Controlling spontaneous emission with nanostructures
Promotion date: 15. December 2010
Promotor: Prof. Dr. Willem Vos
In this thesis experimental results are presented that show that we can control the process of spontaneous emission by placing the emitter close to a nanostructure. Spontaneous emission near interfaces are investigated, in 2D and 3D photonic crystals and near random arrays of nanowires.
The ultimate control over spontaneous emission can be achieved in a photonic crystal where the photonic band gap overlaps in frequency with the emission spectrum of the emitter. Theoretically the LDOS is zero inside an infinite photonic crystal, leaving the emitter forever in its excited state. Although inhibition up to eleven times is very exciting, it doesn’t proof the existence of a band gap, a region with truly zero density of states.
Two dimensional photonic crystals are more easily fabricated than their 3D counterparts but can still interact strongly with light. By placing PbS quantum dots inside 2D centered rectangular macroporous silicon photonic crystals, we showed that the light is strongly redirected inside the photonic crystal. No modification of the decay rate is seen, as expected from density of states calculations.
Finally, CdSe quantum dots are placed inside strongly scattering ensembles of gallium phosphide nanowires to investigate the effect of disorder on the decay dynamics.
Was there a special moment during your thesis project, that you remember very well?
The famous Eureka-moment is a little too romantic, in my perception. For my first article, the deciding measurements only took a week to perform, while working on the experimental equipment as a whole, took about one and a half year. It is a tough job being able to convincingly show that the measurements are correct and reproducible.
The thrill is that you’re doing something nobody has ever done or even seen before. One can say that the photonic crystals I measured on, are eleven times more quiet than it can ever get in a normal vacuum state. That’s exciting and makes you feel you’re doing real science.
However, I believe there was one decisive moment I cherish. We came up with a clever way to line up the crystals, placing them carefully on line in a precision range of one micrometer. After that, I was able to perform the measurements I wanted so badly.
Did the results lead to nice publications?
We had an article published in Physical Review B. At the moment we are busy writing three more articles for some editions of highly ranked papers.
What are your future plans?
Right now, I am working at Philips Research. The work of our team is at the beginning stages of product development, testing the feasibility of new ideas, resulting in proofs of principle.
I like this way of working after the more or less fundamental research activities at Mesa+. There one sets her own goals and problem solving strategies. In a company environment the application is never far away, mostly within six months time. That is very challenging.
On top of that, ten percent of the research time is free at Philips Research. These so-called Friday afternoon sessions I like very much, being able to test own ideas.
What, in your opinion, is important for Mesa+ to stay successful in the future?
Working a great deal at AMOLF in Amsterdam, at the Complex Photonics Systems Group, and at my hometown Utrecht, I somewhat felt like a half member of Mesa+. The institute is doing very well. Still, I think some more interaction between research groups can lead to nice results. The graduate schools are a good development, to enhance cooperation moments. In Amsterdam, I really profited a lot from the nanophotonics group meetings. It’s a nice learning experience to hear what research fellows are doing. The chances of cooperating are getting bigger, this way.