Haijuan Yu

Correlations between elastic moduli and molar volume in metallic glasses

We report clear correlations between bulk modulus (K) and average molar volume Vm, and between Poisson’s ratio ν and Vm for various bulk metallic glasses. The origin for the correlations between elastic moduli and Vm are discussed. The established correlation, associated with Poisson’s ratio ν, and since the ν correlates with plasticity of metallic glasses, indicates that the average molar volume is important factor to be considered for plastic metallic glasses searching. The found correlations also suggest a close relation between the mechanical properties and the short-range atomic bonding, and assist in understanding deformation behavior in metallic glasses.

High-harmonic and single attosecond pulse generation using plasmonic field enhancement in ordered arrays of gold nanoparticles with chirped laser pulses

Coherent XUV sources, which may operate at MHz repetition rate, could find applications in high-precision spectroscopy and for spatio-time-resolved measurements of collective electron dynamics on nanostructured surfaces. We theoretically investigate utilizing the enhanced plasmonic fields in an ordered array of gold nanoparticles for the generation of high-harmonic, extreme-ultraviolet (XUV) radiation. By optimization of the chirp of ultrashort laser pulses incident on the array, our simulations indicate a potential route towards the temporal shaping of the plasmonic near-field and, in turn, the generation of single attosecond pulses. The inherent effects of inhomogeneity of the local fields on the high-harmonic generation are analyzed and discussed. While taking the inhomogeneity into account does not affect the optimal chirp for the generation of a single attosecond pulse, the cut-off energy of the high-harmonic spectrum is enhanced by about a factor of two.

Enhancing plasticity of Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass by precompression

Precompression treatments on Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass rods with tapered ends induced controllable stress distributions and resulted in residual stress accompanied with a few tiny shear bands after unloading. The built-in stress state increased macroscopic plasticity dramatically and produced predictable distributions of shear bands in the cylindrical samples cut from the taper-ended samples. The macroscopic plasticity was interpreted in terms of the competition among different types of shear bands.

Thulium-based bulk metallic glass

We report the formation and properties of a thulium-based bulk metallic glass (BMG). Compared with other known rare-earth (RE) based BMGs, Tm-based BMGs show features of excellent glass formation ability, considerable higher elastic modulus, smaller Poisson’s ratio, high mechanical strength, and intrinsic brittleness. The reasons for the different properties between the Tm-based and other RE-based BMGs are discussed. It is expected that the Tm-based glasses with the unique properties are appropriate candidates for studying some important issues in BMGs.

A 7.81 W 355 nm ultraviolet picosecond laser using La2CaB10O19 as a nonlinear optical crystal

We demonstrate high-power 355 nm ultraviolet (UV) picosecond (ps) laser using a type I phase-matching nonlinear optical crystal of La(2)CaB(10)O(19) (LCB), which possesses the characteristic of non-hygroscopicity. The high-power third harmonic generation was successfully achieved from two types of 1064 nm ps fundamental lasers. The maximum output power of 7.81 W of 355 nm UV laser was obtained with a pump of 35.2 W 1064 nm ps laser (80 MHz repetition rate, 10 ps pulse width) with optical conversion efficiency of 22.2%. The experimental results show that the LCB crystal is a promising candidate for generating high-power UV laser.

85-W Burst-Mode Pluse Fiber Amplifier Based on a Q-Switched Mode-Locked Laser With Output Energy 0.5 mJ per Burst

We report a compact 85-W burst-mode pulse fiber amplifier seeded by a Q-switched mode-locked laser at 1064 nm. At a repetition rate of 154 kHz, the pulse duration of the burst is 4 μs containing 280 of 20-ps pulses with temporal space of ~14 ns, and the total burst energy is about 552 μJ per pulse. The pulse number and the burst repetition frequency can be adjusted from 121 to 154 kHz through increasing the pump power of the seed laser. To the best of our knowledge, this is the first time to observe this type burst pulse amplifier based on the Q-switched mode-locked seed laser. No significant amplified spontaneous emission and stimulated Raman scattering were observed in our experiment when the output power is less than 85 W.

Passive Q-switching in a diode-side-pumped Nd:YAG laser at 1.319 μm

Abstract. We demonstrated a passively Q-switched Nd:YAG laser operating at 1.319 μm using a transmission-type single-wall carbon nanotube (SWCNT) as the saturable absorber. This is the first report on using SWCNT as a Q-switcher for 1.319 μm Nd:YAG laser in a side-pumped configuration. A maximum output power of 780 mW was obtained with 1.15-μs pulse duration and 42.7-kHz repetition rate.

The generation of MHz isolated XUV attosecond pulses by plasmonic enhancement in a tailored symmetric Ag cross nanoantenna with a few-cycle laser

Within a few-cycle laser, the generation of MHz isolated extreme ultraviolet (XUV) attosecond pulses via nanoplasmonic field enhancement in silver nanostructures is theoretically investigated. Numerical techniques are employed to optimize nanoantennas and attain plasmonic field enhancement factors up to 270. In a volume of 15 × 15 × 30 nm−3 in the nanoantenna, the intensity could be enhanced to 1014 W cm−2 for high harmonic generation (HHG). Optimal conditions for the production of MHz isolated attosecond pulses of 140 attosecond duration via HHG have been identified. These findings open up the possibility for the development of a compact source of ultrashort XUV pulses with MHz repetition rates. Moreover, asymmetric cross HHG is proposed to control the polarizations, select the wavelengths by varying the ratio of silver nanoantennas and generate XUV pulses in both polarized directions.

High-power ultrafast solid-state laser using graphene based saturable absorber

We demonstrate a graphene based saturable absorber mode-locked Nd:YVO4 solid-state laser, generating ~14nJ pulses with ~1W average output power. This shows the potential for high-power pulse generation.

A 1319 nm diode-side-pumped Nd YAG laser Q-switched with graphene oxide

We have demonstrated a diode-side-pumped Q-switched Nd:YAG laser operating at 1319 nm with a saturable absorber of graphene oxide fabricated by the vertical evaporation method. The 1319 nm Q-switched laser pulses were realized with average output power of 820 mW, pulse width of 2 μs and repetition rate of 35 kHz. The pulse energy and peak power were 23.4 μJ and 11.7 W, respectively when the optical pump power was 232 W. The experimental results indicate that graphene oxide is an effective saturable absorber for Q-switched lasers.