Rapid Fabrication of High-Entropy Ceramic Nanomaterials for Catalytic Reactions.

Although high-entropy alloys have been intensively studied in the past decade, there are still many requirements for manufacturing processes and application directions to be proposed and developed, but most techniques are focused on high-entropy bulk materials and surface coatings. We fabricated high-entropy ceramic (HEC) nanomaterials using simple pulsed laser irradiation scanning on mixed salt solutions (PLMS method) under low-vacuum conditions. This method, allowing simple operation, rapid manufacturing, and low cost, is capable of using various metal salts as precursors and is also suitable for both flat and complicated 3D substrates. In this work, we engineered this PLMS method to fabricate high-entropy ceramic oxides containing four to seven elements. To address the catalytic performance of these HEC nanomaterials, we focused on CoCrFeNiAl high-entropy oxides applied to the oxygen-evolution reaction (OER), which is considered a sluggish process in water. We performed systematic material characterization to solve the complicated structure of the CoCrFeNiAl HEC as a spinel structure, AB2O4 (A, B = Co, Cr, Fe, Ni, or Al). Atoms in A and B sites in the spinel structure can be replaced with other elements; either divalent or trivalent metals can occupy the spinel lattice using this PLMS process. We applied this PLMS method to manufacture electrocatalytic CoCrFeNiAl HEC electrodes for the OER reaction, which displayed state-of-the-art activity and stability.

Effects of nonlinear phase in cascaded mode-locked Nd:YVO4 laser.

A diode-pumped mode-locked Nd:YVO4 laser via positive cascaded second-order Kerr lens using periodically poled MgO:LN at 1064 nm was reported. Mode-locking performances including output power, bandwidth, pulse duration, and time-bandwidth product were studied under different phase-mismatched conditions. The induced nonlinear phase combined with soft aperture effect yield a stable mode-locked operation in a wide phase-mismatched range (-8π < ∆kL < -π). Additionally, the mode-locking bandwidth was broadened by self-phase modulation and the time-bandwidth product was increased to be more than twice the ideal product for a sech2 pulse shape. Under 11 W diode pump power, the measured average power, pulse repetition rate and pulse duration are 1.3 W, 186 MHz and 2.8 ps, respectively.

Polarization bistability associated with 4F3/2→4I11/2 and 4F3/2→4I13/2 transitions in Nd:YVO4 laser with intra-cavity periodically poled lithium niobate Bragg modulator.

We experimentally demonstrate polarization bistability in a dual-wavelength Nd:YVO4 laser at 1064 nm (4F3/2→4I11/2) and 1342 nm (4F3/2→4I13/2) by using an intra-cavity electro-optic periodically poled lithium niobate (PPLN) Bragg modulator to control the loss at 1064 nm. An inverse hysteresis switch was observed between 1064 nm and 1342 nm lasers with orthogonal polarizations by increasing and reducing the loss induced by the PPLN. The size of the hysteresis increased with increasing pump power. This paper provides an explanation based on cross-gain saturation for this bistable behavior of polarization.

Saturation spectroscopy of CO2 and frequency stabilization of an optical parametric oscillator at 2.77 µm.

We report the frequency stabilization of a CW single-frequency, singly resonant optical parametric oscillator (OPO) to the saturation absorption center of the (12)C(16)O2[10°1,02°1](II)>←00°0 P(14) line at 2.77 µm. The CO2 molecules were excited by the OPO idler wave, and the absorption signal was monitored through the fluorescence at 4.3 µm using a gold-coated longitudinal cell. The idler frequency was stabilized onto the line center by wavelength modulation method. The linewidth of the saturation dip was estimated to be 4.7 MHz, and the achieved frequency stability was 3.9 kHz (3.6×10(-11)).

Triple-wavelength Nd-laser system by cascaded electro-optic periodically poled lithium niobate Bragg modulator.

This study presents a diode-pumped cw triple-wavelength Nd:GdVO4 laser system using an electro-optic periodically poled lithium niobate (PPLN) Bragg modulator. The PPLN consists of two cascaded sections, 20.3 µm and 25.7 µm, functioning as loss modulators for 1063 and 1342 nm at the same Bragg incident angle. When switching the dc voltages on PPLN and applying 25 W pump power, the output wavelength can be selected among 912, 1063, and 1342 nm with output power of 2, 5, and 1.4 W, respectively. The device is capable of triple-wavelength generation simultaneous when applied voltages are 180 (Λ = 20.3 µm) and -50 V (Λ = 25.7 µm) at a 25 W pump power. Gain competition induced power instability was also observed.