Clinical study of treatment of facial scar with ultrapulse CO2 laser and Erbium fractional laser

Objective To observe the effect of uitrapulse CO2 laser combined with Erbium fractional laser on treatment facial scars. Methods Total 70 cases with facial scars were treated with ultrapulse CO2 laser combined with Erbium fractional laser for 3 times with 2 ～ 3 months interval. Firstly,scar resurfacing was performed

Multipass welding of thick section steels using autogenous CO2 laser welding and CO2 laser-MIG hybrid welding

Laser multipass welding techniques for thick section steels have been developed using a new type of UV combined narrow groove. The shape and sizes at the bottom of groove are determined by analyzing the plasma behavior using high speed photographic equipment. A stable autogenous CO2 laser welding process and greater penetration are generated at the root pass because of strong reduction of the plasma volume. According to the waveforms of welding current and arc voltage, and the interaction between the arc and the laser induced plasma, a suitable groove angle is obtained. Laser-double MIG hybrid welding process is studied and the optimum distances between the laser and two arcs are determined. By using autogenous CO2 laser welding, CO2 laser-MIG hybrid welding and laser-double MIG hybrid welding, 28 mm thick steel plates are welded with four passes. The welds produced are assessed by X-ray. No crack is found and there is only a small amount of pores. The experimental results show that the multipuss welding procedures proposed can realize the joining of thick section steels with high efficiency and good quality.

An Efficient Pulsed CH3OH Terahertz Laser Pumped by a TEA CO2 Laser

An efficient pulsed CH3OH terahertz （THz） laser pumped by a TEA CO2 laser is investigated experimentally. To improve photon conversion efficiency and THz laser energy, two cavity configurations of the TEA CO2 laser, which is external and semi-external, are evaluated. The pump intensities are about 4.7 MW/cm2 and 1.2 MW/cm2, respectively. Higher pump intensity and more stable single lines are obtained in the external cavity. For the 3.8 J pump energy of the 9P（16） transition in the external cavity, the maximum terahertz output energy with 570.5 μm wavelength at 160 Pa is 431 μJ. With a 6 J energy pulse in terms of a semi-external cavity, a 353 μJ terahertz emission （570.5 μm） is produced. The corresponding photon conversion efficiencies are 1.36% and 0.705%, increasing by a factor of about 2.

Formation mechanism of a smooth, defectfree surface of fused silica optics using rapid CO2 laser polishing

Surface defects introduced by conventional mechanical processing methods can induce irreversible damage and reduce the service life of optics applied in high-power lasers.Compared to mechanical processing,laser polishing with moving beam spot is a noncontact processing method,which is able to form a defect-free surface.This work aims to explore the mechanism of forming a smooth,defect-free fused silica surface by high-power density laser polishing with coupled multiple beams.The underlying mechanisms of laser polishing was revealed by numerical simulations and the theoretical results were verified by experiments.The simulated polishing depth and machined surface morphology were in close agreement with the experimental results.To obtain the optimized polishing quality,the effects of laser polishing parameters(e.g.overlap rate,pulse width and polishing times)on the polishing quality were experimentally investigated.It was found that the processing efficiency of fused silica materials by carbon dioxide(CO2)laser polishing could reach 8.68 mm2 s−1,and the surface roughness(Ra)was better than 25 nm.Besides,the cracks on pristine fused silica surfaces introduced by initial grinding process were completely removed by laser polishing to achieve a defect-free surface.The maximum laser polishing rate can reach 3.88μm s−1,much higher than that of the traditional mechanical polishing methods.The rapid CO2 laser polishing can effectively achieve smooth,defect-free surface,which is of great significance to improve the surface quality of fused silica optics applied in high-power laser facilities.

Optical modulation of repaired damage site on fused silica produced by CO2 laser rapid ablation mitigation

CO2 laser rapid ablation mitigation(RAM)of fused silica has been used in high-power laser systems owing to its advantages of high efficiency,and ease of implementing batch and automated repairing.In order to study the effect of repaired morphology of RAM on laser modulation and to improve laser damage threshold of optics,an finite element method(FEM)mathematical model of 351 nm laser irradiating fused silica optics is developed based on Maxwell electromagnetic field equations,to explore the 3D near-field light intensity distribution inside optics with repaired site on its surface.The influences of the cone angle and the size of the repaired site on incident laser modulation are studied as well.The results have shown that for the repaired site with a cone angle of 73.3°,the light intensity distribution has obvious three-dimensional characteristics.The relative light intensity on z-section has a circularly distribution,and the radius of the annular intensification zone increases with the decrease of z.While the distribution of maximum relative light intensity on y-section is parabolical with the increase of y.As the cone angle of the repaired site decreases,the effect of the repaired surface on light modulation becomes stronger,leading to a weak resistance to laser damage.Moreover,the large size repaired site would also reduce the laser damage threshold.Therefore,a repaired site with a larger cone angle and smaller size is preferred in practical CO2 laser repairing of surface damage.This work will provide theoretical guidance for the design of repaired surface topography,as well as the improvement of RAM process.

A Kilowatt Radio-Frequency Excited Diffusively Cooled All-Metal Slab Waveguide CO2 Laser

A new type of rf excited diffusively cooled all-metal slab waveguide CO2 laser is presented, in which the waveguide channel is constructed by two copper side walls and two copper electrodes, and the discharge is confined in the slab waveguide channel in terms of the voltage division structure. From this type of structure, over 1 kW laser power is obtained with an efficieney of more than 13%.

Effects of RFTVR and CO2 laser on symptoms improvement, QOL and vas of patients with early laryngeal cancer

Objective: To study the effect of RFTVR and CO2 laser on the improvement of symptoms, QOL and vas of patients with early laryngeal cancer. Methods: In this study, 120 patients with laryngeal cancer diagnosed and treated from January 2015 to December 2016 were taken as research objects. All patients were randomly divided into observation group and control group, 60 patients in each group. Patients in observation group were treated with RFTVR, and patients in control group were treated with new-type fiber-optic CO2 laser. The patients in the two groups were treated with cisplatin injection. The differences of perioperative indexes, swallowing function, pronunciation function, survival period, QOL score and VAS score between the two groups were compared. Results: There was no significant difference in the amount of intraoperative bleeding, operation time and hospitalization time between the two groups (P > 0.05);the correct swallowing of the observation group was significantly higher than that of the control group. After treatment, jitter, shimmer and HNR of the two groups were significantly improved, and jitter and shimmer of the observation group were significantly lower than that of the control group, and HNR was significantly higher than that of the control group (P < 0.05) The QOL score and VAS score of the two groups were significantly improved, and the QOL score of the observation group was significantly higher than that of the control group and the VAS score was significantly lower than that of the control group (P < 0.05);the total survival period and tumor free survival period of the observation group were significantly higher than that of the control group. Conclusion: Compared with CO2 laser treatment, the swallowing function and voice function of patients treated by low temperature plasma radiofrequency ablation were significantly improved, and the life quality of patients was significantly improved by prolonging the survival period of patients..

Coblation: An Alternative to CO2 Laser and Microdebrider for Laryngeal Papillomatosis

Objective: To assess the efficacy of coblation in treating laryngeal papillomatosis and its effect on post operative voice outcome. Study Design: This is a retrospective study. Setting: Tertiary referral centre. Subjects and Methods: All the patients diagnosed with laryngeal papillomatosis between January 2013 to December 2016 were included in this study. Preoperative assessment was done with rigid and flexible laryngoscopy. PRAAT software was used for voice analysis. All patients underwent coblation assisted microlaryngeal surgery. Post operatively patients were followed up at 1 week, 15 days, 1 month, 3 months and 6 months with rigid laryngoscopy. Voice analysis was repeated after 3 months to assess the improvement in voice. Results: Coblation was found to be effective in treating laryngeal papillomatosis. In our series of seven patients, three patients underwent repeat procedure with coblation for recurrence. But longterm follow up these patients did not reveal any recurrence of laryngeal papillomatosis. Voice analysis revealed a significant improvement in measures of perturbation and maximum phonation time. Conclusion: Coblation is a promising alternative to the conventional methods for the treatment of laryngeal papillomas as it can achieve satisfactory disease clearance with good voice quality.

Observation on clinical effect of botulinum toxin type A injection combined with low-energy CO2 fractional laser periocular rejuvenation treatment

Objective To investigate the clinical effect of botulinum toxin type A injection combined with low-energy CO2 fractional laser periocular rejuvenation treatment.Methods The clinical effect of botulinum type A injection alone and botulinum type A injection combined with low-energy CO2 fractional laser was compared in 96 patients who needed to receive periocular rejuvenation treatment from April 2018 to April 2019.Results After the combined low-energy CO2 fractional laser treatment was given on the basis of botulinum toxin type A injection,the follow-up global aesthetic improvement scale(GAIS)scores of the observation group were 86.78±4.67,80.31±3.66,76.94±4.03 and 40.59±4.78.The global aesthetic improvement of the dynamic and static wrinkles was obvious.The total effective rate was 93.7%.The total satisfaction rate of the patients was 95.8%,which was higher than that of the control group(P<0.05).The clinical efficacy was significant.Conclusion The application of the combined periocular rejuvenation treatment can improve the dynamic and static wrinkles simultaneously with remarkable rejuvenation effect,increase the effective rate of treatment and enhance the patients'satisfaction.

Joint performance of CO2 laser-MIG hybrid welding 5083-H116 alloy

Laser-MIG hybrid welding process was dealt with 6 mm thick 5083Hl16 Al-Mg alloy plate in butt-joint configuration. Weld formation principle during hybrid welding was explained. The joint properties and microstructure characteristics of welded joints were analyzed by tensile tests, fractographs observed by optical microscopy and scanning electron microscopy （SEM）. Higher heat input could obtain better mechanical properties, and tensile strength and elongation reached 97.2%, 81% of the base metal, respectively. Fracture position traasited from fusion line to weld center in the higher heat input, and fracture location were only in the center of welded joints for the heat input relatively small.

Influence of laser shock peening on microstructure and high-temperature oxidation resistance of Ti45Al8Nb alloy fabricated via laser melting deposition

Laser shock peening(LSP)was used to enhance the high-temperature oxidation resistance of laser melting deposited Ti45Al8Nb alloy.The microstructure and high-temperature oxidation behavior of the as-deposited Ti45Al8Nb alloy before and after LSP were investigated by scanning electron microscopy,X-ray diffraction,and electron backscatter diffraction.The results indicated that the rate of mass gain in the as-deposited sample after LSP exhibited a decrease when exposed to an oxidation temperature of 900℃,implying that LSP-treated samples exhibited superior oxidation resistance at high temperatures.A gradient structure with a fine-grain layer,a deformed-grain layer,and a coarse-grain layer was formed in the LSP-treated sample,which facilitated the diffusion of the Al atom during oxidation,leading to the formation of a dense Al_(2)O_(3)layer on the surface.The mechanism of improvement in the oxidation resistance of the as-deposited Ti45Al8Nb alloy via LSP was discussed.

Effect of Bi/Si Ratio of BiBSi Glass on Its Structure, Properties and Laser Sealing Shear Strength for Vacuum Glazing

The low-melting glass of Bi2O_(3)-B2O_(3)-SiO_(2)(BiBSi)system was used for the first time for laser sealing of vacuum glazing.Under the condition of constant boron content,how the structure and properties vary with Bi/Si ratio in low-melting glass was investigated.In addition,the relationships between laser power,low-melting glass solder with different Bi/Si ratios and laser sealing shear strength were revealed.The results show that a decrease in the Bi/Si ratio can cause a contraction of the glass network of the low-melting glass,leading to an increase of its characteristic temperature and a decrease of its coefficient of thermal expansion.During laser sealing,the copper ions in the low-melting glass play an endothermic role.A change in the Bi/Si ratio will affect the valence state transition of the copper ions in the low-melting glass.The absorbance of the low-melting glass does not follow the expected correlation with the Bi/Si ratio,but shows a linear correlation with the content of divalent copper ions.The greater the concentration of divalent copper ions,the greater the absorbance of the low-melting glass,and the lower the laser power required for laser sealing.The shear strength of the low melting glass solder after laser sealing was tested,and it was found that the maximum shear strength of Z1 glass sample was the highest up to 2.67 MPa.

Laser‑Induced Highly Stable Conductive Hydrogels for Robust Bioelectronics

Despite the promising progress in conductive hydrogels made with pure conducting polymer,great challenges remain in the interface adhesion and robustness in longterm monitoring.To address these challenges,Prof.Seung Hwan Ko and Taek-Soo Kim’s team introduced a laserinduced phase separation and adhesion method for fabricating conductive hydrogels consisting of pure poly(3,4-ethylenedioxythiophene):polystyrene sulfonate on polymer substrates.The laser-induced phase separation and adhesion treated conducting polymers can be selectively transformed into conductive hydrogels that exhibit wet conductivities of 101.4 S cm^(−1) with a spatial resolution down to 5μm.Moreover,they maintain impedance and charge-storage capacity even after 1 h of sonication.The micropatterned electrode arrays demonstrate their potential in long-term in vivo signal recordings,highlighting their promising role in the field of bioelectronics.

Microstructure and Wear/corrosion Resistance of Stainless Steel Laser-alloyed with Mn+W_(2)C, Mn+NiWC and Mn+SiC

In-situ formed high Mn steel coating reinforced by carbides was formed by laser surface alloying(LSA).Laser alloyed layers on 1Cr18Ni9Ti steel with Mn+W_(2)C(specimen A),Mn+NiWC(specimen B)and Mn+SiC(specimen C)powders were fabricated to improve the wear and corrosion behavior of 1Cr18Ni9Ti steel blades in high speed mixers.Microstructure evolution,phases,element distribution,microhardness,wear and corrosion behavior of the laser alloyed layers were investigated.Results indicated that high Mn steel matrix composites with undissolved W_(2)C,WC and other in-situ formed carbides were formed by LSA with Mn+W_(2)C and Mn+NiWC while SiC totally dissolved into the high Mn matrix when adding Mn+SiC.Ni as the binding phase in Ni-WC powder decreased the crack sensitivity of the alloyed layer as compared with the addition of W_(2)C powder.An improvement in average microhardness was achieved in the matrix in specimen A,B and C,with the value of 615,602 and 277 HV_(0.5),while that of the substrate was 212 HV_(0.5).The increase of microhardness,wear and corrosion resistance is highly corelated to microstructure,formed phases,type and content of carbides,micro-hardness and toughness of the alloyed layers.

Corrosion resistance and antibacterial properties of Ti−3Cu alloy prepared by selective laser melting

The corrosion resistance and antibacterial properties of Ti−3Cu alloy prepared by selective laser melting were evaluated using electrochemical experiments and a variety of antibacterial characterization.It is found that the charge transfer resistance of Ti−3Cu alloy was 4.89×10^(5)Ω∙cm^(2),which was doubled the data obtained by CP-Ti alloy.The antibacterial rates of Ti−3Cu alloy against S.mutans and P.gingivalis were 45.0%and 54.5%.And the antibacterial rates increased with the prolongation of cultivation time,reaching up to 62.8%and 68.6%,respectively.The in-situ nano Ti_(2)Cu precipitates were homogeneously distributed in the matrix of the Ti−3Cu alloy,which was the key reason of increasing the corrosion resistance.Additionally,the microscale electric fields between theα-Ti matrix and the Ti_(2)Cu was responsible for the enhancement of the antibacterial properties.

Two-plasmon-decay instability stimulated by dual laser beams in inertial confinement fusion

Two-plasmon-decay instability(TPD)poses a critical target preheating risk in direct-drive inertial confinement fusion.In this paper,TPD collectively driven by dual laser beams consisting of a normal-incidence laser beam(Beam-N)and a large-angle-incidence laser beam(Beam-L)is investigated via particle-in-cell simulations.It is found that significant TPD growth can develop in this regime at previously unexpected low laser intensities if the intensity of Beam-L exceeds the large-angle-incidence threshold.Both beams contribute to the growth of TPD in a“seed-amplification”manner in which the absolute instability driven by Beam-L provides the seeds that are convectively amplified by Beam-N,making TPD energetically important and causing significant pump depletion and hot-electron generation.

High peak power mini-array quantum cascade lasers operating in pulsed mode

Broad area quantum cascade lasers(BA QCLs)have significant applications in many areas,but suffer from demanding pulse operating conditions and poor beam quality due to heat accumulation and generation of high order modes.A structure of mini-array is adopted to improve the heat dissipation capacity and beam quality of BA QCLs.The active region is etched to form a multi-emitter and the channels are filled with In P:Fe,which acts as a lateral heat dissipation channel to improve the lateral heat dissipation efficiency.A device withλ~4.8μm,a peak output power of 122 W at 1.2%duty cycle with a pulse of 1.5μs is obtained in room temperature,with far-field single-lobed distribution.This result allows BA QCLs to obtain high peak power at wider pump pulse widths and higher duty cycle conditions,promotes the application of the mid-infrared laser operating in pulsed mode in th e field of standoff photoacoustic chemical detection,space optical communication,and so on.

Can laser irradiation improve the strength of weak rock mass?

Controllable rock cracking technology is crucial for the exploration and exploitation of deep underground resources.Many existing studies have been dedicated to the laser-assisted rock-weakening technology.It has been proved that laser irradiation can improve drilling and blasting efficiency when combined with mechanical rock fracturing methods,which are irrelevant for borehole stabilization.To improve the latter,this study used laser ablation for borehole reinforcement.The high-power laser was applied to typical rock samples(sandstone,mudstone and coal)in both dry and saturated conditions.Multi-technique observations and measurements were used to fully understand the peculiar modifications of the specimens under laser treatment,i.e.mechanical loading,acoustic emission(AE)monitoring,digital image correlation(DIC)strain field evaluation,infrared thermography(IRT)monitoring and X-ray computed tomography(CT)scanning.The results showed that,in addition to the effects already demonstrated,laser irradiation can improve the strength of the soft rock,especially in the saturated state.The process involved a complicated phase change including melting and evaporation of the matrix under high-temperature and high-pressure to form a glassy high strength silicate material.This process is similar to the reaction between molten lava and water,or the impact of an asteroid on the earth.Inspired by the results,a conceptual path for a new borehole stabilization technology using laser ablation was outlined.

Review of rare earth oxide doping-modified laser cladding of Fe-based alloy coatings

Conventional Fe-C alloy parts used in mechanical transmission and braking systems exposed to the external environment often suffer from wear and corrosion failures.Surface coating strengthening technologies have been explored to improve the surface performance and prolong service life of these parts.Among these technologies,laser cladding has shown promise in producing Fe-based alloy coatings with superior interfacial bonding properties to the Fe-C alloy substrate.Additionally,the microstructure of the Fe-based alloy coating is more uniform and the grain size is finer than that of surfacing welding,thermal spraying,and plasma cladding,and the oxide film of alloying elements on the coating surface can improve the coating performance.However,Fe-based alloy coatings produced by laser cladding typically exhibit lower hardness,lower wear resistance,corrosion resistance,and oxidation resistance compared to coatings based on Co and Ni alloys.Moreover,these coatings are susceptible to defects such as pores and cracks.To address these limitations,the incorporation of rare-earth oxides through doping in the laser cladding process has garnered significant attention.This approach has demonstrated substantial improvements in the microstructure and properties of Fe-based alloy coatings.This paper reviewed recent research on the structure and properties of laser-cladded Fe-based alloy coatings doped with various rare earth oxides,including La_(2)O_(3),CeO_(2),and Y_(2)O_(3).Specifically,it discussed the effects of rare earth oxides and their concentrations on the structure,hardness,friction,wear,corrosion,and oxidation characteristics of these coatings.Furthermore,the mechanisms by which rare earth oxides influence the coating’s structure and properties were summarized.This review aimed to serve as a valuable reference for the application and advancement of laser cladding technology for rare earth modified Fe-based alloy coatings.

Significant improvement of machinability of C_(f)/SiC composites through matching laser scanning spacing and abrasive belt grain size

To improve the application and service of C_(f)/SiC composites as advanced hightemperature structural materials,it is critical to achieve their high-efficiency and low-damage machining.In this study,the laser-ablating assisted grinding(LAAG)method was presented,and the connection of damage behavior and removal mechanism with laser and grinding processes was revealed.The results demonstrated that the surface of C_(f)/SiC composites after laser ablation was covered with a substantial number of loose oxides primarily composed of SiO2.Laser ablating process,grinding parameter and abrasive belt selection have a significant impact on the machining results.By fabricating an ablative layer with small laser scanning spacing,and selecting small abrasive grains and feed rate during grinding,the machinability was improved and a relatively lowerdamage grinding surface could be obtained.Under the optimal combination of process parameters,the grinding force and temperature of LAAG could be reduced by up to 85%and 35%,respectively.In this case,the subsurface damage of C_(f)/SiC composites occurred only in the form of microcracks rather large-scale fracture,and the formation of interface debonding and matrix cracking was significantly reduced.Furthermore,the grinding chips were mostly shown as micron-sized powders,indicating that the removal mechanism of C_(f)/SiC composites was primarily the microfractured and attrition wear of laser-ablated layer.