Development of low critical temperature superconducting tunnel junctions for application as photon detectors in astronomy
Promotion date: 10 December 2003
During his PhD Guy Brammertz worked in the Research and Scientific Support Department of the European Space Agency (ESA) on a contractual basis, being employed by Aurora Technology. His work at ESA and his PhD research for the larger part coincided. ESA has a formal contract with Twente University for theoretical collaboration and supervision.
Basically the thesis is about a kind of camera, a photon detector, which is used in telescopes for doing astronomy.
It takes images of light. It works in a similar way as a digital camera except that in addition it gives direct information on the energy and the time of impact of every single photon that hits the detector.
Who came up with the idea that you should do a PhD?
I worked for ESA during my graduation thesis. After that the head of the research section asked me to continue and proposed to do a PhD as well.
What was your thesis about?
Basically it is about a kind of camera, a photon detector, which is used in telescopes for doing astronomy. It takes images of light. It works in a similar way as a digital camera except that in addition it gives direct information on the energy and the time of impact of every single photon that hits the detector.
The advantage of the superconducting tunnel junction is that whenever light falls on to the junction, not only one electron (digital camera) is released, but thousands of them. The exact amount of photons released is directly related to the energy of the photon. This allows you to do spectroscopy of very faint sources and to determine, for example, the red shift of very far away galaxies in the spreading universe.
So this is a major step in astronomy?
Yes, the superconducting tunnel junction comes close to an “ideal” detector, but there are drawbacks as well of course. Whereas a CCD-camera can operate at room temperature, these detectors have to be cooled down to almost absolute zero (below one Kelvin).
Even up in space you would need a cooler.
But is there a practical application as yet?
Right now a Tantalum-based device – not the one I have worked with in my thesis - is used at the William Herschel Telescope in La Palma for doing astronomy. So far the detector chips I have been working with were tested in the laboratory only. The results are promising and one day they will be definitely in operation in a telescope.
This technology is also used in a number of other applications, mainly for X-ray detectors. There is a lot of potential.
How did you get involved in all this?
I am from Belgium (in fact the German speaking part) and I did my studies of applied physics engineering with a specialization in space applications at the University of Liège. At the end of my studies I very naïvely send an e-mail to the European Space Agency, asking for doing my graduation thesis there. I was lucky that somebody from Liège already worked there and he made a proposal for doing my graduation thesis at ESA.
I worked on that project for three months and after that I was asked to continue and do a PhD.
Are you going to stay with ESA?
No, I am still there, but my plan is actually to look for a job in industry. I think I have more evolution chances in industry than at the Space Agency. At ESA I am employed on a yearly contract basis, and although the work is very interesting indeed, I do not want to stay in this situation for the next ten years.
I hope to be able to broaden my horizons, in medical industry for instance.
I have only started looking two months ago. So far the positions are not for the taking, but I am hoping for better times.
For the summary of the thesis, click here.(English)
Voor de samenvatting van het proefschrift, click hier. (Nederlands)