Xuechun Lin

Oxygen-Assisted Chemical Vapor Deposition Growth of Large Single-Crystal and High-Quality Monolayer MoS2

Monolayer molybdenum disulfide (MoS2) has attracted great interest due to its potential applications in electronics and optoelectronics. Ideally, single-crystal growth over a large area is necessary to preserve its intrinsic figure of merit but is very challenging to achieve. Here, we report an oxygen-assisted chemical vapor deposition method for growth of single-crystal monolayer MoS2. We found that the growth of MoS2 domains can be greatly improved by introducing a small amount of oxygen into the growth environment. Triangular monolayer MoS2 domains can be achieved with sizes up to ∼350 μm and a room-temperature mobility up to ∼90 cm(2)/(V·s) on SiO2. The role of oxygen is not only to effectively prevent the poisoning of precursors but also to eliminate defects during the growth. Our work provides an advanced method for high-quality single-crystal monolayer MoS2 growth.

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.

High-power cw 671 nm output by intracavity frequency doubling of a double-end-pumped Nd:YVO4 laser.

We report on a high-power (cw) red laser at 671 nm by intracavity frequency doubling of a double-end-pumped 1342 nm Nd:YVO4 laser based on the nonlinear crystal LiB3O5. A red output power of 3.38 W is obtained for a pump power of 27 W, with corresponding optical-to-optical efficiency of 12.5%. The 671 nm beam is nearly diffraction limited.

Generation of 4.3-W coherent blue light by frequency-tripling of a side-pumped Nd:YAG laser in LBO crystals.

High average power nanosecond pulsed light is obtained using a compact all solid state Nd:YAG laser. The laser is operated in Q-switched mode at the 1.3 micron fundamental and internally frequency tripled using two LiB3O5 (LBO) crystals. 4.3 W average power at 440 nm was demonstrated at 3.5 kHz and a pulse width of 150+/-10 ns (FWHM). The beam quality of M2 value is 5+/-1 in both dimensions. The short-term average power stability of the light source is better than 5.6%. Spectral selecting is proposed to increase production efficiency at 440 nm.

Multi-walled carbon nanotube as a saturable absorber for a passively mode-locked Nd:YVO4 laser

Within the family of carbon nanotubes, multi-walled carbon nanotube material has the advantages of low-cost and high laser damage threshold. Therefore, in principle, it is more suitable for high power laser applications. In this letter, a high power continuous wave mode-locking Nd:YVO4 laser using a multi-walled carbon nanotube absorber has been successfully demonstrated. An average output power as high as 1.4 W has been achieved with a slope efficiency of 24%. The repetition rate and pulse width of the mode-locked laser were 68 MHz and 15.5 ps, respectively. The calculated pulse energy and peak power were 20.6 nJ and 1.33 kW, respectively.

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.

20 W High-Power Picosecond Single-Walled Carbon Nanotube Based MOPA Laser System

Compact, high average output power with picosecond pulses laser was achieved through a carbon nanotube based master oscillator power amplifier, MOPA, configuration. The master oscillator was a single-walled carbon nanotube based passively mode-locked Nd:YVO4 laser. Then the ultrashort laser pulses from the master oscillator were amplified by a diode laser pumped ytterbium-doped fiber amplifier. The maximum average output power measured has been successfully achieved to be 20 W with a repetition rate of 82 MHz, and a pulse width of 15.7 ps. The pulse energy and peak power of the output laser were 244 nJ and 15.5 kW, respectively. The amplified spontaneous emission and stimulated Raman scattering were not observed.

Large area growth of monolayer MoS2 film on quartz and its use as a saturable absorber in laser mode-locking

Monolayer MoS2 film on quartz was fabricated by a home-made three-temperature zone chemical vapor deposition method. The photo, AFM image, Raman spectroscopy and HRTEM image showed that high quality as-grown MoS2 film completely covered the whole quartz substrate of a few cm2. A Nd:YVO4 laser with mode-locking operation was obtained by using the monolayer MoS2 on quartz as the saturable absorber (SA). To the best of our knowledge, this is the first report on large-area growth of high quality monolayer MoS2 film on transparent quartz substrate, and the first time that the CVD MoS2 SA was used in mode-locked solid state lasers. Because of the large area, high transmission, low non-saturable loss and high optical damage threshold of this material, it is very suitable for application in mode-locked solid state lasers.

High-power picosecond 355 nm laser based on La2CaB10O19 crystal

Third harmonic generation experiments were performed on a type-I phase-matching La2CaB10O19 crystal cut at θ=49.4° and φ=0.0° with dimensions of 4.0  mm×4.0  mm×17.6  mm. A 1064 nm laser with a maximum average power of 35.2 W was employed as the fundamental light source, which has a pulse width of 10 picoseconds and a pulse repetition rate of 80 MHz. A type-I noncritical phase-matching LBO crystal was used to generate 532 nm lasers. By investigating a series of focusing lens combinations, a picosecond 355 nm laser of 5.3 W was obtained, which is the highest power of picosecond 355 nm laser based on a La2CaB10O19 crystal so far. The total conversion efficiency from 1064 to 355 nm was up to 15.1%.