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We present the design and fabrication of a 4 × 1 fiber combiner with low brightness loss. The effective area ratio (AR) of light transmission was first introduced to estimate the brightness loss. A square core fiber was used as the output fiber of the fiber combiner to achieve a high AR. The adiabatic criterion for tapering multimode fibers was investigated to obtain the structure parameters required for the fabrication. We used an auxiliary fiber of appropriate size to achieve a regular squared fiber bundle and improve bundle cutting and splicing quality. The fiber combiner yielded a high average power transmission efficiency of 97.8% when the brightness ratio was 1.05. In addition, the output power of 1030 W was obtained by combining two LDs. This type of fiber combiner can produce multi-kilowatts laser by combining high power LDs or fiber lasers. And it can be flexibly applied in laser welding, laser cladding, and laser cleaning.

We presented the chemical mask etching method to fabricate an all-fiber cladding light stripper (CLS). The morphology and density of the micron-sized microstructures generated on the fiber surface could be flexibly controlled in fabrication process, which was beneficial to the temperature performance and high-power operation capacity of the device. Based on the method, a theoretical model was developed to optimize the structure of the CLS. Initial experimental processing parameters were also obtained to realize uniform scattering and high attenuation coefficient. An all-fiber cladding light stripper with a high attenuation coefficient of 42 dB was achieved when the stripped cladding light was 1.117 kW. The temperature rising rate was only 0.011 °C/ input-Watt under the condition of air cooling, thanks to all-fiber structure and the uniform scattering design. The average stripped power density reached 9.19 × 106 W/m2 within a 135 mm long CLS. The CLS fabricated by this technique has great application in the high power fiber laser system.

A watt-level directly diode-pumped continuous-wave (CW) Ti:Sapphire oscillator was demonstrated for the first breakthrough by a high-power green laser-diode-pumped module employing the technologies of beam shaping, beam collimation, polarization beam combining, and fiber coupling. A 1.36-W output power and 10.6% of slope efficiency were obtained based on the double-concave (DC) cavity configuration. This is the highest CW output power from Ti:Sapphire (Ti:S) oscillator directly pumped by green laser diodes (LDs) reported so far.

For fiber-coupled green laser-diode pump beam, a simple model was proposed to calculate the average outputs. Then we presented a direct-pumping continuous-wave Ti:Sapphire laser producing an optimized output of 3.8-W with green diodes. It was the highest output of this kind reported so far corresponding to an optical/optical conversion efficiency of 11.5% and a high slope efficiency of 15.7% at 810 nm. A highest power of 1.41-W was also obtained with the single-sided pumping corresponding to a good slope efficiency of 14.3%. High-power green diodes realized the lowest threshold pumping intensity of ~ 16.7 × 103 W/cm2 under hundred-μm-level beam diameter size. This work would benefit the design for the direct-pumping Ti:Sapphire laser as a guide.

We present the second harmonic generation (SHG) of a low power and of both Q-switched mode-locked (QML) and CW (CWML) mode-locked picosecond (ps) laser at 1064 nm based on a single-pass frequency-doubling configuration of an end-pumped passively mode-locked Nd:YVO4 laser in a 3-mm periodically poled MgO-doped lithium-niobate (MgO:PPLN). The maximum SHG conversion efficiency is 27.4% when the laser is operated in the QML mode at an averaged pumping power of 895 mW and the conversion efficiency is reduced to 24.1% in the CWML mode with a maximum averaged pumping power of 1.37 W. The corresponding pulse width of the SHG output is estimated to be 15.5 ps. The repetition rates of the laser are 137 kHz for QML and 78.7 MHz for CWML. The theoretical efficiencies of SHG are calculated in both QML and CWML and the results agree very well with the experiments especially in the QML. This work provides a useful method for efficient frequency conversion for low power mode-locked lasers.

We report a 166 W burst mode pulse fiber amplifier seeded by a Q-switched mode-locked all-fiber laser at 1064 nm based on a fiber-coupled semiconductor saturable absorber mirror. With a pump power of 230 W at 976 nm, the output corresponds to a power conversion efficiency of 74%. The repetition rate of the burst pulse is 20 kHz, the burst energy is 8.3 mJ, and the burst duration is ∼ 20 μ s, which including about 800 mode-locked pulses at a repetition rate of 40 MHz and the width of the individual mode-locked pulse is measured to be 112 ps at the maximum output power. To avoid optical damage to the fiber, the initial mode-locked pulses were stretched to 72 ps by a bandwidth-limited fiber bragg grating. After a two-stage preamplifier, the pulse width was further stretched to 112 ps, which is a result of self-phase modulation of the pulse burst during the amplification.

We demonstrate a 150-mm long cladding light stripper for kW-level operation with high attenuation and low temperature rising. The first 100 mm of the device was designed based on theoretical simulation to achieve uniform extraction of the high-power scattered cladding light and it was constructed by self-developed experimental device for continuous gradient chemical etching. While in the last 50 mm, we reduced the cladding diameter from 400 to 65 μm and then roughed the surface to extract the residual low NA cladding light more efficiently. The power handling capability of this design was tested up to 1.01 kW for an hour stably without causing any damage. The cladding light stripper achieved a high attenuation of 39 dB and a low temperature elevation of 0.05 °C/ input-Watt under the condition of air cooling. The maximum temperature on the surface of the device was only 78.5 °C with an average stripped power density of 7.156 × 106 W/m2. To the best of our knowledge, the cladding light stripper reported here has the highest average stripped power density and attenuation coefficient without compromising temperature performance. This cladding light stripper is well suitable for application in multikilowatts class fiber lasers.

We present the generation of picosecond bursts with controllable pulse number in a passively mode-locked Nd:YVO4 laser with a compound cavity. This is the first time to use a compound cavity with additional SESAM to generate pulse burst. The device is constructed by inserting an HWP in the cavity, which reflects part of light in the main cavity into the auxiliary cavity and then the reflected beam is sent back after a delay in the auxiliary cavity. By controlling the power reflected into the main cavity from the auxiliary cavity, a series of bursts can be created with a selectable pulse number and adjustable temporal separation between the pulses. The temporal separation between two adjacent picosecond pulses in the burst can be adjusted by changing the length difference between two cavities. The temporal width of the burst can be adjusted from picosecond to nanosecond, and the repetition rate of the burst is the same as that in continuous wave mode-locked laser. The generation of the burst is presumably attributed to the temporal addition of laser pulses from the two cavities. This work provides a useful method for generating controllable picosecond laser burst.

Environmental art design is a subject to deal with the relationship between artificial environment and natural environment, and also a subject to create a livable and ecological balanced living environment for human beings. Thus, it is of paramount of importance to study how artificial construction can adapt to the natural environment. To this end, the concept of physics “Resilience” is introduced into the landscape design of urban wetland park, and the strategies of shaping and utilizing resilience landscapes in urban wetland park is discussed in order to provide effective measures to deal with urban flood disaster, realize “sponge function”, promote regional ecological environment balance and sustainable development.

In the letter [1] , the authors’ affiliation were listed incorrectly. The correct affiliation is as follows

The first experimental demonstration of a $1\times 4$ all-fiber power splitter capable of high-power operation is presented. The splitter, prepared by fused taper technique and fusion splicing technique, consists of one input fiber with a core diameter of $400~\mu \text{m}$ (NA $_{\mathrm {CORE}} = 0.22$ ) and four output fibers with a core diameter of $200~\mu \text{m}$ (NA $_{\mathrm {CORE}} = 0.22$ ). The device was tested at a laser power up to 166 W and it achieves a low excess loss of 0.56 dB and an excellent uniformity of less than 0.3 dB in port-to-port power splitting ratio. The results of theoretical simulation by the 3-D beam propagation method show that the performance of this splitter could be optimized further through modifying structure parameters.

We report a compact 85-W burst-mode pulse fiber amplifier seeded by a Q-switched mode-locked laser at 1064 nm. At a repetition rate of 154 kHz, the pulse duration of the burst is 4 μs containing 280 of 20-ps pulses with temporal space of ∼14 ns, and the total burst energy is about 552 μJ per pulse. The pulse number and the burst repetition frequency can be adjusted from 121 to 154 kHz through increasing the pump power of the seed laser. To the best of our knowledge, this is the first time to observe this type burst pulse amplifier based on the Q-switched mode-locked seed laser. No significant amplified spontaneous emission and stimulated Raman scattering were observed in our experiment when the output power is less than 85 W.

We demonstrate a new method for fabricating a (6 + 1) × 1 pump–signal combiner based on the reduction of signal fiber diameter by corrosion. This method avoids the mismatch loss of the splice between the signal fiber and the output fiber caused by the signal fiber taper processing. The optimum radius of the corroded signal fiber was calculated according to the analysis of the influence of the cladding thickness on the laser propagating in the fiber core. Besides, we also developed a two-step splicing method to complete the high-precision alignment between the signal fiber core and the output fiber core. A high-efficiency (6 + 1) × 1 pump–signal combiner was produced with an average pump power transmission efficiency of 98.0% and a signal power transmission efficiency of 97.7%, which is well suitable for application to high-power fiber laser system.

High average power picosecond (~ 100 ps) lasers with narrow-linewidth are in great demand for some specific applications. In this paper, a 240 W Yb-doped double-cladding fiber amplifier system at 1064 nm delivering 112 ps pulses at 40 MHz repetition rate was demonstrated. To prevent possible double-cladding fiber damage, a bandwidth-limited (0.1 nm) fiber Bragg grating (FBG) was used to force a stretched pulse-width of 72 ps and a narrow-linewidth of 23 pm. The laser pulses were then stretched to ~ 100 ps after dispersion management and amplified without notable spectral distortion by nonlinear management. The output of the amplifier produces a pulsed energy of 6 μJ, which corresponds to a peak power of 54 kW. The M 2 factor was measured to be about 1.2 at the maximum power of 240 W. The spectral width was 0.45 nm after the power amplification. Further power-scaling was only limited by available pump power.

We demonstrate a high-power blue diode laser operated at 447 nm combining laser diodes using an optical fiber bundle. As many as 127 diode lasers at 447 nm were coupled into 400 μ m/0.22NA fibers using an aspherical lens group with different focus lengths. The bare fibers were mechanically bundled through high temperature ultraviolet adhesive after the coatings of the 127 fibers were stripped. The diameter of the fiber bundle was 6 mm. The total output power of such a bundle was 152 W with electro-optical conversion efficiency of 27.56% and the RMS power instability was less than ± 1% within 3 h.

Monolayer MoS2 film on quartz was fabricated by a home-made three-temperature zone chemical vapor deposition method. The photo, AFM image, Raman spectroscopy and HRTEM image showed that high quality as-grown MoS2 film completely covered the whole quartz substrate of a few cm2. A Nd:YVO4 laser with mode-locking operation was obtained by using the monolayer MoS2 on quartz as the saturable absorber (SA). To the best of our knowledge, this is the first report on large-area growth of high quality monolayer MoS2 film on transparent quartz substrate, and the first time that the CVD MoS2 SA was used in mode-locked solid state lasers. Because of the large area, high transmission, low non-saturable loss and high optical damage threshold of this material, it is very suitable for application in mode-locked solid state lasers.