattering media to be obtained nondestructively. Characterizing the interaction of terahertz radiation with multilayer medium structures is critical for the development of nondestructive testing technology. Currently, there was much experimental investigation of using TPI for the characterization of terahertz radiation in materials (e.g., pharmaceutical tablet coatings), but there were few theoretical researches on propagation of terahertz radiation in multilayer medium structures. Finite Difference Time Domain (FDTD) algorithm is a proven method for electromagnetic scattering theory, which analyzes continuous electromagnetic problems by employing finite difference and obtains electromagnetic field value at the sampling point to approach the actual continuous solutions. In the present work, we investigated the propagation of terahertz radiation in multilayer medium structures based on FDTD method. The model of multilayer medium structures under the THz frequency plane wave incidence was established, and the reflected radiation properties were recorded and analyzed. The terahertz radiation used was broad-band in the frequency up to 2 THz. A batch of single layer coated pharmaceutical tablets, whose coating thickness in the range of 40~100?m, was computed by FDTD method. We found that the simulation results on pharmaceutical tablet coatings were in good agreement with the experimental results obtained using a commercial system (TPI imaga 2000, TeraView, Cambridge, UK) , demonstrating its usefulness in simulating and analyzing terahertz responses from a multilayered sample.

Tu, Wan-li; Zhong, Shun-cong; Yao, Hai-zi; Shen, Yao-chun

2013-08-01

218

Discrete spectrum terahertz imaging using bow-tie diodes: optimized antenna designs and arrays  

NASA Astrophysics Data System (ADS)

Optimization routes to optimize the operation of InGaAs bow-tie diodes were demonstrated using simulations based on 3D finite-difference time-domain method. Calculations of the electromagnetic field amplitude distribution in a detector plane were performed. Three types of designs - bow-tie diode itself, log-periodic antenna and log-periodic antenna coupled with the bow-tie diode were analyzed; it was determined that frequency properties of such antennacoupled device can be tuned via variation of antenna shape and size. Multi-pixel InGaAs bow-tie diodes arrays of different designs - narrow band and broadband operation - were designed and fabricated. They were demonstrated to be well suited for continuous wave room temperature spectroscopic terahertz imaging at 0.58 THz and at 1.63 THz.

Minkevi?ius, Linas; Madeikis, Karolis; Kašalynas, Irmantas; Venckevi?ius, Rimvydas; Seliuta, Dalius; TamošiÅ«nas, Vincas; Valušis, Gintaras

2013-09-01

219

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.

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

220

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

221

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

222

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

223

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

224

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

NASA Astrophysics Data System (ADS)

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 1.25-2.5THz. A sensitivity threshold of 1.3×10-3W/cm2 was obtained for the FPA with a homemade absolute interferometric power meter. Videos up to 90frames/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.; Knyazev, B. A.; Kulipanov, G. N.; Vinokurov, N. A.

2008-03-01

225

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

226

Pulsed EPR imaging: image reconstruction using selective acquisition sequences.  

PubMed

Pulsed nuclear magnetic resonance imaging (NMRI) apparatus has developed very quickly. On the other hand, the development of apparatus for pulsed electron paramagnetic resonance imaging (EPRI) has been very slow. This fact is due to the extremely reduced relaxation times of the paramagnetic probes. EPR linewidths are larger than typical NMR linewidths. These large linewidths are also responsible for a substantial worsening of spatial resolution. Due to the brevity of the electronic relaxation times, not all the acquisition/reconstruction techniques currently used in NMRI (such as spin-echo, gradient-echo, etc) can be applied in pulsed EPRI. In fact, the usable sequences in pulsed EPRI are only acquisitions from projections, where it is possible to use stationary magnetic field gradients. Moreover, the use of high fixed magnetic field gradients induces a short decay time constant T2*. The low T2* value can make it impossible for the analogue to digital conversion system (ADC) to reproduce signal variations during the whole acquisition interval and the resolution can worsen. A new pulsed EPRI acquisition sequence from projections, based on selective reception, is presented that is particularly useful in solving the problems of worsening of spatial resolution associated with the use of an ADC. In order to demonstrate the capabilities of our acquisition method, simulated numerical tests will also be reported. PMID:10498510

Di Giuseppe, S; Placidi, G; Brivati, J A; Alecci, M; Sotgiu, A

1999-06-01

227

Image reconstruction from Pulsed Fast Neutron Analysis  

SciTech Connect

Pulsed Fast Neutron Analysis (PFNA) has been demonstrated to detect drugs and explosives in trucks and large cargo containers. PFNA uses a collimated beam of nanosecond-pulsed fast neutrons that interact with the cargo contents to produce gamma rays characteristic to their elemental composition. By timing the arrival of the emitted radiation to an array of gamma-ray detectors a three-dimensional elemental density map or image of the cargo is created. The process to determine the elemental densities is complex and requires a number of steps. The first step consists of extracting from the characteristic gamma-ray spectra the counts associated with the elements of interest. Other steps are needed to correct for physical quantities such as gamma-ray production cross sections and angular distributions. The image processing includes also phenomenological corrections that take into account the neutron attenuation through the cargo, and the attenuation of the gamma rays from the point they were generated to the gamma-ray detectors. Additional processing is required to map the elemental densities from the data acquisition system of coordinates to a rectilinear system. This paper describes the image processing used to compute the elemental densities from the counts observed in the gamma-ray detectors.

Bendahan, Joseph; Feinstein, Leon; Keeley, Doug; Loveman, Rob [Ancore Corporation, 2950 Patrick Henry Drive, Santa Clara, California 95054 (United States)

1999-06-10

228

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

229

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

PubMed

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?? W Hz(?½). Transmission imaging experiments at 0.3 THz show the good reliability and sensitivity of the devices in a real practical application. PMID:23618953

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

2013-05-31

230

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

231

Polarization changes in temporal imaging with pulses of random light.  

PubMed

We consider polarization changes of randomly fluctuating electromagnetic pulsed light in temporal imaging. The polarization properties of pulses formed by the time lens are formulated in terms of the Stokes parameters. For Gaussian Schell-model pulses we show that the degree and state of polarization of the time-imaged pulse can be tailored in versatile ways, depending on the temporal polarization and coherence of the input pulse and the system parameters. In particular, weakly polarized central region of the pulse may become fully polarized without energy absorption. The results have potential applications in optical communication, micromachining, and light-matter interactions. PMID:23571989

Voipio, Timo; Setälä, Tero; Friberg, Ari T

2013-04-01

232

Detection of pulsed far-infrared and terahertz light with an atomic force microscope  

NASA Astrophysics Data System (ADS)

We show that a commercial atomic force microscope can be used at room temperature as a detector throughout the infrared spectrum simply by recording the induced oscillation of its cantilever after irradiation by a pulsed laser. The oscillation amplitude can be made larger by spraying an absorbing graphite layer on the tip side. We demonstrate that its good sensitivity is due to a bilayer effect: their different thermal expansion coefficient forcing them to bend under irradiation. For the far-infrared spectral range, this device avoids the use of Helium cooled detectors and their numerous constraints.

Ortega, J.-M.; Glotin, F.; Prazeres, R.; Berthet, J.-P.; Dazzi, A.

2012-10-01

233

Multisensor Image Fusion Using a Pulse Coupled Neural Network  

Microsoft Academic Search

\\u000a Multisensor image fusion has its effective utilization for surveillance. In this paper, we utilize a pulse coupled neural\\u000a network method to merge images from different sensors, in order to enhance visualization for surveillance. On the basis of\\u000a standard mathematical model of pulse coupled neural network, a novel step function is adopted to generate pulses. Subjective\\u000a and objective image fusion performance

Yi Zheng; Ping Zheng

2010-01-01

234

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

235

Terahertz wave spectrum analysis of microstrip structure  

NASA Astrophysics Data System (ADS)

Terahertz wave is a kind of electromagnetic wave ranging from 0.1~10THz, between microwave and infrared, which occupies a special place in the electromagnetic spectrum. Terahertz radiation has a strong penetration for many media materials and nonpolar substance, for example, dielectric material, plastic, paper carton and cloth. In recent years, researchers around the world have paid great attention on terahertz technology, such as safety inspection, chemical biology, medical diagnosis and terahertz wave imaging, etc. Transmission properties of two-dimensional metal microstrip structures in the terahertz regime are presented and tested. Resonant terahertz transmission was demonstrated in four different arrays of subwavelength microstrip structure patterned on semiconductor. The effects of microstrip microstrip structure shape were investigated by using terahertz time-domain spectroscopy system. The resonant terahertz transmission has center frequency of 2.05 THz, transmission of 70%.

Song, Mei-jing; Li, Jiu-sheng

2012-03-01

236

Terahertz wave spectrum analysis of microstrip structure  

NASA Astrophysics Data System (ADS)

Terahertz wave is a kind of electromagnetic wave ranging from 0.1~10THz, between microwave and infrared, which occupies a special place in the electromagnetic spectrum. Terahertz radiation has a strong penetration for many media materials and nonpolar substance, for example, dielectric material, plastic, paper carton and cloth. In recent years, researchers around the world have paid great attention on terahertz technology, such as safety inspection, chemical biology, medical diagnosis and terahertz wave imaging, etc. Transmission properties of two-dimensional metal microstrip structures in the terahertz regime are presented and tested. Resonant terahertz transmission was demonstrated in four different arrays of subwavelength microstrip structure patterned on semiconductor. The effects of microstrip microstrip structure shape were investigated by using terahertz time-domain spectroscopy system. The resonant terahertz transmission has center frequency of 2.05 THz, transmission of 70%.

Song, Mei-jing; Li, Jiu-sheng

2011-11-01

237

IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY, VOL. 1, NO. 2, NOVEMBER 2011 473 One-Dimensional Terahertz Imaging of  

E-print Network

-images of surfactant-stabilized dodecane(C12H26)-brine emulsions are obtained by translating the emulsified region capillary forces, to allow for the formation of a micro-emulsion phase and allow the emulsified oil

Mittleman, Daniel

238

Terahertz imaging: a new non-destructive technique for the quality control of plastic weld joints  

NASA Astrophysics Data System (ADS)

We present the first investigation of plastic weld joints using terahertz waves. Terahertz time-domain spectroscopy clearly reveals contaminations like metal or sand within the weld joint of two high-density polyethylene sheets. Furthermore, areas can be identified where the welding process has failed and the parts to be joined are separated by a small air gap. We show that a three layer structure of polyethylene-air-polyethylene has a characteristic, frequency-dependent transmission behaviour. This allows for a distinction between welded and non-welded material as well as for the calculation of the air layer thickness from the relative transmission spectrum. Consequently, terahertz time-domain spectroscopy provides a promising new non-destructive and even contactless technique, which is desired by the plastics industry for detecting a variety of deviations from the ideal welding process.

Wietzke, S.; Jördens, C.; Krumbholz, N.; Baudrit, B.; Bastian, M.; Koch, M.

2007-04-01

239

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

240

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

241

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

E-print Network

Cabot Street, Lowell, MA 01854 b U.S. Army National Ground Intelligence Center, 2055 Boulders Road of Massachusetts Lowell has produced full-body terahertz imagery using coherent active radar measurement techniques contrasting techniques were used to collect the imagery. Both methods made use of in-house transceivers

Massachusetts at Lowell, University of

242

Terahertz frequency spectrum characterization of coherent heterodyne time-domain spectrometer  

NASA Astrophysics Data System (ADS)

Terahertz wave which can provide innovative sensing and imaging techniques can obtain spectroscopic information unavailable at other wavelengths. The terahertz air-biased-coherent-detection (ABCD) method can achieve the third-order nonlinear susceptibility tensor to produce field-induced optical second harmonic photons. Therefore, the intense terahertz wave generated and detected by the laser-induced air plasma provides a promising ultra-broadband terahertz source and sensor for spectroscopy and imaging technique. Aiming at that purpose, an understanding of the frequency spectrum characterization of terahertz pulse is crucial. In this work, we investigated the variation of the THz pulse bandwidth measured through the third harmonic generation using the coherent detection scheme, by increasing the optical probe pulse power and biased electric field. A bandwidth broadening of the measured THz pulse is observed by increasing either the probe pulse power or the bias voltage strength. We speculate that a pulse shape change of the probe beam and a saturation effect during the second-harmonic generation might cause the bandwidth broaden with probe power. To further investigate the mechanism, we fixed the power of probe laser at 150mW and changed the bias voltage. The results show that the frequency spectrum width becomes wider gradually with the increasing of the bias voltage. A theoretical explaination shows that the bandwidth broadening with bias field might be introduced by a pulse shape change of the bias field induced second harmonic wave. This study reveals that we can control THz intensity and bandwidth by changing probe power and bias voltage in the ABCD system.

Zhao, Ji; Zhang, Liang-liang; Luo, Yi-man; Wu, Tong; Zhang, Cunlin; Zhao, Yue-jin

2013-12-01

243

Direct imaging of hot spots 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) (BSCCO) are a promising source of coherent continuous-wave terahertz radiation. It is thought that at electrical bias conditions under which THz-emission occurs, 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. Here, we perform an imaging study of the temperature distribution at the surface of BSCCO stacks utilizing the temperature-dependent 612 nm fluorescence line of Eu3+ in a europium chelate. The images directly 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, T. M.; Koshelev, A. E.; Kwok, W.-K.; Welp, U.; Vlasko-Vlasov, V. K.; Kadowaki, K.; Minami, H.; Watanabe, C.

2013-04-01

244

Antenna-coupled microbolometer based uncooled 2D array and camera for 2D real-time terahertz imaging  

NASA Astrophysics Data System (ADS)

CEA-Leti has developed a monolithic large focal plane array bolometric technology optimized for 2D real-time imaging in the terahertz range. Each pixel consists in a silicon microbolometer coupled to specific antennas and a resonant quarter-wavelength cavity. First prototypes of imaging arrays have been designed and manufactured for optimized sensing in the 1-3.5THz range where THz quantum cascade lasers are delivering high optical power. NEP in the order of 1 pW/sqrt(Hz) has been assessed at 2.5 THz. This paper reports the steps of this development, starting from the pixel level, to an array associated monolithically to its CMOS ROIC and finally a stand-alone camera. For each step, modeling, technological prototyping and experimental characterizations are presented.

Simoens, F.; Meilhan, J.; Gidon, S.; Lasfargues, G.; Lalanne Dera, J.; Ouvrier-Buffet, J. L.; Pocas, S.; Rabaud, W.; Guellec, F.; Dupont, B.; Martin, S.; Simon, A. C.

2013-09-01

245

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

246

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

247

Pulse sequences for uniform perfluorocarbon droplet vaporization and ultrasound imaging.  

PubMed

Phase-change contrast agents (PCCAs) consist of liquid perfluorocarbon droplets that can be vaporized into gas-filled microbubbles by pulsed ultrasound waves at diagnostic pressures and frequencies. These activatable contrast agents provide benefits of longer circulating times and smaller sizes relative to conventional microbubble contrast agents. However, optimizing ultrasound-induced activation of these agents requires coordinated pulse sequences not found on current clinical systems, in order to both initiate droplet vaporization and image the resulting microbubble population. Specifically, the activation process must provide a spatially uniform distribution of microbubbles and needs to occur quickly enough to image the vaporized agents before they migrate out of the imaging field of view. The development and evaluation of protocols for PCCA-enhanced ultrasound imaging using a commercial array transducer are described. The developed pulse sequences consist of three states: (1) initial imaging at sub-activation pressures, (2) activating droplets within a selected region of interest, and (3) imaging the resulting microbubbles. Bubble clouds produced by the vaporization of decafluorobutane and octafluoropropane droplets were characterized as a function of focused pulse parameters and acoustic field location. Pulse sequences were designed to manipulate the geometries of discrete microbubble clouds using electronic steering, and cloud spacing was tailored to build a uniform vaporization field. The complete pulse sequence was demonstrated in the water bath and then in vivo in a rodent kidney. The resulting contrast provided a significant increase (>15 dB) in signal intensity. PMID:24965563

Puett, C; Sheeran, P S; Rojas, J D; Dayton, P A

2014-09-01

248

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

249

Polarization insensitive terahertz metamaterial absorber.  

PubMed

We present the simulation, implementation, and measurement of a polarization insensitive resonant metamaterial absorber in the terahertz region. The device consists of a metal/dielectric-spacer/metal structure allowing us to maximize absorption by varying the dielectric material and thickness and, hence, the effective electrical permittivity and magnetic permeability. Experimental absorption of 77% and 65% at 2.12 THz (in the operating frequency range of terahertz quantum cascade lasers) is observed for a spacer of polyimide or silicon dioxide respectively. These metamaterials are promising candidates as absorbing elements for thermally based terahertz imaging. PMID:21499411

Grant, J; Ma, Y; Saha, S; Lok, L B; Khalid, A; Cumming, D R S

2011-04-15

250

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

251

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

E-print Network

THz Pulse Transmission Through the Atmosphere Yihong Yang, Student Member, IEEE, Mahboubeh Mandehgar of repetitive broadband THz pulses the record distance of 167 m through the atmosphere with 51% relative in the output pulse structure is composed of phase-locked frequency components extending from 0.07 to 0.37 THz

Oklahoma State University

252

Suspended core polymer fibers with isolated mode for terahertz guiding  

Microsoft Academic Search

The fabrication and characterization of polymer suspended core fibers (porous and non- porous cores) for terahertz guiding is demonstrated for the first time. These novel fibers enable strong mode isolation from perturbations in the surrounding environment. ©2010 Optical Society of America OCIS codes: (040.2235) Far infrared or terahertz; (060.4005) Microstructured fibers; (110.6795) Terahertz imaging

Bora Ung; Mathieu Roze; Anna Mazhorova; Markus Walther; Maksim Skorobogatiy

2011-01-01

253

Generation of elliptically polarized terahertz waves from laser-induced plasma with double helix electrodes.  

PubMed

By applying a helical electric field along a plasma region, a revolving electron current is formed along the plasma and an elliptically polarized far-field terahertz wave pattern is observed. The observed terahertz wave polarization reveals the remarkable role of velocity retardation between optical pulses and generated terahertz pulses in the generation process. Extensive simulations, including longitudinal propagation effects, are performed to clarify the mechanisms responsible for polarization control of air-plasma-based terahertz sources. PMID:22540584

Lu, Xiaofei; Zhang, X-C

2012-03-23

254

Pulsed Terahertz Radition from Femto-second Laser Excited Superconductive YBa2Cu3O7-delta Antenna  

Microsoft Academic Search

We have observed the ultrashort electromagnetic pulse radiation from a current-biased bow-tie structure of YBa2Cu3O7-delta thin film dipole antenna on MgO using 100 fs, 750 nm laser pulses. With the electro-optic detection, we obtained the THz pulses with 1.0 ps full width at half maximum, containing frequency components up to 1.0 THz. The THz peak amplitude dependence shows the saturation

Shyh-Shii Pai; Cheng-Chung Chi

2006-01-01

255

Terahertz-wave spectroscopy for precise histopathological imaging of tumor and non-tumor lesions in paraffin sections.  

PubMed

Terahertz (THz; 10(12) Hz) waves have a frequency from 0.1 to 10 THz between the visible light and microwave domains. THz waves are expected to be useful for analysis of the histological features, without any staining procedure that is an indispensable prerequisite for optical microscopy. It has been demonstrated that THz transmittances at cancer and normal tissues are different. However, spectroscopy that is currently used is applicable for imaging only small areas at fixed-wavelength. In this study, we have developed a spectrometer employing a gallium phosphide (GaP) THz-generator and applied it to examine large areas of tissue specimens using a wide range of wavelengths. We thus examined the whole areas of two paraffin sections (metastatic liver cancer and acute myocardial infarction) in a frequency range of 1 to 6 THz, and compared the THz images of ordinary paraffin sections with the histological features detected by microscopy. THz imaging showed striking contrasts between cancerous and non-cancerous regions at 3.7 THz. Likewise, the precise imaging was achieved in the infarct myocardium at 3.6 THz. Images of THz transmittances in optimal wavelength were well matched with HE histological features both in cancer and myocardial tissues. Cancer regions showed higher transmittance than non-cancerous regions in liver. Old scar regions showed low transmittance, and necrotic regions showed relatively higher transmittance than normal myocardial areas. Thus, THz imaging precisely reflects tissue conditions such as tumor, non-tumor tissues, tissue degeneration and fibrosis. The newly established THz spectroscopy would be useful for pathological diagnosis of routinely processed specimens. PMID:21467828

Miura, Yasuhiro; Kamataki, Akihisa; Uzuki, Miwa; Sasaki, Tetsuo; Nishizawa, Jun-ichi; Sawai, Takashi

2011-01-01

256

Terahertz-time domain spectrometer with 90 dB peak dynamic range  

NASA Astrophysics Data System (ADS)

Many time-domain terahertz applications require systems with high bandwidth, high signal-to-noise ratio and fast measurement speed. In this paper we present a terahertz time-domain spectrometer based on 1550 nm fiber laser technology and InGaAs photoconductive switches. The delay stage offers both a high scanning speed of up to 60 traces / s and a flexible adjustment of the measurement range from 15 ps - 200 ps. Owing to a precise reconstruction of the time axis, the system achieves a high dynamic range: a single pulse trace of 50 ps is acquired in only 44 ms, and transformed into a spectrum with a peak dynamic range of 60 dB. With 1000 averages, the dynamic range increases to 90 dB and the measurement time still remains well below one minute. We demonstrate the suitability of the system for spectroscopic measurements and terahertz imaging.

Vieweg, N.; Rettich, F.; Deninger, A.; Roehle, H.; Dietz, R.; Göbel, T.; Schell, M.

2014-10-01

257

Optimal plasmonic focusing on a metal disc under radially polarized terahertz illumination  

NASA Astrophysics Data System (ADS)

Optimal focusing of surface plasmon polaritons in the center of a metal disc illuminated by radially polarized terahertz pulses is demonstrated. By matching the cylindrical symmetry of the metal structure with the radially polarized terahertz field, surface plasmons are excited along its entire circumference. Constructive interference in the disc center produces a sharp frequency-dependent focal spot well described by a zero-order Bessel function. We map the field distributions on the disc by terahertz (THz) near-field microscopy and compare our results with numerical simulations. For comparison, the behavior of the plasmonic lens under linearly polarized THz illumination is also characterized. The remarkable focusing capabilities of such a plasmonic lens together with its simple structure offer considerable potential for THz sensing and imaging applications.

Waselikowski, Stefan; Fischer, Christian; Wallauer, Jan; Walther, Markus

2013-07-01

258

Pulsed thermography image processing for damage growth monitoring  

NASA Astrophysics Data System (ADS)

An image processing algorithm based on a combination of the most commonly used signal processing techniques in pulsed thermography is applied to monitor the progression of impact damage sites during the full-scale testing of a composite test article. It is demonstrated that the algorithm can be used to monitor damage during a durability and damage tolerance testing. Over the first phase of the test program, although no damage growth was detected, the processed pulsed thermography images showed that the average standard deviation of the measurements was only ~0.08 inches, the equivalent of 2 infrared camera pixels.

Genest, M.

2012-05-01

259

Pulse-modulation imaging-review and performance analysis.  

PubMed

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 integration time for the entire array. Exceptionally high dynamic range (DR) and improved signal-to-noise ratio (SNR) are immediate benefits of this approach. In particular, DR is no longer limited by the power-supply rails as in conventional complementary metal-oxide semiconductor (CMOS) complementary metal-oxide semiconductor active pixel sensors, thus providing relative immunity to the supply-voltage scaling of modern CMOS technologies. In addition, PM imaging naturally supports pixel-parallel analog-to-digital conversion, thereby enabling high temporal resolution/frame rates or an asynchronous event-based array readout. The applications of PM imaging in emerging areas, such as sensor network, wireless endoscopy, retinal prosthesis, polarization imaging, and energy harvesting are surveyed to demonstrate the effectiveness of PM imaging in low-power, high-performance machine vision, and biomedical applications of the future. The evolving design innovations made in PM imaging, such as high-speed arbitration circuits and ultra-compact processing elements, are expected to have even wider impacts in disciplines beyond CMOS image sensors. This paper thoroughly reviews and classifies all common PM image sensor architectures. Analytical models and a universal figure of merit - image quality and dynamic range to energy complexity factor are proposed to quantitatively assess different PM imagers across the entire spectrum of PM architectures. PMID:23850979

Chen, D G; Matolin, D; Bermak, A; Posch, C

2011-02-01

260

Biomedical imaging using hyperpolarized noble gas MRI: Pulse sequence considerations  

NASA Astrophysics Data System (ADS)

Hyperpolarized noble gas MRI is a new technique for imaging of gas spaces and tissues that have been hitherto difficult to image, making it a promising diagnostic tool. The unique properties of hyperpolarized species, particularly the non-renewability of the large non-equilibrium spin polarization, raises questions about the feasibility of hyperpolarized noble gas MRI methods. In this paper, the critical issue of T1 relaxation is discussed and it is shown that a substantial amount of polarization should reach the targets of interest for imaging. We analyse various pulse sequence designs, and point out that total scan times can be decreased so that they are comparable or shorter than tissue T1 values. Pulse sequences can be optimized to effectively utilize the non-renewable hyperpolarization, to enhance the SNR, and to eliminate image artifacts. Hyperpolarized noble gas MRI is concluded to be quite feasible.

Zhao, Lei; Albert, Mitchell S.

1998-02-01

261

Potential for detection of explosive and biological hazards with electronic terahertz systems: One contribution of 16 to a Discussion Meeting 'The terahertz gap: the generation of far-infrared radiation and its applications'  

Microsoft Academic Search

The terahertz (THz) regime (0.1-10 THz) is rich with emerging possibilities in sensing, imaging and communications, with unique applications to screening for weapons, explosives and biohazards, imaging of concealed objects, water content and skin. Here we present initial surveys to evaluate the possibility of sensing plastic explosives and bacterial spores using field-deployable electronic THz techniques based on short-pulse generation and

Min Ki Choi; Alan Bettermann; D. W. van der Weide

2004-01-01

262

Multidimensional imaging using combined stray field and pulsed gradients.  

PubMed

The paper describes an advance in stray field imaging (STRAFI) whereby images of planar samples can be obtained in the stray field of a superconducting magnet without the need for sample rotation. This is achieved by using the static stray magnetic field gradient in combination with pulsed orthogonal gradients. Results of both two- and three-dimensional implementations of the experiment are presented and discussed. An extension to diffusion-weighted imaging is introduced. The technique is expected to prove particularly useful in experiments where high resolution is required in only one direction while lower resolution is acceptable in the orthogonal directions, such as in studies of the drying and curing of paints and varnishes. Arising from the work, a new method for accurately calibrating the radiofrequency pulse width in stray field is found. PMID:11945037

Godward, J; Ciampi, E; Cifelli, M; McDonald, P J

2002-03-01

263

Pulsed Tera-hertz Radition from Femto-second Laser Excited Superconductive YBa2Cu3O7-? Antenna  

NASA Astrophysics Data System (ADS)

We have observed the ultrashort electromagnetic pulse radiation from a current-biased bow-tie structure of YBa2Cu3O7-? thin film dipole antenna on MgO using 100 fs, 750 nm laser pulses. With the electro-optic detection, we obtained the THz pulses with 1.0 ps full width at half maximum, containing frequency components up to 1.0 THz. The THz peak amplitude dependence shows the saturation and a nonlinear behavior with a higher excitation pumping power and with the applied bias currents. The saturation on the dependence with the excitation powers exhibits the bolometric heating in nature. However, the nonlinear characterization of the THz radiation from the superconductive thin film antenna revealed that the inadequacy of pure supercarrier approximation on a two-fluid model. The ultrashort transient response and the deviation from the classical theory are discussed in relation to the quasiparticle dynamics of the nonequilibrium mechanism.

Pai, Shyh-Shii; Chi, Cheng-Chung

2006-03-01

264

Nonperturbative interband response of a bulk InSb semiconductor driven off resonantly by terahertz electromagnetic few-cycle pulses.  

PubMed

Intense multiterahertz pulses are used to study the coherent nonlinear response of bulk InSb by means of field-resolved four-wave mixing spectroscopy. At amplitudes above 5??MV/cm the signals show a clear temporal substructure which is unexpected in perturbative nonlinear optics. Simulations based on a model of a two-level quantum system demonstrate that in spite of the strongly off-resonant character of the excitation the high-field few-cycle pulses drive the interband resonances into a nonperturbative regime of Rabi flopping. The rotating wave approximation breaks down in this case and the system reaches a complete population inversion. PMID:23083284

Junginger, F; Mayer, B; Schmidt, C; Schubert, O; Mährlein, S; Leitenstorfer, A; Huber, R; Pashkin, A

2012-10-01

265

Band gaps in the spectra of terahertz surface plasmons on metallic diffraction gratings  

Microsoft Academic Search

The effect of the appearance of band gaps in the energy spectra of terahertz surface plasmons has been experimentally observed and investigated. The band gaps are formed due to the interference interaction of the surface plasmons excited by pulsed terahertz radiation on metallic diffraction gratings. It has been shown that the experimental dispersion curves of terahertz plasmons are in good

A. V. Andreev; M. M. Nazarov; I. R. Prudnikov; A. P. Shkurinov

2009-01-01

266

Resonant terahertz transmission in subwavelength metallic hole arrays of sub-skin-depth  

E-print Network

evolution of surface-plasmon resonance in terms of array thickness is characterized by use of terahertz time which surface-plasmon coupling of terahertz pulses begins and is enhanced rapidly as the array thickness­12 and semiconductor13­15 arrays. The characteristics of surface-plasmon-enhanced terahertz transmission have been

267

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

E-print Network

THz Pulse Propagation in the Atmosphere Yihong Yang, Student Member, IEEE, Mahboubeh Mandehgar, and Daniel R. Grischkowsky, Fellow, IEEE Abstract--In this paper, we have extracted the THz refractivity of water vapor ( ( ) 1) from the complex spectra of the pre- cise coherent THz-TDS absorption measurement

Oklahoma State University

268

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

269

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

270

Anomalous terahertz transmission in bow-tie plasmonic antenna apertures  

E-print Network

Anomalous terahertz transmission in bow-tie plasmonic antenna apertures Yuping Yang,1,2 Ranjan localized surface plasmon resonances. In addition, with a decreasing aperture size, the contribution of localized plasmons becomes prominent due to an increase in plasmonic lifetime as the terahertz pulses

Oklahoma State University

271

Transit Time Enhanced Bandwidth in Nanostructured Terahertz Emitters  

NASA Astrophysics Data System (ADS)

Monte-Carlo simulations are used to show that the transit time in ˜100 nm gap photoconductive emitters of terahertz radiation is short enough to produce broad-bandwidth pulses. Furthermore, with these calculations we demonstrate that nanostructured contacts remove the need for low-temperature-grown or ion-implanted materials for broad-band terahertz devices.

Corzo-Garcia, S. C.; Alfaro, M.; Castro-Camus, E.

2014-09-01

272

High-speed terahertz reflection three-dimensional imaging for nondestructive  

E-print Network

is obtained, which is made of glass fiber reinforced polymer composite material and has defects) imaging based on electronically controlled optical sampling (ECOPS). ECOPS enables scanning of an axial such as delamination and inclusion, and is compared with an ultrasonic reflection 3D image of the sample. ©2012 Optical

273

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

274

Single pulse frequency compounding protocol for superharmonic imaging.  

PubMed

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. PMID:23787259

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

2013-07-21

275

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

276

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

277

Terahertz wave opto-mechanical scanner for security application  

NASA Astrophysics Data System (ADS)

This paper describes a new opto-mechanical scanner that is hopeful for terahertz imaging in security applications. The target of using this scanner is portal screening of personnel for high-resolution imaging of concealed threat objects. It is not only applied to active terahertz imaging but also applied to passive Terahertz imaging. Terahertz wave can penetrate many materials that are opaque to visible and infrared light, such as plastics, cardboard, textiles and so on. So the terahertz imaging technology has a potential to be applicable in security inspection at airports, stations and other public place. Now, the most terahertz imaging system works at point to point mechanical scan pattern. The speed of this raster scan is too slow to apply in practical field. 2-D terahertz array detector can be applied to real time imaging. But at present their cost is prohibitively high. Fortunately low cost, high performance, opto-mechanically scanner is able to meet the current requirements. An opto-mechanical scanner should be able to rapidly scan a 2-D image of the scene. It also should have high optical efficiency so that an image system can achieve the required thermal sensitivity with the minimum number of receivers. These ensure that it can easily operate at any wavelength, and be active or passive. The opto-mechanically scanning can meets these requirements and is being developed into a high performance, low-cost prototype system that will meet the future needs for terahertz security.

Deng, Chao; Zheng, Yongju; Zhang, Cunlin

2010-11-01

278

Differential pulse code modulation image compression using artifical neural networks  

NASA Astrophysics Data System (ADS)

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 back-propagation learning algorithm is used for the training of the network. Simulation results are presented to compare the performance of the proposed ANN-based nonlinear predictor with that of a global linear predictor as well as an optimized minimum-mean-squared-error (MMSE) linear predictor. Preliminary computer simulations demonstrate that for a typical test image, the zeroth-order entropy of the differential (error) image can be reduced by more than 15% compared to the case where optimum linear predictors are employed. Some future research directions are also discussed.

Rabbani, Majid; Dianat, Soheil A.

1993-04-01

279

CMOS detector arrays in a virtual 10-kilopixel camera for coherent terahertz real-time imaging.  

PubMed

We demonstrate the principle applicability of antenna-coupled complementary metal oxide semiconductor (CMOS) field-effect transistor arrays as cameras for real-time coherent imaging at 591.4 GHz. By scanning a few detectors across the image plane, we synthesize a focal-plane array of 100×100 pixels with an active area of 20×20 mm2, which is applied to imaging in transmission and reflection geometries. Individual detector pixels exhibit a voltage conversion loss of 24 dB and a noise figure of 41 dB for 16 ?W of the local oscillator (LO) drive. For object illumination, we use a radio-frequency (RF) source with 432 ?W at 590 GHz. Coherent detection is realized by quasioptical superposition of the image and the LO beam with 247 ?W. At an effective frame rate of 17 Hz, we achieve a maximum dynamic range of 30 dB in the center of the image and more than 20 dB within a disk of 18 mm diameter. The system has been used for surface reconstruction resolving a height difference in the ?m range. PMID:22344098

Boppel, Sebastian; Lisauskas, Alvydas; Max, Alexander; Krozer, Viktor; Roskos, Hartmut G

2012-02-15

280

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

E-print Network

. Since this signal originates from the tip only, it can be used to characterize free-space terahertz wave. These background signals result from path-length difference modulation, and thus are relevant when phase,18 Whereas an aperture introduces a high wavelength-dependent transmission loss, a small scatterer

Mittleman, Daniel

281

Real-time, T-ray imaging using a sub-terahertz gyrotron  

NASA Astrophysics Data System (ADS)

We demonstrated real-time, active, T-ray imaging using a 0.46 THz gyrotron capable of producing 16 W in continuous wave operation and a pyroelectric array camera with 124-by-124 pixels. An expanded Gaussian beam from the gyrotron was used to maintain the power density above the detection level of the pyroelectric array over the area of the irradiated object. Real-time imaging at a video rate of 48 Hz was achieved through the use of the built-in chopper of the camera. Potential applications include fast scanning for security purposes and for quality control of dry or frozen foods.

Han, Seong-Tae; Torrezan, Antonio C.; Sirigiri, Jagadishwar R.; Shapiro, Michael A.; Temkin, Richard J.

2012-06-01

282

Probing ultrafast optomagnetism by terahertz Cherenkov radiation  

NASA Astrophysics Data System (ADS)

We put forward Cherenkov-type terahertz emission from a moving pulse of magnetization as a method to explore ultrafast optomagnetic phenomena. We propose to use a structure comprising a slab of transparent magnetooptic material coupled to an output prism. An ultrashort laser pulse propagates in the slab and produces transient magnetization via the inverse Faraday effect. The moving magnetization emits a Cherenkov cone of terahertz waves in the output prism. We developed a theory that predicts the detectability of the radiation for a terbium gallium garnet slab covered with a Si prism.

Bakunov, M. I.; Mikhaylovskiy, R. V.; Bodrov, S. B.

2012-10-01

283

Imaging Capability of Terahertz and Millimeter-Wave Instrumentations for NDT of Polymer Materials  

Microsoft Academic Search

The detection of flaws in polymer materials like degradation areas in polymer pipelines in chemical industry, moisture distributions and delaminations in composites used in aircraft industry are today's challenges of NDT of polymers. New imaging technologies based on electromagnetic waves at high frequencies from 0.05 to 2 THz are promising candidates for polymer testing in the next future. A va-

J. BECKMANN; U. ZSCHERPEL; U. EWERT

284

Active terahertz holography  

NASA Astrophysics Data System (ADS)

We present a novel technology to dynamically control the wave front of the terahertz (THz) beam with photo-generated carriers. The computer generated hologram is projected onto a silicon wafer by a conventional optical spatial light modulator. The photo-generated carriers on the silicon surface will from a hologram to modulate the wave front of the input THz beam. Some special field distributions and vortex beams are generated using this method. This technology is broadband, structure free, tunable, and all-optical controllable. It will provide numerous possible applications in future THz imaging and communication systems.

Xie, Zhenwei; Wang, Xinke; Zhang, Yan

2013-12-01

285

Fluorescence lifetime imaging with pulsed diode laser enabled stimulated emission.  

PubMed

We present here a stimulated emission based fluorescence lifetime imaging (FLIM) scheme using a pair of synchronized diode lasers operating at gain switched pulse mode. The two semiconductor lasers, with wavelengths at 635 nm and 700 nm, serve as the excitation and the stimulation light sources for the ATTO647N labeled sample, respectively. FLIM is readily achieved with their relative time delay controlled electronically. The coherent nature of the stimulated emission signal also allows FLIM at long working distance. In this way, a high performance all-semiconductor FLIM module is realized in a flexible, compact, and cost effective configuration. PMID:23263055

Ge, Jianhong; Kuang, Cuifang; Lee, Shin-Shian; Kao, Fu-Jen

2012-12-17

286

Lossless image compression using modular differential pulse code modulation  

NASA Astrophysics Data System (ADS)

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 predictor. Experimental results demonstrate that the proposed technique reduces the bit rate by as much as 10 percent when compared to the lossless JPEG.

Rizvi, Syed A.; Toussaint, Richard; Awad, George

2000-04-01

287

Terahertz imaging with a quantum cascade laser and amorphous-silicon microbolometer array  

NASA Astrophysics Data System (ADS)

Portability, low cost and fast acquisition rates are key features that a THz imaging system should satisfy for extended commercialized applications. With regards to these features, the source - detector association of a THz Quantum Cascade Laser (QCL) with an un-cooled micro-bolometer two-dimensional array looks promising for THz active imaging. QCLs performance is rapidly improving, with higher operating temperatures and output powers recently demonstrated. On the detector side, un-cooled micro-bolometer array opens the way to real-time video rate, with no raster scanning and potential low cost. In parallel to the development of room temperature micro-bolometer sensors specifically designed for the THz range, the authors have characterized experimentally the sensitivity of CEA-LETI standard amorphous Silicon infrared microbolometers illuminated by a 3THz QCL. The sensitivity of these existing sensors is then compared to the expected sensitivity of the CEA-LETI upcoming THz sensors.

Simoens, F.; Durand, T.; Meilhan, J.; Gellie, P.; Maineult, W.; Sirtori, C.; Barbieri, S.; Beere, H.; Ritchie, D.

2009-09-01

288

Fourier Analysis and Structure Determination. Part II: Pulse NMR and NMR Imaging.  

ERIC Educational Resources Information Center

Uses simple pulse NMR experiments to discuss Fourier transforms. Studies the generation of spin echoes used in the imaging procedure. Shows that pulse NMR experiments give signals that are additions of sinusoids of differing amplitudes, frequencies, and phases. (MVL)

Chesick, John P.

1989-01-01

289

Features of plasma glow in low pressure terahertz gas discharge  

NASA Astrophysics Data System (ADS)

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.; Litvak, A. G.; Razin, S. V.; Sidorov, A. V.; Skalyga, V. A.; Zorin, V. G.

2013-12-01

290

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

291

Production of high power femtosecond terahertz radiation  

SciTech Connect

The terahertz (THz) region of the electromagnetic spectrum is attracting interest for a broad range of applications ranging from diagnosing electron beams to biological imaging. Most sources of short pulse THz radiation utilize excitation of biased semiconductors or electro-optic crystals by high peak power lasers. For example, this was done by using an un-doped InAs wafer irradiated by a femtosecond free-electron laser (FEL) at the Thomas Jefferson National Accelerator Facility. Microwatt levels of THz radiation were detected when excited with FEL pulses at 1.06 mm wavelength and 10W average power. Recently substantially higher powers of femtosecond THz pulses produced by synchrotron emission were extracted from the electron beamline. Calculations and measurements confirm the production of coherent broadband THz radiation from relativistic electrons with an average power of nearly 20W, a world record in this wavelength range by a factor of 10,000. We describe the source, presenting theoretical calculations and their experimental verification. Potential applications of this exciting new source include driving new non-linear phenomena, performing pump-probe studies of dynamical properties of novel materials, and studying molecular vibrations and rotations, low frequency protein motions, phonons, superconductor band gaps, electronic scattering, collective electronic excitations (e.g., charge density waves), and spintronics.

Neil, George R.; Carr, G.L.; Gubeli III, Joseph F.; Jordan, K.; Martin, Michael C.; McKinney, Wayne R.; Shinn, Michelle; Tani, Masahiko; Williams, G.P.; Zhang, X.-C.

2003-07-11

292

Homeland Security, Medical, Pharmaceutical and Non-destructive Testing Applications of Terahertz Radiation  

Microsoft Academic Search

The terahertz region of the electromagnetic spectrum (300GHz-10THz) spans the region between radio and light. Recent advances in terahertz source, detector and systems technology are enabling new applications across a number of fields, based on both terahertz imaging and spectroscopy. This paper reviews our recent work on the development of practical systems and applications in security screening for the detection

Michael Kemp

2005-01-01

293

Pump beam diameter dependent terahertz generation from surface emitters - experiment and simulation  

Microsoft Academic Search

We report on terahertz wave generation using transient photoconductivity induced by femtosecond laser pulses in semiconductor surfaces. In particular the dependence of terahertz emission characteristics on pump pulse parameters like diameter and input angle is investigated in detail both experimentally and theoretically. It is shown that the emission in forward (quasi-optical reflection) as well as in backward direction (back to

M. Theuer; C. Imhof; G. Torosyan; F. Ellrich; R. Zengerle; R. Beigang

2008-01-01

294

Effect of a dielectric coating on terahertz surface plasmon polaritons on metal wires  

Microsoft Academic Search

The authors present measurements and calculations on the effect of thin dielectric coatings on the propagation of terahertz pulses along the surface of metal wires. Our measurements show that propagation over only a few centimeters of wire having a thin dielectric coating, strongly distorts the terahertz pulse, which results in a several tens of picoseconds long chirped signal. We demonstrate

Paul C. M. Planken

2005-01-01

295

Below-band-gap excitation of a terahertz surface plasmon-polariton  

Microsoft Academic Search

We analyze the excitation of a surface plasmon-polariton at terahertz frequencies by an optical pulse with tilted intensity front incident on a semiconductor surface. We show that one can achieve an order of magnitude increase in the generated terahertz power by using an optical pulse with frequencies below the band gap compared to the above-band-gap excitation.

M. I. Bakunov; A. V. Maslov; S. B. Bodrov

2006-01-01

296

Laser micromachining of silicon: a new technique for fabricating terahertz imaging arrays  

NASA Astrophysics Data System (ADS)

One of the main obstacles encountered in designing low noise, high efficiency, heterodyne receivers and local oscillator sources at submillimeter wavelengths is the quality and cost of waveguide structures. At wavelengths shorter than 400 micrometers, rectangular waveguide structures, feed-horns, and backshorts become extremely difficult to fabricate using standard machining techniques. We have used a new laser milling technique to fabricate high quality, THz waveguide components and feedhorns. Once metallized, the structures have the properties of standard waveguide components. Unlike waveguide components made using silicon wet-etching techniques, laser-etched components can have almost any cross section, from rectangular to circular. Under computer control, the entire waveguide structure (including the corrugated feedhorn a submillimeter-wave mixer or multiplier can be fabricated to micrometer tolerances in a few hours. Laser etching permits the direct scaling of successful waveguide multiplier and mixer designs to THz frequencies. Since the entire process is computer controlled, the cost of fabricating submillimeter waveguide components is significantly reduced. With this new laser etching process, the construction of high performance waveguide array receivers at THz frequencies becomes tractable. In this paper we will describe the laser etching technique and discuss how it can be used to construct THz imaging arrays. We will also describe the construction of a prototype 810 GHz mixer which utilizes these new construction techniques.

Walker, Christopher K.; Hungerford, A. L.; Narayanan, Gopal; Groppi, C.; Bloomstein, Theodore M.; Palmacci, S. T.; Stern, Margaret B.; Curtin, Jane E.

1998-07-01

297

Coherent Terahertz Radiation at UVSOR-II  

NASA Astrophysics Data System (ADS)

Development of intense terahertz radiation source is progressing at UVSOR-II, based on the mechanism of coherent synchrotron radiation (CSR). The terahertz CSR has successfully been produced by two methods. When the storage ring is operated in the single bunch mode with a sufficiently high beam current, intense bursts of terahertz radiation are emitted. Micro-structures in the longitudinal density distribution of the electron bunches created by a beam instability may be the origin of the radiation. The duration of the bursts is typically 100 micro-seconds. The peak intensity is 10000 times higher than that of the normal synchrotron radiation. The bursts appear chaotically or quasi-periodically depending on the beam current with a typical interval of 10 milli-seconds. It has been also demonstrated that the terahertz CSR could be produced by the laser-bunch slicing method. The density modulation produced on the electron bunch by the laser is the origin of CSR. The repetition rate of the terahertz pulses is 1 kHz, which is same as the laser repetition rate. The intensity per pulse is 105 times higher than that of the normal SR.

Katoh, Masahiro; Hosaka, Masahito; Mochihashi, Akira; Shimada, Miho; Kimura, Shin-ichi; Takashima, Yoshifumi; Takahashi, Toshiharu

2007-01-01

298

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

299

Terahertz Scattering  

NASA Astrophysics Data System (ADS)

Terahertz (THz) Time Domain Spectroscopy (TDS) measurements have the unique ability to detect both the amplitude and phase of the electric field, simultaneously. This eliminates complications introduced by Kramers-Kronig relations typically used in near-infrared spectroscopy. Many materials of interest contain resonant features in their refractive indices in the far-infrared (THz) spectrum, while their packaging materials are generally transparent. Thus, an important application for THz TDS is the ability to see inside packaging materials and detect the material features of their contents. Such applications are promising for security screening (concealed drugs, explosives, etc.) in post offices and airports as well as for non-destructive evaluation (NDE) of products on an assembly line or tissue damage due to burns or cancer [1-6].

Zurk, L. M.; Schecklman, S.

300

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

301

Application of laser pulse stretching scheme for efficiently delivering laser energy in photoacoustic imaging  

PubMed Central

Abstract. 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

2012-01-01

302

Optimization of a Hardware Implementation for Pulse Coupled Neural Networks for Image Applications  

E-print Network

Pulse Coupled Neural Networks are a very useful tool for image processing and visual applications, since it has the advantages of being invariant to image changes as rotation, scale, or certain distortion. Among other ...

Warde, Cardinal

303

One- and two-dimensional photo-imprinted diffraction gratings for manipulating terahertz waves  

E-print Network

Emerging technology based on artificial materials containing metallic structures has raised the prospect for unprecedented control of terahertz waves through components like filters, absorbers and polarizers. The functionality of these devices is static by the very nature of their metallic or polaritonic composition, although some degree of tunability can be achieved by incorporating electrically biased semiconductors. Here, we demonstrate a photonic structure by projecting the optical image of a metal mask onto a thin GaAs substrate using a femtosecond pulsed laser source. We show that the resulting high-contrast pattern of photo- excited carriers can create diffractive elements operating in transmission. With the metal mask replaced by a digital micromirror device, our photo-imprinted photonic structures provide a route to terahertz components with reconfigurable functionality.

Chatzakis, Ioannis; Luo, Liang; Shen, Nian-Hai; Zhang, Lei; Wang, Jigang; Koschny, Thomas; Soukoulis, Costas M

2014-01-01

304

Direct intensity sampling of a modelocked terahertz quantum cascade laser  

NASA Astrophysics Data System (ADS)

Pulses from an actively modelocked terahertz quantum cascade laser are fully characterized using an optical sampling technique to detect the total instantaneous terahertz intensity. By triggering the quantum cascade laser electronics with a femtosecond laser, we are able to measure both the formation of modelocked pulses and the quasi-steady state. The dependence of the pulse width on the modulation power and drive current are investigated. At low drive currents, we measure transform-limited gaussian-shaped pulses with a FWHM of 19 ps.

Freeman, Joshua R.; Maysonnave, Jean; Jukam, Nathan; Cavalié, Pierrick; Maussang, Kenneth; Beere, Harvey E.; Ritchie, David A.; Mangeney, Juliette; Dhillon, Sukhdeep S.; Tignon, Jérôme

2012-10-01

305

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

306

Terahertz Technology Research at NICT  

Microsoft Academic Search

The National Institute of Information and Communications Technology (NICT) has been researching the use of terahertz (THz)\\u000a band from its source to industrial applications. Major accomplishments to date include the development of THz devices such\\u000a as a quantum cascade laser source, a portable stand-off imaging system, an establishment of propagation model, and a spectral\\u000a database. We also encourage applications in

Iwao Hosako; Kaori Fukunaga

2011-01-01

307

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

308

Terahertz radiation from a laser plasma filament  

SciTech Connect

By the use of two-dimensional particle-in-cell simulations, we clarify the terahertz (THz) radiation mechanism from a plasma filament formed by an intense femtosecond laser pulse. The nonuniform plasma density of the filament leads to a net radiating current for THz radiation. This current is mainly located within the pulse and the first cycle of the wakefield. As the laser pulse propagates, a single-cycle and radially polarized THz pulse is constructively built up forward. The single-cycle shape is mainly due to radiation damping effect.

Wu, H.-C.; Meyer-ter-Vehn, J. [Max-Planck-Institut fuer Quantenoptik, D-85748 Garching (Germany); Ruhl, H. [Department fuer Physik der Ludwig-Maximillians-Universitaet, Theresienstrasse 37A, D-80333 Muenchen (Germany); Sheng, Z.-M. [Institute of Plasma Studies, Department of Physics, Shanghai Jiaotong University, Shanghai 200240 (China); Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190 (China)

2011-03-15

309

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

310

Anomalous terahertz transmission in bow-tie plasmonic antenna apertures.  

PubMed

Arrays of subwavelength dipole bow-tie apertures are designed and characterized at terahertz frequencies. For an incident terahertz field perpendicular to the longer axis of the bow tie, a strong resonance enhancement, line narrowing, and a nonmonotonic frequency shift were observed with increasing length of the tapered bow-tie arms. Such characteristic behaviors primarily originate from localized surface plasmon resonances. In addition, with a decreasing aperture size, the contribution of localized plasmons becomes prominent due to an increase in plasmonic lifetime as the terahertz pulses strongly couple with the metallic surface surrounding the bow-tie apertures. PMID:21808352

Yang, Yuping; Singh, Ranjan; Zhang, Weili

2011-08-01

311

Strong terahertz radiation from air plasmas generated by an aperture-limited Gaussian pump laser beam  

SciTech Connect

Terahertz radiation generated by focusing the fundamental laser pulse and its second harmonic into ambient air strongly saturates with increasing pump laser energy. We demonstrate a simple method to control the Gaussian pump laser beam to improve the output of terahertz radiation with an adjustable aperture. With the optimal aperture-limited pump laser beams, the terahertz wave amplitudes can be enhanced by more than eight times depending on the pump laser parameters than those of aperture-free cases.

Peng Xiaoyu; Toncian, Toma; Jung, Ralph; Willi, Oswald [Institut fuer Laser-und Plasmaphysik, Heinrich-Heine-Universitaet Duesseldorf, Duesseldorf, 40225 (Germany); Li Chun; Li Yutong; Wang Weimin; Wang Shoujun; Liu Feng [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100080 (China); Chen Min; Pukhov, Alexander [Institut fuer Theoretische physik I, Heinrich-Heine-Universitaet Duesseldorf, Duesseldorf, 40225 (Germany); Sheng Zhengming; Zhang Jie [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100080 (China); Department of Physics, Shanghai Jiao Tong University, Shanghai, 200240 (China)

2009-03-09

312

Band gaps in the spectra of terahertz surface plasmons on metallic diffraction gratings  

Microsoft Academic Search

The effect of the appearance of band gaps in the energy spectra of terahertz surface plasmons has been experimentally observed\\u000a and investigated. The band gaps are formed due to the interference interaction of the surface plasmons excited by pulsed terahertz\\u000a radiation on metallic diffraction gratings. It has been shown that the experimental dispersion curves of terahertz plasmons\\u000a are in good

A. V. Andreev; M. M. Nazarov; I. R. Prudnikov; A. P. Shkurinov

2009-01-01

313

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

314

Free-space electro-optic sampling of terahertz beams  

Microsoft Academic Search

Free-space electro-optic sampling is an alternative method for the characterization of freely propagating terahertz beams with subpicosecond temporal resolution. In contrast to resonant photoconductive dipole antennas, free-space electro-optic sampling via the linear electro-optic effect (Pockels effect) offers a flat frequency response over an ultrawide bandwidth and the potential for a simple cross-correlation signal of the terahertz and optical pulses.

Q. Wu; X.-C. Zhang

1995-01-01

315

Terahertz wave filter based on photonic crystal  

NASA Astrophysics Data System (ADS)

In the past decade, spectroscopy and imaging in the terahertz region (0.1-10 THz) of the electromagnetic spectrum has been applied in both basic research and potential industrial applications, such as medical diagnosis, security screening, radio astronomy, atmospheric studies, short-range indoor communication, chemical, biological sensing, medical and biological imaging, and detection of explosives. In this paper, we design a narrow bandpass terahertz wave filter using three kinds of two-dimensional photonic crystals. By using finite-difference time-domain (FDTD) method, we examined the transmittance spectra for the proposed terahertz wave filter. The simulated results show that the proposed filter exhibit excellent transmission performance such as high transmission at the central frequency, adjustable bandpass, and good rejection of the sideband frequencies.

Liu, Yu-hang; Li, Jiu-sheng

2011-11-01

316

Terahertz wave filter based on photonic crystal  

NASA Astrophysics Data System (ADS)

In the past decade, spectroscopy and imaging in the terahertz region (0.1-10 THz) of the electromagnetic spectrum has been applied in both basic research and potential industrial applications, such as medical diagnosis, security screening, radio astronomy, atmospheric studies, short-range indoor communication, chemical, biological sensing, medical and biological imaging, and detection of explosives. In this paper, we design a narrow bandpass terahertz wave filter using three kinds of two-dimensional photonic crystals. By using finite-difference time-domain (FDTD) method, we examined the transmittance spectra for the proposed terahertz wave filter. The simulated results show that the proposed filter exhibit excellent transmission performance such as high transmission at the central frequency, adjustable bandpass, and good rejection of the sideband frequencies.

Liu, Yu-hang; Li, Jiu-sheng

2012-03-01

317

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

318

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

319

Integrated heterodyne terahertz transceiver  

DOEpatents

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

320

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

321

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

322

Terahertz pump-probe spectroscopy in YBCO thin films  

Microsoft Academic Search

Terahertz (THz) radiation is ideal for probing many different materials and processes. Photons in the THz regime have energies on the order of an meV, which is an important energy scale for many electronic processes. In this paper we will describe the use of optical rectification of 50 fs IR pulses to generate THz pulses. Using this method, spectrally broad

Anna K. Kristoffersen; H. Tiedje; Robert A. Hughes; Harold K. Haugen; Thomas Timusk; John S. Preston

2004-01-01

323

Highly sensitive coherent detection of terahertz waves at room temperature using a parametric process  

NASA Astrophysics Data System (ADS)

We report the experimental results of coherent detection of narrow-linewidth nanosecond terahertz radiation at room temperature using frequency conversion in a nonlinear MgO :LiNbO3 crystal. Mixing the terahertz radiation with a near-infrared intense pump pulse results in the excitation and amplification of the difference-frequency component, which is detected with an InGaAs-based photodiode. We demonstrate this method in a fast and very sensitive terahertz wave detector. The detector is capable of capturing the temporal profile of terahertz pulses with nanosecond resolution, and is at least one order more sensitive than a typical liquid-He-cooled Si bolometer for detecting nanosecond pulsed terahertz wave beams.

Guo, Ruixiang; Ohno, Seigo; Minamide, Hiroaki; Ikari, Tomofumi; Ito, Hiromasa

2008-07-01

324

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

325

Temperature dependent characterization of terahertz vibrations of explosives and related  

E-print Network

Temperature dependent characterization of terahertz vibrations of explosives and related threat. Zimdars, "THz imaging and sensing for security applications: Explosives, weapons, and drugs," Semicond. Linfield, and A. G. Davies, "Far-infrared spectroscopic characterization of explosives for security

Oklahoma State University

326

Broadband graphene terahertz modulators enabled by intraband transitions.  

PubMed

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. PMID:22510685

Sensale-Rodriguez, Berardi; Yan, Rusen; Kelly, Michelle M; Fang, Tian; Tahy, Kristof; Hwang, Wan Sik; Jena, Debdeep; Liu, Lei; Xing, Huili Grace

2012-01-01

327

Terahertz super thin planar lenses  

NASA Astrophysics Data System (ADS)

Terahertz (THz) radiation is an under developing range in the electromagnetic spectrum. It has attracted a lot of attentions due to its various potential applications. However, THz systems are difficult to be integrated into a smart size due to the limitation of its long wavelength. In this presentation, we propose a new approach to design planar lenses with a thickness of several hundred nanometers in the THz range. The fabricated lenses are characterized with a focal plane imaging system and it is found that they can focus the THz light and image an object well. It is expected that this new approach can pave a way for smart THz systems integration.

Zhang, Yan; Ye, Jiasheng; Hu, Dan; Wang, Xinke; Feng, Shengfei; Sun, Wenfeng

2012-12-01

328

Plasmonic terahertz detectors for biodetection  

E-print Network

Plasmonic terahertz detectors for biodetection N. Pala and M.S. Shur A report is presented on the biodetection capabilities of plasmonic ter- ahertz detectors. Large changes in the terahertz response. Terahertz time domain spectroscopy (TDS) [1], terahertz dielectric spec- troscopy [2], surface

Pala, Nezih

329

RF Pulse Design for Parallel Excitation in Magnetic Resonance Imaging  

E-print Network

Associated with Parallel Excitation .................................... 24 4. VARIABLE-DENSITY TRAJECTORY DESIGN FOR PARALLEL EXCITATION ................................................................................. 28 4.1 Spiral Design... ................................................................................................... 52 5. RF PULSE DESIGN INCORPORATING TISSUE DIELECTRIC PROPERTIES IN PARALLEL EXCITATION ................................................. 55 5.1 Joint RF Pulse and K-space Trajectory Adjustment ................................... 56...

Liu, Yinan

2012-07-16

330

Theoretical foundations of detection of terahertz radiation in laser-plasma interactions  

SciTech Connect

A theory is developed enabling one to calculate the temporal profile and spectrum of a terahertz wave packet from the energy of the second harmonic of optical radiation generated during the nonlinear interaction between terahertz and circularly polarized laser pulses in the skin layer of an overdense plasma. It is shown that the spectral and temporal characteristics of the envelope of the second harmonic of optical radiation coincide with those of the terahertz pulse only at small durations of the detecting laser radiation. For long laser pulses, the temporal profile and spectrum of the second harmonic are mainly determined by the characteristics of optical radiation at the carrier frequency.

Frolov, A. A., E-mail: frolov@ihed.ras.ru [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)

2013-02-15

331

Study of terahertz intensity dependence on time resolved dynamic fringes in the interferometric autocorrelation setup  

NASA Astrophysics Data System (ADS)

Terahertz signal is generated from Low temperature gallium arsenide photoconductive dipole antennas (gap = 5?m, length = 20?m) by focusing 15 fs laser pulses and applying 12V DC across it. Terahertz intensity is detected by Pyroelectric detector (THZ1.5MB-USB). The collinear autocorrelation arrangement provides dynamic fringes which are allowed to be incident on photoconductive antennas to study the variation in terahertz intensity with respect to delay between laser pulses. Interestingly, the profile of THz intensity variation was similar to interferometric autocorrelation signal of laser pulses. The THz power attenuation with its propagation distance in atmosphere was measured.

Venkatesh, M.; Chaudhary, A. K.

2014-10-01

332

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

E-print Network

of subwavelength hole arrays at THz frequencies. Extraordinary trans- mission at two pronounced surface plasmon ±1Effect 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

333

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 is attributed to the coupling between discrete resonant excitation of surface plasmons and continuum nonresonant 23 July 2007; published online 17 August 2007 Transmission spectra of terahertz pulses through

334

Effect of a dielectric coating on terahertz surface plasmon polaritons on metal wires  

E-print Network

Effect of a dielectric coating on terahertz surface plasmon polaritons on metal wires Nick C. J on the propagation of terahertz pulses along the surface of metal wires. Our measurements show that propagation over in the measurements. Our results show the potential of tera- hertz surface plasmon polaritons on metal wires

335

Strip velocity measurements for gated x-ray imagers using short pulse lasers  

NASA Astrophysics Data System (ADS)

Strip velocity measurements of gated X-ray imagers are presented using an ultra-short pulse laser. Obtaining time- resolved X-ray images of inertial confinement fusion shots presents a difficult challenge. One diagnostic developed to address this challenge is the gated X-ray imagers. The gated X-ray detectors (GXDs) developed by Lawrence Livermore National Laboratory and Los Alamos National Laboratory use a microchannel plate (MCP) coated with a gold strip line, which serves as a photocathode. GXDs are used with an array of pinholes, which image onto various parts of the GXD image plane. As the pulse sweeps over the strip lines, it creates a time history of the event with consecutive images. In order to accurately interpret the timing of the images obtained using the GXDs, it is necessary to measure the propagation of the pulse over the strip line. The strip velocity was measured using a short pulse laser with a pulse duration of approximately 1-2 ps. The 200nm light from the laser is used to illuminate the GXD MCP. The laser pulse is split and a retroreflective mirror is used to delay one of the legs. By adjusting the distance to the mirror, one leg is temporally delayed compared to the reference leg. The retroreflective setup is calibrated using a streak camera with a 1 ns full sweep. Resolution of 0.5 mm is accomplished to achieve a temporal resolution of ~5 ps on the GXD strip line.

Ross, P. W.; Cardenas, M.; Griffin, M.; Mead, A.; Silbernagel, C. T.; Bell, P.; Haque, S.

2013-09-01

336

Chirped Pulse Adiabatic Passage in CARS for Imaging of Biological Structure and Dynamics  

SciTech Connect

We propose the adiabatic passage control scheme implementing chirped femtosecond laser pulses to maximize coherence in a predetermined molecular vibrational mode using two-photon Raman transitions. We investigate vibrational energy relaxation and collisional dephasing as factors of coherence loss, and demonstrate the possibility for preventing decoherence by the chirped pulse train. The proposed method may be used to advance noninvasive biological imaging techniques.

Malinovskaya, Svetlana A. [Department of Physics and Engineering Physics, Stevens Institute of Technology Hoboken, NJ 07030 (United States)

2007-12-26

337

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.

338

Motion picture of three-dimensional image of propagating femtosecond laser pulse  

Microsoft Academic Search

We propose a technique to record and observe a propagating ultrashort laser pulse as a form of motion picture of three-dimensional image. The technique is based on the light-in-flight recording by holography and it uses a weakly light-scattering three-dimensional medium to generate the three-dimensional image of the propagating laser pulse. In the reconstruction, we gaze the hologram illuminated with a

Yasuhiro Awatsuji; Kazunari Komai; Masatomo Yamagiwa; Aya Komatsu; Toshihiro Kubota

2005-01-01

339

Development of a new pulsed source for photoacoustic imaging based on aperiodically poled lithium niobate  

PubMed Central

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; Gonzalez, J. E.; Cudney, Roger S.; Rios, Luis A.; Marcu, Laura

2014-01-01

340

Identification of biological tissue using chirped probe THz imaging  

Microsoft Academic Search

We consider the application of pulsed THz imaging systems in biomedical diagnostics and mail\\/packaging inspection. The sub-millimetre spectroscopic measurements obtained from T-ray systems contain a wealth of information about the sample under test. We demonstrate that different types of tissue can be classified based on their terahertz response measured with the chirped probe pulse technique. We demonstrate the performance of

B. Ferguson; S. Wang; D. Gray; D. Abbott; X.-C Zhang

2002-01-01

341

Polarization insensitive, broadband terahertz metamaterial absorber.  

PubMed

We present the simulation, implementation, and measurement of a polarization insensitive broadband resonant terahertz metamaterial absorber. By stacking metal-insulator layers with differing structural dimensions, three closely positioned resonant peaks are merged into one broadband absorption spectrum. Greater than 60% absorption is obtained across a frequency range of 1.86?THz where the central resonance frequency is 5?THz. The FWHM of the device is 48%, which is two and half times greater than the FWHM of a single layer structure. Such metamaterials are promising candidates as absorbing elements for bolometric terahertz imaging. PMID:21886249

Grant, James; Ma, Yong; Saha, Shimul; Khalid, Ata; Cumming, David R S

2011-09-01

342

Review NEW TRENDS IN TERAHERTZ ELECTRONICS  

Microsoft Academic Search

The rapid evolution of terahertz (THz) applications in imaging, material diagnostics, communication systems, etc. stimu- lates an intensive search for new solutions in design and fabrication of compact emitters and receivers. The particular place of THz range in the electromagnetic spectrum ñ between microwaves and the infrared one ñ denes the requirement to merge together different concepts in the development

V. Tamoöifl; D. Seliuta; A. Juozapavi; E. äirmulis; G. Valuöis; A. El Fatimy; Y. Meziani; N. Dyakonova; J. Lusakowski; W. Knap; A. Lisauskas; H. G. Roskos

343

Plasmon enhanced terahertz emission from single layer graphene.  

PubMed

We show that surface plasmons, excited with femtosecond laser pulses on continuous or discontinuous gold substrates, strongly enhance the generation and emission of ultrashort, broadband terahertz pulses from single layer graphene. Without surface plasmon excitation, for graphene on glass, 'nonresonant laser-pulse-induced photon drag currents' appear to be responsible for the relatively weak emission of both s- and p-polarized terahertz pulses. For graphene on a discontinuous layer of gold, only the emission of the p-polarized terahertz electric field is enhanced, whereas the s-polarized component remains largely unaffected, suggesting the presence of an additional terahertz generation mechanism. We argue that in the latter case, 'surface-plasmon-enhanced optical rectification', made possible by the lack of inversion symmetry at the graphene on gold surface, is responsible for the strongly enhanced emission. The enhancement occurs because the electric field of surface plasmons is localized and enhanced where the graphene is located: at the surface of the metal. We believe that our results point the way to small, thin, and more efficient terahertz photonic devices. PMID:25137623

Bahk, Young-Mi; Ramakrishnan, Gopakumar; Choi, Jongho; Song, Hyelynn; Choi, Geunchang; Kim, Yong Hyup; Ahn, Kwang Jun; Kim, Dai-Sik; Planken, Paul C M

2014-09-23

344

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

345

Terahertz radiation by optical rectification in a hydrogen-bonded organic molecular ferroelectric crystal, 2-phenylmalondialdehyde  

E-print Network

Terahertz radiation by optical rectification has been observed at room temperature in a hydrogen-bonded organic molecular ferroelectric crystal, 2-phenyl malondialdehyde (PhMDA). The radiated electromagnetic wave consisted of a single-cycle terahertz pulse with a temporal width of $\\sim$ 0.5 ps. The terahertz radiation amplitude divided by the sample thickness in PhMDA was nearly equivalent to that in a typical terahertz wave emitter ZnTe. This is attributable to a long coherence length in the range of 130 $\\sim$ 800 $\\mu$m for the terahertz radiation from PhMDA. We also discussed the possibility of PhMDA as a terahertz wave emitter in terms of the phase-matching condition.

Guan, W; Sotome, M; Kinoshita, Y; Takeda, R; Inoue, A; Horiuchi, S; Okamoto, H

2014-01-01

346

Terahertz radiation by optical rectification in a hydrogen-bonded organic molecular ferroelectric crystal, 2-phenylmalondialdehyde  

NASA Astrophysics Data System (ADS)

Terahertz radiation by optical rectification has been observed at room temperature in a hydrogen-bonded organic molecular ferroelectric crystal, 2-phenyl malondialdehyde (PhMDA). The radiated electromagnetic wave consisted of a single-cycle terahertz pulse with a temporal width of ˜0.5 ps. The terahertz radiation amplitude divided by the sample thickness in PhMDA was nearly equivalent to that in a typical terahertz wave emitter ZnTe. This is attributable to a long coherence length in the range of 130-800 µm for the terahertz radiation from PhMDA. We also discussed the possibility of PhMDA as a terahertz wave emitter in terms of the phase-matching condition.

Guan, Wenguang; Kida, Noriaki; Sotome, Masato; Kinoshita, Yuto; Takeda, Ryotaro; Inoue, Akito; Horiuchi, Sachio; Okamoto, Hiroshi

2014-09-01

347

Metal-wire terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz (THz) pulses propagating on a metal-wire waveguide are used to perform terahertz time-domain spectroscopy of lactose powder dispersed on top of the wire. The THz pulses are generated by a photoconductive switch at one end of the metal wire and are detected at the other end by electro-optic sampling in a ZnTe crystal that can be moved parallel to the axis of the metal wire. A large enhancement in the peak amplitude of the THz signal is observed by contacting the metal wire to one of the electrodes of the photoconductive switch. The propagation characteristics of the THz pulse along the metal wire and near its end are studied. Potential applications of metal-wire terahertz time-domain spectroscopy are discussed.

Walther, Markus; Freeman, Mark R.; Hegmann, Frank A.

2005-12-01

348

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

349

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

350

Single-chip pulse programmer for magnetic resonance imaging using a 32-bit microcontroller.  

PubMed

A magnetic resonance imaging (MRI) pulse programmer has been developed using a single-chip microcontroller (ADmicroC7026). The microcontroller includes all the components required for the MRI pulse programmer: a 32-bit RISC CPU core, 62 kbytes of flash memory, 8 kbytes of SRAM, two 32-bit timers, four 12-bit DA converters, and 40 bits of general purpose I/O. An evaluation board for the microcontroller was connected to a host personal computer (PC), an MRI transceiver, and a gradient driver using interface circuitry. Target (embedded) and host PC programs were developed to enable MRI pulse sequence generation by the microcontroller. The pulse programmer achieved a (nominal) time resolution of approximately 100 ns and a minimum time delay between successive events of approximately 9 micros. Imaging experiments using the pulse programmer demonstrated the effectiveness of our approach. PMID:17764345

Handa, Shinya; Domalain, Thierry; Kose, Katsumi

2007-08-01

351

Terahertz spectroscopy of intrinsic biomarkers for non-melanoma skin Cecil S. Joseph1*  

E-print Network

Terahertz spectroscopy of intrinsic biomarkers for non-melanoma skin cancer. Cecil S. Joseph1 of human cancers. The aim of this study was to identify intrinsic biomarkers for non-melanoma skin cancer wave terahertz imaging, skin cancer imaging 1. INTRODUCTION 1.1 Non-Melanoma Skin Cancer Non-melanoma

Massachusetts at Lowell, University of

352

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

353

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

354

Physiologically motivated image fusion for object detection using a pulse coupled neural network  

Microsoft Academic Search

This paper presents the first physiologically motivated pulse coupled neural network {(PCNN)-based} image fusion network for object detection. Primate vision processing principles, such as expectation driven filtering, state dependent modulation, temporal synchronization, and multiple processing paths are applied to create a physiologically motivated image fusion network. {PCNN} are used to fuse the results of several object detection techniques to improve

Randy P. Broussard; Steven K. Rogers; Mark E. Oxley; Gregory L. Tarr

1999-01-01

355

An adaptive method for image filtering with pulse-coupled neural networks  

Microsoft Academic Search

Pulse coupled neural network (PCNN) has a specific feature that the fire of one neuron can capture its adjacent neuron to fire due to their spatial proximity and intensity similarity. In this paper, it is indicated that this feature itself is a very good mechanism for image filtering when the image is damaged with pet and salt type noise (PASN).

Junying Zhang; Jiyang Dong; Meihong Shi

2005-01-01

356

Terahertz characterization of pulsed plasmas B. H. Kolner, P. M. Conklin, N. K. Fontaine, R. A. Buckles, and R. P. Scott  

E-print Network

. Buckles, and R. P. Scott Department of Applied Science, University of California, Davis, One Shields Ave Figure 1 shows a diagram of the experimental setup. The generation of the THz pulses takes place

Kolner, Brian H.

357

Characterization of pulsed (plasma focus) neutron source with image plate and application to neutron radiography  

SciTech Connect

Plasma focus device of Mather type developed in house has been used first time for neutron radiography of different objects. The device gives (1.2{+-}0.3) Multiplication-Sign 10{sup 9} neutrons per pulse produced by D-D fusion reaction with a pulse width of 50{+-}5 ns. The method involves exposing sample to be radiographed to thermalized D-D neutrons and recording the image on Fuji-film BAS-ND image plates. The thermal neutron component of the moderated beam was estimated using two image plates: a conventional IP for X-rays and gamma rays, and an IP doped with Gd for detecting neutrons.

Andola, Sanjay; Niranjan, Ram; Rout, R. K.; Kaushik, T. C.; Gupta, S. C. [Applied Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India); Shaikh, A. M. [Raja Ramanna Fellow, Solid State Physics Division (India)

2013-02-05

358

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

359

Characterization of pulsed (plasma focus) neutron source with image plate and application to neutron radiography  

NASA Astrophysics Data System (ADS)

Plasma focus device of Mather type developed in house has been used first time for neutron radiography of different objects. The device gives (1.2±0.3) ×109 neutrons per pulse produced by D-D fusion reaction with a pulse width of 50±5 ns. The method involves exposing sample to be radiographed to thermalized D-D neutrons and recording the image on Fuji-film BAS-ND image plates. The thermal neutron component of the moderated beam was estimated using two image plates: a conventional IP for X-rays and gamma rays, and an IP doped with Gd for detecting neutrons.

Andola, Sanjay; Niranjan, Ram; Shaikh, A. M.; Rout, R. K.; Kaushik, T. C.; Gupta, S. C.

2013-02-01

360

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

361

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

362

Spectral artifacts from non-uniform samples analyzed by terahertz time-domain spectroscopy.  

PubMed

We report the impact of the spatial coherence distortion on the measured absorption spectra and the identification of materials analyzed by terahertz time-domain spectroscopy. It is shown that the deformation of the terahertz beam wave front can result into the overestimation of the electromagnetic absorption, the generation of artificial absorption peaks and even to the disappearance of characteristic absorption peaks. Obtaining clear absorption spectra without artifacts is crucial for applications based on terahertz imaging and spectroscopy. PMID:19550484

Théberge, Francis; Châteauneuf, Marc; Dubois, Jacques; Désilets, Sylvain; Lussier, Louis-Simon

2009-06-22

363

Improved Fat Water Separation with Water Selective Inversion Pulse for Inversion Recovery Imaging in Cardiac MRI  

PubMed Central

Purpose To develop an improved chemical shift-based water-fat separation sequence using a water-selective inversion pulse for inversion-recovery 3D contrast-enhanced cardiac MR. Materials and Methods In inversion-recovery sequences, the fat signal is substantially reduced due to the application of a non-selective inversion pulse. Therefore, for simultaneous visualization of water, fat, and myocardial enhancement in inversion-recovery based sequences such as late Gadolinium enhancement imaging, two separate scans are used. To overcome this, the non-selective inversion pulse is replaced with a water-selective inversion pulse. Imaging was performed in phantoms, 9 healthy subjects and 9 patients with suspected arrhythmogenic right ventricular cardiomyopathy plus 1 patient for tumor/mass imaging. In patients, images with conventional turbo-spin echo (TSE) with and without fat saturation were acquired prior to contrast injection for fat assessment. Subjective image scores (1=poor, 4=excellent) were used for image assessment. Results Phantom experiments showed a fat SNR increase between 1.7 to 5.9 times for inversion times of 150 and 300ms, respectively. The water-selective inversion pulse retains the fat signal in contrast-enhanced cardiac MR, allowing improved visualization of fat in the water-fat separated images of healthy subjects with a score of 3.7 ± 0.6. Patient images acquired with the proposed sequence were scored higher when compared with TSE sequence (3.5 ± 0.7 vs. 2.2 ± 0.5, p<0.05). Conclusion The water-selective inversion pulse retains the fat signal in inversion-recovery based contrast-enhanced cardiac MR, allowing simultaneous visualization of water and fat. PMID:22927327

Havla, Lukas; Basha, Tamer; Rayatzadeh, Hussein; Shaw, Jaime L.; Manning, Warren J.; Reeder, Scott B.; Kozerke, Sebastian; Nezafat, Reza

2012-01-01

364

Electro-optic crystal mosaics for the generation of terahertz radiation  

DOEpatents

Apparatus for the generation of high energy terahertz radiation is presented and comprises laser means effective to produce subpicosecond optical pulses and a mosaic comprising a plurality of planar electro-optic crystals fastened together edge to edge in the form of a grid. The electro-optic crystals are in optical communication with the subpicosecond optical pulses, and behave as a single large electro-optic crystal, producing high energy terahertz radiation by way of optical rectification.

Carrig, Timothy J. (Los Alamos, NM); Taylor, Antoinette J. (Los Alamos, NM); Stewart, Kevin R. (Schenectady, NY)

1996-01-01

365

Electro-optic crystal mosaics for the generation of terahertz radiation  

DOEpatents

Apparatus for the generation of high energy terahertz radiation is presented and comprises laser means effective to produce subpicosecond optical pulses and a mosaic comprising a plurality of planar electro-optic crystals fastened together edge to edge in the form of a grid. The electro-optic crystals are in optical communication with the subpicosecond optical pulses, and behave as a single large electro-optic crystal, producing high energy terahertz radiation by way of optical rectification. 5 figs.

Carrig, T.J.; Taylor, A.J.; Stewart, K.R.

1996-08-06

366

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

367

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

368

A region-based multi-sensor image fusion scheme using pulse-coupled neural network  

Microsoft Academic Search

For most image fusion algorithms split relationship among pixels and treat them more or less independently, this paper proposes a region-based image fusion scheme using pulse-coupled neural network {(PCNN)}, which combines aspects of feature and pixel-level fusion. The basic idea is to segment all different input images by {PCNN} and to use this segmentation to guide the fusion process. In

Min Li; Wei Cai; Zheng Tan

2006-01-01

369

Broadband terahertz wave generation from a MgO:LiNbO3 ridge waveguide pumped by a 1.5 ?m femtosecond fiber laser.  

PubMed

Cherenkov phase-matched terahertz (THz) wave generation from a MgO:LiNbO3 ridge waveguide was studied using optical rectification. Pumping was achieved using 20 and 60 fs laser pulses from a fiber laser centered at 1.56 ?m. Time-domain spectroscopy (TDS) results showed a single-cycle pulse with 20 fs pulse pumping and a near-single-cycle pulse with 60 fs pulse pumping. The spectrum covered the range of 0.1-7 THz, with a signal-to-noise ratio of over 50 dB. The output power measured by a Si bolometer and a deuterated triglycine sulfate pyroelectric detector is shown and compared to that of a commercial photoconductive antenna. This system is believed to be a promising THz source for low-cost, compact, robust, and highly integrated TDS, THz imaging, and tomography systems. PMID:23938900

Fan, Shuzhen; Takeuchi, Hajime; Ouchi, Toshihiko; Takeya, Kei; Kawase, Kodo

2013-05-15

370

978-1-4244-2120-6/08/$25.00 IEEE. Abstract--We present the results of terahertz pulsed imaging  

E-print Network

a traditional diametric compression test3 . An increasing force is applied to the centre of a tablet until consolidation. After compaction, 10 tablets were subjected to a diametric compression test. TPI measurement at various compression forces. Results of TPI measurements are compared to those from diametric compression

Elliott, James

371

Real-time imaging of two-dimensional cardiac strain using a harmonic phase magnetic resonance imaging (HARP-MRI) pulse sequence  

Microsoft Academic Search

The harmonic phase (HARP) method provides automatic and rapid analysis of tagged magnetic resonance (MR) images for quantification and visualization of myocardial strain. In this article, the development and implementation of a pulse se- quence that acquires HARP images in real time are described. In this pulse sequence, a CINE sequence of images with 1-1 spatial modulation of magnetization (SPAMM)

Smita Sampath; J. Andrew Derbyshire; Ergin Atalar; Nael F. Osman; Jerry L. Prince

2003-01-01

372

Terahertz quantum cascade lasers  

E-print Network

The development of the terahertz frequency range has long been impeded by the relative dearth of compact, coherent radiation sources of reasonable power. This thesis details the development of quantum cascade lasers (QCLs) ...

Williams, Benjamin S. (Benjamin Stanford), 1974-

2003-01-01

373

Active terahertz metamaterials  

SciTech Connect

We demonstrate planar terahertz metamaterial devices enabling actively controllable transmission amplitude, phase, or frequency at room temperature via carrier depletion or photoexcitation in the semiconductor substrate or in semiconductor materials incorporated into the metamaterial structure.

Chen, Hou-tong [Los Alamos National Laboratory

2009-01-01

374

Spectroscopy: Nanoscale terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

The advent of terahertz spectroscopy schemes that offer single-photon sensitivity, femtosecond time resolution and nanometre spatial resolution is creating new opportunities for investigating ultrafast charge dynamics in semiconductor structures.

Shigekawa, Hidemi; Yoshida, Shoji; Takeuchi, Osamu

2014-11-01

375

Spectrally modulated stimulated Raman scattering imaging with an angle-to-wavelength pulse shaper  

PubMed Central

The stimulated Raman scattering signal is often accompanied by unwanted background arising from other pump-probe modalities. We demonstrate an approach to overcome this challenge based on spectral domain modulation, enabled by a compact, cost-effective angle-to-wavelength pulse shaper. The pulse shaper switches between two spectrally narrow windows, which are cut out of a broadband femtosecond pulse and selected for on- and off- Raman resonance excitation, at 2.1 MHz frequency for detection of stimulated Raman scattering signal. Such spectral modulation reduced the unwanted pump-probe signals by up to 20 times and enabled stimulated Raman scattering imaging of molecules in a pigmented environment. PMID:23736639

Zhang, Delong; Slipchenko, Mikhail N.; Leaird, Daniel E.; Weiner, Andrew M.; Cheng, Ji-Xin

2013-01-01

376

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

377

Temporal self-imaging effect for periodically modulated trains of pulses.  

PubMed

In this paper, the mathematical description of the temporal self-imaging effect is studied, focusing on the situation in which the train of pulses to be dispersed has been previously periodically modulated in phase and amplitude. It is demonstrated that, for each input pulse and for some specific values of the chromatic dispersion, a subtrain of optical pulses is generated whose envelope is determined by the Discrete Fourier Transform of the modulating coefficients. The mathematical results are confirmed by simulations of various examples and some limits on the realization of the theory are commented. PMID:24977616

Tainta, S; Erro, M J; Garde, M J; Muriel, M A

2014-06-16

378

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

379

* Cecil_Joseph@student.uml.edu; Ph. 978-934-1372 Dual Frequency Continuous Wave Terahertz Transmission Imaging of  

E-print Network

Transmission Imaging of Nonmelanoma Skin Cancers Cecil S. Joseph1* , Anna N. Yaroslavsky2, 3 , Julie L thick sections of nonmelanoma skin cancer were taken at two frequencies of 1.39 THz and 1.63 THz of nonmelanoma skin cancers were acquired with better than 0.5mm spatial resolution. The resulting images were

Massachusetts at Lowell, University of

380

Optical and terahertz energy concentration on the nanoscale in plasmonics  

NASA Astrophysics Data System (ADS)

We introduce an approach to implement full coherent control on nanometer length scales. It is based on spatiotemporal modulation of the surface plasmon polariton (SPP) fields at the thick edge of a nanowedge. The SPP wavepackets propagating toward the sharp edge of this nanowedge are compressed and adiabatically concentrated at a nanofocus, forming an ultrashort pulse of local fields. The profile of the focused waveform as a function of time and one spatial dimension is completely coherently controlled. We establish the principal limits for the nanoconcentration of the terahertz (THz) radiation in metal/dielectric waveguides and determine their optimum shapes required for this nanoconcentration. We predict that the adiabatic compression of THz radiation from the initial spot size of vacuum wavelength R0 ? lambda0 ? 300 microm to the unprecedented final size of R = 100--250 nm can be achieved, while the THz radiation intensity is increased by a factor of 10 to 250. This THz energy nanoconcentration will not only improve the spatial resolution and increase the signal/noise ratio for THz imaging and spectroscopy, but in combination with the recently developed sources of powerful THz pulses, will allow the observation of nonlinear THz effects and a variety of nonlinear spectroscopies (such as two-dimensional spectroscopy), which are highly informative. This should find a wide spectrum of applications in science, engineering, biomedical research and environmental monitoring. We also develop a theory of the spoof plasmons propagating at the interface between a dielectric and a real conductor. The deviation from a perfect conductor is introduced through a finite skin depth. The possibilities of guiding and focusing of spoof plasmons are considered. Geometrical parameters of the structure are found which provide a good guiding of such modes. Moreover, the limit on the concentration by means of planar spoof plasmons in case of non-ideal metal is established. These properties of spoof plasmons are of great interest for THz technology. INDEX WORDS: Nanoplasmonics, Surface plasmon polaritons, Adiabatic concentration, Full coherent control on nanoscale, Nanowedge, Terahertz, Coaxial waveguide, Spoof plasmons, Nanoscale, Nanofocus, Terahertz (THz) energy nanoconcentration

Rusina, Anastasia

381

Pulse-dilation enhanced gated optical imager with 5 ps resolution (invited)  

SciTech Connect

A 5 ps gated framing camera was demonstrated using the pulse-dilation of a drifting electron signal. The pulse-dilation is achieved by accelerating a photoelectron derived information pulse with a time varying potential [R. D. Prosser, J. Phys. E 9, 57 (1976)]. The temporal dependence of the accelerating potential causes a birth time dependent axial velocity dispersion that spreads the pulse as it transits a drift region. The expanded pulse is then imaged with a conventional gated microchannel plate based framing camera and the effective gating time of the combined instrument is reduced over that of the framing camera alone. In the drift region, electron image defocusing in the transverse or image plane is prevented with a large axial magnetic field. Details of the unique issues associated with rf excited photocathodes were investigated numerically and a prototype instrument based on this principle was recently constructed. Temporal resolution of the instrument was measured with a frequency tripled femtosecond laser operating at 266 nm. The system demonstrated 20x temporal magnification and the results are presented here. X-ray image formation strategies and photometric calculations for inertial confinement fusion implosion experiments are also examined.

Hilsabeck, T. J.; Kilkenny, J. D. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Hares, J. D.; Dymoke-Bradshaw, A. K. L. [Kentech Instruments Ltd., Wallingford, Oxfordshire OX10 (United Kingdom); Bell, P. M.; Koch, J. A.; Celliers, P. M.; Bradley, D. K.; McCarville, T.; Pivovaroff, M.; Soufli, R.; Bionta, R. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

2010-10-15

382

Multiexposure speckle contrast imaging using current pulsed VCSELs  

Microsoft Academic Search

We implement multiexposure contrast imaging using VCSELs to quantify cortical blood flow, towards a portable technique. Device characterization and noise compensations algorithms are used to show robustness of our technique in non ideal conditions.

Hart Levy; Dene Ringuette; Ofer Levi

2011-01-01

383

Nanoconcentration of Terahertz Radiation in Plasmonic Waveguides  

E-print Network

Recent years have seen an explosive research and development of nanoplasmonics in the visible and near-infrared (near-ir) frequency regions. One of the most fundamental effects in nanoplasmonics is nano-concentration of optical energy. Plasmonic nanofocusing has been predicted and experimentally achieved. It will be very beneficial for the fundamental science, engineering, environmental, and defense applications to be able to nano-concentrate terahertz radiation (frequency 1 - 10 THz or vacuum wavelength 300 - 30 microns). This will allow for the nanoscale spatial resolution for THz imaging and introduce the THz spectroscopy on the nanoscale, taking full advantage of the rich THz spectra and submicron to nanoscale structures of many engineering, physical, and biological objects of wide interest: electronic components (integrated circuits, etc.), bacteria, their spores, viruses, macromolecules, carbon clusters and nanotubes, etc. In this Letter we establish the principal limits for the nanoconcentration of the THz radiation in metal/dielectric waveguides and determine their optimum shapes required for this nanoconcentration We predict that the adiabatic compression of THz radiation from the initial spot size of light wavelength to the final size of R = 100 - 250 nm can be achieved with the THz radiation intensity increased by a factor of 10 to 250. This THz energy nanoconcentration will not only improve the spatial resolution and increase the signal/noise ratio for the THz imaging and spectroscopy, but in combination with the recently developed sources of powerful THz pulses will allow the observation of nonlinear THz effects and a carrying out a variety of nonlinear spectroscopies (such as two-dimensional spectroscopy), which are highly informative.

Anastasia Rusina; Maxim Durach; Keith A. Nelson; Mark I. Stockman

2008-08-09

384

Terahertz transmission in subwavelength holes of asymmetric metal-dielectric interfaces: The effect of a dielectric layer  

E-print Network

transmission of terahertz pulses in a plasmonic array of subwavelength holes of asymmetric dielectric-metal interfaces is presented. A giant tuning of up to 0.80 THz at the surface plasmon metal-air 1,0 mode at 1Terahertz transmission in subwavelength holes of asymmetric metal-dielectric interfaces: The effect

385

In vivo pulsed magneto-motive ultrasound imaging using high-performance magnetoactive contrast nanoagents  

NASA Astrophysics Data System (ADS)

Previously, pulsed magneto-motive ultrasound (pMMUS) imaging has been introduced as a contrast-agent-assisted ultrasound-based imaging modality capable of visualizing biological events at the cellular and molecular level. In pMMUS imaging, a high intensity pulsed magnetic field is used to excite cells or tissue labeled with magnetic nanoparticles. Then, ultrasound (US) imaging is used to monitor the mechanical response of the tissue to an externally applied magnetic field (i.e., tissue displacement). Signal to noise ratio (SNR) in pMMUS imaging can be improved by using superparamagnetic nanoparticles with larger saturation magnetization. Metal-doped magnetic nanoparticles with enhanced tunable nanomagnetism are suitable candidates to improve the SNR and, therefore, sensitivity of pMMUS imaging, which is essential for in vivo pMMUS imaging. In this study, we demonstrate the capability of pMMUS imaging to identify the presence and distribution of zinc-doped iron oxide nanoparticles in live nude mice bearing A431 (human epithelial carcinoma) xenograft tumors.Previously, pulsed magneto-motive ultrasound (pMMUS) imaging has been introduced as a contrast-agent-assisted ultrasound-based imaging modality capable of visualizing biological events at the cellular and molecular level. In pMMUS imaging, a high intensity pulsed magnetic field is used to excite cells or tissue labeled with magnetic nanoparticles. Then, ultrasound (US) imaging is used to monitor the mechanical response of the tissue to an externally applied magnetic field (i.e., tissue displacement). Signal to noise ratio (SNR) in pMMUS imaging can be improved by using superparamagnetic nanoparticles with larger saturation magnetization. Metal-doped magnetic nanoparticles with enhanced tunable nanomagnetism are suitable candidates to improve the SNR and, therefore, sensitivity of pMMUS imaging, which is essential for in vivo pMMUS imaging. In this study, we demonstrate the capability of pMMUS imaging to identify the presence and distribution of zinc-doped iron oxide nanoparticles in live nude mice bearing A431 (human epithelial carcinoma) xenograft tumors. Electronic supplementary information (ESI) available: Transmission electron microscopy (TEM), powder X-ray diffraction (PXRD) pattern, thermogravimetric analysis (TGA), colloidal stability and biocompatibility of Zn0.4Fe2.6O4 nanoparticles, and comparison between SQUID magnetometry of zinc-doped MCAs and different sizes of iron oxide nanoparticles. See DOI: 10.1039/c3nr03669c

Mehrmohammadi, Mohammad; Shin, Tae-Hyun; Qu, Min; Kruizinga, Pieter; Truby, Ryan L.; Lee, Jae-Hyun; Cheon, Jinwoo; Emelianov, Stanislav Y.

2013-10-01

386

Application of femtotechnologies and terahertz spectroscopy methods in cataract diagnostics  

NASA Astrophysics Data System (ADS)

We study the destructive action of femtosecond pulses (200 fs) on the human cataractous crystalline lens and the transmission of the cataractous lens in the terahertz spectral range of electromagnetic oscillations (0.2-1 THz) in relation to the density of the nucleus of the lens.

Sakhnov, S. N.; Leksutkina, E. V.; Smolyanskaya, O. A.; Usov, A. V.; Parakhuda, S. E.; Grachev, Ya. V.; Kozlov, S. A.

2011-08-01

387

Enhancement in the spectral irradiance of photoconducting terahertz  

E-print Network

optical pulses in biased photoconductors to generate tunable narrow-band terahertz (THz) radiation of radiative current transients in biased photo-conductors.1,4 Coupled with synchronously gated, phase by common ultrafast laser sources as well as below the optical dam- age thresholds of photoconductive media

Heinz, Tony F.

388

Pulse-modulated second harmonic imaging microscope quantitatively demonstrates marked increase of collagen in tumor after chemotherapy  

E-print Network

Pulse-modulated second harmonic imaging microscopes (PM-SHIMs) exhibit improved signal-to-noise ratio (SNR) over conventional SHIMs on sensitive imaging and quantification of weak collagen signals inside tissues. We quantify ...

Raja, Anju M.

389

Influence of raster scan parameters on the image quality for the THz phase imaging in collimated beam with a wide aperture  

NASA Astrophysics Data System (ADS)

We numerically investigated the influence of wavelength of terahertz radiation and size of scanning pinhole on the quality of reconstructed image by terahertz pulse time domain holography method. The improvement of the quality is achieved mainly by reducing the wavelength of the radiation, pinhole size and pinhole step (value of the pinhole displacement at each step) affect the spatial resolution of the reconstructed object and significantly affect the scanning time. However, pinhole does not significantly affect the quality only if pinhole size is not less than used wavelength.

Kulya, M. S.; Petrov, N. V.; Tcypkin, A. N.; Bespalov, V. G.

2014-09-01

390

Efficient transmit beamforming in pulse-echo ultrasonic imaging  

Microsoft Academic Search

A high performance ultrasound imaging system requires accurate control of the amplitude of the array elements, as well as of the time delays between them, both in the transmit and receive modes. In transmission, conventional array aperture windowing implies a different driving voltage for each element of the array, an expensive solution for systems with a large number of channels.

Gabriella Cincotti; Giovanni Cardone; Paola Gori; Massimo Pappalardo

1999-01-01

391

Adaptive Smart Imager for Pulse Structured Light Vision  

Microsoft Academic Search

This paper presents a smart image sensor oriented to the optical impulse detection. The main advantage of this smart sensor is that with incorporated analog processor the effective temporal reception window can be much smaller then that of classic CCD one. This ability will facilitate some artificial vision problems in the nature environment by using fast sequenced structured light in

F. Lavainne; Yang Ni; Francis Devos; P. de Carne

1994-01-01

392

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 tcrahertz 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; Chen, Hou-tong [Los Alamos National Laboratory; Peralta, Xomalin G [SNL; Brener, Igal [SNL

2008-01-01

393

Filtering images contaminated with pep and salt type noise with pulse-coupled neural networks  

Microsoft Academic Search

Pulse coupled neural network (PCNN) has a specific feature that the fire of one neuron can capture its adjacent neurons to\\u000a fire due to their spatial proximity and intensity similarity. In this paper, it is indicated that this feature itself is a\\u000a very good mechanism for image filtering when the image is damaged with pep and salt (PAS) type noise.

Junying Zhang; Zhijun Lu; Lin Shi; Jiyang Dong; Meihong Shi

2005-01-01

394

Hidden images of holography: wavefront reconstruction of abnormalities within pulsed holographic recording  

NASA Astrophysics Data System (ADS)

Unplanned images recorded within holographic space are of candid interest that can reshape audience definition crossing intellectual boundaries. This paper details three examples of off-axis Pulsed Laser transmission holograms that involve holographic portraits. These are movie director Martin Scorsese, former Royal Photographic Society President Mike Austin and a unique recently discovered early pulsed recording of Nick Phillips together with Anton Furst recorded in 1977. Each example was made when operating conditions for the pulsed ruby lasers were optimum, offering a coherence of several meters time-compressed into 25 ns. This gave rise to not only the portrait capture but also others present during the recording session inside the room. This optimum condition captured more than was intended resulting in images that, until now, have remained un-documented.

Richardson, Martin

2014-02-01

395

Ultrafast carrier dynamics and terahertz emission in optically pumped graphene at room temperature  

NASA Astrophysics Data System (ADS)

We report, within a picosecond time scale, fast relaxation and relatively slow recombination dynamics of photogenerated electrons and holes in an exfoliated graphene under infrared pulse excitation. We conduct time-domain spectroscopic studies using an optical pump and terahertz probe with an optical probe technique and show that graphene sheet amplifies an incoming terahertz field. The graphene emission spectral dependency on laser pumping intensity shows a threshold-like behavior, testifying to the occurrence of the negative conductivity and the population inversion. The phase behavior of the measured terahertz electric field also shows clear Lorentzian-like normal dispersion around the gain peak, testifying to the amplification that can be attributed to stimulated emission of photocarriers in the inverted states. The emission spectra clearly narrow at a longer terahertz probe delay time, giving evidence that the quasi-Fermi energy moves closer to the equilibrium at this longer terahertz probe delay time.

Boubanga-Tombet, S.; Chan, S.; Watanabe, T.; Satou, A.; Ryzhii, V.; Otsuji, T.

2012-01-01

396

Real-time image generation with a pulsed coherent laser radar  

Microsoft Academic Search

A kilowatt class, pulsed CO2 laser radar has been developed at Textron under a joint US Army-Air Force program. It is currently undergoing field trials; and successful coherent imaging and tracking experiments have been conducted over the past two years at the Air Force Maui Space surveillance Site. This paper describes the receiver- processor architecture of the laser radar system,

Francis J. Corbett; Michael Groden; Gordon L. Dryden; Mark A. Kovacs; George Pfeiffer

1997-01-01

397

Time-resolved quantitative multiphase interferometric imaging of a highly focused ultrasound pulse  

E-print Network

Time-resolved quantitative multiphase interferometric imaging of a highly focused ultrasound pulse Fabien Souris,1 Jules Grucker,1 Jacques Dupont-Roc,1 Philippe Jacquier,1 Arnaud Arvengas,2 and Fr of the reference beam. Applying this method to time dependent phenomena requires special adap- tations

Paris-Sud XI, Université de

398

Time-resolved quantitative multiphase interferometric imaging of a highly focused ultrasound pulse  

E-print Network

Time-resolved quantitative multiphase interferometric imaging of a highly focused ultrasound pulse Fabien Souris,1, * Jules Grucker,1 Jacques Dupont-Roc,1 Philippe Jacquier,1 Arnaud Arvengas,2 changing the phase of the reference beam. Applying this method to time- dependent phenomena requires

Caupin, Frédéric

399

A neutron imaging device for sample alignment in a pulsed neutron scattering instrument  

SciTech Connect

A neutron-imaging device for alignment purposes has been tested on the INES beamline at ISIS, the pulsed neutron source of Rutherford Appleton Laboratory (U.K.). Its use, in conjunction with a set of movable jaws, turns out extremely useful for scattering application to complex samples where a precise and well-defined determination of the scattering volume is needed.

Grazzi, F.; Scherillo, A.; Zoppi, M. [Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi, via Madonna del Piano 10, 50019 Sesto Fiorentino (Italy)

2009-09-15

400

Intersubband Terahertz Detectors  

NASA Astrophysics Data System (ADS)

The technology at frequencies between 1 and 10 Terahertz lags far behind that at lower end higher frequencies. Intersubband dynamics of electrons and wide semiconductor quantum wells offer opportunities to fabricate Terahertz detectors in extremely high performance, new functionalities, and moderate cryogenic requirements. In this talk, I will first review the relevant physics of intersubband transitions in wide quantum wells, as well as existing detectors based on intersubband transitions. I will then discuss the theory and development of so-called "Tunable antenna coupled intersubband THz" (TACIT) detectors. These are four-terminal phototransistors, in which Terahertz radiation absorbed via an intersubband transition changes the in-plane resistance between a source and drain. The goal of our current research program is to demonstrate a TACIT heterodyne receiver for 1.6 Terahertz which is suitable for space-based THz astrophysics missions, and which operates at lattice temperatures in excess of 20 Calvin while requiring local oscillator power < 1 microwatt. Such a device would eliminate the need to fly either liquid helium, required to cool state of the art superconducting hot-electron bolometer mixers, or few-mW Terahertz sources, required to pump Schottky diode receivers.

Sherwin, Mark S.

2002-03-01

401

Direct detector for terahertz radiation  

DOEpatents

A direct detector for terahertz radiation comprises a grating-gated field-effect transistor with one or more quantum wells that provide a two-dimensional electron gas in the channel region. The grating gate can be a split-grating gate having at least one finger that can be individually biased. Biasing an individual finger of the split-grating gate to near pinch-off greatly increases the detector's resonant response magnitude over prior QW FET detectors while maintaining frequency selectivity. The split-grating-gated QW FET shows a tunable resonant plasmon response to FIR radiation that makes possible an electrically sweepable spectrometer-on-a-chip with no moving mechanical optical parts. Further, the narrow spectral response and signal-to-noise are adequate for use of the split-grating-gated QW FET in a passive, multispectral terahertz imaging system. The detector can be operated in a photoconductive or a photovoltaic mode. Other embodiments include uniform front and back gates to independently vary the carrier densities in the channel region, a thinned substrate to increase bolometric responsivity, and a resistive shunt to connect the fingers of the grating gate in parallel and provide a uniform gate-channel voltage along the length of the channel to increase the responsivity and improve the spectral resolution.

Wanke, Michael C. (Albuquerque, NM); Lee, Mark (Albuquerque, NM); Shaner, Eric A. (Albuquerque, NM); Allen, S. James (Santa Barbara, CA)

2008-09-02

402

Graded Index Microstructured Polymer Optical Fibers for Terahertz Applications  

E-print Network

Graded index microstructured polymer optical fiber incorporating a specially designed air-hole array featuring variable air-hole diameters and inter-hole separation is proposed, fabricated and characterized in view of the fiber potential applications in low-loss, low-dispersion terahertz guidance. The proposed fiber features simultaneously low chromatic and intermodal dispersions, as well as low loss in the terahertz spectral range. We then experimentally demonstrate that proposed fibers exhibit smaller pulse distortion, larger bandwidth and more reliable excitation when compared to the porous fibers of comparable geometry.

Ma, Tian; Wang, Lili; Skorobogatiy, Maksim

2014-01-01

403

In vivo pulsed magneto-motive ultrasound imaging using high-performance magnetoactive contrast nanoagents.  

PubMed

Previously, pulsed magneto-motive ultrasound (pMMUS) imaging has been introduced as a contrast-agent-assisted ultrasound-based imaging modality capable of visualizing biological events at the cellular and molecular level. In pMMUS imaging, a high intensity pulsed magnetic field is used to excite cells or tissue labeled with magnetic nanoparticles. Then, ultrasound (US) imaging is used to monitor the mechanical response of the tissue to an externally applied magnetic field (i.e., tissue displacement). Signal to noise ratio (SNR) in pMMUS imaging can be improved by using superparamagnetic nanoparticles with larger saturation magnetization. Metal-doped magnetic nanoparticles with enhanced tunable nanomagnetism are suitable candidates to improve the SNR and, therefore, sensitivity of pMMUS imaging, which is essential for in vivo pMMUS imaging. In this study, we demonstrate the capability of pMMUS imaging to identify the presence and distribution of zinc-doped iron oxide nanoparticles in live nude mice bearing A431 (human epithelial carcinoma) xenograft tumors. PMID:24080913

Mehrmohammadi, Mohammad; Shin, Tae-Hyun; Qu, Min; Kruizinga, Pieter; Truby, Ryan L; Lee, Jae-Hyun; Cheon, Jinwoo; Emelianov, Stanislav Y

2013-11-21

404

Time-domain terahertz spectroscopy of artificial skin  

NASA Astrophysics Data System (ADS)

Time-domain Terahertz (THz) spectroscopy and imaging is currently evaluated as a novel tool for medical imaging and diagnostics. The application of THz-pulse imaging of human skin tissues and related cancers has been demonstrated recently in-vitro and in-vivo. With this in mind, we present a time-domain THz-transmission study of artificial skin. The skin samples consist of a monolayer of porous matrix of fibers of cross-linked bovine tendon collagen and a glycosaminoglycan (chondroitin-6-sulfate) that is manufactured with a controlled porosity and defined degradation rate. Another set of samples consists of the collagen monolayer covered with a silicone layer. We have measured the THz-transmission and determined the index of refraction and absorption of our samples between 0.1 and 3 THz for various states of hydration in distilled water and saline solutions. The transmission of the THz-radiation through the artificial skin samples is modeled by electromagnetic wave theory. Moreover, the THz-optical properties of the artificial skin layers are compared to the THz-optical properties of freshly excised human skin samples. Based on this comparison the potential use of artificial skin samples as photo-medical phantoms for human skin is discussed.

Corridon, Peter M.; Ascázubi, Ricardo; Krest, Courtney; Wilke, Ingrid

2006-02-01

405

An Exploration of the Utilities of Terahertz Waves for the Nde of Composites  

NASA Astrophysics Data System (ADS)

We report an investigation of terahertz waves for the nondestructive evaluation of composite materials and structures. The modalities of the terahertz radiation used were time domain spectroscopy (TDS) and continuous wave (CW). The composite materials and structures investigated include both non-conducting polymeric composites and carbon fiber composites. Terahertz signals in the TDS mode resembles that of ultrasound; however, unlike ultrasound, a terahertz pulse can detect a crack hidden behind a larger crack. This was demonstrated in thick GFRP laminates containing double saw slots. In carbon composites the penetration of terahertz waves is quite limited and the detection of flaws is strongly affected by the angle between the electric field vector of the terahertz waves and the intervening fiber directions. The structures tested in this study include both solid laminates and honeycomb sandwiches. The defects and anomalies investigated by terahertz waves were foreign material inclusions, simulated disbond and delamination, mechanical impact damage, heat damage, and water or hydraulic fluid ingression. The effectiveness and limitations of terahertz radiation for the NDE of composites are discussed.

Hsu, David K.; Im, Kwang-Hee; Chiou, Chien-Ping; Barnard, Daniel J.

2011-06-01

406

Asymmetric planar terahertz metamaterials  

SciTech Connect

Using terahertz time-domain spectroscopy, we report an experimental observation of three distinct resonances in split ring resonators (SRRs) for both vertical and horizontal electric field polarizations at normal incidence. Breaking the symmetry in SRRs by gradually displacing the capacitive gap from the centre towards the comer of the ring allows for an 85% modulation of the fundamental inductive-capacitive (LC) resonance. Increasing asymmetry leads to the evolution of an otherwise inaccessible high quality factor electric quadrupole resonance that can be exploited for bio-sensing applications in the terahertz region.

Singh, Ramjan [Los Alamos National Laboratory; Al - Naib, Ibraheem A. I. [PHILIPPS UNIV; Koch, Martin [PHILIPPS UNIV; Zhang, Weili [OKLAHOMA STATE UNIV

2010-01-01

407

Development of a high-speed camera system for neutron imaging at a pulsed neutron source  

NASA Astrophysics Data System (ADS)

A neutron energy resolved imaging system with a time-of-flight technique has been newly developed and installed at Japan Proton Accelerator Research Complex (J-PARC) with the aim to investigate more preciously and rapidly a spatial distribution of several elements and crystals in various kinds of materials or substances. A high-speed video camera (CMOS, 1300 k frame/s) equipped system allows to obtain TOF images consecutively resolved into narrow energy ranges with a single pulsed neutrons while conventional CCD camera imaging system could obtain only one TOF image in an arbitral neutron energy region in the pulsed neutron energy region from 0.01 eV to a few keV. Qualities of the images obtained with the system, such as spatial resolution (defined by modulation transfer function, 0.8 line-pairs/mm at En˜0.01 eV), dependence of the brightness on the neutron energy and measurement errors (˜2%) of the system were examined experimentally and evaluated by comparison with those of conventional imaging system. The results obtained in the experiments show that the system can visualize the neutron energy resolved images within a small error even at high speed.

Segawa, M.; Kai, T.; Sakai, T.; Ooi, M.; Kureta, M.

2013-01-01

408

Novel Waveguide Structures in the Terahertz Frequency Range  

NASA Astrophysics Data System (ADS)

Over the last decade, considerable research interest has peaked in realizing an efficient Terahertz (THz) waveguide for potential applications in imaging, sensing, and communications applications. Two of the promising candidates are the two-wire waveguide and the parallel-plate waveguide (PPWG). I present theoretical and experimental evidence that show that the two-wire waveguide supports low loss terahertz pulse propagation, and illustrate that the mode pattern at the end of the waveguide resembles that of a dipole. In comparison to the weakly guided Sommerfeld wave of a single wire waveguide, this two-wire structure exhibits much lower bending losses. I also observe that a commercial 300-Ohm two-wire TVantenna cable can be used for guiding frequency components of up to 0.2 THz, although these cables are generally designed to operate only up to about 800 MHz. The parallel-plate waveguide is another promising candidate that would make an efficient THz waveguide, since it has relatively low Ohmic losses. The transverse electromagnetic mode (TEM) of this waveguide has been generally preferred since it has no cutoff frequency, and therefore no group velocity dispersion. Utilizing this TEM mode, I study the reflection of THz radiation at the end of a PPWG, due to the impedance mismatch between the propagating transverse-electromagnetic mode and the free-space background. I find that for a PPWG with uniformly spaced plates, the reflection coefficient at the output face increases as the plate separation decreases, consistent with predictions by early low frequency ray optical theory. I observe this same trend in tapered PPWGs, when the input separation is fixed, and the output separation is varied. In another study, I investigate how to minimize diffraction losses in PPWGs by using plates with slightly concave surfaces. Using a simple "bouncing plane wave" analysis, I demonstrate how to determine an ideal radius of curvature for a waveguide operating at a given THz frequency. I perform a detailed experimental and simulation study that illustrates, for a waveguide with a plate separation of 1 cm, one can inhibit the diffraction around a frequency of 0.1 THz, when the surface has a curvature of 6.7 cm. Using much longer PPWGs (about 170cm), I reliably measure the overall losses in a PPWG with a radius of curvature of R=6.7 cm, and find it to be less than 1db/m around the design frequency (of 0.1 THz). This is very close to the lowest achieved loss to date with any terahertz waveguide.

Mbonye, Marx

409

Terahertz-induced Kerr effect in amorphous chalcogenide glasses  

NASA Astrophysics Data System (ADS)

We have investigated the terahertz-induced third-order (Kerr) nonlinear optical properties of the amorphous chalcogenide glasses As2S3 and As2Se3. Chalcogenide glasses are known for their high optical Kerr nonlinearities which can be several hundred times greater than those of fused silica. We use high-intensity, single-cycle terahertz pulses with a maximum electrical field strength exceeding 400 kV/cm and frequency content from 0.2 to 3.0 THz. By optical Kerr-gate sampling, we measured the terahertz-induced nonlinear refractive indices at 800 nm to be n2=1.746×10-14cm2/W for As2S3 and n2=3.440×10-14 cm2/W for As2Se3.

Zalkovskij, M.; Strikwerda, A. C.; Iwaszczuk, K.; Popescu, A.; Savastru, D.; Malureanu, R.; Lavrinenko, A. V.; Jepsen, P. U.

2013-11-01

410

Tamper to delay motion and decrease ionization of a sample during short pulse x-ray imaging  

DOEpatents

A system for x-ray imaging of a small sample comprising positioning a tamper so that it is operatively connected to the sample, directing short intense x-ray pulses onto the tamper and the sample, and detecting an image from the sample. The tamper delays the explosive motion of the sample during irradiation by the short intense x-ray pulses, thereby extending the time to obtain an x-ray image of the original structure of the sample.

London, Richard A. (Orinda, CA); Szoke; Abraham (Fremont, CA), Hau-Riege; Stefan P. (Fremont, CA), Chapman; Henry N. (Livermore, CA)

2007-06-26

411

Observation of Amplified Stimulated Terahertz Emission from Optically Pumped Heteroepitaxial Graphene-on-Silicon Materials  

NASA Astrophysics Data System (ADS)

We experimentally observed the fast relaxation and relatively slow recombination dynamics of photogenerated electrons/holes in a heteroepitaxial graphene-on-Si material under pumping with a 1550-nm, 80-fs pulsed fiber laser and probing with the corresponding terahertz beam generated by and synchronized with the pumping laser. The time-resolved electric-nearfield intensity originating from the coherent terahertz photon emission is electrooptically sampled in total-reflection geometry. The Fourier spectrum fairly agrees the product of the negative dynamic conductivity and the expected THz photon spectrum reflecting the pumping photon spectrum. This phenomenon is interpreted as an amplified stimulated terahertz emission.

Karasawa, Hiromi; Komori, Tsuneyoshi; Watanabe, Takayuki; Satou, Akira; Fukidome, Hirokazu; Suemitsu, Maki; Ryzhii, Victor; Otsuji, Taiichi

2011-05-01

412

Stimulated Terahertz Emission from Intra-Excitonic Transitions inCu2O  

SciTech Connect

We report the first observation of stimulated emission of terahertz radiation from internal transitions of excitons. The far-infrared electromagnetic response of Cu{sub 2}O is monitored via broadband terahertz pulses after ultrafast resonant excitation of three-dimensional 3p excitons. Stimulated emission from the 3p to the energetically lower 2s bound level occurs at a photon energy of 6.6 meV, with a cross section of {approx} 10{sup 14} cm{sup 2}. Simultaneous excitation of both exciton levels, in turn, drives quantum beats which lead to efficient terahertz emission sharply peaked at the difference frequency.

Huber, Rupert; Schmid, Ben A.; Shen, Y. Ron; Chemla, Daniel S.; Kaindl, Robert A.

2005-06-16

413

Modelling of an imaging beamline at the ISIS pulsed neutron source  

NASA Astrophysics Data System (ADS)

A combined neutron imaging and neutron diffraction facility, IMAT, is currently being built at the pulsed neutron spallation source ISIS in the U.K. A supermirror neutron guide is required to combine imaging and diffraction modes at the sample position in order to obtain suitable time of flight resolutions for energy selective imaging and diffraction experiments. IMAT will make use of a straight neutron guide and we consider here the optimization of the supermirror guide dimensions and characterisation of the resulting beam characteristics, including the homogeneity of the flux distribution in space and energy and the average and peak neutron fluxes. These investigations take into account some main design criteria: to maximise the neutron flux, to minimise geometrical artefacts in the open beam image at the sample position and to obtain a good energy resolution whilst retaining a large neutron bandwidth. All of these are desirable beam characteristics for the proposed imaging and diffraction analysis modes of IMAT.

Burca, G.; Kockelmann, W.; James, J. A.; Fitzpatrick, M. E.

2013-10-01

414

Terahertz direct-contact refractometer/spectrometer.  

PubMed

A method for terahertz (THz) reflection spectroscopy is presented that utilizes direct contact between the backside of the pulsed emitter and the sample. Changes in the complex reflectivity of the emitter-sample interface are used to measure the spectrum. This method is especially useful for spectroscopy of liquid samples and soft materials. It simplifies the optical apparatus, has good sensitivity, and has capability for use in the construction of miniaturized THz probes. The problem of nonplanar wave fronts inside the emitter is discussed. PMID:17632637

Hirsch, Ole; Alexander, Paul

2007-07-15

415

Contact resistance dynamics at bimetallic interfaces investigated by ultrafast terahertz surface plasmon-mediated transmission spectroscopy  

Microsoft Academic Search

We study free-space terahertz pulse propagation through samples of densely packed Cu microparticles that are coated with Au nano-layers. By coating the Cu particles with Au nano-layers, the terahertz transmission is dramatically attenuated. The substantial attenuation cannot be reconciled by the inherent resistivities of the Cu and Au metals. The experimental results strongly show that the transmission attenuation arises from

K. J. Chau; A. Y. Elezzabi

2006-01-01

416

Generation of terahertz radiation by a surface ballistic photocurrent in semiconductors under subpicosecond laser excitation  

SciTech Connect

An analytical model describing the onset of a surface ballistic photocurrent in cubic semiconductors under femtosecond laser excitation is proposed. It is shown that the contribution of the photocurrent component parallel to the surface to the generation of terahertz pulses may be comparable to the contribution of the perpendicular component. Consideration of the cubic symmetry of a semiconductor leads to the azimuthal anisotropy of terahertz generation.

Ziaziulia, P. A., E-mail: palz@tut.by [Belarussian State University (Belarus); Malevich, V. L. [National Academy of Sciences of Belarus, Stepanov Institute of Physics (Belarus); Manak, I. S. [Belarussian State University (Belarus); Krotkus, A. [Center for Physical Sciences and Technology (Lithuania)

2012-02-15

417

Pulsed light imaging for wide-field dosimetry of photodynamic therapy in the skin  

NASA Astrophysics Data System (ADS)

Photodynamic therapy using aminoluvelinic acid (ALA) is an FDA-approved treatment for actinic keratoses, pre-cancerous skin lesions which pose a significant risk for immunocompromised individuals, such as organ transplant recipients. While PDT is generally effective, response rates vary, largely due to variations in the accumulation of the photosensitizer protoporphyrin IX (PpIX) after ALA application. The ability to quantify PpIX production before treatment could facilitate the use of additional interventions to improve outcomes. While many groups have demonstrated the ability to image PpIX in the clinic, these systems generally require darkening the room lights during imaging, which is unpopular with clinicians. We have developed a novel wide-field imaging system based on pulsed excitation and gated acquisition to image photosensitizer activity in the skin. The tissue is illuminated using four pulsed LED's to excite PpIX, and the remitted light acquired with a synchronized ICCD. This approach facilitates real-time background subtraction of ambient light, precluding the need to darken the exam room. Delivering light in short bursts also allows the use of elevated excitation intensity while remaining under the maximum permissible exposure limits, making the modality more sensitive to photosensitizer fluorescence than standard approaches. Images of tissue phantoms indicate system sensitivity down to 250nM PpIX and images of animals demonstrate detection of PpIX fluorescence in vivo under normal room light conditions.

Davis, Scott C.; Sexton, Kristian; Chapman, Michael Shane; Maytin, Edward; Hasan, Tayyaba; Pogue, Brian W.

2014-03-01

418

Step-scan time-domain terahertz magneto-spectroscopy.  

PubMed

We present a novel approach for terahertz time-domain spectroscopy of magneto-optic phenomena. The setup used in this work combines a tabletop pulsed magnet and a standard terahertz time-domain spectroscopy system. The approach is based on repetitive operation of the pulsed magnet and step-wise increment of the delay time of the time-domain spectroscopy system. The method is demonstrated by plotting the magneto-transmission spectra of linearly polarized THz pulses through the hole gas of a Ge sample and the electron gas of GaAs, InSb and InAs samples. Cyclotron resonance spectra are displayed in the frequency range from 200 GHz to 2 THz and for a magnetic field up to 6 T. The GaAs spectra are analyzed in more detail using simulations based on the Drude model. PMID:22418476

Molter, D; Torosyan, G; Ballon, G; Drigo, L; Beigang, R; Léotin, J

2012-03-12

419

A review of terahertz sources  

NASA Astrophysics Data System (ADS)

Bibliometric data set the scene by illustrating the growth of terahertz work and the present interest in terahertz science and technology. After locating terahertz sources within the broader context of terahertz systems, an overview is given of the range of available sources, emphasizing recent developments. The focus then narrows to terahertz sources that rely on surface phenomena. Three are highlighted. Optical rectification, usually thought of as a bulk process, may in addition exhibit a surface contribution, which, in some cases, predominates. Transient surface currents, for convenience often separated into drift and diffusion currents, are well understood according to Monte Carlo modelling. Finally, terahertz surface emission by mechanical means—in the absence of photoexcitation—is described.

Lewis, R. A.

2014-09-01

420

Giant terahertz gain by excitation of surface plasmon polarities in optically pumped graphene  

NASA Astrophysics Data System (ADS)

Interband photoexcitation in monolayer graphene can produce a weak gain in the terahertz range by only up to 2.3%, but exciting the surface plasmon polaritons mediates the light-matter interaction, resulting in a giant terahertz gain. Nonlinear carrier relaxation/recombination dynamics and resultant stimulated terahertz (THz) photon emission with excitation of surface plasmon polaritons (SPPs) in photoexcited monolayer graphene has been experimentally studied using optical-pump/THz-probe and optical-probe measurement. We observed the spatial distribution of the THz probe pulse intensities under linear polarization of optical pump and THz probe pulses. It was clearly observed that intense THz probe pulse was detected only at the area where the incoming THz probe pulse takes a TM mode being capable of exciting the SPPs. The observed gain factor is in fair agreement with theoretical calculations.

Otsuji, Taiichi; Watanabe, Takayuki; Tombet, Stephane B.; Satou, Akira; Dubinov, Alexander A.; Aleshkin, Vladimir Y.; Mitin, Vladimir; Ryzhii, Victor

2014-05-01

421

Pulsed-light imaging for fluorescence guided surgery under normal room lighting.  

PubMed

Fluorescence guided surgery (FGS) is an emerging technology that has demonstrated improved surgical outcomes. However, dim lighting conditions required by current FGS systems are disruptive to standard surgical workflow. We present a novel FGS system capable of imaging fluorescence under normal room light by using pulsed excitation and gated acquisition. Images from tissue-simulating phantoms confirm visual detection down to 0.25 ?M of protoporphyrin IX under 125 ?W/cm2 of ambient light, more than an order of magnitude lower than that measured with the Zeiss Pentero in the dark. Resection of orthotopic brain tumors in mice also suggests that the pulsed-light system provides superior sensitivity in vivo. PMID:23988926

Sexton, Kristian; Davis, Scott C; McClatchy, David; Valdes, Pablo A; Kanick, Stephen C; Paulsen, Keith D; Roberts, David W; Pogue, Brian W

2013-09-01

422

An imaging proton spectrometer for short-pulse laser plasma experiments  

SciTech Connect

Ultra intense short pulse laser pulses incident on solid targets can generate energetic protons. In additions to their potentially important applications such as in cancer treatments and proton fast ignition, these protons are essential to understand the complex physics of intense laser plasma interaction. To better characterize these laser-produced protons, we designed and constructed a novel, spatially imaging proton spectrometer that will not only measure proton energy distribution with high resolution, but also provide its angular characteristics. The information obtained from this spectrometer compliments those from commonly used diagnostics including radiochromic film packs, CR39 nuclear track detectors, and non-imaging magnetic spectrometers. The basic characterizations and sample data from this instrument are presented.

Chen, H; Hazi, A; van Maren, R; Chen, S; Fuchs, J; Gauthier, M; Pape, S L; Rygg, J R; Shepherd, R

2010-05-11

423

Pulsed-light imaging for fluorescence guided surgery under normal room lighting  

PubMed Central

Fluorescence guided surgery (FGS) is an emerging technology that has demonstrated improved surgical outcomes. However, dim lighting conditions required bycurrent FGS systems are disruptive to standard surgical workflow. We present a novel FGS system capable of imaging fluorescence under normal room lightby using pulsed excitation and gated acquisition. Images from tissue-simulating phantoms confirm visual detection down to 0.25 ?M of protopor-phyrin IX under 125 ?W/cm2 of ambient light, more than an order of magnitude lower than that measured with the Zeiss Pentero in the dark. Resection of orthotopic brain tumors in mice also suggests that the pulsed-light system provides superior sensitivity in vivo. PMID:23988926

Sexton, Kristian; Davis, Scott C.; McClatchy, David; Valdes, Pablo A.; Kanick, Stephen C.; Paulsen, Keith D.; Roberts, David W.; Pogue, Brian W.

2013-01-01

424

Femtosecond pulse shaping enables detection of optical Kerr-effect (OKE) dynamics for molecular imaging  

PubMed Central

We apply femtosecond pulse shaping to generate optical pulse trains that directly access a material’s nonlinear refractive index (n2) and can thus determine time-resolved optical Kerr-effect (OKE) dynamics. Two types of static pulse trains are discussed: The first uses two identical fields delayed in time, plus a pump field at a different wavelength. Time-resolved OKE dynamics are retrieved by monitoring the phase of the interference pattern produced by the two identical fields in the Fourier-domain (FD) as a function of pump–probe–time–delay (where the probe is one of the two identical fields). The second pulse train uses three fields with equal time delays, but with the center field phase shifted by ?/2. In this pulse scheme, changes on a sample’s nonlinear refractive index produce a new frequency in the FD signal, which in turn yields background-free intensity changes in the conjugate (time) domain and provides superior signal-to-noise ratios. The demonstrated sensitivity improvements enable, for the first time to our knowledge, molecular imaging based on OKE dynamics. PMID:25121875

Robles, Francisco E.; Fischer, Martin C.; Warren, Warren S.

2014-01-01

425

ULTRASOUND PULSE-ECHO IMAGING USING THE SPLIT-STEP FOURIER PROPAGATOR  

SciTech Connect

Ultrasonic reflection imaging has the potential to produce higher image resolution than transmission tomography, but imaging resolution and quality still need to be further improved for early cancer detection and diagnosis. We present an ultrasound reflection image reconstruction method using the split-step Fourier propagator. It is based on recursive inward continuation of ultrasonic wavefields in the frequency-space and frequency-wavenumber domains. The inward continuation within each extrapolation interval consists of two steps. In the first step, a phase-shift term is applied to the data in the frequency-wavenumber domain for propagation in a reference medium. The second step consists of applying another phase-shift term to data in the frequency-space domain to approximately compensate for ultrasonic scattering effects of heterogeneities within the breast. We use synthetic ultrasound pulse-echo data recorded around a ring for heterogeneous, computer-generated numerical breast phantoms to study the imaging capability of the method. The phantoms are derived from an experimental breast phantom and a sound-speed tomography image of an in-vivo ultrasound breast data collected usi ng a ring array. The heterogeneous sound-speed models used for pulse-echo imaging are obtained using a computationally efficient, first-arrival-time (time-of-flight) transmission tomography method. Our studies demonstrate that reflection image reconstruction using the split-step Fourier propagator with heterogeneous sound-speed models significantly improves image quality and resolution. We also numerically verify the spatial sampling criterion of wavefields for a ring transducer array.

HUANG, LIANJIE [Los Alamos National Laboratory; QUAN, YOULI [Los Alamos National Laboratory

2007-01-31

426

Terahertz ambipolar dual-wavelength quantum cascade laser.  

PubMed

Terahertz frequency quantum cascade lasers (THz QCLs) are compact solid-state sources of terahertz radiation that were first demonstrated in 2002. They have a broad range of potential applications ranging from gas sensing and non-destructive testing, through to security and medical imaging, with many polycrystalline compounds having distinct fingerprint spectra in the terahertz frequency range. In this article, we demonstrate an electrically-switchable dual-wavelength THz QCL which will enable spectroscopic information to be obtained within a THz QCL-based imaging system. The device uses the same active region for both emission wavelengths: in forward bias, the laser emits at 2.3 THz; in reverse bias, it emits at 4 THz. The corresponding threshold current densities are 490 A/cm(2) and 330 A/cm(2), respectively, with maximum operating temperatures of 98K and 120 K. PMID:19997216

Lever, L; Hinchcliffe, N M; Khanna, S P; Dean, P; Ikonic, Z; Evans, C A; Davies, A G; Harrison, P; Linfield, E H; Kelsall, R W

2009-10-26

427

Intense Terahertz Excitation of Semiconductors  

E-print Network

condensed matter physics, chemistry, bio- physics, medicine, etc. The prerequisites for this book terahertz heterodyne receivers for astro- nomical purposes. The second area, emerging only lately, deals

Ganichev, Sergey

428

Using a neural networks algorithm for high-resolution imaging in pulsed laser radar  

NASA Astrophysics Data System (ADS)

A new imaging method which can obtain the gray levels directly from the output waveform of Pulsed Laser Radar (PLR) is developed. A simple digital signal processing technique and multi layer perceptrons (MLP) type neural network (NN) have been used to obtain the gray level information from the pulse shapes. The method has been implemented in a real PLR to improve contrast and speed of 2D imaging in PLR. To compare the method with the standard method, a picture consists of 16 gray levels (from 0 for black to 1 for white) with both method has been scanned. Because of the ability of NNs in extracting the information from nonlinear and noisy data and preprocessing of the noisy input pulse shapes to the NN, the average and maximum of errors in the gray levels in comparison with standard method more than 88.5% and 72.6% improved, respectively. Because in this method the effect of the noise is decreased, it is possible to make the imaging with the same resolution as in standard method but with a lower averaging in sampling unit and this dramatically increases speed of the measurements.

Joodaki, Mojtaba; Kompa, Guenter; Golam Arshad, Seyed M.; Ahmadi, Vahid; Moravvej-Farshi, Mohammed K.

2001-11-01

429

Fluorescence imaging beyond the ballistic regime by ultrasound pulse guided digital phase conjugation.  

PubMed

Fluorescence imaging has revolutionized biomedical research over the past three decades. Its high molecular specificity and unrivaled single molecule level sensitivity have enabled breakthroughs in a variety of research fields. For in vivo applications, its major limitation is the superficial imaging depth as random scattering in biological tissues causes exponential attenuation of the ballistic component of a light wave. Here we present fluorescence imaging beyond the ballistic regime by combining single cycle pulsed ultrasound modulation and digital optical phase conjugation. We demonstrate a near isotropic 3D localized sound-light interaction zone. With the exceptionally high optical gain provided by the digital optical phase conjugation system, we can deliver sufficient optical power to a focus inside highly scattering media for not only fluorescence imaging but also a variety of linear and nonlinear spectroscopy measurements. This technology paves the way for many important applications in both fundamental biology research and clinical studies. PMID:23241552

Si, Ke; Fiolka, Reto; Cui, Meng

2012-10-01

430

Photoacoustic and ultrasound imaging using dual contrast perfluorocarbon nanodroplets triggered by laser pulses at 1064 nm  

PubMed Central

Recently, a dual photoacoustic and ultrasound contrast agent—named photoacoustic nanodroplet—has been introduced. Photoacoustic nanodroplets consist of a perfluorocarbon core, surfactant shell, and encapsulated photoabsorber. Upon pulsed laser irradiation the perfluorocarbon converts to gas, inducing a photoacoustic signal from vaporization and subsequent ultrasound contrast from the resulting gas microbubbles. In this work we synthesize nanodroplets which encapsulate gold nanorods with a peak absorption near 1064 nm. Such nanodroplets are optimal for extended photoacoustic imaging depth and contrast, safety and system cost. We characterized the nanodroplets for optical absorption, image contrast and vaporization threshold. We then imaged the particles in an ex vivo porcine tissue sample, reporting contrast enhancement in a biological environment. These 1064 nm triggerable photoacoustic nanodroplets are a robust biomedical tool to enhance image contrast at clinically relevant depths. PMID:25401018

Hannah, Alexander S.; VanderLaan, Donald; Chen, Yun-Sheng; Emelianov, Stanislav Y.

2014-01-01

431

Current-density imaging using ultra-low-field MRI with adiabatic pulses.  

PubMed

Magnetic resonance imaging (MRI) allows measurement of electric current density in an object. The measurement is based on observing how the magnetic field of the current density affects the associated spins. However, as high-field MRI is sensitive to static magnetic field variations of only the field component along the main field direction, object rotations are typically needed to image three-dimensional current densities. Ultra-low-field (ULF) MRI, on the other hand, with B0 on the order of 10-100 ?T, allows novel MRI sequences. We present a rotation-free method for imaging static magnetic fields and current densities using ULF MRI. The method utilizes prepolarization pulses with adiabatic switch-off ramps. The technique is designed to reveal complete field and current-density information without the need to rotate the object. The method may find applications, e.g., in conductivity imaging. We present simulation results showing the feasibility of the sequence. PMID:24139338

Nieminen, Jaakko O; Zevenhoven, Koos C J; Vesanen, Panu T; Hsu, Yi-Cheng; Ilmoniemi, Risto J

2014-01-01

432

Photoacoustic and ultrasound imaging using dual contrast perfluorocarbon nanodroplets triggered by laser pulses at 1064 nm.  

PubMed

Recently, a dual photoacoustic and ultrasound contrast agent-named photoacoustic nanodroplet-has been introduced. Photoacoustic nanodroplets consist of a perfluorocarbon core, surfactant shell, and encapsulated photoabsorber. Upon pulsed laser irradiation the perfluorocarbon converts to gas, inducing a photoacoustic signal from vaporization and subsequent ultrasound contrast from the resulting gas microbubbles. In this work we synthesize nanodroplets which encapsulate gold nanorods with a peak absorption near 1064 nm. Such nanodroplets are optimal for extended photoacoustic imaging depth and contrast, safety and system cost. We characterized the nanodroplets for optical absorption, image contrast and vaporization threshold. We then imaged the particles in an ex vivo porcine tissue sample, reporting contrast enhancement in a biological environment. These 1064 nm triggerable photoacoustic nanodroplets are a robust biomedical tool to enhance image contrast at clinically relevant depths. PMID:25401018

Hannah, Alexander S; VanderLaan, Donald; Chen, Yun-Sheng; Emelianov, Stanislav Y

2014-09-01

433

Photoexcited GaAs surfaces studied by transient terahertz time-domain spectroscopy  

Microsoft Academic Search

The transmission characteristics of an air - GaAs interface and the transient absorption and index spectra of the thin, photoexcited surface layer are investigated subsequent to excitation by a femtosecond laser pulse. We find that the total phase change and transmission of a terahertz (THz) probe pulse are dominated by interface effects. This observation has important implications in the interpretation

Michael Schall; Peter Uhd Jepsen

2000-01-01

434

Coherent Detection of Multiband Terahertz Radiation Using a Surface Plasmon-Polariton Based Photoconductive Antenna  

Microsoft Academic Search

We characterize a dipole antenna structure that allows for coherent detection of narrowband terahertz radiation with enhanced sensitivity at the resonant frequency. The antenna incorporates a corrugated metal structure that surrounds the dipole. Each periodically spaced groove in the corrugation couples an approximate replica of the incident THz pulse to a surface plasmon-polariton pulse, which then propagates towards and is

Shuchang Liu; Xiang Shou; Ajay Nahata

2011-01-01

435

Cherenkov radiation of terahertz surface plasmon polaritons from a superluminal optical spot  

Microsoft Academic Search

We propose to use a cylindrically focused ultrashort laser pulse obliquely incident on a semiconductor surface to launch surface plasmon polaritons with frequencies in the terahertz range. The laser pulse creates a spot of nonlinear polarization moving along the semiconductor surface with superluminal velocity. We show theoretically that the spot will emit the surface and free-space waves via Cherenkov mechanism.

M. I. Bakunov; A. V. Maslov; S. B. Bodrov

2005-01-01

436

Analysis of the Hydration Water around Bovine Serum Albumin using Terahertz Coherent Synchrotron Radiation  

E-print Network

. P. J.; Falconer, R. J. Terahertz and far-infrared spectroscopy of alanine-rich peptides with variable ellipticity. Opt. Express 2010, 18, 27431-27444. (13) Cinque, G.; Frogley, M.; Wehbe, K.; Filik, J.; Pijanka, J. Multimode infrared imaging...

Bye, J. W.; Meliga, S.; Ferachou, D.; Cinque, G.; Zeitler, J. A.; Falconer, R. J.

437

Applications of surface plasmon polaritons in terahertz spectral regime  

NASA Astrophysics Data System (ADS)

This thesis presents the experimental work on the applications of surface plasmon polariton (SPP) in terahertz (THz) spectral range. Apertureless near-field optical microscopy (ANSOM) has been widely used to study the localized SPP on various material surfaces. THz ANSOM technique was recently developed to combine the THz time-domain spectroscopy and the ANSOM technique to provide a near-field detection on the localized THz surface waves with improved spatial resolution and signal-noise ratio. We have studied the metal-insulator transition in vanadium dioxide (VO2) thin film using THz ANSOM. We observe a variation of the terahertz amplitude due to the phase transition induced by an applied voltage across the sample. The change of the terahertz signal is related to the abrupt change of the conductivity of the VO2 film at the metal-insulator transition. The subwavelength spatial resolution of this near-field microscopy makes it possible to detect signatures of metallic domains, which exist in the VO2 thin films in the vicinity of the phase transition. We experimentally investigate the propagation of guided waves in finite-width parallel-plate waveguides (PPWGs) in the terahertz spectral range. We observe the propagation of SPPs in this guiding structure, instead of the fundamental transverse electromagnetic (TEM) mode. We find that the two-dimensional (2-D) energy confinement within the finite-width PPWG increases exponentially as the plate separation is reduced. We speculate that edge plasmons play an important role in the energy confinement in this open-structure waveguide. For comparison, the infinite-width PPWGs, the plates of which are much wider than the THz beam size, are also studied with several plate separations. The free-space beam diffraction produces a Gaussian profile along the unconfined direction. The unusual electric field profiles along the vertical direction, perpendicular to the plate are observed. The field enhancement near the metal surfaces are also explained by the SPPs coupled to the metal surfaces. Based on the 2-D energy confinement in the finite-width PPWGs, we design the tapered slot waveguide by slowly tapering the plate width and slot gap. We first study the transverse component of the THz electric field, where a subwavelength 2-D energy confinement is observed. The output spot size strongly depends on the output facet size, where the slot gap and the tip width are in the same scale range. Subwavelength confinement is obtained, corresponding to lambda/4. Further confinement is limited by the spatial resolution of the detecting technique. To overcome this problem, we adapt the THz ASNOM setup to scattering-probe imaging technique, which has been proven to obtain deep subwavelength spatial resolution and great signal-noise ratio. Scattering-probe imaging setup measures the longitudinal component of the electric field of SPPs in the tapered slot waveguides. By slowly tapering the tip width and the slot gap, we squeeze a single-cycle THz pulse down to a size of 10 mum (lambda/260) by 18 mum (lambda/145), a mode area of only 2.6 x 10-5lambda2. We also observe a polarity reversal for the electric field between the guiding region near the upper and lower plates of the waveguide. This polarity flip is similar to that associated with the symmetric plasmon mode of slot waveguides.

Zhan, Hui

438

Pulsed Doppler tissue imaging in endurance athletes: relation between left ventricular preload and myocardial regional diastolic function  

Microsoft Academic Search

The aim of this study was to assess the effects of endurance training on myocardial regional systolic and diastolic function by pulsed Doppler tissue imaging (DTI). Twenty male water polo players and 20 male control subjects underwent standard Doppler echocardiography and pulsed DTI, performed in apical views by placing a sample volume on left ventricular (LV) basal septal and inferior

Pio Caso; Antonello D’Andrea; Maurizio Galderisi; Biagio Liccardo; Sergio Severino; Luigi De Simone; Annibale Izzo; Luigi D’Andrea; Nicola Mininni

2000-01-01

439

Ultrafast single-shot imaging of femtosecond pulse propagation in transparent liquids using a supercontinuum and optical polarigraphy  

NASA Astrophysics Data System (ADS)

We investigated the ultrafast time-resolved single-shot imaging of femtosecond pulse propagation using a supercontinuum and optical polarigraphy in transparent liquids. The probe supercontinuum senses the instantaneous birefringence induced by the laser pulse, and a polarigraphy image with different color distributions could be obtained. By comparing the wavelength distributions and the saturation variation of the images, the recorded polarigraphy images in two samples with different response time were analyzed. In the fast response sample, N-methyl-2-pyrrolidone (NMP), the spectral widths and the saturation values of the polarigraphy image at fixed positions were narrower and higher than those in CS2. Due to the slow response of CS2, the probe light sensed a long-lived birefringence and the polarigraphy image contained more wavelength components at every position along the pump pulse propagation direction.

Wang, Xiaofang; Si, Jinhai; Yan, Lihe; He, Pengchao; Chen, Feng; Hou, Xun

2014-01-01

440

Fabrication technologies for terahertz waveguide  

Microsoft Academic Search

Terahertz waveguide components can now be realised using a variety of methods. The size and geometry of waveguide at terahertz frequencies ideally lends itself to fabrication via a number of micromachining techniques. The use of micromachining allows the realisation of waveguide components that cannot be fabricated via conventional machining at these frequencies. Conventional machining should not, however, be overlooked. Corrugated

Chris M. Mann

1998-01-01