Xiaoli Sun

Dual-wavelength, passively Q-switched Tm:YAP laser with black phosphorus saturable absorber

A compact saturable absorber mirror (SAM) based on multi-layered black phosphorus (BP) nanoplatelets was fabricated and successfully used as an efficient saturable absorber (SA) in a passively Q-switched Tm:YAP laser at 1.9 μm. With the BP SAM, Q-switched pulses with duration of 181 ns and average output power of 3.1 W were generated at a pulse repetition rate of 81 kHz, resulting in a pulse energy of 39.5 μJ, to the best of our knowledge, which is the record among the reports on BP SA-based Q-switched lasers. In addition, the simultaneous dual-wavelength Q-switched operation at both 1969 and 1979 nm has been observed. The results indicate the promising potential of multi-layered BP nanoplatelets as SAs for achieving efficient pulsed lasers at around 2 μm.

Passively mode-locked 1.34 μm bulk laser based on few-layer black phosphorus saturable absorber

By using few-layer black phosphorus (BP) as saturable absorber, an efficient mode-locked Nd:GdVO4 bulk laser operating at 1.34 μm was realized. An average output power of 350 mW was achieved with a slope efficiency of 15%. The corresponding mode-locking pulse repetition rate, pulse duration and pulse energy were 58.14 MHz, 9.24 ps and 3.0 nJ, respectively. To the best of our knowledge, the pulse width is the shortest among the mode-locked 1.34 μm neodymium lasers ever obtained with other two-dimensional materials saturable absorber. The results clearly indicate the few-layered BP is a kind of promising saturable absorber for ultrafast 1.34 μm lasers.

High power single-frequency Innoslab amplifier.

A laser diode array (LDA) end-pumped continuous-wave single-frequency Innoslab amplifier has been demonstrated. The Gaussian ray bundle method was used to model the light propagation in the Innoslab amplifier for the first time to the best of our knowledge. With discrete reflectors, the maximum output of 60 W with a linewidth of 44 MHz was achieved under the pump power of 245 W, corresponding to the optical-optical efficiency of 24.5%. The beam quality factor M2 at the output power of 51 W in the horizontal and vertical direction was measured to be 1.4 and 1.3, respectively. The long-term power instability in 2 h was less than 0.25%.

Watt-Level Continuous-Wave and Black Phosphorus Passive Q-Switching Operation of Ho3+,Pr 3+:LiLuF4 Bulk Laser at 2.95 μm

Efficient continuous wave (CW) and passively Q-switched Ho³⁺,Pr³⁺:LiLuF ₄ (Ho,Pr:LLF) laser operating at 2.95 <italic>μ</italic>m were realized using a 1150-nm Raman fiber laser as the pump source. A CW output power as high as 1.15 W, which we believe to be the highest one ever achieved from Ho ³⁺-doped bulk laser emission around 3 <italic>μ</italic>m, corresponds to an optical-to-optical conversion efficiency of 14.5% and a slope efficiency of 15.5%, respectively. A high-quality saturable absorber (SA) based on multilayered black phosphorus (BP) nanosheet film deposited on a CaF₂ substrate was successfully fabricated and employed. Under the absorbed pump power of 7.36 W, the shortest pulse width of 194.3 ns was obtained, which is the shortest among the two-dimensional materials as SA around 3 <italic>μ</italic>m. The results not only indicated that Ho,Pr:LLF crystal would be a promising mid-infrared (MIR) gain medium for obtaining high power output, but verified that the multilayered BP is a promising optical modulator for generating short pulses in MIR spectral range.

Passively Q-Switched Nd:GdVO4 1.3 μm Laser with Few-Layered Black Phosphorus Saturable Absorber

By using a few-layer black phosphorus (BP) as the saturable absorber (SA), a laser-diode end-pumped stable Q-switched Nd:GdVO4 laser operating at 1.3 μm was realized. A maximum average output power of 452 mW was obtained at 2.22 W absorbed pump power, corresponding to a 34.5% slope efficiency. The shortest pulse width, highest pulse repetition rate, and largest peak power were determined to be 72 ns, 625 kHz, and 10.04 W, respectively. To the best of our knowledge, this pulse duration was the shortest ever reported for passive Q-switched bulk lasers based on two-dimensional materials at 1.3 μm. Results suggested that BP can be used to achieve short laser pulses with high repetition rate at 1.3 μm spectral region.

Tunable Ultrafast Nonlinear Optical Properties of Graphene/MoS2 van der Waals Heterostructures and Their Application in Solid-State Bulk Lasers

For van der Waals (vdW) heterostructures, optical and electrical properties ( e.g., saturable absorption and carrier dynamics) are strongly modulated by interlayer coupling, which may be due to effective charge transfer and band structure recombination. General theoretical studies have shown that the complementary properties of graphene and MoS2 enable the graphene/MoS2 (G/MoS2) heterostructure to be used as an important building block for various optoelectronic devices. Here, density functional theory was used to calculate the work function values of G/MoS2 with different thicknesses of MoS2, and its relaxation dynamic mechanism was illustrated. The results reveal that the G/MoS2 heterostructure interlayer coupling can be tuned by changing the thickness of MoS2, furthering the understanding of the fundamental charge-transfer mechanism in few-layer G/MoS2 heterostructures. The tunable carrier dynamics and saturable absorption were investigated by pump-probe spectroscopy and open-aperture Z-scan technique, respectively. In the experiments, we compared the performances of Q-switched lasers based on G/MoS2 heterostructures with different MoS2 layers. Taking advantage of ultrafast recovery time and good saturable absorption properties, a femtosecond solid-state laser at 1.0 μm with G/MoS2 heterostructure saturable absorber was successfully achieved. This study on interlayer coupling in G/MoS2 may allow various vdW heterostructures with controllable stacking to be fabricated and shows the promising applications of vdW heterostructures for ultrafast photonic devices.

Dual-wavelength synchronously mode-locked Nd:LaGGG laser operating at 1.3 μm with a SESAM

We have demonstrated a diode-end-pumped synchronously dual-wavelength mode-locked Nd3+:(La0.1Gd0.9)3Ga5O12 (Nd:LaGGG) laser operating at 1.3 μm with a semiconductor saturable absorber mirror (SESAM) for the first time to our knowledge. The mode-locked laser emitted an average output power of 530 mW with two wavelengths centered at 1331.2 and 1336.5 nm. The pulse duration and repetition rate were 17 ps and 37.6 MHz, respectively. A frequency beat signal with respect to two stationary wave interference patterns of 0.876 THz was observed from the autocorrelation trace.