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 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.
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.
Q-switched fiber lasers emitting at around 3 μm have been widely applied in various scientific and industrial fields, such as molecular spectroscopy, laser surgery, material processing, remote sensing, and mid-infrared (mid-IR) supercontinuum source generation. Au nanocages (Au-NCs) have attracted much attention recently due to their outstanding saturable absorption properties including broadband absorption, ultrafast optical response (a few picoseconds), and large third-order optical nonlinearity coefficient that caused by local surface plasmon resonance (LSPR). We propose and demonstrate a tunable Er3+ doped ZBLAN fiber laser using Au-NCs as a Q-switcher for the first time. Nonlinear absorption of the Au-NCs was measured by a home-made Ho3+/Pr3+ co-doped mode-locked fiber laser at 2850 nm. The measured modulation depth, saturation intensity and non-saturation loss are 10.73%, 0.11 MW/cm2 and 3.26%, respectively. The central wavelength of the Q-switched pulses could be tuned across 54.1 nm (from 2753.0 to 2807.1 nm). The Q-switched fiber laser delivers a maximum average power of 253.7 mW with corresponding pulse energy of 4.06 μJ and pulse width of 1.30 μs at repetition rate of 62.5 kHz. Our work shows the Au-NCs are promising saturable absorbers (SAs) for 3 μm mid-infrared (mid-IR) pulse generation.
High-resolution, real-time and three-dimensional imaging in thick scattering specimens is of great significance in biology, yet meeting these requirements at the same time is fraught with challenges. In this work, we describe a method that combines structured illumination microscopy (SIM) with dual nonlinear effects, two-photon excitation (2PE) technique and stimulated emission depletion (STED), to further improve the imaging resolution in optical-thick samples relative to SIM. Utilizing a line-scanning geometry shaped by cylindrical lens to form structured illumination pattern, the imaging speed is greatly improved. Theoretical study and simulations are both performed to demonstrate the capability of this method to enhance resolution laterally and the potential for applications in real-time imaging for living tissue.
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