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Lydia Bechger (promotion date: 18 December 2003)

Synthesis and Fluorescence of Opal & Air-Sphere Photonic Crystals

Promotion Date: 18 December 2003

Lydia Bechger was the 2000th PhD graduate at Twente University. It was celebrated with champagne after the defence of her thesis.

Lydia Berchger

My thesis is about the fabrication and characterization of photonic crystals. Photonic crystals are structured materials on a nanometer scale with unusual optical qualities. It is built in layers, each layer having its own refractive index which results in the colour effect you see on CD’s or in opals for instance. My research was about developing a photonic crystal which encloses light: a photonic band gap, which is a frequency range for which light will not propagate in any direction. Light from within the crystal can’t go out and light from the outside cannot go in.

What was your thesis about?

My thesis is about the fabrication and characterization of photonic crystals. Photonic crystals are structured materials on a nanometer scale with unusual optical qualities. It is built in layers, each layer having its own refractive index which results in the colour effect you see on CD’s or in opals for instance. My research was about developing a photonic crystal which encloses light: a photonic band gap, which is a frequency range for which light will not propagate in any direction. Light from within the crystal can’t go out and light from the outside cannot go in. At the beginning I was mainly occupied with the fabrication of photonic crystals. I made various crystals; researching materials and structures that could lead to this photonic band gap. Later on in my project I doped the photonic crystals with dye molecules to check whether the light is indeed enclosed in the crystal. At this stage I also performed a lot of optical measurements.

What makes photonic crystals so interesting?

There is a worldwide interest in photonic crystals. For purposes in the field of physics there are a number of applications that can be thought of: low threshold lasers, or a replacement for electronic switching. But that is as far as I can see still a long way of.

My research is very fundamental. Because I studied chemistry I wanted to know what chemists could do with photonic crystals, perhaps be useful in solar cells enclosing the energy of light. But that also is not for the immediate future, photonic crystals are difficult to produce especially if you want larger structures of perfect domains.

What was the exact result of your research?

One result is that we found it is not favourable to use certain materials in photonic crystals, since they make it more difficult to use dye molecules for lifetime measurements. We also showed that the emission spectrum of a dye molecule is strongly influenced by the structure of the photonic crystal, the onset of a photonic band gap.

How do you protect your own line of research when working so closely in a group?

Well, mine was the first book about actually making photonic crystals according to this new principle. I have written it up and they are my findings. Others continue where I have stopped or do other measurements.

Are you not sorry that you yourself cannot continue?

Yes, in a way. But there is so much to know and you have to draw the line somewhere and start writing. But in the near future I will still be involved with some publications.

And next I am on the lookout for something that is more or less in my line. Shell for instance is looking in to solar energy and there is still a lot to be done in that field. Although I do not think that photonic crystals are as yet within their scope since practical applications are as yet too far off.

How do you apply for a position?

I want to find a job in a research company. The main thing then is to find the right person to contact. It is useless to just randomly apply. There are also special employment agency’s for chemists which I already approached.

Would you like to go abroad?

Well, for now I want to stay in the Netherlands. I started my PhD a bit unconventionally. I was a research technician in the group in Amsterdam. Only in the second half of the first year the idea came up for a promotion study. Then I studied the first 2,5 years in Amsterdam, but then the group moved to Twente. I had to go as well, staying in Amsterdam was no option. Now I do not want to be away again from my partner and social life in Amsterdam.

What did you like best?

The fact that my project was actually a combination of fabricating the samples myself and performing measurements with these samples. Furthermore I really enjoyed swimming during lunchtime in the outdoor swimming pool at the campus.

And what didn’t you like?

I really had a great time during my PhD with no dislikes particularly. But I did not like that after having spent a considerable amount of money on the cover design of my book* I was told by the printers’ that there would be a line on a hundred and fifty or so of my books. Allegedly these lines could not be avoided in the production process. But fortunately they did manage it, and they all look fine.

*The book cover has an embossed look of wrinkled tin foil, the silvery aspect changing colour hue when picked up and moved about, like a hologram or in fact, an opal.

For the summary of the thesis, click here. (English)

Voor de samenvatting van het proefschrift, click hier. (Nederlands)