Instrumentation

DPhil Projects 2020: Instrumentation Development

Building the HARMONI spectrograph – a first light instrument for the ELT.
Myriam Rodrigues & Niranjan Thatte

The Extremely Large Telescope (ELT) currently being built by the European Southern Observatory is a revolutionary scientific project for a 39m diameter primary mirror telescope that will allow us to address many of the most pressing unsolved questions about our Universe: discovering planets around other stars, probing the first objects in the Universe, unveiling the nature and distribution of the dark matter and dark energy which dominate the Universe. The ELT will be the largest optical/near-infrared telescope in the world and will gather 13 times more light than the largest optical telescopes existing today.
The University of Oxford is leading the construction of HARMONI, an integral field spectrograph that will be one of the two “first-light” instruments for the ELT. Integral field spectroscopy, also called 3D spectroscopy, is a recent instrumental technique which allows observers to simultaneously obtain the full set of spectra from all astrophysical sources in a small region of sky. In addition to managing the overall project, the visible and infrared instrumentation group at Oxford is responsible for building a key system of the instrument: the spectrograph units.

We are looking for a motivated D.Phil student who has a keen interest in state-of-the-art instrumentation, to work collaboratively with the spectrograph team. The successful candidate will plan and validate the alignment of the collimator module: from testing alignment concepts with a prototype to the assembly of the first collimator module of HARMONI. The assembly of the collimator involves the alignment of large (>1metre) optics to a high level of accuracy, requiring both inventing the concept & detailing the alignment methodology and tools.
The successful candidate will gain expertise in cryogenic systems, their optical design and fabrication, as well as instrument assembly, integration and testing.

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Calibrating the HARMONI spectrographs: Designing and building a Fabry-Perot interferometer based frequency comb.
Niranjan Thatte, Matthias Tecza & Myriam Rodrigues

The Extremely Large Telescope (ELT) will be the world’s largest telescope, with a primary mirror diameter of 39 meters, and a light collecting area of nearly 1000 m2, almost equal to all the telescopes ever built put together. At Oxford, we are leading the design and development of HARMONI, an adaptive optics assisted, visible and near-infrared integral field spectrograph that will provide the telescope’s spectroscopic capability at first light. Integral field spectrographs pack information very densely on the large format detector arrays, and accurate knowledge of the instrument’s response (line spread function, LSF) is necessary to correctly subtract the bright night-sky background and interpret & analyse the observations. To this end, we need to design and fabricate a calibration source that will produce a series of sharp, tunable, spectral lines spread evenly in wavelength. One way of achieving this is using a Fabry-Perot interferometer.

We are looking for motivated D.Phil student who has a keen interest in state-of-the-art instrumentation. She/he will gain expertise in optical and mechanical design and fabrication, and be able to deliver a complete turn-key system that will provide a vital calibration source for HARMONI.

Millimetre-Wave Superconducting Quantum Amplifiers for Radio Astronomy.
Boon Kok Tan & Kitti Ratter
Instrumentation for astrophysics, sub-mm detectors, condensed matter physics.

Amplification of weak signals with high sensitivity is almost exclusively achieved using high electron mobility transistor (HEMT) amplifiers. They are an integral part of the most highly-sensitive instruments for astronomy, quantum computing, Earth observation and low-temperature physics. HEMT amplifiers however have fundamental drawbacks. The sensitivity does not approach a quantum limited level. They are power hungry, requiring substantial heat dissipation, and both the noise temperature and bandwidth deteriorate rapidly at higher frequencies. There is therefore an intense interest for developing a new amplifier technology with quantum-limited noise performance, high gain over wide bandwidths, ultra-low power dissipation and capable to operate in THz frequency regime.

The emerging technology of superconducting parametric amplifiers (SPAs) has the potential to achieve all these requirements. Amplification is achieved by varying the device reactance via a strong ‘pump’ wave that would allow power transfer from the pump to the weak signal. Because the process relies purely on nonlinear reactive response, dissipation is exceedingly small, therefore allowing the quantum limit to be achieved. They are also small in size, robust and very versatile with high fabrication yield.

Most published work in this area described narrow band SPAs that could operate only at microwave frequencies. In this project, we aim to develop a wideband SPA that would operate at millimetre (mm) wave regime as pre-amplifier for the quantum mixers developed for mm and sub-mm astronomical receivers. The development of such a device will have a huge impact in mm & sub-mm astronomy and B-mode Cosmic Microwave Background (CMB) experiments, as a quantum-noise limited SPA with high gain before the mixer will improve the receiver sensitivity by more than an order of magnitude.

In this highly challenging project, the student will start by studying the theoretical background and simulation technique to model the SPA, along with learning to use commercial electromagnetism software to design the amplifiers. The student will have the chance to get involve in the fabrication of the devices using state-of-the-art clean room facilities, either here in Oxford, or with our other collaborators (Paris, Chalmers, Cambridge etc). The student will also learn how to use sub-Kelvin cryogenics system and other experimental techniques, for measuring the performance of the amplifiers. In particular, the student will investigate the operation of the SPA at mm-wave frequencies, and their performance dependence on the physical temperature and the superconducting materials used to form the SPAs. Finally, the student will integrate the amplifier into an existing mm-wave astronomical receiver and assess the impact on the receiver performance.

The Superconducting Quantum Detector Group in Oxford have a well-equipped laboratory, with all the required instruments to perform the design and test of the amplifiers. Apart from the formal supervision, the student will be assisted by an experienced technician, working along with post-docs in the group, with the support from the electronics, mechanical and photo-fabrications expertise in Oxford Physics. There is also a possibility to get involved in an astronomical observation project as well (with Prof. Dimitra Rigopoulou), including performing the observation using existing mm/sub-mm telescopes.

Further Readings: http://science.sciencemag.org/content/350/6258/307

boonkok.tan@physics.ox.ac.uk, kitti.ratter@physics.ox.ac.uk

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Weak gravitational lensing with the Euclid mission.
Lance Miller

Measurements of weak gravitational lensing are one of the key ways of testing the standard cosmological model and the accuracy of general relativity on cosmological scales. The European Space Agency’s Euclid mission will break new ground in making accurate measurements over about one-third of the entire sky. But to achieve that, we must first accurately model the distorting effect of the Euclid telescope, and at Oxford we have been leading the effort to model the telescope and correct the lensing measurements. Euclid is due launch in 2022 and the survey will take five years to complete. The D.Phil student will work on the modelling and shear measurement, including analysis of the first in-orbit calibration measurements, and should have access to the first of the exciting new survey data to be obtained. The work will involve using scientific programming and simulations to test and improve our physical models of the telescope and its detectors, plus statistical analysis of observational data, and the student should have a role in the first analyses of the early data from the mission.

see: https://www.euclid-ec.org/

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Very high-energy gamma ray astrophysics.
Garret Cotter

Very high-energy (VHE) gamma-ray astrophysics is an exciting field spanning fundamental physics and extreme astrophysical processes. We detect the Cherenkov light emitted when VHE gamma rays from space hit the top of the Earth’s atmosphere, using optical telescopes on the ground fitted with high-speed detectors similar to those used by the Large Hadron Collider. Our science goals include
• Understanding the origin of cosmic rays and their role in the Universe.
• Understanding the natures and variety of particle acceleration around black holes.
• Searching for the ultimate nature of matter and physics beyond the Standard Model.
The Oxford group works on the High Energy Stereoscopic System (H.E.S.S.) in Namibia, which is at present the world’s largest gamma-ray observatory, and on the development of international Cherenkov Telescope Array (CTA; http://www.cta-observatory.org ). This will be the first global observatory for VHE gamma-ray astronomy, and will be sensitive to photon energies up to 1015 eV.
There are openings for both experimental and theoretical work. We are developing software and data analysis techniques for CTA’s small-sized unit telescopes. These will have 2k pixel detectors and front-end amplifiers which feed into custom high-speed electronics. This gives a system that can image at a rate of a billion frames per second. We are also leading the efforts on machine learning techniques for the large volumes of data that will be generated when CTA becomes operational.
On the theoretical/observational side of the programme, recently we have developed new theoretical models for the broad-spectrum emission from steady-state jets that let us use the gamma-ray observations and those at other wavelengths to investigate the physical properties of the jet and the black hole at its base. We now propose to extend these models to look in particular at the entrainment of heavy particles as the jets propagate through their host galaxy, and the resulting possibility of hadronic particle processes within the jets. We will investigate how CTA may be used to determine the physical conditions that lead to flaring and the presence, and extent, of emission from hadronic processes.
We will offer the possibility of joint supervision with the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg, and all students will have the opportunity to gain experience on observing shifts at the H.E.S.S. site.