Stimulated Emission Detection Images Single Nanocrystals At High Speed

A new technique for imaging single molecules that does not rely on fluorescent emitters could find a host of applications in nanotechnology, photonics and photovoltaics. The technique, which was developed by researchers in Barcelona, works by detecting stimulated emission from single quantum dots at room temperature. Its speed makes it possible to trace charge-carrier populations through the entire absorption and emission cycle.

Single-molecule imaging techniques are widely employed in biology. To date, they have been entirely based on detecting spontaneous fluorescence from the sample being imaged. In these fluorescence-based techniques, researchers typically excite the sample at wavelengths at which it absorbs light and then detect redshifted (lower energy) fluorescence signals. This makes it relatively simple to block the background light from the excitation beam and detect only the fluorescence.

However, fluorescence imaging is far from perfect, since it is limited to molecules that fluoresce efficiently. Fluorescent light is also both incoherent and prone to “bleaching”, where the signal fades after the molecule can no longer fluoresce. A third drawback is that spontaneous emission is a relatively slow process, occurring on a timescale of nanoseconds.

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