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In this work, we propose, to the best of our knowledge, the first demonstration of a ~3.5 μm dual-wavelength pumping (DWP) Er3+-doped ZBLAN fiber laser gain switched by 976 nm pulses. The DWP scheme is composed of a pulsed 976 nm laser system and a home-made continuous-wave 1973 nm laser. Stable pulses were obtained with repetition rates ranging between 5.2 kHz and 10 kHz. The maximum output power energy of 50.4 μJ was achieved at 10 kHz with a wavelength of 3445.9 nm. The temporal profile of the pulse trains was characterized by stable relaxation spike pulses containing a series of sub-pulses. The pulse characteristics with respect to the pump energy and the underlying mechanism are discussed. This work makes an effort to better understand the dynamics and theory of the cascade pumping system, and provides a new perspective for the realization of high-power pulses beyond 3 μm.

We report a dual-wavelength tunable passively Q-switched Er3+ -doped ZBLAN fiber laser at ~3 nm using a bulk PtSe2 as a saturation absorber. Stable pulses were generated for average output power of 504.0 mW at 72.9 kHz repetition rate. The corresponding pulse width and pulse energy were measured to be 1.26 μs and 6.92 μJ, respectively. By tuning the feedback angle of the plane ruled grating, the spectra show simultaneous dual-wavelength pulsed operations with tuning range of 51.5 nm (2745.5-2797.0 nm) at the launched pump of 2.27 W.

We report Q-switched Er3+ -doped ZBLAN fiber lasers operating at 2.8 μm based on MIL-68(Al) (MIL: Materials of Institute Lavoisier), for the first time. The nonlinear absorption of MIL-68(Al) was characterized by using a homemade nonlinear absorption measurement system. The modulation depth, non-saturable loss, and saturation peak intensity are determined to be 24.43 %, 58.63%, and 0.0335 GW/cm2, respectively. A piece of 6 mol.% multimode Er3+ -doped ZBLAN fiber was used as the gain medium. The maximum average output power as high as 1.18 W was reached with the shortest pulse duration as short as 546 ns at a repetition rate of 106.71 kHz. The corresponding pulse energy and peak power were 11.03 μJ and 20.19 W, respectively. Then, we replaced the gain fiber with a 7 mol.% single-mode Er3+ -doped ZBLAN fiber and achieved nanosecond pulses with a pulse duration of 846 ns and average output power of 0.734 W. The corresponding pulse energy and peak power were 3.68 μJ and 4.25 W, respectively. Our work shows that the MIL-68(Al) is a promising stable SA for mid-infrared high-power nanosecond laser pulses generation.

In this paper, we investigate the output performance of a continuous-wave Ho3+-doped fluoride fiber laser operating at 3.92 µm from the 5I5 → 5I6 transition of Ho3+ using numerical simulation. A double-clad Ho3+-doped fluoroindate fiber with a doping concentration of 10.0 mol.% is assumed, with direct pumping at 888 nm. We propose simultaneous lasing on the 5I6 → 5I7 transition to enhance the slope efficiency while reducing the threshold and heat accumulation. Simulation results indicate that a slope efficiency of 17% and a threshold of 2.5 W can be obtained using a 9 cm-long fiber. Moreover, with the heat accumulation reduced by >40%, watt level laser output can be achieved in this cascade system at room temperature without the gain fiber being damaged by heat accumulation. The theoretical maximum output power of 1.27 W is 6 times higher than the highest reported value (197 mW), which is limited by the fiber damage due to excess heat load.

Pulsed lasers operating in the mid-infrared are of great importance for numerous applications in spectroscopy, medical surgery, laser processing, and communications. In spite of recent advances with mid-infrared gain platforms, the lack of a capable pulse generation mechanism hinders the development of compact mid-infrared pulsed laser source. Here we show that MIL-68(Al) and MIL-68(Fe), which are aluminum- and iron- based metal-organic frameworks (MOFs) with ordered atoms distribution and periodic mesoporous structure, constitute exceptional optical switches for the mid-infrared. We fabricated the MIL-68(Al) and MIL-68(Fe) via hydrothermal method and prepared reflection-type MIL-68(Al)- and MIL-68(Fe)- saturable absorber mirrors (SAMs). By employing the as-prepared SAMs in the laser cavities, we achieved high-power nanosecond Q-switched fiber lasers at 2.8 µm. Especially, the average output power and pulse duration of the MIL-68(Al) Q-switched fiber laser reached 809.1 mW and 567 ns, respectively. To the best of our knowledge, this is the first time to demonstrate that MIL-68(M) can be efficient optical switches for 3-µm mid-IR laser pulses generation. Our findings reveal that MIL-68(M) is promising saturable absorber for compact and high-performance mid-infrared pulsed lasers.

The incidence of cervical cancer is expected to rise sharply in China. A reliable routine human papillomavirus (HPV) detection and genotyping test to be supplemented by the limited Papanicolaou cytology facilities is urgently needed to help identify the patients with cervical precancer for preventive interventions. To this end, we evaluated a nested polymerase chain reaction (PCR) protocol for detection of HPV L1 gene DNA in cervicovaginal cells. The PCR amplicons were genotyped by direct DNA sequencing. In parallel, split samples were subjected to a Digene HC2 HPV test which has been widely used for “cervical cancer risk” screen. Of the 1826 specimens, 1655 contained sufficient materials for analysis and 657 were truly negative. PCR/DNA sequencing showed 674 infected by a single high-risk HPV, 188 by a single low-risk HPV, and 136 by multiple HPV genotypes with up to five HPV genotypes in one specimen. In comparison, the HC2 test classified 713 specimens as infected by high-risk HPV, and 942 as negative for HPV infections. The high-risk HC2 test correctly detected 388 (57.6%) of the 674 high-risk HPV isolates in clinical specimens, mislabeled 88 (46.8%) of the 188 low-risk HPV isolates as high-risk genotypes, and classified 180 (27.4%) of the 657 “true-negative” samples as being infected by high-risk HPV. It was found to cross-react with 20 low-risk HPV genotypes. We conclude that nested PCR detection of HPV followed by short target DNA sequencing can be used for screening and genotyping to formulate a paradigm in clinical management of HPV-related disorders in a rapidly developing economy.