Browsing by Author "Yeh, Ting-Wei"

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A curvature-tunable random laser
(2019-02-28)
Lee, Ya-Ju
;
Yeh, Ting-Wei
;
Yang, Zu-Po
;
Yao, Yung-Chi
;
Chang, Chen-Yu
The application of random lasers has been restricted due to the absence of a well-defined resonant cavity, as the lasing action mainly depends on multiple light scattering induced by intrinsic disorders of the laser medium to establish the required optical feedback that hence increases the difficulty in efficiently tuning and modulating random lasing emissions. This study investigated whether the transport mean free path of emitted photons within disordered scatterers composed of ZnO nanowires is tunable by a curvature bending applied to the flexible polyethylene terephthalate (PET) substrate underneath, thereby creating a unique light source that can be operated above and below the lasing threshold for desirable spectral emissions. For the first time, the developed curvature-tunable random laser is implemented for in vivo biological imaging with much lower speckle noise compared to the non-lasing situation through simple mechanical bending, which is of great potential for studying the fast-moving physiological phenomenon such as blood flow patterns in mouse ear skin. It is expected that the experimental demonstration of the curvature-tunable random laser can provide a new route to develop disorder-based optoelectronic devices.
Bending-induced tunable threshold in random laser
(2019-01-01)
Lee, Ya-Ju
;
Yeh, Ting-Wei
;
Yang, Zu-Po
;
Yao, Yung-Chi
;
Chang, Chen-Yu
We investigate the case that the transport mean free path of emitted photons within the disordered scatterers, which is composed by the ZnO nanowires, is tunable by a curvature bending applied on the flexible polyethylene terephthalate substrate underneath, thereby creating a unique light source which is able to be operated above and below the lasing threshold for desirable spectral emissions. (C) 2019 The Author(s)
Flexible random lasers with tunable lasing emissions
(2018-06-14)
Lee, Ya-Ju
;
Chou, Chun-Yang
;
Yang, Zu-Po
;
Thi Bich Hanh Nguyen
;
Yao, Yung-Chi
In this study, we experimentally demonstrated a flexible random laser fabricated on a polyethylene terephthalate (PET) substrate with a high degree of tunability in lasing emissions. Random lasing oscillation arises mainly from the resonance coupling between the emitted photons of gain medium (Rhodamine 6G, R6G) and the localized surface plasmon (LSP) of silver nanoprisms (Ag NPRs), which increases the effective cross-section for multiple light scattering, thus stimulating the lasing emissions. More importantly, it was found that the random lasing wavelength is blue-shifted monolithically with the increase in bending strains exerted on the PET substrate, and a maximum shift of similar to 15 nm was achieved in the lasing wavelength, when a 50% bending strain was exerted on the PET substrate. Such observation is highly repeatable and reversible, and this validates that we can control the lasing wavelength by simply bending the flexible substrate decorated with the Ag NPRs. The scattering spectrum of the Ag NPRs was obtained using a dark-field microscope to understand the mechanism for the dependence of the wavelength shift on the exerted bending strains. As a result, we believe that the experimental demonstration of tunable lasing emissions based on the revealed structure is expected to open up a new application field of random lasers.
Graphene Quantum Dot Vertical Cavity Surface-Emitting Lasers
(2019-11-01)
Lee, Ya-Ju
;
Yeh, Ting-Wei
;
Zou, Chen
;
Yang, Zu-Po
;
Chen, Jia-Wen
Nonzero-bandgap graphene quantum dots (GQDs) are novel optical gain materials promising for solution-processed light sources with high cost efficiency and device performance. Currently, there have only been a few reports on the realization of GQDs-based lasers. Herein, we demonstrate for the first time room-temperature lasing emission with green gamut from GQDs in a vertical optical cavity composed of Ta2O5/SiO2 dielectric distributed Bragg reflectors (DBRs). The lasing is enabled by the unique design of the DBR, which not only provides a wide stopband spectrally overlapping with the emission of the GQDs but also allows high transmittance of optical excitation in the UV-light region. This demonstration is a clear evidence of the use of GQDs as optical gain materials and represents an important step forward toward their potential applications in wide-gamut laser displays and projectors.
In Vivo Speckle Contrast Imaging Constructed by Threshold-tunable Random Lasers
(2019-01-01)
Yeh, Ting-Wei
;
Yang, Zu-Po
;
Yao, Yung-Chi
;
Chang, Chen-Yu
;
Tsai, Meng-Tsan
The application of random lasers has been restricted owing to the absence of well-defined resonant cavity, as the lasing action mainly depends on multiple light scatterings induced by intrinsic disorders of laser medium to establish the required optical feedbacks, and hence that increases the difficulty to efficiently tune and modulate random lasing emissions. In this study, we investigate the case that the transport mean free path of emitted photons within the disordered scatterers, which is composed by the ZnO nanowires, is tunable by a curvature bending applied on the flexible polyethylene terephthalate (PET) substrate underneath, thereby creating a unique light source which is able to be operated above and below the lasing threshold for desirable spectral emissions. The developed curvature-tunable random laser, for the first time, is implemented for in vivo biological imaging with much lower speckle noise when compared to the non-lasing situation through a simple mechanical bending, which is of great potential for studying the fast-moving physiological phenomenon like blood flow patterns in mouse's ear skins. As a result, we expect the experimental demonstration on the curvature-tunable random laser can open up a new route towards developing disorder based optoelectronic devices.
Tunable random lasing emissions by manipulating plasmonic coupling strengths on flexible substrates
(2018-01-01)
Yeh, Ting-Wei
;
Chou, Chun-Yang
;
Yang, Zu-Po
;
Nguyen Thi Bich Hanh
;
Yao, Yung-Chi
A random laser is a unique system in which an assembly of disordered scatters is distributed all over the gain medium to sustain the required optical feedbacks by multiple scatterings for the stimulation of lasing action. Due to the absence of well-defined resonance cavity or rigid alignment of optical elements, it is hence difficult to control the random lasing emissions. In this study, we experimentally demonstrated a flexible random laser fabricated on the polyethylene terephthalate (PET) substrate with a high degree of tunability in lasing emissions. Random lasing wavelength is blue-shifted monolithically with the increasing of bending strains exerted on the PET substrate, and the maximum shift of lasing wavelength of similar to 15 nm was achieved as a 50% bending strain is exerted on the PET substrate. Such observation is highly repeatable and reversible, and it validates that we are able to control the lasing wavelengths by simply bending the flexible substrate. The result herein shows a great advance for the applications of flexible optoelectronic devices, including wearable devices, ultrathin display, and health sensors.