Ying-Ying Yang

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.

Promotion of crystallization and magnetic property improvement enhancement of the energy product in Nd5.5Fe66B18.5Cr5Co5 by magnetic field heat treatment

An externally applied magnetic field during heat treatment of a melt spun Nd5.5Fe66B18.5Cr5Co5 alloy can promote its crystallization from amorphous state and induce a grain refinement. The stronger the applied magnetic field, the lower the crystallization temperature. Holding the annealing time for 5 min, the crystallization occurs at 680 degrees C in conventional heat treatment, however, it happens at 650 degrees C when annealed with a 0.15 T field strength and 630 degrees C with a 0.25 T field strength. The maximum energy product for Nd-5.5 Fe66B18.5Cr5Co5 powder under optimum heat treatment with an applied magnetic field can increase about 17% because of the enhancement of exchange coupling role between the soft and hard phase due to the full crystallization and the grain size reduction

Designing and optimizing highly efficient grating for high-brightness laser based on spectral beam combining

A highly efficient nano-periodical grating is theoretically investigated for spectral beam combining (SBC) and is experimentally implemented for attaining high-brightness laser from a diode laser array. The rigorous coupled-wave analysis with the S matrix method is employed to optimize the parameters of the grating. According the optimized parameters, the grating is fabricated and plays a key role in SBC cavity. The diffraction efficiency of this grating is optimized to 95% for the output laser which is emitted from the diode laser array. The beam parameter product of 3.8 mm mrad of the diode laser array after SBC is achieved at the output power of 46.3 W. The optical-to-optical efficiency of SBC cavity is measured to be 93.5% at the maximum operating current in the experiment.

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.

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.

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.

Design and theoretical investigation of nanograting for XUV outcoupler

We have theoretically investigated and optimized a nano-periodical highly-efficient blazed grating, which is used as an outcoupler for extreme-ultraviolet (XUV) radiation. The rigorous coupled-wave analysis (RCWA) with S matrix method is employed to optimize the parameters of the grating. The grating is designed to be etched on top layers of IR reflector, performs as a highly-reflective mirror for IR light and highly-efficient outcoulper for XUV. The diffraction efficiency of -1 order of this XUV outcoupler is greater than 20% in the range near 60 nm, which allows high resolution spectroscopy of the 1s-2s transition in He+ at around 60 nm with extreme precision. The theoretical calculations are verified by the experimental results.

High-output-power third-harmonic generation at 355 nm based on La2CaB10O19 (LCB) crystal in yz plane

Third-harmonic generation (THG) with high output power based on the type-I phase-matching La2CaB10O19 (LCB) crystal was investigated in yz plane (θ=48.7°, φ=90°), in which direction the effective nonlinear coefficient (deff) of LCB is 0.7, much larger than the previous reports in other direction. The maximum output power we obtained at 355 nm was as high as 11.5 W, and the beam quality was measured to 1.47 in x direction and 2.56 in y direction. The angular bandwidth and temperature bandwidth in this direction were measured, which are larger than the previous reports also.

MHz isolated XUV attosecond pulses generation using plasmonic enhancement in asymmetric metallic nanoantenna

We theoretically investigate utilizing the enhanced plasmonic fields in metallic nanostructures. Numerical techniques are employed to optimize nanoantennas to attain the enhanced plasmonic fields up to 270. In the volume of 15 × 15 × 30 nm3 in nanoantenna, the intensity could be enhanced to 1014 W/cm2 for high harmonic generation (HHG). Optimal conditions for the production of MHz isolated attosecond pulse of 140 attosecond 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. our simulations indicate a potential route towards the temporal shaping of the plasmonic near-field and in turn the generation of single attosecond pulses. Such 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. Moreover, the asymmetric cross nanoantennas is proposed to control the polarizations and select the wavelengths via varying the ratio of nanoantennas and generate the XUV pulse in both polarized direction.