William Lanigan

Bio: William Lanigan is an academic researcher from National University of Ireland. The author has contributed to research in topics: Grating & Gaussian beam. The author has an hindex of 3, co-authored 5 publications receiving 55 citations.

Modal analysis of the quasi-optical performance of phase gratings

Abstract: This paper is concerned with the analysis of phase gratings as passive quasi-optical multiplexing devices. One important application of such components is in the local oscillator injection chain of heterodyne array receivers. Gaussian beam mode analysis can be applied as a powerful tool when modelling the optical performance of phase gratings in a real submillimeter system of finite throughput and bandwidth. In our experimental investigations we have concentrated on the Dammann Grating (DG) which is a binary optical component and thus straightforward to manufacture. A number of quartz gratings were fabricated and carefully tested to evaluate the practical limitations of such quasi-optical components. Because of its convenient refractive index quartz can be used to produce gratings with very low reflection losses. The results presented confirm DGs to be particularly suitable multiplexers for sparse arrays of finite bandwidth.

Millimeter-wave profiled corrugated horns for the quad cosmic background polarization experiment

Abstract: In this paper we report on the design and validation process for the profiled corrugated horn antennas, which feed the bolometer array of a cosmology experiment known as QUaD located at the South Pole. This is a cosmic background radiation polarization project, which demands precise knowledge and control of the optical coupling to the signal in order to map the feeble E- and B-polarization mode structure. The system will operate in two millimeter wavelength bands at 100 and 150 GHz. The imaging horn array collects the incoming signal via on-axis front-end optics and a Cassegrain telescope, with a cold stop in front of the array to terminate side-lobe structure at an edge taper of –20dB. The corrugated horn design process was undertaken using in-house analytical software tools, based on modal scattering, specially developed for millimeter -wave profiled horn antennas. An important part of the instrument development was the validation of the horn design, in particular to verify low edge taper levels and the required well-defined band edges. Suitable feed horn designs were measured and were found to be in excellent agreement with theoretical predictions.

Theoretical and experimental investigation of phase gratings

Abstract: We present the results of experimental measurements of a Dammann grating designed to produce a 5 x 5 pattern of beam images at 100GHz

The gaussian beam mode analysis of phase gratings

Abstract: Phase gratings find useful application in array receivers as passive multiplexing devices in the local oscillator injection chain. In particular, the Dammann phase gating is one of the simplest class to model and manufacture, and can be used to generate multiple ima g es of a sin g le input beam in a quasi-optical system. It is a binary grating consisting of a regular arran g ement of milled slots or recesses in some suitable transparent dielectric or conducting block of material. The basic operation of the phase grating can be understood in terms of Fourier optics. However, Gaussian beam mode analysis is a powerful tool when investigating the limitation of the grating in a real submillirneter system of finite throughput and bandwidth. This is especially the case when evaluating the couplin g to an array of horn antenna feeds. In this paper we present the results of our investigation into the modellin g of phase gratings using Gaussian beam modes analysis and discuss new experimental measurements.

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

Abstract: Terahertz (THz) imaging is in its early stages of development but already the potential clinical impact of this new imaging modality is clear. From cancer research to DNA analysis THz technology is improving or even making possible imaging of hitherto inaccessible phenomena. In this paper we present a short review of THz imaging from the point of view of biomedical engineering. We discuss the current state of the art in terms of THz imaging systems; describe current applications, future potential and our own approaches to harnessing this novel technology. We draw attention to open problems in the area with respect to the limitations of the technology before concluding with descriptions of our future work in the area.

Generation of arbitrary order Bessel beams via 3D printed axicons at the terahertz frequency range.

Abstract: We present the generation of arbitrary order Bessel beams at 0.3 THz through the implementation of suitably designed axicons based on 3D printing technology. The helical axicons, which possess thickness gradients in both radial and azimuthal directions, can convert the incident Gaussian beam into a high-order Bessel beam with spiral phase structure. The evolution of the generated Bessel beams are characterized experimentally with a three-dimensional field scanner. Moreover, the topological charges carried by the high-order Bessel beams are determined by the fork-like interferograms. This 3D-printing-based Bessel beam generation technique is useful not only for THz imaging systems with zero-order Bessel beams but also for future orbital-angular-momentum-based THz free-space communication with higher-order Bessel beams.

QUaD: A high-resolution cosmic microwave background polarimeter

Abstract: We describe the QUaD experiment, a millimeter-wavelength polarimeter designed to observe the cosmic microwave background (CMB) from a site at the South Pole. The experiment comprises a 2.64 m Cassegrain telescope equipped with a cryogenically cooled receiver containing an array of 62 polarization-sensitive bolometers. The focal plane contains pixels at two different frequency bands, 100 GHz and 150 GHz, with angular resolutions of 5' and 35, respectively. The high angular resolution allows observation of CMB temperature and polarization anisotropies over a wide range of scales. The instrument commenced operation in early 2005 and collected science data during three successive Austral winter seasons of observation.

Generation of spatial Bessel beams using holographic metasurface.

Abstract: We propose to use backward radiations of leaky waves supported by a holographic metasurface to produce spatial Bessel beams in the microwave frequency regime. The holographic metasurface consists of a grounded dielectric slab and a series of metal patches. By changing the size of metal patches, the surface-impedance distribution of the holographic metasurface can be modulated, and hence the radiation properties of the leaky waves can be designed to realize Bessel beams. Both numerical simulations and experiments verify the features of spatial Bessel beams, which may be useful in imaging applications or wireless power transmissions with the dynamic focal-depth controls.

Generation of Bessel Beams by Two-Dimensional Antenna Arrays Using Sub-Sampled Distributions

Abstract: Bessel beams are proposed as a practical way to generate well collimated and confined beams at mm-waves or THz for quasi-optical applications. To achieve that, we propose the use of two-dimensional antenna arrays as realizable launchers. Truncated Bessel beams with a main lobe width of few wavelengths $(\lambda)$ can propagate over several hundreds of $\lambda$ if the antenna aperture is electrically large. Because such a large aperture would require a large number of antenna elements, sub-sampling distributions are proposed in this work. It is found that arrays with spacings of approximately $4\lambda$ generate high quality beams with very low amplitude oscillations over distances of about $300\lambda$ in vacuum. The optimal excitation function for such arrays greatly departs from the Bessel one. It is synthesized with an analytical method based on a least mean square error minimization. The synthesis method is scalar, but the pseudo-Bessel beams obtained are vectorial and linearly polarized. Theoretical predictions are confirmed by full-wave simulations using Ansoft Designer.