Abstract-Guided-Mode Filters for Terahertz Frequencies Fabricated by 3D Printing

M. Ortiz-Martinez, E. Castro-Camus, A. I. Hernandez-Serrano,

https://link.springer.com/article/10.1007/s10762-019-00602-3

In this article, we present the design and characterization of the first 3D-printed guided-mode filter for terahertz frequencies. The device consist on a diffractive grating fabricated on top of a rectangular dielectric waveguide by 3D printing. Finite difference numerical modeling shows this device acts as a filter at a frequency that can be geometrically engineered and tuned around such frequency by varying the radiation incidence angle. Three devices were designed to operate at 200 GHz, 250 GHz, and 300 GHz; the devices were fabricated and successfully characterized using terahertz time-domain spectroscopy

Abstract-Pixel Statistical Analysis of Diabetic vs. Non-diabetic Foot-Sole Spectral Terahertz Reflection Images

• G. G. Hernandez-Cardoso, 
• M. Alfaro-Gomez, 
• S. C. Rojas-Landeros, 
• I. Salas-Gutierrez, 
• E. Castro-Camus

https://link.springer.com/article/10.1007/s10762-018-0485-3

In this article, we present a series of hydration mapping images of the foot soles of diabetic and non-diabetic subjects measured by terahertz reflectance. In addition to the hydration images, we present a series of RYG-color-coded (red yellow green) images where pixels are assigned one of the three colors in order to easily identify areas in risk of ulceration. We also present the statistics of the number of pixels with each color as a potential quantitative indicator for diabetic foot-syndrome deterioration.

Abstract-Artificial dielectric stepped-refractive-index lens for the terahertz region

A.I. Hernandez-Serrano, Rajind Mendis, Kimberly S. Reichel, Wei Zhang, E. Castro-Camus, and Daniel M. Mittleman

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-3-3702

In this paper we theoretically and experimentally demonstrate a stepped-refractive-index convergent lens made of a parallel stack of metallic plates for terahertz frequencies based on artificial dielectrics. The lens consist of a non-uniformly spaced stack of metallic plates, forming a mirror-symmetric array of parallel-plate waveguides (PPWGs). The operation of the device is based on the TE1 mode of the PPWG. The effective refractive index of the TE1 mode is a function of the frequency of operation and the spacing between the plates of the PPWG. By varying the spacing between the plates, we can modify the local refractive index of the structure in every individual PPWG that constitutes the lens producing a stepped refractive index profile across the multi stack structure. The theoretical and experimental results show that this structure is capable of focusing a 1 cm diameter beam to a line focus of less than 4 mm for the design frequency of 0.18 THz. This structure shows that this artificial-dielectric concept is an important technology for the fabrication of next generation terahertz devices.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-q-plate for the Generation of Terahertz Cylindrical Vector Beams Fabricated by 3D Printing

• A. I. Hernandez-Serrano, 
• E. Castro-Camus, 
• D. Lopez-Mago

https://link.springer.com/article/10.1007%2Fs10762-017-0396-8

We present the design, fabrication, and characterization of a q-plate with continuous birefringence variation at terahertz frequencies. This q-plate was fabricated by three-dimensional printing and is a simple solution for the generation of cylindrical vector beams. This device can find a number of applications in future terahertz technologies such as telecommunications.

Abstract-Terahertz imaging for early screening of diabetic foot syndrome: A proof of concept

• G. G. Hernandez-Cardoso
• , S. C. Rojas-Landeros
• , M. Alfaro-Gomez
• , A. I. Hernandez-Serrano
• , I. Salas-Gutierrez
• , E. Lemus-Bedolla
• , A. R. Castillo-Guzman
• , H. L. Lopez-Lemus
•  & E. Castro-Camus

• http://www.nature.com/articles/srep42124 

Most people with diabetes suffer some deterioration of the feet. Diabetic foot syndrome causes ulceration in about 15% of cases and such deterioration leads to amputation in about 2.5% of diabetic patients, diminishing their quality of life and generating extraordinary costs for patients and public health systems. Currently, there is no objective method for the detection of diabetic foot syndrome in its early stages. We propose terahertz imaging as a method for the evaluation of such deterioration. This screening method could aid the prevention and medical treatment of this condition in the future.

Abstract-The role of bandgap energy excess in surface emission of terahertz radiation from semiconductors

M. Alfaro-Gomez1 and E. Castro-Camus

http://aip.scitation.org/doi/abs/10.1063/1.4974479

We use a Monte-Carlo model to simulate semi-classical photo-carrier dynamics of InAs, InGaAs, and GaAs that leads to terahertz emission. We compare the emission power of all three semiconductors as a function of excitation photonenergy finding that the carrier excess excitation energy is more relevant to explain their performance difference than their mobilities. We conclude that ballistic transport after photoexcitation is the dominant mechanism for terahertz emission instead of diffusion driven or surface field driven charge separation, which were traditionally considered the most relevant mechanisms.

Abstract-Quasi-Wollaston-Prism for Terahertz Frequencies Fabricated by 3D Printing

• A. I. Hernandez-Serrano, 
• E. Castro-Camus
• • 
    

http://link.springer.com/article/10.1007/s10762-016-0350-1

In this letter, we present the design, fabrication, and characterization of a quasi-Wollaston prism for terahertz frequencies based on form birefringence. The prism uses the birefringence induced in a sub-wavelength layered plastic-air structure that produces refraction in different directions for different polarizations. The component was simulated using the finite-difference-time-domain method, fabricated by 3D printing and subsequently tested by terahertz time-domain spectroscopy showing a polarization separation around of 23° for frequencies below 400 GHz, exhibiting cross polarization power extinction ratios better than 1.6 × 10−3 at 200 GHz.

Abstract-Low-cost 3D printed GRIN lens for terahertz applications

A. I. Hernandez-Serrano, M Weidenbach, S. F. Busch, M. Koch, and E. Castro-Camus
https://www.osapublishing.org/abstract.cfm?uri=Sensors-2016-SeTu3E.4

We used 3D printing as a new technique to make gradient-refractive-index (GRIN) lenses for terahertz applications. This new low-cost lenses are demonstrated to work within the diffraction limit below 800 GHz.

© 2016 OSA

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Abstract-Monte Carlo simulation of near-field terahertz emission from semiconductors

S. C. Corzo-Garcia, A. I. Hernandez-Serrano, E. Castro-Camus, and O. Mitrofanov

Phys. Rev. B 94, 045301 – Published 1 July 2016

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.94.045301

We simulated the carrier dynamics in InGaAs after ultrafast photoexcitation. By using a finite-difference time-domain approach we were able to analyze the near terahertz field emission caused by the motion of such carriers. We found that both the current parallel and normal to the interface take a relevant role in the terahertz emission. We also found that the ballistic motion of the carriers after photoexcitation dominates the emission rather than diffusion.

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Abstract-Article Cover Photoconductive devices for terahertz pulsed spectroscopy: a review [Invited]

Photoconductive devices for terahertz pulsed spectroscopy: a review [Invited] 

E. Castro-Camus and M. Alfaro

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-4-3-A36

Photoconductive switches were the key components that allowed the generation and detection of coherent broadband electromagnetic pulses at terahertz frequencies, opening the possibility for performing spectroscopy and, therefore, measuring complex dielectric properties of materials in this band, which was mostly unexplored. In this paper, we present a brief introduction to the operation principles of these devices. Subsequently, we present a review of the current state-of-the-art in this field and discuss the challenges to be faced in future development of these devices.

© 2016 Chinese Laser Press

Full Article  |  PDF Article

Abstract-Highly sensitive terahertz dielectric sensor for small-volume liquid samples

A. Soltani1, H. Neshasteh2, A. Mataji-Kojouri2, N. Born1, E. Castro-Camus3,a), M. Shahabadi2 and M. Koch1

a) Author to whom correspondence should be addressed. Electronic mail: enrique@cio.mx

Appl. Phys. Lett. 108, 191105 (2016); http://dx.doi.org/10.1063/1.4949527

http://scitation.aip.org/content/aip/journal/apl/108/19/10.1063/1.4949527?TRACK=RSS

We present a resonator-based sensor for the measurement of the refractive index of dielectric liquidsamples. The proposed sensor operates on the basis of an electromagnetic resonance between a thinmetallic grating and a reflecting ground plane. The fluid whose refractive index is to be measured fills the region between the metallic grating and the ground plane and causes a considerable shift in the resonance frequency (>500 GHz/RIU). The sensor has a relatively simple structure; therefore, it can be manufactured economically on industrial scales.

Abstract-Fabrication of gradient-refractive-index lenses for terahertz applications by three-dimensional printing

A. I. Hernandez-Serrano, M. Weidenbach, S. F. Busch, M. Koch, and E. Castro-Camus
https://www.osapublishing.org/josab/abstract.cfm?uri=josab-33-5-928

In this article we present the design, fabrication, and characterization of gradient-refractive-index lenses for terahertz (THz) applications. The fabrication was performed by three-dimensional printing. These new low-cost lenses were tested using THz time-domain spectroscopy and imaging in order to measure their optical properties. The results show a focusing capacity within the diffraction limit for frequencies below 700 GHz.

© 2016 Optical Society of America

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Abstract-Terahertz meets sculptural and architectural art: Evaluation and conservation of stone objects with T-ray technology

• K. Krügener
• , M. Schwerdtfeger
• , S. F. Busch
• , A. Soltani
• , E. Castro-Camus
• , M. Koch
•  & W. Viöl
• • http://www.nature.com/articles/srep14842

Conservation of cultural heritage is an area where novel scientific techniques are having enormous impact. Given the value and uniqueness of art pieces, non-invasive diagnostic methods are highly appreciated by conservators. Terahertz radiation has shown enormous potential as non-contact probe that can be used for the three-dimensional reconstruction of internal structure of stone-made objects. In this article we report the evaluation of the internal damage state of two art pieces, a medallion from the Castle of Celle and a window sill from the St. Peter of Trier Cathedral. We also used terahertz radiation to follow and assess the restoration process of the window sill. We found that terahertz spectroscopy is an excellent non-destructive evaluation method for stone artwork that shows enormous potential as a tool for conservation.

Abstract-Quality control of leather by terahertz time-domain spectroscopy

Quality control of leather by terahertz time-domain spectroscopy

A. I. Hernandez-Serrano, S. C. Corzo-Garcia, E. Garcia-Sanchez, M. Alfaro, and E. Castro-Camus  »View Author Affiliations

http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-53-33-7872

We use terahertz time-domain spectroscopy, combined with effective-medium theory, to measure the moisture content and thickness of leather simultaneously. These results demonstrate that this method could become a standard quality control test for the industrial tanning process.

© 2014 Optical Society of America

Abstract-Modifying the polarization state of terahertz radiation using anisotropic twin-domains in LaAlO3

J. Lloyd-Hughes, S. P. P. Jones, E. Castro-Camus, K. I. Doig, and J. L. MacManus-Driscoll  »View Author Affiliations

http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-39-5-1121

Optics Letters, Vol. 39, Issue 5, pp. 1121-1124 (2014)
http://dx.doi.org/10.1364/OL.39.001121

Polarization-resolved terahertz (THz) time-domain spectroscopy was utilized to examine the complex refractive index of lanthanum aluminate (LaAlO3), a rhombohedrally distorted perovskite that exhibits crystallographic twin domains. The uniaxial anisotropy of the refractive index was quantified. The ellipticity of THz radiation pulses after transmission through single domains indicated that LaAlO3 can be used as a quarter- or half-wave plate. The effective anisotropy of [001]-oriented LaAlO3 was found to be reduced when the material exhibited multiple, narrow twin domains.

© 2014 Optical Society of America

Abstract-Leaf water dynamics of Arabidopsis thaliana monitored in-vivo using terahertz time-domain spectroscopy

 

         E. Castro-Camus,

M. Palomar

& A. A. Covarrubias

• http://www.nature.com/srep/2013/131009/srep02910/full/srep02910.html

The declining water availability for agriculture is becoming problematic for many countries. Therefore the study of plants under water restriction is acquiring extraordinary importance. Botanists currently follow the dehydration of plants comparing the fresh and dry weight of excised organs, or measuring their osmotic or water potentials; these are destructive methods inappropriate for in-vivo determination of plants' hydration dynamics. Water is opaque in the terahertz band, while dehydrated biological tissues are partially transparent. We used terahertz spectroscopy to study the water dynamics of Arabidopsis thaliana by comparing the dehydration kinetics of leaves from plants under well-irrigated and water deficit conditions. We also present measurements of the effect of dark-light cycles and abscisic acid on its water dynamics. The measurements we present provide a new perspective on the water dynamics of plants under different external stimuli and confirm that terahertz can be an excellent non-contact probe of in-vivo tissue hydration.

 

Anisotropy in the Terahertz Band

E. Castro-Camus¹  

(1)

Centro de Investigaciones en Óptica A.C., Loma del Bosque 115, Lomas del Campestre, León, Guanajuato, 37150, México

http://link.springer.com/article/10.1007%2Fs10762-013-0018-z/fulltext.html 

E. Castro-Camus

Email: enrique@cio.mx

Day after day, anisotropic properties of materials are finding new applications. Many consumer technologies based on them are currently available, particularly at optical, near-infrared and ultraviolet frequencies. Liquid crystals are the base of an enormous quantity of display devices present in our everyday life ranging from small wrist watches to large television screens, the circular dichroism exhibited by a number of proteins and nucleic acids is providing new information about their molecular structure and biological function, Pockels cells are being used as high speed modulators in optical fiber telecommunications among many other applications. The availability of new technologies to access the terahertz band opened the possibility to study anisotropic properties of materials in the far-infrared which have attracted considerable attention over the last decade owing to their enormous scientific and technological potential.

This special issue contains five invited review articles that cover the most important aspects of the study of anisotropic properties of materials in the terahertz band. The articles included in the issue, enumerated below, represent an up-to-date overview of advances in this field.

1.

Recent advances in birefringence studies at THz frequenciesby K. Wiesauer and C. Jördens from Research Center for Non-destructive Testing (Austria) and the Technische Universität Braunschweig (Germany) provides an overview that includes instrumental advances, analysis techniques and experiments for the extraction of birefringence of materials from time-domain spectroscopic data.

 

2.

Developments in THz range ellipsometry by M. Neshat and P. Armitage from the University of Tehran (Iran) and Johns Hopkins University (USA) presents an overview on the implementation of terahertz time-domain ellipsometry and recent experiments for the determination of complex refractive indices of a variety of materials using this technique.

 

3.

Towards Dynamic, Tunable, and Nonlinear Metamaterials via Near field Interactions: A Review G. R. Keiser et al. from R. Averitt’s group at Boston University (USA) discusses recent advances and applications of anisotropic metamaterials for various applications such as electron spin resonance.

 

4.

Review of anisotropic terahertz material response by T. Arikawa et al. from J. Kono’s group at Rice University (USA) presents a review that includes a phenomenological discussion of the origin of anisotropy, followed by the presentation of a number of experiments in which aligned carbon nanotubes and other materials are studied.

 

5.

Polarization-sensitive THz-TDS and its application to anisotropy sensing by T. Nagashima, M. Tani, and M. Hangyo from the University of Osaka and University of Fukui (Japan) provides an informative review on state-of-the-art instrumental developments that are currently being used for polarimetry and ellipsometry in the terahertz band.