Integrated photonic devices are a key part in the sensing, energy and medical technology sectors. For these technologies, solution-processed methods are desirable due to their simple, low-cost fabrication methods that can be readily scale. Here, we discuss our recent discovery that intrinsic lasing, that is without an external cavity, can be realized at low fluence threshold and in an ultrathin film of coupled, highly crystalline nanospheres with overall thickness on the order of ∼λ/4. The cavity-free geometry consists of zinc oxide nanospheres that collectively localize the in-plane emissive light fields, resulting in excitonic lasing with fluence thresholds an order of magnitude lower than previous UV-blue random and quantum-dot lasers. To understand the effects of near-field environment on the lasing performance, we modify the lasing media locally and conduct optical fluence-dependent measurements to determine the lasing threshold of our samples. We perform ultrafast transient absorption spectroscopy above and below the lasing threshold to probe modification of the carrier dynamics due to changes in the fabrication methods. Finally, with these known fluence threshold values, we image our thin film lasing samples by optical excitation to map their emission profile with high spatial and spectral accuracy. Together with 3D electromagnetic simulations, our results highlight the importance of the near-field environment in modifying the requirements for efficient lasing at the nanoscale.

Spatial and spectral mapping of a random nanoscale lasing media with sub-micron resolution

2019 Fall National Meeting

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