Browsing by Author "Hong, Yu-Heng"

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Effect of Passivation Layer on the Thin Film Perovskite Random Lasers
(2020-05-01)
Mallick, Subha Prakash
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Hong, Yu-Heng
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Chen, Lih-Ren
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Kao, Tsung Sheng
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Lu, Tien-Chang
Novel functionalities of disorder-induced scattering effect in random lasers, attributed to low spatial coherence, draw remarkable attention in high-contrast to superior quality speckle-free imaging applications. This paper demonstrates perovskite-polystyrene (PS)-based random lasing action with robust optical performance at room temperature. Optical characterizations are carried out upon perovskite thin films addition with polystyrene of different mixing concentrations (wt.%). A low threshold lasing operation is achieved with an increasing concentration of polystyrene, accompanying a wavy surface texture with high surface roughness. The rough surface dominating multiple scattering effects leads to enhanced feedback efficiency. Moreover, this study also elucidates efficient fabrication process steps for the development of high quality and durable PS-based random lasers. With the advantages of reduced coherent artifacts and low spatial coherence, speckle free projection images of the USAF (U. S. Air Force MIL-STD-150A standard of 1951) resolution test chart are shown for different PS-based random lasers.
Flexible Organometal-Halide Perovskite Lasers for Speckle Reduction in Imaging Projection
(2019-05-01)
Wang, Yu-Chi
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Li, Heng
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Hong, Yu-Heng
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Hong, Kuo-Bin
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Chen, Fang-Chung
Disorder is emerging as a strategy for fabricating random laser sources with very promising materials, such as perovskites, for which standard laser cavities are not effective or too expensive. We need, however, different fabrication protocols and technologies for reducing the laser threshold and controlling its emission. Here, we demonstrate an effectively solvent-engineered method for high-quality perovskite thin films on a flexible polyimide substrate. The fractal perovskite thin films exhibit excellent optical properties at room temperature and easily achieve lasing action without any laser cavity above room temperature with a low pumping threshold. The lasing action is also observed in curved perovskite thin films on flexible substrates. The lasing threshold can be further reduced by increasing the local curvature, which modifies the scattering strengths of the bent thin film. We also show that the curved perovskite lasers are extremely robust with respect to repeated deformations. Because of the low spatial coherence, these curved random laser devices are efficient and durable speckle-free light sources for applications in spectroscopy, bioimaging, and illumination.
Low Coherence Illumination of Flexible Perovskite Random Lasers
(2018-01-01)
Wang, Yu-Chi
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Hong, Yu-Heng
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Hong, Kuo-Bin
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Kao, Tsung-Sheng
;
Lu, Tien-Chang
We demonstrated that the methylammonium metal-halide perovskites can be exploited as a random laser source for the advanced speckle-free imaging Furthermore, the lasing performance can be actively controlled via the mechanical modulation of supporting substrates.