Browsing by Author "Chen, H. R."

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Anisotropic strain, magnetic properties, and lattice dynamics in self-assembled multiferroic CoFe2O4-PbTiO3 nanostructures
(2014-04-07)
Tsai, C. Y.
;
Chen, H. R.
;
Chang, F. C.
;
Kuo, H. H.
;
Cheng, H. M.
We investigate the anisotropic stress dependent magnetic and phonon behaviors in self-assembled CoFe2O4-PbTiO3 (CFO-PTO) nanostructures deposited on SrRuO3 buffered SrTiO3 substrates of various thickness. The increased vertical compressed stress with increasing thickness enhances the vertical magnetic anisotropy of CFO while gradually reducing the vertical polarization of PTO. By applying the magnetic-field dependent Raman scattering, the CFO-A(1g) and T-2g(1) phonon frequencies shift oppositely because of the magnetostriction. Moreover, the PTO-A(1) mode intensities anomalously enhance and the A(1) and E mode frequencies, respectively, increase and decrease, which prove the existence of the stress-mediated magnetoelectric (ME) effect. This study shows that the ME transmission process is dominated by interfacial stress, which is critical for enhancing the ME efficiency. (C) 2014 AIP Publishing LLC.
Fabrication of aligned single wall carbon nanotube absorbers for high power passive mode-locked Nd:GdVO(4) laser
(2012-01-01)
Cheng, S. Y.
;
Wang, Y. G.
;
Yu, P.
;
Cheng, Y. J.
;
Tang, J.
Using the vertical evaporation technique we fabricated saturable absorbers by transferring the water-soluble single wall carbon nanotubes (SWCNT) onto a hydrophilic quartz substrate. The fast recovery times of the absorber were measured to be 136 and 790 fs. The modulation depth of the absorber was about 2%. Passive mode-locked Nd:GdVO(4) laser using such an absorber was demonstrated. The continuous wave mode-locked pulses with the pulse duration of 12.4 ps and the repetition of 120 MHz were achieved. The maximum average output power of the mode-locked laser is 2.4 W at the pump power of 13 W. Such kind of absorber has potential to be put into practical use for high power solid-state laser mode locking.
Fabrication of aligned single wall carbon nanotube absorbers for high power passive mode-locked Nd:GdVO4 laser
(2012-01-01)
Cheng, S. Y.
;
Wang, Y. G.
;
Yu, P.
;
Cheng, Y. J.
;
Tang, J.
Using the vertical evaporation technique we fabricated saturable absorbers by transferring the water-soluble single wall carbon nanotubes (SWCNT) onto a hydrophilic quartz substrate. The fast recovery times of the absorber were measured to be 136 and 790 fs. The modulation depth of the absorber was about 2%. Passive mode-locked Nd:GdVO4 laser using such an absorber was demonstrated. The continuous wave mode-locked pulses with the pulse duration of 12.4 ps and the repetition of 120 MHz were achieved. The maximum average output power of the mode-locked laser is 2.4 W at the pump power of 13 W. Such kind of absorber has potential to be put into practical use for high power solid-state laser mode locking.
Optical properties of one- and two-dimensional excitons in m-plane ZnO/MgZnO multiple quantum wells
(2016-03-09)
Chen, H. R.
;
Tsai, C. Y.
;
Huang, Y. C.
;
Kuo, C. C.
;
Hsu, H. C.
Five pairs of ZnO/Zn0.9Mg0.1O multiple quantum wells (MQWs) with fixed barrier thickness of 55 nm and three well widths of 4, 8 and 16 nm have been grown on m-plane sapphires by pulsed laser deposition. Due to 2D quantum confinement with decreasing well width, the emission of excitons bound to the basal-plane stacking faults, which are one-dimensionally confined in MQWs, encounters larger blue shift than that of the near-band edge excitons. Furthermore, remarkably reducing coupling of free excitons with A1 longitudinal optical phonons is closely correlated with increasing exciton binding energy but enhanced coupling of E-2-low phonons is a result of increasing interaction with the interface phonons with decreasing well width.
Passive mode-locking in diode-pumped c-cut Nd:LuVO(4) laser with a semiconductor saturable-absorber mirror
(2009-07-01)
Chen, H. R.
;
Lin, J. H.
;
Song, K. T.
;
Lin, K. H.
;
Hsieh, W. F.
We demonstrated a diode-pumped passively mode-locked c-cut Nd:LuVO(4) picosecond laser with a semiconductor saturable-absorber mirror (SESAM) at a wavelength of 1067.8 nm. Due to the wide bandwidth of 0.48 nm, stable mode-locking has been generated with a duration as short as 3.7 ps, which is shorter than for the a-cut Nd:LuVO(4) laser. A maximum output power of 1.67 W was achieved to give a highest peak power of 3.47 KW at 18 W absorbed pump power.
Passive mode-locking in diode-pumped c-cut Nd:LuVO4 laser with a semiconductor saturable-absorber mirror
(2009-07-01)
Chen, H. R.
;
Lin, J. H.
;
Song, K. T.
;
Lin, K. H.
;
Hsieh, W. F.
We demonstrated a diode-pumped passively mode-locked c-cut Nd:LuVO4 picosecond laser with a semiconductor saturable-absorber mirror (SESAM) at a wavelength of 1067.8 nm. Due to the wide bandwidth of 0.48 nm, stable mode-locking has been generated with a duration as short as 3.7 ps, which is shorter than for the a-cut Nd:LuVO4 laser. A maximum output power of 1.67 W was achieved to give a highest peak power of 3.47 KW at 18 W absorbed pump power.
Spin and phonon anomalies in epitaxial self-assembled CoFe2O4-BaTiO3 multiferroic nanostructures
(2014-06-23)
Tsai, C. Y.
;
Cheng, H. M.
;
Chen, H. R.
;
Huang, K. F.
;
Tsai, L. N.
Temperature dependent magnetic and phonon anomalies in epitaxial self-assembled CoFe2O4 (CFO) rods embedded in BaTiO3 (BTO) matrix nanostructures were investigated. The temperature dependence of A(1)(2TO) phonon frequency of BTO indicates that the BTO matrix experiences structural transformations. The lattice strain produced during the structural transformations drives spin reorientation in CFO rods, resulting in anomalous changes of magnetization. Through correlating the phonon anomalies with the increase of in-plane spin ordering, we show the spin-phonon coupling induces the softening of A(1g) and A(1)(2TO) phonons. It suggests that spin strongly couples with lattice strain and phonons in this nanostructure. (C) 2014 AIP Publishing LLC.
Spin and phonon anomalies in epitaxial self-assembled CoFe2O4-BaTiO3 multiferroic nanostructures
(2014-06-23)
Tsai, C. Y.
;
Cheng, H. M.
;
Chen, H. R.
;
Huang, K. F.
;
Tsai, L. N.
Temperature dependent magnetic and phonon anomalies in epitaxial self-assembled CoFe2O4 (CFO) rods embedded in BaTiO3 (BTO) matrix nanostructures were investigated. The temperature dependence of A(1)(2TO) phonon frequency of BTO indicates that the BTO matrix experiences structural transformations. The lattice strain produced during the structural transformations drives spin reorientation in CFO rods, resulting in anomalous changes of magnetization. Through correlating the phonon anomalies with the increase of in-plane spin ordering, we show the spin-phonon coupling induces the softening of A(1g) and A(1)(2TO) phonons. It suggests that spin strongly couples with lattice strain and phonons in this nanostructure. (C) 2014 AIP Publishing LLC.
Stress-mediated magnetic anisotropy and magnetoelastic coupling in epitaxial multiferroic PbTiO3-CoFe2O4 nanostructures
(2013-04-01)
Tsai, C. Y.
;
Chen, H. R.
;
Chang, F. C.
;
Tsai, W. C.
;
Cheng, H. M.
This study reports a self-assembled multiferroic nanostructure, composed of PbTiO3 (PTO) pillars embedded in a CoFe2O4 (CFO) matrix, deposited on MgO(001) by pulsed laser deposition. The epitaxial relationship in the PTO-CFO nanostructure is (100) [101](PTO) parallel to (001) [101](CFO) parallel to (001) [101](MgO), confirming the in-plane aligned polarization of PTO. The perpendicular magnetic anisotropy of this thin film results from the magnetoelastic anisotropy that exceeds the shape anisotropy. The increased frequency and the enhanced intensity of the tetrahedral (T-) site phonon modes by increasing the magnetic field indicate strong magnetoelastic coupling through magnetostriction in this multiferroic nanostructure. The anisotropic Raman strength enhancement of the T-site phonon along different directions suggests the magnetoelastic coupling is most efficient in the in-plane direction. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4800069]