Shuxian Wang

Broadband Few‐Layer MoS2 Saturable Absorbers

The bandgaps of monolayer and bulk molybdenum sulfide (MoS2 ) result in that they are far from suitable for application as a saturable absorption device. In this paper, the operation of a broadband MoS2 saturable absorber is demonstrated by the introduction of suitable defects. It is believed that the results provide some inspiration in the investigation of two-dimensional optoelectronic materials.

Comparison of nitrogen compositions in the as-grown GaNxAs1−x on GaAs measured by high-resolution x-ray diffraction and secondary-ion mass spectroscopy

High-resolution x-ray diffraction (HRXRD) and secondary-ion mass spectroscopy were used to measure the N compositions of a series of as-grown GaNAs samples grown by solid-source molecular-beam epitaxy. We found that N compositions measured by the two methods agree well at lower N compositions (x 3%). The HRXRD measurement by using Vegard’s law to extract the lattice constant of GaNAs, underestimates N composition at larger N compositions. We found that the underestimation is up to 14.3% at the x=4.2%. In order to explain the deviation, a model for analyzing the correlation between lattice parameters and point defects in the epilayer was carried out.

Passively Q-switched nanosecond erbium-doped fiber laser with MoS 2 saturable absorber

Passively Q-switched nanosecond pulsed erbium-doped fiber laser based on MoS(2) saturable absorber (SA) is experimentally demonstrated. The high quality MoS(2) SA deposited on the broadband high-reflectivity mirror with a large modulation depth of 9% was prepared by pulsed laser deposition method. By inserting the MoS(2) SA into an erbium-doped fiber laser, stable Q-switched operation can be achieved with the shortest pulse width of 660 ns, the maximum pulse energy up to 152 nJ and pulse repetition rates varying from 116 to 131 kHz. The experimental results further verify that MoS(2) possesses the potential advantage for stable Q-switched pulse generation at 1.5 μm.

Ultrabroadband MoS2 Photodetector with Spectral Response from 445 to 2717 nm

Photodetectors with excellent detecting properties over a broad spectral range have advantages for the application in many optoelectronic devices. Introducing imperfections to the atomic lattices in semiconductors is a significant way for tuning the bandgap and achieving broadband response, but the imperfection may renovate their intrinsic properties far from the desire. Here, by controlling the deviation from the perfection of the atomic lattice, ultrabroadband multilayer MoS2 photodetectors are originally designed and realized with the detection range over 2000 nm from 445 nm (blue) to 2717 nm (mid-infrared). Associated with the narrow but nonzero bandgap and large photoresponsivity, the optimized deviation from the perfection of MoS2 samples is theoretically found and experimentally achieved aiming at the ultrabroadband photoresponse. By the photodetection characterization, the responsivity and detectivity of the present photodetectors are investigated in the wavelength range from 445 to 2717 nm with the maximum values of 50.7 mA W-1 and 1.55 × 109 Jones, respectively, which represent the most broadband MoS2 photodetectors. Based on the easy manipulation, low cost, large scale, and broadband photoresponse, this present detector has significant potential for the applications in optoelectronics and electronics in the future.

On the non-Arrhenius behavior of negative-bias temperature instability

Evidence from negative-bias temperature stressing of the ultrathin Si3N4∕SiOx gate p-channel field-effect transistor indicates that non-Arrhenius behavior is a consequence of the superposition of two distinct defect generation mechanisms with different power-law time dependence (tn) and activation energy (Ea). The two mechanisms are (1) a hole trapping mechanism (t0.1; Ea∼0.02eV) and (2) the classical hydrogen diffusion mechanism (t0.25; Ea∼0.2–0.3eV). When temperature increases, the latter gradually dominates, causing the exponent n, of the overall time-dependent shift of the device threshold voltage (∣ΔVth∣1+2∝tn), to increase. Eliminating the contribution of the hole trapping mechanism, i.e. ∣ΔVth∣1 from overall threshold voltage shift consistently reproduces ∣ΔVth∣2∝tn characteristics which bear the classical signature of negative-bias temperature instability, i.e., n≈0.25 and is independent of temperature.

Atomic-layer molybdenum sulfide optical modulator for visible coherent light

Coherent light sources in the visible range are playing important roles in our daily life and modern technology, since about 50% of the capability of the our human brains is devoted to processing visual information. Visible lasers can be achieved by nonlinear optical process of infrared lasers and direct lasing of gain materials, and the latter has advantages in the aspects of compactness, efficiency, simplicity, etc. However, due to lack of visible optical modulators, the directly generated visible lasers with only a gain material are constrained in continuous-wave operation. Here, we demonstrated the fabrication of a visible optical modulator and pulsed visible lasers based on atomic-layer molybdenum sulfide (MoS2), a ultrathin two-dimensional material with about 9–10 layers. By employing the nonlinear absorption of the modulator, the pulsed orange, red and deep red lasers were directly generated. Besides, the present atomic-layer MoS2 optical modulator has broadband modulating properties and advantages in the simple preparation process. The present results experimentally verify the theoretical prediction for the low-dimensional optoelectronic modulating devices in the visible wavelength region and may open an attractive avenue for removing a stumbling block for the further development of pulsed visible lasers.

Spectral and lasing investigations of Yb:YSGG crystal.

We report on a systematic study of the absorption and emission spectral properties of (Yb(0.1)Y(0.9))(3)(Sc(1.5)Ga(0.5))Ga(3)O(12) (Yb:YSGG) crystals. The broad fluorescence spectral lines indicate great potential of Yb:YSGG for tunable and ultrafast laser applications. Efficient continuous-wave (cw) laser oscillation was also demonstrated at room temperature (RT), generating an output power of 6.11 W with an optical-to-optical efficiency of 64.2%, and a slope efficiency of 80.1% with respect to absorbed pump power. The laser emission spectrum shifts to shorter wavelengths as the transmission of the output coupler varies from 3% to 20%, a result that can be explained based on the effective gain cross-sections of Yb:YSGG.

Band-gap modulation of two-dimensional saturable absorbers for solid-state lasers

Due to the manifestation of fascinating physical phenomena and materials science, two-dimensional (2D) materials have recently attracted enormous research interest with respect to the fields of electronics and optoelectronics. There have been in-depth investigations of the nonlinear properties with respect to saturable absorption, and many 2D materials show potential application in optical switches for passive pulsed lasers. However, the Eigen band-gap determines the responding wavelength band and constrains the applications. In this paper, based on band-gap engineering, some different types of 2D broadband saturable absorbers are reviewed in detail, including molybdenum disulfide (MoS2), vanadium dioxide (VO2), graphene, and the Bi2Se3 topological insulator. The results suggest that the band-gap modification should play important roles in 2D broadband saturable materials and can provide some inspiration for the exploration and design of 2D nanodevices.

Atomic-Layer Molybdenum Sulfide Passively Modulated Green Laser Pulses

Atomic-layer two-dimensional (2D) semiconductors are considered as fundamental materials for next-generation nano-optoelectronic devices. Based on the third-order optical nonlinearity, saturable absorption, and band-gap structures of 2D semiconductors, 2D broadband optical switchers were proposed and experimentally constructed for modulating the laser operation, especially in the infrared range; meanwhile, few 2D saturable absorbers in visible lasers were reported. Here, we demonstrate the pulsed green praseodymium (Pr3+) bulk laser at the wavelength of 522 nm modulated by an atomic-layer molybdenum sulfide (MoS2) saturable absorber. The results represent the shortest spectral range in which 2D saturable absorbers applied. Associating with the recent development of visible lasers and previous reported MoS2 saturable absorbers, this letter provides a promising optical modulator for visible lasers and experimentally identifies that the MoS2 saturable absorber is a universal device for laser modulation in the spectral range from the green to mid-infrared.

Nonlinear optical response of Au nanorods for broadband pulse modulation in bulk visible lasers

Due to the lack of suitable optical modulators, directly generated Pr3+- and Dy3+-doped bulk visible lasers are limited in the continuous-wave operation; yet, pulsed visible lasers are only sparingly reported recently. It has been theoretically predicated that Au nanorods could modulate the visible light operation, based on the nonlinear optical response of surface plasmon resonance. Here, we demonstrate the saturable absorption properties of Au nanorods in the visible region and experimentally realized the pulsed visible lasers over the spectral range of orange (605 nm), red (639 nm), and deep red (721 nm) with Au nanorods as the optical modulator. We show that Au nanorods have a broad nonlinear optical response and can serve as a type of broadband, low-cost, and eco-friendly candidate for optical switchers in the visible region. Our work also advocates the promise of plasmonic nanostructures for the development of pulsed lasers and other plasmonic devices.