High Pump Energy Research Articles

Pure-quartic soliton self-frequency shift in a mode-locked fiber laser

The pure-quartic soliton (PQS) offers the advantage of a wide spectrum and approximately Gaussian temporal profile, which has the potential to obtain high-energy ultrafast laser pulses. Thus, exploring the role of stimulated Raman scattering in the formation and propagation of PQSs in fiber lasers is crucial, especially considering the greater propensity for highpower and short PQS pulses compared to traditional solitons. Here, we present the modeling of a self-frequency shift (SFS) fiber laser based on the PQS, emphasizing the impact of fourth-order dispersion and the Raman effect. The significant red-shift in wavelength is discovered as the pump energy increases, revealing that the emergence of SFS is a universal attractor in mode-locked PQS fiber laser systems. Our simulations demonstrate that such wavelength tunability is a direct byproduct of the gain bandwidth limit and the stimulated Raman scattering for PQSs inside the fiber cavity, while the evolution dynamics in the gain and passive fiber show obvious differences. However, we find that the effect of SFS in a PQS fiber laser is compromised by a trade-off with the degradation of pulse quality, such as reshaping the oscillating tail and destroying the symmetry of the emission pulse. This Raman-induced nonlinear process under high pump energy facilitates the discovery of the comprehensive complexity of science for PQSs suffering from higher-dimensional forms of nonlinear effects in fiber lasers.

Toward high-energy few-cycle optical vortices with minimized topological charge dispersion.

A simple approach to generate high-energy few-cycle optical vortices with minimized topological charge dispersion is introduced. By means of numerical simulations, it is shown that, by leveraging the intrinsic properties of optical parametric chirped pulse amplification (OPCPA), clean transfer of topological charge from a high-energy narrowband pump pulse to a broadband idler is feasible under certain particular conditions, enabling the generation of high-energy few-cycle vortex pulses with extremely low topological charge dispersion.

Vibrational thermal pool multi-level theoretical model and design simulation of HBr-filled hollow-core fiber gas laser

The hollow-core fiber gas laser (HCFGL) has developed into a significant mid-infrared laser source, but the development of theoretical model still lags behind experimental progress. In this work, we propose a multi-level vibrational thermal pool (VTP) model of HBr-filled HCFs, which comprehensively considers the rovibrational relaxation effects on laser gain in reasonable approximations of transition coefficients, and studies the laser characteristics on multi-line lasing, bottleneck effect, line competition, etc. The VTP model shows more precise results of laser slope efficiency, and threshold than previous models while fitting the experimental data very well, and successfully predicts an output bottleneck at 1 W pump. The P-branch laser is relatively advantageous over the R-branch laser for its larger Einstein <inline-formula><tex-math id="M1">\begin{document}$A$\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20240428_M1.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20240428_M1.png"/></alternatives></inline-formula> coefficient and emission cross section, and the seed injection can intensify the line competition and reach the highest P4 power proportion of 80%. The VTP model reveals that the output of various pump lines has a pattern similar to the Boltzmann distribution, suggesting that the distribution of ground rotational levels limits the laser gain of pump lines. Moreover, we discuss the photon leakage in high-energy pulsed pumping conditions. With the introduction of the leaking coefficient, this model shows relaxation oscillations and laser slope efficiencies close to experimental values and greater than the results in the CW condition, and solves the overpump problem in pulsed pump simulation. Finally, we confirm that the photon leakage is intensified at high repetition rate and the leaking coefficient should relate to the pulse repetition rate. This work develops a comprehensive modeling method for MIR laser simulation and this model is also applicable to various gas-filled HCFGLs.

Photon Energy‐Dependent Optical Spin‐Orbit Torque in Heavy Metal–Ferromagnet Bilayers

AbstractThe manipulation of magnetization through optically generated ultrafast spin currents is a fascinating area that needs a thorough understanding for its potential future applications. In this work, a comprehensive investigation of helicity‐driven optical spin‐orbit torque in heavy metal/ferromagnetic metal heterostructures is presented, specifically cobalt capped with gold or platinum, subject to laser pumping at different wavelengths. The results demonstrate up to tenfold enhancement in optical spin‐orbit torque quantum efficiency for gold compared to platinum of the same thickness when pumped with a visible laser. Additionally, the study provides the first experimental analysis of the photon energy dependence of optical spin‐orbit torque and derives the optical spin orientation spectra for both gold/cobalt and platinum/cobalt heterostructures. A key insight gained from the study is the impact of photon energy‐dependent spin transport in the system, which suggests the use of a high photon energy pump for efficient spin transport. These findings highlight the potential of spin current generation and manipulation in gold/ferromagnet heterostructures for a wide range of applications such as all‐optical magnetization switching, spin‐wave generation and control, and spintronic terahertz emission.

A new static mixer concept for enhanced desalination performance in flow-electrode capacitive deionization (FCDI) systems

Poor electrical conductivity and high pumping energy cost are two major challenges that limit the desalination performance of flow-electrode capacitive deionization (FCDI) systems. In this study, we address these limitations by utilizing low carbon loading suspensions (≤2 wt%) with water-like viscosity in a novel static mixer design, referred to as a membrane-assisted static mixer (MASM). MASMs improved the electrical conductivity of the slurry by minimizing the charge transport distances between the active material and current collector as the ion-exchange membrane was compressed directly against the current collector surface (i.e., zero-gap flow field). Continuous mixing of the active material was achieved by controlling the displacement of the membrane via pressure fluctuations from the peristaltic pumps. A parametric study of three MASM flow field geometries was performed at varying flow rates of 1, 3, 5, 10, 15 and 25 mL min−1 and 0.5, 1, and 2 wt% activated carbon (AC). The best-performing flow configuration (2 wt% AC and 15 mL min−1) showed a high salt removal rate of 4.424 μg NaCl cm−2 s−1 with a total energy consumption of 98.95 kJ mol−1.

Replica symmetry breaking in a colloidal plasmonic random laser with gold-coated triangular silver nanostructures.

Plasmonic random lasers have drawn significant attention recently due to their versatility, low threshold, and the possibility of achieving tunable and coherent/incoherent outputs. However, in this Letter, the phenomenon of replica symmetry breaking is reported in intensity fluctuations of a rarely used colloidal plasmonic random laser (RL) illumination. Triangular nanosilver scatter particles produced incoherent RL action when used in a dimethylformamide (DMF) environment in a Rhodamine-6G gain medium. The use of gold-coated triangular nanosilver as the scatterer in place of triangular nanosilver offered a dual contribution of scattering and lower photo-reabsorption, which caused a reduction in the lasing threshold energy of 39% compared to that obtained with the latter. Further, due to its long-term photostability and chemical properties, a phase transition from the photonic paramagnetic to the glassy phase is observed experimentally in the RL system used. Interestingly, the transition occurs at approximately the lasing threshold value, which is a consequence of stronger correlation of modal behaviors at high input pump energies.

Generation of vortex N 2 <i/> + lasing

Harnessing structured light is fascinating for its multidisciplinary applications, e.g., in remote driving microrobots, sensing, communications, and ultrahigh resolution imaging. Here, we experimentally demonstrated the generation of a vortex N2+ lasing pumped by a wavefront structured near-IR femtosecond pulse with orbital angular momentum. The topological charge of the N2+ lasing was measured to be twofold that of the pump beam. Compared to the case with a pump beam of a plane wavefront, the N2+ lasing generation efficiency is much higher for the vortex pump beam at high pumping energy, which has a higher clamping intensity by reducing the on-axis plasma density. Our results herald a march toward remote structured N2+ lasing.

Design and optimization of a high-energy optical parametric amplifier for broadband, spectrally incoherent pulses.

Spectrally incoherent laser pulses with sufficiently large fractional bandwidth are in demand for the mitigation of laser-plasma instabilities occurring in high-energy laser-target interactions. Here, we modeled, implemented, and optimized a dual-stage high-energy optical parametric amplifier for broadband, spectrally incoherent pulses in the near-infrared. The amplifier delivers close to 400 mJ of signal energy through noncollinear parametric interaction of 100-nJ-scale broadband, spectrally incoherent seed pulses near 1053 nm with a narrowband high-energy pump operating at 526.5 nm. Mitigation strategies for high-frequency spatial modulations in the amplified signal caused by index inhomogeneities in the Nd:YLF rods of the pump laser are explored and discussed in detail.

Optimization criteria of flow-electrode and feed water flow rate to achieve positive net power of flow-electrode capacitive mixing

Flow-electrode capacitive mixing (F-CapMix) produces continuous electricity due to infinite ion storage capacity of the flow-electrode. Researchers have predicted that achieving positive net power from F-CapMix is difficult due to the high pumping energy consumption of flow-electrodes. In this work, the power densities and net power densities of F-CapMix were evaluated under different flow rate condition of feed water (FW) and flow-electrode (FE) using low- and high-viscosity FEs. The power densities increased with a FE flow rate increment and a flow rate reduction of the FW. The power density difference under low and high flow-rate ratios between the FE and FW was small. As the power densities tended to become saturated with the flow rate ratio increase, indicating that a fast flow of the FE in F-CapMix is not necessary. Positive net power densities were achieved at low flow rates. The difference in the net power densities between high- and low-viscosity FEs was smaller than the power density difference between the two FEs, due to the high pumping energy consumption of highly viscous FE. Based on these results, the criteria for flow-rate optimization for the F-CapMix positive net power were suggested.

Upconverting temperature sensors with high activation energy and low pump threshold

Absolute and relative sensitivity of the developed Er3+/Yb3+/Mo6+:Bi2WO6 phosphors.

The Combined Effects of the Membrane and Flow Channel Development on the Performance and Energy Footprint of Oil/Water Emulsion Filtration.

Membrane filtration is a promising technology for oil/water emulsion filtration due to its excellent removal efficiency of microdroplets of oil in water. However, its performance is highly limited due to the fouling-prone nature of oil droplets on hydrophobic membranes. Membrane filtration typically suffers from a low flux and high pumping energy. This study reports a combined approach to tackling the membrane fouling challenge in oil/water emulsion filtration via a membrane and a flow channel development. Two polysulfone (PSF)-based lab-made membranes, namely PSF- PSF-Nonsolvent induced phase separation (NIPS) and PSF-Vapor-induced phase separation (VIPS), were selected, and the flow channel was modified into a wavy path. They were assessed for the filtration of a synthetic oil/water emulsion. The results showed that the combined membrane and flow channel developments enhanced the clean water permeability with a combined increment of 105%, of which 34% was attributed to the increased effective filtration area due to the wavy flow channel. When evaluated for the filtration of an oil/water emulsion, a 355% permeability increment was achieved from 43 for the PSF-NIPS in the straight flow channel to 198 L m-2 h-1 bar-1 for the PSF-VIPS in the wavy flow channel. This remarkable performance increment was achieved thanks to the antifouling attribute of the developed membrane and enhanced local mixing by the wavy flow channel to limit the membrane fouling. The increase in the filtration performance was translated into up to 78.4% (0.00133 vs. 0.00615 kWh m-3) lower in pumping energy. The overall findings demonstrate a significant improvement by adopting multi-pronged approaches in tackling the challenge of membrane fouling for oil/water emulsion filtration, suggesting the potential of this approach to be applied for other feeds.

Experimental and theoretical study of optical properties of pyrromethene (PM‐597) laser dye in binary eco‐friendly solvent

AbstractThe interaction of pyrromethene (PM‐597) laser dye with binary mixture of [1‐butyl‐3‐methylimidazolium tetrafluoro‐borate (BMIM BF4)] ionic liquid with water [BMIM BF4: H2O] as binary eco‐friendly solvent, were investigated experimentally and theoretically by means of photophysical properties, amplified spontaneous emission (ASE), photostability, electronic ground state of molecular structures of PM‐597, BMIM BF4 and mixture of (PM‐597/BMIM BF4) using the density functional theory (DFT) technique, molecular orbitals, energy gap (Eg) among HOMO and LUMO, and the maps of molecular electrostatic potential (MESP) for PM‐597 and mixture of (PM‐597/BMIM BF4) in gas phase were calculated using B3LYP/6‐31G(d) level of theory. The refractive index (nD) and density (ρ) values for binary mixes of ionic liquid with water [BMIM BF4: H2O] with different ratios, increases as molecular mass of ionic liquid (BMIM BF4) in water increases. The frequency doubling Nd‐YAG laser of 532 nm was used to investigate amplified spontaneous emission (ASE). Aside from that, the efficiency of energy conversion was explored. Efficiency is relatively high, and 20.6% was achieved, with good photostability in case of 5 × 10−4 mol/L of PM‐597 in binary mixture of [90% BMIM BF4: 10% H2O] that was a decrease to ~48.3% of the initial amplified spontaneous emission, this output energy was observed after pumping by 72,000 shots at relatively high repetition rate (10 Hz) and pumping energy (40 mJ). In this research, we had used the mixture of [(BMIM BF4: H2O] with different ratios, as binary eco‐friendly solvent instead of harmful organic solvents.

Scalable optical-to-terahertz converter with a prism-coupled plane-parallel lithium niobate plate.

A nonlinear optical converter of femtosecond laser pulses to terahertz radiation, which combines the tilted-pulse-front pumping and prism coupling techniques, is proposed and experimentally tested. In contrast to the conventional tilted-pulse-front scheme with a prism-shaped LiNbO3 crystal, the converter consists of a plane-parallel LiNbO3 plate sandwiched between two dielectric prisms. One prism is used to couple the pump beam into the LiNbO3 plate, another prism couples the generated terahertz radiation out of the plate. The proposed scheme enables scaling to large-diameter LiNbO3 wafers and large-aperture high-energy pump laser beams resulting in generation of strong terahertz fields. In a proof-of-principle experiment with a 1-mm thick, small size (1 × 2 cm2) LiNbO3 plate pumped by a mJ-class laser, the conversion efficiency comparable to that of the conventional scheme (∼0.1%) was demonstrated.

Low-threshold and narrow-emission random lasing in a self-assembly TiN nanoparticle-doped carbon quantum dot/DCM nanowire composite

The random lasing in quantum dot systems is in anticipation for widespread applications in biomedical therapy and image recognition, especially in random laser devices with high brightness and high monochromaticity. Herein, low-threshold, narrowband emission, and stable random lasing is realized in carbon quantum dot (CQD)/DCM nanowire composite-doped TiN nanoparticles, which are fabricated by the mixture of carbon quantum dots and self-assembly DCM dye molecules. The Förster resonance energy transfer process results in a high luminescence efficiency for the composite of carbon dots and DCM nanowires, allowing significant random lasing actions to emerge in CQD/DCM composite as TiN particles are doped that greatly enhance the emission efficiency through the plasmon resonance and random scattering. Thus, sharp and low-threshold random lasing is finally realized and even strong single-mode lasing occurs under higher pumping energy in the TiN-doped CQD/DCM composite. This work provides a promising way in high monochromaticity random laser applications.

Design a novel air to water pressure amplifier powered by PV system for reverse osmosis desalination

This work aims to design a novel standalone small-size air-to-water pressure amplifier (ATWPA) for RO desalination system with low energy consumption. A small DC PV system, pneumatic system, and solar water heater were designed and used to operate the ATWPA at different air pressure (1–5 bar) and heating water (30–45 °C), hence avoiding using a high-pressure and high-energy water pump. The ATWPA has a smart electronic circuit with a feedback system and controls the IR to synchronize the piston movement with pressure and water discharge. The feed air pressure was maximized from 5 bar to 27.9 bar, i.e. the pressure has amplified by 458% where it creates enough pressure to overcome the membrane resistance. The power consumption of ATWPA varied from 0.0 to 3.5 W in compression and suction strokes, respectively and maximum energy consumption was 105 Wh. Increasing feed water temperature and operating air pressure led to increasing freshwater productivity. The preheating of saline water to 45 °C and increasing pressure to 5 bar increased freshwater productivity to 58.8 L/h and decreased energy consumption.

Background-free single-beam coherent Raman spectroscopy assisted by air lasing.

We develop a background-free single-beam coherent Raman scattering technique enabling the high-sensitivity detection of greenhouse gases. In this scheme, Raman coherence prepared by a femtosecond laser is interrogated by self-generated narrowband air lasing, thus allowing single-beam measurements without complex pulse shaping. The unique temporal and spectral characteristics of air lasing are beneficial for improving the signal-to-noise ratio and spectral resolution of Raman signals. With this method, SF6 gas present at a concentration of 0.38% was detected in an SF6-air mixture. This technique provides a simple and promising route for remote detection due to the low divergence of Raman signals and the availability of high-energy pump lasers, which may broaden the potential applications of air lasing.

Explore the correlation between intervalley scattering and phonon bottleneck effect on the hot carrier relaxation in bulk GaSb and InN for hot carrier solar cells

Slowed carrier intervalley scattering (IVS) may trap some photo-excited carriers within side valleys and reduce the overall thermalization rate. On the other hand, the thermalization rate could also be significantly retarded within the gamma valley by slowing the Klemens decay due to a large phononic bandgap via the phonon bottleneck effect (PBE). However, the correlation between IVS and PBE on slowing the carrier relaxation rate is still unclear. Herein, high-quality bulk InN and GaSb with similar electronic bandgap but remarkably different phononic structures are studied to clarify the above correlation through picosecond time-resolved photoluminescence. The occurrence of IVS is controlled by using different pump energies at high carrier density (∼1019 cm−3). The relaxations of carriers excited at the band edge just above and far above the side valley threshold are, therefore, studied in GaSb. It shows that the effective hot carrier lifetime (τ1) of GaSb gets significantly extended with higher pump energy mainly due to more carriers being trapped in side valleys through IVS. Nevertheless, the longest τ1 of GaSb is still shorter than the shortest τ1 of InN with a more polar nature and larger phononic bandgap. This implies that PBE plays a more decisive role in retarding Γ valley carrier relaxation than the slowed IVS. It indicates that the large phononic bandgap and Fröhlich coupling constant are keys to the slow thermalization rate if the Fröhlich interaction dominates. If the deformation potential interaction dominates this process, then low side valley threshold energy and the Fröhlich constant determine the reduction of the overall thermalization rate.

Role of Solvent in Electron-Phonon Relaxation Dynamics in Core-Shell Au-SiO2 Nanoparticles.

Relaxation dynamics of plasmons in Au-SiO2 core-shell nanoparticles have been followed by femtosecond pump-probe technique. The effect of excitation pump energy and surrounding medium on the time constants associated with the hot electron relaxation has been elucidated. A gradual increase in the electron-phonon relaxation time with pump energy is observed and can be attributed to the higher perturbation of the electron distribution in AuNPs at higher pump energy. Variation in time constants for the electron-phonon relaxation in different solvents is rationalized on the basis of their thermal conductivities, which govern the rate of dissipation of heat of photoexcited electrons in the nanoparticles. On the other hand, phonon-phonon relaxation is found to be much less effective than electron-phonon relaxation for the dissipation of energy of the excited electron and the time constants associated with it remain unaffected by thermal conductivity of the solvent.

Hybrids of perovskite nanocrystals and SiO2 microfiber for robust and long-haul transmittable fiber lasers

Fiber lasers have broad prospects for the development of tunable high-performance photonic equipment and active fiber devices. However, they are still facing challenges, such as the limited emission wavelength and relatively high pump energy. Perovskite nanocrystals possess a large absorption cross-section, high quantum efficiency, long Auger lifetime, and tunable emission wavelength, which have been recognized as the promising gain media. In this work, a unique method was developed to form a type of fiber laser device based on high-quality SiO2 microfibers integrated with solution-processed perovskite nanocrystals. By this way, the robust and efficient fiber laser with characteristics of long-haul transmission, tunable laser mode, and high polarization state was effectively obtained. Our results represent a significant advancement in fiber lasers based on favorable perovskite nanocrystals and high-quality SiO2 microfiber and provide new possibilities for active fiber devices.

Ultra low-pressure filtration system for energy efficient microalgae filtration

Microalgae-based products have gained growing interest leading to an increase in large-scale cultivation. However, the high energy associated with microalgae harvesting becomes one of the bottlenecks. This study evaluated an energy-efficient microalga harvesting via ultra-low-pressure membrane (ULPM) filtration (<20 kPa) in combination with aeration. ULPM offered various benefits especially in terms of reducing the energy consumption due to it operated under low transmembrane pressure (TMP). High TMP often associated with high pumping energy hence would increase the amount of energy consumed. In addition, membrane with high TMP would severely affect by membrane compaction. Results showed that membrane compaction leads to up to 66 % clean water permeability loss when increasing the TMP from 2.5 to 19 kPa. The Chlorella vulgaris broth permeabilities decreased from 1660 and 1250 to 296 and 251 L/m2hrbar for corresponding TMPs for system with and without aeration, respectively. However, it was found that membrane fouling was more vulnerable at low TMP due to poor foulant scouring from a low crossflow velocity in which up to 56 % of permeability losses were observed. Membrane fouling is the biggest drawback of membrane system as it would reduce the membrane performance. In this study, aeration was introduced as membrane fouling control to scour-off the foulant from membrane surface and pores. In terms of energy consumption, it was observed that the specific energy consumption for the ULPM were very low of up to 4.4 × 10−3 kWh/m3. Overall, combination of low TMP with aeration offers lowest energy input.