Nanowire lasers are promising for many applications but they operate at a number of wavelengths, whereas single-mode output is preferable for some uses. Now Limin Tong and co-workers at Zhejiang and Peking universities have demonstrated single-mode lasing in a single cadmium selenide nanowire.
In general the cavity in a nanowire laser is equal to the length of the nanowire, with the endfaces of the nanowire acting as the mirrors that define the cavity. It is possible to select just one laser mode by shortening the cavity, but this increases the threshold for laser operation. However, if one end of the nanowire is folded or bent to form a loop, this acts as a mirror. Moreover, the threshold is reduced because the reflectivity of this loop mirror is higher than that of an endface.
Tong and co-workers bend both ends of the nanowire to form two loop mirrors, which means that there are four coupled cavities defined by different combinations of the endfaces and the loop mirrors. The Zhejiang–Peking team then uses the Vernier effect to select the output from one of these cavities. The team also shows that the output wavelength can be tuned by changing the length of the cavity defined by the loop mirrors.
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In the loop. Nature Nanotech (2011). https://doi.org/10.1038/nnano.2011.63
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DOI: https://doi.org/10.1038/nnano.2011.63
