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1

Wavelet compression in medical terahertz pulsed imaging  

Microsoft Academic Search

This paper concerns the robustness of discrete wavelet transform (DWT) compression in terahertz pulsed imaging (TPI). TPI datasets consist of terahertz time-domain series which are sampled at each 'pixel' of the image, leading to file sizes which are typically of the order of several megabytes (MB) per image. This makes efficient compression highly desirable for both transmission and storage. However,

J. W. Handley; A. J. Fitzgerald; E. Berry; R. D. Boyle

2002-01-01

2

Wavelet compression in medical terahertz pulsed imaging  

Microsoft Academic Search

This paper concerns the robustness of discrete wavelet transform (DWT) compression in terahertz pulsed imaging (TPI). TPI datasets consist of terahertz time-domain series which are sampled at each ‘pixel’ of the image, leading to file sizes which are typically of the order of several megabytes (MB) per image. This makes efficient compression highly desirable for both transmission and storage. However,

J W Handley; A J Fitzgerald; E Berry; R D Boyle

2002-01-01

3

Terahertz-pulsed imaging of cancers  

NASA Astrophysics Data System (ADS)

Over the last decade advances in laser and semiconductor technology has allowed the investigation of terahertz region of the electromagnetic spectrum as a potential tool for medical imaging. The terahertz frequency range covers the far infrared wavelengths and is sensitive to librational and vibrational modes of molecules. Terahertz radiation is non-ionizing and is not highly scattered like visible and near infrared light. Terahertz Pulsed Imaging (TPI) has already been demonstrated as an effective tool for differentiating between tissue types in particular normal skin and basal cell carcinoma in vitro. TPI may prove advantageous in distinguishing type, lateral spread and depth of tumors. Here we present recent ex vivo results obtained with a portable TPI system in a clinical setting. It is hoped that this technique could be applied to other epithelial tissues, which give rise to more than 80% of all adult cancers and include common cancers of the skin, oral cavity, breast, colon and prostate.

Wallace, Vincent P.; Woodward, Ruth M.; Fitzgerald, Anthony J.; Pickwell, E.; Pye, Richard J.; Arnone, Donald D.

2003-06-01

4

Wavelet compression in medical terahertz pulsed imaging  

NASA Astrophysics Data System (ADS)

This paper concerns the robustness of discrete wavelet transform (DWT) compression in terahertz pulsed imaging (TPI). TPI datasets consist of terahertz time-domain series which are sampled at each 'pixel' of the image, leading to file sizes which are typically of the order of several megabytes (MB) per image. This makes efficient compression highly desirable for both transmission and storage. However, since the data may be required for diagnostic purposes it is essential that no relevant information is lost or artefacts introduced. We show that for a nylon step wedge the estimates of refractive index and absorption coefficients are not significantly altered when the terahertz data are reconstructed from only 20% of DWT coefficients.

Handley, J. W.; Fitzgerald, A. J.; Berry, E.; Boyle, R. D.

2002-11-01

5

Biomedical applications of terahertz pulse imaging  

NASA Astrophysics Data System (ADS)

We present Terahertz Pulse Imaging (TPI) results of different human tissue types. Our results are part of an initial study to explore the potential of TPI for biomedical applications. A survey of different tissue types has demonstrated the various contrast mechanisms that are available in TPI, allowing different tissue types to be readily identified. This encourages the pursuit of further studies of TPI for a variety of biomedical applications.

Ciesla, Craig M.; Arnone, Donald D.; Corchia, Alessandra; Crawley, David A.; Longbottom, Christopher; Linfield, Edmund H.; Pepper, Michael

2000-05-01

6

Consequences for imaging of the broadband nature of terahertz pulses  

Microsoft Academic Search

In terahertz pulsed imaging, sets comprising images at the different frequencies in the terahertz pulse may be generated. These show the frequency-dependent effects of the subject on the radiation. In this pilot work, features of such image sets were studied with a view to their exploitation for image analysis. Data from test objects and from a slice of tooth were

E Berry; S Reed

7

Tissue classification using terahertz pulsed imaging  

NASA Astrophysics Data System (ADS)

We demonstrate the application of terahertz pulsed imaging (TPI) in reflection geometry as a diagnostic aid for epithelial cancer, specifically basal cell carcinoma. Epithelial cancer, which includes skin, breast and colon cancer, accounts for about 85% of all cancers. The terahertz (THz) region is typically defined in the frequency range of 0.1-10 THz. The sensitivity of terahertz radiation to water makes TPI an ideal technique for the study of skin, particularly as cancerous tissue has been shown to contain more water than normal tissue. Twenty-one ex vivo skin samples from a previous study, which successfully identified all 17 samples exhibiting basal cell carcinoma, were analysed in detail using time-domain algorithms to determine the role of TPI as a diagnostic aid. Eight parameters were assessed, four of which were identified as uncorrelated. The samples were classified into two groups: diseased tissue, and tissue without disease. A sensitivity and specificity greater than 80 % for six of the parameters was attained. These results demonstrate the potential of TPI as a diagnostic aid.

Woodward, Ruth M.; Fitzgerald, Anthony J.; Wallace, Vincent P.

2004-07-01

8

Terahertz pulsed spectroscopic imaging using optimized binary masks  

NASA Astrophysics Data System (ADS)

We report the development of a terahertz pulsed spectroscopic imaging system based on the concept of compressive sensing. A single-point terahertz detector, together with a set of 40 optimized two-dimensional binary masks, was used to measure the terahertz waveforms transmitted through a sample. Terahertz time- and frequency-domain images of the sample comprising 20×20 pixels were subsequently reconstructed. We demonstrate that both the spatial distribution and the spectral characteristics of a sample can be obtained by this means. Compared with conventional terahertz pulsed imaging, no raster scanning of the object is required, and ten times fewer terahertz spectra need be taken. It is therefore ideal for real-time imaging applications.

Shen, Y. C.; Gan, L.; Stringer, M.; Burnett, A.; Tych, K.; Shen, H.; Cunningham, J. E.; Parrott, E. P. J.; Zeitler, J. A.; Gladden, L. F.; Linfield, E. H.; Davies, A. G.

2009-12-01

9

Time-Frequency Analysis in Terahertz-Pulsed Imaging  

Microsoft Academic Search

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

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

10

Three-dimensional terahertz pulse imaging of dental tissue  

NASA Astrophysics Data System (ADS)

Generating images of layered tissue structures can give valuable information to clinicians. However, the provision of accurate imaging of certain tissue structures, like teeth, in 3-dimensions is still a difficult problem. We present a method that relies on the use of pulsed Terahertz radiation to gain 3-dimensional information from teeth samples. The method makes use of Terahertz Pulse Imaging (TPI) to provide depth information. Example images are shown where structures in teeth at depth are rendered. We discuss issues that arise using this imaging method and propose ways in which it could be used in clinical practice.

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

2002-04-01

11

Tissue characterization using terahertz pulsed imaging in reflection geometry  

NASA Astrophysics Data System (ADS)

Terahertz pulsed imaging (TPI™) is a non-ionizing and non-destructive imaging technique that has been recently used to study a wide range of biological materials. The severe attenuation of terahertz radiation in samples with high water content means that biological samples need to be very thin if they are to be measured in transmission geometry. To overcome this limitation, samples could be measured in reflection geometry and this is the most feasible way in which TPI could be performed in a clinical setting. In this study, we therefore used TPI in reflection geometry to characterize the terahertz properties of several organ samples freshly harvested from laboratory rats. We observed differences in the measured time domain responses and determined the frequency-dependent optical properties to characterize the samples further. We found statistically significant differences between the tissue types. These results show that TPI has the potential to accurately differentiate between tissue types non-invasively.

Huang, S. Y.; Wang, Y. X. J.; Yeung, D. K. W.; Ahuja, A. T.; Zhang, Y.-T.; Pickwell-MacPherson, E.

2009-01-01

12

Terahertz pulsed imaging and spectroscopy of breast tumors  

NASA Astrophysics Data System (ADS)

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 were used to provide contrast. The size and shape of tumour regions in the terahertz images were compared with the corresponding histology section. Good correlation was found for area and shape of tumour in the THz images compared to that of histology. In addition, we have also performed spectroscopy study comparing the terahertz properties (absorption coefficient and refractive index) of excised normal breast skin and breast tumor. Both the absorption coefficient and refractive index were higher for tissue containing tumor compared to normal. These changes are consistent with higher water content and structural changes, like increased cell and protein density. This study demonstrates the potential of TPI to image both invasive breast carcinomas and ductal carcinoma in situ using THz and encourages further studies.

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

2006-11-01

13

Compression of Pulsed Terahertz Image Using Discrete Wavelet Transform  

NASA Astrophysics Data System (ADS)

We present the result of data compression using discrete wavelet transform (DWT) in terahertz pulsed imaging (TPI). A test object composed of dielectric materials is imaged by a fast oscillating delay line in reflection geometry. In general, because the size of the original image is from several megabytes (MB) to tens of MB, an adequate compression algorithm that prevents the loss of relevant information is indispensable. We analyze the image by multilevel DWT and obtain the wavelet coefficients of the levels. The images reconstructed from some of the coefficients are compared with the original image. The reconstructed pulse signals and their frequency-domain spectrums for each pixel are compared with the original signals to obtain the optimum decomposition level. The image could be compressed below 15% of its original size without loss of image quality and significant errors in the time and frequency domains.

Shon, Chae-Hwa; Chong, Won-Yong; Kim, Geun-Ju; Jeon, Seok-Gy; Kim, Jung-Il; Jin, Yun-Sik

2007-12-01

14

Visualization and classification in biomedical terahertz pulsed imaging  

NASA Astrophysics Data System (ADS)

'Visualization' in imaging is the process of extracting useful information from raw data in such a way that meaningful physical contrasts are developed. 'Classification' is the subsequent process of defining parameter ranges which allow us to identify elements of images such as different tissues or different objects. In this paper, we explore techniques for visualization and classification in terahertz pulsed imaging (TPI) for biomedical applications. For archived (formalin-fixed, alcohol-dehydrated and paraffin-mounted) test samples, we investigate both time- and frequency-domain methods based on bright- and dark-field TPI. Successful tissue classification is demonstrated.

Löffler, Torsten; Siebert, Karsten; Czasch, Stephanie; Bauer, Tobias; Roskos, Hartmut G.

2002-11-01

15

A promising diagnostic method: Terahertz pulsed imaging and spectroscopy  

PubMed Central

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

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

2011-01-01

16

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

NASA Astrophysics Data System (ADS)

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. By studying the terahertz pulse shape in the time domain we have been able to differentiate between diseased and normal tissue for the study of basal cell carcinoma (BCC). Basal cell carcinoma has shown a positive terahertz contrast, and inflammation and scar tissue a negative terahertz contrast compared to normal tissue. In vivo measurements on the stratum corneum have enabled visualization of the stratum corneum-epidermis interface and the study of skin hydration levels. These results demonstrate the potential of terahertz pulse imaging for the study of skin tissue and its related disorders, both in vitro and in vivo.

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

2002-11-01

17

Development and Application of Terahertz Pulsed Imaging for Nondestructive Inspection of Pharmaceutical Tablet  

Microsoft Academic Search

Terahertz pulsed imaging (TPI) was evaluated for nondestructively characterizing the 3-D internal structures of pharmaceutical tablets. The structural information of a pharmaceutical tablet, such as coating thickness and interface uniformity, was obtained directly from the analysis of the time-domain terahertz waveform. The chemical map of a sample was obtained by using frequency-domain terahertz spectra, together with spectral matching techniques such

Yao-Chun Shen; Philip F. Taday

2008-01-01

18

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

19

TOPICAL REVIEW: Pulsed terahertz tomography  

Microsoft Academic Search

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

S. Wang; X.-C. Zhang

2004-01-01

20

Terahertz polarization imaging  

NASA Astrophysics Data System (ADS)

We present a new method to measure the polarization state of a terahertz pulse by using a modified electro-optic sampling setup. To illustrate the power of this method, we show two examples in which the knowledge of the polarization of the terahertz pulse is essential for interpreting the results: spectroscopy measurements on polystyrene foam and terahertz images of a plastic coin. Both measurements show a sample-induced rotation of the terahertz electric field vector, which is surprisingly large and is a strong function of frequency. A promising aspect of our setup is the possibility of simultaneously measuring both transversal electric field components.

van der Valk, Nick C. J.; van der Marel, Willemine A. M.; Planken, Paul C. M.

2005-10-01

21

Terahertz polarization imaging.  

PubMed

We present a new method to measure the polarization state of a terahertz pulse by using a modified electro-optic sampling setup. To illustrate the power of this method, we show two examples in which the knowledge of the polarization of the terahertz pulse is essential for interpreting the results: spectroscopy measurements on polystyrene foam and terahertz images of a plastic coin. Both measurements show a sample-induced rotation of the terahertz electric field vector, which is surprisingly large and is a strong function of frequency. A promising aspect of our setup is the possibility of simultaneously measuring both transversal electric field components. PMID:16252780

van der Valk, Nick C J; van der Marel, Willemine A M; Planken, Paul C M

2005-10-15

22

Terahertz pulse imaging in reflection geometry of skin tissue using time-domain analysis techniques  

NASA Astrophysics Data System (ADS)

We demonstrate the application of Terahertz Pulse Imaging (TPI) in reflection geometry for the study of skin tissue and related cancers. The terahertz frequency regime of 0.1-100THz excites the vibrational modes of molecules, allowing for spectroscopic investigation. The sensitivity of terahertz to polar molecules, such as water, makes TPI suitable for studying the hydration levels in the stratum corneum and the determination of the lateral spread of skin cancer pre-operatively. By studying the terahertz pulse shape in the time domain we have been able to differentiate between diseased and normal tissue for the study of basal cell carcinoma (BCC). Measurements on scar tissue, which is known to contain less water than the surrounding skin, and on regions of inflammation, show a clear contrast in the THz image compared to normal skin. We discuss the time domain analysis techniques used to classify the different tissue types. Basal cell carcinoma shows a positive terahertz contrast, and inflammation and scar tissue shows a negative terahertz contrast compared to normal tissue. This demonstrates for the first time the potential of TPI both in the study of skin cancer and inflammatory related disorders.

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

2002-06-01

23

Terahertz imaging for styrofoam inspection  

NASA Astrophysics Data System (ADS)

Imaging of styrofoam with the help of ultrashort Terahertz pulses is investigated. With a combination of pulse amplitude and time delay imaging it is possible to speed up the measurement about two orders of magnitudes.

Pradarutti, B.; Riehemann, S.; Notni, G.; Tünnermann, A.

2007-09-01

24

High Speed Terahertz Pulse Imaging in the Reflection Geometry and Image Quality Enhancement by Digital Image Processing  

NASA Astrophysics Data System (ADS)

We describe the formation and enhancement of two dimensional pulsed terahertz (THz) images obtained in the reflection geometry with a high-speed optical delay line. Two test objects are imaged and analyzed with respect to material information and concealed structure. Clear THz images were obtained with various imaging modes and were compared with the X-ray images. The THz image of a sample revealed material features that the X-ray image cannot distinguish. We could enhance the THz image quality using various image processing techniques, such as edge detection, de-noising, high-pass filtering, and wavelet filtering.

Shon, Chae-Hwa; Chong, Won-Yong; Jeon, Seok-Gy; Kim, Geun-Ju; Kim, Jung-Il; Jin, Yun-Sik

2008-01-01

25

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

SciTech Connect

Near-monocycle terahertz (THz)-bandwidth electromagnetic pulses have been used to probe pulsed-discharge argon plasmas at various pressures from 10 to 50 Torr. Time-resolved electric field measurements were made of the THz pulse with and without plasma allowing a full characterization of the real and imaginary parts of the plasma index of refraction. Electron densities n{sub e}{>=}10{sup 13} cm{sup -3} and collision rates {gamma}{sub p}{>=}10{sup 11} s{sup -1} were deduced by applying a simple Lorentz model to the measured time-domain pulse with no plasma and comparing it to the measured pulse with the plasma present. Minimizing the rms error between these in the two-dimensional parameter space (n{sub e},{gamma}{sub p}) fixed the values for each point in time of the plasma evolution. Optical fluorescence imaged transverse to the THz beam path was used to estimate the density profile used in the propagation model.

Kolner, B.H.; Conklin, P.M.; Buckles, R.A.; Fontaine, N.K.; Scott, R.P. [Department of Applied Science, University of California, Davis, One Shields Avenue, Davis, California 95616 (United States)

2005-10-10

26

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

Microsoft Academic Search

Near-monocycle terahertz (THz)-bandwidth electromagnetic pulses have been used to probe pulsed-discharge argon plasmas at various pressures from 10 to 50 Torr. Time-resolved electric field measurements were made of the THz pulse with and without plasma allowing a full characterization of the real and imaginary parts of the plasma index of refraction. Electron densities ne>=1013 cm-3 and collision rates gammap>=1011 s-1

B. H. Kolner; P. M. Conklin; R. A. Buckles; N. K. Fontaine; R. P. Scott

2005-01-01

27

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

28

Terahertz pulse imaging: a pilot study of potential applications in dentistry.  

PubMed

The improvement in the detection of caries offers the possibility for dramatic improvement in dental healthcare. Current caries detection rates suggest that there may be scope for improvement. This paper describes a preliminary study to examine applications of terahertz pulse imaging (TPI) to caries detection. We present results for the detection of early stage caries in the occlusal enamel layer of a range of human tooth cross sections using TPI. Higher attenuation of terahertz radiation was observed in carious enamel as compared with healthy enamel. Hypomineralised enamel had different absorption spectra and contrast compared to carious enamel in TPI images. These results have important implications for extending TPI to other medical imaging applications where both early diagnosis and safety issues are important. PMID:12925826

Crawley, David A; Longbottom, Christopher; Cole, Bryan E; Ciesla, Craig M; Arnone, Don; Wallace, Vincent P; Pepper, Michael

2003-01-01

29

Terahertz pulsed imaging of freshly excised human colonic tissues  

NASA Astrophysics Data System (ADS)

We present the results from a feasibility study which measures properties in the terahertz frequency range of excised cancerous, dysplastic and healthy colonic tissues from 30 patients. We compare their absorption and refractive index spectra to identify trends which may enable different tissue types to be distinguished. In addition, we present statistical models based on variations between up to 17 parameters calculated from the reflected time and frequency domain signals of all the measured tissues. These models produce a sensitivity of 82% and a specificity of 77% in distinguishing between healthy and all diseased tissues and a sensitivity of 89% and a specificity of 71% in distinguishing between dysplastic and healthy tissues. The contrast between the tissue types was supported by histological staining studies which showed an increased vascularity in regions of increased terahertz absorption.

Reid, Caroline B.; Fitzgerald, Anthony; Reese, George; Goldin, Robert; Tekkis, Paris; O'Kelly, P. S.; Pickwell-MacPherson, Emma; Gibson, Adam P.; Wallace, Vincent P.

2011-07-01

30

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

PubMed Central

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

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

2013-01-01

31

Terahertz pulsed imaging study to assess remineralization of artificial caries lesions  

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

32

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

33

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

PubMed

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

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

2013-12-01

34

Non-destructive quantification of pharmaceutical tablet coatings using terahertz pulsed imaging and optical coherence tomography  

NASA Astrophysics Data System (ADS)

Optical coherence tomography (OCT) and terahertz pulsed imaging (TPI) are two powerful techniques allowing high quality cross-sectional images from within scattering media to be obtained non-destructively. In this paper, we report experimental results of using OCT and TPI for quantitatively characterizing pharmaceutical tablet coatings in the thickness range of 10-140 ?m. We found that the spectral OCT system developed in-house has an axial resolution of 0.9 ?m, and is capable of quantifying very thin coatings in the range of 10-60 ?m. The upper limit of 60 ?m within the tablet coating and core is owed to the strong scattering of OCT light, which has relatively short wavelengths in the range of 0.5-1.0 ?m. On the other hand, TPI utilizes terahertz radiation that has substantially long wavelengths in the range of hundreds of microns, and thus is less prone to the scattering problem. Consequently TPI has been demonstrated to be able to quantify thicker coatings in the range of 40-140 ?m and beyond. We concluded that OCT and TPI are two complementary analytical techniques for non-destructive and quantitative characterization of pharmaceutical tablet coatings.

Zhong, Shuncong; Shen, Yao-Chun; Ho, Louise; May, Robert K.; Zeitler, J. Axel; Evans, Mike; Taday, Philip F.; Pepper, Michael; Rades, Thomas; Gordon, Keith C.; Müller, Ronny; Kleinebudde, Peter

2011-03-01

35

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

PubMed

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

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

2013-12-01

36

Terahertz pulse imaging of stratified architectural materials for cultural heritage studies  

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

37

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

PubMed

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

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

2013-07-01

38

Electro-optic measurement of terahertz pulse energy distribution.  

PubMed

An accurate and direct measurement of the energy distribution of a low repetition rate terahertz electromagnetic pulse is challenging because of the lack of sensitive detectors in this spectral range. In this paper, we show how the total energy and energy density distribution of a terahertz electromagnetic pulse can be determined by directly measuring the absolute electric field amplitude and beam energy density distribution using electro-optic detection. This method has potential use as a routine method of measuring the energy density of terahertz pulses that could be applied to evaluating future high power terahertz sources, terahertz imaging, and spatially and temporarily resolved pump-probe experiments. PMID:19947713

Sun, J H; Gallacher, J G; Brussaard, G J H; Lemos, N; Issac, R; Huang, Z X; Dias, J M; Jaroszynski, D A

2009-11-01

39

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

NASA Astrophysics Data System (ADS)

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

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

2002-06-01

40

Multiply scattered broadband terahertz pulses  

Microsoft Academic Search

We describe measurements of single-cycle terahertz pulse propagation in a random medium. The unique capabilities of terahertz time-domain spectroscopy permit the characterization of a multiply scattered field with unprecedented temporal resolution. With these results, we can develop a framework for understanding the statistics of broadband laser speckle. We also describe recent measurements of the polarization dynamics of these diffusively propagating

J. Pearce; Zhongping Jian; D. M. Mittleman

2004-01-01

41

Terahertz multistatic reflection imaging.  

PubMed

We describe a new imaging method using single-cycle pulses of terahertz (THz) radiation. This technique emulates the data collection and image processing procedures developed for geophysical prospecting and is made possible by the availability of fiber-coupled THz receiver antennas. We use a migration procedure to solve the inverse problem; this permits us to reconstruct the location, the shape, and the refractive index of targets. We show examples for both metallic and dielectric model targets, and we perform velocity analysis on dielectric targets to estimate the refractive indices of imaged components. These results broaden the capabilities of THz imaging systems and also demonstrate the viability of the THz system as a test bed for the exploration of new seismic processing methods. PMID:12095212

Dorney, Timothy D; Symes, William W; Baraniuk, Richard G; Mittleman, Daniel M

2002-07-01

42

Terahertz imaging with compressive sensing  

NASA Astrophysics Data System (ADS)

Most existing terahertz imaging systems are generally limited by slow image acquisition due to mechanical raster scanning. Other systems using focal plane detector arrays can acquire images in real time, but are either too costly or limited by low sensitivity in the terahertz frequency range. To design faster and more cost-effective terahertz imaging systems, the first part of this thesis proposes two new terahertz imaging schemes based on compressive sensing (CS). Both schemes can acquire amplitude and phase-contrast images efficiently with a single-pixel detector, thanks to the powerful CS algorithms which enable the reconstruction of N-by- N pixel images with much fewer than N2 measurements. The first CS Fourier imaging approach successfully reconstructs a 64x64 image of an object with pixel size 1.4 mm using a randomly chosen subset of the 4096 pixels which defines the image in the Fourier plane. Only about 12% of the pixels are required for reassembling the image of a selected object, equivalent to a 2/3 reduction in acquisition time. The second approach is single-pixel CS imaging, which uses a series of random masks for acquisition. Besides speeding up acquisition with a reduced number of measurements, the single-pixel system can further cut down acquisition time by electrical or optical spatial modulation of random patterns. In order to switch between random patterns at high speed in the single-pixel imaging system, the second part of this thesis implements a multi-pixel electrical spatial modulator for terahertz beams using active terahertz metamaterials. The first generation of this device consists of a 4x4 pixel array, where each pixel is an array of sub-wavelength-sized split-ring resonator elements fabricated on a semiconductor substrate, and is independently controlled by applying an external voltage. The spatial modulator has a uniform modulation depth of around 40 percent across all pixels, and negligible crosstalk, at the resonant frequency. The second-generation spatial terahertz modulator, also based on metamaterials with a higher resolution (32x32), is under development. A FPGA-based circuit is designed to control the large number of modulator pixels. Once fully implemented, this second-generation device will enable fast terahertz imaging with both pulsed and continuous-wave terahertz sources.

Chan, Wai Lam

43

Evaluating the effect of coating equipment on tablet film quality using terahertz pulsed imaging.  

PubMed

In this study, terahertz pulsed imaging (TPI) was employed to investigate the effect of the coating equipment (fluid bed and drum coater) on the structure of the applied film coating and subsequent dissolution behaviour. Six tablets from every batch coated with the same delayed release coating formulation under recommended process conditions (provided by the coating polymer supplier) were mapped individually to evaluate the effect of coating device on critical coating characteristics (coating thickness, surface morphology and density). Although the traditional coating quality parameter (weight gain) indicated no differences between both batches, TPI analysis revealed a lower mean coating thickness (CT) for tablets coated in the drum coater compared to fluid bed coated tablets (p<0.05). Moreover, drum coated tablets showed a more pronounced CT variation between the two sides and the centre band of the biconvex tablets, with the CT around the centre band being 22.5% thinner than the top and bottom sides for the drum coated tablets and 12.5% thinner for fluid bed coated tablets. The TPI analysis suggested a denser coating for the drum coated tablets. Dissolution testing confirmed that the film coating density was the drug release governing factor, with faster drug release for tablets coated in the fluid bed coater (98 ± 4% after 6h) compared to drum coated tablets (72 ± 6% after 6h). Overall, TPI investigation revealed substantial differences in the applied film coating quality between tablets coated in the two coaters, which in turn correlated with the subsequent dissolution performance. PMID:23563103

Haaser, Miriam; Naelapää, Kaisa; Gordon, Keith C; Pepper, Michael; Rantanen, Jukka; Strachan, Clare J; Taday, Philip F; Zeitler, J Axel; Rades, Thomas

2013-11-01

44

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

45

Terahertz pulse driven Josephson junctions  

NASA Astrophysics Data System (ADS)

The voltage response of a Josephson junction to a pulsed terahertz current is evaluated in the limit of a negligible junction capacitance (overdamped limit). The time-dependent superconductor phase difference across the junction is calculated in the framework of the standard resistive shunted junction model by using a perturbative method. The pulsed current bias affects the time average value of the voltage across the junction and current steps are induced in the current-voltage characteristics for voltage values depending on the pulse repetition rate. The current step height is proportional to the square of the pulse time width ( ?) to the period ( T) ratio. A fast response detector for pulsed Terahertz radiation is proposed, with an expected responsivity of the order of 0.1 V/W and an equivalent noise power of about 3 × 10 -10 W/Hz 1/2.

Camerlingo, Carlo

2011-09-01

46

Holography and phase retrieval in terahertz imaging  

NASA Astrophysics Data System (ADS)

In this paper, we present review and latest results obtained in the scope of terahertz holographic and other methods for phase retrieval in terahertz imaging. Not only accurate change of amplitude, but also rigorous phase retrieval is essential for precise calculation of optical parameters of the samples in terahertz range. Pulse terahertz holography introduced some years ago shows itself as perfect method for overall-object phase retrieval technique, but in the same time it allows measurement with low signal to noise that leads to less precise derivation of sample optical parameters. And certainly just point-by-point terahertz time-domain spectroscopy provides the most precise information of sample phase, but it is rather time consuming and has low spatial resolution as well. The other possible way assumes, in contrary to pulse terahertz holography and spectroscopy, using narrow-band continuous terahertz source, which tunability might also make the measurement process easier. And diffraction patterns registered with microbolometer array or any other terahertz intensity sensor placed at several different distances from the object and/or taken for several different terahertz frequencies are used for phase retrieval in this case. We present both numerical predictions and experimental results for the proposed methods, estimate the achievable spatial and other limits of the techniques and compare them to the others used in different spectral ranges.

Petrov, Nikolay V.; Gorodetsky, Andrei A.; Bespalov, Victor G.

2013-09-01

47

Spectrum to space transformed fast terahertz imaging.  

PubMed

We present an imaging technique in which the broadband frequency information of terahertz (THz) pulses is transformed into spatial resolution. Efficient blazed diffractive gratings spread the individual frequency components over a wide and defined spatial range and f-theta optics are employed to focus the individual components onto a one-dimensional image-line. Measuring the time domain waveform of the THz waves allows therefore for a direct reconstruction of spatial sample characteristics as the spatial domain information is encoded in the terahertz spectrum. We will demonstrate terahertz imaging on selected samples with an improvement in acquisition speed up to two orders of magnitude. PMID:23038561

Schumann, Steffen; Jansen, Christian; Schwerdtfeger, Michael; Busch, Stefan; Peters, Ole; Scheller, Maik; Koch, Martin

2012-08-13

48

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

49

Terahertz imaging for non-destructive evaluation of mural paintings  

NASA Astrophysics Data System (ADS)

The feasibility of applying time-domain, terahertz spectroscopic imaging to the evaluation of underdrawings and paint layers embedded within wall paintings is demonstrated. Metallic and dielectric paint patterns and a graphite drawing are resolved through both paint and plaster overlayers using a pulsed-terahertz reflectometer and imaging system. We calculated the bulk refractive indices of four common pigments and used them to confirm color domains in a terahertz-beam spectral image of a painting.

Jackson, J. B.; Mourou, M.; Whitaker, J. F.; Duling, I. N.; Williamson, S. L.; Menu, M.; Mourou, G. A.

2008-02-01

50

Polarization information for terahertz imaging.  

PubMed

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

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

2008-12-01

51

Prediction of dissolution time and coating thickness of sustained release formulations using Raman spectroscopy and terahertz pulsed imaging.  

PubMed

Raman spectroscopy was implemented successfully as a non-invasive and rapid process analytical technology (PAT) tool for in-line quantitative monitoring of functional coating. Coating experiments were performed at which diprophylline tablets were coated with a sustained release formulation based on Kollicoat SR 30 D. Using PLS a multivariate model was constructed by correlating Raman spectral data with the mean dissolution time as determined by dissolution testing and the coating thickness as measured by terahertz pulsed imaging. By performing in-line measurements it was possible to monitor the progress of the coating process and to detect the end point of the process, where the acquired coating amount was achieved for the desired MDT or coating thickness. PMID:22245221

Müller, Joshua; Brock, Daniela; Knop, Klaus; Axel Zeitler, J; Kleinebudde, Peter

2012-04-01

52

Continuous-wave terahertz imaging of nonmelanoma skin cancers  

NASA Astrophysics Data System (ADS)

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

Joseph, Cecil Sudhir

53

Terahertz imaging for non-destructive evaluation of mural paintings  

Microsoft Academic Search

The feasibility of applying time-domain, terahertz spectroscopic imaging to the evaluation of underdrawings and paint layers embedded within wall paintings is demonstrated. Metallic and dielectric paint patterns and a graphite drawing are resolved through both paint and plaster overlayers using a pulsed-terahertz reflectometer and imaging system. We calculated the bulk refractive indices of four common pigments and used them to

J. B. Jackson; M. Mourou; J. F. Whitaker; I DULINGIII; S. L. Williamson; M. Menu; G. A. Mourou

2008-01-01

54

Applications of terahertz (THz) technology to medical imaging  

Microsoft Academic Search

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

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

1999-01-01

55

Comparison of Terahertz Pulse Imaging and Near-Infrared Spectroscopy for Rapid, Non-Destructive Analysis of Tablet Coating Thickness and Uniformity  

Microsoft Academic Search

In this study, coating thickness and uniformity of production-scale pharmaceutical tablets were investigated using near-infrared\\u000a (NIR) and terahertz pulse imaging (TPI) spectroscopy. Two coating formulations were considered; samples for each coating formulation\\u000a were obtained at 0, 1, 2, 3, 4, and 5% coating weight. NIR spectra were collected, and regressed with respect to batch percent\\u000a weight gain. While standard errors

Robert P. Cogdill; Ryanne N. Forcht; Yaochun Shen; Philip F. Taday; J. Richard Creekmore; Carl A. Anderson; James K. Drennen

2007-01-01

56

Metal wire waveguides for broadband terahertz pulses  

Microsoft Academic Search

Guided propagation of terahertz pulses on metal wires, characterized with the direct measurement of the electric field in the time domain, shows record low loss and negligible group velocity dispersion.

Kanglin Wang; D. M. Mittleman

2004-01-01

57

Terahertz imaging using full-field electrooptic sampling  

Microsoft Academic Search

Real time terahertz imaging is emerging as an important non-destructive imaging tool for medical, quality control, security and other industrial applications. In this thesis, we demonstrate real-time full-field terahertz (THz) imaging of still, moving, and concealed objects, and real-time THz images of the field distribution on the imaging plane. A femtosecond laser pulse from an amplified Ti:sapphire laser system with

Ayesheshim Kebie Ayesheshim

2009-01-01

58

Terahertz imaging using an interferometric array  

NASA Astrophysics Data System (ADS)

Most methods of imaging in the terahertz (THz) spectral region utilize either pulsed-laser sources or require the THz generation and detection sources to be phase coherent. The application of interferometric imaging to the THz range is described. Interferometric imaging offers considerable advantages in this regard due to its ability to image with only a handful of detector elements, image many sources of THz radiation at once, image incoherent as well as coherent sources, and provide spectral information as well as spatial imaging information. The THz interferometric imaging method is potentially useful for remote detection of explosives.

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

2003-09-01

59

Applications of terahertz-pulsed technology in the pharmaceutical industry  

NASA Astrophysics Data System (ADS)

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

Taday, Philip F.

2010-02-01

60

Principle and applications of terahertz molecular imaging  

NASA Astrophysics Data System (ADS)

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

Son, Joo-Hiuk

2013-05-01

61

Non-invasive investigation of art paintings by terahertz imaging  

NASA Astrophysics Data System (ADS)

Terahertz electromagnetic waves propose attractive features such as non-invasive and non-destructive analysis, transparency and good penetration depth through various materials, low scattering and broad spectral bandwidth. In this paper, we demonstrate the capability of terahertz imaging for the investigation of art paintings. The imaging system is able to reveal buried layer information such as a graphite handmade sketch covered by several layers of painting. In addition, taking advantage of the pulsed terahertz emission, we show that it is also possible to evaluate the variations of the painting thickness.

Abraham, E.; Younus, A.; Delagnes, J. C.; Mounaix, P.

2010-09-01

62

Optimal chirped probe pulse length for terahertz pulse measurement.  

PubMed

A detailed analysis of the relationship between the duration of the chirped probe pulse and the bipolar terahertz (THz) pulse length in the spectral encoding technique is carried out. We prove that there is an optimal chirped probe pulse length (or an optimal chirp rate of the chirped probe pulse) matched to the input THz pulse length and derive a rigorous relationship between them. We find that only under this restricted condition the THz signal can be correctly retrieved. PMID:18679511

Peng, Xiao-Yu; Willi, Oswald; Chen, Min; Pukhov, Alexander

2008-08-01

63

Terahertz spectroscopy and imaging for material analysis in conservation science  

Microsoft Academic Search

Terahertz (THz) waves can penetrate opaque materials and fingerprint spectra appear as those in infrared bands. The technique is expected to be used as a new non-invasive analysis method for various materials. Time domain reflection imaging, in particular, uses THz pulses that propagate in specimens, and in this technique, pulses reflected from the internal boundaries of the specimen indicate the

Kaori Fukunaga; Iwao Hosako; Marcello Picollo

2010-01-01

64

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

65

Terahertz imaging applied to cancer diagnosis.  

PubMed

We report on terahertz (THz) time-domain spectroscopy imaging of 10 microm thick histological sections. The sections are prepared according to standard pathological procedures and deposited on a quartz window for measurements in reflection geometry. Simultaneous acquisition of visible images enables registration of THz images and thus the use of digital pathology tools to investigate the links between the underlying cellular structure and specific THz information. An analytic model taking into account the polarization of the THz beam, its incidence angle, the beam shift between the reference and sample pulses as well as multiple reflections within the sample is employed to determine the frequency-dependent complex refractive index. Spectral images are produced through segmentation of the extracted refractive index data using clustering methods. Comparisons of visible and THz images demonstrate spectral differences not only between tumor and healthy tissues but also within tumors. Further visualization using principal component analysis suggests different mechanisms as to the origin of image contrast. PMID:20671358

Brun, M-A; Formanek, F; Yasuda, A; Sekine, M; Ando, N; Eishii, Y

2010-08-21

66

Study on terahertz emission and optical/terahertz pulse responses with superconductors  

NASA Astrophysics Data System (ADS)

Recent progress in terahertz technology has enabled precise investigation of the ultrafast dynamics of excited carriers, nonequilibrium state and nonlinear response of superconductors, resulting in the proposal of novel optoelectronic device applications based on such ultrafast perturbation of supercarriers in the terahertz frequency region. In this paper, we focus on exploratory research in the field of superconductor terahertz science and technology, and present a review of superconducting terahertz sources and the response of superconductors excited by ultrashort electromagnetic pulses, including optical pulses and high-intensity THz pulses.

Kawayama, Iwao; Zhang, Caihong; Wang, Huabing; Tonouchi, Masayoshi

2013-09-01

67

Statistics of Multiply Scattered Broadband Terahertz Pulses  

Microsoft Academic Search

We describe the first measurements of the diffusion of broadband single-cycle optical pulses through a highly scattering medium. Using terahertz time-domain spectroscopy, we measure the electric field of a multiply scattered wave with a time resolution shorter than one optical cycle. This time-domain measurement provides information on the statistics of both the amplitude and phase distributions of the diffusive wave.

Jeremy Pearce; Zhongping Jian; Daniel Mittleman

2003-01-01

68

Pulsed terahertz inspection of non-conducting sandwich composites  

NASA Astrophysics Data System (ADS)

Pulsed terahertz inspection enables accurate, contactless and safe for operating personnel evaluation of non-conducting structures. In this paper we present results of pulsed terahertz testing of various sandwich composite structures incorporating glass and basalt fibers based skin materials and spherecore and balsa wood based core materials. Various Time-Frequency Distributions (TFD) are utilized in order to obtain most valuable defects response.

Lopato, P.; Chady, T.

2013-01-01

69

Terahertz imaging and international safety guidelines  

NASA Astrophysics Data System (ADS)

Terahertz (THz) radiation has a frequency of the order of 101212 Hz. This lies between the infrared and microwave regions of the electromagnetic spectrum; a section labeled the 'THz gap'. Infrared and microwave radiation is used in the medical field; research is underway for an application for THz radiation. At present no formal safety analysis of a THz pulsed imaging (TPI) system has been performed. This will be necessary for future in vivo studies. The radiation is delivered in a train of femtosecond pulses. International guidelines on exposure to non-ionizing radiation, and supporting literature, were reviewed to determine the Maximum Permissible Exposure (MPE) for radiation of this range of wavelengths, both for a single pulse and continuous wave exposure. Two methods of deriving the MPE were identified. Current guidelines for infrared and microwave regions of the electromagnetic spectrum incorporate the THz region. Using conservative parameter estimation an MPE per pulse, over the area of the beam, of 94 W was calculated. At present THz pulsed imaging systems produce pulses of power approximately 1 mW; this lies within the limit calculated using the published guidelines. There are, however, areas requiring further investigation before the technique becomes routine in clinical practice.

Walker, Gillian C.; Berry, Elizabeth; Zinov'ev, Nick N.; Fitzgerald, Anthony J.; Miles, Robert E.; Chamberlain, J. Martyn; Smith, Michael A.

2002-05-01

70

Broadband terahertz pulse propagation in strongly scattering random media  

Microsoft Academic Search

We report on studies of terahertz pulse propagation in strongly scattering random media. The experimental delay, pulse distortion, spectral decay, and power attenuation are in excellent agreement with predictions from a Monte Carlo model.

K. J. Chau; S. Mujumdar; A. Y. Elezzabi

2005-01-01

71

A comparison of terahertz-pulsed imaging with transverse microradiography and microhardness to measure mineral changes in enamel after treatment with fluoride dentifrices  

NASA Astrophysics Data System (ADS)

The aim of this study was to determine the ability of Terahertz Pulsed Imaging (TPI) to measure mineral changes in enamel lesions during de/remineralisation studies. A comparison was made between transverse microradiography (TMR) and microhardness measurements. Artificial lesions were formed in bovine enamel using a solution of 0.1 M lactic acid (pH 5.0) containing 0.2% Carbopol C907 and 50% saturated with hydroxyapatite. The 20 day experimental protocol consisted of four, one-minute treatment periods with dentifrices containing 10, 675, 1385 and 2700ppm fluoride, a 4 h/day acid challenge, and for the remaining time specimens were stored in a 50:50 pooled human / artificial saliva mixture. Terahertz images were generated by positioning the specimens at the focus of the beam and raster scanning the optics to collect the reflections from the air / enamel (AEI) and lesion / enamel (LEI) interface. Significant differences were observed in the intensity change from baseline of the AEI and LEI reflections upon treatment with the four dentifrices. A linear correlation was observed between ?AEI vs ?VHN (r2 = 0.997), ?AEI vs ?KHN (r2 =0.964), ?II (ratio of LEI to AEI) vs ??Z (r2 =0.875) and ?LEI vs ??Z (r2 =0.870). Statistically significant correlations (p<0.05 Pearson correlation coefficient) were also found between the TPI and microhardness / microradiography data. This study has demonstrated that TPI is a useful technology to measure in vitro (and possibly in situ) mineral changes in enamel and is sufficiently sensitive to discriminate between the levels of remineralization produced by the different dentifrices.

Churchley, David; Lippert, Frank; Lynch, Richard; Alton, Jesse; Gonzalez-Cabezas, C.; Eder, J.

2009-02-01

72

Terahertz Medical Imaging  

NASA Astrophysics Data System (ADS)

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

Han, Joon Koo

73

Papyrus imaging with terahertz time domain spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz time domain spectroscopic imaging (THz-TDSI) is a non-ionizing, non-contact and non-destructive measurement technique that has been recently utilized to study cultural heritage artifacts. We will present this technique and the results of non-contact measurements of papyrus texts, including images of hidden papyri. Inks for modern papyrus specimens were prepared using the historical binder, Arabic gum, and two common pigments used to write ancient texts, carbon black and red ochre. The samples were scanned in reflection at normal incidence with a pulse with a spectral range between 0.1 and 1.5 THz. Temporal analysis of the signals provides the depths of the layers, and their frequency spectra give information about the inks.

Labaune, J.; Jackson, J. B.; Pagès-Camagna, S.; Duling, I. N.; Menu, M.; Mourou, G. A.

2010-09-01

74

Achromatic prism-type wave plate for broadband terahertz pulses.  

PubMed

We demonstrated achromatic half- and quarter-wave plates for broadband terahertz pulses using phase retardation by internal total reflection. Prism-type wave plates realized ultra-broadband retardation stability up to 2.5 THz, which was the limitation of our experimental setup. Novel aspects of our work were use of a 3?/4 plate as a quarter-wave plate and a multistacked prism-type (MSP) wave plate for a large-aperture THz beam. Real-time polarization imaging of two crossed bunches of hairs was performed to show the efficiency of the MSP wave plate. We clearly observed polarization dependence of the hair direction. PMID:24784105

Kawada, Yoichi; Yasuda, Takashi; Nakanishi, Atsushi; Akiyama, Koichiro; Hakamata, Kento; Takahashi, Hironori

2014-05-01

75

Terahertz Tools Advance Imaging for Security, Industry  

NASA Technical Reports Server (NTRS)

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

2010-01-01

76

Inexpensive detector for terahertz imaging.  

PubMed

Glow discharge plasma, derived from direct-current gas breakdown, is investigated in order to realize an inexpensive terahertz (THz) room-temperature detector. Preliminary results for THz radiation show that glow discharge indicator lamps as room-temperature detectors yield good responsivity and noise-equivalent power. Development of a focal plane array (FPA) using such devices as detectors is advantageous since the cost of a glow discharge detector is approximately $0.2-$0.5 per lamp, and the FPA images will be diffraction limited. The detection mechanism of the glow discharge detector is found to be the enhanced diffusion current, which causes the glow discharge detector bias current to decrease when exposed to THz radiation. PMID:17932531

Abramovich, A; Kopeika, N S; Rozban, D; Farber, E

2007-10-10

77

Improvements in terahertz imaging using plasmonic spatial beam modulators  

Microsoft Academic Search

There has been a lot of interest in developing high-performance terahertz imaging systems which have valuable applications in surveillance, security screening, medical tomography and nondestructive inspection of various pharmaceutical, agricultural, and industrial products. Conventional terahertz imaging systems based on mechanical scanning of the imaging beam, object or the detector suffer from significantly low acquisition speeds. Additionally, realtime terahertz imaging systems

Mona Jarrahi

2010-01-01

78

Coherent detection of pulsed narrowband terahertz radiation  

Microsoft Academic Search

We demonstrate the generation and coherent detection of narrowband terahertz radiation using a Q-switched laser pumped optical parametric oscillator as the optical source. Narrowband terahertz radiation is produced using conventional difference frequency mixing and coherently detected via a frequency domain technique that relies on coherent upconversion of the terahertz field combined with optical homodyning to suppress background noise. GaSe crystals

Hua Cao; Ajay Nahata

2006-01-01

79

Tailored Terahertz Pulses from a Laser-Modulated Electron Beam  

SciTech Connect

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. [Ernest Orlando Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720 (United States)

2006-04-28

80

Sensing of phase transition in medium with terahertz pulsed spectroscopy  

NASA Astrophysics Data System (ADS)

Phase state identification and phase transition registration in condensed matter are significant applications of terahertz spectroscopy. A set of fundamental and applied problems are associated with the phase state problem. Our report is devoted to the experimental analysis of the spectral characteristics of water and water solution during the phase transition from the solid state to the liquid state via the method of terahertz pulsed spectroscopy. In this work transformation of the sample spectral characteristics during the phase transition were observed and discussed. Possible application of terahertz pulsed spectroscopy as an effective instrument for phase transition sensing was considered.

Zaytsev, Kirill I.; Fokina, Irina N.; Fedorov, Aleksey K.; Yurchenko, Stanislav O.

2014-03-01

81

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

82

Terahertz polarization imaging for colon cancer detection  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

83

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

84

Terahertz imaging: a report on progress  

Microsoft Academic Search

Purpose – The purpose of this paper is to provide details of recent developments in terahertz (THz) imaging technology and its applications. Design\\/methodology\\/approach – This paper first discusses the properties, perceived imaging uses and sources of THz radiation. It then describes passive and active imaging systems through reference to commercial products and their applications. Finally, it considers future prospects and

Robert Bogue

2009-01-01

85

Array technology for terahertz imaging  

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

86

Image plane coded aperture for terahertz imaging  

NASA Astrophysics Data System (ADS)

In the absence of detector arrays, a single pixel coupled with an image plane coded aperture has been shown to be a practical solution to imaging problems in the terahertz and sub-millimeter wave domains. The authors demonstrate two laboratory, real-time, two-dimensional, sub-millimeter wave imagers that are based on an image plane coded aperture. These active imaging systems consist of a heterodyne source and receiver pair, image forming optics, a coded aperture, data acquisition hardware, and image reconstruction software. In one of the configurations, the target is measured in transmission, while in the other it is measured in reflection. In both configurations, images of the targets are formed on the coded aperture, and linear measurements of the image are acquired as the aperture patterns change. Once a sufficient number of linearly independent measurements are obtained, the image is reconstructed by solving a system of linear equations that is generated from the aperture patterns and the corresponding measurements. The authors show that for image sizes envisioned for many current applications, this image reconstruction technique is computationally efficient and can be implemented in real time. Measurements are collected with these systems, and the reconstruction results are presented and discussed.

Furxhi, Orges; Jacobs, Eddie L.; Preza, Chrysanthe

2012-09-01

87

Broadband microwave-to-terahertz near-field imaging  

Microsoft Academic Search

In this paper we present a high performance near-field imaging method suitable for broadband applications. Recent advances in preparing micrometer and submicrometer resolution near-field probes are reported, along with examples of applications of this method both for frequency and time domain measurements. For the latter, pulsed terahertz radiation has been used to probe a broadband (300 GHz-2 THz) spectroscopic response

S. Danylyuk; U. Poppe; F. Kadlec; P. Kuzel; M. Berta; N. Klein; R. C. Pullar; N. M. Alford; H. Romanus

2007-01-01

88

Terahertz imaging of aircraft composites  

Microsoft Academic Search

Damaged aircraft composites were prepared simulating voids, delaminations, puncture holes, burns and paint removal. Terahertz time domain spectroscopy in reflection configuration was assessed as a non-destructive evaluation (NDE) technique and compared to traditional NDE techniques.

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

2009-01-01

89

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

NASA Technical Reports Server (NTRS)

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

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

2009-01-01

90

Medical applications of broadband terahertz pulsed radiation  

Microsoft Academic Search

Advances in semiconductor materials and NIR ultrafast lasers have made it possible to generate and detect broadband electromagnetic pulses with frequencies ranging from 0.1 to over 3 THz (1 THz = 1012 Hz). We present recent work using these THz pulses to image exposed breast cancer and spectroscopic results that indicate differences in the properties of normal and tumourous skin

Anthony Fitzgerald; Emma Pickwell; Vince Wallace; Arnand Purushotham; Sarah Pinder; Mercedes Linan; Richard Pye; Thomas Ha

2005-01-01

91

Terahertz wave reflective sensing and imaging  

Microsoft Academic Search

Sensing and imaging technologies using terahertz (THz) radiation have found diverse applications as they approach maturity. Since the burgeoning of this technique in the 1990's, many THz sensing and imaging investigations have been designed and conducted in transmission geometry, which provides sufficient phase and amplitude contrast for the study of the spectral properties of targets in the THz domain. Driven

Hua Zhong

2006-01-01

92

A Prototype Terrestrial Terahertz Imaging System  

Microsoft Academic Search

Interest in alternative imaging, with an emphasis on medical and security applications, is increasing. The terahertz spectrum is beginning to be explored for these applications. A prototype scanning imaging system is described here. This system currently operates at 1.6 THz and uses a HEB as a heterodyne detection element. Object scanning is accomplished by using an oscillating mirror running at

Ric Zannoni; K. S. Yngvesson; F. Rodriguez-Morales; J. Nicholson; D. Gu; E. Gerecht

2005-01-01

93

Electromagnetic Pulse Technology: Biological and Terahertz Applications  

NASA Astrophysics Data System (ADS)

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

Kumar, Prashanth

94

Direct acoustic phonon excitation by intense and ultrashort terahertz pulses  

SciTech Connect

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

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

2010-12-20

95

Terahertz interferometric and synthetic aperture imaging  

Microsoft Academic Search

The stand-off imaging properties of a terahertz (THz) interferometric array are examined. For this application, the imaged object is in the near-field region limit of the imaging array. In this region, spherical and circular array architectures can compensate for near-field distortions and increase the field of view and depth of focus. Imaging of THz point sources is emphasized to demonstrate

Aparajita Bandyopadhyay; Andrei Stepanov; Brian Schulkin; Michael D. Federici; Amartya Sengupta; Dale Gary; John F. Federici; Robert Barat; Zoi-Heleni Michalopoulou; David Zimdars

2006-01-01

96

Terahertz\\/mm wave imaging simulation software  

Microsoft Academic Search

We have developed a mm wave\\/terahertz imaging simulation package from COTS graphic software and custom MATLAB code. In this scheme, a commercial ray-tracing package was used to simulate the emission and reflections of radiation from scenes incorporating highly realistic imagery. Accurate material properties were assigned to objects in the scenes, with values obtained from the literature, and from our own

M. R. Fetterman; J. Dougherty; W. L. Kiser Jr.

2006-01-01

97

Tailored terahertz pulses from a laser-modulated electronbeam  

SciTech Connect

We present a new method to generate steady and tunable,coherent, broadband terahertz radiation from a relativistic electron beammodulated by a femtosecond laser. We have demonstrated this in theelectron storage ring at the Advanced Light Source. Interaction of anelectron beam with a femtosecond laser pulse copropagating through awiggler modulates the electron energies within a short slice of theelectron bunch with about the same duration of the laser pulse. The bunchdevelops a longitudinal density perturbation due to the dispersion ofelectron trajectories, and the resulting hole emits short pulses oftemporally and spatially coherent terahertz pulses synchronized to thelaser. We present measurements of the intensity and spectra of thesepulses. This technique allows tremendous flexibility in shaping theterahertz 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.

2006-03-06

98

Detection and Segmentation of Concealed Objects in Terahertz Images  

Microsoft Academic Search

Terahertz imaging makes it possible to acquire images of objects concealed underneath clothing by measuring the radiometric temperatures of different objects on a human subject. The goal of this work is to automatically detect and segment concealed objects in broadband 0.1-1 THz images. Due to the inherent physical properties of passive terahertz imaging and associated hardware, images have poor contrast

Xilin Shen; Charles R. Dietlein; Erich Grossman; Zoya Popovic; François G. Meyer

2008-01-01

99

Terahertz imaging using full-field electrooptic sampling  

NASA Astrophysics Data System (ADS)

Real time terahertz imaging is emerging as an important non-destructive imaging tool for medical, quality control, security and other industrial applications. In this thesis, we demonstrate real-time full-field terahertz (THz) imaging of still, moving, and concealed objects, and real-time THz images of the field distribution on the imaging plane. A femtosecond laser pulse from an amplified Ti:sapphire laser system with a pulse duration of 100 fs, repetition rate of 1 kHz, and 800 nm center wavelength is used to generate THz pulses via optical rectification in a 15x15 mm2 by 2 mm thick [110] ZnTe crystal. The THz pulses are collimated to a 1" diameter beam using off-axis parabolic reflectors. An object is placed in the collimated THz beam, and a plastic lens is used to form an image of the object on a second ZnTe crystal (detector). The THz image is detected by free-space electro-optic sampling using a large diameter gating beam derived from the laser source. Video or still images are captured by an 8-bit (30 fps) grayscale CCD camera, and objects hidden behind paper or inside Styrofoam can be clearly seen in real-time. We also study the ring-like spatial intensity distribution of the various frequency components of the THz pulse focused in the image plane by varying the time-delay between the THz and probe beams. Methods for improving signal-to-noise such as frame averaging and dynamic subtraction are also studied.

Ayesheshim, Ayesheshim Kebie

100

Terahertz/mm wave imaging simulation software  

NASA Astrophysics Data System (ADS)

We have developed a mm wave/terahertz imaging simulation package from COTS graphic software and custom MATLAB code. In this scheme, a commercial ray-tracing package was used to simulate the emission and reflections of radiation from scenes incorporating highly realistic imagery. Accurate material properties were assigned to objects in the scenes, with values obtained from the literature, and from our own terahertz spectroscopy measurements. The images were then post-processed with custom Matlab code to include the blur introduced by the imaging system and noise levels arising from system electronics and detector noise. The Matlab code was also used to simulate the effect of fog, an important aspect for mm wave imaging systems. Several types of image scenes were evaluated, including bar targets, contrast detail targets, a person in a portal screening situation, and a sailboat on the open ocean. The images produced by this simulation are currently being used as guidance for a 94 GHz passive mm wave imaging system, but have broad applicability for frequencies extending into the terahertz region.

Fetterman, M. R.; Dougherty, J.; Kiser, W. L., Jr.

2006-10-01

101

Terahertz pulse generation beyond excitation pulse limitation by ?(2) cascaded processes  

Microsoft Academic Search

We propose a novel technique for the generation of high power monocycle terahertz (THz) pulse beyond excitation pulse width limitation. When intense THz electric field generated by optical rectification lies in EO crystal, optical pulse itself gets modulated by emitted THz electric field. It causes excitation pulse compression and consequently gives rise to the enhancement of generation efficiency and its

M. Nagai; M. Jewariya; Y. Ichikawa; H. Ohtake; T. Sugiura; Y. Uehara; K. Tanaka

2009-01-01

102

Papyrus imaging with terahertz time domain spectroscopy  

Microsoft Academic Search

Terahertz time domain spectroscopic imaging (THz-TDSI) is a non-ionizing, non-contact and non-destructive measurement technique\\u000a that has been recently utilized to study cultural heritage artifacts. We will present this technique and the results of non-contact\\u000a measurements of papyrus texts, including images of hidden papyri. Inks for modern papyrus specimens were prepared using the\\u000a historical binder, Arabic gum, and two common pigments

J. Labaune; J. B. Jackson; S. Pagès-Camagna; I. N. Duling; M. Menu; G. A. Mourou

2010-01-01

103

Terahertz spin current pulses controlled by magnetic heterostructures.  

PubMed

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

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

2013-04-01

104

High-speed time domain terahertz security imaging  

Microsoft Academic Search

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

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

2005-01-01

105

Real-Time, Subwavelength Terahertz Imaging  

NASA Astrophysics Data System (ADS)

The fields of biosensing, nanospectroscopy, and plasmonics have great potential for near-field terahertz (THz) technology. In this work, we demonstrate that electro-optic (EO) imaging combined with the brightness of recently developed intense THz sources permits the imaging of subwavelength-size samples without compromising spatial resolution or acquisition time. We report on recent advances in this field and current achievements in optimizing spatial resolution and acquisition time. Near-field imaging demonstrations on field enhancement in metallic-based resonators and metamaterials are also discussed. This development will accelerate our comprehension of subwavelength light-matter interactions at THz frequencies and enable new spectroscopic applications.

Blanchard, F.; Doi, A.; Tanaka, T.; Tanaka, K.

2013-07-01

106

Resolution capability comparison of infrared and terahertz imagers  

Microsoft Academic Search

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

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

2011-01-01

107

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

108

Pulsed-terahertz reflectometry for health monitoring of ceramic thermal barrier coatings.  

PubMed

Terahertz time-domain reflectometry was used to monitor the progress of a thermally grown oxide layer and stress-induced, air-filled voids at the interface of an Yttria-stabilized-zirconia ceramic thermal-barrier coating and a metal surface. The thicknesses of these internal layers, observed in scanning-electron-microscope images to increase with thermal-exposure time, have been resolved - even when changing on the order of only a few micrometers - by distinguishing not only increased delays in the arrival times of terahertz pulses reflected from this multilayer structure, but also changes in the width and shape of the pulses. These unique features can be used to predict the lifetime of thermal-barrier coatings and to indicate or warn of spallation conditions. The trends of the experimental results are also confirmed through Fresnel-reflection time-domain simulations. PMID:20389357

Chen, Chia-Chu; Lee, Dong-Joon; Pollock, Tresa; Whitaker, John F

2010-02-15

109

Tunable and collimated terahertz radiation generation by femtosecond laser pulses  

SciTech Connect

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

Malik, Hitendra K.; Malik, Anil K.

2011-12-19

110

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

111

Reflection imaging system with terahertz-wave parametric oscillator  

Microsoft Academic Search

We demonstrated the reflection imaging system using a terahertz-wave parametric oscillator (TPO). Reflection images were acquired on a test sample consisting of bands of aluminum film, as well as on pig tissue.

T. Ikari; K. Kawase; H. Minamide; Y. Ishikawa; H. Ito

2003-01-01

112

Quantitative coherent scattering spectra in apertureless terahertz pulse near-field microscopes  

NASA Astrophysics Data System (ADS)

We present quantitative coherent measurements of scattering pulses and spectra in terahertz apertureless near-field microscopes. Broadband near-field image contrasts for both amplitude and phase spectra are measured directly from time-domain scattering signals with an unprecedentedly high single-scan signal-to-noise ratio (~48 dB), with approach curves for both short (<200 nm) and long (up to 82 ?m) ranges. By using the line dipole image method, we obtain quantitative broadband THz imaging contrasts with nanoscale resolution.

Moon, Kiwon; Do, Youngwoong; Lim, Meehyun; Lee, Gyuseok; Kang, Hyeona; Park, Kee-Su; Han, Haewook

2012-07-01

113

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

114

Tailored terahertz pulses from a laser-modulated electronbeam  

SciTech Connect

Interaction of an electron beam with a femtosecond laserpulseco-propagating through a wiggler modulates the electronenergieswithin a short slice of the electron bunch comparable with the durationof the laser pulse (Figure 1). Propagating around an electron storagering, this bunch develops a longitudinal density perturbation due to thedispersion of electron trajectories. Figure 1 shows how this createsfemtosecond electron bunch wings which are used for femtosecond x-raylight. In addition, this density perturbation emits temporally andspatially coherent tera-hertz pulses whichare inherently synchronized tothe modulating laser. This gives us a new way to study coherentsynchrotron radaition, and creates an opportunity for tuning the THzemmission specifically for the needs of a given experiment.

Martin, Michael C.; Byrd, John; Hao, Zhao; Robin, David; Sannibale,Fernando; Schoenlein, Robert W.; Zholents, Alexander; Zolotorev, Max

2005-07-19

115

Integrated terahertz pulse generation and amplification in quantum cascade lasers  

NASA Astrophysics Data System (ADS)

Integrated terahertz (THz) pulse generation and amplification in a THz quantum cascade laser (QCL) is demonstrated. Intra-cavity THz pulses are generated by exciting the facet of the quantum cascade laser with an ultrafast Ti:Sapphire laser (~100fs) and detected using electro-optic sampling. Maximum THz field emission is found with an interband transition of 1.535eV (809nm) and by narrowing the excitation laser bandwidth to ~3THz. These resonance conditions correspond to the narrowband excitation of the quantum cascade miniband, indicating that the THz pulse is generated by the photo-excited carriers that are accelerated by the applied field. The generated pulse is subsequently amplified by the narrowband gain of the laser as it propagates through the QCL cavity. As an integrated THz generator-amplifier, the technique avoids the issues associated with the coupling of external THz pulses into sub-wavelength dimensioned cavities.

Dhillon, S. S.; Sawallich, S.; Jukam, N.; Oustinov, D.; Madéo, J.; Rungsawang, R.; Barbieri, S.; Filloux, P.; Sirtori, C.; Marcadet, X.; Tignon, J.

2011-01-01

116

Terahertz wave imaging for landmine detection  

Microsoft Academic Search

Pulsed THz imaging is a promising non-destructive technology based on its high transmission through selected dielectric materials and its capability to provide time-of-flight and spectral information. The traditional method of the pulsed THz imaging is a point-to-point reflective scanning system. The image is acquired by analyzing the peak amplitude information of the THz pulse in the time-domain at each pixel.

Hua Zhong; Nick Karpowicz; Jason Partridge; Xu Xie; Jingzhou Xu; Xi-Cheng Zhang

2004-01-01

117

Scanning laser terahertz near-field imaging system.  

PubMed

We have proposed and developed a scanning laser terahertz (THz) near-field imaging system using a 1.56 ?m femtosecond fiber laser for high spatial resolution and high-speed measurement. To obtain the two-dimensional (2D) THz images of samples, the laser pulses are scanned over a 2D THz emitter plate [DASC: 4'-dimenthylamino-N-methyl-4- stilbazolium p-chlorobenzenesulfonate] by a galvano meter. In this system, THz wave pulses locally generated at the laser irradiation spots transmit through the sample set on the emitter, and the amplitude of the transmitted THz wave pulse is detected by using a typical THz time-domain spectroscopy (THz-TDS) technique. Using this system, we have succeeded in obtaining THz transmission images of a triangle shaped metal sheet of millimeter-size and a human hair sample with a spatial resolution of sub-wavelength order up to ~27 ?m (~?THz/28) at an imaging speed of about 47 seconds/image for 512 x 512 pixels. PMID:22714323

Serita, Kazunori; Mizuno, Shori; Murakami, Hironaru; Kawayama, Iwao; Takahashi, Yoshinori; Yoshimura, Masashi; Mori, Yusuke; Darmo, Juraj; Tonouchi, Masayoshi

2012-06-01

118

Generation of terahertz radiation by focusing femtosecond bichromatic laser pulses in a gas or plasma  

SciTech Connect

The generation of terahertz radiation by focusing two-frequency femtosecond laser pulses is studied. Focusing is carried out both in an undisturbed gas and in a pre-formed plasma. The energy of the terahertz radiation pulses is shown to reduce significantly in the case of focusing in a plasma. (extreme light fields and their applications)

Chizhov, P A; Volkov, Roman V; Bukin, V V; Ushakov, A A; Garnov, Sergei V; Savel'ev-Trofimov, Andrei B

2013-04-30

119

High-speed terahertz imaging toward food quality inspection.  

PubMed

In contrast to conventional x-ray food inspection systems that have difficulty in detecting low-density materials, a terahertz imaging system can even identify insects and plastics embedded in a food matrix. A reflection-mode continuous-wave terahertz imaging system was therefore developed for application to food quality inspection, which requires fast, compact, and low-cost detection. High-speed operation of the terahertz imaging system was achieved through the use of a beam-steering tool. A reasonable compromise between the spatial resolution and the scan length of an aspheric f-theta scanning lens could be achieved by optimizing the lens parameters. PMID:24663370

Ok, Gyeongsik; Park, Kisang; Kim, Hyun Jung; Chun, Hyang Sook; Choi, Sung-Wook

2014-03-01

120

Polarization sensitive terahertz imaging: detection of birefringence and optical axis.  

PubMed

We present a practicable way to take advantage of the spectral information contained in a broadband terahertz pulse for the determination of birefringence and orientation of the optical axis in a glass fiber reinforced polymer with a single measurement. Our setup employs circularly polarized terahertz waves and a polarization-sensitive detector to measure both components of the electromagnetic field simultaneously. The anisotropic optical parameters are obtained from an analysis of the phase and frequency resolved components of the terahertz field. This method shows a high tolerance against the skew of the detection axes and is also independent of a reference measurement. PMID:23188266

Katletz, Stefan; Pfleger, Michael; Pühringer, Harald; Mikulics, Martin; Vieweg, Nico; Peters, Ole; Scherger, Benedikt; Scheller, Maik; Koch, Martin; Wiesauer, Karin

2012-10-01

121

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

PubMed

We have modeled and demonstrated a scalable, compact, fiber-pumped terahertz source based on difference frequency mixing (DFM) in zinc germanium phosphide (ZGP) capable of producing high average and peak-power pulses. Currently, our terahertz source produces 2 mW of average THz power and >40 W of peak power with sub-nanosecond pulses at a repetition rate of 100 kHz in the range of 2-3 THz without cryogenic cooling or ultra-fast optics. This high average power laser-based terahertz output enables the real-time imaging of concealed objects using an off-the-shelf uncooled microbolometer focal-plane array. With this THz system, we have imaged objects obscured inside in a common shipping envelope, demonstrating the potential of compact laser-based terahertz sources for use in security screening applications. PMID:19546954

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

2007-05-14

122

Electronic Terahertz Spectroscopic Imaging of Explosives and Weapons.  

National Technical Information Service (NTIS)

We seek to build imaging arrays for screening personnel through portals using new microwave circuits that produce coherent signals of electronic terahertz (THz) generation and detection integrated circuits. Since we have demonstrated that these circuits c...

D. W. van der Weide

2005-01-01

123

3D Imaging and analysis system using terahertz waves  

Microsoft Academic Search

We have developed the “3D Imaging Analysis System” that uses terahertz waves, the world's first such system for practical applications. This system has an unprecedented capability for nondestructive three-dimensional spectroscopic analysis of the spatial distribution of constituents.

M. Imamura; S. Nishina; A. Irisawa; T. Yamashita; E. Kato

2010-01-01

124

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

125

TeraHertz imaging of hidden paint layers on canvas  

Microsoft Academic Search

We show terahertz reflection images of hidden paint layers in a painting on canvas and compare the results with X-ray Radiography and Infrared Reflectography. Our terahertz measurements show strong reflections from both the canvas\\/paint interface and from the raw umber\\/lead white interface, indicating sufficient refractive-index contrast. Our results show that X-rays cannot be used to image through the lead white

Aurèle J. L. Adam; Paul C. M. Planken; Sabrina Meloni; Joris Dik

2009-01-01

126

Detection of Terahertz Pulses Using a Modified Sagnac Interferometer  

SciTech Connect

We describe a time resolved, interferometric method to detect terahertz (THz) pulses based on Sagnac geometry. A ZnTe electro-optic crystal is placed in one arm of the interferometer, and the THz-induced optical phase shift is demodulated by allowing the two arms to optically interfere. The theorital principle behind this new method is illustrated and a detailed comparison with the traditional electro-optic (EO) sampling technique used in THz time domain spectroscopy is performed. Key features of this new method are highlighted, serving as an aid to identify where this method may be useful in future applications.

Benjamin Clough1; David H. Hurley; Pengyu Han; Jun Liao; Rena Huang3; X. –C. Zhang

2009-12-01

127

Fast continuous terahertz wave imaging system for security  

Microsoft Academic Search

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

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

2009-01-01

128

Single-shot terahertz spectroscopy using pulse-front tilting of an ultra-short probe pulse.  

PubMed

We developed a single-shot terahertz pulse measurement technique using pulse-front tilting of an ultra-short probe pulse and demonstrated single-shot terahertz spectroscopy. A transmission grating was used to introduce a sufficiently large pulse-front tilt angle. A measuring time range of 23.8 ps was achieved. The measured temporal waveforms were corrected in consideration of the nonlinearity arising from the crossed-Nicols arrangement employed and the beam profiles of the probe and terahertz pulses. The characteristic spectrum of lactose was measured with a single terahertz pulse, and the effectiveness of our single-shot technique was confirmed by comparison with a conventional sampling method. PMID:21716352

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

2011-06-01

129

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

Microsoft Academic Search

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

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

2011-01-01

130

Terahertz imaging system using high-Tc superconducting oscillation devices  

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

131

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, Loïc; Bolduc, Martin; Terroux, Marc; Dufour, Denis; Tang, Denis; Châteauneuf, François; Jerominek, Hubert

2011-10-01

132

Active terahertz imaging with Ne indicator lamp detector arrays  

Microsoft Academic Search

The advantages of terahertz (THz) imaging are well known. They penetrate well most non-conducting media and there are no known biological hazards, This makes such imaging systems important for homeland security, as they can be used to image concealed objects and often into rooms or buildings from the outside. There are also biomedical applications that are arising. Unfortunately, THz imaging

N. S. Kopeika; A. Abramovich; O. Yadid-Pecht; Y. Yitzhaky

2009-01-01

133

Generation of radially polarized terahertz pulses via velocity-mismatched optical rectification.  

PubMed

We demonstrate the generation of radially polarized terahertz pulses via optical rectification in a Cherenkov geometry exploiting velocity mismatch, contrary to the traditional approach for generating linearly polarized terahertz beams. A compact system is implemented using 001-cut ZnTe pumped by an ultrafast Yb-doped fiber amplifier. PMID:17356677

Chang, Guoqing; Divin, Charles J; Liu, Chi-Hung; Williamson, Steven L; Galvanauskas, Almantas; Norris, Theodore B

2007-02-15

134

Contrast improvement of terahertz images of thin histopathologic sections.  

PubMed

We present terahertz images of 10 ?m thick histopathologic sections obtained in reflection geometry with a time-domain spectrometer, and demonstrate improved contrast for sections measured in paraffin with water. Automated segmentation is applied to the complex refractive index data to generate clustered terahertz images distinguishing cancer from healthy tissues. The degree of classification of pixels is then evaluated using registered visible microscope images. Principal component analysis and propagation simulations are employed to investigate the origin and the gain of image contrast. PMID:21326635

Formanek, Florian; Brun, Marc-Aurèle; Yasuda, Akio

2010-01-01

135

Nonlinear optical response of graphene to an ultrashort intense terahertz pulse  

Microsoft Academic Search

The optical response of graphene to an ultrashort intense terahertz pulse is described by the extended optical Bloch equations. The interplay of intraband and interband dynamics is important in the nonlinear optical response.

Kenichi L. Ishikawa

2011-01-01

136

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

137

Accuracy of sample material parameters reconstruction using terahertz pulsed spectroscopy  

NASA Astrophysics Data System (ADS)

New experimental and theoretical results for the material parameter reconstruction using terahertz (THz) pulsed spectroscopy (TPS) are presented. The material parameter reconstruction algorithm was realized and experimentally implemented to study the test sample. In order to both verify the algorithm and to estimate the reconstruction accuracy, test sample material parameters obtained with the TPS were compared with the results of the same sample studying by the use of the backward-wave oscillator (BWO) spectroscopy. Thus, high reconstruction accuracy was demonstrated for the spectral range, corresponding to the BWO sensitivity and located between 0.2 and 1.2 THz. The numerical simulations were applied for determining the material parameter reconstruction stability in the presence of white Gaussian noise in TPS waveforms as well as fluctuations in the femtosecond (FS) optical pulse duration. We report a strong dependence of the inverse problem solution stability on these factors. We found that the instability of the FS optical pulse duration used for THz pulses generation and detection limits the material parameter reconstruction with TPS.

Zaytsev, Kirill I.; Gavdush, Arseniy A.; Karasik, Valeriy E.; Alekhnovich, Valentin I.; Nosov, Pavel A.; Lazarev, Vladimir A.; Reshetov, Igor V.; Yurchenko, Stanislav O.

2014-05-01

138

On the generation of terahertz radiation by a phase-modulated optical pulse  

NASA Astrophysics Data System (ADS)

The problem of terahertz radiation generation in a quadratic nonlinear medium by a nanosecond phase-modulated optical pulse possessing the properties of supercontinuum has been investigated. The possibility of generating both broadband and quasi-monochromatic terahertz signals has been demonstrated. The conditions have been revealed under which the generation efficiency of a phase-modulated nanosecond optical pulse is greater than that of a spectrally confined femtosecond signal.

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

2014-02-01

139

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

140

Ray-Rracing Model for Terahertz Imaging of SOFI Inspection  

NASA Astrophysics Data System (ADS)

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

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

2006-03-01

141

High-terahertz-frequency carrier generation by optical pulse for radio-over-fiber applications  

NASA Astrophysics Data System (ADS)

In this study a new design of terahertz frequency carrier generation for radio frequency identification (RFID) application is proposed. The dense wavelength-division multiplexing can be generated and obtained by using a Gaussian or soliton pulse propagating within a modified add-drop filter known as a PANDA ring resonator. The broad bandwidth of terahertz signals can be obtained and are available for useful applications, in which the use of the generated terahertz pulses for RFID application, for instance Ad-Hoc network, uses RFID. Results obtained have shown that the increase in channel capacity can be obtained and useful for the large demand of RFID applications.

Afroozeh, Abdolkarim; Jomtarak, Rangsan; Ali, Jalil; Yupapin, Preecha P.

2011-12-01

142

High-power terahertz pulse sensor with overmoded structure  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

143

Terahertz beam steering using interference of femtosecond optical pulses.  

PubMed

A terahertz (THz) beam steering method is demonstrated by applying the characteristic of grating lobe (GL) radiation from a linear array antenna and the interference of femtosecond optical pulses. A photoconductive device is illuminated by two femtosecond laser beams combined at an angle of less than 0.5°. Considering the interference pattern as a THz point source array, THz GL radiation is generated through the superposition of radiation emitted from all point sources and steered by varying the interval of the interference pattern. The THz beam direction could be changed by 20° at 0.93THz by varying the relative incidence angle of the pump beams by 0.033°. PMID:23037441

Uematsu, Koji; Maki, Ken-ichiro; Otani, Chiko

2012-09-24

144

Spatiotemporal control of ultrashort laser pulses using intense single-cycle terahertz pulses  

NASA Astrophysics Data System (ADS)

We demonstrate that the intense electric field of a subpicosecond single-cycle terahertz pulse can control and manipulate the temporal, spectral, and spatial phase of a copropagating ultrashort laser pulse through the Pockels effect in an electro-optic crystal. In the temporal and spectral domains, the single-cycle THz pulse can impart either a positive or a negative quadratic phase modulation to the probe pulse, leading to a spectral shift, broadening, or pulse expansion or compression. While acting in the spatial domain, the THz-induced phase modulation induces a lenslike effect, providing focusing or defocusing of the copropagating probe beam. The experimental results are in good agreement with simulations. Our study gives a comprehensive picture of the nonlinear spatiotemporal dynamics in the high-field regime driven by the intense single-cycle THz pulse.

Shen, Yuzhen; Carr, G. L.; Murphy, James B.; Tsang, Thomas Y.; Wang, Xijie; Yang, Xi

2008-10-01

145

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

146

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

147

Scattering and propagation of terahertz pulses in random soot aggregate systems  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

148

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

149

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

150

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

Microsoft Academic Search

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

Eyal Gerecht; Lixing You

2008-01-01

151

Development of components for cost effective terahertz measurement system: terahertz quantum cascade laser and terahertz quantum well infrared photo-detector  

Microsoft Academic Search

Terahertz imaging and spectroscopy have attracted a lot of attention in recent years, because monocycle terahertz radiation can be generated using an ultra-short pulse laser and semiconductor device technologies. The availability of monocycle terahertz radiation sources has encouraged innovative research and development activities worldwide in an extremely wide range of applications, from security to medical systems. However, the fundamental device

Iwao Hosako; Norihiko Sekine; Mikhail Patrashin; Hiroaki Yasuda

2007-01-01

152

Terahertz Imaging System Based on a Backward-Wave Oscillator  

Microsoft Academic Search

We present an imaging system designed for use in the terahertz range. As the radiation source a backward-wave oscillator was chosen for its special features such as high output power, good wave-front quality, good stability, and wavelength tunability from 520 to 710 GHz. Detection is achieved with a pyroelectric sensor operated at room temperature. The alignment procedure for the optical

Adrian Dobroiu; Masatsugu Yamashita; Yuichi N. Ohshima; Yasuyuki Morita; Chiko Otani; Kodo Kawase

2004-01-01

153

Single-shot coherent detection of terahertz pulse with broadband spectral coverage  

SciTech Connect

A new scheme using centrosymmetric materials as sensor medium is presented for the single-shot coherence detection of terahertz pulse. The method relies on the electric-field-induced optical second-harmonic generation with linearly chirped optical probe pulse in centrosymmetric medium. The terahertz field is encoded onto the frequency spectrum of the second-harmonic pulse and then decoded with appropriate retrieval algorithm. This approach provides a broadband coherent spectroscopic measurement that can cover the entire terahertz gap and has transform-limited temporal resolution, which is mainly limited by the spectral bandwidth of the optical probe pulse. It can be used widely in the experiments of high field plasma physics and the diagnostics of warm dense plasmas.

Hu Guangyue; Lei Anle; Shen Baifei; Li Ruxin; Xu Zhizhan [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Shanghai 201800 (China)

2009-04-15

154

Detection of the spatiotemporal field of a single-shot terahertz pulse based on spectral holography  

NASA Astrophysics Data System (ADS)

According to electro-optical sampling theory, we propose a new method to detect the spatiotemporal field of a single-shot terahertz pulse by spectral holography for the first time. The single-shot terahertz pulse is coupled into a broadened chirped femtosecond pulse according to electro-optical sampling theory in the detecting system. Then the reference wave and the signal wave are split by Dammann grating and spread into the interference band-pass filter. The filtered sub-waves are at different central-frequencies because of the different incident angles. These sub-waves at different central-frequencies interfere to form sub-holograms, which are recorded in a single frame of a charge coupled device (CCD). The sub-holograms are numerically processed, and the spatiotemporal field distribution of the original terahertz pulse is reconstructed. The computer simulations verify the feasibility of the proposed method.

Wang, Xiao-Lei; Fei, Yang; Li, Lu-Jie; Wang, Qiang; Zhu, Zhu-Qing

2014-06-01

155

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

156

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

Microsoft Academic Search

A scheme for efficient generation of broadband terahertz radiation by a femtosecond laser pulse propagating in a planar sandwichlike structure is proposed. The structure consists of a thin nonlinear core cladded with prisms made of a material with low terahertz absorption. The focused into a line laser pulse propagates in the core as a leaky or waveguide mode and emits

S. B. Bodrov; M. I. Bakunov; M. Hangyo

2008-01-01

157

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

158

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

PubMed Central

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

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

2013-01-01

159

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

Microsoft Academic Search

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

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

2011-01-01

160

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

161

Terahertz parametric sources and imaging applications  

Microsoft Academic Search

We have studied the generation of terahertz (THz) waves by optical parametric processes based on laser light scattering from the polariton mode of nonlinear crystals. Using parametric oscillation of LiNbO3 or MgO-doped LiNbO3 crystal pumped by a nano-second Q-switched Nd:YAG laser, we have realized a widely tunable coherent THz-wave source with a simple configuration. We report the detailed characteristics of

Kodo Kawase; Yuichi Ogawa; Hiroaki Minamide; Hiromasa Ito

2005-01-01

162

Terahertz Lasers Reveal Information for 3D Images  

NASA Technical Reports Server (NTRS)

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

2013-01-01

163

Field-free molecular orientation with terahertz few-cycle pulses  

NASA Astrophysics Data System (ADS)

We demonstrate theoretically an efficient field-free orientation in LiH and LiCl driven by available terahertz few-cycle pulses (TFCPs). Exact results by numerically solving the time-dependent Schrödinger equation including the vibrational and rotational degrees of freedom are compared to the rigid-rotor approximation (RRA) as well as to the impulsive approximation (IA), and the effect of rotational-vibrational coupling on the both RRA and IA is examined in detail. We find that the current available TFCPs may overcome the technical limitation of terahertz half-cycle pulse for enhancing the field-free molecular orientation.

Shu, Chuan-Cun; Yuan, Kai-Jun; Hu, Wen-Hui; Cong, Shu-Lin

2010-06-01

164

Field-free molecular orientation with terahertz few-cycle pulses.  

PubMed

We demonstrate theoretically an efficient field-free orientation in LiH and LiCl driven by available terahertz few-cycle pulses (TFCPs). Exact results by numerically solving the time-dependent Schrodinger equation including the vibrational and rotational degrees of freedom are compared to the rigid-rotor approximation (RRA) as well as to the impulsive approximation (IA), and the effect of rotational-vibrational coupling on the both RRA and IA is examined in detail. We find that the current available TFCPs may overcome the technical limitation of terahertz half-cycle pulse for enhancing the field-free molecular orientation. PMID:20590197

Shu, Chuan-Cun; Yuan, Kai-Jun; Hu, Wen-Hui; Cong, Shu-Lin

2010-06-28

165

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

166

Modeling of millimetre-wave and terahertz imaging systems  

NASA Astrophysics Data System (ADS)

In order to improve the design and analyse the performance of efficient terahertz optical systems, novel quasi-optical components along with dedicated software tools are required. At sub-millimetre wavelengths, diffraction dominates the propagation of radiation within quasi-optical systems and conventional geometrical optics techniques are not adequate to accurately guide the beams or assess optical efficiency. In fact, in general Optical design in the terahertz waveband suffers from a lack of dedicated commercial software packages for modelling the range of electromagnetic propagation regimes that are important in such systems. In this paper we describe the physical basis for efficient CAD software tools we are developing to specifically model long wavelength systems. The goal is the creation of a user-friendly package for optical engineers allowing potential systems to be quickly simulated as well as also providing an analytical tool for verification of existing optical systems. The basic approach to modelling such optical trains is the application of modal analysis e.g. [1][2], which we have extended to include scattering at common off-axis conic reflectors. Other analytical techniques are also ncluded within the CAD software framework such as plane wave decomposition and full physical optics. We also present preliminary analytical methods for characterising standing waves that can occur in terahertz systems and report on novel binary optical components for this wavelength range. Much of this development work has been applied to space instrumentation but is relevant for all Terahertz Imaging systems.

Gradziel, Marcin L.; White, David; Trappe, Neal; Mahon, Ronan J.; Finn, Timothy J.; Withington, Stafford; Murphy, Anthony; O'Sullivan, Creidhe M.

2004-12-01

167

Advanced terahertz imaging system performance model for concealed weapon identification  

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

168

Terahertz imaging for anti-personnel mine detection  

NASA Astrophysics Data System (ADS)

The detection of buried anti-personnel mines has presented problems for current mine detection methods, such as ground penetrating radar. Terahertz (THz) radiation provides the ability to obtain higher resolution images as well as the ability to obtain spectroscopic information on the explosives in and around the buried mines. Propagation of THz in granular media is studied using techniques adapted from material science for foams and ceramics and adapted to sand and soil. We then give early results of 2-D reflection imaging of objects buried in sand. A terahertz time domain reflection system with a GaAs photoconductive emitter, a ZnTe electro-optic detector, and a rapid delay scanning mechanism was used to produce and collect the transmitted THz signal.

Dodson, Caroline; Fitch, Michael J.; Osiander, Robert; Spicer, James B.

2005-05-01

169

Terahertz waves emitted from an optical fiber.  

PubMed

We report a simple method of creating terahertz waves by applying the photo-Dember effect in a (100)-oriented InAs film coated onto the 45-degree wedged-end facet of an optical fiber. The terahertz waves are generated by infrared pulses guided through the optical fiber which is nearly in contact with a sample and then measured by a conventional photo-conductive antenna detector. Using this alignment-free terahertz source, we performed proof-of-principle experiments of terahertz time-domain spectroscopy and near-field terahertz microscopy. We obtained a bandwidth of 2 THz and 180-microm spatial resolution. Using this method, the THz imaging resolution is expected to be reduced to the size of the optical fiber core. Applications of this device can be extended to sub-wavelength terahertz spectroscopic imaging, miniaturized terahertz system design, and remote sensing. PMID:20588503

Yi, Minwoo; Lee, Kanghee; Lim, Jongseok; Hong, Youngbin; Jho, Young-Dahl; Ahn, Jaewook

2010-06-21

170

Advanced terahertz imaging system performance model for concealed weapon identification  

Microsoft Academic Search

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

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

2007-01-01

171

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

172

Broadband terahertz imaging of documents written with lead pencils  

Microsoft Academic Search

Far infrared transmission spectra of several graphite pencil leads on paper have been measured up to 2THz using time-domain spectroscopy. The observation of the gradual absorption depending on the graphite proportion has been assessed for different pencils from hard to soft black-marking graphite leads. The resulting graphite transmittance is used to perform two-dimensional transmission terahertz imaging of written documents.

E. Abraham; A. Younus; A. El Fatimy; J. C. Delagnes; E. Nguéma; P. Mounaix

2009-01-01

173

Enhanced Detection of Broadband Terahertz Field by Filamentation of Chirped Optical Pulses  

Microsoft Academic Search

We report on the signal enhancement in the Air Biased Coherent Detection\\u000a scheme of broadband terahertz fields in the transition from below to\\u000a above the critical power for self-focusing of positively chirped optical\\u000a probe pulses.

M. Clerici; M. Peccianti; M. Shalaby; T. Ozaki; D. Cooke; D. Faccio; R. Morandotti

2011-01-01

174

Spectral shifts as a signature of the onset of diffusion of broadband terahertz pulses  

Microsoft Academic Search

We describe measurements of polarization dynamics as a probe of multiple scattering of photons in a random medium by use of single-cycle terahertz pulses. We measure the degree of polarization and correlate it directly with the single-scattering regime in the time domain. We also measure the evolution of the temporal phase of the radiation and show that the average spectral

Jeremy Pearce; Zhongping Jian; Daniel M. Mittleman

2004-01-01

175

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

176

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

177

Simulation study on cascaded terahertz pulse generation in electro-optic crystals.  

PubMed

We studied cascaded optical rectification processes for intense terahertz (THz) pulse generation in electro-optic crystals using simulations based on one-dimensional coupled propagation equations of THz and optical fields. We found that under ideal conditions of perfect phase matching and no absorption, cascaded optical rectification processes produce intense THz pulses with efficiencies exceeding the Manley-Rowe limit. Large red shifting of the pump light spectrum was observed. Effects of finite optical and THz absorption, phase mismatches, and pulse width were examined using parameters of a ZnTe crystal pumped by 800 nm pulses. THz field enhancement by multiple pulse pumping was also studied. PMID:19547135

Hattori, Toshiaki; Takeuchi, Kousuke

2007-06-25

178

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

179

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

PubMed Central

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

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

2012-01-01

180

Inspection of plastic weld joints with terahertz imaging  

NASA Astrophysics Data System (ADS)

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

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

2007-06-01

181

Nondestructive Evaluation of Aircraft Composites Using Dielectric Properties and Imaging in the Terahertz Spectrum  

Microsoft Academic Search

Terahertz imaging and dielectric property measurements were assessed as nondestructive evaluation techniques for damage to aircraft glass fiber composites. Samples with localized heat damage showed a minimal change in refractive index or absorption coefficient; however, material blistering was detected. Voids were located by terahertz imaging using amplitude and phase techniques. Delamination depths were approximated by measuring the timing of Fabry-Perot

C. D. Stoik; M. J. Bohn; J. L. Blackshire

2009-01-01

182

NONDESTRUCTIVE EVALUATION OF AIRCRAFT COMPOSITES USING DIELECTRIC PROPERTIES AND IMAGING IN THE TERAHERTZ SPECTRUM  

Microsoft Academic Search

Terahertz imaging and dielectric property measurements were assessed as nondestructive evaluation techniques for damage to aircraft glass fiber composites. Samples with localized heat damage showed a minimal change in refractive index or absorption coefficient; however, material blistering was detected. Voids were located by terahertz imaging using amplitude and phase techniques. Delamination depths were approximated by measuring the timing of Fabry-Perot

C. D. Stoik; M. J. Bohn; J. L. Blackshire

2009-01-01

183

Intense terahertz pulses from SLAC electron beams using coherent transition radiation  

SciTech Connect

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

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

2013-02-15

184

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

185

Broadband and high power monocycle terahertz pulse generation by ?(2) cascaded processes in LiNbO3  

Microsoft Academic Search

We propose a novel technique for the generation of high power monocycle terahertz pulse beyond the excitation pulse width limitation. Optical pulse may get modulated by emitted intense THz electric field. This causes excitation pulse compression and consequently gives rise to the enhancement of generation efficiency and its bandwidth. We experimentally demonstrate this chi(2) cascaded processes using tilted wavefront excitation

Mukesh Jewariya; Masaya Nagai; Yuki Ichikawa; Hideyuki Ohtake; Toshiharu Sugiura; Yuzuru Uehara; Koichiro Tanaka

2009-01-01

186

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

SciTech Connect

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

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

2009-12-15

187

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

188

Terahertz Emission of Ferromagnetic Ni-Fe Thin Films Excited by Ultrafast Laser Pulses  

NASA Astrophysics Data System (ADS)

It is believed that the ultrafast demagnetization process in ferromagnetic film is intrinsically a thermal effect, which is induced by ultrafast laser pulses. We present experimental evidence that such ultrafast demagnetization of the NiFe thin film can radiate electromagnetic waves in the terahertz range. We also demonstrate that the magnitude of the terahertz electromagnetic pulse emitted from ferromagnetic films after pulsed laser excitation can be tuned by the Gilbert damping factor ?, which is conventionally used to describe damping of GHz precession motion of magnetization. Different damping factors are obtained by varying the normal metal film adjacent to the magnetic film via spin pumping. The measured radiated electric field in the far field is found to be proportional to the Gilbert damping factor.

Shen, Jian; Zhang, Huai-Wu; Li, Yuan-Xun

2012-06-01

189

Terahertz imaging system performance model for concealed-weapon identification  

NASA Astrophysics Data System (ADS)

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

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

2008-03-01

190

Terahertz imaging system performance model for concealed weapon identification  

NASA Astrophysics Data System (ADS)

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

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

2005-11-01

191

Millimeter-Wave and Submillimeter-Wave/Terahertz Passive Imaging System Requirements: A Phenomenological Perspective.  

National Technical Information Service (NTIS)

The phenomenology of imaging in the millimeter-wave (MMW) and submillimeter-wave (SMMW)/terahertz (THz) frequency regimes is investigated and described. The primary factors related to imaging in these frequency regimes are phenomenologically driven and in...

S. R. Murrill

2013-01-01

192

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

193

Quantum theory of terahertz emission due to ultrashort pulse ionization of gases.  

PubMed

A microscopic model is developed to analyze terahertz (THz) emission after ultrashort one- and two-color laser-pulse excitations of an atomic gas. Optical Bloch equations are derived to describe the pulse-induced ionization in the many-atom system including the Coulombic scattering of the ionized electrons. The model captures the continuous transition between the tunneling and the multiphoton ionization regimes. Numerical evaluations for a wide range of pulse configurations identify optimized excitation conditions for strong THz emission. PMID:24483572

Schuh, K; Scheller, M; Hader, J; Moloney, J V; Koch, S W

2013-12-01

194

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

SciTech Connect

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

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

2013-10-15

195

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 3.8±0.4%, 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

196

Method for large and rapid terahertz imaging  

DOEpatents

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

Williams, Gwyn P.; Neil, George R.

2013-01-29

197

Terahertz Pulse Emission from Nanostructured (311) Surfaces of GaAs  

NASA Astrophysics Data System (ADS)

In the present work, azimuthal angle dependences of the terahertz (THz) pulse emission from lower symmetry, (311) planes of porous GaAs samples have been studied. GaAs porous layers were prepared by pulsed anodic electrochemical etching of n-type (311) GaAs wafers in mixed acidic fluoride-iodide electrolyte. It has been discovered that the anodic electrochemical etching of the GaAs sample significantly enhances its terahertz radiation emissivity. It was shown theoretically that for this crystallographic plane the contributions of both optical rectification (OR) and electric-field-induced optical rectification (EFIOR) effects are characterized by different azimuthal angle dependences. Experimental measurements were compared with the theoretical calculations of the azimuthal angle dependencies; it has been shown that both nonlinear optical effects are necessary to take into account when explaining the experimental observations.

Adomavi?ius, R.; Adamonis, J.; Bi?i?nas, A.; Krotkus, A.; Atrashchenko, A.; Evtikhiev, V.; Ulin, V.; Kaliteevski, M.; Abram, R.

2012-06-01

198

Broadband terahertz pulse emission from ZnGeP2.  

PubMed

Optical rectification is demonstrated in (110)-cut ZnGeP(2) (ZGP) providing broadband terahertz (THz) generation. The source is compared to both GaP and GaAs over a wavelength range of 1150 nm to 1600 nm and peak-intensity range of 0.5 GW/cm(2) to 40 GW/cm(2). ZGP peak-to-peak field amplitude is larger than in the other materials due to either lower nonlinear absorption or larger second-order nonlinearity. This material is well suited for broadband THz generation across a wide range of infrared excitation wavelengths. PMID:22378394

Rowley, J D; Pierce, J K; Brant, A T; Halliburton, L E; Giles, N C; Schunemann, P G; Bristow, A D

2012-03-01

199

Generation of 1.5 microJ single-cycle terahertz pulses by optical rectification from a large aperture ZnTe crystal.  

PubMed

We demonstrate the generation muJ-level, single-cycle terahertz pulses by optical rectification from a large-aperture ZnTe single crystal wafer. Energies up to 1.5 muJ per pulse and a spectral range extending to 3 THz were obtained using a 100 Hz Ti:sapphire laser source and a 75-mmdiameter, 0.5-mm-thick, (110) ZnTe crystal, corresponding to an average power of 150 muW and an energy conversion efficiency of 3.1 x 10(-5). We also demonstrate real-time imaging of the focused terahertz beam using a pyroelectric infrared camera. PMID:19550589

Blanchard, F; Razzari, L; Bandulet, H C; Sharma, G; Morandotti, R; Kieffer, J C; Ozaki, T; Reid, M; Tiedje, H F; Haugen, H K; Hegmann, F A

2007-10-01

200

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

PubMed

We demonstrate terahertz (THz) imaging and spectroscopy of a 15 × 15-mm2 single-layer graphene film on Si using broadband THz pulses. The THz images clearly map out the THz carrier dynamics of the graphene-on-Si sample, allowing us to measure sheet conductivity with sub-mm resolution without fabricating electrodes. The THz carrier dynamics are dominated by intraband transitions and the THz-induced electron motion is characterized by a flat spectral response. A theoretical analysis based on the Fresnel coefficients for a metallic thin film shows that the local sheet conductivity varies across the sample from ?(s) = 1.7 × 10(-3) to 2.4 × 10(-3) ?(-1) (sheet resistance, ?(s) = 420 - 590 ?/sq). PMID:21263550

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

2011-01-01

201

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

202

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

SciTech Connect

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

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

2013-07-15

203

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

204

Terahertz detectors for long wavelength multi-spectral imaging.  

SciTech Connect

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

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

2007-10-01

205

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

206

Imaging terahertz radar for security applications  

NASA Astrophysics Data System (ADS)

Detection of concealed threats is a key issue in public security. In short range applications, passive imagers operating at millimeter wavelengths fulfill this task. However, for larger distances, they will suffer from limited spatial resolution. We will describe the design and performance of 0.8-THz imaging radar that is capable to detect concealed objects at a distance of more than 20 meter. The radar highlights the target with the built-in cw transmitter and analyses the returned signal making use of a heterodyne receiver with a single superconducting hot-electron bolometric mixer. With an integration time of 0.3 sec, the receiver distinguishes a temperature difference of 2 K at the 20 m distance. Both the transmitter and the receiver use the same modified Gregorian telescope consisting from two offset elliptic mirrors. The primary mirror defines limits the lateral resolution of the radar to 2 cm at 20 m distance. At this distance, the field of view of the radar has the diameter 0.5 m. It is sampled with a high-speed conical scanner that allows for a frame time less than 5 sec. The transmitter delivers to the target power with a density less than ten microwatt per squared centimeter, which is harmless for human beings. The radar implements a sensor fusion technique that greatly improves the ability to identify concealed objects.

Semenov, Alexei; Richter, Heiko; Böttger, Ute; Hübers, Heinz-Wilhelm

2008-05-01

207

Single-shot spatiotemporal measurements of high-field terahertz pulses  

SciTech Connect

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

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

2011-06-17

208

Ultrafast spatiotemporal dynamics of terahertz generation by ionizing two-color femtosecond pulses in gases.  

PubMed

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. PMID:20867920

Babushkin, I; Kuehn, W; Köhler, C; Skupin, S; Bergé, L; Reimann, K; Woerner, M; Herrmann, J; Elsaesser, T

2010-07-30

209

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

210

JTC based concealed object detection in terahertz imaging  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

211

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

212

Electronic response of graphene to an ultrashort intense terahertz radiation pulse  

NASA Astrophysics Data System (ADS)

We have recently reported a study (Ishikawa 2010 Phys. Rev. B 82 201402) on a nonlinear optical response of graphene to a normally incident terahertz radiation pulse within the massless Dirac fermion (MDF) picture, where we have derived physically transparent graphene Bloch equations (GBE). Here we extend it to the tight-binding (TB) model and oblique incidence. The derived equations indicate that interband transitions are governed by the temporal variation of the spinor phase along the electron path in the momentum space and predominantly take place when the electron passes near the Dirac point. At normal incidence, the equations for electron dynamics within the TB model can be cast into the same form of GBE as for the MDF model. At oblique incidence, the equations automatically incorporate photon drag and satisfy the continuity equation for electron density. Single-electron dynamics strongly depend on the model and pulse parameters, but the rapid variations are averaged out after momentum-space integration. Direct current remaining after the pulse is generated in graphene irradiated by an intense monocycle terahertz pulse, even if it is linearly polarized and normally incident. The generated current depends on the carrier-envelope phase, pulse intensity and Fermi energy in a complex manner.

Ishikawa, Kenichi L.

2013-05-01

213

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

214

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

Microsoft Academic Search

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

Sushil Kumar; Alan W. M. Lee

2008-01-01

215

Resonant photo-thermal conversion for sub-terahertz imaging  

NASA Astrophysics Data System (ADS)

An original design of generic interest is proposed for fast imaging, in the field of sub-terahertz frequencies, by means of resonant coupling between an ultra-thin photo-thermal converter and a metallic grid upstream an infrared camera. The material is a sheet of polyimide material with a high content of absorptive carbon inclusions. We make use of the large difference between the IR and THz wavelengths in a quarter-wave planar geometry, to ensure a highly efficient and stable conversion process. A complete setup has been implemented for demonstration purposes, using the beam from a Gunn diode at 110 GHz. Experimental results are in good agreement with the predictions from the numerical model, which helps to validate the concept and the requirements for geometrical adjustment.

Jolly, Alain; Chassagne, Bruno; Jolly, Jean-Claude

2013-01-01

216

Physics-based processing for terahertz reflection spectroscopy and imaging  

NASA Astrophysics Data System (ADS)

The spectra obtained from Terahertz (THz) reflection imaging can be distorted by scattering from rough interfaces, layers, and granular inclusions. Since the facets of the object being imaged are not generally aligned normal to the THz beam, the received signal is produced from diffuse scattering, which can be appreciably lower in signal strength than specular returns. These challenges can be addressed with advanced signal processing approaches based upon the coherent and incoherent combination of returns from multiple sensors and frequencies. This paper presents two examples of physics-based processing strategies applied to THz imaging spectroscopy. The first method is based on synthetic aperture processing of a 2D sensor array to provide variable depth focused images of buried inclusions (a ball bearing embedded in polyethylene sample). The second method uses correlation processing to coherently combine multiple sensors and multiple frequencies to extract material signatures from measurements of THz scattering from rough interfaces. Results for both methods show an increase in performance relative to conventional imaging or spectroscopy approaches.

Zurk, L. M.; Henry, S. C.; Schecklman, S.; Duncan, D. D.

2010-11-01

217

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

218

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

219

Development of high-efficiency etalons with an optical shutter for terahertz laser pulses.  

PubMed

A high-efficiency etalon operated in the terahertz (THz) frequency region has been proposed to generate a THz pulse train. To achieve high-conversion efficiency to the pulse train, an optical shutter is employed in this etalon. The etalon is composed of a silicon (Si) plate as an input coupler and an indium-tin-oxide (ITO)-coated glass plate as an output coupler. After THz light is introduced into the etalon through the Si plate, the optical shutter pulse irradiates the Si surface to generate a photoconductive layer that acts as a highly reflective mirror for THz light. A THz pulse train and its comb-shaped spectrum have been realized by the use of the proposed etalon with the optical shutter. A finesse F of 9.04 was achieved at the free spectral range of 75 GHz in this etalon. PMID:23263086

Tsubouchi, Masaaki; Kumada, Takayuki

2012-12-17

220

Generating High-Power Short Terahertz Electromagnetic Pulses with a Multifoil Radiator  

NASA Astrophysics Data System (ADS)

We describe a multifoil cone radiator capable of generating high-field short terahertz pulses using short electron bunches. Round flat conducting foil plates with successively decreasing radii are stacked, forming a truncated cone with the z axis. The gaps between the foil plates are equal and filled with some dielectric (or vacuum). A short relativistic electron bunch propagates along the z axis. At sufficiently high particle energy, the energy losses and multiple scattering do not change the bunch shape significantly. When passing by each gap between the foil plates, the electron bunch emits some energy into the gap. Then, the radiation pulses propagate radially outward. For transverse electromagnetic waves with a longitudinal (along the z axis) electric field and an azimuthal magnetic field, there is no dispersion in these radial lines; therefore, the radiation pulses conserve their shapes (time dependence). At the outer surface of the cone, we have synchronous circular radiators. Their radiation field forms a conical wave. Ultrashort terahertz pulses with gigawatt-level peak power can be generated with this device.

Vinokurov, Nikolay A.; Jeong, Young Uk

2013-02-01

221

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

222

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

Microsoft Academic Search

We present a terahertz (THz) imaging system with a Backward Wave Oscillator (BWO). BWO Continuous-Wave THz imaging is a new approach to non-destructive testing. Many materials that are opaque to visible and infrared light are transparent to THz radiation. THz wave image provides a higher spatial resolution than microwave image by having much shorter wavelength. It also poses no known

Hongyang Yuan; Xinhao Ge; Cunlin Zhang

2008-01-01

223

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

224

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

NASA Astrophysics Data System (ADS)

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

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

2009-07-01

225

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

NASA Astrophysics Data System (ADS)

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

Jha, Pallavi; Kumar Verma, Nirmal

2014-06-01

226

A real-time terahertz time-domain polarization analyzer with 80-MHz repetition-rate femtosecond laser pulses.  

PubMed

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

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

2013-01-01

227

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

228

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

229

Distributed Bragg pulse shapers for terahertz modulation and ultrafast communications  

NASA Astrophysics Data System (ADS)

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

Purchase, Kenneth Graham

1998-11-01

230

Recording of Terahertz Pulses of Microsecond Duration Using the Thermoacoustic Effect  

NASA Astrophysics Data System (ADS)

We consider the possibility of using a thermoacoustic detector (TAD) for recording of high-power pulse radiation at frequencies of 0.55, 0.68, and 0.87 THz. Electromagnetic wave is transformed into an acoustic wave in a structure consisting of a 10-nm thick chromium film deposited on a quartz substrate and a layer of the immersion liquid that is in contact with the film. It is shown that for the pulse of microsecond duration (3-10 ?s) the waveform detected by the thermoacoustic detector is matched with high accuracy to the derivative of the terahertz pulse profile. For recording of electromagnetic radiation in the 0.5-0.9 THz frequency range it is possible to employ the simplified design of TAD, in which a transparent quartz substrate is in contact with a layer of water or ethanol.

Andreev, V. G.; Vdovin, V. A.; Kalynov, Yu. K.

2014-01-01

231

Fresnel formulas for the forced electromagnetic pulses and their application for optical-to-terahertz conversion in nonlinear crystals.  

PubMed

We show that the usual Fresnel formulas for a free-propagating pulse are not applicable for a forced terahertz electromagnetic pulse supported by an optical pulse at the end of a nonlinear crystal. The correct linear reflection and transmission coefficients that we derive show that such pulses can experience a gain or loss at the boundary. This energy change depends on linear dielectric constants only. We also predict a regime where a complete disappearance of the forced pulse under oblique incidence occurs, an effect that has no counterpart for free-propagating pulses. PMID:18233142

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

2007-11-16

232

Detection of explosives by Terahertz synthetic aperture imaging—focusing and spectral classification  

Microsoft Academic Search

In the adaptation of Terahertz (THz) synthetic aperture imaging to stand-off screening of concealed weapons and explosives, the incoming THz wavefronts exhibit significant curvature that must be considered in the image reconstruction. Consequently, the imaging array must be focused at a specific distance to correct for the wavefront curvature. In addition to the focusing correction, detection of explosives requires spectral

Alexander Sinyukov; Ivan Zorych; Zoi-Heleni Michalopoulou; Dale Gary; Robert Barat; John F. Federici

2008-01-01

233

Non-destructive imaging with compact and portable terahertz systems  

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

234

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

235

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

236

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

237

Modeling of Atmospheric Effects on Terahertz Imaging Systems.  

National Technical Information Service (NTIS)

The terahertz (THz) electromagnetic frequency band is a potentially useful domain for remote sensing in military and Homeland Security applications. Sensors operating in this band gain some of the material penetrating abilities of radio waves, some of the...

D. H. Tofsted S. G. O'Brien

2006-01-01

238

Terahertz Imaging of cyclotron emission from quantum Hall conductors  

Microsoft Academic Search

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

Susumu Komiyama

2006-01-01

239

Experimental Study of the Pulsed Terahertz Gyrotron with Record-Breaking Power and Efficiency Parameters  

NASA Astrophysics Data System (ADS)

We describe the results of studying experimentally a high-power (hundreds of kilowatts) pulsed (pulse duration of about 30 ?s) subterahertz gyrotron with the generation frequency corresponding to one of the atmosphere transparency windows. The gyrotron with an operating frequency of 0.67 THz, a power of more than 200 kW and an efficiency of 20-25% was used in the experiments on ignition of a localized discharge in a plasma. The paper presents the data about measurements of the temperature field of the emitter, calorimetric measurements of the power and efficiency of the gyrotron, and the design of the quasioptical converter of radiation to a narrow wave beam. The first experiments with the terahertz discharge in a focused wave beam of the gyrotron are briefly described.

Glyavin, M. Yu.; Luchinin, A. G.; Bogdashov, A. A.; Manuilov, V. N.; Morozkin, M. V.; Rodin, Yu.; Denisov, G. G.; Kashin, D.; Rogers, G.; Romero-Talamas, C. A.; Pu, R.; Shkvarunetz, A. G.; Nusinovich, G. S.

2014-01-01

240

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

SciTech Connect

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

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

2011-01-15

241

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

242

Discrete Pulse Transform of Images  

Microsoft Academic Search

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

Roumen Anguelov; Inger Fabris-rotelli

2008-01-01

243

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

NASA Astrophysics Data System (ADS)

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

Li, Min; Mi, Xian-Wu

2009-12-01

244

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

Microsoft Academic Search

We have modeled and demonstrated a scalable, compact, fiber-pumped terahertz source based on difference frequency mixing (DFM) in zinc germanium phosphide (ZGP) capable of producing high average and peak-power pulses. Currently, our terahertz source produces 2mW of average THz power and >40W of peak power with sub-nanosecond pulses at a repetition rate of 100kHz in the range of 2-3THz without

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

2007-01-01

245

Continuous-wave terahertz spectroscopic imaging at over 1 THz for pharmaceutical applications  

Microsoft Academic Search

Spectroscopic images were obtained using a system combining a tunable continuous-wave terahertz laser with an InP-based Schottky barrier diode detector integrating a broadband log-periodic antenna. The distribution of polymorphic forms in pharmaceutical tablets was observed in obtained at images over 1 THz.

K. Ajito; H.-J. Song; A. Hirata; A. Wakatsuki; Y. Muramoto; N. Shigekawa; T. Kumashiro; D. Asa; T. Nagatsuma; N. Kukutsu; Y. Kado

2010-01-01

246

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

247

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

248

Broadband terahertz lasing in aligned molecules  

Microsoft Academic Search

No broadband lasing medium like Ti:Saph has been demonstrated yet for terahertz radiation. We show that laser-aligned molecules can amplify broadband terahertz radiation, allowing high-energy chirped-pulse amplification at terahertz frequencies.

Andrew G. York; Howard Milchberg

2008-01-01

249

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

PubMed Central

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

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

2013-01-01

250

Terahertz technology: a boon to tablet analysis.  

PubMed

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

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

2009-05-01

251

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

SciTech Connect

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

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

2011-06-17

252

Compact Femtosecond Pulse Approach to Explosives Detection Combining InN-Based Time Domain Terahertz Spectroscopy and Laser-Induced Breakdown Spectroscopy.  

National Technical Information Service (NTIS)

The feasibility of attaining improved explosives detection and identification using complementary InN-based time-domain terahertz spectroscopy (TDTS) and laser-induced breakdown spectroscopy (LIBS) techniques employing 1550-nm femtosecond (fs) pulse techn...

A. Sampath D. Stratis-Cullum M. Wraback

2008-01-01

253

Interferometric terahertz imaging for detection of lethal agents using artificial neural network analyses  

Microsoft Academic Search

Interferometric imaging is a non-invasive, non-contact method to detect concealed lethal agents employing spectral imaging in the terahertz (THz) range. Parallel to the experimental testing over short range, extensive modeling simulates reconstructed images of lethal agents at different frequencies applying interferometric techniques. Near-field correction to such imaging has been accounted for and edge probe algorithm and consequent artificial neural network

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

2006-01-01

254

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

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

255

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

SciTech Connect

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

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

2010-04-09

256

Terahertz frequency standard  

NASA Astrophysics Data System (ADS)

An idea of highly stable terahertz pulse train designing by transforming stabilized optical femtosecond pulses using photoconducting antenna is offered. Experimental data obtained with THz pulsed spectrometer were used for creating a numerical mathematical model of THz comb.

Tsapenko, Konstantin P.; Lazarev, Vladimir A.; Leonov, Stanislav O.; Pnev, Aleksey B.

2014-03-01

257

Terahertz control of nanotip photoemission  

NASA Astrophysics Data System (ADS)

The active control of matter by strong electromagnetic fields is of growing importance, with applications all across the optical spectrum from the extreme-ultraviolet to the far-infrared. In recent years, phase-stable terahertz fields have shown tremendous potential for observing and manipulating elementary excitations in solids. In the gas phase, on the other hand, driving free charges with terahertz transients provides insight into ultrafast ionization dynamics. Developing such approaches for locally enhanced terahertz fields in nanostructures will create new means to govern electron currents on the nanoscale. Here, we use single-cycle terahertz transients to demonstrate extensive control over nanotip photoelectron emission. The terahertz near-field is shown to either enhance or suppress photocurrents, with the tip acting as an ultrafast rectifying diode. We record phase-resolved sub-cycle dynamics and find spectral compression and expansion arising from electron propagation within the terahertz near-field. These interactions produce rich spectro-temporal features and offer unprecedented control over ultrashort free electron pulses for imaging and diffraction.

Wimmer, L.; Herink, G.; Solli, D. R.; Yalunin, S. V.; Echternkamp, K. E.; Ropers, C.

2014-06-01

258

Real-Time Terahertz Imaging Using a Quantum Cascade Laser and Uncooled Microbolometer Focal Plane Array.  

National Technical Information Service (NTIS)

Real-time imaging in the terahertz (THz) spectral range was achieved using an uncooled, 160 120 pixel infrared microbolometer camera and a milliwatt- scale quantum cascade laser (QCL). By replacing the camera's original focusing optics with a Tsurupica-ba...

B. N. Behnken

2008-01-01

259

Spectroscopy and imaging system using a frequency agile ring-cavity terahertz-wave parametric oscillator  

Microsoft Academic Search

A spectroscopy and imaging system using a ring cavity terahertz (THz) wave parametric oscillator was developed. We demonstrate the differentiation of tissue types in a watery microtomed biological section using differences of water concentration. The contrast of differentiation for watery tissues was improved over that of the dried tissue.

Tomofumi Ikari; Koichi Akiyama; Hiroaki Minamide; Hiromasa Ito

2007-01-01

260

Terahertz inverse synthetic aperture radar imaging using self-mixing interferometry with a quantum cascade laser.  

PubMed

We propose a terahertz (THz)-frequency synthetic aperture radar imaging technique based on self-mixing (SM) interferometry, using a quantum cascade laser. A signal processing method is employed which extracts and exploits the radar-related information contained in the SM signals, enabling the creation of THz images with improved spatial resolution. We demonstrate this by imaging a standard resolution test target, achieving resolution beyond the diffraction limit. PMID:24784063

Lui, H S; Taimre, T; Bertling, K; Lim, Y L; Dean, P; Khanna, S P; Lachab, M; Valavanis, A; Indjin, D; Linfield, E H; Davies, A G; Raki?, A D

2014-05-01

261

Terahertz beam steering and frequency tuning by using the spatial dispersion of ultrafast laser pulses.  

PubMed

We demonstrate a terahertz (THz) beam steering method using difference frequency generation that is based on the principle of phased array antennas. A strip-line photoconductive antenna was illuminated by two spatially dispersed beams produced from an ultrafast laser. THz radiation with a bandwidth of 65 GHz was generated from the overlapping area of the two beams, between which the frequency difference was approximately constant. We confirmed that the THz beam can be steered by tilting one of the incident pump beams so as to change their relative phase relation. The steering range of the THz beam was 29 degrees when the angle between the incident pump beams was only varied within a range of 0.155 degrees, that is, 187 times less. In addition, by laterally shifting one of the pump beams, the frequency of the THz radiation could be tuned from 0.3 to 1.7 THz. This technique can be applied to high-speed terahertz imaging and spectroscopy systems. PMID:18607423

Maki, Ken-ichiro; Otani, Chiko

2008-07-01

262

Design of an on-line measuring system for 0.14THz high-power terahertz pulse  

NASA Astrophysics Data System (ADS)

An on-line measuring system, including an aperture-coupling structure and a novel high-power pulse detector, is proposed in this paper to measure the output pulses from high-power 0.14THz surface wave oscillator (SWO). At first a T-type coupling structure between the TM01 mode of circular waveguide with radius of 6mm and TE10 mode of rectangular waveguide WR6 is designed. Based on loose coupling theory,the coupling degree of this structure is derived and calculated, reaching about -47dB with the aperture radius of 0.4mm and length of 0.5mm. The reasonable coincidence is found between the theoretical computation and numerical simulation employing the three-dimensional finite difference time domain method. Then a novel high-power terahertz pulse detector based on hot electron effect in semiconductors is developed for the detection of output pulses from T-type coupling structure. With hot electron theory, the working principle of the detector is elucidated, also its sensitivity is simply analyzed, showing that this detector is capable of handling the pulse power as high as 2kW. The present 0.14THz on-line measuring system would be convenient to monitor the terahertz pulse shape and pulse power during the application researches of SWO besides increasing the accuracy of its pulse power measurement.

Wang, Guangqiang; Wang, Jianguo; Li, Xiaoze; Tong, Changjiang; Wang, Xuefeng

2011-02-01

263

Dielectric Covered Planar Antennas at Submillimeter Wavelengths for Terahertz Imaging  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

264

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

265

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

Microsoft Academic Search

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

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

2011-01-01

266

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

Microsoft Academic Search

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

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

2000-01-01

267

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

Microsoft Academic Search

A non-invasive means to detect and characterize concealed agents of mass destruction in near real-time with a wide field-of-view is under development. The method employs spatial interferometric imaging of the characteristic transmission or reflection frequency spectrum in the Terahertz range. However, the successful (i.e. low false alarm rate) analysis of such images will depend on correct distinction of the true

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

2004-01-01

268

A low cost alternative to terahertz imaging for security and defense applications  

Microsoft Academic Search

A new near-infrared (NIR) imaging technique has been devel- oped that can be used for applications previously considered possible to image only by using terahertz (THz) waves. The tech- nique developed at the University of Warwick uses NIR beams of light—around the wavelengths found in ordinary domes- tic remote controls—and signal recovery techniques commonly used in astronomy. This alternative technique

Geoff Diamond

2008-01-01

269

Real-time, continuous-wave terahertz imaging by use of a microbolometer focal-plane array  

Microsoft Academic Search

Real-time, continuous-wave terahertz imaging is demonstrated with a 10 mW, 2.52 THz (118.8 µm) far-infrared gas laser and a 160×120 element microbolometer camera. The microbolometer camera is designed for wavelengths of 7.5-14 µm but retains sensitivity at terahertz (THz) frequencies. The setup has no moving parts, and transmission-mode THz images can be obtained at the video rate of 60 frames\\/s.

Alan Wei Min Lee; Qing Hu

2005-01-01

270

A Fiber-Laser Pumped, High-Power Terahertz Wave Source Based on Optical Rectification of Femtosecond Pulses in 4-Dimethylamino-N-methyl-4-stilbazolium Tosylate Crystal  

NASA Astrophysics Data System (ADS)

We demonstrate a compact, broadband, and high-power terahertz wave-generation scheme via optical rectification of femtosecond pulses in a 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal. We used a femtosecond fiber laser with a high repetition rate and an average power of a few hundred milliwatts to illuminate the DAST crystal. The terahertz waves emitted from the DAST crystal were measured using a calibrated pyroelectric sensor. We obtained an average power of 18 ?W, more than two orders of magnitude greater than the average terahertz power emitted by a typical photoconductive antenna.

Tripathi, Saroj R.; Murate, Kousuke; Uchida, Hirohisa; Takeya, Kei; Kawase, Kodo

2013-07-01

271

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

272

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

PubMed Central

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

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

2013-01-01

273

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

PubMed

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

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

2013-01-01

274

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

SciTech Connect

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

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

2011-02-15

275

High Efficient, Intense and Compact Pulsed D2O Terahertz Laser Pumped With a TEA CO2 Laser  

NASA Astrophysics Data System (ADS)

A high efficient, intense and compact pulsed D2O terahertz laser is presented, which is pumped by a multi-transverse mode TEA CO2 laser. For D2O gas as the active medium, with the cavity length of 120 cm, pulse energy of the THz laser has been investigated as the variation of pump energy and gas pressure. When the pump energy was 1.41 J, the maximum single pulse energy of 6.2 mJ was achieved at the wavelength of 385 ?m. Photon conversion efficiency as high as 36.5% was obtained when laser operated at the maximum output energy. As the pump energy was raised from 0.57 to 1.41 J, the optimum pressure was slightly changed from 400 to 700 Pa. The THz pulse consisted of a spike pulse with pulse width of 120 ns and a tail pulse with pulse width of about 170 ns. The peak power of the spike pulse is about 44.3 kW. Comparing with the occurring time and pulse width of pump pulse, 70 ns delay and 10ns broadening were observed in the THz spike pulse.

Geng, Lijie; Qu, Yanchen; Zhao, Weijiang; Du, Jun

2013-12-01

276

An ultrafast terahertz scanning tunnelling microscope  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

277

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

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

278

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

279

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

280

Passive stand-off terahertz imaging with 1 hertz frame rate  

Microsoft Academic Search

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

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

2008-01-01

281

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

Microsoft Academic Search

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

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

2011-01-01

282

Terahertz laser frequency combs  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

283

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

SciTech Connect

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

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

2011-05-15

284

Passive millimetre-wave imaging and how it differs from terahertz imaging.  

PubMed

It is well known that millimetre-wave systems can penetrate poor weather, dust and smoke far better than infrared or visible systems. Imaging in this band offers the opportunity to be able to navigate and perform surveillance in these conditions of poor visibility. Furthermore, the ability to penetrate dielectrics such as plastic and cloth has opened up the opportunity of detecting weapons and contraband hidden under people's clothing. The optical properties of materials have a direct impact on the applicability of imaging systems. In the terahertz band solids have absorptions which can be assigned to vibrational modes. Lattice modes occur at the lowest frequencies and polythene, for example, has a lattice mode at 2.4 THz. Solids have no such absorptions in the millimetre bands (30-300 GHz) and image contrast is produced by differences in transmission, reflection and absorption. A novel, real-time, mechanically scanned, passive millimetre-wave imager has been designed. The antenna elements are based on a combination of a Schmidt camera and a conical scanner, both of which have their origins in optical systems. Polarization techniques, which were developed for operation in the centimetric band, are used to fold the optics. Both 35 GHz and 94 GHz versions have been constructed. PMID:15306527

Appleby, R

2004-02-15

285

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

NASA Astrophysics Data System (ADS)

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

Li, Zhuo; Cui, Tie Jun

2010-03-01

286

Terahertz imaging using the Jefferson Lab -- FEL high power broadband terahertz source  

Microsoft Academic Search

Imaging using THz radiation is of considerable interest due to the non-ionizing nature of the radiation as well as the relative transmission, absorption, and reflection of various materials of interest. With a source of sufficient power and spectral characteristics, it is possible to realize imaging capabilities that were not previously possible. At the Jefferson Lab -- Free Electron Laser Facility,

J. Michael Klopf; Matthew Coppinger; Nathan Sustersic; James Kolodzey; Gwyn P. Williams

2007-01-01

287

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

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

288

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

Microsoft Academic Search

The terahertz characteristics of a dense-magnetized-collisional-bounded plasma under normal incident are analyzed in this study, which is of practical significance in plasma diagnostics with electromagnetic waves. We theoretically calculate the reflection, absorption, and transmission coefficients for right- and left-handed polarized terahertz waves through a uniform, magnetized, and collisional plasma slab bounded by lossless transparent walls. The power absorption spectra in

Chengxun Yuan; Zhongxiang Zhou; Xiaoli Xiang; Hongguo Sun; Shaozhi Pu

2010-01-01

289

Higgs Amplitude Mode in the BCS Superconductors Nb1-xTixN Induced by Terahertz Pulse Excitation  

NASA Astrophysics Data System (ADS)

Ultrafast responses of BCS superconductor Nb1-xTixN films in a nonadiabatic excitation regime were investigated by using terahertz (THz) pump-THz probe spectroscopy. After an instantaneous excitation with the monocycle THz pump pulse, a transient oscillation emerges in the electromagnetic response in the BCS gap energy region. The oscillation frequency coincides with the asymptotic value of the BCS gap energy, indicating the appearance of the theoretically anticipated collective amplitude mode of the order parameter, namely the Higgs amplitude mode. Our result opens a new pathway to the ultrafast manipulation of the superconducting order parameter by optical means.

Matsunaga, Ryusuke; Hamada, Yuki I.; Makise, Kazumasa; Uzawa, Yoshinori; Terai, Hirotaka; Wang, Zhen; Shimano, Ryo

2013-08-01

290

Focusing and imaging of a virtual all-optical tunable terahertz Fresnel zone plate.  

PubMed

A virtual all-optical tunable terahertz Fresnel zone plate is achieved utilizing the localized distribution of the transient electron plasma on a silicon wafer. Its focusing and imaging performance are experimentally demonstrated. Experimental results show that the effect of the virtual zone plate is the same as an actual one. Adjusting the spatial pattern of the electron plasma, the central wavelength and the focal length of the virtual zone plate can be all-optically dynamically steered. The research is a significant step to the development of tunable optical imaging elements. PMID:24322118

Wang, Xinke; Xie, Zhenwei; Sun, Wenfeng; Feng, Shengfei; Cui, Ye; Ye, Jiasheng; Zhang, Yan

2013-11-15

291

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

292

Coherent three-dimensional terahertz imaging through self-mixing in a quantum cascade laser  

NASA Astrophysics Data System (ADS)

We demonstrate coherent terahertz (THz) frequency imaging using the self-mixing effect in a quantum cascade laser (QCL). Self-mixing voltage waveforms are acquired at each pixel of a two-dimensional image of etched GaAs structures and fitted to a three-mirror laser model, enabling extraction of the amplitude and phase parameters of the reflected field. From the phase, we reconstruct the depth of the sample surface, and we show that the amplitude can be related to the sample reflectance. Our approach is experimentally simple and compact, and does not require frequency stabilization of the THz QCL.

Dean, Paul; Valavanis, Alex; Keeley, James; Bertling, Karl; Leng Lim, Yah; Alhathlool, Raed; Chowdhury, Siddhant; Taimre, Thomas; Li, Lianhe H.; Indjin, Dragan; Wilson, Stephen J.; Raki?, Aleksandar D.; Linfield, Edmund H.; Giles Davies, A.

2013-10-01

293

Terahertz imaging system for stand-off detection of threats  

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

294

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

295

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

296

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

297

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

SciTech Connect

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

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

2005-05-31

298

Probing ultrafast temperature changes of aqueous solutions with coherent terahertz pulses.  

PubMed

We introduce an infrared pump-terahertz probe technique to measure the thermalization dynamics of aqueous solutions with a time resolution <200??fs. This technique makes use of the sensitivity of the terahertz absorption to the temperature of the hydrogen bond network. The thermalization dynamics of different aqueous solutions are measured and compared to the dynamics inferred from ultrafast infrared pump-infrared probe measurements on the intramolecular stretch vibration of water. This technique can shed new light on important aspects of energy transfer and heat dynamics and is applicable to a wide range of systems. PMID:24686587

Backus, Ellen H G; Tielrooij, Klaas-Jan; Bonn, Mischa; Bakker, Huib J

2014-04-01

299

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

NASA Astrophysics Data System (ADS)

To monitor the density of photo-generated charge carriers on a semiconductor surface, we demonstrate a detectorless imaging system based on the analysis of the optical feedback in terahertz quantum cascade lasers. Photo-excited free electron carriers are created in high resistivity n-type silicon wafers via low power (?40 mW/cm2) continuous wave pump laser in the near infrared spectral range. A spatial light modulator allows to directly reconfigure and control the photo-patterned intensity and the associated free-carrier density distribution. The experimental results are in good agreement with the numerical simulations.

Mezzapesa, F. P.; Columbo, L. L.; Brambilla, M.; Dabbicco, M.; Vitiello, M. S.; Scamarcio, G.

2014-01-01

300

Materials for terahertz science and technology  

Microsoft Academic Search

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

Bradley Ferguson; Xi-Cheng Zhang

2002-01-01

301

Portable video rate time domain terahertz line imager for security and aerospace nondestructive examination  

NASA Astrophysics Data System (ADS)

A portable video rate time-domain terahertz (TD-THz) reflection line-scanner suitable for aerospace destructive examination (NDE) and security inspection is described. The imager scans a line 6 inches wide and collects a TD-THz cross-sectional "B-scan" of the sub-surface structure at rates up to 30 Hz. The imager is hand-held. By rolling the scanner over surface, a radiographic two dimensional "C-Scan" image can be stitched together from the individual lines at a rate of 1-4 inches per second (depending on desired resolution). The case is 8.7 in. wide (12.9 in. with wheels), 12.5 in. long, and 7.9 in. high. The weight is approximately 11 lbs. Example images taken with the scanner of radome THz NDE are shown.

Zimdars, David; Fichter, G.; Megdanoff, C.; Murdock, M.; Duling, Irl; White, Jeffrey; Williamson, S. L.

2010-04-01

302

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

303

Diffuse reflection imaging at terahertz frequencies for security applications  

Microsoft Academic Search

We report diffuse reflection imaging of concealed powdered samples in atmospheric air using a quantum cascade laser operating at 2.83 THz. The imaging system uses a helium-cooled silicon bolometer for mapping radiation diffusely reflected and scattered from samples, and a room-temperature pyroelectric sensor for simultaneously acquiring a specular image. A range of powders concealed within plastic packaging and standard FedEx

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

2007-01-01

304

Millimeter-Wave and Terahertz Imaging in Security Applications  

NASA Astrophysics Data System (ADS)

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

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

305

Real-Time, Two-Dimensional Terahertz Beam Imaging.  

National Technical Information Service (NTIS)

In ARO STTR Phase 1 program, we have demonstrated the concept and developed a real-time, two-dimensional THz wave imaging system. The THz imaging system uses electro-optic crystals and is capable of time-domain far-infrared spectroscopy across a frequency...

X. Zhang Z. Jiang

1999-01-01

306

Identification and classification of chemicals using terahertz reflective spectroscopic focal-plane imaging system  

NASA Astrophysics Data System (ADS)

We present terahertz (THz) reflective spectroscopic focal-plane imaging of four explosive and bio-chemical materials (2, 4-DNT, Theophylline, RDX and Glutamic Acid) at a standoff imaging distance of 0.4 m. The 2 dimension (2-D) nature of this technique enables a fast acquisition time and is very close to a camera-like operation, compared to the most commonly used point emission-detection and raster scanning configuration. The samples are identified by their absorption peaks extracted from the negative derivative of the reflection coefficient respect to the frequency (-dr/dv) of each pixel. Classification of the samples is achieved by using minimum distance classifier and neural network methods with a rate of accuracy above 80% and a false alarm rate below 8%. This result supports the future application of THz time-domain spectroscopy (TDS) in standoff distance sensing, imaging, and identification.

Zhong, Hua; Redo-Sanchez, Albert; Zhang, X.-C.

2006-10-01

307

On infrared and terahertz imaging of surface plasmons in high-Tc superconductors  

NASA Astrophysics Data System (ADS)

Recent scattering-mode scanning near-field optical microscopy (s-SNOM) experiments have imaged surface plasmons in graphene at infrared frequencies.footnotetextZ. Fei et al., Nature, 487, 82 (2012). The scanning probe launches surface plasmons and detects their standing-wave interference pattern upon reflection from the sample edge. The surface plasmon dispersion relation directly relates the standing wave fringe separation and amplitude decay to the optical constants of the sample. We have modeled surface plasmon s-SNOM imaging for high-Tc superconductor (HTSC) thin films. Our results indicate that surface plasmons can be imaged in HTSCs at frequencies near or below the superconducting gap. This would allow for a direct measurement of HTSC optical constants below the gap. For known HTSCs such as YBCO, this is in the far-IR or terahertz range. Our simulations show that this method can also distinguish between superconducting and normal states at the nanoscale.

Stinson, H. T.; Fei, Z.; Rodin, A. S.; McLeod, A. S.; Fogler, M. M.; Basov, D. N.

2013-03-01

308

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

309

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

310

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

311

Terahertz holography for imaging amplitude and phase objects.  

PubMed

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

Hack, Erwin; Zolliker, Peter

2014-06-30

312

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

SciTech Connect

Interactions of 100-fs laser pulses with solid targets at intensities of 10{sup 18} W/cm{sup 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{sup -8} to 10{sup -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.

Li Chun; Zhou Mulin; Ding Wenjun; Du Fei; Liu Feng; Li Yutong; Wang Weimin; Ma Jinglong; Chen Liming; Lu Xin; Dong Quanli; Wang Zhaohua; Wei Zhiyi [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190 (China); Sheng Zhengming; Zhang Jie [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190 (China); Key Laboratory for Laser Plasmas of the Ministry of Education of China and Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China); Lou Zheng; Shi Shengcai [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)

2011-09-15

313

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

314

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

315

Broadband Terahertz Pulses Generated by a Compact Femtosecond Photonic Crystal Fiber Amplifier  

Microsoft Academic Search

We demonstrate a scalable, compact, high-power, and broadband terahertz (THz) source based on a cutting-edge large-mode-area photonic-crystal-fiber amplifier system. A 3-mm (110)-cut bulk GaP crystal was used as the THz emitter based on an optical rectification technique. Systematic optimization of the operation parameters allowed a THz output up to 150 ?W to be achieved with an input laser power of

Feng Liu; You-Jian Song; Qi-Rong Xing; Ming-Lie Hu; Yan-Feng Li; Chang-Lei Wang; Lu Chai; Wei-Li Zhang; Aleksei M. Zheltikov; Ching-Yue Wang

2010-01-01

316

Narrowband continuous-wave terahertz generation and imaging  

NASA Astrophysics Data System (ADS)

The output of seeded, dual periodically poled lithium niobate (PPLN) optical parametric generators (OPG) are combined in the nonlinear crystal 4-dimthylamino-N-methyl-4-stilbazolium-tosylate (DAST) to produce a widely tunable narrowband THz source via difference frequency generation (DFG). We have demonstrated that by employing this type of configuration we are able to tune our system seamlessly, without mode-hops, from 1.5 THz to 21THz with a minimum bandwidth of 3.1 GHz. The bandwidth of the source was measured by using the THz transmission spectrum of water vapor lines over a 3-meter path length. By selecting of the DFG pump wavelength to be at 1380 nm and the signal wavelength to tune over a range from 1380 nm to 1570 nm, we produced several maxima in the output THz spectrum that was dependent on the phase matching ability of the DAST crystal and the efficiency of our pyro-electric detector. Due to the effects of dispersive phase matching, filter absorption of the THz waves, and two-photon absorption multiple band gaps in the overall spectrum occur and are discussed. Employing the dual generator scheme, we have obtained THz images at several locations in the spectrum using an infrared camera that runs at a rate of 35 frames per second. We have demonstrated the ability to image 13 THz to 20 THz under static conditions. We will present images of carbon fibers illuminated at different THz frequencies.

Dolasinski, Brian; Powers, Peter

2014-03-01

317

Terahertz phase contrast imaging of sorption kinetics in porous coordination polymer nanocrystals using differential optical resonator.  

PubMed

The enhancement of light-matter coupling when light is confined to wavelength scale volumes is useful both for studying small sample volumes and increasing the overall sensing ability. At these length scales, nonradiative interactions are of key interest to which near-field optical techniques may reveal new phenomena facilitating next-generation material functionalities and applications. Efforts to develop novel chemical or biological sensors using metamaterials have yielded innovative ideas in the optical and terahertz frequency range whereby the spatially integrated response over a resonator structure is monitored via the re-radiated or leaked light. But although terahertz waves generally exhibit distinctive response in chemical molecules or biological tissue, there is little absorption for subwavelength size sample and therefore poor image contrast. Here, we introduce a method that spatially resolves the differential near-field phase response of the entire resonator as a spectral fingerprint. By simultaneously probing two metallic ring resonators, where one loaded with the sample of interest, the differential phase response is able to resolve the presence of guest molecules (e.g. methanol) as they are adsorbed or released within the pores of a prototypical porous coordination polymer. PMID:24921804

Blanchard, F; Sumida, K; Wolpert, C; Tsotsalas, M; Tanaka, T; Doi, A; Kitagawa, S; Cooke, D G; Furukawa, S; Tanaka, K

2014-05-01

318

Power-scalable, polarization-stable, dual-colour DFB fibre laser system for CW terahertz imaging  

Microsoft Academic Search

Imaging with electromagnetic radiation in the terahertz (THz) range has received a large amount of attention during recent years. THz imaging systems have diverse potential application areas such as security screening, medical diagnostics and non-destructive testing. We will discuss a power-scalable, dual-colour, polarization-maintaining distributed feedback (DFB) fibre laser system with an inherent narrow linewidth from the DFB fibre laser oscillators.

Finn Eichhorn; Jens Engholm Pedersen; Peter Uhd Jepsen

2008-01-01

319

Photonic time-division multiplexing (OTDM) using ultrashort picosecond pulses in a terahertz optical asymmetric demultiplexer (TOAD)  

NASA Astrophysics Data System (ADS)

The performance of a terahertz optical asymmetric demultiplexer (TOAD) operating with an ordinary fiber and with a DDF and DIF (dispersion decreasing and increasing fiber) configurations, for three lengths of fiber ( ?=?/2,2? and 5?) and using soliton and quasi-soliton laser profiles for the control pulse, was studied. The numerical simulations show that the increase of the fiber length leads to the decrease of the power for the first and second demultiplexed pulses and leads to a broadening of these pulses, with the exception of the TOAD operating with the DDF fiber. For the TOAD operating with a basic telecommunication fiber one see that the increase of the power of the control power lead to a strong compression of the demultiplexed pulse. Operating the TOAD using a DDF fiber one can say that the control power necessary to demultiplex the signal pulse is always lower compared with the TOAD with the normal telecommunication fiber. This is a strong suggestion that the use of the DDF fiber will allow the use of less control power. Our simulations considering the TOAD operating with a DDF and DIF with a linear profile conclude that it is possible to operate the TOAD with lower control power using a DDF fiber setup. For this device the demultiplexed pulses will present a compression on time duration and will be insensitive to the time profile of the control pulse. We also did simulations with the TOAD operating with DDF in four different profiles: hyperbolic, exponential, linear and Gaussian. For all the profiles the increase of the length of the fiber also decreases the pump power of the three first peaks for the soliton and quasi-soliton regimes. The first critical power is always lower for the quasi-soliton regime compared to the soliton regime for all profiles under consideration and all lengths of the TOAD under consideration. It was also observed that for all the profiles and lengths of fiber one has pulse compression for the switched pulse. For the ?=2? fiber with the hyperbolic profile, both soliton and quasi-soliton profiles present the lowest critical power and the highest compression factors for all the considered profiles.

Melo, A. M.; Lima, J. L. S.; de Oliveira, R. S.; Sombra, A. S. B.

2002-05-01

320

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

321

Real-time, continuous-wave terahertz imaging by use of a microbolometer focal-plane array.  

PubMed

Real-time, continuous-wave terahertz imaging is demonstrated with a 10 mW, 2.52 THz (118.8 microm) far-infrared gas laser and a 160 x 120 element microbolometer camera. The microbolometer camera is designed for wavelengths of 7.5-14 microm but retains sensitivity at terahertz (THz) frequencies. The setup has no moving parts, and transmission-mode THz images can be obtained at the video rate of 60 frames/s. The peak signal-to-noise ratio is estimated to be 13 dB for a single frame of video, acquired in 16 ms. With this setup, THz imaging through a FedEx envelope is demonstrated, showing the feasibility of real-time mail screening. PMID:16208900

Lee, Alan Wei Min; Hu, Qing

2005-10-01

322

A 1.35 mJ ammonia Fabry–Perot cavity terahertz pulsed laser with metallic capacitive-mesh input and output couplers  

Microsoft Academic Search

An efficient ammonia Fabry–Perot (F–P) cavity terahertz (THz) laser has been studied experimentally in this article. The input and output couplers also served as sealed windows fabricated by depositing nickel capacitive metallic meshes on ZnSe and high-resistivity silicon substrates have been constructed as a F–P oscillator. Using the THz laser, the properties related to THz pulsed laser such as beam

Chun-chao Qi; Du-luo Zuo; Yan-zhao Lu; Liang Miao; Jie Yin; Zu-hai Cheng

2010-01-01

323

Superhuman Vision - Seeing with Terahertz  

NSDL National Science Digital Library

This article is an introduction to terahertz waves and imaging applications that use them. An explanation of how the reflection and absorption of these electromagnetic waves can be used to generate 3D images and identify materials is provided. The site also presents components developed to improve the performance and functionality of terahertz imaging systems.

2006-12-28

324

Terahertz NDE for Metallic Surface Roughness Evaluation  

NASA Technical Reports Server (NTRS)

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

Madaras, Eric I.; Anastasi, Robert F.

2006-01-01

325

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

326

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

NASA Astrophysics Data System (ADS)

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

Catapano, Ilaria; Soldovieri, Francesco

2014-05-01

327

Optimization of single-cycle terahertz generation in LiNbO3 for sub-50 femtosecond pump pulses.  

PubMed

We compare different tilted-pulse-front pumping schemes for single-cycle THz generation in LiNbO(3) crystals both theoretically and experimentally in terms of conversion efficiency. The conventional setup with a single lens as an imaging element has been found to be highly inefficient in the case of sub-50 fs pump pulses, mainly due to the resulting chromatic aberrations. These aberrations are avoided in the proposed new setup, which employs two concave mirrors in a Keplerian telescope arrangement as the imaging sequence. This partially compensates spherical aberrations and results in a ca. six times higher conversion efficiency in the case of 35-fs optical pump pulse duration compared to the single-lens setup. A THz field strength of 60 kV/cm was obtained using 0.5 mJ pump pulses. The divergence of the THz beam has been found experimentally to depend on the pump imaging scheme employed. PMID:23546064

Kunitski, Maksim; Richter, Martin; Thomson, Mark D; Vredenborg, Arno; Wu, Jian; Jahnke, Till; Schöffler, Markus; Schmidt-Böcking, Horst; Roskos, Hartmut G; Dörner, Reinhard

2013-03-25

328

Underwater modulated pulse laser imaging system  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

329

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

PubMed

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

Simoens, François; Meilhan, Jérôme

2014-03-28

330

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

Microsoft Academic Search

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

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

2011-01-01

331

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

332

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

PubMed

The development of self-assembled nanostructure technologies has recently opened the way towards a wide class of semiconductor integrated devices, with progressively optimized performances and the potential for a widespread range of electronic and photonic applications. Here we report on the development of field effect transistors (FETs) based on semiconductor nanowires (NWs) as highly-sensitive room-temperature plasma-wave broadband terahertz (THz) detectors. The electromagnetic radiation at 0.3?THz is funneled onto a broadband bow-tie antenna, whose lobes are connected to the source and gate FET electrodes. The oscillating electric field experienced by the channel electrons, combined with the charge density modulation by the gate electrode, results in a source-drain signal rectification, which can be read as a DC signal output. We investigated the influence of Se-doping concentration of InAs NWs on the detection performances, reaching responsivity values higher than 100 V W?¹, with noise-equivalent-power of ?10?? W Hz(?½). Transmission imaging experiments at 0.3 THz show the good reliability and sensitivity of the devices in a real practical application. PMID:23618953

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

2013-05-31

333

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

334

Imaging embryonic development with ultrashort pulse microscopy  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

335

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

NASA Astrophysics Data System (ADS)

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

Fang, Qiang

336

15-Terahertz pulse generation arising from modulation instability oscillation in a colliding-pulse mode-locking dye laser  

SciTech Connect

15-Thz trains of a few-tens-of-femtoseconds optical pulses were generated by modulation instability oscillation in a colliding-pulse mode-locked dye laser. A repeatable and stable modulation instability regime was obtained with the laser operating in the anomalous-dispersion regime and with a low saturable-absorber concentration. Autocorrelation measurements indicate that subpulses were completely separated in the real time. Variations of the modulation with the pump power and the amount of dispersion in the cavity are in good agreement with the modulation instability theory.

Wang, C.; Baldeck, P. L.; Budansky, Y.; Alfano, R.

1989-05-15

337

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

338

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

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

339

Transient Increase of the Energy Gap of Superconducting NbN Thin Films Excited by Resonant Narrow-Band Terahertz Pulses  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

340

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

PubMed

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

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

2013-06-28

341

Terahertz spectroscopic investigations of leather in terahertz wave range  

NASA Astrophysics Data System (ADS)

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

Song, Mei-jing; Li, Jiu-sheng

2011-11-01

342

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

343

Nonstationary time-domain statistics of multiply scattered broadband terahertz pulses  

Microsoft Academic Search

We examine the time-domain statistics of randomly varying electric fields generated by multiple scattering of single-cycle electromagnetic pulses in a random medium. This analysis emphasizes the fact that these measured random fields are not stationary, as is commonly assumed for diffusing photons generated with a narrowband light source. We demonstrate that the nonstationarity is a consequence of the time dependence

Jeremy Pearce; Kevin Doyle; Zhongping Jian; Jason Deibel; Daniel M. Mittleman

2006-01-01

344

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

345

Double-pulsed diffusional kurtosis imaging.  

PubMed

Diffusional kurtosis imaging (DKI) is extended to double-pulsed-field-gradient (d-PFG) diffusion MRI sequences. This gives a practical approach for acquiring and analyzing d-PFG data. In particular, the leading d-PFG effects, beyond what conventional single-pulsed field gradient (s-PFG) provides, are interpreted in terms of the kurtosis for a diffusion displacement probability density function (dPDF) in a six-dimensional (6D) space. The 6D diffusional kurtosis encodes the unique information provided by d-PFG sequences up to second order in the b-value. This observation leads to a compact expression for the signalmagnitude, and it suggests novel data acquisition and analysis methods. Double-pulsed DKI (DP-DKI) is demonstrated for in vivo mouse brain with d-PFG data obtained at 7 T. PMID:24623712

Jensen, Jens H; Hui, Edward S; Helpern, Joseph A

2014-04-01

346

Two-pulse structured illumination imaging.  

PubMed

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

Kristensson, Elias; Berrocal, Edouard; Aldén, Marcus

2014-05-01

347

Coded excitation of broadband terahertz using optical rectification in poled lithium niobate  

Microsoft Academic Search

We demonstrate coded excitation of broadband terahertz using optical rectification in poled lithium niobate patterned with a 53-bit binary phase code. Digital pulse compression produces near single-cycle terahertz pulses at 1.2 THz.

T. BumaandT; T. B. Norris

2005-01-01

348

Sampling of broadband terahertz pulses with thick electro-optic crystals  

Microsoft Academic Search

The authors show by experiment and theory that thick electro-optic crystals are suitable media for sampling electromagnetic radiation from 0.3 to 50 THz with 10 fs visible laser pulses. For example, the detection of frequencies above 10 THz with a 250 mum thick, -oriented ZnTe crystal is as efficient as that with a 10 mum thin crystal. This surprising behavior

Tobias Kampfrath; Jan Nötzold; Martin Wolf

2007-01-01

349

A terahertz molecular switch.  

PubMed

We present time-dependent results describing the current through a molecular device, modeled as a complex with two active centers connected to leads under bias. We show that, at a properly adjusted external voltage, a passing terahertz electromagnetic pulse may cause a transition between states of finite and negligible current, suggesting that the system might be useful as a nanoscopic switch in the terahertz range. A phase diagram defining the bias region in which the transition takes place within a short time is given. As described, the physical processes involved are of an entirely different nature than those in ordinary photodetectors. PMID:12786110

Orellana, P; Claro, F

2003-05-01

350

Terahertz wave generation and propagation in thin-film lithium niobate produced by crystal ion slicing  

Microsoft Academic Search

Terahertz phonon-polariton generation and real-space imaging with femtosecond optical pulses are demonstrated in a 10-?m-thick film of single-crystalline lithium niobate that was generated through crystal ion slicing. The film dispersion properties were characterized throughout the polariton wavelength range of 5–100 ?m, revealing substantial slab waveguide behavior at the longer wavelengths.

David W. Ward; Eric R. Statz; Keith A. Nelson; Ryan M. Roth; Richard M. Osgood

2005-01-01

351

Terahertz wave generation and propagation in thin-film lithium niobate produced by crystal ion slicing  

Microsoft Academic Search

Terahertz phonon-polariton generation and real-space imaging with femtosecond optical pulses are demonstrated in a 10-mum-thick film of single-crystalline lithium niobate that was generated through crystal ion slicing. The film dispersion properties were characterized throughout the polariton wavelength range of 5-100 mum, revealing substantial slab waveguide behavior at the longer wavelengths.

David W. Ward; Eric R. Statz; Keith A. Nelson; Ryan M. Roth; Richard M. Osgood

2005-01-01

352

Pulsed EPR imaging of nitroxides in mice  

NASA Astrophysics Data System (ADS)

Nitroxides, unlike trityl radicals, have shorter T2s which until now were not detectable in vivo by a time-domain pulsed Electron Paramagnetic Resonance (EPR) spectrometer at 300 MHz since their phase memory times were shorter than the spectrometer recovery times. In the current version of the time-domain EPR spectrometer with improved spectrometer recovery times, the feasibility of detecting signals from nitroxide radicals was tested. Among the nitroxides evaluated, deuterated 15N-Tempone ( 15N-PDT) was found to have the longest T2. The signal intensity profile as a function of concentration of these agents was evaluated and a biphasic behavior was observed; beyond a nitroxide concentration of 1.5 mM, signal intensity was found to decrease as a result of self-broadening. Imaging experiments were carried out with 15N-PDT in solutions equilibrated with 0%, 5%, 10%, and 21% oxygen using the single point imaging (SPI) modality in EPR. The image intensity in these tubes was found to depend on the oxygen concentration which in turn influences the T2 of 15N-PDT. In vivo experiments were demonstrated with 15N-PDT in anesthetized mice where the distribution and metabolism of 15N-PDT could be monitored. This study, for the first time shows the capability to image a cell-permeable nitroxide in mice using pulsed EPR in the SPI modality.

Hyodo, Fuminori; Matsumoto, Shingo; Devasahayam, Nallathamby; Dharmaraj, Christopher; Subramanian, Sankaran; Mitchell, James B.; Krishna, Murali C.

2009-04-01

353

Efficient Cherenkov-type terahertz generation in Si-prism-LiNbO3-slab structure pumped by nanojoule-level ultrashort laser pulses  

NASA Astrophysics Data System (ADS)

We demonstrate, both theoretically and experimentally, that a sandwich-type structure consisting of a thin LiNbO3 slab and Si prism outcoupler can be an efficient convertor of unamplified laser pulses into broadband terahertz radiation. Pumping a 1 cm long sandwich structure with a 35 ?m thick LiNbO3 slab by 8 nJ, 100 fs optical pulses from Ti:sapphire oscillator we achieved the conversion efficiency of 0.8×10-4, i.e., two orders of magnitude higher than in the conventional generation scheme with ZnTe crystal. Using laser oscillator as a pump has an advantage of high repetition rate and, therefore, potentially high signal-to-noise ratio (~50 dB in our experiment).

Bakunov, M. I.; Mashkovich, E. A.; Tsarev, M. V.; Gorelov, S. D.

2012-10-01

354

TUNABLE TERAHERTZ GENERATION IN QUASI-PHASEMATCHED GALLIUM ARSENIDE  

Microsoft Academic Search

Sources of electromagnetic radiation with terahertz (THz) frequencies have been actively investigated during the last decade for applications in imaging and spectroscopic sensors. Femtosecond optical pulses have been shown to efficiently generate THz waves in quasi-phasematched (QPM) gallium arsenide (GaAs) (1). In this work we demonstrate a picosecond system creating a near diffraction-limited THz source with 1 mW of average

Joseph E. Schaar; Konstantin L. Vodopyanov; Martin M. Fejer

355

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

356

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

357

Superconducting phase shifter in the development of a Terahertz Imaging Radar System. Final technical report, August 1986-January 1987  

SciTech Connect

A Terahertz Imaging Radar System which exploits superconductive electronics for all of its major components is described in this report. In particular, the importance of the superconducting millimeter(mm)-wave phase shifter in the development of such systems was fully investigated. The experimental and theoretical results presented are better than the authors expected to achieve under Phase I of the project. Conventional technology is unable to provide the high frequencies required to obtain small apertures for target acquisition. Superconducting technology offers a high-performance, very broadband and low-power, mm- and sub-mm wave phase shifter based on superconducting microstrips. The physics of the non-equilibrium superconductivity underlying the operation of the superconducting microstrip phase shifter has been studied. Theoretical analysis and numerous experimental results show that superconducting stripline modulation leading to phase velocity reduction and subsequent phase shift is achievable by quasi-particle injection. A digital N-bit phase shifter based on the superconducting microstrip transmission line is proposed for development. The implementations of such a mm and sub-mm wave phase shifter will fulfill a crucial need in the development of the Terahertz Imaging Radar.

Baliga, S.; Radparvar, M.; Faris, S.M.

1987-10-01

358

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

PubMed

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

Yasumatsu, Naoya; Watanabe, Shinichi

2012-02-01

359

Image reconstruction from Pulsed Fast Neutron Analysis  

NASA Astrophysics Data System (ADS)

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

Bendahan, Joseph; Feinstein, Leon; Keeley, Doug; Loveman, Rob

1999-06-01

360

Image reconstruction from Pulsed Fast Neutron Analysis  

SciTech Connect

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

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

1999-06-10

361

Terahertz Mapping of Microstructure and Thickness Variations  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

362

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

363

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

364

Characterizing large-area electro-optic crystals toward two-dimensional real-time terahertz imaging.  

PubMed

We have characterized the homogeneity of large-area (>10 mm x 10 mm) CdTe(110) and ZnTe(110) crystals using a raster electro-optic scanning method to assess their usability in two-dimensional electro-optic terahertz (THz) imaging with parallel read out. The spatial variation in the detected THz signal (at 0.2 and 0.645 THz, respectively) is due to nonuniform residual birefringence and scattering. For CdTe, this depends critically on the growth method, and has an important contribution from slip planes in the crystals, as is evident in the scanned images. For the highest-quality CdTe(110) crystals investigated, the rms signal variations are less than 15%, comparable to those for ZnTe(110). For electro-optic scanning, we introduce a hybrid measurement system based on a fs Nd:glass laser and a continuous-wave electronic THz source. PMID:19767938

Meng, Fanzhen; Thomson, Mark D; Blank, Volker; von Spiegel, Wolff; Löffler, Torsten; Roskos, Hartmut G

2009-09-20

365

Plasma Sensing Using Terahertz Waves  

NASA Astrophysics Data System (ADS)

The terahertz (THz) region of the electromagnetic spectrum, the far-infrared, has numerous applications towards characterizing low-energy phenomena in a number of wide and diverse materials. One of these exciting new areas is in plasma diagnostics. There are many experimental and theoretical methods to determine plasma parameters in a dc glow discharge. Pulsed terahertz (THz) techniques such as THz-Time Domain Spectroscopy (THz-TDS) can offer a non-contact solution towards characterizing various plasma properties. Further studies in the area of millimeter and microwave radiation have shown that the interaction of the THz radiation with fundamental plasma such as DC glow discharge plasma can be utilized towards development of inexpensive detection schemes and detectors. Here we discuss the importance of these schemes in lieu of imaging systems and describe experiments we have conducted which support these results. In particular we find that a typical Drude model approach is insufficient in describing the transmission of the THz waves through the "cold" plasma. Results are given in the area of this promising research.

Altan, H.

366

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

2013-08-01

367

Terahertz calculations for the Australian synchrotron  

SciTech Connect

The development of terahertz radiation (T-rays) is spurring new applications in spectroscopy and imaging. To maximize the use of T-rays in more applications, a high average terahertz power is needed. Rather than using fast diodes or laser sources, this paper will show that a synchrotron can generate high average power T-rays. This is achieved by creating an electron bunch in the synchrotron ring with high intensity in the terahertz frequency region via Thomson scattering.

Chien Aun Chan; Samuel P. Mickan; Gwyn P. Williams; Derek Abbott

2004-03-01

368

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

369

Modeling of an electrically tunable quantum dot photodetector for terahertz detection  

Microsoft Academic Search

The terahertz region (1-10 THz) has potential applications in many areas, such as chemical sensing, medical imaging and free-space optical communications. With the demonstration of terahertz sources, it is quite necessary to develop the detection technology in terahertz. Here we propose an electrically tunable quantum dot infrared photodetector to detect the terahertz region. The proposed detector applies a lateral electrical

Wei Wu; Dibyendu Dey; Omer G. Memis; Hooman Mohseni

2010-01-01

370

Terahertz Amplifier Based On Gain Switching In a Quantum Cascade Laser  

NASA Astrophysics Data System (ADS)

A terahertz quantum cascade laser and an integrated Auston-switch are coupled to perform ultrafast gain switching. The resulting non-equilibrium gain is not clamped above laser threshold and large amplification of input terahertz pulses is demonstrated.

Jukam, N.; Rungsawang, R.; Dhillon, S. S.; Oustinov, D.; Madéo, J.; Barbieri, S.; Manquest, C.; Sirtori, C.; Khanna, S. P.; Linfield, E.; Davies, A. G.; Tignon, J.

2011-12-01

371

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

372

The SPARC linear accelerator based terahertz source  

SciTech Connect

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

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

2013-03-04

373

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

374

Two-pulse biexponential-weighted 23Na imaging.  

PubMed

A new method is proposed for acquiring 3D biexponential-weighted sodium images with two instead of three RF pulses to allow for shorter repetition time at high magnetic fields (B0?7 T) and reduced SAR. The second pulse converts single- into triple-quantum coherences in regions containing sodium ions which are restricted in mobility. Since only single-quantum coherences can be detected, an image acquired after the second pulse is intrinsically single-quantum-filtered and can be used to generate a biexponential-weighted sodium image by a weighted subtraction with the spin-density-weighted image acquired between the pulses. The proposed sequence generates biexponential-weighted sodium images of in vivo human brain with 140% higher SNR than triple-quantum-filtered sodium images and 4% higher SNR than a biexponential-weighted sequence with three RF pulses at equal acquisition time and with 1/3 lower SAR. As SAR is reduced, accordingly repetition time can be spared to obtain even higher SNR-time efficiency. In comparison to a difference image generated from two images of a double-readout sequence, the proposed two-pulse sequence yields about 14% higher SNR. Our new two-pulse biexponential-weighted sequence allows for acquisition of full 3D data sets of the human brain in vivo with a nominal resolution of (5 mm)(3) in about 10 min. PMID:24530955

Benkhedah, Nadia; Bachert, Peter; Nagel, Armin M

2014-03-01

375

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

376

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

377

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

378

Screening mail for powders using terahertz technology  

Microsoft Academic Search

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 mum) 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.

Mike Kemp

2011-01-01

379

Metal wires for terahertz wave guiding  

Microsoft Academic Search

Sources and systems for far-infrared or terahertz (1THz = 1012Hz) radiation have received extensive attention in recent years, with applications in sensing, imaging and spectroscopy. Terahertz radiation bridges the gap between the microwave and optical regimes, and offers significant scientific and technological potential in many fields. However, waveguiding in this intermediate spectral region still remains a challenge. Neither conventional metal

Kanglin Wang; Daniel M. Mittleman

2004-01-01

380

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

381

21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.  

Code of Federal Regulations, 2011 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....

2011-04-01

382

21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.  

Code of Federal Regulations, 2010 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....

2010-04-01

383

21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.  

Code of Federal Regulations, 2011 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)...

2011-04-01

384

21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.  

Code of Federal Regulations, 2012 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)...

2012-04-01

385

21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.  

... 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....

2014-04-01

386

21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.  

Code of Federal Regulations, 2012 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....

2012-04-01

387

21 CFR 892.1550 - Ultrasonic pulsed doppler imaging system.  

... 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)...

2014-04-01

388

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

389

Analysis of Pulsed THz Imaging Using Optical Character Recognition  

Microsoft Academic Search

Using a reflection-based pulsed THz imaging system built upon our ErAs:GaAs photoconductive switch and a gated receiver, we quantify image quality at different detection bands (centered at 100, 400, and 600 GHz). Zero-bias Schottky diode detectors mounted in various waveguide sizes are used to tune the operational frequency bands of the imaging system, while the rest of the imaging system

Zachary D. Taylor; Rahul S. Singh; Elliott R. Brown; Jon E. Bjarnason; Micah P. Hanson; Arthur C. Gossard

2009-01-01

390

Applications of pulse radiolysis to imaging sciences.  

National Technical Information Service (NTIS)

This review outlines the similarities between photolysis and radiolysis and highlight the differences. It focuses on time-resolved variants of the two disciplines, flash photolysis vs pulse radiolysis. These studies provide mechanistic insight into the be...

D. Meisel

1996-01-01

391

Image reconstruction from Pulsed Fast Neutron Analysis  

Microsoft Academic Search

Pulsed Fast Neutron Analysis (PFNA) has been demonstrated to detect drugs and explosives in trucks and large cargo containers. PFNA uses a collimated beam of nanosecond-pulsed fast neutrons that interact with the cargo contents to produce gamma rays characteristic to their elemental composition. By timing the arrival of the emitted radiation to an array of gamma-ray detectors a three-dimensional elemental

Joseph Bendahan; Leon Feinstein; Doug Keeley; Rob Loveman

1999-01-01

392

Highly Sensitive Vibrational Imaging by Femtosecond Pulse Stimulated Raman Loss  

PubMed Central

Nonlinear vibrational imaging of live cells and organisms is demonstrated by detecting femtosecond pulse stimulated Raman loss. Femtosecond pulse excitation produced a 12 times larger stimulated Raman loss signal than picosecond pulse excitation. The large signal allowed real-time imaging of the conversion of deuterated palmitic acid into lipid droplets inside live cells, and three-dimensional sectioning of fat storage in live C. elegans. With the majority of the excitation power contributed by the Stokes beam in the 1.0 to 1.2 ?m wavelength range, photodamage of biological samples was not observed.

Zhang, Delong; Slipchenko, Mikhail N.; Cheng, Ji-Xin

2011-01-01

393

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

394

Continuous-Wave Terahertz Photomixer Systems for Real-World Applications  

Microsoft Academic Search

The terahertz (THz) region is beginning to be exploited for many “real world” applications. The development of pulsed photoconductive\\u000a THz generation and detection has already yielded a range of successful products, and further research into both applications\\u000a and complementary THz technologies promises much more. In security screening, THz radiation has potential to image through\\u000a clothing to detect concealed objects. In

Ian Gregory; Hideaki Page; Lee Spencer

395

Quantitative analysis and measurements of near-field interactions in terahertz microscopes.  

PubMed

We demonstrated quantitative analysis and measurements of near-fields interactions in a terahertz pulse near-field microscope. We developed a self-consistent line dipole image method for the quantitative analysis of the near-field interaction in THz scattering-type scanning optical microscopes. The measurements of approach curves and relative contrasts on gold and silicon substrates were in excellent agreement with calculations. PMID:21716385

Moon, Kiwon; Jung, Euna; Lim, Meehyun; Do, Youngwoong; Han, Haewook

2011-06-01

396

Design of an on-line measuring system for 0.14THz high-power terahertz pulse  

Microsoft Academic Search

An on-line measuring system, including an aperture-coupling structure and a novel high-power pulse detector, is proposed in this paper to measure the output pulses from high-power 0.14THz surface wave oscillator (SWO). At first a T-type coupling structure between the TM01 mode of circular waveguide with radius of 6mm and TE10 mode of rectangular waveguide WR6 is designed. Based on loose

Guangqiang Wang; Jianguo Wang; Xiaoze Li; Changjiang Tong; Xuefeng Wang

2011-01-01

397

Theory of a laser-plasma method for detecting terahertz radiation  

SciTech Connect

A theory is developed for calculating the spectrum and the shape of a terahertz wave packet from the temporal profile of the energy of the second harmonic of the laser field generated during nonlinear interaction of laser and terahertz pulses in an optical-breakdown plasma. The spectral and temporal characteristics of the second-harmonic envelope and a terahertz pulse are shown to coincide only for short laser pulses. For long laser pulses, the second-harmonic spectral line shifts to the red and its temporal profile is determined by the time integral of the electric field of terahertz radiation.

Frolov, A. A., E-mail: frolov@ihed.ras.ru [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation); Borodin, A. V.; Esaulkov, M. N.; Kuritsyn, I. I.; Shkurinov, A. P. [Moscow State University (Russian Federation)

2012-06-15

398

Pulse Processing System for the RADMAP Radiation Modulation Aperture Imager  

SciTech Connect

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

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

2007-12-31

399

PUPA: a pulse programming assistant for NMR imaging  

SciTech Connect

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

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

1987-12-01

400

An efficient cavity for optically pumped terahertz lasers  

NASA Astrophysics Data System (ADS)

The efficiency of a simply designed cavity for optically pumped pulsed terahertz lasers is studied experimentally. A coated Ge and a crystal quartz act as the input and output windows, respectively. The thickness of the Ge window is designed according to etalon effects to maximize terahertz reflectivity. NH3 is filled in the cavity as the active medium. When NH3 is pumped by the 10P(32) line of a TEA CO2 laser, intense 151.5 ?m terahertz radiation is emitted. As high as 19.6 mJ terahertz radiation is extracted from 1.57 J pump energy. The corresponding photon conversion efficiency reaches 35.3%.

Miao, Liang; Zuo, Duluo; Jiu, Zhixian; Cheng, Zuhai

2010-08-01

401

Pulse modulation CMOS image sensor for bio-fluorescence imaging applications  

Microsoft Academic Search

For wide dynamic range, compatibility with digital circuits, and low-voltage operation, the pulse modulation technique is suitable for an implanted bioimage sensor. We demonstrate bio-fluorescence imaging of the hippocampus in a sliced mouse brain using a pulse modulation-based image sensor. The sensor architecture and system configuration are discussed. In addition, we develop an imaging device for implantation into a mouse

Jun Ohta; Takahashi Tokuda; Keiichiro Kagawa; Masahiro Nunoshita; Sadao Shiosaka

2005-01-01

402

Terahertz detection and carbon nanotubes  

ScienceCinema

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

Leonard, Francois

2014-06-13

403

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

PubMed

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

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

2012-10-01

404

Generation of terahertz radiation from ionizing two-color laser pulses in Ar filled metallic hollow waveguides.  

PubMed

The generation of THz radiation from ionizing two-color femtosecond pulses propagating in metallic hollow waveguides filled with Ar is numerically studied. We observe a strong reshaping of the low-frequency part of the spectrum. More precisely, after several millimeters of propagation the spectrum is extended from hundreds of GHz up to approximately 150 THz. For longer propagation distances, nearly single-cycle near-infrared pulses with wavelengths around 4.5 microm are obtained by appropriate spectral filtering, with an efficiency of 0.1-1%. PMID:20588814

Babushkin, I; Skupin, S; Herrmann, J

2010-04-26

405

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

406

Real-time terahertz imaging of nonmetallic objects for security screening and anti-counterfeiting applications  

NASA Astrophysics Data System (ADS)

We report the use of a 160×120 pixel microbolometer camera, under illumination by a milliwatt-scale 3.6 THz quantum cascade laser, for real-time imaging of materials which are exclusively nonmetallic in character. By minimizing diffraction effects suffered by the camera system and operating the laser at bias currents approaching saturation values, an imaging scheme was developed in which overlapping samples of nonmetallic materials can be imaged with high fidelity and long persistence times. Furthermore, an examination of various security features embedded within domestic and foreign currency notes suggests that this imaging scheme could serve a future role in detection of assorted counterfeiting practices.

Behnken, Barry N.; Karunasiri, Gamani

2008-10-01

407

A novel method to suppress noise in marine radar images based on pulse-pulse correlation  

NASA Astrophysics Data System (ADS)

As the X-band marine radar often suffers from interference of electromagnetic waves of the same frequency transmitted by radars in its vicinity, the acquired images frequently contain co-channel interference noise. The noise degrades the quality of the marine radar images and is unfavorable to the processing and interpretation of the marine radar images. To suppress the noise in marine radar images, a novel method based on pulse-pulse correlation is proposed. This method includes three steps: threshold segmentation, noise extraction and noise fixing. In the threshold segmentation step, the threshold T is calculated based on the K distribution sea clutter model. In the noise extraction step, a 3×3 window is applied. By using the window, the pixels of noise can be extracted, and at the same time the pixels of non-noise can be discarded. In the noise fixing step, the strategy of piecewise interpolation is applied. At the region near to the image center, the triangulation with linear interpolation algorithm is applied; at the region far from the image center, the nearest neighbor algorithm is applied. The real X band marine radar image was used to test the performance of the proposed method. The obtained results show that the proposed method is able to reduce the co-channel interference noise from the marine radar images significantly and keep the information of objects in the images such as ships and islands. Besides, the proposed method can be fast in speed of operation.

Ding, Xianwen; Chen, Peng; He, Shengqi; Zheng, Zongsheng

2011-11-01

408

Pulse Shape Discrimination on the INTEGRAL Imaging Spectrometer  

Microsoft Academic Search

NASA is providing a Pulse Shape Discrimination (PSD) system for the Ge detectors of the Imaging Spectrometer (SPI) on ESA's INTEGRAL mission. This will reduce the background and improve the sensitivity between approximately 400 keV and 2 MeV. The dominant background contributor for the detectors in this energy range will be beta- decays from Ge isotopes activated by cosmic rays.

R. T. Skelton; J. L. Matteson; S. A. Slassi-Sennou; R. P. Lin; N. W. Madden; P. von Ballmoos; J. Knoedlseder

2000-01-01

409

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

410

Real-time terahertz imaging of nonmetallic objects for security screening and anti-counterfeiting applications  

Microsoft Academic Search

We report the use of a 160×120 pixel microbolometer camera, under illumination by a milliwatt-scale 3.6 THz quantum cascade laser, for real-time imaging of materials which are exclusively nonmetallic in character. By minimizing diffraction effects suffered by the camera system and operating the laser at bias currents approaching saturation values, an imaging scheme was developed in which overlapping samples of

Barry N. Behnken; Gamani Karunasiri

2008-01-01

411

Speckle in active millimeter-wave and terahertz imaging and spectroscopy  

Microsoft Academic Search

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

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

2007-01-01

412

Active terahertz holography  

NASA Astrophysics Data System (ADS)

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

Xie, Zhenwei; Wang, Xinke; Zhang, Yan

2013-12-01

413

Pulsed holography for combustion diagnostics. [image reconstruction  

NASA Technical Reports Server (NTRS)

Image reconstruction and data extraction techniques were considered with respect to their application to combustion diagnostics. A system was designed and constructed that possesses sufficient stability and resolution to make quantitative data extraction possible. Example data were manually processed using the system to demonstrate its feasibility for the purpose intended. The system was interfaced with the PDP-11-04 computer for maximum design capability. It was concluded that the use of specialized digital hardware controlled by a relatively small computer provides the best combination of accuracy, speed, and versatility for this particular problem area.

Klein, N.; Dewilde, M. A.

1980-01-01

414

Terahertz emission from ultrafast ionizing air in symmetry-broken laser fields.  

PubMed

A transient photocurrent model is developed to explain coherent terahertz emission from air irradiated by a symmetry-broken laser field composed of the fundamental and its second harmonic laser pulses. When the total laser field is asymmetric across individual optical cycles, a nonvanishing electron current surge can arise during optical field ionization of air, emitting a terahertz electromagnetic pulse. Terahertz power scalability is also investigated, and with optical pump energy of tens of millijoules per pulse, peak terahertz field strengths in excess of 150 kV/cm are routinely produced. PMID:19532704

Kim, Ki-Yong; Glownia, James H; Taylor, Antoinette J; Rodriguez, George

2007-04-16

415

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

416

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

417

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

418

Features of plasma glow in low pressure terahertz gas discharge  

SciTech Connect

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

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

2013-12-15

419

Terahertz heterodyne imaging with InGaAs-based bow-tie diodes  

NASA Astrophysics Data System (ADS)

Room-temperature detection and imaging in transmission and reflection geometries at 0.591 THz with planar asymmetrically shaped InGaAs diodes (also called bow-tie diodes) are demonstrated in direct and heterodyne mode. The sensitivity of the diodes is found to be 6 V/W in direct mode, and the noise-equivalent power (NEP) in direct and heterodyne mode is estimated to be about 4 nW/Hz and 230 fW/Hz for a local-oscillator power of 11 ?W, respectively. The improvement of the dynamic range by heterodyning over direct power detection amounts to about 20 dB using pixel read-out times relevant to real-time imaging conditions.

Minkevi?ius, Linas; Tamošiunas, Vincas; Kašalynas, Irmantas; Seliuta, Dalius; Valušis, Gintaras; Lisauskas, Alvydas; Boppel, Sebastian; Roskos, Hartmut G.; Köhler, Klaus

2011-09-01

420

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

421

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

422

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

423

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

424

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

425

Digital pulse processor for ion beam microprobe imaging  

NASA Astrophysics Data System (ADS)

Capabilities of spectroscopic ion beam analysis (IBA) techniques that are available in ion microprobe facilities can be greatly improved by the use of digital pulse processing. We report here development of a digital multi parameter data acquisition system suitable for IBA imaging applications. Input signals from charge sensitive preamplifier are conditioned by using a simple circuit and digitized with fast ADCs. The digitally converted signals are processed in real time using FPGA. Implementation of several components of the system is presented.

Bogovac, M.; Jakši?, M.; Wegrzynek, D.; Markowicz, A.

2009-06-01

426

Pulse Shape Discrimination on the INTEGRAL Imaging Spectrometer  

Microsoft Academic Search

NASA is providing a Pulse Shape Discrimination (PSD) system for the Ge detectors of the Imaging Spectrometer (SPI) on ESA’s INTEGRAL mission. This will reduce the background and improve the sensitivity between approximately 400 keV and 2 MeV. The dominant background contributor for the detectors in this energy range will be ?? decays from Ge isotopes activated by cosmic rays.

R. T. Skelton; J. L. Matteson; S. A. Slassi-Sennou; R. P. Linf; N. W. Madden; P. von Ballmoos; J. Knoedlseder

2000-01-01

427

Nondestructive evaluation of aircraft composites using terahertz time domain spectroscopy  

Microsoft Academic Search

Terahertz time domain spectroscopy was used for nondestructive evaluation of aircraft glass fiber composites stressed with bending and heating damage. Refractive index and absorption coefficients were measured for both damaged and undamaged composites. The two dimensional extent of the heat damage could be shown with either a simple phase or amplitude terahertz imaging technique.

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

2008-01-01

428

Terahertz Scattering  

NASA Astrophysics Data System (ADS)

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

Zurk, L. M.; Schecklman, S.

429

Real-time terahertz wave imaging by nonlinear optical frequency up-conversion in a 4-dimethylamino-N'-methyl-4'-stilbazolium tosylate crystal  

NASA Astrophysics Data System (ADS)

Real-time terahertz (THz) wave imaging has wide applications in areas such as security, industry, biology, medicine, pharmacy, and arts. In this letter, we report on real-time room-temperature THz imaging by nonlinear optical frequency up-conversion in organic 4-dimethylamino-N'-methyl-4'-stilbazolium tosylate crystal. The active projection-imaging system consisted of (1) THz wave generation, (2) THz-near-infrared hybrid optics, (3) THz wave up-conversion, and (4) an InGaAs camera working at 60 frames per second. The pumping laser system consisted of two optical parametric oscillators pumped by a nano-second frequency-doubled Nd:YAG laser. THz-wave images of handmade samples at 19.3 THz were taken, and videos of a sample moving and a ruler stuck with a black polyethylene film moving were supplied online to show real-time ability. Thanks to the high speed and high responsivity of this technology, real-time THz imaging with a higher signal-to-noise ratio than a commercially available THz micro-bolometer camera was proven to be feasible. By changing the phase-matching condition, i.e., by changing the wavelength of the pumping laser, we suggest THz imaging with a narrow THz frequency band of interest in a wide range from approximately 2 to 30 THz is possible.

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

2014-03-01

430

Multichannel terahertz time-domain spectroscopy system at 1030 nm excitation wavelength.  

PubMed

We present Terahertz (THz) imaging with a 1D multichannel time-domain spectroscopy (TDS) system which operates with a photoconductive array of 15 detection channels excited by a 1030 nm femtosecond fiber laser. The emitter and detector are photoconductive antennas based on InGaAs/InAlAs multi-layer heterostructures (MLHS). We characterized the THz optics and the resolution of the system. The performance is demonstrated by the multichannel imaging of two samples. A simultaneous measurement of 15 THz pulses with a pixel pitch of 1 mm increases the measurement speed of the TDS system by factor 15. PMID:24921495

Brahm, Anika; Wilms, Annika; Dietz, Roman J B; Göbel, Thorsten; Schell, Martin; Notni, Gunther; Tünnermann, Andreas

2014-06-01

431

Contrast ratio optimisation in terahertz optical asymmetric demultiplexers  

NASA Astrophysics Data System (ADS)

Numerical simulations are undertaken to optimise the contrast ratios of terahertz optical asymmetric demultiplexer (TOAD) devices subject to frequency-detuned signal and control picosecond optical pulses. Optimum control pulse widths and pulse energies as well as optimum small-signal gains of semiconductor optical amplifiers (SOAs) are identified for achieving maximum contrast ratios in TOAD devices.

Tang, J. M.; Spencer, P. S.; Rees, P.; Shore, K. A.

2000-08-01

432

Systematic study of broadband terahertz gas sensor  

Microsoft Academic Search

Broadband terahertz wave detection through field-induced second harmonic generation was systematically investigated using selected gases. The dependences of the detected second harmonic intensity on probe pulse energy, bias field strength, gas pressure, and third order nonlinear susceptibility are systematically investigated with xenon, nitrogen, SF6, and alkanes. Experiment results reveal that the detected second harmonic intensity quadratically depends on the third

Xiaofei Lu; Nicholas Karpowicz; Yunqing Chen; X.-C. Zhang

2008-01-01

433

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

434

Characterisation of crystalline-amorphous blends of sucrose with terahertz-pulsed spectroscopy: the development of a prediction technique for estimating the degree of crystallinity with partial least squares regression.  

PubMed

The control of the amorphous and crystalline states of drugs and excipients is important in many instances of product formulation, manufacture, and packaging, such as the formulation of certain (freeze-dried) fast melt tablets. This study examines the use of terahertz-pulsed spectroscopy (TPS) coupled with two different data analytical methods as an off-line tool (in the first instance) for assessing the degree of crystallinity in a binary mixture of amorphous and polycrystalline sucrose. The terahertz spectrum of sucrose was recorded in the wave number range between 3 and 100 cm(-1) for both the pure crystalline form and for a mixture of the crystalline and amorphous (freeze-dried) form. The THz spectra of crystalline sucrose showed distinct absorption bands at ?48, ?55, and ?60 cm(-1) while all these features were absent in the amorphous sucrose. Calibration models were constructed based on (1) peak area analysis and (2) partial least square regression analysis, with the latter giving the best LOD and LOQ of 0.76% and 2.3%, respectively. The potential for using THz spectroscopy, as a quantitative in-line tool for percent crystallinity in a range of complex systems such as conventional tablets and freeze-dried formulations, is suggested in this study. PMID:24306674

Ermolina, I; Darkwah, J; Smith, G

2014-04-01

435

Single pulse frequency compounding protocol for superharmonic imaging  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

436

Single pulse frequency compounding protocol for superharmonic imaging.  

PubMed

Second harmonic imaging is currently accepted as the standard in commercial echographic systems. A new imaging technique, coined as superharmonic imaging (SHI), combines the third till the fifth harmonics, arising during nonlinear sound propagation. It could further enhance the resolution and quality of echographic images. To meet the bandwidth requirement for SHI a dedicated phased array has been developed: a low frequency subarray, intended for transmission, interleaved with a high frequency subarray, used in reception. As the bandwidth of the elements is limited, the spectral gaps in between the harmonics cause multiple (ghost) reflection artifacts. A dual-pulse frequency compounding method aims at suppressing those artifacts at a price of a reduced frame rate. In this study we explore a possibility of performing frequency compounding within a single transmission. The traditional frequency compounding method suppresses the ripples by consecutively emitting two short Gaussian bursts with a slightly different center frequency. In the newly proposed method, the transmit aperture is divided into two parts: the first half is used to send a pulse at the lower center frequency, while the other half simultaneously transmits at a slightly higher center frequency. The suitability of the protocol for medical imaging applications in terms of the steering capabilities was performed in a simulation study with INCS and the hydrophone measurements. Moreover, an experimental study was carried out to find the optimal parameters for the clinical imaging protocol. The latter was subsequently used to obtain the images of a tissue mimicking phantom containing strongly reflecting wires. Additionally, the images of a human heart in the parasternal projection were acquired. The scanning aperture with the developed protocol amounts to approximately 90°, which is sufficient to capture the cardiac structures in the standard anatomical projections. The theoretically estimated and experimentally measured grating lobe levels are equal to -28.3 dB and -35.9 dB, respectively. A considerable improvement in the axial resolution of the SHI component (0.73 mm) at -6 dB in comparison with the third harmonic (2.23 mm) was observed. A similar comparison in terms of the lateral resolution slightly favored the superharmonic component by 0.2 mm. Additionally, the images of the tissue mimicking phantom exhibited the absence of the multiple reflection artifacts. The in-vivo acquisition allows one to clearly observe the dynamic of the mitral valve leaflets. The new method is equally effective in eliminating the ripple artifacts associated with SHI as the dual-pulse technique, while the full frame rate is maintained. PMID:23787259

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

2013-07-21

437

Crossover between surface field and photo-Dember effect induced terahertz emission  

NASA Astrophysics Data System (ADS)

Pulsed terahertz emission from semiconductor surface illuminated by femtosecond laser pulse is analyzed. The analysis is based on the Boltzmann transport equation. It is shown that terahertz emission is induced by the surface field if the photon energy is close to the band-gap energy. The terahertz emission is controlled by the photo-Dember effect when the photon energy significantly exceeds the band-gap energy. A compact criterion for the crossover between the two mechanisms of terahertz emission is obtained. The analytical results are compared to the results of detailed Monte Carlo simulations.

Reklaitis, Antanas

2011-04-01

438

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

439

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

440

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

441

Frequency-agile terahertz-wave generation and detection using a nonlinear optical conversion, and their applications for imaging  

Microsoft Academic Search

We have developed widely tunable terahertz (THz)-wave sources using nonlinear optical crystals. In the 1–3 THz region, a frequency-agile THz-wave parametric oscillator in a ring-cavity configuration has been realized using MgO-doped LiNbO3 as the nonlinear crystal. An organic 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal is promising for THz-wave generation in an ultra-wide range 1–40 THz. Difference-frequency generation from DAST, pumped using a

Hiroaki Minamide; Hiromasa Ito

2010-01-01

442

A new ultrasound contrast imaging approach based on the combination of multiple imaging pulses and a separate release burst  

Microsoft Academic Search

A new ultrasound contrast imaging technique is described that optimally employs the rupture of the contrast agent. It is based on a combination of multiple high frequency, broadband, imaging pulses and a separate release burst. The imaging pulses are used to survey the target before and after the rupture and release of free gas bubbles. In this way, both processes

Peter J. A. Frinking; E. I. Cespedes; J. Kirkhorn; H. G. Torp; N. de Jong

2001-01-01

443

Terahertz radiation characteristics of charge-ordered manganite Pr 0.7Ca 0.3MnO 3 thin films excited by ultrafast optical pulses  

NASA Astrophysics Data System (ADS)

Terahertz radiation characteristics of photoswitching devices made on charge-ordered manganites Pr 0.7Ca 0.3MnO 3 have been investigated for thin films grown at different temperatures. We report that the temperature dependence of the THz radiation near the charge ordering temperature strongly depends on the growth condition of Pr 0.7Ca 0.3MnO 3, while that near the magnetic transition temperature does not.

Kida, Noriaki; Tonouchi, Masayoshi

2003-05-01

444

Mode-locking of a terahertz laser by direct phase synchronization.  

PubMed

A novel scheme to achieve mode-locking of a multimode laser is demonstrated. Traditional methods to produce ultrashort laser pulses are based on modulating the cavity gain or losses at the cavity roundtrip frequency, favoring the pulsed emission. Here, we rather directly act on the phases of the modes, resulting in constructive interference for the appropriated phase relationship. This was performed on a terahertz quantum cascade laser by multimode injection seeding with an external terahertz pulse, resulting in phase mode-locked terahertz laser pulses of 9 ps duration, characterized unambiguously in the time domain. PMID:23037209

Maysonnave, J; Maussang, K; Freeman, J R; Jukam, N; Madéo, J; Cavalié, P; Rungsawang, R; Khanna, S P; Linfield, E H; Davies, A G; Beere, H E; Ritchie, D A; Dhillon, S S; Tignon, J

2012-09-10

445

Beam-Profiling and Wavefront-Sensing of THz Pulses at the Focus of a Substrate-Lens  

Microsoft Academic Search

We report combined wavefront detection and beam profiling of single-cycle terahertz (THz) pulses. In our system, the electric field is recorded highly resolved in two spatial and one temporal dimension before and after propagation through an optical component. Using this approach, we examine the imaging properties of a hyperhemispherical silicon lens as it is commonly used in THz dipole antennas.

Andreas Bitzer; Hanspeter Helm; Markus Walther

2008-01-01

446

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

447

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