Haohai Yu

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.

Dual-wavelength synchronously mode-locked Nd:CNGG laser

We have experimentally demonstrated a dual-wavelength synchronously mode-locked Nd:CNGG laser based on the semiconductor saturable absorber mirror technique. Mode locking was achieved simultaneously on two gain bands of the crystal that have a central wavelength separation of 2.4 nm. The fundamental mode-locked pulse train has a repetition rate of 88 MHz and pulse duration of 5 ps, with an average output power of approximately 90 mW. Autocorrelation measurements show that each of the synchronously mode-locked pulses consists of a train of quasi-periodic beat pulses with a 660 fs pulse width and a 0.63 THz repetition rate.

Graphene mode-locked femtosecond laser at 2 μm wavelength

We experimentally demonstrated a passively mode-locked femtosecond laser by using a graphene-based saturable absorber mirror (graphene SAM) in the spectral region of 2 μm. The graphene SAM was fabricated by transferring chemical-vapor-deposited, high-quality, and large-area graphene on a highly reflective plane mirror. Stable mode-locked laser pulses as short as 729 fs were obtained with a repetition rate of 98.7 MHz and an average output power of 60.2 mW at 2018 nm.

Graphene saturable absorber for Q-switching and mode locking at 2 μm wavelength [Invited]

Graphene saturable absorber mirror (SAM) was successfully fabricated by transferring large-size graphene flake on dielectric coating mirror. The graphene transferred on the mirror was tested by Raman spectrum measurement and scanning electron microscope imaging. With the graphene SAM, passive Q-switching and continuous wave (CW) mode locking were experimentally demonstrated in a bulk laser at 2 μm wavelength.

Subpicosecond pulse generation from a Nd:CLNGG disordered crystal laser

We report on a diode-pumped passively mode-locked subpicosecond Nd:CLNGG disordered crystal laser for the first time to our knowledge. Owing to the large inhomogeneous broadening and spectrum splitting of the disordered crystal, the Nd:CLNGG laser generated 900 fs mode-locked pulses with a repetition rate of approximately 88 MHz at 1061 nm wavelength. With a single-emitter laser diode pumping, a maximum average output power of 486 mW was achieved with a slope efficiency of 26%. Our experimental results show that the four-level Nd:CLNGG disordered crystal could be an excellent alternative for subpicosecond pulse generation.

High-power dual-wavelength laser with disordered Nd:CNGG crystals

We demonstrate the high-power dual-wavelength laser output with disordered Nd:CNGG laser crystals. Continuous-wave output power of 4.03 W was obtained under the incident pump power of 15.62 W. In the passively Q-switched operation, the shortest pulse width, largest pulse energy, and highest peak power were achieved to be 12.9 ns, 173.16 microJ, and 12.3 kW, respectively, with Cr(4+):YAG crystals as the saturable absorbers. By spectral analysis, the output lasers were found to have dual wavelengths. We believed that the passively Q-switched dual-wavelength laser should be possible to be used as a source for the generation of terahertz radiation.

Compact passively Q-switched diode-pumped Tm:LiLuF4 laser with 1.26 mJ output energy.

We demonstrate efficient continuous-wave (CW) and passively Q-switched Tm:LiLuF(4) laser operation near 1.9 μm. The CW slope efficiency reached 54.8% with respect to absorbed power. Stable passive Q-switching with Cr(2+):ZnS saturable absorbers resulted in minimum pulse duration of 7.6 ns and maximum pulse energy and peak power of 1.26 mJ and 166 kW, respectively.

Enhancement of passive Q-switching performance with mixed Nd:Lu x Gd 1−x VO 4 laser crystals

Passive Q-switching operation has been demonstrated with a class of mixed Nd:Lu(x)Gd(1-x)VO(4) laser crystals. With respect to that obtained with Nd:GdVO(4), the passive Q-switching performance, including threshold, pulse energy, and peak power, was found to be greatly enhanced with the mixed vanadate crystals. The shortest pulse width of 6.2 ns, largest pulse energy of 192.5 microJ, and highest peak power of 31.1 kW were obtained at the incident pump power of 13.75 W with the mixed crystal for x=0.5.

Large energy pulse generation modulated by graphene epitaxially grown on silicon carbide.

Graphene grown by thermal decomposition of a two-inch 6H silicon carbide (SiC) wafers surface was used to modulate a large energy pulse laser. Because of its saturable absorbing properties, graphene was used as a passive Q-switcher, and because of its high refractive index the SiC substrate was used as an output coupler. Together they formed a setup where the passively Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal laser was realized with the pulse energy of 159.2 nJ. Our results illustrate the feasibility of using graphene as an inexpensive Q-switcher for solid-state lasers and its promising applications in integrated optics.

CW and Q-switched laser output of LD-end-pumped 1.06μm c-cut Nd:LuVO 4 laser

The continuous-wave (cw) and pulsed laser performances of laser-diode (LD)-end-pumped c-cut Nd:LuVO(4) at 1.06 mum were achieved for the first time. Maximum cw output of 2.35W was obtained. Compared with the cw laser output of a-cut Nd:LuVO(4) crystal, the efficient emission cross-section of the c-cut crystal has been calculated to be 3.24x10(-19)cm(2). The largest pulse repetition rate, shortest pulse width, largest pulse energy and highest peak power were measured to be 20 kHz, 12 ns, 84.93 muJ and 7.02 kW, respectively, by using Cr(4+):YAG crystals as the saturable absorbers in the passive pulsed laser output experiments.