680 research outputs found
Gaussian beam mode analysis of standing waves between two coupled corrugated horns
Abstract—In this paper we present the theoretical analysis of
the effects of standing waves between coupled horn antennas that
can occur in terahertz quasi-optical 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 quasi-optical
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 quasi-optical system operating at a
frequency of 0.480 THz
Gaussian beam mode analysis of standing waves between two coupled corrugated horns
Abstract—In this paper we present the theoretical analysis of
the effects of standing waves between coupled horn antennas that
can occur in terahertz quasi-optical 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 quasi-optical
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 quasi-optical system operating at a
frequency of 0.480 THz
The quasi-optical analysis of Bessel beams in the far infrared
We discuss the Gaussian beam mode analysis of Bessel beams, eigen-solutions of the wave-equation in cylindrical polar coordinates which neither change form nor spread out as they propagate. Approximate, limited diffraction finite aperture, pseudo-Bessel beams having intense on-axis 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 pseudo-Bessel beams can be usefully approximated by high-order Gaussian–Laguerre modes, which have similar propagation characteristics. The size of the on-axis spot produced by an axicon, and its depth of focus, can be estimated from a single best-fit high-order 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 model the propagation of Bessel beams through complex systems of long wavelength optical components, such as apertures, mirrors, and lenses. We report the experimental generation and measurement of a 0.1 THz Bessel beam, and show that useful performance is possible for an axicon having a scale size just one order of magnitude greater than the wavelength. This work confirms the technical feasibility of designing and building long-wavelength optical systems based on Bessel beams
Quasi-optical multiplexing using reflection phase gratings
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 wave-front. We report on work we are undertaking to
develop all reflection quasi-optical multiplexing systems so as to reduce reflection
losses at the grating and minimise the number of surfaces that can contribute to
standing wave effects in the optical system. As part of this endeavour we have also
developed a quasi-optical technique for analysing the inevitable degradation due to
multiple reflections on transmission grating design. This analysis is based on the
Gaussian beam mode technique, and a further application of this technique allows one
to assess tolerance limitations on the grating
Quasi-optical multiplexing using reflection phase gratings
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 wave-front. We report on work we are undertaking to
develop all reflection quasi-optical multiplexing systems so as to reduce reflection
losses at the grating and minimise the number of surfaces that can contribute to
standing wave effects in the optical system. As part of this endeavour we have also
developed a quasi-optical technique for analysing the inevitable degradation due to
multiple reflections on transmission grating design. This analysis is based on the
Gaussian beam mode technique, and a further application of this technique allows one
to assess tolerance limitations on the grating
Bacterial manipulation of the Integrated Stress Response: a new perspective on infection
Host immune activation forms a vital line of defence against bacterial pathogenicity. However, just as hosts have evolved immune responses, bacteria have developed means to escape, hijack and subvert these responses to promote survival. In recent years, a highly conserved group of signalling cascades within the host, collectively termed the integrated stress response (ISR), have become increasingly implicated in immune activation during bacterial infection. Activation of the ISR leads to a complex web of cellular reprogramming, which ultimately results in the paradoxical outcomes of either cellular homeostasis or cell death. Therefore, any pathogen with means to manipulate this pathway could induce a range of cellular outcomes and benefit from favourable conditions for long-term survival and replication. This review aims to outline what is currently known about bacterial manipulation of the ISR and present key hypotheses highlighting areas for future research
Experimental Verification of Electromagnetic Simulations of a HIFI Mixer Sub-Assembly
Phase II of the study "Far-Infrared 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 submillimeter-wave optical system. In this paper, we use the
software packages to predict the behaviour of a Mixer Sub-Assembly (MSA) of
HIFI, and we compare the simulations with near-field 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 through-focus experiment, which give a good
first-order indication of the agreement between measured and simulated
behaviour of a typical submillimeter-wave optical system
Optical requirements and modelling of coupling devices for the SAFARI instrument on SPICA
The next generation of space missions targeting far-infrared bands will require large-format arrays of extremely low-noise detectors. The development of Transition Edge Sensors (TES) array technology seems to be a viable solution for future mm-wave to Far-Infrared (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 over-moded light pipes are used to concentrate energy onto multi-moded 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
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