Browsing by Author "Chen, Yao-Hui"

Now showing 1 - 3 of 3

Coherent acoustic phonon oscillation accompanied with backward acoustic pulse below exciton resonance in a ZnO epifilm on oxide-buffered Si(111)
(2016-08-17)
Lin, Ja-Hon
;
Shen, Yu-Kai
;
Liu, Wei-Rein
;
Lu, Chia-Hui
;
Chen, Yao-Hui
Unlike coherent acoustic phonons (CAPs) generated from heat induced thermal stress by the coated Au film, we demonstrated the oscillation from c-ZnO epitaxial film on oxide buffered Si through a degenerate pump-probe technique. As the excited photon energy was set below the exciton resonance, the electronic stress that resulted from defect resonance was used to induce acoustic wave. The damped oscillation revealed a superposition of a high frequency and long decay CAP signal with a backward propagating acoustic pulse which was generated by the absorption of the penetrated pump beam at the Si surface and selected by the ZnO layer as the acoustic resonator.
Investigation of random lasing characteristics from dye-doped twisted nematic liquid crystals in wedge cell
(2016)
Lin, Sheng Hung
;
Chen, Po-Yen
;
Wu, Jin-Jei
;
Chen, Yao-Hui
;
Tsay, Shwu-Yun
The output polarization and slope efficiency of random laser could be controlled by the rubbing direction of PI and temperature, respectively, from dye-doped twisted nematic liquid crystals within wedge cell.
Room temperature excitonic dynamics of non-polar a-plane ZnO epifilms
(2016-09)
Lin, Ja-Hon
;
Liu, Wei-Rein
;
Lin, Yi-Chin
;
Su, Hsing-Jung
;
Chen, Hou-Ren
Pump polarization dependent carrier dynamics, particularly excitonic dynamics, of non-polar a-plane zinc oxide (ZnO) epifilms with two different thicknesses were investigated using time resolved measurements. Unlike the electron and hole dynamics through the above-bandgap excitation, transient differential reflectance (TDR) traces revealed similar trends under two orthogonal pump polarization conditions relative to the c-axis (E-pu +/- c and E-pu vertical bar vertical bar c) of a-ZnO around near-exciton-resonance excitation. By means of a band diagram, the bandgap renormalization (BGR) effect can be reasonably explained by the screening of the Coulomb potential energy due to the accumulation of relaxed free carriers that were initially excited through the absorption of two cascaded pump photons via the excitonic level, a process known as two photon absorption (TPA). Thus, the modulation depths of the TPA around zero time delay, due to simultaneous absorption of one pump and one probe photon via the excitonic level, increased linearly with the pump fluence, proportional to the modulation depth resulting from the BGR effects. (C) 2016 Author(s).