科创中国

Precision drilling with picosecond laser has been advocated to significantly improve the quality of micro-holes with reduced recast layer thickness and almost no heat affected zone.However,a detailed comparison between nanosecond and picosecond laser drilling techniques has rarely been reported in previous research.In the present study,a series of micro-holes are manufactured on stainless steel 304 using a nanosecond and a picosecond laser drilling system,respectively.The quality of the micro-holes,e.g.,recast layer,micro-crack,circularity,and conicity,etc,is evaluated by employing an optical microscope,an optical interferometer,and a scanning electron microscope.Additionally,the micro-structure of the samples between the edges of the micro-holes and the parent material is compared following etching treatment.The researching results show that a great amount of spattering material accumulated at the entrance ends of the nanosecond laser drilled micro-holes.The formation of a recast layer with a thickness of~25μm is detected on the side walls,associated with initiation of micro-cracks.Tapering phenomenon is also observed and the circularity of the micro-holes is rather poor.With regard to the micro-holes drilled by picosecond laser,the entrance ends,the exit ends,and the side walls are quite smooth without accumulation of spattering material,formation of recast layer and micro-cracks.The circularity of the micro-holes is fairly good without observation of tapering phenomenon.Furthermore,there is no obvious difference as for the micro-structure between the edges of the micro-holes and the parent material.This study proposes a picosecond laser helical drilling technique which can be used for effective manufacturing of high quality micro-holes.

The porcelain fracture caused by low metal-ceramic bond strength is a critical issue in porcelain fused to metal(PFM)restorations.Surface roughening methods,such as sand blasting,acid etching and alkaline degreasing for the metal matrix are used to increase bond strength.However,the metal matrix of PFM processed by selective laser melting(SLM)has natural rough surface.To explore the effect of the original roughness on metal-ceramic bond strength,two groups of specimen are fabricated by SLM.One group of specimen surface is polished smooth while another group remains the original rough surface.The dental porcelain is fused to the specimens'surfaces according to the ISO 9693:1999 standard.To gain the bond strength,a three-point bending test is carried out and X ray energy spectrum analysis(EDS),scanning electron microscope(SEM)are used to show fracture mode.The results show that the mean bond strength is 116.5±16 MPa of the group with rough surface(Ra=17.2),and the fracture mode is cohesive.However,when the surface is smooth(Ra=3.8),the mean bond strength is 74.5 MPa 5 MPa and the fracture mode is mixed.The original surface with prominent structures formed by the partly melted powder particles,not only increases surface roughness but also significantly improves the bond strength by forming strong mechanical lock effect.Statistical analysis(Student's t-test)demonstrates a significant difference(p<0.05)of the mean value of bond strength between the two groups.The experiments indicate the natural rough surface can enhance the metal-ceramic bond strength to over four times the minimum value(25 MPa)of the ISO 9693:1999 standard.It is found that the natural rough surface of SLM-made PFM can eliminate the porcelain collapse defect produced by traditional casting method in PFM restorations.

目的:观察长脉冲1064nmNd:YAG激光治疗婴幼儿皮肤血管瘤临床疗效,并探讨影响疗效的相关因素.方法:应用长脉冲1064nmNd:YAG激光治疗婴幼儿皮肤血管瘤215例,其中鲜红斑痣19例,草莓状血管瘤179例,混合型血管瘤17例.分析其疗效与病变类型、瘤体大小、病变部位及治疗次数的关系.结果:215例患儿中治愈133例,显效67例.有效8例.无效7例,痊愈率和有效率分别为61.9%和93.1%.疗效与血管瘤的病变类型、瘤体的大小以及治疗次数有关,但与其病变部位无明显相关性.治疗后暂时性色素沉着、暂时性色素减退、浅表性瘢痕、头部毛发减少或消失的发生率分别为48.8%、8.3%、4.6%和3.7%.结论:长脉冲1064nmNd:YAG激光治疗婴幼儿皮肤血管瘤疗效好,安全性较高,不良反应轻,可在临床上推广使用.

目的:观察双模式Nd:YAG激光治疗黄褐斑的临床疗效以及相关影响因素.方法:应用双模式Nd:YAG激光治疗82例女性黄褐斑患者,总治疗次数为5次,每次间隔2周,治疗结束后由医生及受试者本人对激光治疗进行疗效评价,并随访12周记录复发情况,对各相关影响因素与治疗疗效进行统计学分析.结果:82例患者治疗前黄褐斑平均面积及严重程度指数(MASI)评分(12.58±6.55)分,5次激光治疗后降为(7.72±5.13)分,随访12周后的平均MASI评分为(8.14±5.82)分.Logistic回归分析显示Wood灯下分型(P=0.003,OR:6.062)、心境情况(P=0.027,OR=3.791)、防晒霜使用情况(P=0.003,OR=3.544)与疗效相关;而表皮型(P=0.025,OR=9.223)、心境平和(P=0.030,OR=6.757)、防晒霜使用情况(P=0.001,OR=9.702)、起病年龄(P=0.004,OR=8.937)与复发情况相关.结论:双模式Nd:YAG激光是治疗黄褐斑的有效手段.皮损表浅、保持心境平和、养成良好的防晒习惯是黄褐斑激光治疗疗效及降低复发的有利因素,起病年龄早是降低复发的有利因素.

为了计算二极管抽运Nd∶ YAG晶体温度场及热形变场,建立了端面绝热、周边恒温的晶体热模型.基于Nd∶ YAG晶体导热系数及热形变系数与其温度的函数关系,应用Newton切线法对热传导方程进行求解,得到了变导热系数和变热形变系数矩形截面Nd∶YAG晶体端面抽运下的温度场和热形变场的一般表达式,同时计算了Nd∶ YAG晶体在不同抽运功率和抽运光斑半径下内部温度场和热形变场的分布变化.结果表明,使用钕离子质量分数为0.01、尺寸为3mm*3mm*8mm的Nd∶ YAG晶体,在功率为60W、光斑半径为450μm的抽运光照射下,变导热系数的Nd∶ YAG晶体端面最大温升为55.7℃,最大热形变量为2.85μm,而按传统将Nd∶ YAG晶体导热系数、热形变系数均视为定值时,晶体端面最大温升为43.4℃,端面最大热形变为2.84μm.