High average power (105†W) Fe:ZnSe laser pumped by radiation of laser diode side-pumped Er:YAG lasers.

A high average power re-frequency operation Fe:ZnSe laser using laser diode side-pumped free-running Er:YAG lasers as activating sources is presented. Two pieces of subsurface layer doped Fe:ZnSe polycrystal are adoptive in a reflective resonator configuration and face-cooled by liquid nitrogen. A maximal Fe:ZnSe laser power of 105 W at a wavelength of 4.1 µm is achieved upon pumping by ten home-made Er:YAG lasers with fiber coupled output working at a frequency of 250 Hz and a pulse duration of ∼420 µs. Corresponding to the maximum Fe:ZnSe laser power, the optical-optical efficiency and slope efficiency with respect to the absorbed pump power are 43% and 44% respectively. The beam quality factor M2 is measured to be 3.4. To the best of our knowledge, it is the highest output average power of an Fe:ZnSe laser reported.

A longitudinal examination of the measurement properties and invariance of the Sleep Condition Indicator in Chinese healthcare students.

BACKGROUND: The Sleep Condition Indicator (SCI), an insomnia measurement tool based on the updated Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria with sound psychometric properties when applied in various populations, was evaluated here among healthcare students longitudinally, to demonstrate its measurement properties and invariance in this particularly high-risk population. METHODS: Healthcare students of a Chinese university were recruited into this two-wave longitudinal study, completing the simplified Chinese version of the SCI (SCI-SC), Chinese Regularity, Satisfaction, Alertness, Timing, Efficiency, Duration (RU_SATED-C) scale, Chinese Patient Health Questionnaire-4 (PHQ-4-C), and sociodemographic variables questionnaire (Q-SV) between September and November 2022. Structural validity, measurement invariance (MI), convergent and discriminant validity, internal consistency, and test-retest reliability of the SCI-SC were examined. Subgroups of gender, age, home location, part-time job, physical exercise, and stress-coping strategy were surveyed twice to test cross-sectional and longitudinal MI. RESULTS: We identified 343 valid responses (62.9% female, mean age = 19.650 ± 1.414 years) with a time interval of seven days. The two-factor structure was considered satisfactory (comparative fit index = 0.953-0.989, Tucker-Lewis index = 0.931-0.984, root means square error of approximation = 0.040-0.092, standardized root mean square residual = 0.039-0.054), which mostly endorsed strict invariance except for part-time job subgroups, hence establishing longitudinal invariance. The SCI-SC presented acceptable convergent validity with the RU_SATED-C scale (r ≥ 0.500), discriminant validity with the PHQ-4-C (0.300 ≤ r < 0.500), internal consistency (Cronbach's alpha = 0.811-0.835, McDonald's omega = 0.805-0.832), and test-retest reliability (intraclass correlation coefficient = 0.829). CONCLUSION: The SCI-SC is an appropriate screening instrument available for assessing insomnia symptoms among healthcare students, and the promising measurement properties provide additional evidence about validity and reliability for detecting insomnia in healthcare students.

9 kilowatt-level direct-liquid-cooled Nd:YAG multi-module QCW laser.

An average 9 kilowatt-level direct-D2O-cooled side-pumped Nd:YAG multi-disk laser resonator at QCW mode with a pulse width of 250µs is presented, in which the straight-through geometry is adopted the oscillating laser propagates through 40 Nd:YAG thin disks and multiple cooling D2O flow layers in the Brewster angle. Much attention has been paid on the design of the gain module, including an analysis of the loss of the laser resonator and the design of the Nd:YAG thin disk. Experimentally, laser output with the highest pulse energy of more than 20 J is obtained at a repetition frequency of 10 Hz. At high repetition frequency, the average output power 9.8 kW with ηo-o = 26% and 9.1 kW with ηo-o = 21.8% are achieved in the stable resonator and unstable resonator, respectively, and in the corresponding beam quality factor ßstable= 14.7 and ßunstable= 9.5 respectively. To the best of our knowledge, this is the first demonstration of a 9 kilowatt-level direct-liquid-cooled Nd:YAG thin disk laser resonator.

Waveguide random laser based on a disordered ZnSe-nanosheets arrangement.

A waveguide scheme is constructed by coating the matrix of randomly distributed ZnSe nanosheet structures with a layer of dye-doped polymer, which provides strong feedback or gain channels for the emission from the dye molecules and enables successful running of a random laser with FWHM of ~0.65 nm. The strong scattering by the nanostructures and the strong confinement provided by the active waveguide layer are the key essentials for the narrow-band and low-threshold operation of this random laser. The random laser scheme reveals an obvious two-threshold behavior, which is corresponding to the thresholds of TM and TE modes. The feedback mechanisms for laser action are investigated by power Fourier transforming of the spectra. This kind of active waveguide not only provides high quality confinement of the radiation for efficient amplification, but also enables possible directional output of this kind of random laser.

7kW direct-liquid-cooled side-pumped Nd:YAG multi-disk laser resonator.

A direct-liquid-cooled side-pumped Nd:YAG multi-disk QCW laser resonator is presented, in which the oscillating laser propagates through multiple thin disks and cooling flow layers in Brewster angle. Twenty Nd:YAG thin disks side-pumped by LD arrays are directly cooled by flowing deuteroxide at the end surfaces. A laser output with the highest pulse energy of 17.04 J is obtained at the pulse width of 250 µs and repetition rate of 25 Hz, corresponding to an optical-optical efficiency of 34.1% and a slope efficiency of 44.5%. The maximum average output power of 7.48 kW is achieved at the repetition rate of 500 Hz. Due to thermal effects, the corresponding optical-optical efficiency decreases to 30%. Under the 12.5 kW pumping condition while not oscillating, the wavefront of a He-Ne probe passing through the gain module is as low as 0.256 µm (RMS) with the defocus and tetrafoil subtracted.

[Characterization of Nd Doped Films Prepared by Femtosecond Pulsed Laser Deposition].

Thin films of Nd:YAG and Nd:Glass were prepared on Si(100) substrate by pulsed laser deposition technology. The morphology of film surface and cross section, composition, absorption spectrum and photoluminescence (PL) spectra of films were investigated by scanning electron microscope (SEM), energy disperse spectroscopy (EDS), Fourier transform infrared spectrometer (FTIR), optical parametric oscillator (OPO) and grating spectrometer. The results show that both Nd:YAG films and Nd:Glass films grown on the substrates at room temperature are amorphous. Nd:YAG films grown by PLD contain Nd element with 0.15 at. % stoichiometric proportion. The absorption spectrum of bulk Nd:YAG target rather than deposited films exhibit two absorption peaks at 750 and 808 nm. There are no evident peaks in the photoluminescence spectra curve of Nd:YAG films. However, the photoluminescence spectra of Nd:Glass films with two sharp peaks at the wavelength of 877 and 1064 nm are observed. It indicates that Nd is doped into glass host as optically active Nd(3+) ions when Nd:Glass films grow at room temperature. But for Nd:YAG films, Nd don't incorporate into YAG host as Nd(3+) ions.

Fiber-based tunable microcavity fluidic dye laser.

We investigate a tunable fluidic dye laser formed by a microcavity filled with a dye solution. We achieve a wide 18 nm tunability of the laser wavelength by controlling the cavity length for the first time. The microcavity is made of a silica capillary and two aligned fibers with end faces Au-coated. The Rhodamine 6G dye solution flowing through the microcavity is pumped by 532 nm wavelength laser pulses. Laser emission around 570 nm in the form of TE mode with a threshold of about 58 µJ/pulse is obtained. This work suggests a fiber-based convenient approach to achieve wavelength tunability and integration with lab-on-a-chip systems.

High-efficiency visible-light-driven oxidation of primary C-H bonds in toluene over a CsPbBr3 perovskite supported by hierarchical TiO2 nanoflakes.

Photocatalytic oxidation of toluene to valuable fine chemicals is of great significance, yet faces challenges in the development of advanced catalysts with both high activity and selectivity for the activation of inert C(sp3)-H bonds. Halide perovskites with remarkable optoelectronic properties have shown to be prospective photoactive materials, but the bulky structure with a small surface area and severe recombination of photogenerated electron-hole pairs are obstacles to application. Here, we fabricate a hierarchical nanoflower-shaped CsPbBr3/TiO2 heterojunction by assembling CsPbBr3 nanoparticles on 2D TiO2 nanoflake subunits. The design significantly downsizes the size of CsPbBr3 from micrometers to nanometers, and forms a type II heterojunction with intimate interfacial contact between CsPbBr3 and TiO2 nanoflakes, thereby accelerating the separation and transfer of photogenerated charges. Moreover, the formed hierarchical heterojunction increaseslight absorption by refraction and scattering, offers a large surface area and enhances the adsorption of toluene molecules. Consequently, the optimized CsPbBr3/TiO2 exhibits a high performance (10 200 µmol g-1 h-1) for photocatalytic toluene oxidation with high selectivity (85%) for benzaldehyde generation under visible light. The photoactivity is about 20 times higher than that of blank CsPbBr3, and is among the best photocatalytic performances reported for selective oxidation of toluene under visible light irradiation.

[Spatial localized distribution of modes in two-dimension random medium].

Based on the time dependent theory, FDTD algorithm was used to numerically solve Maxwell's equations and rate equations. By dividing the two-dimension random medium, the emission spectra of different region under different pumping intensities were obtained. The calculated results show that the emission spectra of different region are different, the energy of emission is mainly distributed in some certain region, and the pumping efficiency is different. Also spatial extent overlap of modes is reproduced. With this method, the dependence of random distribution on lasing can be analyzed and it should be useful for the preparation of pseudo-random medium.

A CEEMD-ARIMA-SVM model with structural breaks to forecast the crude oil prices linked with extreme events.

This paper develops an integrated framework to forecast the volatility of crude oil prices by considering the impacts of extreme events (structural breaks). The impacts of extreme events are vital to improving prediction accuracy. Aiming to demonstrate the crude oil price fluctuation and the impacts of external events, this paper employs the complementary ensemble empirical mode decomposition (CEEMD). It decomposes the crude oil price into some constituents at various frequencies to extract a market fluctuation, a shock from extreme events and a long-term trend. The shock from extreme events is found to be the most crucial element in deciding the crude oil prices. Then we combine the iterative cumulative sum of squares (ICSS) test with the Chow test to get the structural breaks and analyze the extreme event impacts. Finally, this paper combines the structural breaks, the autoregressive integrated moving average (ARIMA) model, and the support vector machine (SVM) to make a forecast of the crude oil prices. The empirical process proves that the CEEMD-ARIMA-SVM model with structural breaks performs the best when compared with the other ARIMA-type models and SVM-type models. The framework offers an insightful view to help decision-makers and can be used in many areas. Supplementary Information: The online version contains supplementary material available at 10.1007/s00500-022-07276-5.

Ultrathin Two-Dimensional ZnIn2S4/Nix-B Heterostructure for High-Performance Photocatalytic Fine Chemical Synthesis and H2 Generation.

Photocatalytic H2 evolution coupled with organic transformation provides a new avenue to cooperatively produce clean fuels and fine chemicals, enabling a more efficient conversion of solar energy. Here, a novel two-dimensional (2D) heterostructure of ultrathin ZnIn2S4 nanosheets decorated with amorphous nickel boride (Nix-B) is prepared for simultaneous photocatalytic anaerobic H2 generation and aromatic aldehydes production. This ZnIn2S4/Nix-B catalyst elaborately combines the ultrathin structure advantage of the ZnIn2S4 semiconductor and the cocatalytic function of Nix-B. A high H2 production rate of 8.9 mmol h-1 g-1 is delivered over the optimal ZnIn2S4/Nix-B with a stoichiometric production of benzaldehyde, which is about 22 times higher than ZnIn2S4. Especially, the H2 evolution rate is much higher than the value (2.8 mmol h-1 g-1) of the traditional photocatalytic half reaction of H2 production with triethanolamine as a sacrificial agent. The apparent quantum yield reaches 24% at 420 nm, representing an advanced photocatalyst system. Moreover, compared with traditional sulfide, hydroxide, and even noble metal modified ZnIn2S4/M counterparts (M = NiS, Ni(OH)2, Pt), the ZnIn2S4/Nix-B also maintains markedly higher photocatalytic activity, showing a highly efficient and economical advantage of the Nix-B cocatalyst. This work sheds light on the exploration of 2D ultrathin semiconductors decorated with novel transition metal boride cocatalyst for efficient photocatalytic organic transformation integrated with solar fuel production.

Effective random laser action in Rhodamine 6G solution with Al nanoparticles.

We have studied the random laser action in Rhodamine 6G (Rh6G) ethylene glycol solution with Al nanoparticles. The experiment results are obtained by pumping with a nanosecond (7 ns) laser pulse, which demonstrated the existence of effective random laser emission. It is found that the threshold of the random laser depends on the concentration of the Rh6G and the concentration of Al nanoparticles. The concentration and diameter of Al nanoparticles have effects on the optical path; a higher concentration or a larger diameter results in a shorter optical path length. Also multimode survival and mode competition have been observed at a relatively high concentration (0.08 M) of Rh6G, where the concentration of Al nanoparticles is 0.0015 M.