Gas Laser Research Articles

High-brightness scalable continuous-wave single-mode photonic-crystal laser

Realizing large-scale single-mode, high-power, high-beam-quality semiconductor lasers, which rival (or even replace) bulky gas and solid-state lasers, is one of the ultimate goals of photonics and laser physics. Conventional high-power semiconductor lasers, however, inevitably suffer from poor beam quality owing to the onset of many-mode oscillation1,2, and, moreover, the oscillation is destabilized by disruptive thermal effects under continuous-wave (CW) operation3,4. Here, we surmount these challenges by developing large-scale photonic-crystal surface-emitting lasers with controlled Hermitian and non-Hermitian couplings inside the photonic crystal and a pre-installed spatial distribution of the lattice constant, which maintains these couplings even under CW conditions. A CW output power exceeding 50 W with purely single-mode oscillation and an exceptionally narrow beam divergence of 0.05° has been achieved for photonic-crystal surface-emitting lasers with a large resonant diameter of 3 mm, corresponding to over 10,000 wavelengths in the material. The brightness, a figure of merit encapsulating both output power and beam quality, reaches 1 GW cm−2 sr−1, which rivals those of existing bulky lasers. Our work is an important milestone toward the advent of single-mode 1-kW-class semiconductor lasers, which are expected to replace conventional, bulkier lasers in the near future.

P194 Computed cardiopulmonography (CCP) and the idealised lung clearance index (iLCI) in early-stage cystic fibrosis

LCI is a sensitive parameter to track CF lung disease but is influenced by extra-pulmonary factors such as equipment deadspace, breathing volume and rate which can reduce accuracy. This study explores a novel approach, CCP, to calculate an idealised LCI (iLCI). CCP utilises two components: (a) a novel, accurate laser gas analyser (LGA; Smith NMJ et al. Sci Rep. 2021) and (b)a lung model with extra-pulmonary factors removed.

Er/Yb co-doped 345-W all-fiber laser at 1535 nm using hybrid fiber.

The 1.5-µm fiber laser is widely used in the fields of laser lidar, remote sensing, and gas monitoring because of its advantages of being eye-safe and exhibiting low atmospheric transmission loss. However, due to the ∼1-µm amplified spontaneous emission (ASE) of the Er/Yb co-doped fiber (EYDF), it is difficult to improve the laser power. Here, we simulated the effect of the Er3+ concentration and the seed power on ∼1-µm ASE, and fabricated a large mode area EYDF by the modified chemical vapor deposition process. Additionally, a piece of ytterbium-doped fiber was introduced into the master oscillator power amplifier (MOPA) configuration to absorb the generated ∼1-µm ASE simultaneously. Experimental results show that an output power of 345 W with a slope efficiency of 43% at 1535 nm is obtained in an all-fiber configuration, profiting from effective suppression of ∼ 1-µm ASE. To the best of our knowledge, this is the highest output power available with an Er/Yb co-doped fiber from an all-fiber MOPA configuration.

Influence of the Relative Position of Powder–Gas Jet and Laser Beam on the Surface Properties of Inconel 625 Coatings Produced by Extreme High-Speed Laser Material Deposition (EHLA)

Laser material deposition (LMD) is a widely used coating process in industry. However, to increase its economic appeal, higher process speeds are required. The solution to this challenge is an innovative modification known as extreme high-speed laser material deposition (EHLA). EHLA allows for an impressive increase in process speed from 2 m/min for conventional LMD to 500 m/min. With the ability to adjust process parameters, EHLA can generate tailor-made surface properties, expanding its potential application beyond current industrial uses. In this novel study, we explore the effects of relative positioning between tools (laser beam and powder–gas jet) and substrate on the surface properties of EHLA coatings. By laterally and axially offsetting the tools, the proportional energy coupling of the laser radiation into the powder–gas jet and substrate can be modified. Altering the position of the powder–gas jet can also affect the weld pool flow or number of particle attachments, thereby affecting surface properties. This approach allows for the adjustment of surface roughness over a wide range—from smooth, quasi-laser-polished surfaces to rough surfaces covered with particle adhesions.

Population inversion mechanism of optically pumped metastable rare gas based on laser-induced preionization

A 532 nm laser was used to induce ionization of Ar–He mixture, and metastable 4s [3/2]2 level Ar atoms were prepared. The interaction mechanism between laser, Ar atoms, He atoms and free electrons in laser-induced plasma (LIP) was revealed. Through time-resolved atomic emission spectroscopy, two regimes separated by a few microseconds were found during temporal evolution of Ar I 811.5 nm (4p [5/2]3→4s [3/2]2) line. It was demonstrated that the first regime was generated by the “photoexcitation + radiation + collisional relaxation” process, while the second regime was generated by the “ion-electron recombination” process. The above conclusion was confirmed again by the temporal evolution of electron temperature and electron density, and it was also demonstrated that the ionization of Ar atoms induces the ionization of He atoms. A 811.5 nm laser was utilized to excite the metastable 4s [3/2]2 level Ar atoms to the 4p [5/2]3 level, when changing the delay time of the 811.5 nm laser lagging behind the 532 nm laser, the generated 912.3 nm (4p [1/2]1→4s [3/2]2) fluorescence intensity also showed different pattern of variations. The analysis indicated that “photoexcitation + radiation + collisional relaxation”, “ion-electron recombination” and quenching processes will affect the density of metastable 4s [3/2]2 level Ar atoms. Amplified spontaneous emission (ASE) signal at 912.3 nm was obtained along the direction of pump laser. This work verifies the feasibility of optically pumped metastable rare gas laser (OPRGL) based on laser-induced preionization, and provides an alternative scheme for the future development of OPRGL.

Low-Temperature Gas Cooling Correction Trajectory Offset Technology of Laser-Induced Thermal Crack Propagation for Asymmetric Linear Cutting Glass

Laser-induced thermal crack propagation (LITP) is a high-quality and efficient processing method that has been widely used in fields such as glass cutting. However, the problem of trajectory deviation often arises in actual cutting operations, especially in asymmetric cutting. To address this issue, a low-temperature gas cooling trajectory deviation correction technique was proposed in this study. This technique modifies the temperature and stress distribution by spraying low-temperature gas onto the processing surface and maintaining a relative position with the laser, thereby correcting the trajectory deviation. The finite element simulation software ABAQUS was employed to numerically simulate the dynamic propagation of temperature fields, thermal stress, and cracks in the asymmetric linear cutting and circular cutting of soda-lime glass with the proposed low-temperature gas cooling trajectory deviation correction technique, and the correction mechanism was elucidated. In the simulation results, the optimal relative distance (ΔX) between the low-temperature gas and scanning laser was obtained by analyzing the transverse tensile stress. Based on the analysis of the experimental and numerical simulation results, it is concluded that the cryogenic gas cooling technique can effectively correct the trajectory deviation phenomenon of asymmetric linear cutting of soda lime glass by LITP.

Quantifying the partial ionization effect of gold in the transition region between condensed matter and warm dense matter

It is now well known that solids under ultra-high-pressure shock compression will enter the warm dense matter (WDM) regime which connects condensed matter and hot plasma. How condensed matter turns into the WDM, however, remains largely unexplored due to the lack of data in the transition pressure range. In this letter, by employing the unique high-Z three-stage gas gun launcher technique developed recently, we compress gold into TPa shock pressure to fill the gap inaccessible by the two-stage gas gun and laser shock experiments. With the aid of high-precision Hugoniot data obtained experimentally, we observe a clear softening behavior beyond ~560 GPa. The state-of-the-art ab-initio molecular dynamics calculations reveal that the softening is caused by the ionization of 5d electrons in gold. This work quantifies the partial ionization effect of electrons under extreme conditions, which is critical to model the transition region between condensed matter and WDM.

Role of Cu percentage in the Sn-xCu alloy on the mechanical performance at Sn-xCu/ENIG interface produced by laser soldering

PurposePb-free solders have been developed to replace the standard Sn–Pb eutectic solder since the prohibition on Pb used in solders. The Sn–Ag–Cu series of lead-free solders is the most extensively used in the electronics industry. The Ag3Sn, which forms during isothermal ageing, can significantly degrade solder joint reliability. Sn–Ag–Cu solder’s high price further hindered its use in the electronics industry. This paper aims to investigate different copper percentages into Sn–xCu solder alloy to improve its microstructure and strength performance.Design/methodology/approachThe solder alloys used in this work were Sn–xCu, where x = 0.0, 0.3, 0.5, 0.7, 1.0 Wt.%, which was soldered onto electroless nickel immersion gold (ENIG) substrate using carbon dioxide (CO2) gas laser. Then these samples were subjected to isothermal aging for 0, 200, 500, 1,000 and 2,000 h. The Sn–xCu solder alloy was fabricated through a powder metallurgy process.FindingsMicrostructure characterization showed that Cu addition resulted in fine and rounded shape of Cu–Sn–Ni particles. Shear strength of Sn–xCu solder joints was increased with increasing Cu content, but at aging duration of 1,000 h, it dropped slightly. It is believed that the strength improved due to the increment of diffusion rate during isothermal aging.Practical implicationsIn a Cu–Sn solder, the recommended amount is 1.0 Wt.% of Cu. In extensive aging procedures, it was discovered that Sn1.0Cu solder improved the reliability of solder joints. The findings indicated that the innovative solder alloys might satisfy the needs of high-reliability applications.Originality/valueThe study shows that the right amount of Cu enhances the solidification of Sn–Cu solder, increasing the shear force of the Cu–Sn solder joint. The Sn1.0Cu exhibits a ductile fracture on the top microstructure, improving the joint’s average shear strength.

Assessing the influence of non-uniform gas speed on the melt pool depth in laser powder bed fusion additive manufacturing

PurposeThis paper aims to investigate the influence of nonuniform gas speed across the build area on the melt pool depth during laser powder bed fusion. This study focuses on whether a nonuniform gas speed is a source of process variation within an individual build.Design/methodology/approachParts with many single-track laser scans were printed and characterized in different locations across the build area coupled with corresponding gas speed profile measurements. Cross-sectional melt pool depth, width and area are compared against build location/gas speed profiles, scan direction and laser scan speed.FindingsThis study shows that the melt pool depth of single-track laser scans produced on parts are highly variable. Despite this, trends were found showing a reduction in melt pool depth for slow laser scan speeds on the build platform near the inlet nozzle and when the laser scans are parallel to the gas flow direction.Originality/valueA unique data set of single-track laser scan cross-sectional melt pool measurements and gas speed measurements was generated to assess process variation associated with nonuniform gas speed. Additionally, a novel sample design was used to increase the number of single-track tests per part, which is widely applicable to studying process variation across the build area.

Corrosion behaviors according to the welding process of superduplex stainless steel welded tubes: Gas tungsten arc welding vs. laser beam welding

The corrosion behaviors of superduplex stainless steel welded tubes in an acidic brine environment were examined by comparing the welds formed by the two welding processes of tungsten inert gas (TIG) welding and laser beam (LB) welding. In contrast to TIG-welds with a larger bead size, higher oxide inclusion, and lower N content, the poor corrosion resistance of as-welded LB-weld sample recovered after post-weld heat treatment (PWHT) by restoring the phase balance and dissolving the deleterious inhomogeneities around the fusion line. The key metallurgical factor controlling the corrosion behavior of LB-welded steel tubes, and underlying corrosion mechanism were also provided.

Influence of the position relationship between gas–liquid interface and laser focus on plasma evolution characteristics in jet LIBS technology

In order to understand the characteristics of breakdown process, plasma evolution and spectral emission in liquid jets laser-induced breakdown spectroscopy methods under the influence of the position variation between laser focus and gas–liquid interface, this work takes the plasma generated by laser-induced liquid jets as the object of study and discusses the changes in the spatial and temporal evolution characteristics and spectral radiation of the plasma when the position parameters between the laser focal point and the gas–liquid interface are different. The initial breakdown position is always between the front interface and the focus when the laser focus moves along the vertical direction of the interface, forming a phenomenon like ‘interface effect’. The relationship between laser pulse energy and breakdown probability exhibits a law similar to a ‘hysteresis curve’ in the study of breakdown threshold. In this work, plasma with smaller size, rounder shape, stronger radiation, higher temperature, and higher density can be produced when the focus position is in the liquid column 0.2 mm away from the front interface. Simultaneously, the spectral signal intensity and signal-to-back ratio of the characteristic peaks of target elements in water reach maximum values, and the spectral signal becomes more stable (relative standard deviation value reaches 2%). The Ca element’s ion radiation at 393.366 nm and atomic radiation at 422.673 nm are studied using narrow-band filtering imaging and time-space resolution spectroscopy. The findings demonstrate that the laws of ion and atomic radiation are not perfectly consistent in space and time.

Cavity-Enhanced Raman Spectroscopy for Detection of Trace Gaseous Impurities in Hydrogen for Fuel Cells

Gaseous impurities contained in hydrogen (H2) profoundly affect the performance of hydrogen proton-exchange membrane fuel cells. We demonstrate the utility of cavity-enhanced Raman spectroscopy as a unique approach for detection of gaseous impurities. A dense-pattern multipass cavity which is composed of four spherical mirrors placed in a Z-shaped configuration is used to enhance the Raman signal by extending the laser-gas interaction length. A total of 85 spots are identified on the 2-inch-diameter front (or rear) mirror, which indicates that 510 beams exist in the cavity. Detection limits of the impurity gases, including oxygen (O2), nitrogen (N2), carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), ammonia (NH3), and hydrogen sulfide (H2S), reach sub-ppm- and ppb-levels at a total pressure of 0.1 and 2.5 MPa, respectively. This satisfies the detection requirements according to the maximum allowable concentration for these gases. Our cavity-enhanced Raman spectroscopy (CERS) apparatus can simultaneously measure multiple gases with high sensitivity and selectivity with no sample destruction. It has excellent application prospects in gaseous impurity analysis for the quality assessment of gaseous energy.

Importance of the average radius of coal particles on determining the methane diffusion coefficient.

The average radius of coal particles is an estimate of the diffusion path in the particle method for determining the diffusion coefficient. It is currently calculated using the arithmetic mean of coal particle sieved intervals. This calculation, however, ignores the coal particle size distribution, resulting in significant deviations when calculating the gas diffusion coefficient. An appropriate average radius calculation method should consider the particle size distribution and the physical essence of diffusion. To accomplish this, a series of methods for calculating the mean particle diameters and their physical significance were reviewed. Next, coal samples were sieved into three intervals, and gas diffusion tests and laser particle size distribution were conducted. Results show that coal particles are within the sieving interval, ranging from 42.01 to 76.18%. By solving the diffusion coefficients using four mean particle diameters based on particle size distribution and diffusive mass transfer, the difference between the arithmetic mean value and these diameters is up to 89.06%. [Formula: see text] and [Formula: see text] are preferred for the calculation of the average radius since they are compatible with coal particle shape and the physical meaning of diffusive mass transfer.

Metastable argon dynamics in a pulsed microplasma at 43 GHz

Short pulses of millimeter wave (MMW) radiation at 43 GHz create microplasma within a photonic crystal for pressures from 40 to 600 Torr (1.3 × 103–8.0 × 104 Pa). Gas breakdown occurs within a photonic crystal, which acts as an electromagnetic resonator to create a strong initial electric field. The time response of the argon metastable density is experimentally determined during the pulse and in the afterglow using laser absorption. The metastable density overshoots the steady-state condition at the beginning of the pulse and during the afterglow. Modeling is presented to understand these observations. The overproduction of argon 1s5 at the beginning of each pulse is due to a concurrent overshoot in the MMW electric field within the photonic crystal. This field overheats the plasma electrons and enhances the production of excited states. The burst of argon metastables observed in the afterglow is due to the pooled energy of the plasma stored in electrons, ions, and excited states of argon. Understanding metastable production is an important intermediate step to ionization and is also critical in the study of diode-pumped rare gas lasers.

Eddy covariance assessment of alternate wetting and drying floodwater management on rice methane emissions

Reducing methane emissions and water use is critical for combating climate change and declining aquifers on food production. Reductions in irrigation water use and methane emissions are known benefits of practicing alternate wetting and drying (AWD) over continuous flooding (CF) water management in lowland rice (Oryza sativa L.) production systems. In a two-year (2020 and 2021) study, methane emissions from large farm-scale (∼50 ha) rice fields managed under CF and AWD in soils dominated by Sharkey clay (Sharkey clay, clay over loamy, montmorillonitic non-acid, thermic Vertic halauepet) were monitored using the eddy covariance method (EC). In the EC system, an open-path laser gas analyzer was used to monitor air methane gas density in the constant flux layer of the atmosphere over the rice-crop canopies. Total water pumped into the field for floodwater management was higher in CF compared to AWD by 24 and 14% in 2020 and 2021, respectively. Considerable variations between seasons in the amount of methane emitted from the CF and AWD treatments were observed: CF emitted 29 and 75 kg ha−1 and AWD emitted 14 and 34 kg ha−1 methane in 2020 and 2021, respectively. Notwithstanding, the extent of reduction in methane emissions due to AWD over CF was similar for each crop season (52% in 2020 and 55% in 2021). Rice grain yield harvested differed by only ±2% between AWD and CF. This investigation of large-scale system-level evaluation, using the EC method, confirmed that by practicing AWD floodwater management in rice, water pumped from aquifers could be reduced by about a quarter and methane emissions from rice fields could be cut down by about half without affecting grain yields, thereby promoting sustainable water management and greenhouse gas emission reduction during rice production in the Lower Mississippi Delta.

Investigation into the laser polishing of an austenitic stainless steel

Gas shielding is critical for improving the quality of laser polishing. The processing effects of laser polishing under the chamber and nozzle gas shielding were compared and analyzed. The influence of the volume flow rate on the surface roughness of the polished workpiece was analyzed, determining the optimal volume flow rate (Q = 5 L/min). At the optimum volume flow rate, the effects of laser power and scanning speed on surface roughness were explored in further research on nozzle gas shielding laser polishing with wider application prospects. A shielding gas jet model for nozzle gas shielding laser polishing was established and verified. The influence mechanism of the shielding gas jet on the polished surface topography was explored using the established shielding gas jet model and laser polishing model, revealing the formation mechanism of surface ripples on the polished surface: the shielding gas jet acts as a perturbation of the molten pool, causing the Marangoni instability of the molten pool when the Marangoni number exceeds the critical Marangoni number.

Improved whole rock low detection limit gold analysis by LA-ICP-MS utilizing pressed-powder-pellets

Analysis of Au in geological materials has been proven useful for understanding geological processes related to the formation of various Au-rich ore deposits. However, the Au concentration in the related source rocks is extremely low (∼<1 ng g−1) and the methodologies allowing analysis at sub-ng g−1 levels are time-consuming, costly and generally involve the handling of hazardous chemicals. Here we present an improved method for low Au concentration analysis by laser-ablation inductively-coupled-plasma mass-spectrometry (LA-ICP-MS) of pressed-powder-pellets (PPP). Fine instrumental tuning for key parameters such as ICP-MS sample gas flow, torch position, RF power, laser frequency, ablation style and laser gas flow allows increasing the Au sensitivity while keeping oxide production low. The latter is critical when analyzing low Au concentrations as the ICP-MS analysis can be impaired by 181Ta16O and 180Hf16O1H interferences. Reducing oxide production and quantifying interferences by analyses of matrix-matched Ta- and Hf-doped pellets, allow for efficient corrections. The method improves the method limit of detection with values as low as 0.10–0.05 ng g−1 Au and routine analysis of reference materials shows that Au analysis by PPP-LA-ICP-MS is reliable. This contribution highlights that the PPP-LA-ICP-MS method is suitable for investigating Au distribution and behavior in Au-depleted rocks.

Influencing Factors of the Specific Total Loss of Non-Oriented Electrical Steels Processed by Laser Cutting

Specific total loss is one of the most important evaluation indexes for the magnetic properties of non-oriented electrical steel sheets. The aim of this study is to investigate the influencing mechanisms of laser cutting parameters as well as the sample characteristics on the specific total loss of thin non-oriented electrical steel sheets processed by laser cutting using a machine learning method. Eight input parameters were finally considered; namely, silicon and manganese contents, thickness of the steel sheets, laser nozzle diameter, laser power, cutting speed, the pressure of process gas, and laser defocus, while one output parameter, the specific total loss, was evaluated. It was found that the specific total loss was positively correlated with the sample thickness, but negatively correlated with silicon and manganese contents, the process gas pressure and laser nozzle diameter. In addition, laser power and cutting speed exhibit complicated non-linear relationships with the specific total loss.

Revealing Local Temporal Profile of Laser Pulses of Intensity above 1014 W/cm2

We demonstrated a method for in situ temporal characterization of an intense femtosecond laser pulse around its focus where the laser intensity exceeds 1014 W/cm2. Our method is based on the second harmonic generation (SHG) by a relatively weak femtosecond probe pulse and the intense femtosecond pulses under analysis in the gas plasma. With the increase in the gas pressure, it was found that the incident pulse evolves from a Gaussian profile to a more complicated structure featured by multiple peaks in the temporal domain. Numerical simulations of filamentation propagation support the experimental observations of temporal evolution. This simple method can be applied to many situations involving femtosecond laser-gas interaction, when the temporal profile of the femtosecond pump laser pulse with an intensity above 1014 W/cm2 cannot be measured in traditional ways.

Optimization of laser machining parameters of SS 314 using response surface methodology

Stainless steel (SS) is an essential industrial and structural material that is challenging to be machined by conventional methods due to its very high melting temperature and the oxides that are formed. Still, as an alternate method, it can be machined by a laser. The primary objective of the current study is to optimize the CO2 laser beam cutting process parameters (viz. are (i) laser power, (ii) cutting speed, and (iii) gas pressure) on surface characteristics of machining 5 mm Stainless Steel (SS 314). Using Response Surface Methodology (RSM) optimization approach and the Box Behnken method, the process parameter of laser cutting were optimized while minimizing the surface roughness. RSM suggested a quadratic regression equation for surface roughness prediction in terms of process parameters. The optimum process parameters obtained are laser power = 1.2 kW, gas pressure = 0.579 bar, and the cutting speed = 2.4 m/min, which results in surface roughness of 2.132 µm.