Full Spectral and Angular Characterization of Highly Directional Emission from Nanocrystal Quantum Dots Positioned on Circular Plasmonic Lenses

We design a circular plasmonic lens
for collimation of light emission
from nanocrystal quantum dots at room temperature in the near IR spectral
range. We implement a two-dimensional k-space imaging technique to
obtain the full spectral-angular response of the surface plasmon resonance
modes of the bare plasmonic lens. This method is also used to map
the full spectral-angular emission from nanocrystal quantum dots positioned
at the center of the circular plasmonic lens. A narrow directional
emitting beam with a divergence angle of only ∼4.5° full
width at half-maximum is achieved with a spectrally broad bandwidth
of 30 nm. The spectrally resolved k-space imaging method allows us
to get a direct comparison between the spectral-angular response of
the resonant surface plasmon modes of the lens and the emission pattern
of the quantum dots. This comparison gives a clear and detailed picture
of the direct role of these resonant surface waves in directing the
emission. The directional emission effect agrees well with calculations
based on the coupled mode method. These results are a step toward
fabricating an efficient room-temperature single photon source based
on nanocrystal quantum dots.