100x reduction in fluorescence lifetime of a single molecule

31.10.2012, 16:43

Newsletter 5

Spontaneous emission plays a central role in most optical phenomena, its rate being determined by the radiative decay of the excited state of the emitter. Because optical emitters are (sub)nanometer in size, the strength of their dipole moments is limited, yielding fluorescence lifetimes in the nanosecond range. If the lifetime can be shortened, the power that can be extracted from a single emitter is enhanced. Optical antennas made of two nanostructures promise lifetime modifications of several orders of magnitude. We have recently used scanning probe technology (see figure) to realize an antenna made of two gold nanospheres. Measurements of the fluorescence signal yielded enhancement factors of 3 for one sphere and 28 for two. Additionally, measurements of the fluorescence lifetime of a single molecule yielded 20 ns with no nanoparticle (figure, i), 1.5 ns when placed on a single gold nanoparticle (ii) and 180 ps when sandwiched between two nanoparticles (iii) – an enhancement factor of 111. The measurements were performed on a molecular system with near-unity intrinsic quantum efficiency; the antenna effect would be more dramatic for emitters with lower quantum efficiency.

 

Contact: vahid.sandoghdar(at)mpl.mpg(dot)de
Group: Sandoghdar Division
Reference: K.-G. Lee, et al.,?Optics Express 20, 23331 (2012).