High frequency single-mode resonators for EPR spectroscopy enabling rotations of the sample about two orthogonal axes

A novel single-mode resonant structure which enables the rotation of the sample about two orthogonal axes is investigated in view of electron paramagnetic resonance applications. The proposed solution is based on cylindrical nonradiative resonators laterally loaded by the sample holder. The resulting structure can still operate in nonradiative regime, although no longer rotationally invariant. These theoretical predictions, based on symmetry considerations, are confirmed by means of a finite element numerical modelling. Theoretical and computational results are then substantiated by experimental investigations at millimeter wavelengths. As a result, a single-mode resonator which enables all the relevant rotations of the sample is demonstrated at millimeter wavelengths for the first time. In this resonator the intensity of the microwave field on the sample and its orientation with respect to the static magnetic field can be kept constant during the rotations. Therefore, a complete characterization of anisotropic systems is possible at the highest sensitivity, without the need of split-coil magnets. Possible applications at very high frequencies are discussed.Comment: 19 pages, 8 figue

Millimeter-Wave Lumped Element Superconducting Bandpass Filters for Multi-Color Imaging

The opacity due to water vapor in the Earth's atmosphere obscures portions of the sub-THz spectrum (mm/sub-mm wavelengths) to ground based astronomical observation. For maximum sensitivity, instruments operating at these wavelengths must be designed to have spectral responses that match the available windows in the atmospheric transmission that occur in between the strong water absorption lines. Traditionally, the spectral response of mm/sub-mm instruments has been set using optical, metal-mesh bandpass filters [1]. An alternative method for defining the passbands, available when using superconducting detectors coupled with planar antennas, is to use on-chip, superconducting filters [2]. This paper presents the design and testing of superconducting, lumped element, on-chip bandpass filters (BPFs), placed inline with the microstrip connecting the antenna and the detector, covering the frequency range from 209–416 GHz. Four filters were designed with pass bands 209–274 GHz, 265–315 GHz, 335–361 GHz and 397–416 GHz corresponding to the atmospheric transmission windows. Fourier transform spectroscopy was used to verify that the spectral response of the BPFs is well predicted by the computer simulations. Two-color operation of the pixels was demonstrated by connecting two detectors to a single broadband antenna through two BPFs. Scalability of the design to multiple (four) colors is discussed

Broadband coated lens solutions for FIR-mm-wave instruments

This paper presents recent results of ongoing European Space Agency funded program of work aimed at developing large dielectric lenses suitable for future satellite missions, with a particular focus on requirements for CMB polarimetry. Two lens solutions are being investigated: (i) polymer lenses with broadband multi-layer antireflection coatings; (ii) silicon lenses with surface-structured anti-reflection coating represented by directly machined pyramidal features. For each solution, base materials with and without coatings have been optically characterized over a range of temperatures down to ∼10 K. Full lens solutions are under manufacture and will be tested in a bespoke large cryo-optical facility

The 2017 Terahertz Science and Technology Roadmap

Science and technologies based on terahertz frequency electromagnetic radiation (100GHz-30THz) have developed rapidly over the last 30 years. For most of the 20th century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to “real world” applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2016, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 17 sections that cover most of the key areas of THz Science and Technology. We hope that The 2016 Roadmap on THz Science and Technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies

Static and reconfigurable devices for near-field and far-field terahertz applications

The terahertz frequency electromagnetic radiation has gathered a growing interest from the scientific and technological communities in the last 30 years, due to its capability to penetrate common materials, such as paper, fabrics, or some plastics and offer information on a length scale between 100 µm and 1 mm. Moreover, terahertz radiation can be employed for wireless communications, because it is able to sustain terabit-per-second wireless links, opening to the possibility of a new generation of data networks. However, the terahertz band is a challenging range of the electromagnetic spectrum in terms of technological development and it falls amidst the microwave and optical techniques. Even though this so-called “terahertz gap” is progressively narrowing, the demand of efficient terahertz sources and detectors, as well as passive components for the management of terahertz radiation, is still high. In fact, novel strategies are currently under investigation, aiming at improving the performance of terahertz devices and, at the same time, at reducing their structure complexity and fabrication costs. In this PhD work, two classes of devices are studied, one for near-field focusing and one for far-field radiation with high directivity. Some solutions for their practical implementation are presented. The first class encompasses several configurations of diffractive lenses for focusing terahertz radiation. A configuration for a terahertz diffractive lens is proposed, numerically optimized, and experimentally evaluated. It shows a better resolution than a standard configuration. Moreover, this lens is investigated with regard to the possibility to develop terahertz diffractive lenses with a tunable focal length by means of an electro-optical control. Preliminary numerical data present a dual-focus capability at terahertz frequencies. The second class encompasses advanced radiating systems for controlling the far-field radiating features at terahertz frequencies. These are designed by means of the formalism of leaky-wave theory. Specifically, the use of an electro-optical material is considered for the design of a leaky-wave antenna operating in the terahertz range, achieving very promising results in terms of reconfigurability, efficiency, and radiating capabilities. Furthermore, different metasurface topologies are studied. Their analytical and numerical investigation reveals a high directivity in radiating performance. Directions for the fabrication and experimental test at terahertz frequencies of the proposed radiating structures are addressed

The First Multichroic Receiver and Results from ACTPol.

The Cosmic Microwave Background (CMB) is a unique and powerful tool for the study of cosmology and fundamental physics. The next frontier of CMB research is to extract the wealth of cosmological information available from its polarization. Accurate measurement of this polarization signal will enable us to probe inflation, provide an alternative means to measure the neutrino mass sum and number of neutrino species; improve our understanding of dark energy; explore the reionization history of our Universe; probe the large scale structure through gravitational lensing; and enable a multitude of other astrophysical studies. The polarized signatures of the early universe are extremely weak, dominated by foregrounds, and its measurement is susceptible to instrumental effects. Extracting the information contained in these faint signals requires instruments with high sensitivity, excellent control over systematic errors, and careful data analysis. The Atacama Cosmology Telescope Polarimeter (ACTPol) is a state-of-the-art experiment that measures CMB polarization over finer angular scales from the Atacama desert in Chile. In this thesis, I present an overview of this project and then describe my work on the project including development of a new polarization sensitive dichroic camera for ACTPol designed to increase the sensitivity of CMB telescopes and enable high precision measurements of CMB polarization; the development of novel metamaterial antireflection coatings for silicon lenses; diffraction from panel gaps; calibration of detector pass-bands; and a detailed description of my analysis of the polarization properties of extragalactic point sources discovered with the ACTPol data. I conclude with a discussion of the science of ACTPol, and the impact of my technical work on future CMB experiments.PHDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135767/1/dattar_1.pd

Extraordinary THz Transmission with a Small Beam Spot:the Leaky Wave Mechanism

The discovery of extraordinary optical transmission (EOT) through patterned metallic foils in the late 1990s was decisive for the development of plasmonics and cleared the path to employ small apertures for a variety of interesting applications all along the electromagnetic spectrum. However, a typical drawback often found in practical EOT structures is the large size needed to obtain high transmittance peaks. Consequently, practical EOT arrays are usually illuminated using an expanded (mimicking a plane wave) beam. Here, it is shown with numerical and experimental results in the THz range that high transmittance peaks can be obtained even with a reduced illumination spot exciting a small number of holes, provided that the structure has a sufficient number of lateral holes out of the illumination spot. These results shed more light on the prominent role of leaky waves in the underlying physics of EOT and have a direct impact on potential applications