| Abstract |
Chapter 1 contains a general introduction to this field. It lists our motivations and clarifies our goals. It also explains the relationship between the different chapters.
Chapter 2 describes the experimental setup we built for our new experiments at near-infrared and visible wavelengths. After a discussion about the requirements and the different possibilities, we decided to build an advanced microscope setup ourselves. With this setup we are able to study emission of light sources in photonic crystals, with special attention to accurate, spatial positioning possibilities. In addition, the structures can be cooled down to very low temperatures (down to −265 ◦C). The setup is computer controlled, so that we are able to automatically map emission properties of a sample. The design of the setup is such that all components can be used separately, which makes this setup very flexible.
Chapter 3 contains characterization measurements on our light sources, quantum dots made of lead (Pb) and selenium (Se). Here we find the effective light absorption cross section of the dots, which is around 10−16 to 10−15 cm2 (10−16 means 1 divided by a 1 with 16 zeros). In addition, the absorption and emission strengths have been determined and the results have been used to explain why, contrary to expectations, the larger quantum dot light sources emit light faster than the smaller dots in lead selenide. In this chapter we also conclude that the individual quantum dots can emit a much larger range of colors than expected.
Chapter 4 considers the first measurements on the photonic crystals with the light sources: our samples. Because the desired silicon crystals were not yet finished, we put our quantum point light sources in so-called air sphere crystals (see Figure 1.3 for illustration). These crystals are made of titanium dioxide (titania): a mineral that provides the white color in paper, paint and toothpaste, for example. First, the crystals are characterized using optical microscopy and reflection measurements. Then, measurements are made to measure how much light from the quantum points leaves the sample at a certain angle. We show that the results are strongly determined by scattering and interference of the light in the photonic crystal. An escape model is applied to quantitatively describe the distribution of the emitted light over the possible exit angles.
Chapter 5 contains the experimental details that need to be taken into account when we want to measure how long an excited light source takes to return to its ground state while emitting light. Especially for measurements at near-infrared wavelengths of light, the signal to be measured barely rises above the noise of the detector. We show how in this situation, by choosing the right experimental settings, we can still detect the interesting signals.
Chapter 6 uses the knowledge from the previous chapter to measure the emission rate of quantum point light sources in photonic crystals. To adjust the LDOS, we change the period of the crystal and show that this is accompanied by a change in the emission rate. In this chapter, we demonstrate for the first time in the world that we can control these so-called quantum light sources at near-infrared wavelengths using photonic crystals. We measured an emission acceleration of 29 % and an inhibition of 51 %. This is an important success that brings us a big step closer to experiments with photonic band gap materials. This demonstration also means that the setup we built meets the experimental requirements.
Chapter 7 explains the technique we developed to be able to find the same small structures in different setups. Instead of artificial markers, we show that intrinsic structures on samples are sufficient to serve as a reference frame. The method is illustrated with practical examples. We will need this technique later to find our cavities in photonic crystals.
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