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Author = Withington, Stafford;
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Displaying Results 1  15 of 15 on page 1 of 1
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Analysis of standing waves in millimetrewave optics
(2007)
Whale, Mark; Trappe, Neil; Murphy, J.Anthony; Withington, Stafford
Analysis of standing waves in millimetrewave optics
(2007)
Whale, Mark; Trappe, Neil; Murphy, J.Anthony; Withington, Stafford
Abstract:
In this paper, we expand a theoretical framework for modelling standing waves in millimeter/submillimetre optical systems. Standing waves or multiple reflections have been traditionally difficult to model but this analytical method proves to be very versatile in dealing with reflections between typical quasioptical components such as lenses, apertures and mirrors. Using a full multi moded description of the feed horn (typically a corrugate horn), which is then transformed to equivalent free space Gaussian modes, a full mode matching scattering matrix approach is utilized to analyze any optical path/element, in which track is kept of both the backward and forward propagating components of the fields. We present an analysis of the reflected power from complicated cascaded optical apertures in a situation similar to a stray light baffle. Interesting constructive and destructive interference conditions can be observed from these structures and can be uniquely modelled with the presented...
http://eprints.maynoothuniversity.ie/9857/
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Developments in QuasiOptical Design for THz
(2004)
O'Sullivan, Créidhe; Murphy, J.Anthony; Cahill, Gary; Gradziel, Marcin; Trappe, Ne...
Developments in QuasiOptical Design for THz
(2004)
O'Sullivan, Créidhe; Murphy, J.Anthony; Cahill, Gary; Gradziel, Marcin; Trappe, Neil; White, David R.; Yurchenko, V.; Withington, Stafford; Jellema, Willem
Abstract:
Optical design in the terahertz (THz) waveband suffers from a lack of dedicated software tools for modelling the range of electromagnetic and quasioptical propagation conditions encountered in typical systems. Optical engineers are forced to use packages written for very different wavelength systems and there is often a lack of confidence in the results because of possible inappropriate underlying physical models. In this paper we describe the analytical techniques and dedicated CAD software tools (MODAL1) that we are developing for longwavelength design and analysis in the THz waveband. Our basic approach to modelling longwavelength propagation is the application of modal analysis appropriate to the problem under investigation2,3. We have extended this to include the efficient description of common offaxis (tilted) components such as simple curved reflectors4. In earlier research we have investigated the conditions under which approximate methods (ray tracing, paraxial modes) c...
http://eprints.maynoothuniversity.ie/9851/
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Experimental Verification of Electromagnetic Simulations of a HIFI Mixer SubAssembly
(2003)
Jellema, Willem; Wesselius, P.; Withington, Stafford; Yassin, Ghassan; Murphy, J.Anthon...
Experimental Verification of Electromagnetic Simulations of a HIFI Mixer SubAssembly
(2003)
Jellema, Willem; Wesselius, P.; Withington, Stafford; Yassin, Ghassan; Murphy, J.Anthony; O'Sullivan, Créidhe; Trappe, Neil; Peacocke, T.; Leone, B.
Abstract:
Phase II of the study "FarInfrared Optics Design & Verification", commissioned by the European Space Agency (ESA), we investigate the ability of several commercial software packages (GRASP, CODEV, GLAD and ASAP) to predict the performance of a representative example of a submillimeterwave optical system. In this paper, we use the software packages to predict the behaviour of a Mixer SubAssembly (MSA) of HIFI, and we compare the simulations with nearfield measurements at 480 GHz. In order to be able to distinguish between the predictions of the packages, we move the corrugated horn of the MSA through its nominal focus position. A unique feature of the experimental arrangement is that the measured position of every field point is known absolutely to within fractions of a wavelength. In this paper we present the results of this throughfocus experiment, which give a good firstorder indication of the agreement between measured and simulated behaviour of a typical subm...
http://eprints.maynoothuniversity.ie/9860/
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FarInfrared Optics Design & Verification
(2002)
O'Sullivan, Créidhe; AtadEttedgui, Eli; Duncan, William; Henry, David; Jellema, W...
FarInfrared Optics Design & Verification
(2002)
O'Sullivan, Créidhe; AtadEttedgui, Eli; Duncan, William; Henry, David; Jellema, Willem; Murphy, J.Anthony; Trappe, Neil; van de Stadt, H.; Withington, Stafford; Yassin, Ghassan
Abstract:
Compact quasioptics are difficult to design with any confidence using techniques developed for visible wavelengths. In this paper we investigate the performance of existing software design tools (ASAP, CODE V, GLAD) as well as a Gaussian beam mode analysis technique not yet available as commercial software. We have devised a set of test cases and used these to study the underlying methodologies and physics of these packages and we probe their suitability for the analysis of submillimetrewave systems and components. We have used the physical optics package GRASP as our benchmark software.
http://eprints.maynoothuniversity.ie/9837/
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Gaussian beam mode analysis of partial reflections in simple quasioptical systems fed by horn antennas
(2003)
Murphy, J.Anthony; Trappe, Neil; Withington, Stafford
Gaussian beam mode analysis of partial reflections in simple quasioptical systems fed by horn antennas
(2003)
Murphy, J.Anthony; Trappe, Neil; Withington, Stafford
Abstract:
Lowlevel reflections are particularly troublesome in sensitive highresolution spectral line receivers in the submillimetre and terahertz wavebands, giving rise to baseline ripple on spectra which is hard to distinguish from wide lines. In typical systems for submillimetrewave astronomy, for example, a lens or flat dielectric plate is often used as a cryostat window placed close to a feed horn. Partial reflection from such interfaces can give rise to return loss at the horn throat, which is considerably higher than for the horn radiating into free space. A full scattering matrix approach based on a combination of standard waveguide modes and quasioptical Gaussian beam modes can be used to analyse standing waves due to partial reflections, in which track is kept of both the backward and forward going components of the propagating fields. In this paper, we consider how such an analytical tool can be set up and we present typical examples of interest in which horn antennas feed simp...
http://eprints.maynoothuniversity.ie/9835/
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Gaussian beam mode analysis of standing waves between two coupled corrugated horns
(2005)
Trappe, Neil; Murphy, J.Anthony; Withington, Stafford; Jellema, Willem
Gaussian beam mode analysis of standing waves between two coupled corrugated horns
(2005)
Trappe, Neil; Murphy, J.Anthony; Withington, Stafford; Jellema, Willem
Abstract:
Abstract—In this paper we present the theoretical analysis of the effects of standing waves between coupled horn antennas that can occur in terahertz quasioptical systems. In particular we illustrate the approach for the case of two coupled horn antennas as the distance between them is varied. The full mode matching scattering matrix approach is based on combining a standard waveguide mode description of the horn antenna and a quasioptical Gaussian beam description of the free space propagation. Track is kept of both the backward and forward going components of the propagating fields.We compare theoretical predictions with actual experimental test results for a quasioptical system operating at a frequency of 0.480 THz.
http://eprints.maynoothuniversity.ie/2076/
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Modal analysis of the quasioptical performance of phase gratings
(1999)
Murphy, J.Anthony; O'Sullivan, Créidhe; Trappe, Neil; Lanigan, William; Colgan, R....
Modal analysis of the quasioptical performance of phase gratings
(1999)
Murphy, J.Anthony; O'Sullivan, Créidhe; Trappe, Neil; Lanigan, William; Colgan, R.; Withington, Stafford
Abstract:
This paper is concerned with the analysis of phase gratings as passive quasioptical 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 quasioptical 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.
http://eprints.maynoothuniversity.ie/61/
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Optical Modelling using Gaussian Beam Modes for the Terahertz Band.
(2009)
O'Sullivan, Créidhe; Murphy, J.Anthony; Gradziel, Marcin; Lavelle, John; Peacocke,...
Optical Modelling using Gaussian Beam Modes for the Terahertz Band.
(2009)
O'Sullivan, Créidhe; Murphy, J.Anthony; Gradziel, Marcin; Lavelle, John; Peacocke, Tully; Trappe, Neil; Curran, Gareth S.; White, David R.; Withington, Stafford
Abstract:
Special approaches unique to the waveband are required for the modelling of terahertz optical systems. Ray tracing is inadequate because in typical instruments the propagating beams are not very many wavelengths in diameter and a "quasioptical" approach is required in which Fresnel diffraction effects can be efficiently and accurately simulated. Typically, it is also necessary to be able to simulate the coupling of quasioptical beams to feed antenna structures to predict optical performance. In many systems the beams can be considered to be coherent and their propagation through a beam guide consisting of refocussing elements can be efficiently modelled using modal analysis, especially useful for quick design purposes, beam control and optimisation. This modal approach has been extended to allow for aberrations and truncation particularly relevant in compact mirror based systems. At the same time physical optics, although computationally intensive, is also a useful tool...
http://eprints.maynoothuniversity.ie/1910/
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Optical requirements and modelling of coupling devices for the SAFARI instrument on SPICA
(2011)
Trappe, Neil; Gao, J.R.; Glowacka, D.M.; Goldie, D.J.; Griffin, D.; Khosropanah, P.; Ma...
Optical requirements and modelling of coupling devices for the SAFARI instrument on SPICA
(2011)
Trappe, Neil; Gao, J.R.; Glowacka, D.M.; Goldie, D.J.; Griffin, D.; Khosropanah, P.; Mauskopf, P.D.; Morozov, Dmitry; Murphy, J.Anthony; O'Sullivan, Créidhe; Ridder, Marcel; Withington, Stafford
Abstract:
The next generation of space missions targeting farinfrared bands will require largeformat arrays of extremely lownoise detectors. The development of Transition Edge Sensors (TES) array technology seems to be a viable solution for future mmwave to FarInfrared (FIR) space applications where low noise and high sensitivity is required. In this paper we concentrate on a key element for a high sensitivity TES detector array, that of the optical coupling between the incoming electromagnetic field and the phonon system of the suspended membrane. An intermediate solution between free space coupling and a single moded horn is where overmoded light pipes are used to concentrate energy onto multimoded absorbers. We present a comparison of modelling techniques to analyse the optical efficiency of such light pipes and their interaction with the front end optics and detector cavity.
http://eprints.maynoothuniversity.ie/9845/
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Perturbation analysis of Gaussianbeammode scattering at offaxis ellipsoidal mirrors
(1996)
Murphy, J.Anthony; Withington, Stafford
Perturbation analysis of Gaussianbeammode scattering at offaxis ellipsoidal mirrors
(1996)
Murphy, J.Anthony; Withington, Stafford
Abstract:
We present an approximate technique, based on the principles of multimode Gaussian optics and perturbation theory, for calculating the distortions that occur when an offaxis ellipsoidal mirror is placed in the path of a weakly diffracting beam. More specifically, we calculate the Gaussianbeammode scattering matrices of offaxis ellipsoidal mirrors. The technique can be applied when the phase errors across the surface of the mirror are small. In this case, power is only scattered into a few neighbouring modes, and simple closedform expressions can be derived for the elements of the scattering matrix.
http://eprints.maynoothuniversity.ie/60/
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Quasioptical multiplexing using reflection phase gratings
(2000)
Lanigan, W.; Trappe, Neil; Murphy, J.Anthony; Colgan, R.; O'Sullivan, Créidhe; Wit...
Quasioptical multiplexing using reflection phase gratings
(2000)
Lanigan, W.; Trappe, Neil; Murphy, J.Anthony; Colgan, R.; O'Sullivan, Créidhe; Withington, Stafford
Abstract:
Heterodyne array receiver systems for both ground based and satellite telescope facilities are now becoming feasible for imaging in the submillimetre/terahertz regions of the EM spectrum. Phase gratings can be usefully employed as high efficiency passive multiplexing devices in the local oscillator (LO) injection chain of such receivers, ensuring that each element of the array is adequately biased and that the reflected LO power level at the array is minimised. For the wavelengths of interest both transmission and reflection gratings can be manufactured by milling an appropriate pattern of slots into the surface(s) of a suitable material. Thus, the required phase modulation is produced by the resulting pattern of varying optical path lengths suffered by the incident wavefront. We report on work we are undertaking to develop all reflection quasioptical multiplexing systems so as to reduce reflection losses at the grating and minimise the number of surfaces that ...
http://eprints.maynoothuniversity.ie/9861/
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The Gaussian beam mode analysis of classical phase aberrations in diffractionlimited optical systems
(2003)
Trappe, Neil; Murphy, J.Anthony; Withington, Stafford
The Gaussian beam mode analysis of classical phase aberrations in diffractionlimited optical systems
(2003)
Trappe, Neil; Murphy, J.Anthony; Withington, Stafford
Abstract:
Gaussian beam mode analysis (GBMA) offers a more intuitive physical insight into how light beams evolve as they propagate than the conventional Fresnel diffraction integral approach. In this paper we illustrate that GBMA is a computationally efficient, alternative technique for tracing the evolution of a diffracting coherent beam. In previous papers we demonstrated the straightforward application of GBMA to the computation of the classical diffraction patterns associated with a range of standard apertures. In this paper we show how the GBMA technique can be expanded to investigate the effects of aberrations in the presence of diffraction by introducing the appropriate phase error term into the propagating quasioptical beam. We compare our technique to the standard diffraction integral calculation for coma, astigmatism and spherical aberration, taking—for comparison—examples from the classic text 'Principles of Optics' by Born and Wolf. We show the advantages of GBMA for a...
http://eprints.maynoothuniversity.ie/9836/
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The Gaussian Beam Mode Analysis of Phase Gratings
(1999)
O'Sullivan, Créidhe; Murphy, J.Anthony; Trappe, Neil; Lanigan, William; Colgan, R....
The Gaussian Beam Mode Analysis of Phase Gratings
(1999)
O'Sullivan, Créidhe; Murphy, J.Anthony; Trappe, Neil; Lanigan, William; Colgan, R.; Withington, Stafford
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 images of a single input beam in a quasioptical system. It is a binary grating consisting of a regular arrangement 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 coupling to an array of horn antenna feeds. In this paper we present the results of our investigation into the modelling of phase gratings using Gaussian beam modes analysis and discuss new experimental measur...
http://eprints.maynoothuniversity.ie/9862/
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The quasioptical analysis of Bessel beams in the far infrared
(2005)
Trappe, Neil; Mahon, R.; Lanigan, William; Murphy, J.Anthony; Withington, Stafford
The quasioptical analysis of Bessel beams in the far infrared
(2005)
Trappe, Neil; Mahon, R.; Lanigan, William; Murphy, J.Anthony; Withington, Stafford
Abstract:
We discuss the Gaussian beam mode analysis of Bessel beams, eigensolutions of the waveequation in cylindrical polar coordinates which neither change form nor spread out as they propagate. Approximate, limited diffraction finite aperture, pseudoBessel beams having intense onaxis spots with large depths of field can be produced experimentally in the far infrared by using plastic conical lenses, known as axicons. We illustrate the physical insight provided by Gaussian beam mode analysis of such systems. Such pseudoBessel beams can be usefully approximated by highorder Gaussian–Laguerre modes, which have similar propagation characteristics. The size of the onaxis spot produced by an axicon, and its depth of focus, can be estimated from a single bestfit highorder Gaussian–Laguerre mode, and a more detailed description of behaviour can be achieved by adding a few additional modes of neighbouring orders. The strength of Gaussian beam mode analysis is that it is straightforward to ...
http://eprints.maynoothuniversity.ie/9834/
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Theoretical and experimental study of highQ resonant modes in terahertz optical systems
(2004)
Jellema, Willem; Withington, Stafford; Trappe, Neil; Murphy, J.Anthony; Wild, Wolfgang
Theoretical and experimental study of highQ resonant modes in terahertz optical systems
(2004)
Jellema, Willem; Withington, Stafford; Trappe, Neil; Murphy, J.Anthony; Wild, Wolfgang
Abstract:
The existence of multiple reflections in terahertz optical system causes numerous problems in applications ranging from astronomical to medical instrumentation. We have performed a detailed theoretical study, using waveguide and freespace modal matching, of the highQ modes that appear on THz optical paths. Highly accurate measurements at 0.48 THz reproduce in detail the complex behaviour that was predicted theoretically. This work opens up the possibility of designing schemes for removing these troublesome effects.
http://eprints.maynoothuniversity.ie/9859/
Displaying Results 1  15 of 15 on page 1 of 1
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