Rational design of porous Fex-N@MOF as a highly efficient catalyst for oxygen reduction over a wide pH range

Lanthanide-doped LiYF4 (Ln:YLF) is commonly used for a broad variety of optical applications, such as lasing, photon upconversion and optical refrigeration. When synthesized as nanocrystals (NCs), this material is also of interest for biological applications and fundamental physical studies. Until now, it was unclear how Ln:YLF NCs grow from their ionic precursors into tetragonal NCs with a well-defined, bipyramidal shape and uniform dopant distribution. Here, we study the nucleation and growth of ytterbium-doped LiYF4 (Yb:YLF), as a template for general Ln:YLF NC syntheses. We show that the formation of bipyramidal Yb:YLF NCs is a multistep process starting with the formation of amorphous Yb:YLF spheres. Over time, these spheres grow via Ostwald ripening and crystallize, resulting in bipyramidal Yb:YLF NCs. We further show that prolonged heating of the NCs results in the degradation of the NCs, observed by the presence of large LiF cubes and small, irregular Yb:YLF NCs. Due to the similarity in chemical nature of all lanthanide ions our work sheds light on the formation stages of Ln:YLF NCs in general. 

https://pubs.acs.org/doi/pdf/10.1021/acs.chemmater.3c00502

Nucleation and Growth of Bipyramidal Yb:LiYF4 Nanocrystals─Growing Up in a Hot Environment

In order to improve the output power of solar-pumped single-crystal fiber (SCF) lasers, we propose a novel solar concentrating system, to the best of our knowledge, consisting of a parabolic mirror, a 3D compound parabolic concentrator, and a hollow-core reflector. By ray tracing with TracePro, the influence of the fiber's diameter and the hollow reflector's shape on the solar absorption efficiency is theoretically investigated. A typical Nd:YAG SCF with a core diameter of 1 mm, length of 150 mm, and doping concentration of 1 at.% is selected for a simulation of laser operation. The output characteristics of the laser are analyzed by solving the rate equation and power transmission equation; the maximum output power and solar-to-laser conversion efficiency are 60.62 W and 4.64%, respectively. The thermal effects of the laser are simulated by Comsol software. When the input solar power is 1307.4 W, the temperature decreases sharply first and then saturates along the SCF fiber, with the maximum value of 69.18°C at the input fiber end. This concentrating system can effectively overcome the limitation of end-launching solar power into SCFs and has great potential in improving the output power of solar fiber lasers.

Theoretical analysis of a 60  W solar-pumped single crystal fiber laser.

https://robots.iopscience.iop.org/article/10.1088/1612-202X/ab86b2/pdf

High-energy femtosecond laser system based on a fiber laser seeder, Yb:YAG single crystal fiber and chirped volume Bragg grating

Abstract We report nanosecond (ns) cavity-dumped operation of a low-cost diode-pumped Cr:LiSAF laser around 1000 nm. The system is pumped with one 1-W single-emitter multimode diode at 665 nm. A Pockell cell (PC) and thin-film-polarizer (TFP) combination placed inside the cavity chops up an adjustable portion of the intracavity power and creates a variable time-dependent output coupler. Via adjusting the length and magnitude of the electrical signal going into the PC, output pulses with pulsewidths in the 2.5–500 ns range and with peak power levels above 10 W are generated at repetition rates up to 100 kHz. The central wavelength of the pulses could be smoothly tuned in the 985–1030 nm region, and is only limited by the anti-reflection coating bandwidth of the current PC and TFP. This versatile nanosecond source with 100 nJ level energies could serve as an attractive low-cost seed source for Yb-based amplifiers, including the cryogenic Yb:YLF systems. 

/pdf/cavity-dumped-nanosecond-cr-lisaf-laser-in-the-985-1030-nm-7aiv925o.pdf

Cavity-dumped nanosecond Cr:LiSAF laser in the 985–1030 nm region for versatile seeding of Yb-based amplifiers

Fiber rods of 10% doped Yb:YLF were fabricated with the micro-pulling-down technique and characterized. The crystal a axis was oriented along the rod length, allowing polarized emission with the largest cross section available in the c direction. Laser experiments showed that these fiber samples perform similarly to crystals grown by the standard Czochralski method. Intrinsic slope efficiency of ∼50% was measured in both cases, with small comparable intracavity losses, proving the good quality of the fiber material.

Laser investigation of Yb:YLF crystals fabricated with the micro-pulling-down technique

Single-crystal fiber Yb-doped LiLuF4 grown by the micro-pulling-down method was tested in a high-power pumped amplifier setup seeded by a passively Q-switched Yb:YLF laser. With 82-W absorbed pump power and 130-μJ injected pulse energy, the amplifier yielded 1.05-mJ pulses with 110-ns duration at 5.2 kHz, linearly polarized with excellent beam quality. These results prove the high optical quality and promising performance of this new material technology exploiting birefringent Yb-doped materials at very high pump power. 

1-mJ multi-kHz nanosecond pulses from a single-crystal Yb:LiLuF4 amplifier seeded by a passively-Q-switched laser

25 W continuous-wave Yb:LiLuF4 single-crystal-fiber laser oscillator

We present, to the best of our knowledge, the first demonstration of a single crystal fiber solid-state amplifier based on a birefringent Yb3+-doped thin crystal grown by the micro-pulling-down method. We measured a small signal gain >30 in a four-passes Yb:LiLuF4 amplifier pumping with a 120-W maximum power fiber-coupled laser diode. At an absorbed pump power of 80 W, a maximum output power of 8.4 W was obtained seeding the 42-mm-long, 2%Yb3+-doped single crystal fiber sample with 0.8 W at 1021 nm. Even at the maximum incident pump power, the amplified laser beam polarization and spatial quality were excellent (M2=1.15×1.06).

Multi-watt amplification in a birefringent Yb:LiLuF4 single crystal fiber grown by micro-pulling-down.

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Laser investigation of Yb:YLF crystals fabricated with the micro-pulling-down technique

1-mJ multi-kHz nanosecond pulses from a single-crystal Yb:LiLuF4 amplifier seeded by a passively-Q-switched laser

25 W continuous-wave Yb:LiLuF4 single-crystal-fiber laser oscillator

Multi-watt amplification in a birefringent Yb:LiLuF4 single crystal fiber grown by micro-pulling-down.