Yu Xuan-Yi

Large-area high-performance SERS substrates with deep controllable sub-10-nm gap structure fabricated by depositing Au film on the cicada wing.

Noble metal nanogap structure supports strong surface-enhanced Raman scattering (SERS) which can be used to detect single molecules. However, the lack of reproducible fabrication techniques with nanometer-level control over the gap size has limited practical applications. In this letter, by depositing the Au film onto the cicada wing, we engineer the ordered array of nanopillar structures on the wing to form large-area high-performance SERS substrates. Through the control of the thickness of the Au film deposited onto the cicada wing, the gap sizes between neighboring nanopillars are fine defined. SERS substrates with sub-10-nm gap sizes are obtained, which have the highest average Raman enhancement factor (EF) larger than 2 × 108, about 40 times as large as that of commercial Klarite® substrates. The cicada wings used as templates are natural and environment-friendly. The depositing method is low cost and high throughput so that our large-area high-performance SERS substrates have great advantage for chemical/biological sensing applications.

Nanocrystal formation and structure in oxyfluoride glass ceramics

The up-conversion luminescent property of the oxyfluoride glass ceramics 30SiO2.15Al2O3. (50–x)PbF2.xCdF2 doped with 4ErF3.1YbF3 has been investigated. Up-conversion luminescent intensity of Er3+ ions increased obviously after heat-treatment due to co-doping with CdF2. The structure model of nanocrystals PbxCd1−xF2 was determined and the effect of CdF2 in oxyfluoride glass ceramics was explained by the analysis of x-ray diffraction data. Different nucleation temperatures of samples with different compositions were obtained by differential thermal analysis curves and the results showed the growth process of different nanocrystals in glass ceramics.

High Power Widely Tunable Narrow Linewidth All-Solid-State Pulsed Titanium-Doped Sapphire Laser

We report a widely tunable, narrow linewidth, pulsed Ti:sapphire laser pumped by an all-solid-state Q-switched intra-cavity frequency-doubled Nd:YAG laser. By using four dense flint glass prisms as intra-cavity dispersive elements, the output wavelength can be continuously tuned over 675–970 nm and the spectral linewidth is shortened to 0.5nm. The maximum output power of 6.65 W at 780nm is obtained under 23.4 W pump power with repetition rate of 5.5kHz; corresponding to an conversion efficiency of 28.4%. Due to the gain-switching characteristics of the Ti:sapphire laser, the output pulse duration is as short as 17.6 ns.

Red Up-Conversion Luminescence Process in Oxyfluoride Glass Ceramics Doped with Er3+/Yb3+

The phonon-assisted quantum cutting (PQC) model is presumed to clarify the red up-conversion luminescence process in Er3+/Yb3+ co-doped glass ceramics by the excitation and emission spectra. The red up-conversion luminescence of Er3+ ions mainly comes from three-photon absorption by the PQC process when the rare earth ions are doped in the glass ceramics and excited by 980 nm pumped-laser. Er3+ ions absorb three-photons and relax to the 4G11/2 state and then emit red up-conversion luminescence by the PQC process. The factor coefficient for the relation of pump-laser power and up-conversion intensity (P-I) is found by the analysis of excitation spectra of the red luminescence, which plays a major role to understand the true red up-conversion luminescence process. The new P-I relation is explained by the model of PQC.

High efficiency continuous-wave tunable signal output of an intracavity singly resonant optical parametric oscillator based on periodically poled lithium niobate

In this paper we report on a continuous-wave (CW) intracavity singly resonant optical parametric oscillator (ICSRO) based on periodically poled LiNbO3 (PPLN) pumped by a diode-end-pumped CW Nd:YVO4 laser. Considering the thermal lens effects and diffraction loss, an optical ballast lens and a near-concentric cavity are adopted for better operation. Through varying the grating period and the temperature, the tunable signal output from 1406 nm to 1513 nm is obtained. At a PPLN grating period of 29 μm and a temperature of 413 K, a maximum signal output power of 820 mW at 1500 nm is achieved when the 808 nm pump power is 10.9 W, leading to an optical-to-optical conversion efficiency of 7.51%.

All-Solid-State Nd:YAG Laser Operating at 1064 nm and 1319 nm under 885 nm Thermally Boosted Pumping

We report a high-efficiency Nd:YAG laser operating at 1064 nm and 1319 nm, respectively, thermally boosted pumped by an all-solid-state Q-switched Ti:sapphire laser at 885 nm. The maximum outputs of 825.4 mW and 459.4 mW, at 1064 nm and 1319 nm respectively, are obtained in a 8-mm-thick 1.1 at. % Nd:YAG crystal with 2.1 W of incident pump power at 885 nm, leading to a high slope efficiency with respect to the absorbed pump power of 68.5% and 42.0%. Comparative results obtained by the traditional pumping at 808 nm are presented, showing that the slope efficiency and the threshold with respect to the absorbed pump power at 1064 nm under the 885 nm pumping are 12.2% higher and 7.3% lower than those of 808 nm pumping. At 1319 nm, the slope efficiency and the threshold with respect to the absorbed pump power under 885 nm pumping are 9.9% higher and 3.5% lower than those of 808 nm pumping. The heat generation operating at 1064 nm and 1319 nm is reduced by 19.8% and 11.1%, respectively.

Performance of gain-switched all-solid-state quasi-continuous-wave tunable Ti:sapphire laser system

We have made a gain-switched all-solid-state quasi-continuous-wave (QCW) tunable Ti:sapphire laser system, which is pumped by a 532 nm intracavity frequency-doubled Nd:YAG laser. Based on the theory of gain-switching and the study on the influencing factors of the output pulse width, an effective method for obtaining high power and narrow pulse width output is proposed. Through deliberately designing the pump source and the resonator of the Ti:sapphire laser, when the repetition rate is 6 kHz and the length of the cavity is 220 mm, at an incident pump power of 22 W, the tunable Ti:sapphire laser from 700 to 950 nm can be achieved. It has a maximum average output power of 5.6 W at 800 nm and the pulse width of 13.2 ns, giving an optical conversion efficiency of 25.5% from the 532 nm pump laser to the Ti:sapphire laser.

An All-Solid-State Tunable Dual-Wavelength Ti:Sapphire Laser with Quasi-Continuous-Wave Outputs

A high power dual-wavelength Ti:sapphire laser system with wide turning range and high efficiency is described, which consists of two prism-dispersed resonators pumped by an all-solid-state frequency-doubled Nd:YAG laser. Tunable dual-wavelength outputs, with one wavelength range from 750 nm to 795 nm and the other from 800 nm to 850 nm, have been demonstrated. With a pump power of 23 W at 532 nm, a repetition rate of 6.5 kHz and a pulse width of 67.6 ns, the maximum dual-wavelength output power of 5.6 W at 785.3 nm and 812.1 nm, with a pulse width of 17.2 ns and a line width of 2 nm, has been achieved, leading to an optical-to-optical conversion efficiency of 24.4%.

Pump-tuning KTP optical parametric oscillator with continuous output wavelength pumped by a pulsed tunable Ti:sapphire laser

We report on the implementation of a KTP optical parametric oscillator pumped by a pulsed tunable Ti:sapphire laser. Two major improvements were achieved, including the connection of the signal and idler tuning ranges and the high-output conversion efficiency through the signal and idler tuning ranges. Both in the signal and idler, the continuous output wavelength from 1.261 to 2.532µm was obtained by varying the pump wavelength from 0.7 to 0.98µm. The maximum output pulse energy was 27.2mJ and the maximum conversion efficiency was 35.7% at 1.311µm (signal).