Chih-Ya Tsai

High-power, passively mode-locked Nd:GdVO 4 laser using single-walled carbon nanotubes as saturable absorber

The single-walled carbon nanotubes (SWCNTs) have been widely investigated for making SWCNTs a promising saturable absorber for mode-locking a laser. The SWCNT-SAs have been used for mode-locking lasers operated near 1.0 and 1.5 µm. Until recently, the SWCNT-SAs have been widely used to passively mode-lock the diode-pumped solid-state lasers [1,2]. However, the output power of these lasers is still very low (less than 500 mW) due to the low heat resistance of the polymer material in the SWCNT/polymer composite film. In this paper, the SWCNT-SA film is fabricated without the polymer material by using a vertical evaporation technique [3], and then used in the passive mode-locking of Nd:GdVO4 laser at 1-µm. We obtain the highest output power to our knowledge with the new prepared SWCNT-SA film.

Passive mode locking of ytterbium- and erbium-doped all-fiber lasers using graphene oxide saturable absorbers.

Broadband graphene oxide/PVA films were used as saturable absorbers (SAs) for mode locking erbium-doped fiber laser (EDFL) and ytterbium-doped fiber laser (YDFL) at 1.06 μm and 1.55 μm. They provide modulation depths of 3.15% and 6.2% for EDFL and YDFL, respectively. Stable self-starting mode-locked pulses are obtained for both lasers, confirming that the graphene oxide is cost-effective. We have generated mode-locked pulses with spectral width, repetition rate, and pulse duration of 0.75 nm, 9.5 MHz, and 2.7 ps. This is the shortest pulse duration directly obtained from an all-normal-dispersion YDFL with graphene-oxide saturable absorber.

Complex oxide-noble metal conjugated nanoparticles.

Hybrid nanoparticles (NPs) composed of multiple components offer new opportunities for next-generation materials. In this study, a paradigm for the noble metal/ternary complex oxide hybrid NPs is reported by adopting pulsed laser ablation in liquids. As model hybrids, gold-spinel heterodimer (Au-CoFe2O4) and gold-pervoskite heterodimer (Au-SrTiO3) NPs are investigated. This work has demonstrated the diverse playgroup of NP conjugation enlarged by complex oxides.

High-quality and Large-size Topological Insulator Bi2Te3-Gold Saturable Absorber Mirror for Mode-Locking Fiber Laser.

A novel high-quality, large-size, reflection-type topological insulator Bi2Te3-Gold (BG) film-based nonlinear optical modulator has been successfully fabricated as a two-dimensional saturable absorber mirror (SAM) by pulsed laser deposition (PLD). This BG-SAM possesses saturation fluence of 108.3 μJ/cm2, modulation depth (ΔR) of 6.5%, non-saturable loss of 38.4%, high damage threshold above 1.354 mJ/cm2 and excellent uniformity providing for the generation of passive mode-locked (ML) pulses for erbium-doped fiber lasers (EDFLs) on a large sample area. Under 124 mW 976 nm pumping, We obtained 452-fs continuous-wave ML pulses with pulse energy of 91 pJ and full width at half-maximum (FWHM) of 6.72-nm from this EDFL. The results clearly evidence that the PLD is an efficient method for fabricating BG-SAM that is suitable for a compact ultrafast ML fiber laser system.

High-power passively continuous-wave and Q-switching mode-locked Nd:LuVO 4 laser by few-layer graphene-oxide films

Using a series of different concentration polymer-free graphene oxide (GO) films as saturable absorbers (SAs), we demonstrate high-power passively continuous-wave mode-locking (CW-ML) and Q-switching mode-locking (QS-ML) for a Nd:LuVO4 laser at 1 μm. CW-ML pulses of 6.62 ps with maximum output power of 3.89 W have been achieved to give the highest pulse peak power of 4.85 kW and pulse energy of 32.14 nJ under 15-W pumping by using SAs of 84.4% transmittance. Using SAs with a lower transmittance having a larger modulation depth of 75.9% and 63.4%, we obtain both the CW-ML pulses of 4.85-ps and QS-ML pulses with 2.73 W and 1.92 W output powers, respectively.

Vibrational dynamics at C and Ge interfaces

Abstract In this report, we present the experimental results of vibrational energy relaxation and dephasing dynamics at hydrogenated/deuterated diamond and germanium surfaces. Both infrared absorption and Raman spectroscopy have been exploited in this experimental study. A full group-theoretical analysis based on site-symmetry induced representation is employed to reveal the symmetry properties of the surface vibrations and to deduce the selection rules for vibrational dynamics. The low-frequency surface vibrational modes, which are responsible for surface vibrational dynamics, are identified according to their induced representations. General guidelines for the vibrational dynamics at strongly chemisorbed systems are presented and discussed.

Stable and self-starting passively mode-locked fiber laser for 1.06 μm and 1.55 μm by using graphene oxide saturable absorber

Graphene oxide/PVA film is used as saturable absorber for mode locking erbium-doped fiber laser and ytterbium-doped fiber laser. It provides modulation depths of 2.6% and 6% at 1.06 μm and 1.55 μm, respectively. Stable mode-locked pulses are obtained for both lasers confirming that graphene oxide is cost-effective for 1.06-μm and 1.55-μm pulse generations.