Hongkun Nie

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.

Diode-end-pumped Ho, Pr:LiLuF_4 bulk laser at 295 μm

A diode-end-pumped continuous-wave (CW) and passively Q-switched Ho, Pr:LiLuF4 (Ho, Pr:LLF) laser operation at 2.95 μm was demonstrated for the first time, to the best of our knowledge. The maximum CW output power was 172 mW. By using a monolayer graphene as the saturable absorber, the passively Q-switched operation was realized, in which regimes with the highest output power, the shortest pulse duration, and the maximum repetition rate were determined to be 88 mW, 937.5 ns, and 55.7 kHz, respectively. The laser beam quality factor M2 at the maximum CW output power were measured to be Mx2=1.48 and My2=1.47.

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.

83.4 W, 17.69 kHz spectral bandwidth, continuous-wave, beam densely folded Innoslab amplifier

Combined with the advantages of the narrow bandwidth of a non-planar ring oscillator seed laser and the structure of a direct pumped Innoslab amplifier, a high-efficiency and high-power continuous-wave (CW) single-frequency laser was obtained by densely folding the seed laser beam in an Innoslab amplifier with a wedged multi-folded configuration. A maximum output power of 83.4 W of a single-frequency amplifier with a bandwidth of 17.69 kHz was obtained under a pump power of 234 W, corresponding to an optical-to-optical conversion efficiency of 33.2%. The beam quality factor M2 at the maximum output power in horizontal and vertical directions was measured to be 1.15 and 1.24, respectively. The long-term power instability in 2 h was less than 1.63%.