Microstructure and mechanical properties analysis of β-tricalcium phosphate/carbon nanotubes scaffold based on rapid prototyping

β-TCP ceramic scaffolds were fabricated with selective laser sintering (SLS) in this work. Carbon nanotubes (CNTs) were mixed with porous β-TCP matrix to enhance the mechanical performance of the bone tissue engineering scaffolds. Scaffold reconstruction and microstructure analysis were fulfilled based on micro-computed tomography (Micro-CT) scanning data. Results show that the strength of scaffold mixed with 0.2% CNTs reaches 0.819 MPa which has been improved by 85.7% compared with that without CNTs. Micro-CT analysis shows that the scaffold has a good interconnectivity, and pore size mainly distributes in the two regions of 60-340 μm and 500-620 μm.

CO_(2)激光輔助的聲帶息肉激光切除術與傳統喉顯微器械手術術後嗓音分析及嗓音障礙指數分析

Objective To compare the effects on voice of endolaryngeal microsurgery(EMS)with cold instruments and a new method,"carbon dioxide laser(CO_(2)Laser)"for vocal fold polyps.Methods Twenty-five patients with vocal fold polyps suffering from dysphonia who were treated in Macao Kiang Wu Hospital,Department of Otolaryngology Head and Neck Surgery were included in the study.Voice analysis was performed in a soundproof room,holding the microphone 15 cm away from the patients mouth and by recording a sustained[a,e,i,o,u]vowel for at least 5 seconds.Fundamental frequency(F0),Jitter and Shimmer parameters were evaluated in terms of vocal analysis.All patients were asked to fill in a questionnaire,to discuss the voice handicap index(VHI)after adequate explanation.EMS was performed with a carbon dioxide laser and cold knife on 15 and 10 patients,respectively.Patient follow-up was performed 1 week,2weeks and 4weeks after surgery.Changes in F0,Jitter and Shimmer values were measured and recorded.VHI was also completed and reassessed.Results Postoperatively,there was no significant difference in VHI scores between two groups(P>0.05).There was no significant difference in voice analysis values between two groups postoperatively,(P>0.05).Conclusion In the treatment of vocal polyps,EMS with both CO_(2)laser and traditional cold knife is effective.

Combination of ablative fractional carbon dioxide laser and platelet-rich plasma treatment to improve hypertrophic scars:a retrospective clinical observational study

Background:Hypertrophic scars are one of the main complications that affect the quality of life of patients after burns.Many methods have been shown to be effective in the treatment of hypertrophic scars,such as ablative fractional CO_(2) laser(AFCL)and platelet-rich plasma(PRP).However,there are few studies on the effect of the combined application of these measures.The purpose of this study was to explore the therapeutic effect of AFCL combined with PRP on hypertrophic burn scars.Methods:A retrospective clinical observation study was conducted on 50 patients with hypertrophic burn scars.The AFCL+PRP group included 31 patients who received AFCL combined with PRP treatment;the AFCL group included 19 patients who received AFCL treatment only.The University of North Carolina 4P Scar Scale(UNC4P)and the Vancouver Scar Scale(VSS)scores that were collected before each treatment were used as indicators of the effectiveness of the previous treatment.The scores recorded at the second,fourth and seventh months were analysed.Results:The demographic data of the 2 groups were not significantly different.Before treatment,therewas no difference in the UNC4P and VSS scores between the 2 groups.Therewas a significant decline in the UNC4P and VSS total scores over 6 months in both groups(p<0.05)and scores in the 2 groups were comparable after 3 and 6 months(p<0.05).UNC4P scores in the AFCL+PRP group decreased from a mean of 8.26 to 2.61(p<0.05)with a concomitant drop in VSS scores from a mean of 11.74 to 6.06(p<0.01).In the AFCL group UNC4P and VSS scores decreased from 7.68 to 4.63(p<0.05)and from 10.89 to 8.16(p<0.05),respectively.The sub-items of these 2 assessments were analysed and the results suggest that AFCL combined with PRP can comprehensively improve scarring.Conclusions:This study shows that PRP is an effective adjunct for AFCL in the treatment of hypertrophic burn scars and that the combination of PRP and AFCL proved to be more useful than AFCL alone.This combination may be a new and effective clinical practice for the treatment of scars.However,larger and higher-level clinical studies are still needed to determine its efficacy and possible mechanisms.

Experimental investigation of the effects of laser parameters on laser propulsion

The effects of main laser parameters, such as pulse energy, pulse duration, frequency, and work time on laser propulsion of 'air-breathing mode', are investigated experimentally with a high power and high repetition frequency TEA-CO_2 pulsed laser. The results show that the momentum coupling coefficient C_m decreases with increasing the pulse energy for single pulse tests and pulse duration of about 1 μs. Either higher or lower frequency will reduce C_m in multi-pulse tests, which suggests an optimal frequency for the maximum C_m. As to the work time, the longer the work time is, the less the C_m will be.

Design of LICVD equipment for preparation of nano powder and study on laser threshold

A laser-induced chemical vapor deposition (LICVD) nanometer equipment is designed and fabricated. The design conception of key parts is expatiated. The energy threshold of SiH4 decomposing is studied. In the condition of same reactive gas flux, the laser energy threshold decreases with the increase of SiH4 concentration. In the condition of same SiH4 concentration, with the increase of reactive gas flux, the laser energy threshold which induces SiH4 decomposition increases linearly at the beginning, and when the flux is more than 100 ml/min, it turns to increase slowly. The factors which influence the laser threshold are analyzed.

Q-switched ytterbium doped fiber laser using multi-walled carbon nanotubes saturable absorber

A Q-switched ytterbium-doped fiber laser （YDFL） is proposed and demonstrated using a newly developed multi-walled carbon nanotubes polyethylene oxide （MWCNTs-PEO） film as a passive saturable absorber （SA）. The saturable absorber is prepared by mixing the MWCNTs homogeneous solution into a dilute PEO polymer solution before it is left to dry at room temperature to produce thin film. Then the film is sandwiched between two FC/PC fiber connectors and integrated into the laser cavity for Q-switching pulse generation. The laser generates a stable pulse operating at wavelength of 1060.2 nm with a threshold pump power of 53.43 mW. The YDFL generates a stable pulse train with repetition rates ranging from 7.92 to 24.27 kHz by varying 980-nm pump power from 53.42 to 65.72 mW. At 59.55-mW pump power, the lowest pulse width and the highest pulse energy are obtained at 12.18 μs and 143.5 n J, respectively.

Wear resistance of laser cladding and plasma spray welding layer on stainless steel surface

The effect of coatings, which are formed with laser cladding and plasma spray welding on lCrl8Ni9Ti base metal, on wear resistance is studied, A 5-kW transverse flowing CO2 laser is used for cladding Co base alloy powder pre-placed on the substrate. Comparing with the plasma spray coatings, the spoiled rate of products with laser clad layers was lower and the rate of finished products was higher. Their microstructure is extremely fine. They have close texture and small size grain. Their dilution resulting from the compositions of the base metal and thermal effect on base metal are less. The hardness, toughness, and strength of the laser cladding layers are higher. Wear tests show that the laser layers have higher properties of anti-friction, anti-scour and high-temperature sliding strike. The wear resistance of laser clad layers are about one time higher than that of plasma spray welding layer.

Ablative Carbon Dioxide Laser Treatment for Papular Scars of Nose and Chin Due to Acne: A Case Series

Introduction:Papular scarring of the nose and chin due to acne is an under-reported,under-recognized,and under-treated condition.Ablative carbon dioxide laser therapy(10,600 nm,continuous mode,energy of 15W)under local anesthesia is one of the choice.Here,we report series of patients with papular acne scars successfully treated with ablative carbon dioxide laser.Cases presentation:Five patients with papular scars of the nose and chin due to acne were treated at an outpatient dermatology clinic.All had type V skin according to the Fitzpatrick skin classification.Ablative carbon dioxide laser therapy(10,600 nm,continuous mode,energy of 15W)was performed under topical anesthesia.The patients were re-examined at 2-to 3-week intervals,and laser treatment was repeated as needed.Discussion:All of the five patients showed encouraging results.Good cosmetic results were achieved in all patients.The drawbacks of treatment were mild to moderate pain during the procedure and the need for posttreatment skin care.Conclusion:Ablative carbon dioxide laser therapy can potentially be used as a safe and effective treatment for papular scars of the nose and chin due to acne.

Q-switched fiber laser using carbon platinum saturable absorber on side-polished fiber

A 1550 nm Q-switched fiber laser using a carbon platinum saturable absorber deposited on side-polished fiber（SPF） is proposed and demonstrated. The SPF is approximately 2 mm with a polarization-dependent loss（PDL）of 0.4 dB and an insertion loss of 2.5 dB. A stable Q-switched output spectrum is obtained at 1559.34 nm with a peak power of ~6 mW, a pulse width of 1.02 μs, pulse energy of 5.8 nJ, average output power of 0.76 mW, and a repetition rate of 131.6 kHz taken at a pump power of 230.0 mW. A signal-to-noise ratio of 49.62 d B indicates that the Q-switched pulse is highly stable.

Mechanism of laser welding on dissimilar metals between stainless steel and W-Cu alloy

CO2 laser is employed to join a piece of powder metallurgical material （PMM） to a stainless steel in butt joint welding mode. The powder Ni35, as a filler powder, is used. The weld metal comes from three parts of stainless steel, powder Ni35, and Cu in W-Cu PMM. It is indicated that some parts of the W-Cu base metal are heated by laser and the metal Cu at the width of 0.06--0.12 mm from the edge is melted into the melting pool in the laser welding process. The formation of firm weld joint is just because that the melting liquid metal could fill the position occupied by metal Cu and surround the metal W granules fully. The analysis results indicate that the mechanism of the laser welding for stainless steel and W-Cu alloy is a special mode of fusion-brazing welding.

Laser induced self-propagating high-temperature synthesis of TiNi alloy

TiNi alloy, especially porous TiNi, a good biocompatible material, can be made by laser induced self-propagating high-temperature synthesis (SHS). A 40-W CO2 laser was used to ignite the powders of Ti and Ni, and TiNi intermetallic compound was synthesized by SHS in a reaction kettle of stainless steel. High-speed photography, X-ray diffraction, and scanning electron microscopy were used to investigate and analyze the reaction process, phase composing, and microstructure of the product, respectively. The influence factors on the reaction process and the product were discussed. The results indicate that laser induced SHS is an efficient, energy-saving method; The phase ingredient of the product consists of TiNi, Ti2Ni, and Ni3Ti. With the increase of the preparing pressure of the sample, the reacting rate decreases; With the increase of the laser power and the preheating temperature, the reacting rate increases. Under the condition of 30℃/min, the synthesis reaction had been carried out consistently and completely.

Midinfrared optical frequency comb based on difference frequency generation using high repetition rate Er-doped fiber laser with single wall carbon nanotube film

We demonstrated stable midinfrared(MIR) optical frequency comb at the 3.0 μm region with difference frequency generation pumped by a high power, Er-doped, ultrashort pulse fiber laser system. A soliton mode-locked161 MHz high repetition rate fiber laser using a single wall carbon nanotube was fabricated. The output pulse was amplified in an Er-doped single mode fiber amplifier, and a 1.1–2.2 μm wideband supercontinuum(SC) with an average power of 205 m W was generated in highly nonlinear fiber. The spectrogram of the generated SC was examined both experimentally and numerically. The generated SC was focused into a nonlinear crystal, and stable generation of MIR comb around the 3 μm wavelength region was realized.

Mode-locked 2 μm fiber laser with a multi-walled carbon nanotube as a saturable absorber

We propose and demonstrate a passively mode-locked fiber laser operating at 1951.8 nm using a commercial thulium-doped fiber （TDF） laser, a homemade double-clad thulium-ytterbium co-doped fiber （TYDF） as the gain media, and a multi-walled carbon nanotube （MWCNT） based saturable absorber （SA）. We prepare the MWCNT composite by mixing a homogeneous solution of MWCNTs with a diluted polyvinyl alcohol （PVA） polymer solution and then drying it at room temperature to form a film. The film is placed between two fiber connectors as a SA before it is integrated into a laser ring cavity. The cavity consists of a 2 m long TDF pumped by a 800 nm laser diode and a 15 m long homemade TYDF pumped by a 905 nm multimode laser diode. A stable mode-locking pulse with a repetition rate of 34.6 MHz and a pulse width of 10.79 ps is obtained when the 905 nm multimode pump power reaches 1.8-2.2 W, while the single-mode 800 nm pump power is fixed at 141.5 mW at all times. To the best of our knowledge, this is the first reported mode-locked fiber laser using a MWCNT-based SA.

Effect of nitrogen pressure on optical properties and microstructure of diamond-like carbon films grown by pulsed laser deposition

The effect of nitrogen pressure on optical properties of hydrogen-free diamond-like carbon (DLC) films deposited by pulsed laser ablation graphite in different background pressures of nitrogen is reported. By varying nitrogen pressures from 0.05 to 15.00 Pa, the photoluminescence is gradually increased and optical transmittance is gradually decreased. Atomic force microscopy (AFM) is used to observe the surface morphology of the DLC films. The results indicate that the surface becomes unsmoothed and there are some globose particles on the films surface with the rise of nitrogen pressures. The microstructure of the films is characterized using Raman spectroscopy.

Self-starting harmonic mode-locked Tm-Bi co-doped germanate f iber laser with carbon nanotube-based saturable absorber

We report a ring cavity passively harmonic mode-locked fiber laser using a newly developed thulium- bismuth co-doped fiber （TBF） as a gain medium in conjunction with a carbon nanotube （CNT）-based saturable absorber. The TBF laser generates a third harmonic mode-locked soliton pulse train with a high repetition rate of 50 MHz and a pulse duration of 1.86 ps. The laser operates at 1 901.6 nm with an average power of 6.6 mW, corresponding to a pulse energy of 0.132 nJ, at a 1 552 nm pump power of 723.3 roW.

Study of technique and performance of laser beam welding for W18Cr4V and 65Mn

In this experiment, we used 7-kW continuous wave (CW) CO2 low order mode laser and YAG impulse laser to deeply weld high-speed steel (W18Cr4V) and spring steel (65Mn). To welded joint, we analyzed its microstructure, micro hardness and fracture appearance for different welding technology by metallography microscope, scanning electron microscopy and bending strength test, discussed its action of fracture and the relation between its structural transformation and strength. At last, we offered an optimum welding technology having no welding defect by the comparison and analysis of processing property.

Efficacy and safety of a dual-scan protocol for carbon dioxide laser in the treatment of split-thickness skin graft contraction in a red Duroc pig model

Background:Fractional CO_(2) laser plays an important role in scar management post split-thickness skin graft by loosening the graft contracture and restoring the smoothness of the surface.However,the optimal treatment protocol remains unknown.This study applied a dual-scan protocol to achieve both releasing and ablation of contracted skin graft.We comprehensively describe this treatment method and compare the efficacy and safety between this dual-scan method and the conventional mono-scan mode.Methods:A hypercontracted scar model after split-thickness skin grafting in red Duroc pigs was established.All scars meeting the inclusion criteria were randomly divided into four groups:high fluence–low density(HF–LD),low fluence–high density(LF–HD),combined group and control group.The energy per unit areawas similar in the HF–LD and LF–HD groups.Two laser interventions were performed at a 6-week interval.The efficacy of the treatment was evaluated by objective measures of scar area,release rate,elasticity,thickness and flatness,while the safetywas evaluated based on adverse reactions and melanin index.Collagen structurewas observed histologically.The animals were followed up for a maximum of 126 days after modeling.Results:A total of 28 contracted scars were included,7 in each group.At 18 weeks postoperatively,the HF–LD and the combined groups showed significantly increased scar release rate(p=0.000)and elasticity(p=0.036)and decreased type I/III collagen ratio(p=0.002)compared with the control and LF–HD groups.In terms of flatness,the combined group was significantly better than the HF–LD group for elevations<1mm(p=0.019).No significant skin side effects,pigmentation or scar thickness changes were observed at 18 weeks.Conclusions:Dual-scan protocol could achieve superficial ablation and deep release of contracted split-thickness skin graft in a single treatment,with similar contraction release and texture improvement compared to a single deep scan.Its main advantage is to restore a smoother scar appearance.Adequate laser penetration was necessary for the release of contracted scars.

Microstructure and properties of plastic deformed martensite induced by laser shock processing

Firstly, 45# steel was quenched by the NEL-2500A rapidly axial flow CO2 laser. The experimental parameters were the laser power of 750 W, the laser beam diameter of 4 mm, the scanning velocity of 7 mm/s. The thickness of coating layer was 0.1 mm and the width was 8 mm. Secondly, the martensite induced by laser quench was shocked by Nd:YAG laser. The parameters of laser shock processing were the wavelength of 1.06 μm, the pulse duration of 23 ns, and the output energy of 16-20 J. The laser was focused on a spot of φ7 mm. K9 optical glass was used as confinement. The sample was coated with black paint 86-1 (the thickness is about 0.025 mm). By testing and analysis of samples which were treated by laser quench and laser quench+shock with transmission electron microscope (TEM), it was discovered that the surface layer of martensite was deformed plastically by laser shock processing. In the secondary hardened zones, there were a lot of slender secondary twin crystal martensites, dislocation tangles, and cellular dislocations. Compared with that of the hardened zones through laser quench only, the residual stress and mechanical properties of the secondary hardened zones were improved and increased through laser compound method.

Er-doped all-fiber laser mode-locked by graphitic carbon nitride nanosheets

Few-layer graphitic carbon nitride （g-C-N-） nanosheets were fabricated and utilized as a saturable absorber for mode-locking in an Er-doped fiber laser with net normal dispersion. Tile g-CaN,-/polyvinyl alcohol （PVA） hybrid-film-based saturable absorber has a modulation depth of 4.01% and a saturation intensity of 7.5 MW/cm2. By integrating g-C3N4-PVA mode-locker into the laser cavity, a mode-locked operation could be obtained. The achieved mode-locking pulse centered at 1530.3 nm has a pulse width of 530 ps. Its repetition rate is 40.8 MHz, and the corresponding signal-to-noise ratio is about 55 dB.

550 MHz carbon nanotube mode-locked femtosecond Cr:YAG laser

We demonstrate a femtosecond Cr：YAG laser mode-locked by a carbon nanotube saturable absorber mirror（CNT-SAM） at a repetition rate of 550 MHz. By employing the CNT-SAM, which exhibits a modulation depth of 0.51% and a saturation fluence of 28 μJ∕cm^2 at 1.5 μm, we achieved a compact bulk Cr：YAG laser with selfstarting mode-locked operation near 1.5 μm, delivering an average output power of up to 147 m W and a pulse duration of 110 fs. To our knowledge, this system provides the highest repetition rate among reported CNT-SAM mode-locked Cr：YAG lasers and the shortest pulse duration among saturable absorber mode-locked Cr：YAG lasers with repetition rates above 500 MHz.