On the one side, there are tiny fragments of diamond. Besides carbon diamond contains other atoms as natural impurities. These impurity atoms or so-called colour centres are responsible for the yellow or blue colours of natural diamond.
a) Sketch of the direct laser writing process. A femtosecond laser beam is focussed into the photoresist in order to polymerize well defined 3D structures. (b) Scanning electron micrograph of such a structure after development containing several key photonic elements, such as waveguides, couplers and microdisc resonators. Scale bar is 5 µm. Figure: Oliver Benson
(a) Sketch of the experimental configuration. The excitation spot is scanned over the resonator disc. Photons are detected at both waveguide outputs simultaneously. (b) Photon counts collected at one end of the waveguide while scanning the excitation spot with a second objective. The circle highlights the position of a single NV-centre. Shape distortions are due to non closed-loop piezo-scanning. Scale bar is 5 µm. Figure: Oliver Benson
Due to their very small size of only a few millionths of a millimetre, some of the diamond fragments contained only a single colour centre, which could be excited optically with the help of laser light. The colour centre releases its energy by emission of single quanta of light, or photons, which are thus generated in a controlled way one-by-one.
The researchers now mixed the diamond fragments with a special photo resist. A focussed laser beam irradiating the resist layer induced local polymerisation, i.e. the resist was turned into plastic. In this way it was possible to write nearly arbitrary three-dimensional structures, which contain single diamond fragments with single colour centres. The research team at first fabricated optical waveguides and resonators for efficient collection and routing of the photons emitted from the colour centres.
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