Lasing by Template-Assisted Self-Assembled Quantum Dots

Miniaturized laser sources with low threshold power are required for integrated photonic devices. Photostable core/shell nanocrystals are well suited as gain material and their laser properties can be exploited by direct patterning as distributed feedback (DFB) lasers. Here, the 2nd-order DFB resonators tuned to the photoluminescence wavelength of the QDs are used. Soft lithography based on template-assisted colloidal self-assembly enables pattern resolution in the subwavelength range. Combined with the directional Langmuir-Blodgett arrangement, control of the waveguide layer thickness is further achieved. It is shown that a lasing threshold of 5.5 mJ cm(-)(2) is reached by a direct printing method, which can be further reduced by a factor of ten (0.6 mJ cm(-)(2)) at an optimal waveguide thickness. Moreover, it is discussed how one can adjust the DFB geometries to any working wavelength. This colloidal approach offers prospects for applications in bioimaging, biomedical sensing, anti-counterfeiting, or displays.