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1

Terahertz pulsed imaging of liver cirrhosis  

Microsoft Academic Search

Terahertz Pulsed Imaging (TPItrade) is a coherent imaging technique that can be used to reveal the dielectric properties of samples. Liver cirrhosis is a common disease that can lead to hepatocellular carcinoma. It has been previously studied in the microwave region and the dielectric parameters of human cirrhotic liver were quantified. In this study, we characterized the refractive index and

Shengyang Huang; Yi-xiang Wang; Jun Yu; A. T. Ahuja; V. P. Wallace; Yuan-ting Zhang; E. Pickwell-Macpherson

2009-01-01

2

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 5-120 cm-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

3

Terahertz pulsed imaging and spectroscopy of breast tumors  

Microsoft Academic Search

We have developed a portable terahertz pulsed imaging system (TPI Imaga1000) for use in a clinical environment. The system uses photoconduction to generate and detect terahertz radiation with frequency content from 0.1-4 THz. Here, we report on a study using TPI for imaging breast tumours ex vivo. Several breast samples were imaged and parameters from the time domain impulse functions

Vincent P. Wallace; Emma MacPherson; Anthony J. Fitzgerald; Thomas Lo; Elena Provenzano; Sarah Pinder; Anand Purushotham

2006-01-01

4

Terahertz pulsed spectroscopy and imaging for pharmaceutical applications: a review.  

PubMed

The terahertz region of the electromagnetic spectrum spans the frequency range between the infrared and the microwave. Traditionally the exploitation of this spectral region has been difficult owing to the lack of suitable source and detector. Over the last ten years or so, terahertz technology has advanced considerably with both terahertz pulsed spectroscopy (TPS) and terahertz pulsed imaging (TPI) instruments now commercially available. This review outlines some of the recent pharmaceutical applications of terahertz pulsed spectroscopy and imaging. The following application areas are highlighted: (1) discrimination and quantification of polymorphs/hydrates, (2) analysis of solid form transformation dynamics, (3) quantitative characterisation of tablet coatings: off-line and on-line, (4) tablet coating and dissolution, (5) spectroscopic imaging and chemical mapping. This review does not attempt to offer an exhaustive assessment of all anticipated pharmaceutical applications; rather it is an attempt to raise the awareness of the emerging opportunities and usefulness offered by this exciting technology. PMID:21237260

Shen, Yao-Chun

2011-01-13

5

Chemical sensing and imaging with pulsed terahertz radiation  

Microsoft Academic Search

Over the past decade, terahertz spectroscopy has evolved into a versatile tool for chemically selective sensing and imaging\\u000a applications. In particular, the potential to coherently generate and detect short, and hence, broadband terahertz pulses\\u000a led to the development of efficient and compact spectrometers for this interesting part of the electromagnetic spectrum, where\\u000a common packaging materials are transparent and many chemical

Markus Walther; Bernd M. Fischer; Alex Ortner; Andreas Bitzer; Andreas Thoman; Hanspeter Helm

2010-01-01

6

Optical properties of tissue measured using terahertz-pulsed imaging  

NASA Astrophysics Data System (ADS)

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

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

2003-06-01

7

WAVELET DENOISING OF OPTICAL TERAHERTZ PULSE IMAGING DATA  

Microsoft Academic Search

Terahertz pulse imaging (TPI) systems are used to obtain sub-millimeter spectroscopic measurements for a wide range of applications. This letter highlights the use of wavelet de-noising to markedly improve the SNR of the obtained data, increasing the SNR by up to 10 dB. A comparison of di erent wavelet families and properties is presented and the results demonstrated on THz

Bradley Ferguson; Derek Abbott

2001-01-01

8

A promising diagnostic method: Terahertz pulsed imaging and spectroscopy.  

PubMed

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

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

2011-03-28

9

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

10

Density mapping and chemical component calibration development of four-component compacts via terahertz pulsed imaging  

Microsoft Academic Search

The purpose of this research was to investigate suitable procedures for generating multivariate prediction vectors for quantitative composition and density analysis of intact solid oral dosage forms using terahertz pulsed imaging (TPI) spectroscopy. Both frequency- (absorbance and refractive index) and time-domain data are presented. A set of calibration and prediction samples were created according to a quaternary mixture design with

Ryanne Palermo; Robert P. Cogdill; Steven M. Short; James K. Drennen III; Philip F. Taday

2008-01-01

11

An efficient method-development strategy for quantitative chemical imaging using terahertz pulse spectroscopy  

Microsoft Academic Search

The purpose of our research was to investigate efficient procedures for generating multivariate prediction vectors for quantitative\\u000a chemical analysis of solid dosage forms using terahertz pulse imaging (TPI) reflection spectroscopy. A set of calibration\\u000a development and validation tablet samples was created following a ternary mixture of anhydrous theophylline, lactose monohydrate,\\u000a and microcrystalline cellulose (MCC). Spectral images of one side of

Robert P. Cogdill; Steven M. Short; Ryanne Forcht; Zhenqi Shi; Yaochun Shen; Philip F. Taday; Carl A. Anderson; James K. Drennen

2006-01-01

12

Terahertz pulsed imaging in vivo: measurements and processing methods  

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

13

Terahertz pulsed imaging, a novel process analytical tool to investigate the coating characteristics of push–pull osmotic systems  

Microsoft Academic Search

The aim of this study was to investigate coating characteristics of push–pull osmotic systems (PPOS) using three-dimensional terahertz pulsed imaging (3D-TPI) and to detect physical alterations potentially impacting the drug release. The terahertz time-domain reflection signal was used to obtain information on both the spatial distribution of the coating thickness and the coating internal physical mapping. The results showed that

Vincent Malaterre; Maireadh Pedersen; Joerg Ogorka; Robert Gurny; Nicoletta Loggia; Philip F. Taday

2010-01-01

14

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

2012-03-25

15

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

16

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(Ž) SR:Kollicoat(Ž) 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 0.13mm(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

2013-05-27

17

Delayed release tablet dissolution related to coating thickness by terahertz pulsed image mapping.  

PubMed

Delayed release dosage forms such as Asacol employ coatings that are engineered to breakdown and release the drug topically at the nominal pH of the lower intestinal tract. Asacol tablets were found to dissolve in an erratic fashion when they are dissolved in buffers below pH 7 which can occur naturally. In this study Terahertz pulsed imaging (TPI) was used to accurately map the coating thickness of a group of Asacol tablets that were subsequently dissolved using the USP method at pH 6.8. The mean dissolution times were found to correlate with the average coating thickness measured over all surfaces. Thickness values for a single randomly selected face did not correlate well with the dissolution results. The speed and ease of TPI mapping may make it an attractive replacement for wet dissolution testing both in product development and eventually for process analysis. PMID:17722005

Spencer, John A; Gao, Zongming; Moore, Terry; Buhse, Lucinda F; Taday, Philip F; Newnham, David A; Shen, Yaochun; Portieri, Alessia; Husain, Ajaz

2008-04-01

18

Terahertz pulsed imaging, a novel process analytical tool to investigate the coating characteristics of push-pull osmotic systems.  

PubMed

The aim of this study was to investigate coating characteristics of push-pull osmotic systems (PPOS) using three-dimensional terahertz pulsed imaging (3D-TPI) and to detect physical alterations potentially impacting the drug release. The terahertz time-domain reflection signal was used to obtain information on both the spatial distribution of the coating thickness and the coating internal physical mapping. The results showed that (i) the thickness distribution of PPOS coating can be non-destructively analysed using 3D-TPI and (ii) internal physical alterations impacting the drug release kinetics were detectable by using the terahertz time-domain signal. Based on the results, the potential benefits of implementing 3D-TPI as quality control analytical tool were discussed. PMID:19013522

Malaterre, Vincent; Pedersen, Maireadh; Ogorka, Joerg; Gurny, Robert; Loggia, Nicoletta; Taday, Philip F

2008-10-31

19

Pulsed and widely tunable terahertz sources for security: imaging and spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz imaging and spectroscopy are being studied for inspecting packages and personnel, but advanced THz sources with much greater power are needed to increase the signal-to-noise ratio, and much greater frequency bandwidth to obtain more information about the target. Photomixing in resonant laser-assisted field emission is a new method that shows potential for increasing both the output power and frequency bandwidth by more than an order of magnitude. Tunneling electrons have a resonance with a radiation field, so a highly focused laser diode (670 nm, 30 mW) increases the emitted current enough to be seen with an oscilloscope, in good agreement with simulations. The electron-emitting tip is much smaller than optical wavelengths, so the surface potential follows each cycle of the incident radiation. Electron emission responds to the electric field with a delay ?< 2 fs, and the current-voltage characteristics of field emission are highly nonlinear. Thus, photomixing in laser-assisted field emission can cause current oscillations that may be tuned from DC to 500 THz (1/delay). A field emission current density of 1012 A/m2 can be generated using a 20 pJ 70 fs pulse from a Ti:sapphire laser, to provide 200 W THz pulses. Microwave prototypes for 1-10 GHz are now being tested.

Hagmann, Mark J.; McBride, B. A.; Hagmann, Zulaima S.

2004-09-01

20

Imaging with terahertz radiation  

NASA Astrophysics Data System (ADS)

Within the last several years, the field of terahertz science and technology has changed dramatically. Many new advances in the technology for generation, manipulation, and detection of terahertz radiation have revolutionized the field. Much of this interest has been inspired by the promise of valuable new applications for terahertz imaging and sensing. Among a long list of proposed uses, one finds compelling needs such as security screening and quality control, as well as whimsical notions such as counting the almonds in a bar of chocolate. This list has grown in parallel with the development of new technologies and new paradigms for imaging and sensing. Many of these proposed applications exploit the unique capabilities of terahertz radiation to penetrate common packaging materials and provide spectroscopic information about the materials within. Several of the techniques used for terahertz imaging have been borrowed from other, more well established fields such as x-ray computed tomography and synthetic aperture radar. Others have been developed exclusively for the terahertz field, and have no analogies in other portions of the spectrum. This review provides a comprehensive description of the various techniques which have been employed for terahertz image formation, as well as discussing numerous examples which illustrate the many exciting potential uses for these emerging technologies.

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

2007-08-01

21

High speed terahertz reflection imaging  

NASA Astrophysics Data System (ADS)

Terahertz imaging has shown great potential in several biomedical areas such as burn imaging, detection of skin cancer, and pharmaceutical tablet imaging. The development of each of these application has been limited by slow imaging speed (tens of minutes to hours) and small scan areas (less than 10 square centimeters). Elsewhere to date, the sample itself must be mechanically raster scanned due to the free space optical coupling of femtosecond laser pulses driving the terahertz generating and detecting elements. This paper reports on the development of a freely positionable fiber optic coupled terahertz transceiver which may be raster scanned over a stationary object. Image acquisition times of less than 8 minutes for a 20x20 cm area (400 sq cm area) raster scanning a terahertz transceiver over a stationary object; and of less than 1 minute for image acquisition with a movable object raster scanning the object have been demonstrated. High speed stationary imaging will allow the practical investigation on human and animal subjects.

Zimdars, David

2005-04-01

22

Reflection-type pulsed terahertz imaging with a phase-retrieval algorithm  

SciTech Connect

We propose and demonstrate a scheme for two-dimensional terahertz reflection imaging using a time-domain phase-retrieval algorithm based on the dispersion relations of complex reflection coefficients. With this scheme, topographic images--as well as the dielectric functions of a structured sample--can be obtained. A composite sample made of a semiconductor and metals is characterized within depth and lateral errors of 50 {mu}m and 100 {mu}m.

Ino, Y.; Heroux, J.B.; Mukaiyama, T.; Kuwata-Gonokami, M. [Department of Applied Physics, University of Tokyo (Japan) and Solution Oriented Research for Science and Technology (JST), 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

2006-01-23

23

Terahertz phonon polariton imaging  

NASA Astrophysics Data System (ADS)

In this article, we primarily review the time-resolved imaging of THz phonon polariton, which is generated by femtosecond laser in ferroelectric crystal. We pay more attention to the imaging in thin crystal, which can be used as an integration platform for terahertz-optics or terahertz-electrics. The imaging techniques, which can get quantitatively in-focus time-resolved images, are introduced in more detail. They have made enormous progress in recent years, and are powerful tools for the research of phonon polariton, optics, and THz wave. We also briefly introduce the generation principle and general propagation properties of THz phonon polariton.

Wu, Qiang; Chen, Qing-Quan; Zhang, Bin; Xu, Jing-Jun

2013-04-01

24

Intense ultrashort terahertz pulses: generation and applications  

NASA Astrophysics Data System (ADS)

Ultrashort terahertz pulses derived from femtosecond table-top sources have become a valuable tool for time-resolved spectroscopy during the last two decades. Until recently, the pulse energies and field strengths of these pulses have been generally too low to allow for the use as pump pulses or the study of nonlinear effects in the terahertz range. In this review article we will describe methods of generation of intense single cycle terahertz pulses with emphasis on optical rectification using the tilted-pulse-front pumping technique. We will also discuss some applications of these intense pulses in the emerging field of nonlinear terahertz spectroscopy.

Hoffmann, Matthias C.; András Fülöp, József

2011-03-01

25

Fast three-dimensional terahertz computed tomography using real-time line projection of intense terahertz pulse.  

PubMed

We demonstrated fast three-dimensional transmission terahertz computed tomography by using real-time line projection of intense terahertz beam generated by optical rectification in lithium niobate crystal. After emphasizing the advantage of intense terahertz pulse generation for two-dimensional spatio-temporal terahertz imaging, peak-to-peak amplitudes of pulsed terahertz electric field have been used to obtain a series of projection images at different rotation angles. Then a standard reconstruction algorithm has been employed to perform final three-dimensional reconstruction. Test samples including a medicine capsule have been investigated with a total acquisition time to only 6 minutes. PMID:23389223

Jewariya, Mukesh; Abraham, Emmanuel; Kitaguchi, Takayuki; Ohgi, Yoshiyuki; Minami, Masa-Aki; Araki, Tsutomu; Yasui, Takeshi

2013-01-28

26

Intense ultrashort terahertz pulses: generation and applications  

Microsoft Academic Search

Ultrashort terahertz pulses derived from femtosecond table-top sources have become a valuable tool for time-resolved spectroscopy during the last two decades. Until recently, the pulse energies and field strengths of these pulses have been generally too low to allow for the use as pump pulses or the study of nonlinear effects in the terahertz range. In this review article we

Matthias C. Hoffmann; József András Fülöp

2011-01-01

27

Terahertz imaging of burned tissue  

NASA Astrophysics Data System (ADS)

There are over 2 million reported burn injuries each year in the United States with 75,000 of these incidents resulting in hospitalization. Current medical imaging modalities have limited capabilities to assess initial burn damage and monitor healing progress. Some of these limitations can be attributed to modality occlusion from bandages, dried tissue and/or blood and inflammation. Since terahertz radiation can see through textiles and bandages1, previous studies2,3 suggested that terahertz radiation, in a reflectance configuration, could be used for non-invasive analysis of tissue thermal damage and healing status. In this study, we perform an analysis of the terahertz absorption and reflection properties of the tissue constituents comprising a wound area, and provide a feasibility assessment of the capabilities of terahertz imaging to provide a clinical tool for initial burn analysis and healing progress.

Dougherty, Joseph P.; Jubic, Gregory D.; Kiser, William L., Jr.

2007-02-01

28

Terahertz movie of internal transmission imaging.  

PubMed

Recently terahertz imaging using two-dimensional E-O sampling has attracted much interest because it can acquire real-time terahertz images unlike a conventional raster scan method. We are applying this technique to the non-destructive measurement of opaque materials in a visible range. We acquired 10-fps consecutive terahertz transmission images: dripping water in a plastic pipe and metal included in a piece of gum. Since the obtained images were confirmed to be proportional to the electric field of the terahertz waves, the images in the present paper are useful for quantitative analysis. We also showed the signal-to-noise ratio of the terahertz images. PMID:19550845

Yasuda, Takashi; Kawada, Yoichi; Toyoda, Haruyoshi; Takahashi, Hironori

2007-11-12

29

Control of terahertz pulse generation by optical pulse shaping  

Microsoft Academic Search

We present the use of a programmable optical pulse-shaper based on a liquid crystal amplitude and phase modulator to control the production of terahertz pulses in a ZnTe crystal. A genetic algorithm is used to optimize the pump pulse shape for a desired outcome, avoiding the need for prior knowledge of the required optical pulse shape. As an example we

Matthew R. Harper; Richard A. Dudley; Stephen N. Lea; Helen S. Margolis

2007-01-01

30

Principle and applications of terahertz molecular imaging.  

PubMed

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. PMID:23618745

Son, Joo-Hiuk

2013-04-25

31

Terahertz Imaging of Subjects With Concealed Weapons.  

National Technical Information Service (NTIS)

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 coher...

A. J. Gatesman C. S. Joseph J. C. Dickinson T. M. Goyette Z. G. Root

2006-01-01

32

Terahertz interferometric imaging of RDX  

NASA Astrophysics Data System (ADS)

Experimental results of homodyne terahertz interferometric 2-D imaging of RDX are presented. Continuous waves at 0.25-0.6 THz are used to obtain images of a C-4 sample at several THz frequencies. The performance of an N element detector array is imitated by only one detector placed at N positions. The distance between the C-4 sample and the detector array is ~30 cm. By taking interferometric images at several THz frequencies RDX can be recognized by the spectral peak at 0.82 THz. Simulations of interferometric images of two point sources of spherical waves are presented. The terahertz interferometric imaging method can be used in defense and security applications to detect concealed weapons, explosives as well as chemical and biological agents.

Sinyukov, Alexander M.; Barat, Robert B.; Gary, Dale E.; Michalopoulou, Zoi-Heleni; Zorych, Ivan; Zimdars, David; Federici, John F.

2007-05-01

33

Terahertz imaging with compressed sensing and phase retrieval  

Microsoft Academic Search

We describe a novel, high-speed pulsed terahertz (THz) Fourier imaging system based on compressed sens- ing (CS), a new signal processing theory, which allows image reconstruction with fewer samples than tra- ditionally required. Using CS, we successfully reconstruct a 6464 image of an object with pixel size 1.4 mm using a randomly chosen subset of the 4096 pixels, which defines

Wai Lam Chan; Matthew L. Moravec; Richard G. Baraniuk; Daniel M. Mittleman

2008-01-01

34

Ultrafast pulse shaping: A new twist on terahertz pulses  

NASA Astrophysics Data System (ADS)

The generation of light pulses with programmable waveforms opens up exciting new avenues for coherent control. Researchers in Japan have now introduced a way to tailor the polarization state of custom-shaped terahertz pulses at the push of a button.

Cocker, Tyler L.; Huber, Rupert

2013-09-01

35

Attenuated internal reflection terahertz imaging.  

PubMed

We present a terahertz (THz) imaging technique based on attenuated internal reflection, which is ideally suited for the analysis of liquid and biological samples. Inserted in a THz time-domain system, and using a high-resistivity low loss silicon prism to couple the THz wave into the sample, the detection scheme is based on the relative differential spectral phase of two orthogonal polarizations. Biological sample imaging as well as subwavelength (?/16) longitudinal resolution are demonstrated. PMID:23454932

Wojdyla, Antoine; Gallot, Guilhem

2013-01-15

36

Novel setups for extremely high power single-cycle terahertz pulse generation by optical rectification  

NASA Astrophysics Data System (ADS)

Recently, the generation of near-single-cycle terahertz pulses with 10 ?J energy was demonstrated by optical rectification of ultrashort laser pulses with tilted pulse front in LiNbO3. Here, an optimized imaging setup is proposed for the creation of the tilted pulse front inside the LiNbO3 crystal. Furthermore, a compact setup is proposed which creates the tilted pulse front without imaging, where there is no principal limitation on the pump spot size and, hence, on the terahertz energy. According to model calculations, application of these setups can increase the efficiency by one order of magnitude for 5 mm spot size.

Pálfalvi, L.; Fülöp, J. A.; Almási, G.; Hebling, J.

2008-04-01

37

Fast frequency-resolved terahertz imaging  

NASA Astrophysics Data System (ADS)

We propose a fast, frequency-resolved, real-time, terahertz imaging method. With our method, images at two specific terahertz frequencies can be acquired in 1 min. Three kinds of drugs (L-histidine, maltose, and CBZ3), which have absorption peaks in the terahertz region, were distinguished in 3 min by using our method. This technique can be used in industrial applications, such as nondestructive testing.

Yasuda, Takashi; Kawada, Yoichi; Toyoda, Haruyoshi; Nakanishi, Atsushi; Akiyama, Koichiro; Takahashi, Hironori

2011-03-01

38

Fast frequency-resolved terahertz imaging.  

PubMed

We propose a fast, frequency-resolved, real-time, terahertz imaging method. With our method, images at two specific terahertz frequencies can be acquired in 1 min. Three kinds of drugs (L-histidine, maltose, and CBZ3), which have absorption peaks in the terahertz region, were distinguished in 3 min by using our method. This technique can be used in industrial applications, such as nondestructive testing. PMID:21456777

Yasuda, Takashi; Kawada, Yoichi; Toyoda, Haruyoshi; Nakanishi, Atsushi; Akiyama, Koichiro; Takahashi, Hironori

2011-03-01

39

Static terahertz imaging at a distance for concealed weapon detection  

Microsoft Academic Search

Using a high-powered pulsed terahertz source and electro-optic detection, a method for and examples of static THz imaging of targets at a distance of greater than 3 meters (no THz component is closer than 3 m from the target) are presented. The THz signal in all 200 times 200 pixels of an image are collected simultaneously to generate THz imagery

Matthew B. Campbell; Merrick J. DeWitt; Edwin J. Heilweil

2007-01-01

40

Novel setups for extremely high power single-cycle terahertz pulse generation by optical rectification  

Microsoft Academic Search

Recently, the generation of near-single-cycle terahertz pulses with 10 muJ energy was demonstrated by optical rectification of ultrashort laser pulses with tilted pulse front in LiNbO3. Here, an optimized imaging setup is proposed for the creation of the tilted pulse front inside the LiNbO3 crystal. Furthermore, a compact setup is proposed which creates the tilted pulse front without imaging, where

L. Pálfalvi; J. A. Fülöp; G. Almási; J. Hebling

2008-01-01

41

Novel setups for extremely high power single-cycle terahertz pulse generation by optical rectification  

Microsoft Academic Search

Recently, the generation of near-single-cycle terahertz pulses with 10 ?J energy was demonstrated by optical rectification of ultrashort laser pulses with tilted pulse front in LiNbO3. Here, an optimized imaging setup is proposed for the creation of the tilted pulse front inside the LiNbO3 crystal. Furthermore, a compact setup is proposed which creates the tilted pulse front without imaging, where

L. Pa´lfalvi; G. Alma´si; J. Hebling

2008-01-01

42

Imaging of osteoarthritis using a hand-held terahertz probe  

Microsoft Academic Search

A hand-held terahertz (THz) probe system is being developed for medical use by Teraview Ltd. We use this prototype system to investigate the terahertz characteristics of osteoarthritis (OA). Excised femoral knee joints with symptoms of osteoarthritis were measured. In this paper we analyze the typical terahertz response of the diseased samples and explain how the reflected terahertz pulse could be

K. W. C. Kan; Wing-Sze Lee; W. H. Cheung; E. Pickwell-MacPherson

2009-01-01

43

Reshaping of freely propagating terahertz pulses by diffraction  

Microsoft Academic Search

We discuss the application of diffraction theory to the reshaping of freely propagating terahertz pulses by narrow apertures. This is accomplished by using two separate electrooptic sampling detectors. The first contains a narrow electrode geometry that does not modify the frequency content of the incident terahertz field, while the second contains a narrow gap between two large electrodes. The latter

Ajay Nahata; Tony F. Heinz

1996-01-01

44

Terahertz interferometric imaging of a concealed object  

NASA Astrophysics Data System (ADS)

Experimental results of two-dimensional homodyne terahertz interferometric imaging are presented. The performance of an N element detector array is imitated by only one detector placed at N positions. Continuous waves at 0.25-0.3 THz are used to detect concealed objects: a metal object and an RDX sample. The terahertz interferometric imaging method can be used in defense and security applications to detect concealed weapons, explosives as well as chemical and biological agents.

Sinyukov, Alexander M.; Bandyopadhyay, Aparajita; Sengupta, Amartya; Barat, Robert B.; Gary, Dale E.; Michalopoulou, Zoi-Heleni; Zimdars, David; Federici, John F.

2006-10-01

45

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

46

Tailored Terahertz Pulses from a Laser-Modulated Electron Beam  

NASA Astrophysics Data System (ADS)

We present a new method to generate steady and tunable, coherent, broadband terahertz radiation from a relativistic electron beam modulated by a femtosecond laser. We have demonstrated this in the electron storage ring at the Advanced Light Source. Interaction of an electron beam with a femtosecond laser pulse copropagating through a wiggler modulates the electron energies within a short slice of the electron bunch with about the same duration of the laser pulse. The bunch develops a longitudinal density perturbation due to the dispersion of electron trajectories, and the resulting hole emits short pulses of temporally and spatially coherent terahertz pulses synchronized to the laser. We present measurements of the intensity and spectra of these pulses. This technique allows tremendous flexibility in shaping the terahertz pulse by appropriate modulation of the laser pulse.

Byrd, J. M.; Hao, Z.; Martin, M. C.; Robin, D. S.; Sannibale, F.; Schoenlein, R. W.; Zholents, A. A.; Zolotorev, M. S.

2006-04-01

47

Terahertz imaging of subjects with concealed weapons  

Microsoft Academic Search

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.

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

2006-01-01

48

Terahertz polarization pulse shaping with arbitrary field control  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

49

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

50

Terahertz interferometric and synthetic aperture imaging  

NASA Astrophysics Data System (ADS)

Experimental results of homodyne terahertz interferometric 1-D and 2-D imaging are presented. Continuous waves at 0.25-0.3 THz are used to detect a metal object behind a barrier. The performance of an N element detector array is imitated by only one detector placed at N positions. The reconstructed images are in a good agreement with theoretical predictions. The terahertz interferometric imaging method can be used in defense and security applications to detect concealed weapons, explosives as well as chemical and biological agents.

Sinyukov, Alexander M.; Bandyopadhyay, Aparajita; Sengupta, Amartya; Barat, Robert B.; Gary, Dale E.; Michalopoulou, Zoi-Heleni; Zimdars, David; Federici, John F.

2006-06-01

51

Terahertz Near-Field Imaging  

NASA Astrophysics Data System (ADS)

The terahertz (THz) frequency range has proven to be a very interesting frequency range for imaging applications. The smallest spatial features that can theoretically be resolved is limited by diffraction to values of about half of a wavelength, which corresponds to 150 ?m for a frequency of 1 THz. To overcome this diffraction limit, THz near-field techniques have been developed. Some of these techniques are unique for the THz frequency range and others are derived from similar techniques used in, for example, the visible region of the electromagnetic spectrum. An interesting feature of many of these near-field techniques is that they measure the electric field rather than the intensity. This makes it also possible to study the near-electromagnetic field itself with a resolving power, as defined as the ratio of the spatial resolution to the wavelength, and bandwidth which are practically unobtainable in the visible region of the electromagnetic spectrum. This chapter describes a number of different techniques to overcome the diffraction limit in the THz frequency range and also the results that have been obtained with them.

Planken, Paul C. M.; Adam, Aurčle J. L.; Kim, DaiSik

52

Terahertz wave imaging: horizons and hurdles  

NASA Astrophysics Data System (ADS)

Terahertz (THz) science will profoundly impact biotechnology. It has tremendous potential for applications in imaging, medical diagnosis, health monitoring, environmental control and chemical and biological identification. THz research will become one of the most promising research areas in the 21st century for transformational advances in imaging, as well as in other interdisciplinary fields. However, terahertz wave (T-ray) imaging is still in its infancy. This paper discusses the uniqueness and limitations of T-ray imaging, identifies the major challenges impeding T-ray imaging and proposes solutions and opportunities in this field. It also concentrates on the generation, propagation and detection of T-rays by the use of femtosecond optics.

Zhang, X.-C.

2002-11-01

53

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.

2006-06-01

54

Concealed weapon identification using terahertz imaging sensors  

NASA Astrophysics Data System (ADS)

Terahertz imaging sensors are being considered for providing a concealed weapon identification capability for military and security applications. In this paper the difficulty of this task is assessed in a systematic way. Using imaging systems operating at 640 GHz, high resolution imagery of possible concealed weapons has been collected. Information in this imagery is removed in a controlled and systematic way and then used in a human observer perception experiment. From the perception data, a calibration factor describing the overall difficulty of this task was derived. This calibration factor is used with a general model of human observer performance developed at the US Army Night Vision and Electronic Sensors Directorate to predict the task performance of observers using terahertz imaging sensors. Example performance calculations for a representative imaging sensor are shown.

Jacobs, Eddie L.; Moyer, Steve; Franck, Charmaine C.; DeLucia, Frank C.; Casto, Corey; Petkie, Douglas T.; Murrill, Steven R.; Halford, Carl E.

2006-06-01

55

New Analytical Method for Cellulose Acetate Electrophoresis Using Terahertz Imaging  

NASA Astrophysics Data System (ADS)

We propose a new method of analyzing the results of cellulose acetate electrophoresis by terahertz imaging. To verify accuracy of terahertz imaging of cellulose acetate electrophoresis, we compared the images obtained by terahertz imaging with those obtained by the one-side staining method. To obtain accurate information about the distribution of medical molecules in cellulose acetate by terahertz imaging, owing to the low concentration, a suitable imaging spatial resolution is required to estimate the distribution accurately in the cellulose acetate membrane. Here, we have improved the spatial resolution by reducing the absorption of the diffusion of the terahertz signal from the sample surface. Using the terahertz imaging system, we obtained terahertz images of the cellulose acetate with a glycine sensitivity of 3.71 ?g/mm2 and an l-methionine sensitivity of 6.22 ?g/mm2. Comparison of the terahertz and staining images showed that the new imaging method using the terahertz imaging system has a good possibility for cellulose acetate membrane electrophoresis analysis even for relatively low-concentration electrophoresis.

Zhang, Hong Bing; Mitobe, Kazutaka; Suzuki, Masafumi; Yoshimura, Noboru

2009-06-01

56

Enhanced terahertz pulses emission from inas surface by femtosecond laser pulses with tilted intensity front  

Microsoft Academic Search

It is shown that using femtosecond laser pulses with tilted intensity front allows controlling the direction of terahertz emission from InAs surface and by that way achieving significant increase in the generated power.

Yu. Avetisyan; K. Khachatryan; R. Beigang

2008-01-01

57

Intense terahertz sources based on tilted pulse-front excitation and their potential applications in imaging, nonlinear THz spectroscopy and attosecond pulse generation  

Microsoft Academic Search

The generation of THz pulses having tens of microjoules energy by tilted pulse-front excitation is reviewed. Possibilities of further up-scaling the THz energy as well as existing and future applications of these pulses are analyzed.

János Hebling; József A. Fülöp; László Pálfalvi; Gábor Almási

2010-01-01

58

High-resolution terahertz tomography using 17-fs ultrashort-pulse fiber laser  

Microsoft Academic Search

We describe the generation and detection of coherent broadband terahertz waves using ultrashort-pulse fiber laser, and its application to terahertz tomography. A pulse compression technique using nonlinear and dispersion effects of optical fibers leads to the development of high-peak-power 17- fs ultrashort- pulse fiber laser. With the optical rectification in an organic crystal, 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST), ultra-broad terahertz pulses are

J. Takayanagi; S. Kanamori; K. Suizu; M. Yamashita; T. Ouchi; S. Kasai; H. Ohtake; H. Uchida; N. Nishizawa; K. Kawase

2008-01-01

59

Terahertz generation with tilted-front laser pulses: Dynamical theory predicts the ways to higher terahertz yield  

Microsoft Academic Search

A dynamical theory of terahertz emission from a femtosecond laser pulse with tilted intensity front in an electro-optic crystal is developed. Applying the theory to GaAs pumped by a fiber laser and cryogenically cooled LiNbO3 pumped by a Ti:sapphire laser predicts the ways to higher terahertz yield.

Michael I. Bakunov; Sergey B. Bodrov; Maxim V. Tsarev; Evgeniy Mashkovich

2010-01-01

60

Enhancement of Laser-Induced Fluorescence by Intense Terahertz Pulses in Gases  

Microsoft Academic Search

The enhancement of laser-induced fluorescence by in- tense terahertz pulses was studied both theoretically and experi- mentally using selected gases. Semiclassical physical picture incor- porating photoionization, electron heating, impact excitation, and dissociative recombination was used to explain the plasma dynam- ics under terahertz radiation in picosecond scale. The dependences of enhanced fluorescence on the terahertz field, laser intensity, and atomic

Jingle Liu; Xi-Cheng Zhang

2011-01-01

61

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

62

Nonlinear Terahertz Spectroscopy in Solids with Single-Cycle Terahertz Pulses  

NASA Astrophysics Data System (ADS)

We present novel generation methods of intense terahertz single cycle pulses. The Cherenkov scheme with tilted wave-front technique in the LiNbO3 crystal gives us the maximum electric field larger than 1 MV/cm, which ponderomotive energy is as large as 10 eV. The ponderomotive energy is strong enough to ionize bound electronic states in solids such as donors and accepters and easy to induce nonlinear optical effects in solids.

Tanaka, K.

2013-03-01

63

Theoretical model of terahertz radiation generation by laser pulses with tilted wave fronts  

Microsoft Academic Search

A theoretical model is proposed for terahertz radiation generation by femtosecond laser pulses with tilted wave fronts. Self-consistent\\u000a evolution of the optical and terahertz pulses is investigated. The red shift of the pumping pulse spectrum and the formation\\u000a of short-long-wave quasi-solitons are examined.

A. N. Bugai; S. V. Sazonov

2009-01-01

64

Terahertz reflection imaging for package and personnel inspection  

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. Time domain terahertz imaging can be employed in reflection mode to image beneath clothing with sub millimeter resolution. Fiber optic coupled terahertz transmitter and generator arrays can be constructed to more quickly objects such as shoes, or larger portions of the body. The application of commercially available time domain terahertz spectroscopy equipment to imaging through clothing on simulant personnel is shown to distinguish harmful from innocuous objects.

Zimdars, David; White, Jeffrey S.

2004-09-01

65

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

66

Terahertz continuous-wave transmission imaging system and its application in security inspections  

NASA Astrophysics Data System (ADS)

A terahertz continuous-wave transmission imaging system and its applications in security inspections are reported. A Gunn oscillator is utilized as emitter and an unbiased Schottky diode is employed as detector in this system. The sample is placed on an X-Y two-dimensional stage which is controlled by a computer. The intensity information of the terahertz wave after passing though the sample is collected by the Schottky diode and fed into the computer. Two-dimensional image is obtained by scanning the sample point by point. Compared with the terahertz pulse imaging system, this system is compact, simple, and portable. Tennis bat with sheath and knife in the box are imaged by using this system. The results obtained here show that this new technology can be widely used in security inspections.

Zhang, Yandong; Deng, Chao; Sun, Wenfeng; Zhang, Yan; Zhang, Cunlin

2008-03-01

67

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

68

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

69

Molecular imaging with terahertz waves.  

PubMed

We demonstrate a highly sensitive THz molecular imaging (TMI) technique involving differential modulation of surface plasmons induced on nanoparticles and obtain target specific in vivo images of cancers. This technique can detect quantities of gold nanoparticles as small as 15 ľM in vivo. A comparison of TMI images with near infrared absorption images shows the superior sensitivity of TMI. Furthermore, the quantification property of TMI is excellent, being linearly proportional to the concentration of nanoparticles. The target specificity issue is also addressed at the ex vivo and cell levels. The high thermal sensitivity of TMI can help extend photonic-based photothermal molecular imaging researches from the in vitro level to the in vivo level. The TMI technique can be used for monitoring drug delivery processes and for early cancer diagnosis. PMID:21369228

Oh, Seung Jae; Choi, Jihye; Maeng, Inhee; Park, Jae Yeon; Lee, Kwangyeol; Huh, Yong-Min; Suh, Jin-Suck; Haam, Seungjoo; Son, Joo-Hiuk

2011-02-28

70

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

71

Theory of terahertz pulse generation through optical rectification in a nonlinear optical material with a finite size  

SciTech Connect

The full analytical solutions for plane terahertz waves generated through optical rectification in a slab of a nonlinear optical material are calculated. Terahertz dispersion, absorption of both optical and terahertz waves, and multiple reflections are considered. The results are valid for an arbitrary difference between the optical group index and the terahertz refractive index, including equal indices. It is demonstrated that the full terahertz wave is freely propagating and has no contribution of a 'forced' pulse.

Schneider, Arno [Institute of Quantum Electronics, ETH Zurich, Zurich (Switzerland)

2010-09-15

72

Single-cycle strong terahertz pulse generation from a vacuum-plasma interface driven by intense laser pulses  

NASA Astrophysics Data System (ADS)

Single-cycle strong terahertz pulses can be generated by irradiating ultrashort intense laser pulses onto a tenuous plasma slab. At the plasma surface, laser ponderomotive force accelerates electrons and induces net currents, which radiate terahertz pulses. Our theoretical model suggests that if ?L>2?/?p , with ?L as the laser-pulse duration and ?p as the plasma frequency, the emission frequency is around ?L-1 . On the other hand, the emission frequency is around ?p/2? if ?L<2?/?p . Our numerical simulations support the theoretical model, showing that such a terahertz source is capable of providing megawatt power, field strengths of MV/cm, and broad frequency tunability.

Dong, X. G.; Sheng, Z. M.; Wu, H. C.; Wang, W. M.; Zhang, J.

2009-04-01

73

Metamaterial based devices for terahertz imaging  

NASA Astrophysics Data System (ADS)

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

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

2010-02-01

74

Super-resolution reconstruction of terahertz images  

NASA Astrophysics Data System (ADS)

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

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

2008-05-01

75

Resolution capability comparison of infrared and terahertz imagers  

NASA Astrophysics Data System (ADS)

Infrared and terahertz are two imaging technologies that differ fundamentally in numerous aspects. Infrared imaging is an efficient passive technology whereas terahertz technology is an active technology requiring some kind of illumination to be efficient. What's more, the detectors are also different and yield differences in the fundamental physics when integrated in a complete system. One of these differences lies in the size of the detectors. Infrared detectors are typically larger than the infrared wavelengths whereas terahertz detectors are typically smaller than the wavelength of illumination. This results in different constraints when designing these systems, constraints that are imposed by the resolution capabilities of the system. In the past INO has developed an infrared imaging camera core of 1024×768 pixels and tested some microscanning devices to improve its sampling frequency and ultimately its resolution. INO has also engineered detectors and camera cores specifically designed for active terahertz imaging with smaller dimensions (160×120 pixels). In this paper the evaluation of the resolution capabilities of a terahertz imager at the pixel level is performed. The resolution capabilities for the THz are evaluated in the sub-wavelength range, which is not actually possible in the infrared wavebands. Based on this evaluation, the comparison between the resolution limits of infrared detectors and the terahertz detectors at the pixel level is performed highlighting the differences between the wavebands and their impact on system design.

Bergeron, Alain; Marchese, Linda; Savard, Éric; Lenoc, Loďc; Bolduc, Martin; Terroux, Marc; Dufour, Denis; Tang, Denis; Châteauneuf, François; Jerominek, Hubert

2011-10-01

76

Optimizing two-dimensional tilted-front laser pulses for efficient terahertz generation  

Microsoft Academic Search

We developed a theory that describes terahertz generation with tilted-front femtosecond laser pulses in electro-optic crystals, a technique providing record experimental efficiencies nowadays. The theory accounts for the transverse size of the laser beam and allows us to explore the dependence of the conversion efficiency on laser focusing. We calculated the radiation patterns inside the crystal and studied the terahertz

Michael I. Bakunov; Sergey B. Bodrov; Maxim V. Tsarev

2008-01-01

77

High speed scanning of terahertz pulse by a rotary optical delay line  

Microsoft Academic Search

We demonstrate high speed scanning of a time-domain terahertz pulse by a rotary optical delay line (RODL) incorporated into a photoconductive antenna based terahertz system. The delay line of RODL consists of six rotating convex reflective blades with a rotating speed controlled for a wide range of scan repetition rates. It can perform path length scans of 2.1 cm at

Geun-Ju Kim; Seok-Gy Jeon; Jung-Il Kim; Yun-Sik Jin

2008-01-01

78

Single-cycle terahertz pulses with amplitudes exceeding 1 MV\\/cm generated by optical rectification in LiNbO3  

Microsoft Academic Search

Using the tilted-pump-pulse-front scheme, we generate single-cycle terahertz (THz) pulses by optical rectification of femtosecond laser pulses in LiNbO3. In our THz generation setup, the condition that the image of the grating coincides with the tilted-optical-pulse front is fulfilled to obtain optimal THz beam characteristics and pump-to-THz conversion efficiency. By using an uncooled microbolometer-array THz camera, it is found that

H. Hirori; A. Doi; F. Blanchard; K. Tanaka

2011-01-01

79

Terahertz single pixel imaging based on a Nipkow disk.  

PubMed

We describe a terahertz single pixel imaging system based on a Nipkow disk. Nipkow disks have been used for fast scanning imaging systems since the first experimental television was invented in 1926. In our work, a Nipkow disk with 24 scanning lines was used to provide an axial resolution of 2 mm/pixel. We also show that by implementing a microscanning technique the axial resolution can be further improved to 0.5 mm/pixel. Imaging of several objects was demonstrated to show that this simple scanning system is promising for fast or real time terahertz imaging applications. PMID:22555712

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

2012-05-01

80

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

81

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

82

Terahertz emission from a laser pulse with tilted front: Phase-matching versus Cherenkov effect  

Microsoft Academic Search

A theory that describes the terahertz generation via optical rectification of a femtosecond laser pulse with tilted front in an electro-optic crystal is developed. The theory accounts for the transverse size of the laser pulse and allows us to explore the dependence of the terahertz yield on laser focusing. Two typical experimental situations-LiNbO3 excited with Ti:sapphire laser at room and

M. I. Bakunov; S. B. Bodrov; M. V. Tsarev

2008-01-01

83

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

84

Fiber-based pulse stretcher for narrowband terahertz pulse generation with a chirped-pulse beating method  

NASA Astrophysics Data System (ADS)

We theoretically show that it is possible to generate chirp-free terahertz (THz) pulses with a chirped-pulse beating method by using an optical fiber as a pulse stretcher. Proper choices of the core radius and the dopant fraction of the core material of a step-index single-mode optical fiber eliminate the third-order spectral phase of the fiber, thus giving the pump laser pulse a purely linear chirp. We also show that even a standard commercial single-mode optical fiber can give THz pulses of lower chirp than the lower limit for a grating pair. We perform experiments to verify our theory.

Yoshida, Tetsuya; Kamada, Shohei; Murata, Shuhei; Aoki, Takao

2013-10-01

85

Enhancement of terahertz pulse emission by optical nanoantenna.  

PubMed

Bridging the gap between ultrashort pulsed optical waves and terahertz (THz) waves, the THz photoconductive antenna (PCA) is a major constituent for the emission or detection of THz waves by diverse optical and electrical methods. However, THz PCA still lacks employment of advanced breakthrough technologies for high-power THz emission. Here, we report the enhancement of THz emission power by incorporating optical nanoantennas with a THz photoconductive antenna. The confinement and concentration of an optical pump beam on a photoconductive substrate can be efficiently achieved with optical nanoantennas over a high-index photoconductive substrate. Both numerical and experimental results clearly demonstrate the enhancement of THz wave emission due to high photocarrier generation at the plasmon resonance of nanoantennas. This work opens up many opportunities for diverse integrated photonic elements on a single PCA at THz and optical frequencies. PMID:22339093

Park, Sang-Gil; Jin, Kyong Hwan; Yi, Minwoo; Ye, Jong Chul; Ahn, Jaewook; Jeong, Ki-Hun

2012-02-24

86

Towards gigawatt terahertz emission by few-cycle laser pulses  

NASA Astrophysics Data System (ADS)

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 10-4.

Wang, Wei-Min; Kawata, Shigeo; Sheng, Zheng-Ming; Li, Yu-Tong; Zhang, Jie

2011-07-01

87

Terahertz imaging and holography with a high-power free electron laser  

Microsoft Academic Search

In this paper we describe the terahertz imagers which characteristics are adequate for measurement of high power terahertz radiation. Three imaging techniques were employed on the Novosibirsk terahertz free electron laser (NFEL): near-infrared thermograph, thermosensitive visible light interferometer, and \\

V. S. Cherkasskyl; B. A. Knyazev; S. V. Kozlov; V. V. Kubarev; G. N. Kulipanov; A. N. Matveenko; V. M. Popik; D. N. Root; P. D. Rudych; O. A. Shevchenko; A. V. Trifutina; N. A. Vinokurov

2005-01-01

88

Terahertz Imaging and Spectroscopy Based on Hot Electron Bolometer (HEB) Heterodyne Detection.  

National Technical Information Service (NTIS)

Imaging and spectroscopy at terahertz frequencies have great potential for healthcare, plasma diagnostics, and homeland security applications. Terahertz frequencies correspond to energy level transitions of important molecules in biology and astrophysics....

E. Gerecht L. You

2008-01-01

89

Terahertz Spectroscopy and Imaging for Defense and Security Applications  

Microsoft Academic Search

Terahertz (THz) radiation, which occupies a relatively unexplored portion of the electromagnetic spectrum between the mid-infrared and microwave bands, offers innovative sensing and imaging technologies that can provide information unavailable through conventional methods such as microwave and X-ray techniques. With the advancement of THz technologies, THz sensing and imaging will impact a broad range of interdisciplinary fields, including chemical and

Hai-Bo Liu; Hua Zhong; Nicholas Karpowicz; Yunqing Chen; Xi-Cheng Zhang

2007-01-01

90

Terahertz imaging and spectroscopy for landmine detection  

NASA Astrophysics Data System (ADS)

Pulsed THz (100 GHz - 30 THz) Imaging Spectroscopy combines three ways of mine detection in one system, high resolution radar, depth ranging, and infrared spectroscopy. It allows minefield detection, single mine imaging, and near-zero false alarm due to the capabilities of explosives / plastic identification using spectroscopy with working distances to 1000 feet. We have previously demonstrated imaging capabilities with 1 mm spatial resolution on a rubber O-ring embedded in sand. The estimated transmission depth in moist sand is 1 to 3 cm, which should be sufficient for imaging anti-personnel mines. In this work, we present initial results investigating the feasibility of THz spectroscopy in the frequency range from 1 to 10 THz to detect and identify explosives and related compounds (ERCs). A major component of this effort is chemical modeling to obtain spectroscopic information on ERCs and environmental background. A time-domain THz system using femtosecond laser pulses is also being developed.

Fitch, Michael J.; Schauki, Dunja; Kelly, Craig A.; Osiander, Robert

2004-04-01

91

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 0.2 to 2.6 THz 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

92

Continuous-wave terahertz scanning image resolution analysis and restoration  

NASA Astrophysics Data System (ADS)

Resolution of continuous-wave (CW) terahertz scanning image is limited by many factors among which the aperture effect of finite focus diameter is very important. We have investigated the factors that affect terahertz (THz) image resolution in details through theory analysis and simulation. On the other hand, in order to enhance THz image resolution, Richardson-Lucy algorithm has been introduced as a promising approach to improve image details. By analyzing the imaging theory, it is proposed that intensity distribution function of actual THz laser focal spot can be approximatively used as point spread function (PSF) in the restoration algorithm. The focal spot image could be obtained by applying the pyroelectric camera, and mean filtering result of the focal spot image is used as the PSF. Simulation and experiment show that the algorithm implemented is comparatively effective.

Li, Qi; Yin, Qiguo; Yao, Rui; Ding, Shenghui; Wang, Qi

2010-03-01

93

Electric field ionization of gallium acceptors in germanium induced by single-cycle terahertz pulses  

NASA Astrophysics Data System (ADS)

The electric field ionization of gallium acceptors in germanium was studied by using terahertz-pump-terahertz-probe spectroscopy. As the pump electric field increases, the distinct absorptions due to acceptor transitions centered at 2.0 and 2.2 THz decrease, and simultaneously, a free carrier response emerges in the lower frequency region. These behaviors clearly show that the terahertz-pump pulse ionizes neutral acceptors. The pump electric field dependence of the released hole density is reproduced by a model assuming direct field-assisted tunneling of acceptors.

Mukai, Y.; Hirori, H.; Tanaka, K.

2013-05-01

94

Three-dimensional imaging of optically opaque materials using nonionizing terahertz radiation  

Microsoft Academic Search

Terahertz electromagnetic radiation has already been shown to have a wide number of uses. We consider spe- cific applications of terahertz time-domain imaging that are inherently three-dimensional. This paper high- lights the ability of terahertz radiation to reveal subsurface information as we exploit the fact that the radia- tion can penetrate optically opaque materials such as clothing, cardboard, plastics, and

Vincent P. Wallace; Emma MacPherson; J. Axel Zeitler; Caroline Reid

2008-01-01

95

Terahertz imaging performance model for concealed weapon identification  

NASA Astrophysics Data System (ADS)

Terahertz imaging is becoming more viable for many applications due to advances in detector and emitter technologies. One of the applications for THz imaging is the detection and identification of concealed weapons (e.g., in airport security screening lines). The path described here provides an imaging performance model for the application of concealed weapon identification. The approach is the typical U.S. Army target acquisition model for sensor performance prediction coupled to the acquire methodology for weapon identification performance prediction.

Jacobs, Eddie; Driggers, Ronald G.; Krapels, Keith A.; De Lucia, Frank C.; Petkie, Douglas T.

2004-12-01

96

REVIEW ARTICLE: Terahertz-wave sources and imaging applications  

NASA Astrophysics Data System (ADS)

An overview is given on the field of the terahertz-frequency electromagnetic waves, their properties and emerging applications. Some widespread sources with their advantages and drawbacks are presented; an emphasis is placed on the parametric generation sources that we build and use in our research. Several applications are then described: imaging techniques based on transmission, reflection and scattering, results in chemical imaging and electric field imaging, as well as linear scanning and the measurement of optical properties of highly-absorbing liquids.

Dobroiu, Adrian; Otani, Chiko; Kawase, Kodo

2006-11-01

97

Terahertz emission from a laser pulse with tilted front: Phase-matching versus Cherenkov effect  

NASA Astrophysics Data System (ADS)

A theory that describes the terahertz generation via optical rectification of a femtosecond laser pulse with tilted front in an electro-optic crystal is developed. The theory accounts for the transverse size of the laser pulse and allows us to explore the dependence of the terahertz yield on laser focusing. Two typical experimental situations-LiNbO3 excited with Ti:sapphire laser at room and cryogenic temperatures-are considered. It is shown that depending on temperature the dominant generation mechanism can be either phase-matching or Cherenkov effect. The parameters of the laser pulse (transverse size, tilt angle, and pulse duration) and crystal size maximizing the terahertz yield for LiNbO3 are calculated.

Bakunov, M. I.; Bodrov, S. B.; Tsarev, M. V.

2008-10-01

98

Efficient generation of subpicosecond terahertz radiation by phase-matched optical rectification using ultrashort laser pulses with tilted pulse fronts  

Microsoft Academic Search

We report on the generation of subpicosecond terahertz (THz) electromagnetic radiation in a nonlinear crystal by ultrashort laser pulses with a tilted pulse front. Free-space THz pulses with an energy of 98 pJ and a repetition rate of 200 kHz have been obtained by optical rectification using 2.3 muJ near-infrared laser pulses in a LiNbO3 crystal cooled down to 77

Andrei G. Stepanov; János Hebling; Jürgen Kuhl

2003-01-01

99

TERAHERTZ IMAGING, MILLIMETER-WAVE RADAR  

Microsoft Academic Search

The millimeter wave (MMW) band of frequencies extends from 30 GHz to 300 GHz, with some fuzziness on both ends of this spectrum.\\u000a The terahertz (THz) band extends from about 200 GHz to about 30 THz, despite the fact that the lower frequencies in this range\\u000a are not strictly 1012 Hz or higher. These bands are also variously called submillimeter,

R. W. McMillan

100

Propagation of terahertz pulses in photoexcited media: analytical theory for layered systems.  

PubMed

Optical pump-terahertz probe spectroscopy has become a widely used experimental tool for the investigation of the ultrafast far-infrared response of polar systems. In this paper the authors present an analytical method of calculating the propagation of ultrashort terahertz pulses in photoexcited media. The transient terahertz wave form transmitted through the sample is equal to a product of the incident terahertz field (at a mixed frequency), transient susceptibility, and a so called transfer function which depends on the properties of the sample in equilibrium. The form of the transfer function is derived for general layered systems and for specific cases including one-dimensional photonic crystals, thin films, and bulk samples. Simplified expressions directly applicable to the analysis of the experimental results related to the most common sample geometries are shown and discussed. PMID:17640136

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

2007-07-14

101

Near-field terahertz imaging with a dynamic aperture  

SciTech Connect

By introduction of an optical gating beam on a semiconductor wafer, near-field terahertz (THz) imaging with a dynamic aperture has been realized. The spatial resolution is determined by the focus size of the optical gating bean and the near-field diffraction effect. THz imaging with subwavelength spatial resolution (better than 50 {mu}m ) is demonstrated. (c) 2000 Optical Society of America.

Chen, Q.; Jiang, Zhiping; Xu, G. X.; Zhang, X.-C.

2000-08-01

102

Picosecond transient photoconductivity in functionalized pentacene molecular crystals probed by terahertz pulse spectroscopy.  

PubMed

We have measured transient photoconductivity in functionalized pentacene molecular crystals using ultrafast optical pump-terahertz probe techniques. The single crystal samples were excited using 800 nm, 100 fs pulses, and the change in transmission of time-delayed, subpicosecond terahertz pulses was used to probe the photoconducting state over a temperature range from 10 to 300 K. A subpicosecond rise in photoconductivity is observed, suggesting that mobile carriers are a primary photoexcitation. At times longer than 4 ps, a power-law decay is observed consistent with dispersive transport. PMID:12485104

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

2002-11-11

103

Picosecond Transient Photoconductivity in Functionalized Pentacene Molecular Crystals Probed by Terahertz Pulse Spectroscopy  

NASA Astrophysics Data System (ADS)

We have measured transient photoconductivity in functionalized pentacene molecular crystals using ultrafast optical pump-terahertz probe techniques. The single crystal samples were excited using 800nm, 100fs pulses, and the change in transmission of time-delayed, subpicosecond terahertz pulses was used to probe the photoconducting state over a temperature range from 10 to 300K. A subpicosecond rise in photoconductivity is observed, suggesting that mobile carriers are a primary photoexcitation. At times longer than 4ps, a power-law decay is observed consistent with dispersive transport.

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

2002-11-01

104

Coherent Control of Molecular Orientation by a Terahertz Few-Cycle Laser Pulse  

NASA Astrophysics Data System (ADS)

The coherent control of molecular orientation by a terahertz few-cycle laser pulse is theoretically studied. It is demonstrated that the field-free molecular orientation results from the interference contributions between the odd and even rotational wave packet, and therefore the constructive and destructive interferences lead to the observation of the positive and negative orientations, corresponding to the positive and negative degrees. Furthermore, the enhancement or suppression of the molecular orientation can be coherently manipulated by precisely controlling the carrier-envelope phase of the terahertz few-cycle pulse.

Qin, Chao-Chao; Liu, Yu-Zhu; Zhang, Xian-Zhou; Liu, Yu-Fang

2013-02-01

105

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

106

Simultaneous determination of thickness and refractive index based on time-of-flight measurements of terahertz pulse.  

PubMed

We present a simple technique for simultaneous determination of thickness and refractive index of plane-parallel samples in the terahertz radiation domain. The technique uses time-of-flight measurements of the terahertz pulse. It has been employed on nine different polymers and semiconductor materials, which are transparent for terahertz frequencies. Our results of thickness measurement are in good agreement with micrometer reading. The accuracy in the determination of refractive index is on the order of two decimal points. PMID:22858978

Hussain, Babar; Ahmed, Mushtaq; Nawaz, M; Saleem, M; Razzaq, M; Aslam Zia, M; Iqbal, M

2012-07-20

107

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

108

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

109

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

110

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

111

Terahertz interferometric synthetic aperture tomography for confocal imaging systems.  

PubMed

Terahertz (THz) interferometric synthetic aperture tomography (TISAT) for confocal imaging within extended objects is demonstrated by combining attributes of synthetic aperture radar and optical coherence tomography. Algorithms recently devised for interferometric synthetic aperture microscopy are adapted to account for the diffraction-and defocusing-induced spatially varying THz beam width characteristic of narrow depth of focus, high-resolution confocal imaging. A frequency-swept two-dimensional TISAT confocal imaging instrument rapidly achieves in-focus, diffraction-limited resolution over a depth 12 times larger than the instrument's depth of focus in a manner that may be easily extended to three dimensions and greater depths. PMID:22513671

Heimbeck, M S; Marks, D L; Brady, D; Everitt, H O

2012-04-15

112

Generation of multicycle terahertz phonon-polariton waves in a planar waveguide by tilted optical pulse fronts  

NASA Astrophysics Data System (ADS)

We demonstrate generation of frequency-tunable, multicycle terahertz phonon-polariton waves in a LiNbO3 slab waveguide. Because the waveguide modes show considerable phase-velocity dispersion, we are able to enhance frequency-selected narrowband terahertz waves by using femtosecond optical pulses whose intensity fronts are tilted at angles that meet the appropriate noncollinear phase-matching conditions. The pump light is spread across a large area of the crystalline waveguide within which coherent terahertz wave generation occurs, averting material damage, while yielding peak-to-peak terahertz field amplitudes in the waveguide of 50 kV/cm.

Lin, Kung-Hsuan; Werley, Christopher A.; Nelson, Keith A.

2009-09-01

113

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

Microsoft Academic Search

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

Y. Liu; A. Houard; B. Prade; S. Akturk; A. Mysyrowicz; V. T. Tikhonchuk

2007-01-01

114

Efficient generation of terahertz radiation by the method of optical rectification of terawatt laser pulses  

Microsoft Academic Search

Factors that lead to a decrease in the width and the mean frequency of the spectrum of terahertz (THz) radiation that were observed in recent experiments on optical rectification of powerful (˜0.5 TW) femtosecond laser pulses with a tilted amplitude front in a lithium niobate crystal are considered. A simple method is proposed that allows one to avoid the above

A. G. Stepanov

2009-01-01

115

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

116

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

PubMed

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

2012-03-01

117

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

118

An algorithm for the detection of handguns in terahertz images  

NASA Astrophysics Data System (ADS)

This paper presents an algorithm for detecting handguns in terahertz images. Terahertz radiation is capable of penetrating certain materials which are opaque at optical wavelengths, such as clothing, without the harmful effects of ionizing radiation. The approach taken is to segment objects of interest and classify them based on shape. We use a modified version of an active contour algorithm found in the open literature. Modifications include: a pre-processing step that includes clutter filtering and seeding of an initial contour; and a post-processing step that removes clutter pixels from the segmentation. The features used for classification are moment-based and Fourier shape descriptors. Classification as handgun or non-handgun from these features is done via Fisher's linear discriminant.

Lingg, Andrew J.; Rigling, Brian D.

2009-05-01

119

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

120

Damping modulated terahertz emission of ferromagnetic films excited by ultrafast laser pulses  

NASA Astrophysics Data System (ADS)

Ultrafast demagnetization processes in ferromagnetic films have been shown to produce terahertz (THz) emission. We present an experimental demonstration that, following ultrafast optical excitation, the magnitude of terahertz electromagnetic pulses emitted from a ferromagnetic film is proportional to the Gilbert damping constant, which is conventionally used to describe the damping of magnetization precession. The damping of a ferromagnetic thin film is tuned by using an adjacent nonmagnetic layer, which does not change the magnetization and anisotropy of the ferromagnetic film, allowing an unambiguous determination of the relationship between the THz emission and the damping constant.

Shen, Jian; Fan, Xin; Chen, Zhiyuan; DeCamp, Matthew F.; Zhang, Huaiwu; Xiao, John Q.

2012-08-01

121

LIGHT SOURCE: Terahertz emission in tenuous gases irradiated by ultrashort laser pulses  

NASA Astrophysics Data System (ADS)

Mechanism of terahertz (THz) pulse generation in gases irradiated by ultrashort laser pulses is investigated theoretically. Quasi-static transverse currents produced by laser field ionization of gases and the longitudinal modulation in formed plasmas are responsible for the THz emission at the electron plasma frequency, as demonstrated by particle-in-cell simulations including field ionization. The THz field amplitude scaling with the laser amplitude within a large range is also discussed.

Wang, Wei-Min; Sheng, Zheng-Ming; Wit, Hui-Chun; Chen, Min; Li, Chun; Zhang, Jie; Mima, K.

2009-06-01

122

Single-Shot Measurement of the Full Spatiotemporal Field of a Terahertz Pulse  

Microsoft Academic Search

In this paper, we describe a method for single-shot measurement of the full spatiotemporal electric field of a freely propagating terahertz pulse based on electro-optic (E-O) sampling technique and pulsed digital holography. From a captured digital hologram, we could numerically recover the complete THz electric field E(x, y, t) by a reconstruction algorithm. The spatial and temporal resolutions are limited

Lujie Li; Xiaolei Wang; Hongchen Zhai

2010-01-01

123

Ultrafast Spatiotemporal Dynamics of Terahertz Generation by Ionizing Two-Color Femtosecond Pulses in Gases  

SciTech Connect

We present a combined theoretical and experimental study of spatiotemporal propagation effects in terahertz (THz) generation in gases using two-color ionizing laser pulses. The observed strong broadening of the THz spectra with increasing gas pressure reveals the prominent role of spatiotemporal reshaping and of a plasma-induced blueshift of the pump pulses in the generation process. Results obtained from (3+1)-dimensional simulations are in good agreement with experimental findings and clarify the mechanisms responsible for THz emission.

Babushkin, I. [Weierstrass-Institut fuer Angewandte Analysis und Stochastik, 10117 Berlin (Germany); Kuehn, W.; Reimann, K.; Woerner, M.; Herrmann, J.; Elsaesser, T. [Max-Born-Institut fuer Nichtlineare Optik und Kurzzeitspektroskopie, 12489 Berlin (Germany); Koehler, C. [Max Planck Institute for the Physics of Complex Systems, 01187 Dresden (Germany); Skupin, S. [Max Planck Institute for the Physics of Complex Systems, 01187 Dresden (Germany); Friedrich Schiller University, Institute of Condensed Matter Theory and Optics, 07743 Jena (Germany); Berge, L. [CEA-DAM, DIF, 91297 Arpajon (France)

2010-07-30

124

Fast continuous terahertz wave imaging system for security  

NASA Astrophysics Data System (ADS)

Continuous terahertz wave (CW THz) has been widely used in imaging field. However, the speed of imaging calls for an improvement for security screening since the speed of previous CW imaging systems which scan point to point is too slow to be applied in security field. To increase the imaging speed, we proposed a fast CW-THz imaging system in which a galvanometer is introduced. The galvanometer makes the beams reflected in different angles by vibrating at a certain frequency which can significantly decrease the image acquisition time compared to traditional CW-THz imaging system. Furthermore, the system is compact due to source and detector of small size. Examples of measurements of concealed weapons are presented and discussed. Ideal results of better resolution are obtained.

Song, Qian; Zhao, Yuejin; Redo-Sanchez, Albert; Zhang, Cunlin; Liu, Xiaohua

2009-05-01

125

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

126

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

127

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

128

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

129

Terahertz imaging and spectroscopy based on hot electron bolometer (HEB) heterodyne detection  

NASA Astrophysics Data System (ADS)

Imaging and spectroscopy at terahertz frequencies have great potential for healthcare, plasma diagnostics, and homeland security applications. Terahertz frequencies correspond to energy level transitions of important molecules in biology and astrophysics. Terahertz radiation (T-rays) can penetrate clothing and, to some extent, can also penetrate biological materials. Because of their shorter wavelengths, they offer higher spatial resolution than do microwaves or millimeter waves. We are developing hot electron bolometer (HEB) mixer receivers for heterodyne detection at terahertz frequencies. HEB detectors provide unprecedented sensitivity and spectral resolution at terahertz frequencies. We describe the development of a two-pixel focal plane array (FPA) based on HEB technology. Furthermore, we have demonstrated a fully automated, two-dimensional scanning, passive imaging system based on our HEB technology operating at 0.85 THz. Our high spectral resolution terahertz imager has a total system noise equivalent temperature difference (NE?T) value of better than 0.5 K and a spatial resolution of a few millimeters. HEB technology is becoming the basis for advanced terahertz imaging and spectroscopic technologies for the study of biological and chemical agents over the entire terahertz spectrum.

Gerecht, Eyal; You, Lixing

2008-02-01

130

Terahertz imaging using an interferometric array  

NASA Astrophysics Data System (ADS)

It has been suggested that interferometric/ synthetic aperture imaging techniques, when applied to the THz regime, can provide sufficient imaging resolution and spectral content to detect concealed explosives and other weapons from a standoff distance. The interferometric imaging method is demonstrated using CW THz generation and detection. Using this hardware, the reconstruction of THz images from a point source is emphasized and compared to theoretical predictions.

Federici, John F.; Gary, Dale; Barat, Robert; Zimdars, David

2005-05-01

131

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

132

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

133

High conversion efficiency, high energy terahertz pulses by optical rectification in cryogenically cooled lithium niobate.  

PubMed

We demonstrate highly efficient terahertz (THz) generation by optical rectification (OR) of near-optimum pump pulses centered at 1.03 ?m in cryogenically cooled lithium niobate. Using a close to optimal pulse duration of 680 fs and a pump energy of 1.2 mJ, we report conversion efficiencies above 3.8ą0.4%, which is more than an order of magnitude higher than previously reported. The results confirm the advantage of using cryogenic cooling of the lithium niobate crystal that significantly reduces the THz absorption, enabling the scaling of THz pulse energies to the millijoule level via OR. PMID:23455302

Huang, Shu-Wei; Granados, Eduardo; Huang, Wenqian Ronny; Hong, Kyung-Han; Zapata, Luis E; Kärtner, Franz X

2013-03-01

134

Cancer Diagnosis by Terahertz Molecular Imaging Technique  

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

135

Measurement depth enhancement in terahertz imaging of biological tissues.  

PubMed

We demonstrate the use of a THz penetration-enhancing agent (THz-PEA) to enhance the terahertz (THz) wave penetration depth in tissues. The THz-PEA is a biocompatible material having absorption lower than that of water, and it is easily absorbed into tissues. When using glycerol as a THz-PEA, the peak value of the THz signal which was transmitted through the fresh tissue and reflected by a metal target, was almost doubled compared to that of tissue without glycerol. THz time-of-flight imaging (B-scan) was used to display the sequential glycerol delivery images. Enhancement of the penetration depth was confirmed after an artificial tumor was located below fresh skin. We thus concluded that the THz-PEA technique can potentially be employed to enhance the image contrast of the abnormal lesions below the skin. PMID:24104004

Oh, Seung Jae; Kim, Sang-Hoon; Jeong, Kiyoung; Park, Yeonji; Huh, Yong-Min; Son, Joo-Hiuk; Suh, Jin-Suck

2013-09-01

136

Efficient generation of terahertz radiation by the method of optical rectification of terawatt laser pulses  

Microsoft Academic Search

Factors that lead to a decrease in the width and the mean frequency of the spectrum of terahertz (THz) radiation that were\\u000a observed in recent experiments on optical rectification of powerful (?0.5 TW) femtosecond laser pulses with a tilted amplitude\\u000a front in a lithium niobate crystal are considered. A simple method is proposed that allows one to avoid the above

A. G. Stepanov

2009-01-01

137

Zitterbewegung in thin-film topological insulators in the presence of a terahertz pulse  

NASA Astrophysics Data System (ADS)

Zitterbewegung (trembling motion) in thin-film topological insulators in the presence of a terahertz pump pulse has been considered. An analytical expression for the electric current density has been derived, which describes the electric current induced by the motion of an electron wave packet. The electron subsystem has been considered in the long-wavelength approximation, and the electromagnetic field has been described classically in the constant-pump approximation. The numerical analysis of the results has been carried out.

Belonenko, M. B.; Yanyushkina, N. N.

2012-12-01

138

An Approach for Sub-Second Imaging of Concealed Objects Using Terahertz (THz) Radar  

NASA Astrophysics Data System (ADS)

High-resolution, long-range detection of person-borne concealed weapons has recently been demonstrated using a terahertz imaging radar. However, the radar’s image acquisition time must be greatly shortened, from minutes to less than one second, before the system can be effectively deployed in a real-life threat environment. Here we analyze the major system modifications necessary for increasing the speed of a terahertz imaging radar by up to two orders of magnitude.

Cooper, K. B.; Dengler, R. J.; Llombart, N.; Bryllert, T.; Chattopadhyay, G.; Mehdi, I.; Siegel, P. H.

2009-12-01

139

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

Microsoft Academic Search

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

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

2007-01-01

140

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

NASA Astrophysics Data System (ADS)

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

Zabolotskii, A. A.

2013-07-01

141

Single attosecond pulse from terahertz-assisted high-order harmonic generation  

SciTech Connect

High-order harmonic generation by few-cycle 800 nm laser pulses in neon gas in the presence of a strong terahertz (THz) field is investigated numerically with propagation effects taken into account. Our calculations show that the combination of THz fields with up to 12 fs laser pulses can be an effective gating technique to generate single attosecond pulses. We show that in the presence of the strong THz field only a single attosecond burst can be phase matched, whereas radiation emitted during other half cycles disappears during propagation. The cutoff is extended and a wide supercontinuum appears in the near-field spectra, extending the available spectral width for isolated attosecond pulse generation from 23 to 93 eV. We demonstrate that phase-matching effects are responsible for the generation of isolated attosecond pulses, even in conditions when single-atom response yields an attosecond pulse train.

Balogh, Emeric [Department of Optics and Quantum Electronics, University of Szeged, H-6701 Szeged (Hungary); Kovacs, Katalin [Department of Optics and Quantum Electronics, University of Szeged, H-6701 Szeged (Hungary); National Institute for R and D of Isotopic and Molecular Technologies, RO-400293 Cluj-Napoca (Romania); Dombi, Peter; Farkas, Gyozo [Research Institute for Solid State Physics and Optics, H-1525 Budapest (Hungary); Fulop, Jozsef A.; Hebling, Janos [Department of Experimental Physics, University of Pecs, H-7624 Pecs (Hungary); Tosa, Valer [National Institute for R and D of Isotopic and Molecular Technologies, RO-400293 Cluj-Napoca (Romania); Varju, Katalin [HAS Research Group on Laser Physics, University of Szeged, H-6701 Szeged (Hungary)

2011-08-15

142

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

143

A compact real time passive terahertz imager  

Microsoft Academic Search

Passive millimetre wave imaging is now an established and accepted technology that is finding viable commercial applications in many areas, particularly security and border control. The upper frequency of operation has largely been governed by the availability of solid state uncooled detectors to around 100GHz. Passive operation at higher frequencies potentially offers some unique features such as higher optical resolution

Chris Mann

2006-01-01

144

Generation of multicycle terahertz phonon-polariton waves in a planar waveguide by tilted optical pulse fronts  

Microsoft Academic Search

We demonstrate generation of frequency-tunable, multicycle terahertz phonon-polariton waves in a LiNbO3 slab waveguide. Because the waveguide modes show considerable phase-velocity dispersion, we are able to enhance frequency-selected narrowband terahertz waves by using femtosecond optical pulses whose intensity fronts are tilted at angles that meet the appropriate noncollinear phase-matching conditions. The pump light is spread across a large area of

Kung-Hsuan Lin; Christopher A. Werley; Keith A. Nelson

2009-01-01

145

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

146

High efficiency, modular, optical pulse shaping technique for tunable terahertz generation from InAs  

NASA Astrophysics Data System (ADS)

We demonstrate a high energy throughput, modular optical laser pulse shaping technique for generating tunable, narrowband, terahertz radiation from the surface of InAs. We achieve a frequency selectivity (?f/f) of 0.10 at 1.18 THz and demonstrate an energy throughput of up to 98% using two etalons to create a sequence of optical pulses. In contrast with previously reported schemes, our technique does not rely on interferometry or involve diffractive optical elements, making it robust and relatively inexpensive to implement. This technique can be expanded with additional etalons in order to achieve greater frequency selectivity without sacrificing efficiency.

Adipa, Samuel; Lytle, Amy L.; Gagnon, Etienne

2013-02-01

147

Efficient generation of terahertz radiation by the method of optical rectification of terawatt laser pulses  

NASA Astrophysics Data System (ADS)

Factors that lead to a decrease in the width and the mean frequency of the spectrum of terahertz (THz) radiation that were observed in recent experiments on optical rectification of powerful (˜0.5 TW) femtosecond laser pulses with a tilted amplitude front in a lithium niobate crystal are considered. A simple method is proposed that allows one to avoid the above transformation of the spectrum and to ensure a high efficiency of generation of THz radiation when laser pulses with a power of several TW are used.

Stepanov, A. G.

2009-10-01

148

Upconversion of a relativistic Coulomb field terahertz pulse to the near infrared  

NASA Astrophysics Data System (ADS)

We demonstrate the spectral upconversion of a unipolar subpicosecond terahertz (THz) pulse, where the THz pulse is the Coulomb field of a single relativistic electron bunch. The upconversion to the optical allows remotely located detection of long wavelength and nonpropagating components of the THz spectrum, as required for ultrafast electron bunch diagnostics. The upconversion of quasimonochromatic THz radiation has also been demonstrated, allowing the observation of distinct sum- and difference-frequency mixing components in the spectrum. Polarization dependence of first and second order sidebands at ?opt+/-?THz, and ?opt+/-2?THz, respectively, confirms the ?(2) frequency mixing mechanism.

Jamison, S. P.; Berden, G.; Phillips, P. J.; Gillespie, W. A.; MacLeod, A. M.

2010-06-01

149

Zitterbewegung in Thin Films of Topological Insulators with Hexagonal Lattice Irradiated by Terahertz Pulses  

NASA Astrophysics Data System (ADS)

We study the Zitterbewegung effect (trembling motion) in thin films of topological insulators with a hexagonal lattice in the presence of terahertz pulse pumping. We derive the analytical expression for the current density, which describes the current induced by the motion of a wave packet of electrons. The electronic subsystem is considered in the long-wavelength approximation, and the electromagnetic field is treated classically in the approximation of a constant pumping. We reveal the possibility to control individual electron wave packets by manipulating with optical pulses.

Yanyushkina, Natalia N.; Zhukov, Alexander V.; Belonenko, Mikhail B.; George, Thomas F.

150

Efficient generation of subpicosecond terahertz radiation by phase-matched optical rectification using ultrashort laser pulses with tilted pulse fronts  

NASA Astrophysics Data System (ADS)

We report on the generation of subpicosecond terahertz (THz) electromagnetic radiation in a nonlinear crystal by ultrashort laser pulses with a tilted pulse front. Free-space THz pulses with an energy of 98 pJ and a repetition rate of 200 kHz have been obtained by optical rectification using 2.3 ?J near-infrared laser pulses in a LiNbO3 crystal cooled down to 77 K. The emitted THz beam has a divergence smaller than 40 mrad, which is close to the diffraction limit. Spectral analysis of the generated THz beam with a Michelson interferometer reveals an approximately 1.5 THz broad asymmetric peak centered at 2 THz and a pulse duration of less than 500 fs.

Stepanov, Andrei G.; Hebling, János; Kuhl, Jürgen

2003-10-01

151

An Approach for Sub-Second Imaging of Concealed Objects Using Terahertz (THz) Radar  

Microsoft Academic Search

High-resolution, long-range detection of person-borne concealed weapons has recently been demonstrated using a terahertz imaging\\u000a radar. However, the radar’s image acquisition time must be greatly shortened, from minutes to less than one second, before\\u000a the system can be effectively deployed in a real-life threat environment. Here we analyze the major system modifications necessary\\u000a for increasing the speed of a terahertz

K. B. Cooper; R. J. Dengler; N. Llombart; T. Bryllert; G. Chattopadhyay; I. Mehdi; P. H. Siegel

2009-01-01

152

A self-consistent regime of generation of terahertz radiation by an optical pulse with a tilted intensity front  

NASA Astrophysics Data System (ADS)

We derived a self-consistent system of nonlinear wave equations describing the terahertz generation in dielectric uniaxial crystals by optical pulsed radiation with a tilted wavefront. The numerical analysis of the system of equations showed that the generation of a broadband one-period terahertz signal is accompanied by a red shift of the carrier frequency of the optical pulse, the magnitude of the shift being proportional to the pulse intensity. The generation efficiency with respect to energy reached a maximum at a certain distance of propagation in the crystal, after which the efficiency decreased. A satisfactory agreement was obtained between theoretical calculations and experimental data of other investigations.

Bugai, A. N.; Sazonov, S. V.; Shashkov, Andrei Yu

2012-11-01

153

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

154

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/A 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 [Department of Chemistry, Stanford University, Stanford, California 94305 (United States); PULSE Institute for Ultrafast Energy Science, SLAC National Accelerator Laboratory, 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; Ghimire, Shambhu [PULSE Institute for Ultrafast Energy Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Wen, Haidan [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Reis, David A. [PULSE Institute for Ultrafast Energy Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Stanford Institute for Materials and Energy Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Department of Applied Physics, Stanford University, Stanford, California 94305 (United States); Loos, Henrik; Fisher, Alan S. [Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Lindenberg, Aaron M. [PULSE Institute for Ultrafast Energy Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); 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)

2011-10-03

155

Pulsed terahertz bi-directional reflection distribution function (BRDF) measurements of materials and obscurants  

NASA Astrophysics Data System (ADS)

We report a pulsed method to measure reflection and scattering from several samples with different degrees of surface roughness and material properties at terahertz frequencies. Reflection from a flat gold mirror shows that the full width half maximum (FWHM) of the terahertz beam angular spread is <4° for frequency range 0.2 THz to 3 THz with signal-to-noise of 65 dB. Measurement of a paper index card, used as a low scattering sample, shows that the reflection/scattering properties are essentially similar to the system signature response except for multiple reflections between the front and back surfaces of the sample. Sixty-grit sandpaper shows multiple scattering events with almost no signal reflected from the flat backing paper surface. Corduroy cloth shows periodic reflections in the time domain, which correspond to diffraction lobes in the spectral domain.

Lo, Shu-Zee A.; Heilweil, Edwin J.

2011-09-01

156

Catadioptric optics for high-resolution terahertz imager  

NASA Astrophysics Data System (ADS)

INO has developed infrared camera systems with microscanning capabilities in order to increase image resolution. It has been shown in previous works that the image quality may be improved even if the pixel pitch is smaller than the point spread function. This paper introduces a catadioptric optics system with fully integrated microscan for improved resolution in the THz band. The design, inspired by the INO's HRXCAM infrared camera core and adapted for terahertz wavelengths, includes two mirrors and one refractive element. It has a 11.9 degree full field of view and an effective F-number of 1.07 over a wide spectral range, from 100 ?m to 1.5 mm wavelength. This diffraction limited optics is used to provide video rate high quality THz images. A THz camera, with 160 x 120 pixel and 52 ?m pitch detector, is combined with the microscan objective to provide a 320 x 240 pixel image with a 26 ?m sampling step. Preliminary imaging results using a THz illumination source at 118 ?m wavelength are presented. A comparison between standard and microscanned images is also presented.

Blanchard, Nathalie; Marchese, Linda; Martel, Anne; Terroux, Marc; Savard, Éric; Chevalier, Claude; Mercier, Luc; Gagnon, Lucie; Lambert, Julie; Bolduc, Martin; Bergeron, Alain

2012-05-01

157

Generation of 10 ?J ultrashort terahertz pulses by optical rectification  

Microsoft Academic Search

Generation of near single-cycle pulses centered at 0.5 THz frequency with up to 10 ?J energy, 100 ?W average power, and 5.0 MW peak power was demonstrated by tilting the intensity front of a femtosecond optical pump pulse from a 10 Hz Ti:sapphire laser to match the phonon-polariton phase velocity to the group velocity of the pump pulses in a

K.-L. Yeh; M. C. Hoffmann; J. Hebling; Keith A. Nelson

2007-01-01

158

Terahertz imaging - new steps toward real-life applications  

Microsoft Academic Search

We are studying several novel steps toward real-life applications of terahertz and millimeter waves, such as, i) Non-destructive detection of illicit drugs using spectral fingerprints, ii) Laser-terahertz emission microscope for semiconductor device under test, iii) Real-time inspection system to detect micro-leak defects in the seal of flexible plastic packages, iv) Prism-shaped Fabry-Perot etalon for absorption measurement, v) Development of terahertz

Kodo Kawase

2004-01-01

159

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

160

Accelerator- and laser-based sources of high-field terahertz pulses  

NASA Astrophysics Data System (ADS)

At present we are witnessing a rapid development of sources for terahertz (THz) pulses with very strong electromagnetic fields. These pulses are reaching a stage where they can be used to not only probe, but also uniquely control a variety of processes that range from fundamental dynamics in individual atoms and molecules, through phase transitions in solids to a wealth of interactions in biological materials. In this review, we are presenting an overview of two major directions in the generation of such radiation. Large-scale accelerator-based sources offer unprecedented pulse energies coupled with a wide tuning range and extreme repetition rates. Laser-based sources, on the other hand, are laboratory-scale instruments and thus are very attractive in their availability to the wide scientific community. The capabilities of different variants of these THz sources are evaluated and compared with each other. In addition, powerful techniques for the temporal characterization of THz pulses are discussed.

Stojanovic, Nikola; Drescher, Markus

2013-10-01

161

Terahertz pulse detection by the GaAs Schottky diodes  

NASA Astrophysics Data System (ADS)

We present the results of experimental studies of physical properties of the detection process of GaAs Schottky diodes for terahertz frequency radiation. The development of technology in the THz frequency band has a rapid progress recently. Considered as an extension of the microwave and millimeter wave bands, the THz frequency offers greater communication bandwidth than is available at microwave frequencies. The Schottky barrier contact has an important role in the operation of many GaAs devices. GaAs Schottky diodes have been the primary nonlinear device used in millimeter and sub millimeter wave detectors and receivers. GaAs Schottky diodes are especially interesting due to their high mobility transport characteristics, which allows for a large reduction of the resistance-capacitance (RC) time constant and thermal noise. In This work are investigated the electrical and photoelectric properties of GaAs Schottky diodes. Samples were obtained by deposition of different metals (Au, Ni, Pt, Pd, Fe, In, Ga, Al) on semiconductor. For fabrication metal-semiconductor (MS) structures is used original method of metal electrodepositing. In this method electrochemical etching of semiconductor surface occurs just before deposition of metal from the solution, which contains etching material and metal ions together. For that, semiconductor surface cleaning processes and metal deposition carries out in the same technological process. In the experiments as the electrolyte was used aqueous solution of chlorides. Metal deposition was carried out at room temperature.

Laperashvili, Tina; Kvitsiani, Orest; Imerlishvili, Ilia; Laperashvili, David

2010-04-01

162

A self-consistent regime of generation of terahertz radiation by an optical pulse with a tilted intensity front  

SciTech Connect

We derived a self-consistent system of nonlinear wave equations describing the terahertz generation in dielectric uniaxial crystals by optical pulsed radiation with a tilted wavefront. The numerical analysis of the system of equations showed that the generation of a broadband one-period terahertz signal is accompanied by a red shift of the carrier frequency of the optical pulse, the magnitude of the shift being proportional to the pulse intensity. The generation efficiency with respect to energy reached a maximum at a certain distance of propagation in the crystal, after which the efficiency decreased. A satisfactory agreement was obtained between theoretical calculations and experimental data of other investigations. (generation of terahertz radiation)

Bugai, A N; Sazonov, S V; Shashkov, Andrei Yu

2012-11-30

163

Medical applications of terahertz imaging: a review of current technology and potential applications in biomedical engineering  

Microsoft Academic Search

Terahertz (THz) imaging is in its early stages of development but already the potential clinical impact of this new imaging modality is clear. From cancer research to DNA analysis THz technology is improving or even making possible imaging of hitherto inaccessible phenomena. In this paper we present a short review of THz imaging from the point of view of biomedical

K. Humphreys; J. P. Loughran; M. Gradziel; W. Lanigan; T. Ward; J. A. Murphy; C. O'Sullivan

2004-01-01

164

Real-time passive terahertz imaging system for standoff concealed weapons imaging  

NASA Astrophysics Data System (ADS)

The performance of stand-off imaging systems of concealed weapons in the mm-wave range remains limited by the relatively poor angular resolution using practical aperture sizes. For this reason, increasing the operating frequency of the systems is desired, but in practice is hard to realize due to the lack of affordable, low noise amplifiers well beyond 100 GHz. In this paper we present a passive terahertz imaging system which acquires passive terahertz (~200 GHz - ~1 THz) imagery near video frame rate. The system, one copy of which is built in Finland and the other in the U.S., is based on a 64 pixel linear array of superconducting antenna-coupled microbolometers operated within a commercial cryogen-free closed cycle cryocooler, and utilizes conical scanning Schmidt optics. Quantitative measurements on the imager resolution metrics (thermal, spatial and temporal) will be presented. The results from field tests at the Helsinki-Vantaa airport will be presented.

Luukanen, Arttu; Grönberg, Leif; Grönholm, Markus; Lappalainen, Petteri; Leivo, Mikko; Rautiainen, Anssi; Tamminen, Aleksi; Ala-Laurinaho, Juha; Dietlein, Charles R.; Grossman, Erich N.

2010-04-01

165

Dependence on chirp rate and spectral resolution of the terahertz field pulse waveform measured by electro-optic detection using a chirped optical pulse and a spectrometer and its effect on terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

Single-shot measurement of a terahertz field pulse waveform by electro-optic sampling using a chirped optical pulse and a spectrometer was demonstrated by and Jiang and Zhang [Appl. Phys. Lett. 72, 1945 (1998)]. We have performed an experimental and theoretical investigation into the dependence of the waveform thus measured on the chirp rate and spectral resolution. It was found that the waveform exhibits multicyclic behavior at a chirp rate of -0.24 THz2, which corresponds to a chirped-pulse width of over 10 ps, for the monocyclic original terahertz field, while it approaches the monocyclic behavior with decreasing pulse width. Further, broadening of the spectral resolution of the spectrometer gives rise to a monocyclic waveform in the chirp rate range where the waveform is expected to be multicyclic. In addition, we have derived an analytical expression for the terahertz field pulse waveform thus measured without using the method of stationary phase. The theoretical results were found to be consistent with measured ones. Finally, we examined the spectral bandwidth and resolution of terahertz spectroscopy using this method.

Murakami, H.; Shimizu, K.; Katsurada, M.; Nashima, S.

2008-11-01

166

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

167

Whispering-gallery-mode terahertz pulse propagation on a curved metallic plate  

NASA Astrophysics Data System (ADS)

We demonstrate terahertz (THz) pulse propagation on a cylindrical aluminum plate, with low loss and negligible dispersion via transverse-electric type whispering gallery (WG) modes. We observe an apparent superluminal effect where the group velocity is greater than c, and explain this phenomenon by means of a plane-wave description of the WG modes. The propagation loss is dominated by the diffraction loss due to unbounded lateral spreading, with a negligible ohmic-loss contribution. Both experimental and theoretical results indicate a total loss as low as 2.6 dB/m at a frequency of 0.47 THz.

Mendis, Rajind; Mittleman, Daniel M.

2010-07-01

168

Terahertz imaging of excised oral cancer at frozen temperature  

PubMed Central

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

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

2013-01-01

169

Phase-sensitive terahertz emission from gas targets irradiated by few-cycle laser pulses  

NASA Astrophysics Data System (ADS)

The effect of the carrier envelope phase (CEP) of few-cycle laser pulses on terahertz (THz) emission from gas targets is investigated by analysis and two-dimensional particle-in-cell simulations. For linearly polarized (LP) light, the THz amplitude depends on the CEP phase sinusoidally. For circularly polarized (CP) light, the THz amplitude is independent of the phase, but its polarization plane rotates with the phase. By measuring the THz amplitude or polarization direction, one can determine the CEP of LP or CP laser pulses, respectively. We find that when the ionization degree of atoms is lower than 10%, the phase dependence of the THz radiation is insensitive to intensity and duration of the laser pulse, which is preferable for the phase determination.

Wu, Hui-Chun; Meyer-ter-Vehn, Jürgen; Sheng, Zheng-Ming

2008-04-01

170

Single-cycle terahertz pulses with amplitudes exceeding 1 MV/cm generated by optical rectification in LiNbO3  

NASA Astrophysics Data System (ADS)

Using the tilted-pump-pulse-front scheme, we generate single-cycle terahertz (THz) pulses by optical rectification of femtosecond laser pulses in LiNbO3. In our THz generation setup, the condition that the image of the grating coincides with the tilted-optical-pulse front is fulfilled to obtain optimal THz beam characteristics and pump-to-THz conversion efficiency. By using an uncooled microbolometer-array THz camera, it is found that the THz beam leaving the output face of the LN crystal can be regarded as a collimated rather than point source. The designed focusing geometry enables tight focus of the collimated THz beam with a spot size close to the diffraction limit, and the maximum THz electric field of 1.2 MV/cm is obtained.

Hirori, H.; Doi, A.; Blanchard, F.; Tanaka, K.

2011-02-01

171

Terahertz spectroscopy of liver cirrhosis: investigating the origin of contrast  

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

172

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

173

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

SciTech Connect

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. (terahertz radiation)

Vinokurov, Nikolai A; Knyazev, Boris A; Kulipanov, Gennadii N [G.I. Budker Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation); Dem'yanenko, M A; Esaev, D G [A.V.Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation); Chashchina, O I; Cherkasskii, Valerii S [Novosibirsk State University, Novosibirsk (Russian Federation)

2009-05-31

174

Wave shape recovery for terahertz pulse field detection via photoconductive antenna.  

PubMed

For photoconductive (PC) antennae used as terahertz (THz) detectors, traditional data processing methods should be improved because the space-charge and radiation field screening effects and the time dependence of photocarriers density have not been considered. Through developing a double-probe-pulse THz detection technique and using an equivalent-circuit model to describe PC antennae, we present a new method to restore the THz-field wave shape from the measurement data of currents between two electrodes on the antenna. This method is verified to be effective through building a special THz time-domain spectroscopy system with double probes. This work is significant for the accurate determination of pulse THz fields. PMID:23811898

Liu, Jinsong; Zou, Si; Yang, Zhengang; Wang, Kejia; Ye, Kefei

2013-07-01

175

Real-time terahertz near-field microscope.  

PubMed

We report a terahertz near-field microscope with a high dynamic range that can capture images of a 370 x 740 ?m2 area at 35 frames per second. We achieve high spatial resolution (14 ?m corresponding to ?/30 for a center frequency at 0.7 THz) on a large area by combining two novel techniques: terahertz generation by tilted-pulse-front excitation and electro-optic balanced imaging detection using a thin crystal. To demonstrate the microscope capability, we reveal the field enhancement at the gap position of a dipole antenna after the irradiation of a terahertz pulse. PMID:21643077

Blanchard, F; Doi, A; Tanaka, T; Hirori, H; Tanaka, H; Kadoya, Y; Tanaka, K

2011-04-25

176

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

177

Terahertz Technology: A Boon to Tablet Analysis  

PubMed Central

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

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

2009-01-01

178

Elimination of Fresnel Reflection Boundary Effects and Beam Steering in Pulsed Terahertz Computed Tomography  

NASA Astrophysics Data System (ADS)

For the past few decades there has been tremendous innovation and development of Terahertz (THz) science and imaging. In particular, the technique of 3-D computed tomography has been adapted from the X-Ray to the THz range. However, the finite refractive index of materials in the THz range can severally refract probing THz beams during the acquisition of tomography data. Due to Fresnel reflection power losses at the boundaries as well as steering of the THz beam through the sample, refractive effects lead to anomalously high local attenuation coefficients near the material boundaries of a reconstructed image. These boundary phenomena can dominate the reconstructed THz-CT images making it difficult to distinguish structural defect(s) inside the material. In this paper an algorithm has been developed to remove the effects of refraction in THz-CT reconstructed images. The algorithm is successfully implemented on cylindrical shaped objects.

Mukherjee, Suman; Federici, John; Lopes, Paulo; Cabral, Miguel

2013-09-01

179

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.

180

Feasibility Study on Terahertz Imaging of Corrosion on a Cable Metal Shield  

NASA Astrophysics Data System (ADS)

The possibility of nondestructive diagnosis of corrosion on a metallic shielding layer in a power cable by time-domain imaging and spectroscopic measurements using terahertz waves was examined experimentally. First, absorbance was measured in a THz frequency range for copper oxide, basic copper carbonate, and copper chloride. Next, two copper plates, uncorroded and corroded, were placed in contact with each other horizontally, and a terahertz wave was scanned over them in order to get two-dimensional images. When the plate is corroded to form either basic copper carbonate or copper chloride, the intensity of reflected wave becomes lower than when the plate is uncorroded. It seems that the terahertz wave was scattered more on the surface of the corroded copper plate and was absorbed by the corrosion. Therefore, this research indicates the feasibility of nondestructive diagnosis to detect corrosion on a shield metal in a power cable.

Komatsu, Marina; Sato, Ryo; Mizuno, Maya; Fukunaga, Kaori; Ohki, Yoshimichi

2012-12-01

181

Efficient population transfer in modulation doped single quantum wells by intense few-cycle terahertz pulses  

NASA Astrophysics Data System (ADS)

We demonstrate the direct observation of non-equilibrium intersubband dynamics in a modulation-doped multiple quantum well sample subject to intense few-cycle terahertz (THz) pulses. The transmission spectra show a distinct dependence on the incident THz field strength and contain signatures of a multitude of nonlinear effects that can be observed owing to the large THz-pulse bandwidth. We focus our attention on a case of transient nonlinear refractive index caused by the efficient transfer of electronic population from the ground state to higher-excited states of the quantum well sample. By comparing the experimental results with a one-dimensional finite-difference model going beyond the slowly varying envelope approximation, we prove that, depending on the pulse shape, the leading part of the intense pulse efficiently transfers electrons from the ground state to higher lying excited states. For weak electric fields and small-population transfer, the linear Lorentz model holds. For strong electric fields, up to 55 and 20% of the ground-state electrons are transferred to the first and second excited subbands, respectively, which could lead to the observation of the optical gain.

Dietze, Daniel; Darmo, Juraj; Unterrainer, Karl

2013-06-01

182

Development of a 4 K Stirling-Type Pulse Tube Cryocooler for a Mobile Terahertz Detection System  

NASA Astrophysics Data System (ADS)

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.; Garaway, I.

2010-04-01

183

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

184

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

185

Wrist pulse (image)  

MedlinePLUS

To measure the pulse at the wrist, place the index and middle finger over the underside of the opposite wrist, below the base ... firmly with flat fingers until you feel the pulse in the radial artery.

186

Radial pulse (image)  

MedlinePLUS

... heart. The arteries are the vessels with the "pulse", a rhythmic pushing of the blood in the ... a refilling of the heart chamber. To determine heart rate, one feels the beats at a pulse point ...

187

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

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

188

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

NASA Astrophysics Data System (ADS)

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

di, Zhi-Gang; Yao, Jian-Quan; Jia, Chun-Rong; Xu, De-Gang; Bing, Pi-Bin; Yang, Peng-Fei; Zheng, Yi-Bo

2010-11-01

189

Chemical recognition in terahertz time-domain spectroscopy and imaging  

NASA Astrophysics Data System (ADS)

In this paper, we present an overview of chemical recognition with ultrashort THz pulses. We describe the experimental technique and demonstrate how signals for chemical recognition of substances in sealed containers can be obtained, based on the broadband absorption spectra of the substances. We then discuss chemical recognition in combination with THz imaging and show that certain groups of biological substances may give rise to characteristic recognition signals. Finally, we explore the power of numerical prediction of absorption spectra of molecular crystals and illuminate some of the challenges facing state-of-the-art computational chemistry software.

Fischer, B.; Hoffmann, M.; Helm, H.; Modjesch, G.; Jepsen, P. Uhd

2005-07-01

190

Pulse images recognition using fuzzy neural network  

Microsoft Academic Search

The automatic recognition of pulse images is the key in the research of computerized pulse diagnosis. In order to automatically differentiate the pulse patterns by using small samples in pulse diagnosis, a fuzzy neural network for classifying pulse images based on the knowledge of experts in traditional Chinese pulse diagnosis was designed. The designed classifier can make hard decision and

Lisheng Xu; Max Q.-H. Meng; Kuanquan Wang; Lu Wang; Naimin Li

2009-01-01

191

Optical generation of narrow-band terahertz packets in periodically inverted electro-optic crystals: conversion efficiency and optimal laser pulse format.  

PubMed

We explore optical-to-terahertz conversion efficiencies which can be achieved with femto- and picosecond optical pulses in electro-optic crystals with periodically inverted sign of second-order susceptibility. Optimal crystal lengths, pulse durations, pulse formats and focusing are regarded. We show that for sufficiently short (femtosecond) optical pulses, with a pulsewidth much shorter than the inverse terahertz frequency, conversion efficiency does not depend on pulse duration. We also show that by mixing two picosecond pulses (bandwidth-limited or chirped), one can achieve conversion efficiency, which is the same as in the case of femtosecond pulse with the same pulse energy. Additionally, when the group velocity dispersion of optical pulses is small, one can substantially exceed Manley -Rowe conversion limit due to cascaded processes. PMID:19503563

Vodopyanov, Konstantin L

2006-03-20

192

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

2013-10-28

193

Antenna-coupled uncooled Nb5N6 microbolometers for terahertz imaging  

NASA Astrophysics Data System (ADS)

In recent years our team has done a lot of work toward the goal of sensitive, inexpensive detectors for terahertz detection. In this paper we describe simple fabrication steps and the characterizations of uncooled Nb5N6 microbolometers for terahertz imaging. The best dc responsivity of the Nb5N6 microbolometer is -760 V/W at the bias current of 0.19 mA. A typical noise voltage as low as 10 nV/Hz1/2 yields a low noise equivalent power (NEP) of 1.3×10-11 W/Hz1/2 at a modulation frequency above 4 kHz. We constructed a quasi-optical type receiver by attaching this uncooled Nb5N6 microbolometer to the hyperhemispherical silicon lens. Subsequently, the imaging experiment is performed using this Nb5N6 microbolometer receiver at a THz imaging system.

Tu, X. C.; Mao, Q. K.; Xu, L.; Wan, C.; Sun, Z. L.; Kang, L.; Chen, J.; Wu, P. H.

2013-05-01

194

Terahertz-Pulse Radiation Properties of Oxygen-Deficient YBa2Cu3O7-? Thin Films  

NASA Astrophysics Data System (ADS)

By measuring the detailed characteristics of terahertz-pulse (THz-pulse) radiation and applying THz time-domain spectroscopy, we investigate the generation mechanism of THz-pulse radiation from biased YBa2Cu3O7-? (YBCO) thin films with various carrier concentrations. To vary the carrier concentration, the oxygen deficiency of the YBCO samples was systematically varied. With decreasing carrier concentration, the THz-pulse width increases and the response speed of supercarriers to illumination by femtosecond optical pulses tends to decrease. By examining the radiated waveforms, we clarify the influence of carrier doping not only on the relaxation process of quasiparticles but also on the excitation process. A suitably underdoped YBCO film results in maximum efficiency for generating THz radiation. This tendency is difficult to explain if we only consider the variation in transmittance, which has been the approach till now. Instead, we suggest that a variation in quasiparticle excitation efficiency due to carrier doping should also be considered.

Tominari, Yukihiro; Inoue, Ryotaro; Kawayama, Iwao; Murakami, Hironaru; Tonouchi, Masayoshi

2013-10-01

195

Terahertz-Pulse Radiation Properties of Oxygen-Deficient YBa2Cu3O7-? Thin Films  

NASA Astrophysics Data System (ADS)

By measuring the detailed characteristics of terahertz-pulse (THz-pulse) radiation and applying THz time-domain spectroscopy, we investigate the generation mechanism of THz-pulse radiation from biased YBa2Cu3O7-? (YBCO) thin films with various carrier concentrations. To vary the carrier concentration, the oxygen deficiency of the YBCO samples was systematically varied. With decreasing carrier concentration, the THz-pulse width increases and the response speed of supercarriers to illumination by femtosecond optical pulses tends to decrease. By examining the radiated waveforms, we clarify the influence of carrier doping not only on the relaxation process of quasiparticles but also on the excitation process. A suitably underdoped YBCO film results in maximum efficiency for generating THz radiation. This tendency is difficult to explain if we only consider the variation in transmittance, which has been the approach till now. Instead, we suggest that a variation in quasiparticle excitation efficiency due to carrier doping should also be considered.

Tominari, Yukihiro; Inoue, Ryotaro; Kawayama, Iwao; Murakami, Hironaru; Tonouchi, Masayoshi

2013-08-01

196

Maximizing terahertz pulse amplitude from low temperature gallium arsenide photo conductive semiconductor switch  

NASA Astrophysics Data System (ADS)

An antenna radiates when a time rate of change of signal arrives at the structure from a generator, after travelling through a transmitting medium. THz radiation in a photoconductive semiconductor switches (PCSS) follows the same principles. Here the signal is produced by the photoconductive action, which travels through the bulk to the metallic contacts. In the simulation analysis, therefore, one needs to analyze the substrate with semiconductor code to characterize the generated pulse and then use Maxwell's equation solver for the antenna (contact) analysis. This is because of the unavailability of a comprehensive simulation code that can solve both Maxwell's and semiconductor equations in tandem. In this study, two different commercially available simulation codes were used to optimize the THZ radiation from a GaAs PCSS. Results show that the 50 X 50 microm PCSS material produces a central frequency of 1.75 Terahertz, and a pulse amplitude of approximately 0.22 A at an optimum bias voltage of 1100 Volts. The PCSS was illuminated for 350 fs with a 0.78 microm beam, 50 Mw/cm2 in intensity. The FWHM of the generated pulse 0.4 ps, and the rise time is 0.275 ps. In the antenna analysis, results show that the rectangular patch antenna had a maximum return loss (S11) of approximately -30 dB and had multiple resonant frequencies. The maximum S11 was achieved at 5.6845 THz. The directivity of the main lobe was found out to be 6.2 dB with an angular width of 36.9 degrees. The main lobe was directed at 148 degrees. The side lobes were found out to be -6.8 dB.

Ray, Sampad

197

All-Electronic Generation and Detection of Terahertz Free-Space Radiation with Subpicosecond Pulses  

NASA Astrophysics Data System (ADS)

This work describes the first all-electronic system for generating and detecting freely-propagating pulses having frequency content from 6 GHz to beyond 3 terahertz. The key technologies used are monolithic Schottky diode nonlinear transmission line circuits and sampling bridges, built on GaAs and cooled cryogenically so that they produce and measure step waveforms having 880 fs fall times and 3.5 volt amplitudes, the first electrically-generated subpicosecond waveforms ever reported. To describe how this record-setting performance was achieved, the limitations of Schottky diodes on GaAs are discussed, along with measurements and models to illustrate how the cutoff frequencies of these devices improve by ~2x at liquid nitrogen temperatures. Then the design and fabrication of nonlinear transmission lines and diode samplers are treated. Following these topics, the properties of integrated antennas on dielectric half -spaces are examined, with measurements and models presented to enhance understanding. Finally, the quasi-optical systems that employ these diverse elements are discussed. Simulations of the systems based on models developed throughout the work show good correspondence with actual measurements. This work concludes with some ideas for future directions and applications for these systems, such as spectroscopy, secure wideband communications systems, and small-scale, ultra -wideband radar.

van der Weide, Daniel Warren

198

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

199

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

Microsoft Academic Search

High resolution imaging in the terahertz (THz) frequency range is investigated theoretically in this paper through the use\\u000a of the high frequency methods in computational electromagnetics (CEM). Physical optics (PO), shooting and bouncing ray (SBR)\\u000a and truncated-wedge incremental length diffraction coefficients (TW-ILDCs) methods are combined together to compute the scattered\\u000a fields, which are then used to construct the inverse synthetic

Zhuo Li; Tie Jun Cui

2010-01-01

200

Time-resolved terahertz spectroscopy of semiconductor quantum dots  

Microsoft Academic Search

Spectroscopy in the far-infrared part of the electromagnetic spectrum based on the time-domain measurements of transient terahertz pulses has become a standard experimental technique. In the first part of this thesis we present results regarding applications of this technique to the problem of near-field, sub-wavelength imaging and the effect of finite-size beams in optical pump\\/terahertz probe experiments. The second part

Georgi Dakovski

2008-01-01

201

Pulse Image Recognition Using Fuzzy Neural Network  

Microsoft Academic Search

The automatic recognition of pulse images is the key in the research of computerized pulse diagnosis. In order to automatically differentiate the pulse patterns by using small samples, a fuzzy neural network to classify pulse images based on the knowledge of experts in traditional Chinese pulse diagnosis was designed. The designed classifier can make hard decision and soft decision for

L. S. Xu; Max Q.-H. Meng; K. Q. Wang

2007-01-01

202

Breast cancer tissue diagnosis at terahertz frequencies  

NASA Astrophysics Data System (ADS)

This paper investigates the feasibility of using terahertz pulsed imaging to detect breast cancer in a reflection imaging geometry. Spectroscopic terahertz data is used to simulate the reflected time domain response functions of healthy fibrous breast tissue and breast cancer tissue. Previously we have looked at the refractive index and absorption coefficient separately to characterize tissues. In this work we investigate their combined effects and identify parameters of the simulated reflected impulse response function and corresponding spectroscopic properties with a view to improving our ability to distinguish between the fibrous and cancer tissues in the breast.

Pickwell-MacPherson, Emma; Fitzgerald, Anthony J.; Wallace, Vincent P.

2012-02-01

203

Pulsed bipolar CMOS imager  

Microsoft Academic Search

This paper will describe an acti ve pixel CMOS-compatible im- ager aimed at high resolution still cameras. We will discuss pixel operation, column sense circuits, serial output, and show results from existing imagers. In this abstract, we show results from a prototype 640x480 imager with 5.9x5.9 ?m2 pixels built in 0.8 ?m double-poly CMOS with one additional base implant.

Tobi Delbruck; Nicholas Mascarenhas; Min-Hwa Chi; Albert Bergemont; Carver Mead

204

Application of a high-temperature superconducting detector to terahertz imaging  

NASA Astrophysics Data System (ADS)

The performance of a high temperature superconducting junction detector is evaluated. The detector has been built to explore applications of terahertz imaging. The detector device is a high-temperature superconductor (HTS) Josephson junction, which is integrated with a thin-film ring-slot antenna. The ring-slot antenna is patterned on a magnesium oxide (MgO) substrate which is compatible with the detector's YBCO superconducting material lattice. A hyper-hemispherical lens made from high resistivity float zone silicon (HRFZ-Si) is mounted on the rear side of the substrate. The lens couples energy from an imaging system onto the antenna which couples the energy into the device. An existing terahertz imaging system is used in conjunction with the detector to allow for the exploration of relevant applications. The imaging system is based on a conventional quasi-optical design with a backward-wave oscillator as the source and raster scans samples for image acquisition. The imaging capability of the system has been assessed by trialing a range of applications in both transmission and reflection modes. Applications explored include imaging concealed weapons in packaging, non-destructive testing of materials, and imaging devices through plastic structures. The results generated by the imaging system demonstrate its capability for these applications.

Hellicar, Andrew D.; Du, Jia; Hanham, Stephen M.; Li, Li

2009-05-01

205

InGaAs-based bow-tie diode for spectroscopic terahertz imaging  

NASA Astrophysics Data System (ADS)

Suitability of InGaAs-based bow-tie diodes for a spectroscopic terahertz imaging is demonstrated by inspecting explosive simulators packed in a thick plastic container. The transmission images were obtained within the frequency range of 0.58-2.52 THz at room temperature using optimized bow-tie diode connection scheme. Content of sucrose and tartaric acid in the test samples was discriminated. Measured absorbance was found to be in a good correlation with Fourier spectroscopy data. Performance of room temperature THz imaging using the bow-tie diode was compared versus a commercial pyro-electric sensor.

Kašalynas, I.; Venckevi?ius, R.; Seliuta, D.; Grigelionis, I.; Valušis, G.

2011-12-01

206

Dependence of Terahertz Electric Fields on Electric Bias and Modulation Frequency in Pulsed Terahertz Emissions from Electrically-Modulated Photoconductive Antenna Detected with Free-Space Electro-Optic Sampling  

Microsoft Academic Search

We investigated the dependence of terahertz (THz) electric fields on electric bias and modulation frequency in the pulsed THz emissions from electrically modulated photoconductive antennas detected with free-space electro-optic sampling. The linear dependence of the THz electric field on the electric bias achieves distortion-free modulation of the THz pulse even for deep modulation. We confirmed that the signal-to-noise ratio in

Takeshi Yasui; Tsutomu Araki

2005-01-01

207

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

208

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

209

Optically- and Electrically-Stimulated Terahertz Radiation Emission from Indium Nitride  

NASA Astrophysics Data System (ADS)

Indium nitride is a novel narrow band gap semiconductor. The material is a potential strong source of terahertz frequency electromagnetic radiation with applications in time-domain terahertz spectroscopy and imaging systems. This article reviews recent experimental research on terahertz emission from the binary compound semiconductor indium nitride excited by near-infrared laser beams or microseconds electrical pulses. Advantages of indium nitride as terahertz radiation source material are discussed. It is demonstrated that different mechanisms contribute to the emission of terahertz radiation from indium nitride. The emission of up to 2.4 ?W of THz radiation power is observed when InN is excited with near-infrared femtosecond laser pulses at an average power of 1 W.

Wilke, Ingrid; Ding, Yujie J.; Shubina, Tatiana V.

2012-06-01

210

Propagation through terahertz waveguides with photonic crystal boundaries  

Microsoft Academic Search

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

Adam L. Bingham

2007-01-01

211

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

2012-02-01

212

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

213

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

214

A general approach to low noise readout of terahertz imaging arrays.  

PubMed

This article describes the theory and design of an ultra-low noise electronic readout circuit for use with room temperature video-rate terahertz imaging arrays. First, the noise characteristics of various imaging detectors, including low resistance bolometers and high resistance diodes are discussed. Theoretical approaches to white and 1/f noise mitigation are examined, and a corresponding low-noise readout circuit is designed, built, and tested. It is shown that the circuit is capable of achieving detector limited noise performance for use in room temperature terahertz imaging systems. A thorough noise analysis of the circuit provides the necessary information for applying the readout circuit to any type of imaging detector, and more generally, any measurement of small signals from various source impedances in the presence of white and 1/f noise. W-band measurements of an 8-element, high-resistance detector array, and a 32-element, low-resistance detector array demonstrate the usefulness of the readout circuit. Finally, recommended circuit configurations for various detectors in the literature are provided, with theoretical performance metrics summarized. PMID:21721729

Chisum, Jonathan D; Grossman, Erich N; Popovi?, Zoya

2011-06-01

215

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

NASA Astrophysics Data System (ADS)

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

Ammicht Quinn, R.; Rampp, B.

2009-05-01

216

Ferroelectric soft mode in a SrTiO3 thin film impulsively driven to the anharmonic regime using intense picosecond terahertz pulses.  

PubMed

The ferroelectric soft mode in a SrTiO(3) thin film was impulsively driven to a large amplitude using intense picosecond terahertz pulses. As the terahertz electric field increased, the soft-mode absorption peak exhibited blueshifting and spectral narrowing. A classical anharmonic oscillator model suggests that the induced displacement is comparable to that of the ferroelectric phase transition. The spectral narrowing indicates that the displacement exceeds that induced by any inhomogeneities in the film, demonstrating that the method can be used to explore intrinsic quartic anharmonicity. PMID:22463665

Katayama, I; Aoki, H; Takeda, J; Shimosato, H; Ashida, M; Kinjo, R; Kawayama, I; Tonouchi, M; Nagai, M; Tanaka, K

2012-02-28

217

Foreign Object Detection by Sub-Terahertz Quasi-Bessel Beam Imaging  

PubMed Central

Food quality monitoring, particularly foreign object detection, has recently become a critical issue for the food industry. In contrast to X-ray imaging, terahertz imaging can provide a safe and ionizing-radiation-free nondestructive inspection method for foreign object sensing. In this work, a quasi-Bessel beam (QBB) known to be nondiffracting was generated by a conical dielectric lens to detect foreign objects in food samples. Using numerical evaluation via the finite-difference time-domain (FDTD) method, the beam profiles of a QBB were evaluated and compared with the results obtained via analytical calculation and experimental characterization (knife edge method, point scanning method). The FDTD method enables a more precise estimation of the beam profile. Foreign objects in food samples, namely crickets, were then detected with the QBB, which had a deep focus and a high spatial resolution at 210 GHz. Transmitted images using a Gaussian beam obtained with a conventional lens were compared in the sub-terahertz frequency experimentally with those using a QBB generated using an axicon.

Ok, Gyeongsik; Choi, Sung-Wook; Park, Kyung Hyun; Chun, Hyang Sook

2013-01-01

218

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.

2008-05-01

219

Design and fabrication of diffraction imaging elements for common Gaussian laser beam in terahertz frequency  

NASA Astrophysics Data System (ADS)

A special software is constructed effectively for reconstructing the fine phase distribution of the diffracted Gaussian laser beams in the terahertz frequency range, according to common diffraction theory. The fine surface microrelief patterns of the elements, which originate from the simple patterns in photomask and further etched onto the surface of {100}- oriented silicon wafer by a low cost and rapid method, are created by the software above according to the phase distribution designed. Being different with the traditional silicon diffractive lenses fabricated by multiple level processes, the elements produced by the method introduced by us can transfer common Gaussian beams into desired images through created fine patterns over the surface of the elements. Two typical type of diffractive elements, which are used to transform common Gaussian laser beams in terahertz frequency into highly focused spot or so-called common focus, and the desired figure of the "umber one", are designed and fabricated. For testing the element, the LASER SIEIR 50 of Coherent Company is used to generate common Gaussian laser beams (the diameter of the beams is ~10mm), and the PYROCAM THERE of Spiricon Company is also used to display the images acquired. Experimental results show that the elements can be used to form needed light fields and expected images, respectively.

Liu, Jianfeng; Gong, Jinhui; Liu, Kan; Zhang, Xinyu; Xie, Changsheng

2011-11-01

220

Screening mail for powders using terahertz technology  

NASA Astrophysics Data System (ADS)

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

Kemp, Mike

2011-10-01

221

Terahertz Plasmonic Structures  

NASA Astrophysics Data System (ADS)

Here, we review the background physics of surface plasmons and plasmonic devices. In doing so, we describe how terahertz radiation can be used to excite plasmonic effects. These effects are shown to be beneficial for applications such as terahertz waveguiding, sensing, imaging and wavefront engineering.

Baragwanath, Adam J.; Gallant, Andrew J.; Chamberlain, J. Martyn

222

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

PubMed

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

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

2013-05-20

223

Dynamically phase-matched terahertz generation.  

PubMed

We present the generation of intense terahertz pulses by optical rectification of 780 nm pulses in a large area gallium phosphide crystal. The velocity mismatch between optical and terahertz pulses thereby limits the bandwidth of the terahertz pulses. We show that this limitation can be overcome by a dynamic modification of the refractive index of the gallium phosphide crystal through generation of hot phonons. This is confirmed by excellent agreement between experimental results and model calculations. PMID:22446219

Dietze, Daniel; Unterrainer, Karl; Darmo, Juraj

2012-03-15

224

Speckle in active millimeter-wave and terahertz imaging and spectroscopy  

NASA Astrophysics Data System (ADS)

Wideband millimeter-wave imaging techniques and systems have been developed at Pacific Northwest National Laboratory (PNNL) for concealed weapon detection and other applications. These techniques evolved from singlefrequency millimeter-wave holographic imaging methods to wideband three-dimensional planar and cylindrical techniques and systems. The single-frequency holographic method was derived from optical and ultrasonic holography techniques. Speckle is highly significant in this case, and is caused by constructive and destructive interference from multiple scattering locations or depths within a single resolution cell. The wideband three-dimensional techniques developed at PNNL significantly reduce the speckle effect through the use of high depth resolution obtained from the wide bandwidth of the illumination. For these techniques, speckle can still be significant in some cases and affect image quality. In this paper, we explore the situations in which speckle occurs and its relationship to lateral and depth resolution. This will be accomplished through numerical simulation and demonstrated in actual imaging results. Speckle may also play a significant role in altering reflection spectra in wideband terahertz spectra. Reflection from rough surfaces will generate speckle, which will result in significant variation in the reflection spectrum as measured over very wide bandwidths. This effect may make if difficult to interpret spectral absorption features from general reflectance data. In this paper, physical optics numerical simulation techniques will be used to model the reflection from arbitrary random surfaces and explore the effect of the surface on the reflection spectra and reconstructed image. Laboratory imaging and numerical modeling results in the millimeter-wave through the terahertz frequency ranges are presented.

Sheen, David M.; McMakin, Douglas L.; Hall, Thomas E.

2007-05-01

225

Speckle in Active Millimeter-Wave and Terahertz Imaging and Spectroscopy  

SciTech Connect

Wideband millimeter-wave imaging techniques and systems have been developed at PNNL for concealed weapon detection and other applications. These techniques evolved from single-frequency millimeter-wave holographic imaging methods to wideband three-dimensional planar and cylindrical techniques and systems. The single-frequency holographic method was derived from optical and ultrasonic holography techniques. Speckle is highly significant in this case, and is caused by constructive and destructive interference from multiple scattering locations or depths within a single resolution cell. The wideband three-dimensional techniques developed at PNNL significantly reduce the speckle effect through the use of high depth resolution obtained from the wide bandwidth of the illumination. For these techniques, speckle can still be significant in some cases and affect image quality. In this paper, we explore the situations in which speckle occurs and it's relationship to lateral and depth resolution. This will be accomplished through numerical simulation and demonstrated in actual imaging results. Speckle may also play a significant role in altering reflection spectra in wideband terahertz spectra. Reflection from rough surfaces will generate speckle, which will result in significant variation in the reflection spectrum as measured over very wide bandwidths. This effect may make if difficult to interpret spectral absorption features from general reflectance data. In this paper, physical optics numerical simulation techniques will be used to model the reflection from arbitrary random surfaces and explore the effect of the surface on the reflection spectra and reconstructed image. Laboratory imaging and numerical modeling results in the millimeter-wave through the terahertz frequency ranges are presented.

Sheen, David M.; McMakin, Douglas L.; Hall, Thomas E.

2007-04-01

226

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

227

Ultrafast far-infrared dynamics probed by terahertz pulses: a frequency domain approach. I. Model systems.  

PubMed

Time-resolved terahertz spectroscopy has become a widely used experimental tool for the investigation of ultrafast dynamics of polar systems in the far infrared. We have recently proposed an analytical method for the extraction of a transient two-dimensional susceptibility from the experimental data [N?mec, Kadlec, and Kuzel, J. Chem. Phys. 117, 8454 (2002)]. In the present paper the methodology of optical pump-terahertz probe experiments is further developed for direct application in realistic experimental situations. The expected two-dimensional transient response function is calculated for a number of model cases (including Drude dynamics of free carriers, harmonic and anharmonic oscillator modes); these results serve as a basis for the interpretation of experimental results. We discuss also the cases where only partial (one-dimensional) information about the system dynamics can be experimentally obtained. PMID:15836328

N?mec, H; Kadlec, F; Surendran, S; Kuzel, P; Jungwirth, P

2005-03-01

228

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

PubMed

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. PMID:16178600

Mics, Zoltan; Kadlec, Filip; Kuzel, Petr; Jungwirth, Pavel; Bradforth, Stephen E; Apkarian, V Ara

2005-09-01

229

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

230

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

NASA Astrophysics Data System (ADS)

Temperature-dependent increase of the terahertz (THz) electric field emitted from the surfaces of optically pumped narrow-gap semiconductors InAs, InSb, and CdxHg1-xTe is presented. In the case of Cd0.2Hg0.8Te increase up to 15 17 times has been observed, when cooling the sample from the room temperature to close to liquid-helium temperatures, and THz emission from this material becomes comparable to that of p-InAs emitter. This effect was explained in terms of the increased photoexcited electron excess energy due to the positive temperature coefficient for energy bandgap of CdxHg1-xTe, as well as by weaker surface field screening and carrier carrier scattering. Temperature-dependent modification of the shape of THz pulses emitted from InSb surfaces has been observed and attributed to plasma oscillation of the cold electrons.

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

2008-10-01

231

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

PubMed

Interactions of 100-fs laser pulses with solid targets at intensities of 10(18) W/cm(2) 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 from second harmonic dominant, three-halves harmonic dominant, to vanishing of both harmonics. Two-dimensional particle-in-cell simulation also suggests that this observation is correlated with the plasma density scale length change. The results demonstrate that the THz emission is closely related to the laser-plasma interaction processes. The emission is strong when resonance absorption is a key feature of the interaction, and becomes much weaker when parametric instabilities dominate. PMID:22060511

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

2011-09-09

232

Investigating antibody interactions with a polar liquid using terahertz pulsed spectroscopy.  

PubMed

In this article, we use terahertz spectroscopy to study the dielectric properties of the peroxidase-conjugated affinity purified goat anti-cat immunoglobulin G and the fluorescein-conjugated affinity purified goat anti-cat immunoglobulin G when they interact with polar liquids. The influence of protein concentration, as well as presence of glycerol as a cosolvent, is determined by estimation of the effective hydration shell radius of the protein in solution. The dielectric spectra in this study are measured over the frequency range 0.1-1.3 THz and it is found that the dielectric properties are dependent on the type of the charges in the hydrogen-bonded antibodies' networks. Our results indicate that the terahertz dielectric properties of polar liquids are strongly affected by the presence of the antibody and suggest that the dielectric spectrum is particularly powerful in the study of structural and conformational properties of proteins. Therefore, terahertz spectroscopy is a very sensitive approach to investigate structural features of biological systems. PMID:21190675

Sun, Yiwen; Zhang, Yuanting; Pickwell-Macpherson, Emma

2011-01-01

233

Terahertz tomographic imaging of XVIIIth Dynasty Egyptian sealed pottery.  

PubMed

A monochromatic millimeter-wave imaging system coupled with an infrared temperature sensor has been used to investigate historic objects preserved at the Museum of Aquitaine (France). In particular, two-dimensional and three-dimensional analyses have been performed in order to reveal the internal structure of nearly 3500-year-old sealed Egyptian jars. PMID:21743572

Caumes, Jean-Pascal; Younus, Ayesha; Salort, Simon; Chassagne, Bruno; Recur, Benoît; Ziéglé, Anne; Dautant, Alain; Abraham, Emmanuel

2011-07-10

234

Terahertz time-domain reflectometry of multilayered systems  

Microsoft Academic Search

Presented in this work are applications of terahertz pulse ranging, spectroscopy and imaging to the nondestructive evaluation of three disparate multilayer systems for the detection and measurement of hidden layers, as well as the extraction of system information that will aid in its maintenance, repair or replacement. Thermal protection systems for turbine engine components were investigated. Thermal barrier coatings (TBC)

J. Bianca Jackson

2008-01-01

235

Real-Time Imaging Using a High-Power Monochromatic Terahertz Source: Comparative Description of Imaging Techniques with Examples of Application  

NASA Astrophysics Data System (ADS)

Gradually appearing high-power terahertz sources require the development of adequate imaging techniques. This paper describes four imaging techniques (with a thermal recorder, temperature-sensitive phosphor plates, a visible-light thermal sensitive Fizeau interferometer, and an uncooled microbolometer array) applied with the Novosibirsk terahertz free electron laser as a radiation source. The space and time resolutions of the devices were examined thoroughly. Examples of the application of these techniques, including in-line holography and real-time moving-objects detection, are given.

Knyazev, Boris A.; Cherkassky, Valery S.; Choporova, Yulia Yu.; Gerasimov, Vasily V.; Vlasenko, Maxim G.; Dem'yanenko, Mikhail A.; Esaev, Dmitry G.

2011-10-01

236

Detection of foreign bodies in foods using continuous wave terahertz imaging.  

PubMed

Foreign bodies (FBs) in food are health hazards and quality issues for many food manufacturers and enforcement authorities. In this study, continuous wave (CW) terahertz (THz) imaging at 0.2 THz with an output power of 10 mW was compared with X-ray imaging as techniques for inspection of food for FBs. High-density FBs, i.e., aluminum and granite pieces of various sizes, were embedded in a powdered instant noodle product and detected using THz and X-ray imaging. All aluminum and granite pieces (regular hexahedrons with an edge length of 1 to 5 mm) were visualized by both CW THz and X-ray imaging. THz imaging also detected maggots (length = 8 to 22 mm) and crickets (length = 35 and 50 mm), which were embedded in samples as low density FBs. However, not all sizes of maggot pieces embedded in powdered instant noodle were detected with X-ray imaging, although larger crickets (length = 50 mm and thickness = 10 mm) were detected. These results suggest that CW THz imaging has potential for detecting both high-density and low-density FBs embedded in food. PMID:22221375

Lee, Young-Ki; Choi, Sung-Wook; Han, Seong-Tae; Woo, Deog Hyun; Chun, Hyang Sook

2012-01-01

237

Production of high power femtosecond terahertz radiation  

Microsoft Academic Search

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

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

2003-01-01

238

Passive imaging with pulsed ultrasound insonations  

PubMed Central

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

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

2012-01-01

239

21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 false Ultrasonic pulsed doppler imaging system. 892.1550 Section...Devices § 892.1550 Ultrasonic pulsed doppler imaging system. (a) Identification. An ultrasonic pulsed doppler imaging system is a device that...

2010-04-01

240

21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.  

Code of Federal Regulations, 2010 CFR

...2009-04-01 false Ultrasonic pulsed doppler imaging system. 892.1550 Section...Devices § 892.1550 Ultrasonic pulsed doppler imaging system. (a) Identification. An ultrasonic pulsed doppler imaging system is a device that...

2009-04-01

241

21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 false Ultrasonic pulsed echo imaging system. 892.1560 Section...Devices § 892.1560 Ultrasonic pulsed echo imaging system. (a) Identification. An ultrasonic pulsed echo imaging system is a device...

2010-04-01

242

21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.  

Code of Federal Regulations, 2010 CFR

...2009-04-01 false Ultrasonic pulsed echo imaging system. 892.1560 Section...Devices § 892.1560 Ultrasonic pulsed echo imaging system. (a) Identification. An ultrasonic pulsed echo imaging system is a device...

2009-04-01

243

Detecting hidden objects: Security imaging using millimetre-waves and terahertz  

Microsoft Academic Search

There has been intense interest in the use of millimetre wave and terahertz technology for the detection of concealed weapons, explosives and other threats. Radiation at these frequencies is safe, penetrates barriers and has short enough wavelengths to allow discrimination between objects. In addition, many solids including explosives have characteristic spectroscopic signatures at terahertz wavelengths which can be used to

Mike C. Kemp

2007-01-01

244

Mobile source of high-energy single-cycle terahertz pulses  

NASA Astrophysics Data System (ADS)

The Teramobile laser facility was used to realize the first mobile source of high-power THz pulses. The source is based on a tilted-pulse-front pumping THz generation scheme optimized for application of terawatt laser pulses. Generation of 50-?J single-cycle electromagnetic pulses centered at 0.19 THz with a repetition rate of 10 Hz was obtained for incoming 700-fs 120-mJ near-infrared laser pulses. The corresponding laser-to-THz photon conversion efficiency is approximately 100%.

Stepanov, A. G.; Henin, S.; Petit, Y.; Bonacina, L.; Kasparian, J.; Wolf, J.-P.

2010-10-01

245

Mobile source of high-energy single-cycle terahertz pulses  

Microsoft Academic Search

The Teramobile laser facility was used to realize the first mobile source of high-power THz pulses. The source is based on a tilted-pulse-front\\u000a pumping THz generation scheme optimized for application of terawatt laser pulses. Generation of 50-?J single-cycle electromagnetic\\u000a pulses centered at 0.19 THz with a repetition rate of 10 Hz was obtained for incoming 700-fs 120-mJ near-infrared laser pulses.\\u000a The

A. G. Stepanov; S. Henin; Y. Petit; L. Bonacina; J. Kasparian; J.-P. Wolf

2010-01-01

246

Image Processing with Pulse Coupled Neural Networks  

Microsoft Academic Search

The Pulse Coupled Neural Network {(PCNN)} differs from conventional Artificial Neural Networks by having time dependent output and not requiring training (supervised or unsupervised). The basic {PCNN} algorithm consists of five coupled equations, one of which is non-linear. In an image processing application, the {PCNN} output takes the form of a series of pulses that are a function of the

M. P. Schamschula; R. Inguva; J. L. Johnson

2000-01-01

247

Generation of 10 muJ ultrashort terahertz pulses by optical rectification  

Microsoft Academic Search

Generation of near single-cycle pulses centered at 0.5 THz frequency with up to 10 muJ energy, 100 muW average power, and 5.0 MW peak power was demonstrated by tilting the intensity front of a femtosecond optical pump pulse from a 10 Hz Ti:sapphire laser to match the phonon-polariton phase velocity to the group velocity of the pump pulses in a

K.-L. Yeh; M. C. Hoffmann; J. Hebling; Keith A. Nelson

2007-01-01

248

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

249

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

250

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

251

News and Views: Deep Impact explores; Mercury mysteries; Selene radar maps the Moon; Terahertz imaging repurposed for security devices; Solitons tracked spreading into the magnetosphere; Enceladus enigma  

NASA Astrophysics Data System (ADS)

The potential of astronomical imaging for security devices has been realized with the release of a passive terahertz imaging system suitable for security screening. Solitary waves that propagate without losing energy, in theory, have been observed in the Earth's magnetosphere by the Cluster mission.

2008-04-01

252

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

Microsoft Academic Search

In this dissertation I report the development of high power pulsed fiber laser systems. These systems utilize phosphate glass fiber for active elements, instead of the industry-standard silica fiber. Because the phosphate glass allows for much higher doping of rare-earth ions than silica fibers, much shorter phosphate fibers can be used to achieve the same gain as longer silica fibers.

Matthew A. Leigh

2008-01-01

253

Half-cycle-pulse terahertz emission from an ultrafast laser plasma in a solid target.  

PubMed

Coherent far-IR radiation is observed upon the generation of dense laser-driven plasma in a solid copper target. The coherent radiation demonstrates a strong half-cycle-pulse nature with temporal dynamics as fast as 150 fs. Comparisons between the data and radiation models are discussed. This measurement demonstrates a new method of performing ultrafast laser-plasma diagnostics in solid targets. PMID:19037423

Gao, Yuan; Drake, Tara; Chen, Zhiyuan; Decamp, Matthew F

2008-12-01

254

Terahertz sources and detectors  

NASA Astrophysics Data System (ADS)

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

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

2005-05-01

255

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

256

Terahertz and Infrared Surface Wave Beams and Pulses on Gyrotropic, Nonlinear and Metamaterial Interfaces  

NASA Astrophysics Data System (ADS)

This work is devoted to theoretical study of surface plasmon polariton propagation on metal or metamaterial - dielectric interfaces where media can possess optical or magnetooptical activity or cubic nonlinearity. On the interface of gyrotropic media surface wave changes its polarization and profile as well as in case of interface of media with cubic nonlinearity. Surface wave propagation constant can be modified by magnetization leading to magnetooptical intensity effect. The properties of plasmons in gratings are also considered including excitation, dispersion and existence of various types of modes. The theory of surface wave and pulsed beam diffraction in gyrotropic, nonlinear and layered media is developed. We also present waveguide for surface waves based on layered metamaterial - dielectric interfaces suppressing diffraction spreading.

Sukhorukov, A. P.; Ignatyeva, D. O.; Kalish, A. N.

2011-10-01

257

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

258

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

PubMed

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

Hisatake, Shintaro; Nagatsuma, Tadao

2013-07-01

259

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.

Liu, Jie; Insana, Michael F.

2009-01-01

260

Preface: Heterostructure terahertz devices  

Microsoft Academic Search

The terahertz (THz) range of frequencies is borderline between microwave electronics and photonics. It corresponds to the frequency bands of molecular and lattice vibrations in gases, fluids, and solids. The importance of the THz range is in part due to numerous potential and emerging applications which include imaging and characterization, detection of hazardous substances, environmental monitoring, radio astronomy, covert inter-satellite

Victor Ryzhii

2008-01-01

261

Terahertz spectroscopic imaging using noncollinear electro-optic sampling and a multistep mirror without shifting the object  

NASA Astrophysics Data System (ADS)

We previously developed a high-speed terahertz spectroscopic imaging method based on electro-optic sampling with a noncollinear geometry of the THz beam and probe laser beam and using a multistep mirror in the path of the probe beam. We set the incident probe laser into MAST at a 45° angle, to prevent interference between adjacent beams. However, this produced beam vignetting, so imaging had to be performed twice, between sample movements, and this increased the imaging time accordingly. Thus, we improved the probe-laser imaging system after reflecting from the MAST to correct for the effects of diffraction. This prevents interference from adjacent beams and allows the angle of incidence on the MAST to be set to 0°, enabling the entire sample surface to be imaged in one measurement. As a result, we are able to perform measurements in 40 seconds, half the time of the previous method, and obtain a 28x28-pixel spectral image with spatial resolution of 1.07 mm. To verify the imaging performance, we also measured test samples, showing that the shape and thickness of items inside an opaque plastic case can be distinguished using amplitude and phase images, and metallic foreign objects can be detected. We also evaluated the method and were able to show the validity of the spectral imaging results by distinguishing the transmission or blocking of arbitrary frequency components.

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

2012-10-01

262

Pulse tube cooler for flight hyperspectral imaging  

Microsoft Academic Search

A new version of TRW's miniature pulse tube cooler system maintains the short wave infrared–focal plane array (SWIR–FPA) (with wavelength spectrum of 0.9–2.5 ?m in the hyperspectral imaging spectrometer for the Hyperion Instrument) interface at a temperature of 110 K. The cooler provides the nominally required cooling load of 0.84W to the FPA via a cold thermal strap, at 72%

C. K Chan; Pamela Clancy; John Godden

1999-01-01

263

Free space terahertz optoelectronics  

Microsoft Academic Search

Free-space terahertz electro-optic sampling and magneto-optic sampling provide new methods for the measurement of freely-propagating pulsed electromagnetic radiation. Our recent experimental results of electro-optic detection of THz beams demonstrate an oscillation period of a mid-infrared THz beam as short as 31 fs. The upper-limit of frequency bandwidth reaches to 37 THz (8 ?m). We also demonstrate, for the first time,

X.-C. Zhang

1997-01-01

264

Powermeters and 2D beam imaging systems on the Novosibirsk terahertz free electron laser  

Microsoft Academic Search

Two types of powermeters for the Novosibirsk terahertz free electron laser (NovoFEL) are considered in this paper. The first one is an expositional etalon device on the basis of a heat isolated sapphire plate. The calorimeter is shown to have a constant emissivity of 0.74 in the entire generation range of NovoFEL. The second device is a CW calorimeter with

V. V. Kubarev; E. V. Makashov; K. S. Palagin; S. S. Serednyakov; M. G. Fedotov

2007-01-01

265

Terahertz Imaging of Water Trees Generated in Low-density Polyethylene  

NASA Astrophysics Data System (ADS)

Research was carried out whether it is possible to detect water trees in a low density polyethylene sheet by terahertz light. The attenuation of the reflected intensity of THz light was observed on several points in the sample under a polyvinylchloride sheet. The intensity distribution of the reflected light agrees with the distribution of water trees in the sample. Therefore, the distribution of water trees would be detectable even if the trees are invisible to naked eyes.

Sato, Ryo; Komatsu, Marina; Fuse, Norikazu; Nakamichi, Yoshinobu; Mizuno, Maya; Fukunaga, Kaori; Ohki, Yoshimichi

266

Superconducting hot-electron nanobolometer-sensor arrays for supersensitive imaging radiometers of terahertz frequency range  

Microsoft Academic Search

Development of various supersensitive detector arrays, based on superconducting bolometers for purpose of passive radio vision at terahertz frequencies including radiometers for ground-based and space astronomy security and medical diagnostics systems is in progress. One of the most popular detector devices are the hot-electron bolometer-sensors operated at the superconducting transition edge (TES nanobolometers) and their arrays that include also the

A. N. Vystavkin; A. G. Kovalenko; S. V. Shitov; O. V. Koryukin; I. A. Kon; A. A. Kuzmin; A. V. Uvarov; A. S. Il'in

2010-01-01

267

Saturation and Polarization Characteristics of 1.56 ?m Optical Probe Pulses in a LTG-GaAs Photoconductive Antenna Terahertz Detector  

NASA Astrophysics Data System (ADS)

The characteristics of low temperature-grown GaAs photoconductive antenna (PCA) terahertz detectors probed by 1.56 ?m laser pulses are investigated. The influence of TM and TE polarized probe, as well as the saturation characteristics are studied for 2 ?m- and 5 ?m-gap PCA's. Different polarization characteristics at low probe powers and at the saturation regimes were observed. Results are explained in terms of the polarization-dependent photocarrier distribution at the PCA gap arising from tight focusing. This work also demonstrates using a 1.56 ?m probe for a GaAs PCA to achieve ~60 dB SNR; matching its performance characteristics for above-bandgap probes.

Estacio, Elmer S.; Hibi, Masakazu; Saito, Katsuya; Que, Christopher T.; Furuya, Takashi; Miyamaru, Fumiaki; Nishizawa, Seizi; Yamamoto, Kohji; Tani, Masahiko

2013-05-01

268

Real-time passive terahertz imaging system for standoff concealed weapons imaging  

Microsoft Academic Search

The performance of stand-off imaging systems of concealed weapons in the mm-wave range remains limited by the relatively poor angular resolution using practical aperture sizes. For this reason, increasing the operating frequency of the systems is desired, but in practice is hard to realize due to the lack of affordable, low noise amplifiers well beyond 100 GHz. In this paper

Arttu Luukanen; Leif Grönberg; Markus Grönholm; Petteri Lappalainen; Mikko Leivo; Anssi Rautiainen; Aleksi Tamminen; Juha Ala-Laurinaho; Charles R. Dietlein; Erich N. Grossman

2010-01-01

269

The SPARC linear accelerator based terahertz source  

NASA Astrophysics Data System (ADS)

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.; Catani, L.; Cianchi, A.; Marchetti, B.; Mostacci, A.; Palumbo, L.; Ronsivalle, C.; Di Gaspare, A.; Ortolani, M.; Perucchi, A.; Calvani, P.; Limaj, O.; Nicoletti, D.; Lupi, S.

2013-03-01

270

Terahertz Quantum-Cascade Transmission-Line Metamaterials  

NASA Astrophysics Data System (ADS)

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

Tavallaee, Amir Ali

271

Single-pulse terahertz coherent control of spin resonance in the canted antiferromagnet YFeO3, mediated by dielectric anisotropy  

NASA Astrophysics Data System (ADS)

We report on the coherent control of terahertz (THz) spin waves in a canted antiferromagnet yttrium orthoferrite, YFeO3, associated with a quasiferromagnetic (quasi-FM) spin resonance at a frequency of 0.3 THz, using a single-incident THz pulse. The spin resonance is excited impulsively by the magnetic field component of the THz pulse. The intrinsic dielectric anisotropy of YFeO3 in the THz range allows for coherent control of both the amplitude and the phase of the excited spin wave. The coherent control is based on simultaneous generation of two interfering phase-shifted spin waves whose amplitudes and relative phase, dictated by the dielectric anisotropy of the YFeO3 crystal, can be controlled by varying the polarization of the incident THz pulse with respect to the crystal axes. The spatially anisotropic decay of the THz-excited FM spin resonance in YFeO3, leading to an increasingly linear polarization of the THz oscillation at the spin resonance frequency, suggests a key role of magnon-phonon coupling in spin-wave energy dissipation.

Jin, Zuanming; Mics, Zoltán; Ma, Guohong; Cheng, Zhenxiang; Bonn, Mischa; Turchinovich, Dmitry

2013-03-01

272

Photo-designed terahertz devices  

PubMed Central

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

Okada, Takanori; Tanaka, Koichiro

2011-01-01

273

Terahertz radar cross section measurements.  

PubMed

We perform angle- and frequency-resolved radar cross section (RCS) measurements on objects at terahertz frequencies. Our RCS measurements are performed on a scale model aircraft of size 5-10 cm in polar and azimuthal configurations, and correspond closely to RCS measurements with conventional radar on full-size objects. The measurements are performed in a terahertz time-domain system with freely propagating terahertz pulses generated by tilted pulse front excitation of lithium niobate crystals and measured with sub-picosecond time resolution. The application of a time domain system provides ranging information and also allows for identification of scattering points such as weaponry attached to the aircraft. The shapes of the models and positions of reflecting parts are retrieved by the filtered back projection algorithm. PMID:21164990

Iwaszczuk, Krzysztof; Heiselberg, Henning; Jepsen, Peter Uhd

2010-12-01

274

Design, theory, and measurement of a polarization-insensitive absorber for terahertz imaging  

NASA Astrophysics Data System (ADS)

We present the theory, design, and realization of a polarization-insensitive metamaterial absorber for terahertz frequencies. Effective-medium theory is used to describe the absorptive properties of the metamaterial in terms of optical constants—a description that has been thus far lacking. From our theoretical approach, we construct a device that yields over 95% absorption in simulation. Our fabricated design consists of a planar single unit-cell layer of metamaterial and reaches an absorptivity of 77% at 1.145 THz.

Landy, N. I.; Bingham, C. M.; Tyler, T.; Jokerst, N.; Smith, D. R.; Padilla, W. J.

2009-03-01

275

Measurement of dielectric properties in gigahertz to terahertz frequency range  

Microsoft Academic Search

Measurement of the dielectric constant of thin film in the frequency range of gigahertz (GHz) to terahertz (THz) is crucial for future integrated circuit (IC) interconnect technology. This research focuses on the use of time domain terahertz pulse technology for such characterization. In particular, the goniometric phase shift of a reflected electro magnetic pulse as a function of incident angle

Ming Li

2000-01-01

276

Evolution of image processing methods for pulsed thermal imaging  

NASA Astrophysics Data System (ADS)

Pulsed thermal imaging is a commonly used infrared thermal imaging technology for nondestructive evaluation of engineering materials. It provides a complete interrogation and therefore a potentially complete quantification of the thermal properties of a test material. Two distinct applications have been pursued in the development of data/imaging processing methods: one for material property measurement and the other for flaw or discontinuity detection. For property measurement, theoretical models for one-and multi-layer materials are used to determine thickness-averaged material properties. For flaw detection, various image-processing methods are developed to enhance and extract the thermal contrast induced by subsurface flaw/discontinuities. This study examines the evolution of these methods and compares the differences of flaw-detection methods for detection and characterization of delamination flaws.

Sun, J. G.

2013-01-01

277

Phase-Sensitive Reflective Imaging Device in the mm-wave and Terahertz Regions  

NASA Astrophysics Data System (ADS)

Two Free Electron Laser sources have been developed at ENEA-Frascati for a variety of applications: A Compact Free Electron Laser (C-FEL) that provides coherent radiation in the frequency range between 90 and 150 GHz Gallerano et al. (Infrared Phys. and Techn. 40:161, 1999), and a second source, FEL-CATS, which utilizes a peculiar radio-frequency structure to generate coherent emission in the range 0.4 to 0.7 THz Doria et al. (Phys. Rev. Lett 93:264801, 2004). The high peak power of several kW in 15 to 50 ps pulses, makes these sources particularly suitable for the assessment of exposure limits in biological systems and for long range detection. In this paper we present a phase-sensitive reflective imaging device in the mm-wave and THz regions, which has proven to be a valuable tool in the biological Ramundo-Orlando et al. (Bioelectromagnetics 28:587-598, 2007), environmental Doria et al. (2005) and art conservation fields Gallerano et al. (2008). Different setups have been tested at different levels of spatial resolution to image objects from a few centimeter square to larger sizes. Images have been compared to identify and characterize the contrast mechanism.

Gallerano, Gian Piero; Doria, Andrea; Germini, Marzia; Giovenale, Emilio; Messina, Giovanni; Spassovsky, Ivan P.

2009-12-01

278

Security applications of terahertz technology  

NASA Astrophysics Data System (ADS)

Recent events have accelerated the quest for ever more effective security screening to detect an increasing variety of threats. Many techniques employing different parts of the electromagnetic spectrum from radio up to X- and gammaray are in use. Terahertz radiation, which lies between microwave and infrared, is the last part to be exploited for want, until recently, of suitable sources and detectors. This paper describes practical techniques for Terahertz imaging and spectroscopy which are now being applied to a variety of applications. We describe a number of proof-of-principle experiments which show that Terahertz imaging has the ability to use very low levels of this non-ionising radiation to detect hidden objects in clothing and common packing materials and envelopes. Moreover, certain hidden substances such as plastic explosives and other chemical and biological agents may be detected from their characteristic Terahertz spectra. The results of these experiments, coupled with availability of practical Terahertz systems which operate outside the laboratory environment, demonstrate the potential for Terahertz technology in security screening and counterterrorism.

Kemp, Michael C.; Taday, P. F.; Cole, Bryan E.; Cluff, J. A.; Fitzgerald, Anthony J.; Tribe, William R.

2003-08-01

279

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

280

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

281

Terahertz near-field vectorial imaging of subwavelength apertures and aperture arrays.  

PubMed

We present measurements of the complete terahertz (THz) electric near-field distribution, E(x), E(y) and E(z), in both the time- and frequency-domains, for subwavelength apertures and subsections of subwavelength aperture arrays. Measuring the individual components of the THz near-field with subwavelength spatial resolution, as they emerge from these structures, illustrates how the field interacts with the apertures. We observe the small but measurable y- and z-components of the electric field for both single apertures and arrays. Resonant contributions, attributed to Bloch modes, are detected and we observe the presence of a longitudinal field component, E(z), within the different array apertures, which can be attributed to a diffractive effect. These measurements illustrate in detail the individual THz field components emerging from subwavelength apertures and provide a direct measure of two important mechanisms that contribute to the net transmission of light through arrays. PMID:19687986

Knab, J R; Adam, A J L; Nagel, M; Shaner, E; Seo, M A; Kim, D S; Planken, P C M

2009-08-17

282

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

SciTech Connect

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

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

2006-09-02

283

Designing experiments for demonstration of isotope-selective distribution transfer using terahertz wave  

NASA Astrophysics Data System (ADS)

Design of experiments to demonstrate the isotope-selective displacement of rotational state distribution is reported for future demonstration using realistic terahertz pulse train. Elements to be designed include species used as a target and methods to prepare the target, to prepare THz pulse train, and to measure the distribution. As a result, lithium chloride has been chosen as the target molecule, which is prepared as He-seeded supersonic molecular beam produced with a high-temperature CW nozzle. The terahertz pulse train is prepared by a three-stage interferometer or etalon. The rotational state distribution is measured by momentum imaging spectroscopy. Numerical simulation of the selective displacement is carried out under the chosen condition.

Yokoyama, Keiichi

2012-07-01

284

Coherent optical computing for T-ray imaging.  

PubMed

Single-point imagery of 2D objects is proposed by exploiting the extreme broadband nature of an ultrafast terahertz wave. In the proposed imagery, a collimated terahertz beam is illuminated on an object, and the scattered fields are measured through a hole at the Fourier plane in a conventional terahertz time-domain spectroscope. This arrangement allows conversion of radial spatial frequencies of the object to the temporal spectrum of the pulse. Hence, a 2D image can be readily obtained by rotating a hole around the optical axis. Experimental results confirm that a complicated object can be reliably imaged using only 30 waveform measurements. PMID:20160800

Lee, Kanghee; Jin, Kyung Hwan; Ye, Jong Chul; Ahn, Jaewook

2010-02-15

285

Novel colored pulse laser photography for high speed imaging  

Microsoft Academic Search

In order to improve the imaging quality of conventional laser photography, this study proposes a new system for colored pulse laser photography to obtain high speed color microscopic imaging. Based on the RGB synthesis technique, three channels of red, green, and blue images are acquired from three cameras with three independent laser light sources. Then, a high quality color image

Chien-Sheng Liu; Cheng-Hsien Lin; Chia-Hsu Chen; Po-Heng Lin; Chung-l Huang; Cheung-Wen Chang; Chih-Hsun Lin; Yung-Nien Sun

2009-01-01

286

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

287

Pulsed Magneto-motive Ultrasound Imaging Using Ultrasmall Magnetic Nanoprobes  

PubMed Central

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

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

2011-01-01

288

Experimental imaging performance evaluation for alternate configurations of undersea pulsed laser serial imagers  

Microsoft Academic Search

This paper examines imaging performance bounds for undersea electro-optic identification (EOID) sensors that use pulsed laser line scanners to form serial images, typically utilizing one laser pulse for each formed image element. The experimental results presented include the use of two distinct imaging geometries; firstly where the laser source and single element optical detector are nearly co-aligned (near monostatic) and

Fraser R. Dalgleish; Anni K. Vuorenkoski; Gero Nootz; Bing Ouyang; Frank M. Caimi

2011-01-01

289

CFAR radar image detection in pulse jamming  

Microsoft Academic Search

It is shown that the appearance of strong pulse jamming in the reference window causes drastic degradation in the performance of CA CFAR (cell averaging constant false alarm rate) binary integration processors. The technique for pulse jamming suppression employed in this work is the use of filters matched to a broadband pulse with a large time-bandwidth product. In particular, the

Christo Kabakchiev; Vera Behar

1996-01-01

290

Enhanced terahertz transmission by surface plasmon resonance  

NASA Astrophysics Data System (ADS)

The surface plasmon resonance (SPR) between metal and dielectric material has a good enhancement on electromagnetic wave transmission. In this paper, a series of two-dimension (2D) metal gratings and spiral structures with different geometrical size were experimentally tested by Terahertz time-domain spectroscopy (THz-TDS). The experiment results show that the 2D metal gratings have almost 70% increment on terahertz transmission than the pure silicon substrate in the range of 0.2-2.5THz, which indicates a strong coupling in the terahertz range, and the resonance mode shows a blue shift. On the other hand, the influence of different radiation directions was analyzed. It presents that the slightly higher transmission can be achieved when terahertz wave radiate from the front side than the back side. It reveals that surface plasmon resonance can enhance the terahertz transmission efficiently and has potential applications in security imaging, biological analysis and spectroscopy.

Wen, Yongzheng; Yang, Jiancheng; Yu, Xiaomei; Zhao, Yuejin; Liu, Xiaohua; Dong, Liquan

2012-02-01

291

Novosibirsk terahertz free electron laser: instrumentation development and experimental achievements  

NASA Astrophysics Data System (ADS)

Nowadays, the Novosibirsk free electron laser (NovoFEL) is the most intense radiation source in the terahertz spectral range. It operates in the continuous mode with a pulse repetition rate of up to 11.2 MHz (5.6 MHz in the standard mode) and an average power of up to 500 W. The radiation wavelength can be precisely tuned from 120 to 240 mm with a relative line width of 0.3-1%, which corresponds to the Fourier transform limit for a micropulse length of 40-100 ps. The laser radiation is plane-polarized and completely spatially coherent. The radiation is transmitted to six user stations through a nitrogen-filled beamline. Characteristics of the NovoFEL radiation differ drastically from those of conventional low-power (and often broadband) terahertz sources, which enables obtaining results impossible with other sources, but necessitates the development of special experimental equipment and techniques. In this paper, we give a review of the instrumentation developed for control and detection of high-power terahertz radiation and for the study of interaction of the radiation with matter. Quasi-optic elements and systems, one-channel detectors, power meters, real-time imagers, spectroscopy devices and other equipment are described. Selected experimental results (continuous optical discharge, material and biology substance ablation, real-time imaging attenuated total reflection spectroscopy, speckle metrology, polarization rotation by an artificial chiral structure, terahertz radioscopy and imaging) are also presented in the paper. In the near future, after commissioning another four electron racetracks and two optical resonators, intense radiation in the range from 5 to 240 ľm will be available for user experiments.

Knyazev, B. A.; Kulipanov, G. N.; Vinokurov, N. A.

2010-05-01

292

Pulse tube cooler for flight hyperspectral imaging  

NASA Astrophysics Data System (ADS)

A new version of TRW's miniature pulse tube cooler system maintains the short wave infrared-focal plane array (SWIR-FPA) (with wavelength spectrum of 0.9-2.5 ?m in the hyperspectral imaging spectrometer for the Hyperion Instrument) interface at a temperature of 110 K. The cooler provides the nominally required cooling load of 0.84W to the FPA via a cold thermal strap, at 72% stroke consuming 14.7 W of electrical power, when the heat reject temperature is at 300 K. This cooler can operate up to 90% stroke, having 1.5 W cooling load, thus having 79% performance margin for the Hyperion mission. Before the installation and operation of the cooler onto the instrument, both the mechanical and the electronics assemblies underwent the environmental tests of launch vibration, thermal vacuum cycling, and burn-in. The cooler performance in terms of mechanical efficiency, electronics efficiency, load lines, temperature stability, self-induced vibrational force reduction, ripple current reduction, and magnetic radiated emission was measured and are reported here.

Chan, C. K.; Clancy, Pamela; Godden, John

293

Initial carrier-envelope phase of few-cycle pulses determined by terahertz emission from air plasma  

NASA Astrophysics Data System (ADS)

The evolution of THz waveform generated in air plasma provides a sensitive probe to the variation of the carrier envelope phase (CEP) of propagating intense few-cycle pulses. Our experimental observation and calculation reveal that the number and positions of the inversion of THz waveform are dependent on the initial CEP, which is near 0.5? constantly under varied input pulse energies when two inversions of THz waveform in air plasma become one. This provides a method of measuring the initial CEP in an accuracy that is only limited by the stability of the driving few-cycle pulses.

Xu, Rongjie; Bai, Ya; Song, Liwei; Liu, Peng; Li, Ruxin; Xu, Zhizhan

2013-08-01

294

21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.  

Code of Federal Regulations, 2013 CFR

... Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1550 Ultrasonic pulsed doppler imaging system. (a)...

2013-04-01

295

21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.  

Code of Federal Regulations, 2013 CFR

... Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1560 Ultrasonic pulsed echo imaging system. (a) Identification....

2013-04-01

296

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

297

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

Microsoft Academic Search

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

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

1998-01-01

298

Golay pulse encoding for microbubble contrast imaging in ultrasound.  

PubMed

We present a technique that uses Golay phase encoding, pulse inversion, and amplitude modulation (GPIAM) for microbubble contrast agent imaging with ultrasound. This technique improves the contrast-to-tissue ratio (CTR) by increasing the time-bandwidth product of the insonating waveforms. A nonlinear pulse compression algorithm is used to compress the signal energy upon receive. A 6.5-dB improvement in CTR was observed using an 8-chip GPIAM sequence compared to a conventional pulse-inversion amplitude-modulation sequence. The CTR improvement comes at the cost of a reduction in frame rate: GPIAM coding uses four input pulses whereas most contrast imaging sequences require two or three pulses. Our results showed that the microbubble response can be phase encoded and subsequently compressed using a nonlinear matched-filtering algorithm, in order to enhance the signal from the contrast agent, while maintaining resolution and suppressing the tissue signal. PMID:18019246

Leavens, Claudia; Williams, Ross; Foster, F Stuart; Burns, Peter N; Sherar, Michael D

2007-10-01

299

Wide-range broadband terahertz emission from high ?(2) dendrimer  

NASA Astrophysics Data System (ADS)

Electro-optic dendrimer was used to generate CW terahertz radiation via difference frequency method. In case of electro-optic excitation, the pump-THz conversion is not limited either by emission saturation or by heat dissipation. Especially, the difference frequency generation (DFG) uses two-photon excitation that eliminates the use of a femtosecond pulsed laser and allows for producing both continuous wave (CW) and pulsed terahertz radiation. This report outlines a wideband terahertz spectrometer that is designed around an EO dendrimer terahertz source. This source allows for a wide terahertz range and higher output power. The spectrometer (TeraSpectra) was calibrated with a polyethylene card. It was found that the TeraSpectra reproduces known absorbance peaks of polyethylene with many additional peaks not discovered before. The main origin of these additional peaks is from the fact that the TeraSpectra is sensitive to many resonances possible in a molecule.

Rahman, Anis; Rahman, Aunik

2012-02-01

300

Recent development of terahertz wave sensing and imaging science, technology, and applications  

Microsoft Academic Search

Recent advances in THz science and technology make it one of the most promising research areas in the 21st century for sensing and imaging, as well as in other interdisciplinary fields. We believe new T-ray capabilities will impact a range of interdisciplinary fields and industrial companies, including: communications, imaging, medical diagnosis, health monitoring, environmental control, and chemical and biological identification.

X.-C. Zhang

2006-01-01

301

Ultrafast carrier transport in GaAs measured by optical pump-terahertz probe spectroscopy  

Microsoft Academic Search

Femtosecond optical pump-terahertz probe studies of carrier dynamics and transport characteristics in semi-insulating GaAs have been investigated under different pump powers at room temperature. The transmission of the terahertz pulse is monitored as a function of delay time between pump and probe pulse, we found that because the more optical generated carriers under the higher power, the terahertz transmission decreased

Hai-Yan Yang; Yu-Lei Shi; Qing-Li Zhou; Dong-Mei Zhao; Lei Li; Cun-Lin Zhang

2009-01-01

302

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

303

Single-shot measurement of a terahertz electric-field waveform using a reflective echelon mirror  

NASA Astrophysics Data System (ADS)

Single-shot measurements of terahertz (THz) electric-field waveforms are demonstrated using a reflective echelon mirror, which produces multiple probe pulses with different time-delays. The polarization rotation of the probe pulses, due to the electro-optic effect induced by the THz electric field generated from grating-coupled LiNbO3, was imaged onto a two-dimensional complementary metal-oxide-semiconductor camera. A waveform with a weak peak field strength of 0.6 kV/cm was obtained with a good signal-to-noise ratio, demonstrating precise single-shot detection of the THz electric field waveform.

Minami, Yasuo; Hayashi, Yusuke; Takeda, Jun; Katayama, Ikufumi

2013-07-01

304

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

305

Image fusion by pulse couple neural network with shearlet  

NASA Astrophysics Data System (ADS)

The shearlet representation forms a tight frame which decomposes a function into scales and directions, and is optimally sparse in representing images with edges. An image fusion method is proposed based on the shearlet transform. Firstly, transform the image A and image B by the shearlets. Secondly, a pulse couple neural network (PCNN) is used for the frequency subbands, which uses the number of output pulses from the PCNN's neurons to select fusion coefficients. Finally, an inverse shearlet transform is applied on the new fused coefficients to reconstruct the fused image. Some experiments are performed in images such as multi-focus images, multi-sensor images, medical images and multispectral images comparing the proposed algorithm with the wavelet, contourlet and nonsubsampled contourlet method based on the PCNN. The experimental results show that the proposed algorithm can not only extract more important visual information from source images, but also effectively avoid the introduction of artificial information. It significantly outperforms the traditional multiscale transform image fusion methods in terms of both visual quality and objective evaluation criteria such as MI and QAB/F.

Geng, Peng; Wang, Zhengyou; Zhang, Zhigang; Xiao, Zhong

2012-06-01

306

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

307

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

308

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

Microsoft Academic Search

We observe a 3 order of magnitude enhancement of the terahertz energy radiated by a femtosecond pulse undergoing filamentation in air in the presence of a static electric field. Measurements of terahertz pulse duration, spectrum, polarization, and radiation pattern elucidate the physical processes responsible for this radiation. A theoretical model explains the results and predicts another 3 orders of magnitude

Aurélien Houard; Yi Liu; Bernard Prade; Vladimir T. Tikhonchuk; André Mysyrowicz

2008-01-01

309

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

310

Impact of frequency and polarization diversity on a terahertz radar's imaging performance  

Microsoft Academic Search

The Jet Propulsion Laboratory's 675 GHz, 25 m standoff imaging radar can achieve >1 Hz real time frame rates over 40x40 cm fields of view for rapid detection of person-borne concealed weapons. In its normal mode of operation, the radar generates imagery based solely on the time-of-flight, or range, between the radar and target. With good clothing penetration at 675

Ken B. Cooper; Robert J. Dengler; Nuria Llombart

2011-01-01

311

Impact of frequency and polarization diversity on a terahertz radar's imaging performance  

NASA Astrophysics Data System (ADS)

The Jet Propulsion Laboratory's 675 GHz, 25 m standoff imaging radar can achieve >1 Hz real time frame rates over 40x40 cm fields of view for rapid detection of person-borne concealed weapons. In its normal mode of operation, the radar generates imagery based solely on the time-of-flight, or range, between the radar and target. With good clothing penetration at 675 GHz, a hidden object will be detectable as an anomaly in the range-to-surface profile of a subject. Here we report on results of two modifications in the radar system that were made to asses its performance using somewhat different detection approaches. First, the radar's operating frequency and bandwidth were cut in half, to 340 GHz and 13 GHz, where there potential system advantages include superior transmit power and clothing penetration, as well as a lower cost of components. In this case, we found that the twofold reduction in range and cross-range resolution sharply limited the quality of through-clothes imagery, although some improvement is observed for detection of large targets concealed by very thick clothing. The second radar modification tested involved operation in a fully polarimetric mode, where enhanced image contrast might occur between surfaces with different material or geometric characteristics. Results from these tests indicated that random speckle dominates polarimetric power imagery, making it an unattractive approach for contrast improvement. Taken together, the experiments described here underscore the primary importance of high resolution imaging in THz radar applications for concealed weapons detection.

Cooper, Ken B.; Dengler, Robert J.; Llombart, Nuria

2011-05-01

312

Subwavelength hybrid terahertz waveguides.  

PubMed

We introduce and present general properties of hybrid terahertz waveguides. Weakly confined Zenneck waves on a metal-dielectric interface at terahertz frequencies can be transformed to a strongly confined yet low-loss subwavelength mode through coupling with a photonic mode of a nearby high-index dielectric strip. We analyze confinement, attenuation, and dispersion properties of this mode. The proposed design is suitable for planar integration and allows easy fabrication on chip scale. The superior waveguiding properties at terahertz frequencies could enable the hybrid terahertz waveguides as building blocks for terahertz integrated circuits. PMID:20052215

Nam, Sung Hyun; Taylor, Antoinette J; Efimov, Anatoly

2009-12-01

313

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

314

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

315

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

316

Stable terahertz carrier generation with soliton oscillator  

Microsoft Academic Search

This paper focuses the design of an oscillator for stable terahertz carrier generation with soliton pulses. The proposed soliton oscillator generates periodic train of ultra short-width impulses using the background noise from amplifier as an input. The oscillator is made stable with a series combination of NLTL and a unique adaptive bias controlled amplifier. A new NLTL has been designed

Monjur Morshed; Kaiser Habib; Biplob Kumar Daas; M. A. Quaium; M. Akram

2008-01-01

317

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

318

Characterization of burn injuries using terahertz time-domain spectroscopy  

NASA Astrophysics Data System (ADS)

The accuracy rates of the clinical assessment techniques used in grading burn injuries remain significantly low for partial thickness burns. In this paper, we present experimental results from terahertz characterization of 2nd and 3rd degree burn wounds induced on a rat model. Reflection measurements were obtained from the surface of both burned and normal skin using pulsed terahertz spectroscopy. Signal processing techniques are described for interpretation of the acquired terahertz waveform and differentiation of burn wounds. Furthermore, the progression of burn injuries is shown by comparison between acute characterization and 72-hours survival studies. While the water content of healthy and desiccated skin has been considered as a source of terahertz signal contrast, it is demonstrated that other biological effects such as formation of post-burn interstitial edema as well as the density of the discrete scattering structures in the skin (such as hair follicles, sweat glands, etc.) play a significant role in the terahertz response of the burn wounds.

Arbab, M. Hassan; Dickey, Trevor C.; Winebrenner, Dale P.; Chen, Antao; Mourad, Pierre D.

2011-02-01

319

Hidden object detection: security applications of terahertz technology  

NASA Astrophysics Data System (ADS)

Recent events have led to dramatic changes to the methods employed in security screening. For example, following the failed shoe bombing, it is now common for shoes to be removed and X-rayed at airport checkpoints. There is therefore an increasing focus on new Recent events have led to dramatic changes to the methods employed in security screening. For example, following the failed shoe bombing, it is now common for shoes to be removed and X-rayed at airport checkpoints. There is therefore an increasing focus on new technologies that can be applied to security screening, either to simplify or speed up the checking process, or to provide additional functionality. Terahertz (THz) technology is a promising, emerging candidate. In previous publications we have shown how our THz pulsed imaging systems can be used to image threat items, and have demonstrated that explosive materials have characteristic THz spectra. We have also demonstrated that nonmetallic weaponry can be imaged when concealed beneath clothing. In this work we examine more closely the properties of barrier and potential confusion materials. We demonstrate that barrier materials have smooth spectra with relatively low attenuation. We further demonstrate that the terahertz spectra of several common chemicals and medicines are distinct from those of threat materials.

Tribe, William R.; Newnham, David A.; Taday, Philip F.; Kemp, Michael C.

2004-04-01

320

Photocarriers dynamics in silicon wafer studied with optical-pump terahertz-probe spectroscopy  

NASA Astrophysics Data System (ADS)

Optical pump-terahertz probe spectroscopy is employed to investigate the optical characteristics of silicon wafer. The wafer surface undergoes a phase transition from insulator to metal for terahertz wave with increasing pump fluence. The real part of the pump-induced conductivity shows strong frequency dependence, which can be well described with Drude-Smith model. Our results also demonstrate that the photoexcited Si layer acts as a broadband terahertz pulse antireflection coating with proper pump fluence. In addition, it is observed that the terahertz pulse apparently arrives at the detector earlier when silicon is optically excited.

Li, Gaofang; Li, Dong; Jin, Zuanming; Ma, Guohong

2012-09-01

321

Finite amplitude distortion-based inhomogeneous pulse echo ultrasonic imaging  

Microsoft Academic Search

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

Ted Christopher

1997-01-01

322

Semiconductor terahertz emitters  

NASA Astrophysics Data System (ADS)

There is a demand for more efficient sources of electromagnetic radiation in the terahertz (THz, 1012 Hz) frequency region. One common method of generating THz-frequency radiation is to direct fs pulses of near-infrared laser radiation onto a material which then re-radiates. This approach permits coherent pulses of THz radiation to be produced which, for example, may be used for time-domain spectroscopy (TDS). There are three principal mechanisms by which THz radiation is generated under the stimulus of ultra-short pulses: optical rectification (OR) in electro-optic materials, photoconductivity (PC) from materials with suitable electrodes, and surface-field (SF) effects in other cases. The III-V compound semiconductor GaAs doped with the acceptor impurity Be produces relatively small amounts of THz radiation via the OR and SF mechanisms, but relatively large amounts via the PC mechanism. We have studied the PC emission of THz radiation from layers of GaAs(Be) grown epitaxially on GaAs substrates. The THz power generated depends on the bias applied to the electrodes approximately quadratically. This is typical of the PC mechanism. The dependence of the THz power on the power of the pump beam is approximately linear. In general, the THz generated tends to decrease as the doping level increases. If the doping level exceeds the Mott limit and the material becomes highly conductive then the photoconductivity and consequently the THz production are quenched.

Hargreaves, S.; Lewis, R. A.; Henini, M.

2007-12-01

323

Study on applications of terahertz technology  

NASA Astrophysics Data System (ADS)

Terahertz (THz) technology, as new research topic and technology field which is paid more and more attention by the researchers and governments, has some unique properties which is different from other electromagnetic wave. THz wave is regarded to have potential application in many fields. Existing and emerging applications of terahertz technology in imaging, medicine, biology, space exploration, covert communications, compact radar ranges, industrial controls, terahertz microscopy, terahertz tomography, and homeland security have stimulated intensive research effort in photonics and electronics technologies bracketing the famous terahertz gap from the high and low frequency sides, respectively. Cutoff frequencies and maximum frequencies of operation of InGaAs-based Heterostructure Bipolar Transistors and High Electron Mobility Transistors are now approaching or even exceeding 600 GHz. New ideas of using plasma resonances of two-dimensional electrons for tunable detection and emission of terahertz radiation are being explored and proven experimentally. Plasma effects in polarization-induced electrons and holes in granular pyroelectric/semiconductor heterostructures hold promise of an active THz medium tunable by external electric field or light.

Luo, Ji-jun; Hou, Su-xia; Xu, Jun; Li, Juan-juan

2008-03-01

324

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

325

Recording and reconstruction of in-line holograms of amplitude objects in the terahertz frequency range using a free electron laser  

NASA Astrophysics Data System (ADS)

Until now, holography experiments in the terahertz frequency range have been performed using only pulsed broadband sources and the time domain imaging technique. In this paper, we study the feasibility of the classical holographic technique in this spectral region using the Novosibirsk free electron laser as a high-power monochromatic terahertz source. Gabor (in-line) holograms of amplitude objects (metal masks) are recorded with the help of a temperature-sensitive phosphor image plate and a CCD camera operated in the visible range at a wavelength of 130 ?m. The holograms are reconstructed by the Fresnel-Kirchhoff integral calculation in the image plane. Contrast of the images increases when several individually reconstructed holograms are summed up in a standard way. Spatial resolution of the reconstructed images amounts to 0.4 mm.

Choporova, Yu. Yu.; Vlasenko, M. G.; Gerasimov, V. V.; Irgalin, T. N.; Knyazev, B. A.; Cherkassky, V. S.

2012-01-01

326

Computed tomography using a terahertz quantum cascade laser and quantum well photo-detector  

NASA Astrophysics Data System (ADS)

Terahertz computed tomographic imaging has been performed based on an imaging system which includes a terahertz quantum cascade laser as the light source and a terahertz quantum well photo-detector. The main reconstruction methods of filtered back projection, iterative analysis and the wavelet reconstruction technique are adopted and compared. The reconstructed quality has been discussed with respect to projection numbers, contrast and geometric preservation. We have applied parameter structural similarity to quantitatively analyze the image quality at the end.

Gu, L.; Zhou, T.; Tan, Z. Y.; Cao, J. C.

2013-10-01

327

Investigation of Terra Cotta artefacts with terahertz  

NASA Astrophysics Data System (ADS)

Terahertz Time Domain Imaging has been used in the last few years for the investigation of cultural heritage. In this article, the authors demonstrate the possibility to apply it for the investigation of clay artifacts. Tomographic images were obtained of a model in reflection, and an Egyptian vessel in transmission.

Labaune, Julien; Jackson, J. Bianca; Fukunaga, Kaori; White, Jeffrey; D'Alessandro, Laura; Whyte, Alison; Menu, Michel; Mourou, Gerard

2011-10-01

328

Multispectral angular domain imaging with a tunable pulsed laser  

NASA Astrophysics Data System (ADS)

Angular Domain Imaging (ADI) is an imaging technique that is capable of generating three dimensional images of attenuating targets embedded in a scattering medium. In ADI, an angular filter is positioned between the sample and the detector to discriminate between quasi-ballistic photons and scattered photons. Quasi-ballistic photons have undergone relatively few forward directed scattering events, and can be used to generate a projection image representative of the imaging target. Scattered photons have undergone many scattering events and contain little information regarding the imaging target, thereby leading to decreased image contrast. Our implementation of ADI utilizes a silicon micro-channel array to reject scattered photons based on the angle at which they exit the sample. The objective of this work was to collect ADI images with a tunable pulsed laser within the visible range. Samples were illuminated at 13 wavelengths between 460 nm and 700 nm. An angular filter array of 80 ?m × 80 ?m tunnels 2-cm long was used to select the quasiballistic photons. Images were detected with a linear 16-bit linear CCD. The phantom consisted of a 0.7 mm attenuating target submerged in one of four IntralipidR dilutions (0.15%-0.3%) contained within a 1 cm path length cuvette. Image contrast ranged from 0.02 at 460 nm and 0.3% IntralipidR to 1 at 680 nm at 0.15% IntralipidR. For a given scattering level, contrast increased at longer wavelengths. Resolution varied minimally with wavelength. The results suggested that multispectral ADI with a tunable pulsed laser is feasible and may find utility in imaging thin tissue samples in the future.

Ng, Eldon; Vasefi, Fartash; Carson, Jeffrey J. L.

2012-02-01

329

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

330

Propagation through terahertz waveguides with photonic crystal boundaries  

NASA Astrophysics Data System (ADS)

Scope and method of study. The research presented in this dissertation investigates the integration of photonic crystal lattices into parallel plate waveguides at terahertz frequencies. The experimental data was obtained by measuring the terahertz pulses through the photonic crystal waveguides in a standard terahertz time-domain spectroscopy system. The terahertz pulses were generated and detected via optoelectronic means utilizing lithographically fabricated transmitting and receiving antennas and a femtosecond laser. Findings and conclusions. The main findings of this research are that metallic photonic crystal waveguides are a potential two-dimensional interconnect, and photonic waveguides act as an excellent guided-wave filter. The photonic crystal waveguides demonstrate attenuation approximating that of a comparable metallic waveguide, and demonstrate the capability to integrate guided-wave components with a high level of performance. The photonic waveguides act as a powerful filter, and the mode-matching theory allows complete design control over the waveguides.

Bingham, Adam L.

331

Detection of colon cancer by terahertz techniques  

NASA Astrophysics Data System (ADS)

Normal and cancer affected samples of colon tissue have been measured using transmission time-domain terahertz spectroscopy and continuous wave terahertz imaging. We show that it is possible to distinguish between normal and cancerous regions in the samples when they are fixed in formalin or embedded in paraffin. Plots of the refractive index of normal and cancer affected tissues as well as 2-D transmission THz images are shown. Experimental results will be presented and the conditions for discrimination between normal and affected tissue will be discussed.

Wahaia, Faustino; Valusis, Gintaras; Bernardo, Luis M.; Almeida, Abílio; Moreira, J. Agostinho; Lopes, Patricia C.; Macutkevic, Jan; Kasalynas, Irmantas; Seliuta, Dalius; Adomavicius, Ramunas; Henrique, Rui; Lopes, Machado

2011-05-01

332

Photo-induced insulator-metal phase transition observed by the terahertz pump-probe spectroscopy  

Microsoft Academic Search

We investigated the ultrafast terahertz response to the photoexcitation for vanadium dioxide single crystals and thin films using the optical-pump terahertz-probe technique at room temperature. The optical excitation at 800 nm induced an ultrafast decrease of the transmittance of the terahertz pulse within 0.7 ps, and then the transmittance decreases gradually up to 100 ps. The decrease of the transmittance

Makoto Nakajima; Naoko Takubo; Zenji Hiroi; Yutaka Ueda; Tohru Suemoto

2009-01-01

333

Study of photo-induced phenomena in VO 2 by terahertz pump-probe spectroscopy  

Microsoft Academic Search

The ultrafast terahertz response to the photoexcitation in vanadium dioxide was investigated using the optical-pump terahertz-probe technique at room temperature. The optical excitation at 790nm induced an ultrafast decrease of the transmittance of the terahertz pulses corresponding to the increase of the electronic conductivity within 0.7ps, and then the transmittance decreases gradually up to 100ps. This two-step behavior is very

M. Nakajima; N. Takubo; Z. Hiroi; Y. Ueda; T. Suemoto

2009-01-01

334

Terahertz-frequency electrical conductivity measurements of ultrashort laser-ablated plasmas  

Microsoft Academic Search

We investigate the phase transitions of intense ultrashort laser-heated solids, from the cold solid to the hot dense plasma state, by measuring the complex electrical conductivity (or refractive index) transients at terahertz (1 THz = 1012 Hz) frequencies. Using optical-pump, terahertz-probe spectroscopy, we measured the phase shifts and absorption of terahertz probe pulses that were reflected from the warm dense

K. Y. Kim; B. Yellampelle; J. H. Glownia; A. J. Taylor; G. Rodriguez

2006-01-01

335

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

336

The ultrafast photoconductive characteristics of GaAs bulk investigated by optical-pump terahertz probe spectroscopy  

Microsoft Academic Search

The ultrafast photoconductive characteristics of GaAs bulk were investigated by the optical-pump terahertz-probe spectroscopy (OPTP) at room temperature. In our experiment, a significant decrease of the terahertz transmittance has been observed when the time delay between the optical pump pulse and the terahertz probe pulse was adjusted. It can be concluded that the electronic states of the GaAs became metallic,

Bin Jin; Qing-Li Zhou; Cunlin Zhang

2008-01-01

337

Features of the scattering of focused terahertz radiation from the probe of a terahertz near-field microscope  

NASA Astrophysics Data System (ADS)

The scattering of pulsed terahertz radiation from metallic probes in the form of thin cylinders and cones with a small opening angle, which are used in apertureless terahertz near-field microscopes, has been investigated. The extrema of the waveform of pulsed terahertz radiation scattered from a free probe are linearly shifted with a change in the vertical position of the probe, and the spectral distribution is characterized by an inversely proportional frequency dependence. In the presence of a reflecting surface under the probe, when new excitation and detection directions appear, the spectrum of scattered terahertz radiation does not differ from the spectrum of the incident radiation. The experimental data are in mutual agreement with the theoretical results obtained within the model of the generation of diffraction edge waves at the interface of inhomogeneous excitation between the excitation region and shadow region.

Trukhin, V. N.; Samoylov, L. L.; Khor'kov, D. P.

2013-02-01

338

Terahertz radiation from a laser plasma filament.  

PubMed

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. PMID:21517604

Wu, H-C; Meyer-Ter-Vehn, J; Ruhl, H; Sheng, Z-M

2011-03-15

339

Optical pump terahertz probe studies of semiconducting polymers  

Microsoft Academic Search

Optical-pump terahertz-probe spectroscopy (OPTP) has been applied to study charge generation, transport and the evolution of the photo-induced excited states in thin film organic semiconductors, with emphasis on their relevance to photovoltaic technology. In these experiments the response of the photoexcited material to the AC electric field of a terahertz (THz) pulse was measured. From this response, the evolution of

Paul D. Cunningham

2010-01-01

340

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

341

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

2013-07-08

342

Automated analysis of multiple-pulse particle image velocimetry data  

SciTech Connect

An application of multiple-pulse particle image velocimetry to the study of particle motion in a two-phase flow through a cylindrical tube bank is described. An algorithm is developed that automatically analyzes the digital, multiply exposed pictures of this flow and determines the particle trajectories, using a linear particle image tracking method. From these trajectories particle velocities as well as points of impact and angles of incidence and rebound for particles that collide with the cylinder surfaces are determined. This algorithm is sufficiently rapid that data can be collected and analyzed contemporaneously.

Ramer, E.R.; Shaffer, F.D. (Pittsburgh Energy Technology Center, U.S. Department of Energy, P.O. Box 10940, Pittsburgh, Pennsylvania 15236-0940 (United States))

1992-02-20

343

The simulation of adaptive optical image even and pulse noise and research of image quality evaluation  

NASA Astrophysics Data System (ADS)

As optical image becomes more and more important in adaptive optics area, and adaptive optical telescopes play a more and more important role in the detection system on the ground, and the images we get are so many that we need find a suitable method to choose good quality images automatically in order to save human power, people pay more and more attention in image's evaluation methods and their characteristics. According to different image degradation model, the applicability of different image's quality evaluation method will be different. Researchers have paid most attention in how to improve or build new method to evaluate degraded images. Now we should change our way to take some research in the models of degradation of images, the reasons of image degradation, and the relations among different degraded images and different image quality evaluation methods. In this paper, we build models of even noise and pulse noise based on their definition and get degraded images using these models, and we take research in six kinds of usual image quality evaluation methods such as square error method, sum of multi-power of grey scale method, entropy method, Fisher function method, Sobel method, and sum of grads method, and we make computer software for these methods to use easily to evaluate all kinds of images input. Then we evaluate the images' qualities with different evaluation methods and analyze the results of six kinds of methods, and finally we get many important results. Such as the characteristics of every method for evaluating qualities of degraded images of even noise, the characteristics of every method for evaluating qualities of degraded images of pulse noise, and the best method to evaluate images which affected by tow kinds of noise both and the characteristics of this method. These results are important to image's choosing automatically, and this will help we to manage the images we get through adaptive optical telescopes base on the ground.

Wen, Changli; Xu, Yuannan; Xu, Rong; Liu, Changhai; Men, Tao; Niu, Wei

2013-09-01

344

Optical pump-terahertz probe investigation of carrier relaxation in radiation-damaged silicon-on-sapphire  

Microsoft Academic Search

We use an optical pump - terahertz probe technique to study relaxation dynamics of photoexcited carriers in semiconductors. The optical pump pulse (400\\/800 nm, 100 fs) from an amplified Ti:sapphire laser generates free carriers within the optical penetration depth of the semiconductor surface, and the transmission of the terahertz (THz) probe pulse is monitored as a function of delay time

Frank A. Hegmann; Kristine P. Lui

2002-01-01

345

Terahertz emission from a two-color plasma filament in a slot waveguide  

NASA Astrophysics Data System (ADS)

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.

2012-02-01

346

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

347

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

348

64 ?W pulsed terahertz emission from growth optimized InGaAs/InAlAs heterostructures with separated photoconductive and trapping regions  

NASA Astrophysics Data System (ADS)

We present results on optimized growth temperatures and layer structure design of high mobility photoconductive Terahertz (THz) emitters based on molecular beam epitaxy grown In0.53Ga0.47As/In0.52Al0.48As 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 × 10-3.

Dietz, Roman J. B.; Globisch, Björn; Gerhard, Marina; Velauthapillai, Ajanthkrishna; Stanze, Dennis; Roehle, Helmut; Koch, Martin; Göbel, Thorsten; Schell, Martin

2013-08-01

349

TOPICAL REVIEW: Biomedical applications of terahertz technology  

Microsoft Academic Search

We review the development of terahertz (THz) technology and describe a typical system used in biomedical applications. By considering where the THz regime lies in the electromagnetic spectrum, we see that THz radiation predominantly excites vibrational modes that are present in water. Thus, water absorption dominates spectroscopy and imaging of soft tissues. However, there are advantages of THz methods that

E. Pickwell; V. P. Wallace

2006-01-01

350

A multifunctional, reconfigurable pulse generator for high-frequency ultrasound imaging.  

PubMed

High-frequency (>20 MHz) ultrasound (HFUS) imaging systems have made it possible to image small structures with fine spatial resolution. They find a variety of biomedical applications in dermatology, ophthalmology, intravascular imaging, and small-animal imaging. One critical technical challenge of HFUS is to generate high-voltage, high-frequency pulsed signals to effectively excite the transducer for a high SNR. This paper presents the development of a multifunctional, reconfigurable pulse generator for HFUS imaging. The pulse generator can produce a high-voltage unipolar pulse, a bipolar pulse, or arbitrary pulses for B-mode imaging, Doppler measurement, and modulated excitation imaging. The characteristics of the pulses, such as timing, waveform, and frequency are reconfigurable by a high-speed field-programmable gate array (FPGA). Customized software was developed to interface with the FPGA through a USB connector for pulse selection, and easy, flexible, real-time pulse management. The hardware was implemented in a compact, printed circuit board (PCB)-based scheme using state-of-the-art electronics for costeffectiveness and fully digital control. Testing results show that the unipolar pulse can reach over 165 Vpp with a 6-dB bandwidth of 70 MHz, and the bipolar pulse and arbitrary pulses can reach 150 and 60 Vpp with central frequencies of 60 and 120 MHz, respectively. PMID:22828850

Qiu, Weibao; Yu, Yanyan; Tsang, Fu; Sun, Lei

2012-07-01

351

High-powered tunable terahertz source based on a surface-emitted terahertz-wave parametric oscillator  

NASA Astrophysics Data System (ADS)

A high-powered pulsed terahertz (THz)-wave has been parametrically generated via a surface-emitted THz-wave parametric oscillator (TPO). The effective parametric gain length under the noncollinear phase matching condition was calculated for optimization of the parameters of the TPO. A large volume crystal of MgO:LiNbO3 was used as the gain medium. THz-wave radiation covering a frequency range from 0.87 to 2.73 THz was obtained. The average power of the THz-wave was 9.12 ?W at 1.75 THz when the pump energy was 94 mJ, corresponding to an energy conversion efficiency of about 9.7×10-6 and a photon conversion efficiency of about 0.156%. The THz-wave power in our experiments is high enough for practical applications to spectrum analysis and imaging.

Li, Zhongyang; Bing, Pibin; Yao, Jianquan; Xu, Degang; Zhong, Kai

2012-09-01

352

Terahertz digital holography  

NASA Astrophysics Data System (ADS)

Terahertz wave (THz, also name T-Ray) belongs to far-infrared electromagnetic radiation. Since its unique properties, THz techniques have been paid more and more attentions during the past decades. In this field, THz digital holography is an important research branch, which can accurately extract three-dimensional optical information of objects. Based on features of this technique, it greatly reduces the experimental time and clearly presents the diffraction phenomena of the transmitted THz waves. We elucidated our works about the THz digital holography in recent years. Some key techniques in the THz digital holography are selected as research objects, which are the reflection measurement, quasi-near-field measurement, balanced electro-optic (EO) imaging, and polarization detection. From these four aspects, including the measurement mode, improvement of the spatial resolution, optimization of the signal to noise ratio (SNR), and acquirement of the polarization information, the THz digital holography imaging system has been investigated experimentally and theoretically. These works enhance the performances of the system and promote the practicability of the THz digital holography. Although there are a lot of theoretical and technical difficulties to be overcome in the practical applications, it is firmly believed that the THz digital holography will present strong abilities in factory and research fields in the future.

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

2011-11-01

353

Efficient measurement of broadband terahertz optical activity  

NASA Astrophysics Data System (ADS)

We report a method to determine the four Stokes parameters of each spectral component in a broadband terahertz (THz) pulse by using a continuously rotating analyzer and a standard THz time domain spectroscopy (THz-TDS) instrument. A complete characterization of the polarization state at each frequency is obtained through a single time-domain measurement. Our method requires no specialized THz emitters or detectors; it is, therefore, perfectly general and suitable for any existing THz-TDS apparatus.

Aschaffenburg, Daniel J.; Williams, Michael R. C.; Talbayev, Diyar; Santavicca, Daniel F.; Prober, Daniel E.; Schmuttenmaer, Charles A.

2012-06-01

354

Single pulse frequency compounding protocol for superharmonic imaging  

NASA Astrophysics Data System (ADS)

Second harmonic imaging is currently adopted as standard in commercial echographic systems. A new imaging technique, coined as superharmonic imaging (SHI), combines the 3rd till the 5th harmonics, arising during nonlinear sound propagation. It could further enhance 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 reflection artifacts. Recently, we introduce a dual-pulse frequency compounding (DPFC) method to suppress those artifacts at price of a reduced frame rate. In this study we investigate the feasibility of performing the frequency compounding protocol within a single transmission. The traditional DPFC method constructs each trace in a post-processing stage by summing echoes from two emitted pulses, the second slightly frequency-shifted compared to the first. 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 the higher center frequency. The suitability of the protocol for medical imaging applications in terms of the steering capabilities was performed in a simulation study using the FIELD II toolkit. Moreover, an experimental study was performed to deduce the optimal parametric set for implementation of the clinical imaging protocol. The latter was subsequently used to obtain the images of a tissue mimicking phantom containing strongly reflecting wires. For in-vitro acquisitions the SHI probe with interleaved phased array (44 odd elements at 1MHz and 44 even elements at 3.7MHz elements, optimized for echocardiography) was connected to a fully programmable ultrasound system. The results of the Field II simulations demonstrated that the angle between the main and grating lobe amounted to 90°. The difference in the fundamental pressure level between those lobes was equal to -26.8 dB. Those results suggest that the superharmonic content in the grating lobe was acceptably low. A considerable improvement in the axial resolution of the SHI component (0.73 mm) at -6 dB in comparison with the 3rd 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 an absence of the multiple reflection artifacts in the focal and post-focal regions. 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, Mikhail G.; van Neer, Paul L. M. J.; Matte, Guillaume M.; Verweij, Martin D.; de Jong, Nico

2011-03-01

355

Enhanced pulsed magneto-motive ultrasound imaging using superparamagnetic nanoclusters  

PubMed Central

Recently, pulsed magneto-motive ultrasound (pMMUS) imaging augmented with ultra-small magnetic nanoparticles has been introduced as a tool capable of imaging events at molecular and cellular levels. The sensitivity of a pMMUS system depends on several parameters, including the size, geometry and magnetic properties of the nanoparticles. Under the same magnetic field, larger magnetic nanostructures experience a stronger magnetic force and produce larger displacement, thus improving the sensitivity and signal-to-noise ratio (SNR) of pMMUS imaging. Unfortunately, large magnetic iron-oxide nanoparticles are typically ferromagnetic and thus are very difficult to stabilize against colloidal aggregation. In the current study we demonstrate improvement of pMMUS image quality by using large size superparamagnetic nanoclusters characterized by strong magnetization per particle. Water-soluble magnetic nanoclusters of two sizes (15 and 55 nm average size) were synthesized from 3 nm iron precursors in the presence of citrate capping ligand. The size distribution of synthesized nanoclusters and individual nanoparticles was characterized using dynamic light scattering (DLS) analysis and transmission electron microscopy (TEM). Tissue mimicking phantoms containing single nanoparticles and two sizes of nanoclusters were imaged using a custom-built pMMUS imaging system. While the magnetic properties of citrate-coated nanoclusters are identical to those of superparamagnetic nanoparticles, the magneto-motive signal detected from nanoclusters is larger, i.e. the same magnetic field produced larger magnetically induced displacement. Therefore, our study demonstrates that clusters of superparamagnetic nanoparticles result in pMMUS images with higher contrast and SNR.

Mehrmohammadi, M; Yoon, KY; Qu, M; Johnston, KP; Emelianov, SY

2011-01-01

356

Ultrasonic pulse-inversion fundamental imaging with liposome microbubbles at 25-50 mhz  

Microsoft Academic Search

Pulse inversion based fundamental imaging was proposed for the enhancement of contrast detection in a previous study. Performance of the imaging method was tested with a commercial contrast agent (LevovistŽ) at 1.5-3 MHz. In this study, we applied pulse inversion fundamental imaging at 25-50 MHz with liposome microbubbles that were produced in-house. The pulse inversion technique involves two firings with

Chen-Han Li; Ai-Ho Liao; Ja-An Ho; Pai-Chi Li

2005-01-01

357

Novel sources and detectors for coherent tunable narrow-band terahertz radiation in free space  

Microsoft Academic Search

A novel scheme for the optical generation and coherent detection of tunable narrow-band far-infrared radiation in free space is described. This technique involves the optical heterodyning of two linearly chirped broadband pulses to produce a quasi-sinusoidal intensity modulation at tunable terahertz frequencies. The frequency content of the narrow-band terahertz radiation produced by mixing chirped optical pulses in a nonlinear op-

Aniruddha S. Weling; David H. Auston

1996-01-01

358

Ultrafast terahertz spectroscopy for measuring carrier dynamics in nanoscale photovoltaic materials  

Microsoft Academic Search

Femtosecond pump-probe methods are useful tools for investigating transient electronic and vibrational states of conducting materials and molecular photochemistry. Ultraviolet and visible excitation pulses (<150 fs, <20 muJ, 400-800 nm) with time-delayed broadband terahertz (~500 GHz to 3 THz) probing pulses (Time-Resolved Terahertz Spectroscopy; TRTS) are used to measure linear spectroscopic transmission changes resulting from exciton and free carrier population

Okan Esenturk; Joseph S. Melinger; Edwin J. Heilweil

2010-01-01

359

Terahertz reconfigurable devices using graphene  

NASA Astrophysics Data System (ADS)

This paper reviews the first demonstrations of broadband graphene terahertz modulators as well as recent progress on reconfigurable terahertz devices using graphene. Although atom-thick, single layer graphene is capable of efficiently tuning terahertz absorption meanwhile introducing negligible insertion loss. Recent developments in terms of transmission-mode and reflection-mode electro-absorption modulators are reviewed. Moreover, an application of these devices is presented and discussed: arrays of graphene electro-absorption modulators as electrically reconfigurable patterns for terahertz cameras.

Sensale Rodriguez, Berardi; Xing, Huili G.

2013-09-01

360

Pulse Coupled Neural Networks for the Segmentation of Magnetic Resonance Brain Images.  

National Technical Information Service (NTIS)

This research develops an automated method for segmenting Magnetic Resonance (MR) brain images based on Pulse Coupled Neural Networks (PCNN). The method developed and presented uses a PCNN to both filter and segment MR brain images. The technique begins b...

S. L. Abrahamson

1996-01-01

361

An analysis of Freedman's "image pulse" model in air.  

PubMed

The "image pulse" model developed by Freedman calculates the echoes generated from convex objects in an underwater environment after insonification with a narrow-band transient signal. The model uses the source radiation and the solid angle subtended at the transducer by the scattering body to determine the echo structure. Work has been completed in adapting this model for use in an air environment using noncoincident transmitters and receivers. Experiments were conducted to measure the amplitudes of the echoes off a range of convex objects, at distances up to 1.4 m, after insonification with a Polaroid transducer. These measured amplitudes were compared to those predicted by the model, with the results for cones highlighting the limitations of the model. Spheres, however, performed significantly better, with an average error of under 5%, indicating that the model should be reasonably accurate at calculating the echoes off convex objects with a smoothly varying surface. PMID:11051488

Tsakiris, J; McKerrow, P

2000-10-01

362

Terahertz CMOS circuit design and applications for ultra-high data rate (?100Gbps) communication  

Microsoft Academic Search

Wedged between traditional microwave and optics, the term żTerahertzż was first named by Fleming to designate EM spectrum range from 300 GHz to 3 THz. It remains one of the least tapped spectra over time. Terahertz image and spectroscopic systems have drawn substantial attention recently due to their unique capabilities in detecting and\\/or analyzing concealed objects through fog and fabrics.

M.-C. F. Chang

2009-01-01

363

Applying laser pulse stretching technique on photoacoustic imaging for efficiently delivering laser energy  

NASA Astrophysics Data System (ADS)

High-energy and short-duration outputs from lasers are desirable to improve the photoacoustic image quality when imaging deeply-seated lesions. In many clinical applications, optical fibers are used to couple the high-energy laser pulse to tissue. These high peak intensity pulses can damage an optical fiber input face if the damage threshold is exceeded. It is necessary to reduce the peak intensity to minimize the fiber damage and to delivery sufficient light for imaging. In this paper, a laser-pulse-stretching technique is introduced to reduce the peak intensity of laser pulses. To demonstrate the technique, an initial 17ns pulse was stretched to 37ns by a ring-cavity laser-pulse-stretching system, and the laser peak power reduced to 42%. The stretched pulse increased the fiber damage threshold by 1.5-fold. Three ultrasound transducers centered at 1.3MHz, 3.5MHz, 6MHz frequencies were simulated and the results showed that the photoacoustic signal of 0.5mm-diameter target obtained with 37ns pulse was about 98%, 91% and 80% respectively using the same energy as with the 17ns pulse. Simulations were validated using a broadband hydrophone. Quantitative comparisons of photoacoustic images obtained with three corresponding ultrasound transducers showed that the image quality was not affected by stretching the pulse.

Wang, Tianheng; Kumavor, Patrick D.; Zhu, Quing

2012-02-01

364

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

365

Ultrafast broadband mid-infrared pump, terahertz probe spectroscopy  

Microsoft Academic Search

We report a novel ultrafast optical system capable of directly pumping low energy excitations in complex materials and probing the photoinduced changes in their properties with terahertz pulses, benchmarked through mid-infrared-pump, THz-probe measurements on InSb.

K. M. Dani; J. F. O'Hara; Q. McCulloch; F. Chen; A. K. Azad; G. Dakovski; S. A. Crooker; A. J. Taylor; R. P. Prasankumar

2010-01-01

366

Generation of Intense Terahertz Radiation via Optical Methods  

Microsoft Academic Search

The development of new sources in the terahertz (THz) spectral region has attracted much attention over the past 20 years. In particular, the last three years have seen a surge of new laser-based techniques for generating intense, few-cycle THz pulses in the microjoule energy range, thus paving the way to the study of the nonlinear optical properties of various materials

François Blanchard; Gargi Sharma; Luca Razzari; Xavier Ropagnol; Heidi-Christina Bandulet; François Vidal; Roberto Morandotti; Jean-Claude Kieffer; Tsuneyuki Ozaki; Henry Tiedje; Harold Haugen; Matt Reid; Frank Hegmann

2011-01-01

367

Efficient Terahertz Emission from InAs Nanowires.  

National Technical Information Service (NTIS)

We observe intense pulses of far-infrared electromagnetic radiation emitted from arrays of InAs nanowires. The terahertz radiation power efficiency of these structures is 15 times higher than a planar InAs substrate. This is explained by the preferential ...

A. Katzenmeyer D. V. Seletskiy J. G. Cederberg M. E. Toimil-Molares M. P. Hasselbeck

2011-01-01

368

Combustion Diagnostics with Terahertz Tomography  

NASA Astrophysics Data System (ADS)

The objective of this project is to capture the spectroscopic signature and temperature of combustion process as a function of position using terahertz (THz) time-domain spectroscopy and imaging. The development of a system that can monitor the temperature of an exhaust plume and its chemical make-up as a function of position would be of immeasurable value to the further development of jet engines and their mid-life diagnostics. Current techniques available require different set-ups for each measurement, position and chemical. Our approach to tomographic reconstruction consists of utilizing 8 separate THz transmitter- receiver pairs arranged around the object, allowing all of the tomographic slices to be taken at the same instant. We will present preliminary data demonstrating THz tomographic imaging of solid objects and calibration of spectroscopic and thermal measurement capabilities by THz characterization of water vapors and flames. We will further show ongoing work to produce a THz tomographic reconstruction of a simple flame.

Schroeder, Nicholas; Eichorn, Fin; Deibel, Jason

2008-10-01

369

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

370

Terahertz spectroscopy of human skin constituents in suspension  

NASA Astrophysics Data System (ADS)

Continuous wave terahertz imaging has the potential to offer a non-invasive medical imaging modality for detecting different types of human cancers. The aim of this study was to identify frequencies of interest for continuous wave terahertz imaging of skin cancer. The absorption characteristics of water, collagen, and elastin were studied in the range between 20 and 100cm-1. In addition, we have recorded and analyzed the teraherz absorption spectra of several substances that are present in human skin (i.e. tryptophan, tyrosine, melanin, urocanic acid, keratin) and their water suspensions with the goal of using them as biomarkers for skin cancer detection.

Joseph, Cecil; Yaroslavsky, Anna; Al-Arashi, Munir; Gatesman, Andrew; Goyette, Thomas; Giles, Robert

2008-03-01

371

Detection of colon cancer by terahertz techniques  

NASA Astrophysics Data System (ADS)

Human normal and cancer affected samples of colon tissue have been measured using transmission time-domain terahertz spectroscopy and continuous wave terahertz imaging. We show that it is possible to distinguish between normal and cancerous regions in the samples when they are fixed in formalin or embedded in paraffin. The still noticeable contrast in the dried paraffin-embedded tissues could indicate that there are additional contrast-contributing factors other than water, which is the main goal of the present work. Plots of the refractive index of normal and cancer affected tissues as well as 2-D transmission THz images are shown. Experimental results are presented and the conditions for discrimination between normal and affected formalin-fixed and paraffin-embedded tissue are discussed.

Wahaia, Faustino; Valusis, Gintaras; Bernardo, Luis M.; Almeida, Abílio; Moreira, Joaquim A.; Lopes, Patricia C.; Macutkevic, Jan; Kasalynas, Irmantas; Seliuta, Dalius; Adomavicius, Ramunas; Henrique, Rui; Lopes, Machado

2011-12-01

372

Techniques for CFAR radar image detection in pulse jamming  

Microsoft Academic Search

The presence of strong pulse jamming in a reference window used by Cell-Averaging CFAR detectors for noise power estimation can cause drastic degradation in performance even if the CA CFAR detectors employ binary integration. The technique for pulse jamming suppression discussed in this work is the use of filters matched to a broadband transmitted pulse in combination with an excision

Christo Kabakchiev; Vera Behar

1996-01-01

373

High dynamic velocity range particle image velocimetry using multiple pulse separation imaging.  

PubMed

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

2010-12-23

374

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.

Persoons, Tim; O'Donovan, Tadhg S.

2011-01-01

375

Nonrelativistic electron bunch train for coherently enhanced terahertz radiation sources  

SciTech Connect

We propose to generate a train of prebunched electron beams for producing coherently enhanced Smith-Purcell radiation [S. J. Smith and E. M. Purcell, Phys. Rev. 92, 1069 (1953)] in the terahertz wavelength range. In this scheme, a train of picosecond laser pulses is produced to drive a photoemission gun to generate a train of 50 keV electron pulses. The parameters are chosen so that the space-charge effect does not destroy the pulse time structure. Smith-Purcell radiation from the electron pulse train is enhanced due both to the short length of the individual electron bunch and to the repetitive structure of the beam. Example systems producing coherent terahertz power at about 1 mW are described.

Li Yuelin; Kim, Kwang-Je [Accelerator Systems Division and Argonne Accelerator Institute, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

2008-01-07

376

Retrieval of terahertz spectra through ultrafast electro-optic modulation  

NASA Astrophysics Data System (ADS)

Ultrafast electro-optic modulation on a narrow band optical pulse is utilized to spectrally resolve coherent terahertz radiation. This technique requires no moving parts and has the potential to measure THz spectra with a resolution better than 10 GHz, limited by the bandwidth of the optical probe field or optical spectrometer. The dynamic range of this device is limited by the detection capabilities of an optical spectrometer, providing a highly efficient method of spectral reconstruction of both narrow band and broadband terahertz radiation.

Chen, Z.; Gao, Y.; Decamp, M. F.

2011-07-01

377

An exploration of the utilities of terahertz waves for the NDE of composites  

SciTech Connect

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. [Center for Nondestructive Evaluation, Iowa State University, Ames, Iowa 50011 (United States)

2011-06-23

378

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

379

Pulsed magneto-motive optical coherence tomography for remote cellular imaging.  

PubMed

We developed pulsed magneto-motive optical coherence tomography (PMM-OCT) to reduce environmental temperature in the measurement volume and to expand the effective magnetic field distance from a pulse source. The proposed PMM-OCT system consisted of a spectral-domain OCT system and a customarily designed electrical pulse generator. The enhanced magnetic field allowed the proposed system to be able to image magnetically labeled cells in a distance as far as 30 mm away from the pulse generator. As an easy and sensitive approach, our PMM-OCT may be beneficially applied to a molecular-level imaging systems. PMID:22941000

Koo, Jasung; Lee, Changho; Kang, Hyun Wook; Lee, Yong Wook; Kim, Jeehyun; Oh, Junghwan

2012-09-01

380

Pulsed neutron spectroscopic imaging for crystallographic texture and microstructure  

NASA Astrophysics Data System (ADS)

A time-of-flight (TOF) spectroscopic neutron imaging at a pulsed neutron source is expected to be a new material analysis tool because this method can non-destructively investigate the spatial dependence of the crystallographic and metallographic information in a bulk material. For quantitative evaluation of such information, a spectral analysis code for the transmission data is necessary. Therefore, we have developed a Rietveld-like analysis code, RITS. Furthermore, we have applied the RITS code to evaluation of the position dependence of the crystal orientation anisotropy, the preferred orientation and the crystallite size of a welded ?-iron plate, and we successfully obtained the information on the texture and the microstructure. However, the reliability of the values given by the RITS code has not been evaluated yet in detail. For this reason, we compared the parameters provided by the RITS code with the parameters obtained by the neutron TOF powder diffractometry and its Rietveld analysis. Both the RITS code and the Rietveld analysis software indicated values close to each other, but there were systematic differences on the preferred orientation and the crystallite size.

Sato, Hirotaka; Kamiyama, Takashi; Iwase, Kenji; Ishigaki, Toru; Kiyanagi, Yoshiaki

2011-09-01

381

Terahertz waves, T-rays, and T-birds  

Microsoft Academic Search

Optoelectronic generation of terahertz bandwidth electromagnetic pulses has made access to the previously hard-to-reach far-infrared region of the electromagnetic spectrum possible. Within about ten years, this technique has evolved from a lab curiosity to a technology that now has tremendous promise for applications. This shift is partially driven by the advent of compact, practical, and cheaper femtosecond pulse lasers. In

M. C. Nuss

1998-01-01

382

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

383

Graphene Terahertz Plasmon Oscillators  

Microsoft Academic Search

In this paper we propose and discuss coherent terahertz sources based on charge density wave (plasmon) amplification in two-dimensional graphene. The coupling of the plasmons to interband electron-hole transitions in population inverted graphene layers can lead to plasmon amplification through stimulated emission. Plasmon gain values in graphene can be very large due to the small group velocity of the plasmons

Farhan Rana

2008-01-01

384

Silicon Stokes terahertz laser  

SciTech Connect

A Raman-type silicon laser at terahertz frequencies has been realized. Stokes-shifted stimulated emission has been observed from silicon crystals doped by antimony donors when optically excited by an infrared free electron laser. The Raman lasing was obtained due to resonant scattering on electronic states of a donor atom.

Pavlov, S. G.; Huebers, H.-W. [Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin (Germany); Hovenier, J. N.; Klaassen, T. O. [Kavli Institute of Nanoscience Delft, Delft University of Technology, Postbus 5046, 2600 GA Delft (Netherlands); Carder, D. A.; Phillips, P. J.; Redlich, B. [FOM-Institute for Plasma Physics, Postbus 1207, 3430 BE, Nieuwegein (Netherlands); Riemann, H. [Institute of Crystal Growth, Max-Born-Str. 2, 12489 Berlin (Germany); Zhukavin, R. Kh.; Shastin, V. N. [Institute for Physics of Microstructures, Russian Academy of Sciences, GSP-105, 603950 Nizhny Novgorod (Russian Federation)

2007-04-10

385

Silicon Stokes terahertz laser  

NASA Astrophysics Data System (ADS)

A Raman-type silicon laser at terahertz frequencies has been realized. Stokes-shifted stimulated emission has been observed from silicon crystals doped by antimony donors when optically excited by an infrared free electron laser. The Raman lasing was obtained due to resonant scattering on electronic states of a donor atom.

Pavlov, S. G.; Hübers, H.-W.; Hovenier, J. N.; Klaassen, T. O.; Carder, D. A.; Phillips, P. J.; Redlich, B.; Riemann, H.; Zhukavin, R. Kh.; Shastin, V. N.

2007-04-01

386

Reconfigurable Terahertz Metamaterials  

Microsoft Academic Search

We demonstrate reconfigurable anisotropic metamaterials at terahertz frequencies where artificial ``atoms'' reorient within unit cells in response to an external stimulus. This is accomplished by fabricating planar arrays of split ring resonators on bimaterial cantilevers designed to bend out of plane in response to a thermal stimulus. We observe a marked tunability of the electric and magnetic response as the

Hu Tao; A. C. Strikwerda; K. Fan; W. J. Padilla; X. Zhang; R. D. Averitt

2009-01-01

387

Terahertz Quantum Well Photodetectors  

Microsoft Academic Search

The terahertz (THz) part of the electromagnetic spectrum promises a wide range of new and novel, some may be disruptive, applications. However, the development of technologies in the THz spectrum or the very far infrared region has been slow mainly because of the lack of convenient detectors and lasers. There are a few competing new approaches for better detectors, and

H. C. Liu; Hui Luo; Chun-ying Song; Zbig R. Wasilewski; A. J. SpringThorpe; J. C. Cao

2008-01-01

388

A robust and fast imaging algorithm without derivative operations for UWB pulse radars  

Microsoft Academic Search

Target shape estimation with UWB pulse radars is promising as an imaging technique for household robots. We have already proposed a fast imaging algorithm, SEABED based on a reversible transform BST (Boundary Scattering Transform) between the received signals and the target shape. However the target image obtained by SEABED deteriorates in a noisy environment because it utilizes a derivative of

Shouhei Kidera; Takuya Sakamoto; Toru Sato

2006-01-01

389

Terahertz emission from various organic crystals  

Microsoft Academic Search

We have measured terahertz emission from various organic crystals excited by femtosecond pulses. Our four emitters are 3,5-dimethyl-1-(4-nitrophyenyl)-1,2,4-triazole (DMNT), 3,9-dinitro-5a,6,11a,12-tetrahydro-[1,4]benzoxazino [3,2-b][1,4] benzoxazine (DNBB), 1-(2-thienyl)-3-(4-methyl-phenyl) propenone (TC-28), and 1-(3-thienyl)-3-(4-bromphenyl) propenone (TC-122). Bandwidths of these emitters are achieved to be more than 4 THz.

M. Suzuki; M. Tonouchi; M. Yoshimura; M. Takagi; Y. Takahashi; S. Onduka; S. Brahadeeswaran; Y. Mori; T. Sasaki

2006-01-01

390

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

391

Generation and Detection of Coherent Tunable Terahertz Radiation in Free Space  

Microsoft Academic Search

This thesis presents a novel technique of generating tunable narrowband millimeter and submillimeter-wave radiation in free space using femtosecond optical excitation derived from mode-locked lasers and broadband amplifiers. This scheme relies on the optical heterodyning of two linearly chirped optical pulses to generate a quasi-sinusoidal intensity modulation at tunable terahertz frequencies. The frequency content of the narrowband terahertz radiation produced

Aniruddha S. Weling

1996-01-01

392

Artificial 'olfactory' images from a chemical sensor using a light-pulse technique  

Microsoft Academic Search

A technique is described which allows the determination of the chemical composition of gas mixtures. A continuous sensing surface is used in conjunction with a scanning pulsed light source to produce images that permit the analysis of the gases detected. The detecting surface is made up of various catalytic metals arranged on a large-area field-effect device, across which a pulsed

I. Lundstrom; R. Erlandsson; U. Frykman; E. Hedborg; A. Spetz; H Sundgren; S Welin; F Winquist

1991-01-01

393

Shadowgraphic imaging of metal drilling with a long pulse excimer laser  

Microsoft Academic Search

A shadowgraphic imaging technique is used for studying the interaction between the laser beam and the material during laser drilling. The used laser is a XeCl excimer laser with a nearly diffraction limited beam and 175 ns pulse length. We studied how and when the material is removed. Holes are drilled with a series of pulses in aluminum and Hastelloy

Aart Schoonderbeek; Cornelis A. Biesheuvel; Ramon M. Hofstra; Klaus-Jochen Boller; Johan Meijer

2003-01-01

394

Annealing temperature dependence of terahertz wave detection by low-temperature-grown-GaAs-based photoconductive antennas gated by 1560 nm optical pulses  

Microsoft Academic Search

We have studied THz detection performance of low-temperature-grown GaAs (LT-GaAs) photoconductive switches gated with 1560-nm-optical pulses. LT-GaAs is annealed in the range of 500-600degC. Although the sample annealed at 600degC is most sensitive at frequencies below 1 THz, that annealed at 550degC is superior to others at higher frequencies than 1 THz.

M. Suzuki; M. Tonouchi; M. Kamakura; Y. Kadoya; M. Yoshimura; M. Takagi; Y. Takahashi; S. Onduka; S. Brahadeeswaran; Y. Mori; T. Sasaki

2006-01-01

395

Ultrafast carrier relaxation in radiation-damaged silicon on sapphire studied by optical-pump-terahertz-probe experiments  

Microsoft Academic Search

We investigate the relaxation of photogenerated carriers in radiation-damaged silicon on sapphire using a collinear optical-pump-terahertz-probe arrangement. Carrier densities greater than 1020 cm-3 are injected using 400 nm, 100 fs pump pulses, and the change in transmission of the terahertz-probe pulse is measured as a function of pump-probe delay. The time-dependent carrier density is deduced using a thin-film Drude model.

K. P. H. Lui; F. A. Hegmann

2001-01-01

396

Ultrafast carrier relaxation in radiation-damaged silicon on sapphire studied by optical-pump–terahertz-probe experiments  

Microsoft Academic Search

We investigate the relaxation of photogenerated carriers in radiation-damaged silicon on sapphire using a collinear optical-pump–terahertz-probe arrangement. Carrier densities greater than 1020 cm?3 are injected using 400 nm, 100 fs pump pulses, and the change in transmission of the terahertz-probe pulse is measured as a function of pump–probe delay. The time-dependent carrier density is deduced using a thin-film Drude model.

K. P. H. Lui; F. A. Hegmann

2001-01-01

397

EDITORIAL: Photonic terahertz technology  

NASA Astrophysics Data System (ADS)

In recent years, when reading newspapers and journals or watching TV, one has been able to find feature presentations dealing with the prospects of terahertz (THz) technology and its potential impact on market applications. THz technology aims to fill the THz gap in the electro-magnetic spectrum in order to make the THz frequency regime, which spans the two orders of magnitude from 100 GHz to 10 THz, accessible for applications. From the lower-frequency side, electronics keeps pushing upwards, while photonic approaches gradually improve our technological options at higher frequencies. The popular interest reflects the considerable advances in research in the THz field, and it is mainly advances in the photonic branch, with the highlight being the development of the THz quantum cascade laser, which in recent years have caught the imagination of the public, and of potential users and investors. This special issue of Semiconductor Science and Technology provides an overview of key scientific developments which currently represent the cutting edge of THz photonic technology. In order to be clear about the implications, we should define exactly what we mean by 'THz photonic technology', or synonymously 'THz photonics'. It is characterized by the way in which THz radiation (or a guided THz wave) is generated, namely by the use of lasers. This may be done in one of two fundamentally different schemes: (i) by laser action in the terahertz frequency range itself (THz lasers), or (ii) by down-conversion processes (photomixing) involving the radiation of lasers which operate in the visible, near-infrared or infrared spectral ranges, either in pulsed or continuous-wave mode. The field of THz photonics has grown so considerably that it is out of the question to cover all its aspects in a single special issue of a journal. We have elected, instead, to focus our attention on two types of development with a potentially strong impact on the THz field: first, on significant advances of the technology itself, and second, on specific applications considered capable of fostering the transmutation of THz technology as a whole into a market technology. We decided for reasons of conciseness to leave out technologies which require more than table-top equipment (free-electron lasers, THz sources based on electrons accelerated to relativistic speed, etc) as well as fairly mature techniques (such as backward-wave oscillators which, although they are not strictly lasers, also exhibit gain). More difficult was the decision not to consider fascinating ideas for novel sources and detectors which until now have existed only on paper or have just entered the process of fundamental investigation. As we ourselves are working on such a concept (the Bloch-gain laser), we are fully aware of the fact that some of these ideas may have a strong impact on the field of THz photonics in the near future. After selection of the topics we wanted to cover, we contacted colleagues who are prominent in their respective fields of research and are grateful that most of them responded positively, expressing their willingness to share their knowledge with the readers of this journal. They took care not only to describe their own work but to give ample reference to the status of their respective specialized field of work. Before summarizing the contributions, we want to address all colleagues in the field who feel that they should have been asked to contribute but were not. To you we want to apologize. We can only hope for your understanding of the constraints of this endeavour. The collection of invited contributions is grouped into five topics. The first is entitled 'Pulsed THz Systems' and contains four papers dealing with the state of the art in source and detector development of measurement systems employing femtosecond Ti:sapphire lasers. The first paper, by Planken et al, describes the state of the art of the most common types of optoelectronic THz systems, namely those with femtosecond lasers operating at high repetition rate (~100 MHz). The system described by Planke

Lisauskas, Alvydas; Löffler, Torsten; Roskos, Hartmut G.

2005-07-01

398

New pulse sequences for T1- and T1/T2-contrast enhancing in NMR imaging.  

PubMed

Improved pulse sequences DIFN (abbreviation of the words: DIFferentiation by N pulses), 90 degrees - tau1 - 180 degrees tau1 - . . . 180 degrees - tau1 with optimised time intervals tau1- for T1 measurement and contrast enhancing in NMR imaging are presented. The pulse sequences DIFN have a better sensitivity to T1 than the well-known pulse sequence SR. In contrast to the IR pulse sequence, the information given by the DIFN pulse sequence is more reliable, because the NMR signal does not change its sign. For a given time interval tau0 < or = (0.1 - 0.3) T(1) the DIFN pulse sequences serve as T1-filters. They pass the signal components with relatively short T1 < T(1) and suppress the components with relatively long T1 < T(1). The effects of the radiofrequency field inhomogeneity and inaccurate adjusting of pulse lengths are also considered. It is also proposed in this work to use the joint T1T2-contrast in NMR imaging obtained as a result of applying the DIFN pulse sequences in combination with the well-known Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence. The region of interest, where the contrast should be especially enhanced, is specified by the two times at which measurements are performed, which allow the amplitudes of pixels to reach some defined levels by spin-lattice and spin-spin relaxation. PMID:9814781

Andreev, N K; Hakimov, A M; Idiyatullin, D S

1998-10-01

399

Tunable terahertz radiation from a tunnel ionized magnetized plasma cylinder  

SciTech Connect

A scheme of producing tunable terahertz radiation using a short pulse laser to tunnel ionize a gas jet immersed in a magnetic field is examined. The free electrons born inside the laser pulse retain a finite transverse drift after the passage of the pulse, setting themselves in transverse oscillations at frequencies {omega}{sub R},{omega}{sub L}=[(2{omega}{sub p}{sup 2}+{omega}{sub c}{sup 2}){sup 1/2}{+-}{omega}{sub c}]/2, shifted from that without magnetic field at {omega}{sub p}/{radical}(2), where {omega}{sub p} is the electron plasma frequency and {omega}{sub c} is the cyclotron frequency. The oscillating electron cylinder emits coherent terahertz radiation with ambient magnetic field providing the frequency tunability. The presence of an axial density ripple controls the angular orientation of the emitted radiation.

Liu, C. S.; Tripathi, V. K. [Department of Physics, University of Maryland, College Park, Maryland 20742 (United States)

2009-01-01

400

Image segmentation by EM-based adaptive pulse coupled neural networks in brain magnetic resonance imaging.  

PubMed

We propose an automatic hybrid image segmentation model that integrates the statistical expectation maximization (EM) model and the spatial pulse coupled neural network (PCNN) for brain magnetic resonance imaging (MRI) segmentation. In addition, an adaptive mechanism is developed to fine tune the PCNN parameters. The EM model serves two functions: evaluation of the PCNN image segmentation and adaptive adjustment of the PCNN parameters for optimal segmentation. To evaluate the performance of the adaptive EM-PCNN, we use it to segment MR brain image into gray matter (GM), white matter (WM) and cerebrospinal fluid (CSF). The performance of the adaptive EM-PCNN is compared with that of the non-adaptive EM-PCNN, EM, and Bias Corrected Fuzzy C-Means (BCFCM) algorithms. The result is four sets of boundaries for the GM and the brain parenchyma (GM+WM), the two regions of most interest in medical research and clinical applications. Each set of boundaries is compared with the golden standard to evaluate the segmentation performance. The adaptive EM-PCNN significantly outperforms the non-adaptive EM-PCNN, EM, and BCFCM algorithms in gray mater segmentation. In brain parenchyma segmentation, the adaptive EM-PCNN significantly outperforms the BCFCM only. However, the adaptive EM-PCNN is better than the non-adaptive EM-PCNN and EM on average. We conclude that of the three approaches, the adaptive EM-PCNN yields the best results for gray matter and brain parenchyma segmentation. PMID:20042313

Fu, J C; Chen, C C; Chai, J W; Wong, S T C; Li, I C

2009-12-29

401

A compact terahertz burst emission system driven with 1 ?m fiber laser  

NASA Astrophysics Data System (ADS)

In this work we propose a compact, easily tunable terahertz burst generation system based on the mixing of two linearly chirped optical pulses in the Michelson interferometer. The use of linearly chirped optical pulses ejected straight from the fiber laser enabled us to avoid bulky external optical pulse stretching schemes. Even for non-compensated third and higher order dispersion that is taking place in the optical fiber terahertz bursts of relatively narrow bandwidth of 55 GHz were registered. The system operation range determined from the power measurements reached 2 THz.

Adamonis, Juozas; Rusteika, Nerijus; Danilevi?ius, Rokas; Krotkus, Ar?nas

2013-04-01

402

Terahertz coherent control of surface plasmon polariton propagation in subwavelength metallic hole arrays  

NASA Astrophysics Data System (ADS)

We demonstrate the terahertz coherent control of extraordinary transmission through subwavelength metallic hole arrays with double terahertz pulses. The interference of excitations of surface plasmon polaritons (SPPs) by two THz pulses sequence is employed to control the propagation of SPPs in the periodical structure. As a result, the THz wave transmission is controllable by adjusting the arriving time of the control THz pulse. Our results reveal that THz extraordinary transmission in subwavelength structure arises from the excitation of SPPs of the structures, which provides a universal ultrafast means to control the SPPs motion in various THz subwavelength structures.

Li, Gaofang; Jin, Zuanming; Xue, Xin; Lin, Xian; Ma, Guohong; Hu, Shuhong; Dai, Ning

2012-05-01

403

Incoherent optical differential pulse code modulation (ODPCM) technique for image information compression  

NASA Astrophysics Data System (ADS)

The basic principle of using an incoherent optical system to simulate the digital optical differential pulse code modulation (ODPCM) for image compression and the calculation of image compression ratio. The design and development of the optical sampler and the optical interpolator are demonstrated. Some preliminary experimental results on the transmitted, compressed image and the received, restored image of a binary picture, obtained on an incoherent optical setup with a real-time PROM spatial light modulator for baseline subtraction, are reported.

Lin, Ning; Wu, Changfa; Ye, Jianxiang

1988-05-01

404

Applications of Terahertz Time-Domain Reflectometry  

NASA Astrophysics Data System (ADS)

A reflection-type terahertz (THz) time-domain spectroscopy (TDS) is applied to non-contact and non-destructive diagnosis of the surface and inner-structure of test samples. Raster scan imaging and THz optical coherence tomography (THz-OCT) are demonstrated for a bank bill, a high voltage cable and an indented impression on a memo-pad paper. The watermark of the bank bill, the indented impression, and a flaw in the cable are detected successfully. These results indicate that THz imaging is potentially useful for the analysis of surfaces and inner-structures of products made with various materials.

Kitahara, Hideaki; Takano, Keisuke; Ikeda, Takeshi; Tani, Masahiko; Hangyo, Masanori

405

A modulated pulse laser for underwater detection, ranging, imaging, and communications  

NASA Astrophysics Data System (ADS)

A new, modulated-pulse, technique is currently being investigated for underwater laser detection, ranging, imag- ing, and communications. This technique represents a unique marriage of pulsed and intensity modulated sources. For detection, ranging, and imaging, the source can be congured to transmit a variety of intensity modulated waveforms, from single-tone to pseudorandom code. The utility of such waveforms in turbid underwater envi- ronments in the presence of backscatter is investigated in this work. The modulated pulse laser may also nd utility in underwater laser communication links. In addition to exibility in modulation format additional variable parameters, such as macro-pulse width and macro-pulse repetition rate, provide a link designer with additional methods of optimizing links based on the bandwidth, power, range, etc. needed for the application. Initial laboratory experiments in simulated ocean waters are presented.

Cochenour, Brandon; Mullen, Linda; Muth, John

2012-05-01

406

Terahertz Spectroscopy of Biomolecules  

NASA Astrophysics Data System (ADS)

A novel, continuous-wave (CW) terahertz spectrometer has been constructed to investigate the flexibility and dynamics of small biological molecules. Hydrogen bonding interactions, torsional vibrations, and conformational changes are expressed in this far-infrared region of the spectrum. Terahertz (THz) radiation (0 - 4 THz or 0 - 133 wavenumber) is generated at the difference frequency of two near-infrared pump lasers by optical heterodyne mixing at the surface of a solid-state photomixer. This spectrometer has been used to probe the low-frequency vibrational modes of several members of the vitamin B-complex including riboflavin, pantothenic acid, and biotin. Interpretation of these unique THz spectra has been aided by low-frequency Raman experiments as well as ab initio predictions for normal mode frequencies and intensities. Instrumental details, vitamin B-complex analyses, and preliminary results for myoglobin and other large biomolecules will be presented.

Korter, Timothy; Plusquellic, David; Hight Walker, Angela; Heilweil, Edwin

2002-03-01

407

Frequency-domain approach to evaluation of data obtained in optical pump-terahertz probe experiments  

Microsoft Academic Search

Describes the increasing effort to develop optical pump-terahertz probe (OPTP) experiments as a tool for studying transient processes following excitation by an optical pulse, e.g. in semiconductors, superconductors and solvated chromophores. If the timescale of the investigated process is much longer (hundreds of ps) than the duration of the THz probing pulse, the experimental data can be evaluated using the

R. Kadlec; H. Nemec; P. Kuzel

2002-01-01

408

Terahertz-wave induced non-linear optical effects in semiconductors  

Microsoft Academic Search

Recent development of ultrashort pulse technologies allows us to drive large amplitude motion of electron and ion coherently. The intense terahertz (THz) pulse resonant with the vibration frequency is promising to drive vibrations more directly and in coherent manner. In the case of semiconductors, one may coherently control the electronic system in the sub-level structures of quantum structures with intense

Koichiro Tanaka

2010-01-01

409

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

410

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

411

Recent Progress on Compact and Portable Terahertz Source Based on Parametric Conversion from Dual-Frequency Solid-State Laser Pulses  

NASA Astrophysics Data System (ADS)

We review the progress made on power scaling and compact and portable THz sources. By reversely stacking GaP plates, we improved photon conversion efficiency from 25% to 40%, which is the maximum value. As the number of the plates was increased from 4 to 5, the output power was decreased due to back conversion. We also investigated THz generation by mixing two frequencies generated by a single Nd:YLF solid-state laser. The average output power reached 1 ?W. By introducing two Nd:YLF crystals, we significantly improved the output power to 4.5 ?W. Such a configuration allowed us to generate different output frequencies. We have also reviewed our effort of making the THz source further compact by exploiting passively Q-switched laser pulses.

Ding, Yujie J.; Zhao, Pu; Li, Da

2013-02-01

412

Resolution-enhanced polarization imaging with focused thermal pulses  

NASA Astrophysics Data System (ADS)

The non-destructive measurement of electrical polarization and space charge densities is a key technique in electret research. The principal idea behind these methods is a non-uniform deformation or heating, which gives rise to a short-circuit current that can be recorded in the time or frequency domain, and which carries information about the polarization depth profile. In recent years, thermal pulses and thermal waves have been used successfully to obtain three-dimensional polarization maps in polymeric electrets by scanning the beam of a pulsed or intensity-modulated cw laser across the sample surface. However, the polarization maps in these experiments were reconstructed using a relatively simplistic one-dimensional heat diffusion model that does not take into account lateral heat diffusion in the metal electrode. A two-dimensional ``coupled neighbors'' model was developed, where the current signal from several adjacent beam pointings along a scan line is coupled together, and a Monte Carlo method is used for the deconvolution. Simulations show that the new approach enhances the lateral resolution by a factor of 2-3×, since it avoids the information loss occurring when three-dimensional polarization measurements are processed with a one-dimensional thermal model. We also present an augmented, low-noise thermal-pulse instrument where thermal pulses are initiated by a pulse-modulated diode laser.

Aryal, Saurav; Mellinger, Axel

2013-10-01

413

Green light stimulates terahertz emission from mesocrystal microspheres  

NASA Astrophysics Data System (ADS)

The discovery of efficient sources of terahertz radiation has been exploited in imaging applications, and developing a nanoscale terahertz source could lead to additional applications. High-frequency mechanical vibrations of charged nanostructures can lead to radiative emission, and vibrations at frequencies of hundreds of kilohertz have been observed from a ZnO nanobelt under the influence of an alternating electric field. Here, we observe mechanical resonance and radiative emission at ~0.36 THz from core-shell ZnO mesocrystal microspheres excited by a continuous green-wavelength laser. We find that ~0.016% of the incident power is converted into terahertz radiation, which corresponds to a quantum efficiency of ~33%, making the ZnO microspheres competitive with existing terahertz-emitting materials. The mechanical resonance and radiation stem from the coherent photo-induced vibration of the hexagonal ZnO nanoplates that make up the microsphere shells. The ZnO microspheres are formed by means of a nonclassical, self-organized crystallization process, and represent a straightforward route to terahertz radiation at the nanoscale.

Wu, X. L.; Xiong, S. J.; Liu, Z.; Chen, J.; Shen, J. C.; Li, T. H.; Wu, P. H.; Chu, Paul K.

2011-02-01

414

Combined simulated annealing and Shinnar-Le Roux pulse design of slice-multiplexed RF pulses for multi-slice imaging.  

PubMed

Slice-multiplexed RF pulses have recently been introduced for simultaneous multi-slice imaging. Their novel aspect is that each slice is given a different linear phase profile, and hence a different slice-rephasing requirement, by the pulse. During readout, extra slice gradients are applied such that when one slice is rephased, the others are dephased to prevent aliasing. In this paper, an improved method of designing slice-multiplexed RF pulses is presented: component pulses which are optimized with simulated annealing for a specific rephasing are combined using Shinnar-Le Roux methods. In this way, non-linearities at higher flip angles are taken into account and more slices can be excited. Bloch simulations show the phase and amplitude profile of component pulses are faithfully preserved in the multiplexed pulse. Three- and four-slice multiplex pulses are demonstrated in gradient- and spin-echo in-vivo imaging. PMID:16828567

Lee, K J; Paley, M N J; Wild, J M

2006-07-07

415

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

416

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

417

Low-loss terahertz waveguides exploiting surface-plasmon modes  

Microsoft Academic Search

Finite element analysis, based on the vector H-field formulation and incorporating the perturbation technique, is used to calculate the complex propagation characteristics of silver\\/polystyrene (PS) coated hollow glass waveguides for terahertz (THz) frequency radiation. The mode profiles, which after emerging from the waveguide travel through either a horizontal or vertical polarizer are also presented and camera images of these profiles

B. M. A. Rahman; Christos Themistos; Tanvir Huda; Kenneth T. V. Grattan

2007-01-01

418

Requirements on Photon Counting Detectors for Terahertz Interferometry  

NASA Astrophysics Data System (ADS)

Future Terahertz astronomy requires higher angular resolution observations. One possibility is to use photon counting interferometry, which is similar to the intensity interferometry demonstrated by Hanbury Brown and Twiss in 1956. In terahertz frequencies, it will be possible to measure all the photon arrivals and can identify bunched photons from thermal sources to measure correlation amplitude and time delay of the photon arrivals. By obtaining the complex visibility, aperture synthesis images can be obtained. I name this technology as photon counting terahertz interferometry (PCTI). From scientific case study, requirements to the detectors are high photon counting rate and accurate time resolution. I discuss on requirements on possible detector technologies such as superconducting single photon detectors (SSPD), superconducting tunnel junction (STJ) detectors and charge sensitive infrared photo-transistors (CSIP).

Matsuo, Hiroshi

2012-06-01

419

Helicity sensitive terahertz radiation detection by field effect transistors  

NASA Astrophysics Data System (ADS)

Terahertz light helicity sensitive photoresponse in GaAs/AlGaAs high electron mobility transistors. The helicity dependent detection mechanism is interpreted as an interference of plasma oscillations in the channel of the field-effect-transistors (generalized Dyakonov-Shur model). The observed helicity dependent photoresponse is by several orders of magnitude higher than any earlier reported one. Also, linear polarization sensitive photoresponse was registered by the same transistors. The results provide the basis for a new sensitive, all-electric, room-temperature, and fast (better than 1 ns) characterisation of all polarization parameters (Stokes parameters) of terahertz radiation. It paves the way towards terahertz ellipsometry and polarization sensitive imaging based on plasma effects in field-effect-transistors.

Drexler, C.; Dyakonova, N.; Olbrich, P.; Karch, J.; Schafberger, M.; Karpierz, K.; Mityagin, Yu.; Lifshits, M. B.; Teppe, F.; Klimenko, O.; Meziani, Y. M.; Knap, W.; Ganichev, S. D.

2012-06-01

420

Optimization of pulse train presaturation for CEST imaging in clinical scanners.  

PubMed

Chemical exchange saturation transfer (CEST) imaging depends on the performance of radiofrequency saturation during the experiment. Scanner specifications, in particular limited pulse width and duty-cycle, and specific absorption rate guidelines restrict the full exploitation of CEST effects in clinical MR systems. The purpose of this study was to optimize techniques for effective pulse train presaturation for CEST imaging in a whole-body MR scanner. Theoretical analysis and simulations of the spectral properties of radiofrequency pulse trains demonstrated the significance of pulse width ?(P) and interpulse delay ?(D) for effective and selective labeling of a chemically exchanging proton pool. CEST experiments with model solutions, e.g., creatine dissolved in water, showed best performance of pulse trains with ?(P) = ?(D) = 100 msec, regarding minimum direct water saturation in z-spectra and distinct magnetization transfer ratio asymmetry that can be determined quantitatively. Saturation efficiency of trains of Gaussian-shaped radiofrequency pulses using this timing was evaluated in MR imagers with field strengths of 1.5, 3, and 7 T. The proposed saturation pulse train does not require hardware modifications, offers low specific absorption rate, and can be used in a standard clinical setup. PMID:21337418

Schmitt, Benjamin; Zaiss, Moritz; Zhou, Jinyuan; Bachert, Peter

2011-02-17

421

Tunable narrowband terahertz generation in lithium niobate crystals using a binary phase mask.  

PubMed

We present a simple scheme of narrowband terahertz (THz) generation by optical rectification in the lithium niobate crystal covered by a binary phase mask. It is shown that a single-domain crystal illumination by spatiotemporal shaped fs-laser pulses is equivalent to the formation of a transversally patterned, quasi-phase-matching structure. Decrease of the optical beam size on the mask leads to an increase of the THz-wave linewidth from 17 GHz to a few THz. The frequency of the generation was tuned in the range of 0.4-1.0 THz by building images of the mask in the crystal with various magnifications. Application results of the presented THz source for measuring transmittance of the superconducting NbN thin film in the 4.2-15 K temperature range are also presented. PMID:23503271

Zhang, Caihong; Avetisyan, Yuri; Abgaryan, Gevorg; Kawayama, Iwao; Murakami, Hironaru; Tonouchi, Masayoshi

2013-03-15

422

Time-resolved Terahertz spectroscopy using a Ti:Sapphire laser oscillator  

NASA Astrophysics Data System (ADS)

In time-resolved terahertz spectroscopy, electromagnetic radiation in the frequency range 0.3 - 3 THz (corresponding to wavelengths of 0.1 - 1.0 mm) is used to probe the dynamic properties of charge carriers within materials. When a sample material is excited using an ultrafast optical laser pulse, the terahertz probe that passes through the sample a time later reveals the subsequent behavior of the charge carriers in the sample. Real-time mapping of the dynamics can then be achieved through a pump-probe delay experiment. To date, most time-resolved terahertz spectroscopy has relied on high-power laser systems in order both to excite the sample as well as to generate the probing terahertz radiation. Here, we investigate the feasibility of adapting this technology to a relatively less expensive Ti:sapphire laser oscillator. We present preliminary data and discuss challenges going forward.

Kharel, Pradosh; Waquar, Wassam; Gagnon, Etienne

2013-03-01

423

Measurement of pH in Fluidic Chip Using a Terahertz Chemical Microscope  

NASA Astrophysics Data System (ADS)

A terahertz chemical microscope (TCM) has been developed to visualize the chemical concentration of solutions in fluidic chips. Chemical potential — terahertz transducers were newly developed and applied to the bottom surfaces of the flow channels. When femtosecond laser pulses hit the transducers, terahertz waves are radiated from them. Since the amplitude of terahertz waves can be related to the chemical potential on the surface of the device, the distribution of chemical reactions on the surface can be visualized by scanning the laser on the device. Here, we report the demonstration of mapping of pH values using TCM with a spatial resolution of less than 1 mm. The pH distribution of the flow channels filled with 0.01 M NaOH and HCl was successfully visualized. In addition, the neutralization process was monitored.

Kiwa, Toshihiko; Oka, Shohei; Minami, Yuji; Kawayama, Iwao; Tonouchi, Masayoshi; Tsukada, Keiji

424

Terahertz Frequency Dynamics of Ferroelectric Nanowires  

NASA Astrophysics Data System (ADS)

A thorough understanding of ferroelectric nanostructures is imperative considering their utility in creating nanoscale devices for the technology of the future. One such ferroelectric nanostructure which may prove useful in the design of nanosensors is the nanowire. We report our study on ferroelectric nanowires of Pb(Zr0.4Ti0.6)O3 alloy done using classic molecular dynamics with first-principle-based effective Hamiltonian[1] and Evans-Hoover thermostat. We found that 1) the polarization of such nanowires can be reversed and 2) that the nanowires temperature can be controlled by the application of a terahertz electric field pulse. The dependence of these properties on the frequency, width, and amplitude of the pulse is explored and discussed in addition to a possible energy dissipation mechanism. [1] L. Bellaiche et al, Phys. Rev. Lett. 8, 5427 (2000).

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

2012-02-01

425

Image restoration in chirp-pulse microwave CT (CP-MCT)  

Microsoft Academic Search

Chirp-pulse microwave computed tomography (CP-MCT) is a technique for imaging the distribution of temperature variations inside biological tissues. Even if resolution and contrast are adequate to this purpose, a further improvement of image quality is desirable. In this paper, we discuss the blur of CP-MCT images and we propose a method for estimating the corresponding point spread function (PSF). To

Mario Bertero; Michio Miyakawa; Patrizia Boccacci; Francesco Conte; Kentaroh Orikasa; Masatoshi Furutani

2000-01-01

426

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

427

Effect of pulse slippage on beat wave THz generation in a rippled density magnetized plasma  

NASA Astrophysics Data System (ADS)

Beat wave excitation of terahertz radiation by nonlinear mixing of two laser pulses in a ripple density magnetized plasma is investigated allowing for the effect of pulse slippage. The lasers' ponderomotive-force-induced electron drift couples with the density ripple to produce a nonlinear current that resonantly drives the terahertz at the beat frequency. Density ripple provides the phase matching while the magnetic field, transverse to the direction of laser propagation, provides a transverse component to current density. However, the group velocity mismatch between the lasers and the terahertz radiation leads to slippage of the latter behind the laser pulses leading to saturation of the terahertz amplitude.

Kumar, Manoj; Rajouria, Satish Kumar; K, Magesh Kumar K.

2013-10-01

428

Anisotropic effects of terahertz emission from laser sparks in air  

SciTech Connect

Strong terahertz (THz) radiation can be generated by intense femtosecond laser pulses propagating in air. The excitation of transient current induced in the wake just behind the laser pulse is studied in detail using numerical simulations on the basis of Maxwell's equations for THz-band fields and hydrodynamic model for the plasma motion. It is shown that the thermal effects, anisotropic in character in the case of linear polarized laser field, can explain observed quadrupole-type THz radiation pattern in the experiment performed by Akhmedzhanov et al. [Radiophys. Quantum Electron. 52, 482 (2009)]. Taking into account the transverse structure of the plasma filament, our numerical code enables us to calculate the spatial distribution and temporal evolution of terahertz electron current, its spectrum, and angular emission pattern. It is shown that an expansion of full fields in terms of azimuthal modes is a useful tool for research of THz generation in many situations of practical interest.

Zharova, N. A.; Mironov, V. A.; Fadeev, D. A. [Institute of Applied Physics, Russian Academy of Sciences, 46 Ulianov Street, Nizhny Novgorod 603950 (Russian Federation)

2010-11-15

429

Magneto-optical imaging of magnetic domain pattern produced by intense femtosecond laser pulse irradiation  

NASA Astrophysics Data System (ADS)

An important and intriguing area of research is laser plasma generated giant magnetic field pulses. Interaction of ultrashort high intensity laser pulses with matter involves several mechanisms for generating ultrastrong magnetic fields. By irradiating a magnetic recordable tape constituting of ?-Fe2O3 particles with an intense p-polarized femtosecond laser pulses (˜ 10^16 W cm-2, 100fs), we have found complex magnetic field patterns stored in the tape. We image the local magnetic field distribution around the irradiated region [1] using the high sensitivity magneto-optical imaging technique. We understand the complex magnetic domains patterns recoded on the tape in terms of interesting instabilities [1] generated in the plasma produced during the irradiation of the tape with intense laser pulses. [0pt] [1] Jaivardhan Sinha, Shyam Mohan, S. S Banerjee, S. Kahaly, G. Ravindra Kumar, Phys. Rev. E 77, 046118(2008). *satyajit@iitk.ac.in

Sinha, Jaivarhan; Mohan, Shyam; Banerjee, S. S.; Kahaly, S.; Kumar, G. Ravindra

2009-03-01

430

A Versatile High Speed 250 MHz Pulse Imager for Biomedical Applications  

PubMed Central

A versatile 250 MHz pulse electron paramagnetic resonance (EPR) instrument for imaging of small animals is presented. Flexible design of the imager hardware and software makes it possible to use virtually any pulse EPR imaging modality. A fast pulse generation and data acquisition system based on general purpose PCI boards performs measurements with minimal additional delays. Careful design of receiver protection circuitry allowed us to achieve very high sensitivity of the instrument. In this article we demonstrate the ability of the instrument to obtain three dimensional images using the electron spin echo (ESE) and single point imaging (SPI) methods. In a phantom that contains a 1 mM solution of narrow line (16 ?T, peak-to-peak) paramagnetic spin probe we achieved an acquisition time of 32 seconds per image with a fast 3D ESE imaging protocol. Using an 18 minute 3D phase relaxation (T2e) ESE imaging protocol in a homogeneous sample a spatial resolution of 1.4 mm and a standard deviation of T2e of 8.5% were achieved. When applied to in vivo imaging this precision of T2e determination would be equivalent to 2 torr resolution of oxygen partial pressure in animal tissues.

Epel, Boris; Sundramoorthy, Subramanian V.; Mailer, Colin; Halpern, Howard J.

2009-01-01

431

Temporal self-imaging effects: theory and application for multiplying pulse repetition rates  

Microsoft Academic Search

A time-domain equivalent of the spatial Talbot or self-imaging phenomenon appears when a periodic temporal signal propagates through a dispersive medium under first-order dispersion conditions. The effect is of great interest because it can be applied for multiplying the repetition rate of an arbitrary periodic pulse train without distorting the individual pulse features and essentially without loss of energy. In

José Azańa; Miguel A. Muriel

2001-01-01

432

Study of Optimal Cavity Parameter in Optically Pumped D2O Gas Terahertz Laser  

NASA Astrophysics Data System (ADS)

Heavy water gas (D2O gas) which owns special structure property, can generate terahertz radiation by optically pumping technology, and its 385 ?m wavelength radiation can be widely used. In this research, on the base of semi-classical density matrix theory, we set up a three-level energy system as its theoretical model, a TEA-CO2 laser 9R (22) output line (? = 9.26 ?m) acted as pumping source, D2O gas molecules were operating medium, the expressions of pumping absorption coefficient G p and Terahertz signal gain coefficient G s were deduced. It was shown that the gain of Terahertz signal was related with the energy-level parameters of operating molecules and some operating parameters of the Terahertz laser cavity, mainly including cavity length. By means of iteration method, the output power density of Terahertz pulse signal was calculated numerically. Changing the parameter of cavity length and keeping others steady, the relationship curve between the output power intensity (Is) of Terahertz pulse laser and the operating cavity length (L) was obtained. The curve showed that the power intensity (Is) increased with cavity length (L) in a certain range, but decreased when the length (L) exceeded some value because of the absorption effect, and there was an optimal cavity length for the highest output power. We used a grating tuned TEA-CO2 laser as pumping power and a sample tube of variable length in 70-160 cm as terahertz laser operating cavity to experiment. The results of theoretical calculation and experiment matched with each other, and it is helpful for miniaturizing terahertz laser volume to make it practical.

He, Zhihong; Zhang, Yuping; Zhang, Huiyun; Zhang, Qingmao; Liao, Jianhong; Zhou, Yongheng; Liu, Songhao; Luo, Xizhang

2010-05-01

433

Ultrafast X-ray Experiments Using Terahertz Excitation  

Microsoft Academic Search

With the availability of the first generation of X-ray free electron lasers, pump-probe measurements with femtosecond resolution and high brilliance are now possible. For condensed matter systems, a wealth of modes in the mid-infrared (MIR) and terahertz (THz) regime determine the physics such that targeted excitation with ultrashort pulses at long wavelength becomes an important tool. We will briefly discuss

Matthias C. Hoffmann; Joshua J. Turner

2012-01-01

434

Novosibirsk terahertz free electron laser: instrumentation development and experimental achievements  

Microsoft Academic Search

Nowadays, the Novosibirsk free electron laser (NovoFEL) is the most intense radiation source in the terahertz spectral range. It operates in the continuous mode with a pulse repetition rate of up to 11.2 MHz (5.6 MHz in the standard mode) and an average power of up to 500 W. The radiation wavelength can be precisely tuned from 120 to 240

B A Knyazev; G N Kulipanov; N A Vinokurov

2010-01-01

435

Spectroscopic imaging with improved gradient modulated constant adiabaticity pulses on high-field clinical scanners.  

PubMed

The purpose of this work was to design and implement constant adiabaticity gradient modulated pulses that have improved slice profiles and reduced artifacts for spectroscopic imaging on 3T clinical scanners equipped with standard hardware. The newly proposed pulses were designed using the gradient offset independent adiabaticity (GOIA, Tannus and Garwood[13]) method using WURST modulation for RF and gradient waveforms. The GOIA-WURST pulses were compared with GOIA-HSn (GOIA based on nth-order hyperbolic secant) and FOCI (frequency offset corrected inversion) pulses of the same bandwidth and duration. Numerical simulations and experimental measurements in phantoms and healthy volunteers are presented. GOIA-WURST pulses provide improved slice profile that have less slice smearing for off-resonance frequencies compared to GOIA-HSn pulses. The peak RF amplitude of GOIA-WURST is much lower (40% less) than FOCI but slightly higher (14.9% more) to GOIA-HSn. The quality of spectra as shown by the analysis of lineshapes, eddy currents artifacts, subcutaneous lipid contamination and SNR is improved for GOIA-WURST. GOIA-WURST pulse tested in this work shows that reliable spectroscopic imaging could be obtained in routine clinical setup and might facilitate the use of clinical spectroscopy. PMID:20163975

Andronesi, Ovidiu C; Ramadan, Saadallah; Ratai, Eva-Maria; Jennings, Dominique; Mountford, Carolyn E; Sorensen, A Gregory

2010-01-28

436

Spectroscopic imaging with improved gradient modulated constant adiabaticity pulses on high-field clinical scanners  

NASA Astrophysics Data System (ADS)

The purpose of this work was to design and implement constant adiabaticity gradient modulated pulses that have improved slice profiles and reduced artifacts for spectroscopic imaging on 3 T clinical scanners equipped with standard hardware. The newly proposed pulses were designed using the gradient offset independent adiabaticity (GOIA, Tannus and Garwood [13]) method using WURST modulation for RF and gradient waveforms. The GOIA-WURST pulses were compared with GOIA-HSn (GOIA based on nth-order hyperbolic secant) and FOCI (frequency offset corrected inversion) pulses of the same bandwidth and duration. Numerical simulations and experimental measurements in phantoms and healthy volunteers are presented. GOIA-WURST pulses provide improved slice profile that have less slice smearing for off-resonance frequencies compared to GOIA-HSn pulses. The peak RF amplitude of GOIA-WURST is much lower (40% less) than FOCI but slightly higher (14.9% more) to GOIA-HSn. The quality of spectra as shown by the analysis of lineshapes, eddy currents artifacts, subcutaneous lipid contamination and SNR is improved for GOIA-WURST. GOIA-WURST pulse tested in this work shows that reliable spectroscopic imaging could be obtained in routine clinical setup and might facilitate the use of clinical spectroscopy.

Andronesi, Ovidiu C.; Ramadan, Saadallah; Ratai, Eva-Maria; Jennings, Dominique; Mountford, Carolyn E.; Sorensen, A. Gregory

2010-04-01

437

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

438

Spectroscopic Imaging with Improved Gradient Modulated Constant Adiabadicity Pulses on High-Field Clinical Scanners  

PubMed Central

The purpose of this work was to design and implement constant adiabadicity gradient modulated pulses that have improved slice profiles and reduced artifacts for spectroscopic imaging on 3T clinical scanners equipped with standard hardware. The newly proposed pulses were designed using the gradient offset independent adiabaticity (GOIA, Tannus and Garwood, 1997) method using WURST modulation for RF and gradient waveforms. The GOIA-WURST pulses were compared with GOIA-HSn (GOIA based on nth-order hyperbolic secant) and FOCI (Frequency Offset Corrected Inversion) pulses of the same bandwidth and duration. Numerical simulations and experimental measurements in phantoms and healthy volunteers are presented. GOIA-WURST pulses provide improved slice profile that have less slice smearing for off-resonance frequencies compared to GOIA-HSn pulses. The peak RF amplitude of GOIA-WURST is much lower (40% less) than FOCI but slightly higher (14.9% more) to GOIA-HSn. The quality of spectra as shown by the analysis of line-shapes, eddy currents artifacts, subcutaneous lipid contamination and SNR is improved for GOIA-WURST. GOIA-WURST pulse tested in this work shows that reliable spectroscopic imaging could be obtained in routine clinical setup and might facilitate the use of clinical spectroscopy.

Andronesi, Ovidiu C.; Ramadan, Saadallah; Ratai, Eva-Maria; Jennings, Dominique; Mountford, Carolyn E.; Sorensen, A. Gregory

2011-01-01

439

Preface: Heterostructure terahertz devices  

NASA Astrophysics Data System (ADS)

The terahertz (THz) range of frequencies is borderline between microwave electronics and photonics. It corresponds to the frequency bands of molecular and lattice vibrations in gases, fluids, and solids. The importance of the THz range is in part due to numerous potential and emerging applications which include imaging and characterization, detection of hazardous substances, environmental monitoring, radio astronomy, covert inter-satellite communications, as well as biological and medical applications. During the last decades marked progress has been achieved in the development, fabrication, and practical implementation of THz devices and systems. This is primarily owing to the utilization of gaseous and free electron lasers and frequency converters using nonlinear optical phenomena as sources of THz radiation. However, such devices and hence the systems based on them are fairly cumbersome. This continuously stimulates an extensive search for new compact and efficient THz sources based on semiconductor heterostructures. Despite tremendous efforts lasting several decades, the so-called THz gap unbridged by semiconductor heterostructure electron and optoelectron devices still exists providing appropriate levels of power of the generated THz radiation. The invention and realization of quantum cascade lasers made of multiple quantum-well heterostructures already resulted in the partial solution of the problem in question, namely, in the successful coverage of the high-frequency portion of the THz gap (2-3 THz and higher). Further advancement to lower frequencies meets, perhaps, fundamental difficulties. All this necessitates further extensive theoretical and experimental studies of more or less traditional and novel semiconductor heterostructures as a basis for sources of THz radiation. This special issue includes 11 excellent original papers submitted by several research teams representing 14 institutions in Europe, America, and Asia. Several device concepts which appear to be feasible for the realization of novel THz devices are put forward and discussed in this collection of experimental and theoretical papers. The issue starts with a paper by Akis et al which deals with a theoretical study of the operation of high electron mobility transistors at THz frequencies. For this, the authors use the numerical simulations using a full-band, cellular Monte Carlo transport model coupled to a full Poisson equation solver. The next three papers by Reklaitis, Balocco et al , and Mikhailov and Zieglel are devoted to considering new ideas related to frequency multiplication which can lead to the up-conversion of ac signals to THz frequencies. For this purpose, different concepts of the devices based on nontrivial heterostructures and materials are proposed and studied. The paper by Knap et al provides an overview of the authors experimental results on the plasma effects infield effect transistors. These effects can be used for the resonant detection of THz radiation and its emission. The observed THz emission from more complex device structures, namely, dual grating gate heterostrucures, which is attributed to the self-excitation of plasma waves, is discussed by Otsuji and his co-workers. The following two papers (by Ryzhii et al and Popov et al) deal with the development of device models and using the one which could explain the results of experimental observations described in the paper by Otsuji et al . In both these papers, the mechanisms of plasma wave instability in spatially periodic heterostructures are analyzed. In the paper by Starikov and his colleagues, an idea to utilize the transit-time resonance assisted by optical phonon emissionis revived and revisited. As demonstrated, this mechanism in the electron system in nitride-made heterostructures can lead to negative dynamic conductivity in the THz range of frequencies and, hence, be used for the generation of THz radiation. In the paper by Millithaler et al, Monte Carlo simulations are used to study the voltage fluctuationsaffected by the plasma oscillations in two-terminal

Ryzhii, Victor

2008-08-01

440

Terahertz wave filter based on frequency-selective surface structure  

NASA Astrophysics Data System (ADS)

Terahertz radiations, which refer to the frequencies from 100GHz to 10THz, lie in the frequency gap between the infrared and microwave, have received considerable attention during the past decades. Due to their special prosperties, THz radiations have been applied in many fields such as gases, semiconductors, explosives materials, and environment pollutants. The technique is based on recording the time dependence of the electric field of a short electromagnetic pulse transmitted through a sample. The ratio of the Fourier transforms of the data recorded with and without the sample yields the complex transmission coefficient of the sample in the frequency domain. The absorption coefficient and the refractive index of the material studied are directly related to the amplitude and phase respectively of the transmitted field. Terahertz wave filter, a frequency-selective surface structure, has been characterized by terahertz time-domain spectroscopy in the region from 0.1 to 3THz. We have compared THz-TDS measurement and calculation results of the mode-matching theory of the terahertz wave filter, and find that the two data sets agree very closely. The peak of the transmittance of about 90.5%occurs at 0.45THz for the first case and the peak of the transmittance of about 89.4% occurs at 0.79THz for the second case.

Sun, Chao; Li, Jiu-sheng

2011-11-01

441

Ultrasound contrast imaging: influence of scatterer motion in multi-pulse techniques.  

PubMed

In ultrasound contrast imaging, many techniques based on multiple transmissions have been proposed to increase the contrast-to-tissue ratio (CTR). They are generally based on the response of static scatterers inside the imaged region. However, scatterer motion, for example in blood vessels, has an inevitable influence on multi-pulse techniques, which can either enhance or degrade the technique involved. This paper investigates the response of static nonlinear media insonated by multi-pulses with various phase shifts, and the influence of scatterer motion on multi-pulse techniques. Simulations and experimental results from a single bubble and clouds of bubbles show that the phase shift of the echoes backscattered from bubbles is dependent on the transmissions' phase shift, and that the bubble motion influences the efficiency of multi-pulse techniques: fundamental and second-harmonic amplitudes of the processed signal change periodically, exhibiting maximum or minimum values, according to scatterer motion. Furthermore, experimental results based on the second-harmonic inversion (SHI) technique reveal that bubble motion can be taken into account to regulate the pulse repetition frequency (PRF). With the optimal PRF, the CTR of SHI images can be improved by about 12 dB compared with second-harmonic images. PMID:24081255

Lin, Fanglue; Cachard, Christian; Mori, Riccardo; Varray, Francois; Guidi, Francesco; Basset, Olivier

2013-10-01

442

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

443

Mechanically tunable terahertz metamaterials  

NASA Astrophysics Data System (ADS)

Electromagnetic device design and flexible electronics fabrication are combined to demonstrate mechanically tunable metamaterials operating at terahertz frequencies. Each metamaterial comprises a planar array of resonators on a highly elastic polydimethylsiloxane substrate. The resonance of the metamaterials is controllable through substrate deformation. Applying a stretching force to the substrate changes the inter-cell capacitance and hence the resonance frequency of the resonators. In the experiment, greater than 8% of the tuning range is achieved with good repeatability over several stretching-relaxing cycles. This study promises applications in remote strain sensing and other controllable metamaterial-based devices.

Li, Jining; Shah, Charan M.; Withayachumnankul, Withawat; Ung, Benjamin S.-Y.; Mitchell, Arnan; Sriram, Sharath; Bhaskaran, Madhu; Chang, Shengjiang; Abbott, Derek

2013-03-01

444

Tunable terahertz fishnet metamaterial  

NASA Astrophysics Data System (ADS)

This paper describes and demonstrates a terahertz (THz) frequency tunable fishnet metamaterial (TFMM) using an electrically controlled polymer dispersed liquid crystal (PDLC) matrix. In contrast to other PDLC-based devices, the TFMM employs a novel method for encapsulating PDLC using a thin (1.5 ?m) polyimide ``skin layer'' to form a uniform surface for metal electrodes while minimizing the Fabry-Perot effect of the skin layer on the TFMM measurements. The tunability was verified by measuring the frequency shift in the reflection coefficient (0.01 THz), with an observed minimum negative refractive index of -15 at 0.55 THz.

Chang, Cheng-Ling; Wang, Wei-Chih; Lin, Hong-Ren; Ju Hsieh, Feng; Pun, Yue-Bun; Chan, Chi-Hou

2013-04-01

445

Ultrafast Terahertz Spectroscopy for Measuring Carrier Dynamics in Nanoscale Photovoltaic Materials  

Microsoft Academic Search

Femtosecond pump-probe methods are useful tools for investigating\\u000a transient electronic and vibrational states of conducting materials and\\u000a molecular photochemistry. Ultraviolet and visible excitation pulses\\u000a (150 fs, 20 mu J, 400-800 nm) with time-delayed broadband terahertz\\u000a (similar to 500 GHz to 3 THz) probing pulses (Time-Resolved Terahertz\\u000a Spectroscopy; TRTS) are used to measure linear spectroscopic\\u000a transmission changes resulting from exciton and

Okan Esenturk; Joseph S. Melinger; Edwin J. Heilweil

2010-01-01