Design of low-threshold compact Au-nanoparticle lasers.

We performed a rigorous study to reduce threshold gain of Au-nanoparticle lasers in the deep-subwavelength scale with the consideration of strong interband transitions in Au and device dimensions. We found that the high-threshold optical gain of the nanolaser (over 10(5)cm(-1), which is matched with the result estimated from a previous article [Nature 460, 1110 (2009)]) arises from the high interband transition of Au near 530nm. It can be shown that by increasing the background index, as well as optimizing the lasing wavelength and device dimensions, the threshold gain (cavity volume) can be reduced by 43% (90%).