There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Research into terahertz technology is now receiving increasing attention around the world, and devices exploiting this waveband are set to become increasingly important in a very diverse range of applications. Here, an overview of the status of the technology, its uses and its future prospects are presented.

Cutting-edge terahertz technology

We present a metamaterial that acts as a strongly resonant absorber at terahertz frequencies. Our design consists of a bilayer unit cell which allows for maximization of the absorption through independent tuning of the electrical permittivity and magnetic permeability. An experimental absorptivity of 70% at 1.3 terahertz is demonstrated. We utilize only a single unit cell in the propagation direction, thus achieving an absorption coefficient α=2000 cm-1. These metamaterials are promising candidates as absorbing elements for thermally based THz imaging, due to their relatively low volume, low density, and narrow band response.

A metamaterial absorber for the terahertz regime: Design, fabrication and characterization

This Review covers the state-of-the-art technologies on photonics-based terahertz communications, which are compared with competing technologies based on electronics and free-space optical communications. Future prospects and challenges are also discussed. Almost 15 years have passed since the initial demonstrations of terahertz (THz) wireless communications were made using both pulsed and continuous waves. THz technologies are attracting great interest and are expected to meet the ever-increasing demand for high-capacity wireless communications. Here, we review the latest trends in THz communications research, focusing on how photonics technologies have played a key role in the development of first-age THz communication systems. We also provide a comparison with other competitive technologies, such as THz transceivers enabled by electronic devices as well as free-space lightwave communications.

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Advances in terahertz communications accelerated by photonics

The terahertz region of the electromagnetic spectrum, spanning from 100 GHz through 10 THz, is of increasing importance for a wide range of scientific, military and commercial applications. This interest is spurred by the unique properties of this spectral band and the very recent development of convenient terahertz sources and detectors. However, the terahertz band is also extremely challenging, in large part because it spans the transition from traditional electronics to photonics. This paper reviews the importance of this frequency band and summarizes the efforts of scientists and engineers to span the "terahertz technology gap." The emphasis is on solid-state circuits that use nonlinear diodes to translate the functionality of microwave technology to much higher frequencies.

Opening the terahertz window with integrated diode circuits

The terahertz frequency absorption spectraof DNA molecules reflect low-frequencyinternal helical vibrations involvingrigidly bound subgroups that are connectedby the weakest bonds, including thehydrogen bonds of the DNA base pairs,and/or non-bonded interactions. Althoughnumerous difficulties make the directidentification of terahertz phonon modes inbiological materials very challenging, ourresearch has shown that such measurementsare both possible and fruitful. Spectra ofdifferent DNA samples reveal a large numberof modes and a reasonable level ofsequence-specific uniqueness. In an attemptto show that the long wavelength absorptionfeatures are intrinsic properties ofbiological materials determined by phononmodes, a normal mode analysis has been usedto predict the absorption spectra ofpolynucleotide RNA Poly[G]-Poly[C]. Directcomparison demonstrated a correlationbetween calculated and experimentallyobserved spectra of the RNA polymers, thusconfirming that the fundamental physicalnature of the observed resonance structureis caused by the internal vibration modesin the macromolecules.In this work we demonstrate results fromFourier-Transform Infrared (FTIR)spectroscopy of DNA macromolecules andrelated biological materials in theterahertz frequency range. Carefulattention was paid to the possibility ofinterference or etalon effects in thesamples, and phenomena were clearlydifferentiated from the actual phononmodes. In addition, we studied thedependence of transmission spectra ofaligned DNA and polynucleotide film sampleson molecule orientation relative to theelectromagnetic field, showing the expectedchange in mode strength as a function ofsample orientation. Further, the absorptioncharacteristics were extracted from thetransmission data using the interferencespectroscopy technique, and a stronganisotropy of terahertz characteristics wasdemonstrated.

THz-Spectroscopy of Biological Molecules.

The spectral performance of freestanding resonant metal-mesh bandpass filters operating with center frequencies ranging from 585 GHz to 2.1 THz is presented. These filters are made up of a 12-μm-thick copper film with an array of cross-shaped apertures that fill a circular area with a 50-mm diameter. The filters exhibit power transmission in the range 97–100% at their respective center frequencies and stop-band rejection in excess of 18 dB. The theoretically predicted nondiffracting properties of the meshes are experimentally verified through high-resolution beam mapping. Scalability of the filter spectra with mesh dimensions is demonstrated over a wide spectral range. Several modeling methods are considered, and results from the models are shown.

Resonant metal-mesh bandpass filters for the far infrared

A novel whiskerless Schottky diode has been developed in which shunt capacitance is minimized by means of an etched surface channel. This structure is easily fabricated and the DC I-V characteristics areas good as those of the best available whisker-contacted devices. Preliminary RF characterization in an unoptimized mount at 110 GHz has yielded room temperature SSB mixer noise temperature of 950 K and SSB conversion loss of 6.4 dB. The diode is robust and can be operated at cryogenic temperatures. Potential applications include waveguide and planar mixers, planar arrays, multipliers, varactor tuners, and microwave integrated circuits.

A Novel Whiskerless Schottky Diode for Millimeter and Submillimeter Wave Application

The operation of GaAs Schottky barrier diodes, the critical mixer element used in heterodyne receivers for a variety of scientific applications in the terahertz frequency range, is reviewed. The constraints that the receiver system places on the diodes are considered, and the fundamental guidelines for device optimization are presented. The status of ongoing research, both experimental and theoretical, is examined. Emphasis is placed on investigations of the various effects that can limit diode performance at these high frequencies. Investigations of planar diode technology are summarized, and the potential replacement of whisker-contacted devices with planar structures is considered. >

Thomas W. Crowe

Papers

Opening the terahertz window with integrated diode circuits

THz-Spectroscopy of Biological Molecules.

Resonant metal-mesh bandpass filters for the far infrared

A Novel Whiskerless Schottky Diode for Millimeter and Submillimeter Wave Application

GaAs Schottky Diodes for THz Mixing Applications