High-power femtosecond mid-infrared (MIR) lasers are of vast importance to both fundamental research and applications. We report a high-power femtosecond master oscillator power amplifier laser system consisting of a single-mode Er:ZBLAN fiber mode-locked oscillator and pre-amplifier followed by a large-mode-area Er:ZBLAN fiber main amplifier. The main amplifier is actively cooled and bidirectionally pumped at 976 nm, generating a slope efficiency of 26.9%. Pulses of 8.12 W, 148 fs at 2.8 μm with a repetition rate of 69.65 MHz are achieved. To the best of our knowledge, this is the highest average power ever achieved from a femtosecond MIR laser source. Such a compact ultrafast laser system is promising for a wide range of applications, such as medical surgery and material processing.

We demonstrate broadband mid-infrared supercontinuum generation in a piece of indium fluoride fiber pumped by an ultralow repetition rate noise-like pulse mode-locked fiber laser. This figure-9 mode-locked Tm-doped fiber laser has a long laser cavity by inserting a piece of standard single mode fiber and a piece of dispersion compensation fiber, which delivers mode-locked noise-like pulse with a repetition rate of ∼190 kHz. The mode-locked noise-like pulse train has a low pulse duty cycle of 4.38 × 10 ⁻⁴ . With only one Tm-doped fiber amplifier, the ultra-low repetition rate noise-like pulse is amplified to ∼3 W. The pulse energy is boosted to ∼15 μJ with a peak power of ∼6.5 kW. Pumping a piece of highly nonlinear indium fluoride fiber with the amplified noise-like pulse, a flat mid-infrared supercontinuum with a covering range from ∼1500 nm to ∼4100 nm can be achieved. Due to the low operational power, no cooling installations are required to control the temperature of the supercontinuum laser system. This all-fiber mid-infrared SC laser source has a relatively simple architecture and low cost. This study demonstrates the great advantages of this type of ultra-low repetition rate noise-like pulses in mid-infrared supercontinuum generation.

A detailed analysis of theexcited state absorption (ESA) transition ⁴ I _13/2 → ⁴ I _9/2 which occurs in erbium (Er) doped ZBLAN fiber lasers is performed through numerical modeling. It is found that the ESA plays a significant role in enhancing the 2.8 μ m lasing of Er ³⁺ ions. The ESA promotes the ions residing in ⁴ I _13/2 (the lower state of the 2.8 μ m laser) to ⁴ I _9/2 , where the ions subsequently decay to ⁴ I _11/2 (the upper state of the 2.8 μ m laser) rapidly. An energy recycling is consequently realized via the ESA. The ESA can be activated in cascaded 2.8 μ m/1.6 μ m Er-doped ZBLAN fiber lasers by absorbing the 1.6 μ m signal. Through numerical simulation it is found that in cascaded lasers the slope efficiency of the 2.8 μ m laser can be elevated to ∼48% with the assistance of the ESA, a value that surpasses the Stokes limit (∼35%) substantially and agrees well with the experimental results previously reported. It is also found that the ESA-induced energy recycling is exothermic, an effect that is non-ignorable in the high-power circumstance. Moreover, the injection of an additional 1.6 μ m pump for directly exploiting the ⁴ I _13/2 → ⁴ I _9/2 ESA is simulated using the model. It is found that as the second pump is introduced, the 2.8 μ m lasing almost entirely relies on the ESA-induced energy recycling, and hence, the laser is capable of operating under very low 976 nm pump power. The simulation results indicate that the 2.8 μ m lasing in Er-doped ZBLAN fiber lasers can even be realized using a single 1.6 μ m pump, via a combination of the ⁴ I _15/2 → ⁴ I _13/2 and ⁴ I _13/2 → ⁴ I _9/2 transition. The outcomes of this work can inspire the development of novel, high-performance 2.8 μ m Er-doped ZBLAN fiber lasers.

High-power tunable femtosecond mid-infrared (MIR) pulses are of great interest for many scientific and industrial applications. Here we demonstrate a compact fluoride-fiber-based system that generates single solitons tunable from 3 to 3.8 μm. The system is composed of an Er:ZBLAN fiber oscillator and amplifier followed by a fusion-spliced Dy:ZBLAN fiber amplifier. The Er:ZBLAN fiber amplifier acts as a power booster as well as a frequency shifter to generate Raman solitons up to 3 μm. The Dy:ZBLAN fiber amplifier transfers the energy from the residual 2.8 μm radiation into the Raman solitons using an in-band pumping scheme, and further extends the wavelength up to 3.8 μm. Common residual pump radiation and secondary solitons accompanying the soliton self-frequency shift (SSFS) are recycled to amplify Raman solitons, consequently displaying a higher output power and pulse energy, a wider shifting range, and an excellent spectral purity. Stable 252 fs pulses at 3.8 μm with a record average power of 1.6 W and a pulse energy of 23 nJ are generated. This work provides an effective way to develop high-power widely tunable ultrafast single-soliton MIR laser sources, and this method can facilitate the design of other SSFS-based laser systems for single-soliton generation.

We report a high-average-power mid-infrared ultrafast laser system consisting of a fluoride fiber mode-locked oscillator and a nonlinear amplifier. A backward pumping scheme was used in the amplifier to simultaneously realize pulse amplification and self-compression. The input signal polarization was demonstrated to play an important role in the self-compression process. Through the optimization of input polarization, a 4.13 W average-power 59 fs pulse at 2.8 µm was achieved, with an estimated pulse energy of 42.2 nJ and a peak power of 715 kW. To the best of our knowledge, this is the highest average-power pulse with sub-100-fs duration generated from a mid-infrared fiber laser system to date.

A 2D heterostructure with dense SnS₂ nanoplates vertically anchored on a graphene aerogel (SnS₂@GA) was achieved via a controlled self-assembly process followed by a thermally induced sulfidation treatment for high-performance sodium-ion batteries.