基于CO2激光单点加热的微泡腔制备及其性能研究

为了简化微泡腔的制备工艺,在传统CO_2激光双向加热方案的基础上,采用CO_2激光单点加热毛细管。通过精确控制加热温度和气体流速,制备出半球形的微泡腔,进而通过调节激光光斑,增加加热面积的方式制备出球形的微泡腔。使用光学显微镜和原子力显微镜(AFM)对制备的球形微泡腔进行表征,并通过COMSOL仿真验证了所制备微泡腔的性能。所制备的微泡腔表面光滑,壁厚最薄处可达到亚微米量级。研究结果表明,通过CO_2激光单点加热制备的微泡腔的壁厚存在轻微的不均匀性,但其谐振Q值仍然较高,可广泛应用于传感领域。     

纳结构的连续激光复合微纳探针刻划加工

为了加工形貌稳定且尺寸尽可能小的纳结构,建立了一套连续激光复合微纳探针的加工系统,并研究了光纤探针导光的连续激光辐照微纳探针的近场增强效应以及该系统的加工性能。首先,根据表面等离子体激元理论仿真分析了激光辐照原子力显微镜(AFM)探针的近场增强因子,并研究了微纳探针的针尖温度场和针尖热膨胀。接着,搭建了基于光纤探针导光的连续激光复合微纳探针的纳结构加工系统。最后,对聚乙烯片状材料样品进行了纳结构加工。结果显示:加工得到的纳米点尺度为200nm左右;纳米线的尺度为30~40nm。结果表明:光纤探针导光连续激光复合微纳探针系统避免了复杂的空间光路结构,是一种成本低廉,结构简单的系统,能够实现纳结构的加工。     

电子科技大学研制出微纳光纤珐珀传感器

电子科技大学研制出微纳光纤珐珀传感器,利用激光微加工技术制作光纤珐珀腔具有方法简单、一次成型。电子科技大学通信学院光纤技术研究中心饶云江教授团队在国际上应用157nm和飞秒激光微加工技术制作出新一代微纳光纤珐珀传感器。据悉,与传统手工制作方法相比,利用激光微加工技术制作光纤珐珀腔具有方法简单、一次成型、能够实现光纤珐珀腔的高质量批量制造等突出优点,     

保偏光纤转轴熔接Sagnac干涉环的光学游标效应及温度传感器

为了实现高灵敏度的温度传感,通过在基于保偏光纤Sagnac干涉仪的Sagnac环内增加一段保偏光纤,控制两段保偏光纤快轴熔接角度接近45°,设计并制造了保偏光纤转轴熔接Sagnac干涉环结构。在理论上通过Jones矩阵推导了保偏光纤转轴熔接Sagnac干涉环的干涉谱公式,基于仿真分析研究了主要参数对保偏光纤转轴熔接Sagnac干涉环输出特性的影响。仿真结果表明,保偏光纤转轴熔接Sagnac干涉环实现了光学游标效应,两段保偏光纤的平均长度、两段保偏光纤的长度差分别影响保偏光纤转轴熔接Sagnac干涉环输出干涉谱的波长间隔和包络周期;在实验中,将保偏光纤转轴熔接Sagnac干涉环应用在光纤温度传感器中。实验结果表明,在2cm的感温区域,保偏光纤转轴熔接Sagnac干涉环温度传感器的灵敏度就达到了-2.44nm/℃,是普通Sagnac干涉环温度传感器(-0.163nm/℃)的14.97倍。     

双芯光纤马赫-曾德尔干涉仪的温度特性

对适用于温度传感的双芯光纤马赫-曾德尔干涉仪进行了研究,并通过将一根单模双芯光纤熔接在两根单模光纤之间,制得了双芯光纤马赫-曾德尔干涉仪型梳状滤波器.用干涉原理分别分析了该器件传输谱的自由空间谱宽与波长、双芯光纤的长度和两纤芯间的有效折射率差的关系,实验检测了它的温度特性.结果显示,随着温度的升高,该器件的传输谱发生红...     

具有温度补偿的拱形增敏微纳光纤磁场传感器

提出了一种基于铽镝铁(TbDyFe)的具有温度补偿的拱形增敏微纳光纤磁场传感器。传感器由光纤布拉格光栅(FBG),拱形微纳光纤和TbDyFe组成,拱形微纳光纤通过紫外胶(UV glue)粘接在TbDyFe上。与非拱形微纳光纤相比,拱形光纤可将TbDyFe的伸长转化为光纤曲率半径的变化,引起干涉波长偏移,从而实现磁场灵敏度的提高。随着磁场强度升高,拱形微纳光纤的干涉波长蓝移,灵敏度为47.81 pm/mT,FBG对磁场不敏感,拱形微纳光纤传感器的磁场灵敏度比非拱形高11.66倍。升温过程中拱形微纳光纤的干涉波长发生蓝移,温度灵敏度为43.02 pm/℃,FBG的干涉波长发生红移,温度灵敏度为9.34 pm/℃。磁场传感器显示出良好的重复性和线性,级联的FBG对磁场不敏感,可以实现对磁场传感器的温度补偿。     

激光诱导空化微纳制造实验研究

概述了激光微纳制造应用前景。通过单脉冲激光作用在水中,击穿水的阈值产生空化作用,从而在铝板上制造出了孔状的微纳结构。并且应用高速摄影仪和水听计分析了其制造机理,主要为微射流和等离子冲击波共同作用的结果。最后,提出了激光诱导空化微纳制造在表面结构微纳成型具有较好的定域性,但是表面控形和不同位置加工机理需要进一步探索研究。     

微纳热压印真空装置研制

在非真空环境中进行微纳压印,在模板和聚合物基底之间会形成气泡,降低微纳结构的转印质量,针对该问题,研制了一种微纳热压印真空装置。该装置包括:用于调整压头板位姿的球状自适应调整结构,以半导体热电致冷器为加热和致冷器件的温度控制装置,真空罩,密封系统。计算了热压印过程需要的加热和制冷功率,进行了升降温和保温性能实验、真空性能实验和应用实验,实验结果验证此装置整体性能良好,适用于微纳热压印。     

丙酮对碳纳米管薄膜微纳光纤传输光的能量分布影响

基于薄膜微纳光纤中传播光能量分布的理论,在实验研究基础上,进一步用模场分析仪观察微纳光纤在表面镀有碳纳米管薄膜包层后,与丙酮气体接触时,其传输光的能量分布规律和倏逝场的变化。实验可知,在一定浓度的丙酮环境下,没有碳纳米管薄膜包层时,微纳光纤中传输光能量呈对称分布,当有碳纳米管薄膜包层时,其能量分布不再对称,并且能量分布的直径宽度增加。     

高折射率镀膜聚合物波导传感器的制备

为了提高利用倏逝波传感的光纤传感器的灵敏度问题,仿真并验证了一种基于高折射率镀膜的光纤传感器.首先两根光纤之间利用激光诱导波导自行成技术形成聚合物波导,并在波导表面镀上一层高折射率Ta2O5薄膜以增强波导表面倏逝波强度,从而增加传感器灵敏度.根据聚合物波导制备结果,使用COMSOL Multiphysics?软件对Ta...     

A comparative study on the processing parameters during fibre and CO2 laser surface treatments of silicon nitride engineering ceramic

This paper demonstrates a comparative study of a relatively novel fibre laser and a conventional CO₂ laser to surface-process silicon nitride (Si₃N₄) engineering ceramic. The objective of the research is to investigate the threshold of the novel fibre laser and compare it to the conventionally used CO₂ laser to process Si₃N₄ engineering ceramic and to produce a laser surface treatment free from major surface cracking without using any of the pre- or post heating techniques as this would increase the cost of the process and add more expense to the product when considering a bigger view point. The results showed that the fibre laser surface processing of the Si₃N₄ engineering ceramic differed to that of the CO₂ laser as the Gaussian beam modes, the beam quality factors, wavelength and the beam delivery systems were different between the two lasers. This consequently had a different effect on the surface of the Si₃N₄ engineering ceramic. The CO₂ laser wavelength when surface treating the Si₃N₄ engineering ceramic was being absorbed more than that of the fibre laser as higher power density and same traverse speed was used to reach the threshold for the Si₃N₄ engineering ceramic.     

In Situ analysis of CO2 laser irradiation on controlling progression of erosive lesions on dental enamel

The present study aimed to evaluate in situ the effect of CO₂ laser irradiation to control the progression of enamel erosive lesions. Fifty‐six slabs of bovine incisors enamel (5 × 3 × 2.5 mm³) were divided in four distinct areas: (1) sound (reference area), (2) initial erosion, (3) treatment (irradiated or nonirradiated with CO₂ laser), (4) final erosion (after in situ phase). The initial erosive challenge was performed with 1% citric acid (pH = 2.3), for 5 min, 2×/day, for 2 days. The slabs were divided in two groups according to surface treatment: irradiated with CO₂ laser (λ = 10.6 µm; 0.5 W) and nonirradiate. After a 2‐day lead‐in period, 14 volunteers wore an intraoral palatal appliance containing two slabs (irradiated and nonirradiated), in two intraoral phases of 5 days each. Following a cross‐over design during the first intraoral phase, half of the volunteers immersed the appliance in 100 mL of citric acid for 5 min, 3×/day, while other half of the volunteers used deionized water (control). The volunteers were crossed over in the second phase. Enamel wear was determined by an optical 3D profilometer. Three‐way ANOVA for repeated measures revealed that there was no significant interaction between erosive challenge and CO₂ laser irradiation (P = 0.419). Erosive challenge significantly increased enamel wear (P = 0.001), regardless whether or not CO₂ laser irradiation was performed. There was no difference in enamel wear between specimens CO₂‐laser irradiated and non‐irradiated (P = 0.513). Under intraoral conditions, CO₂ laser irradiation did not control the progression of erosive lesions in enamel caused by citric acid. Microsc. Res. Tech. 77:586–593, 2014. © 2014 Wiley Periodicals, Inc.     

Experimental investigation on CO2 laser-assisted micro-slot milling characteristics of borosilicate glass

Demands for micro-machining on glass have been increasing in various industries due to the unique properties of glass, such as transparency or biocompatibility. However, micro-channel fabrication on glass with high precision has been challenging due to its brittle characteristics. This research presents the CO₂ laser-assisted micro-milling process and investigates the machining characteristics experimentally. Micro-channels without cracks were fabricated using micro-end mill and CO₂ laser irradiation as an assisting heat source. Compared to the process without laser heating in the same matching conditions, the average surface roughness was reduced by 96%, and cutting force was reduced by 28% and 66% for the feed and thrust direction, respectively. Continuous and sheared chips were observed with laser heating, indicating the process is in ductile-regime machining. Through the investigation of machining parameters, it was found that micro-channels with low average surface roughness can be achieved at the proper laser power when the workpiece is heated up to the strain point at tool position, at low feed rate, and at high axial depth of cut, as long as the tool withstands the cutting forces. Consequently, it can be concluded that it is possible to increase the material removal rate in micro-milling of borosilicate glass with high quality by using the CO₂ laser, which was found to be an effective and suitable heating method.     

In-process monitoring of the cutting front of CO2 laser cutting with off-axis optical fibre

A new method is presented in this study to test a way that can effectively provide detailed information on the surface morphology during CO₂ laser cutting by directly measuring the emitted light from the cutting front. The system consists of a copper tube, glass fibre, polymer fibre and photodiode sensor. In this study, the laser power was modulated from 50 Hz to 300 Hz to disturb the natural burning cycle during gas assisted CO₂ laser cutting. The optical fibre was set at 75° to the cutting direction. The wave frequency of the detected signal was very close to the striation frequency of the cut surface, which shows that the sensing system designed and developed in this research can effectively in-process monitor the CO₂ laser cutting process.     

Development and research of a laser photo-acoustic SF<Subscript>6</Subscript> gas analyzer

An analysis of various optical schemes for the development of a laser SF₆ gas analyzer based on a CO₂ laser operating in free-running mode and a resonant photo-acoustic detector (PAD) is presented. The use of a sealed gas-filled cell to normalize PAD signals on the absorbed power in the cell is suggested. Compensation for the influence of the tuning of the CO₂ laser wavelength near 10.6 μm on measured SF₆ concentration is possible. The results of experimental studies of a laser photo-acoustic SF₆ gas analyzer at various concentrations, including in the air flow, are presented. It is shown experimentally that the relative measurement error of the SF₆ concentration due to the instability of the laser radiation wavelength does not exceed 5% in the range from ~80 ppb to 40 ppm. The limit of the sensitivity of the developed gas analyzer was ~1 ppb SF₆.     

Microhardness and SEM after CO2 laser irradiation or fluoride treatment in human and bovine enamel

Background: It remains uncertain as to whether or not CO₂ laser is able to hinder demineralization of enamel. The possibility to use bovine instead of human teeth on anticariogenic studies with laser has not yet been determined. Purpose: To compare the ability of CO₂ laser and fluoride to inhibit caries‐like lesions in human enamel and to test whether a similar pattern of response would hold for bovine enamel. Study Design: Ninety‐six enamel slabs (2 × 2 × 4 mm) (48 from bovine and 48 from human teeth) were randomly distributed according to surface treatment (n = 12): CO₂ laser, 5% sodium fluoride varnish (FV), 1.23% acidulated phosphate fluoride (APF) gel, or no treatment (control). Specimens were subjected to a 14‐day in vitro cariogenic challenge. Microhardness (SMH) was measured at 30 μm from the surface. For ultrastructural analysis, additional 20 slabs of each substrate (n = 5) received the same treatment described earlier and were analyzed by SEM. Results: ANOVA and Tukey test ascertained that CO₂ laser promoted the least mineral loss (SMH = 252^a). Treatment with FV resulted in the second highest values (207^b), which was followed by APF (172^c). Untreated specimens performed the worst (154^d). SEM showed no qualitative difference between human and bovine teeth. APF and control groups exhibited surfaces covered by the smear layer. A granulate precipitate were verified on FV group and fusion of enamel crystals were observed on lased‐specimens. Conclusions: CO₂ laser may control caries progression more efficiently than fluoride sources and bovine teeth may be a suitable substitute for human teeth in studies of this nature. Microsc. Res. Tech. 73:1030–1035, 2010. © 2010 Wiley‐Liss, Inc.     

POWER RADIO FREQUENCY CIRCUIT DESIGN FOR A SMALL CO2 SLAB WAVEGUIDE LASER

The design, construction, and test of a radio frequency oscillator-amplifier is presented in this paper. The RF circuit is inserted as part of the electrodes of an in-house-built compact CO₂ waveguide laser. Our circuit was designed to have a frequency at 81 MHz and its signal output between 90 W and 150 W. Capacitive discharge is evaluated over a period of time and, after a correct positioning of several inductors parallel-distributed along the laser electrodes, a steady and uniform plasma discharge was created. The overall RF circuit-laser test is done with a typical gas mixture of CO₂-N₂-He with proportion of 1:1:3, correspondingly, and at a final pressure of 40 Torr. Under these conditions, a maximum optical output power greater than 10.7 W was obtained for an input feed RF power of 147 W.     

Registration of picosecond CO<Subscript>2</Subscript> laser pulses by means of two-stage parametric transformation in nonlinear crystals

A technique for registering the temporal structure of picosecond pulses of CO₂ laser radiation with an energy of 1.5–4.5 μJ at a wavelength of 10.27 μm using two-stage parametric transformation of IR radiation frequency into visible light under pumping of nonlinear crystals by Nd:YAG-laser radiation in a Q-switched mode is described. A GaSe nonlinear crystal was used at the first stage of transformation (10.27 μm + 1.064 μm → 0.964 μm). Radiation was further transformed (1.064 μm + 0.960 μm → 0.506 μm) by using the same pumping in an α-HIO₃ nonlinear crystal. For the first time, no additional optical elements were present between the stages of the frequency transformer in the proposed optical scheme. The transformed radiation was registered with a Hamamatsu Temporal Disperser C1587 streak camera in a region of the photocathode maximum spectral sensitivity of ～0.5 μm with a temporal resolution of up to 2 ps. The minimum recorded pulse duration of the CO₂ laser was ～45 ps.     

Using a Nd:YAG laser and six axes robot to cut zinc-coated steel

Zinc-coated steel sheets are important materials in the automobile and home appliance industries. Currently, lasers are the preferred tools for metal cutting because of their good cutting quality, flexibility and excellent features and results, as compared to traditional tools. The solid-state Nd:YAG laser has successfully replaced the gaseous CO₂ laser for metal cutting; its small size and short wavelength makes it suitable for cutting bright and metal-coated materials, as well as being able to be transmitted via optical fibers and robots to cut complicated three dimensional and curved shapes. In this work, the Nd:YAG laser is used to cut 1 mm zinc coated steel sheets. We demonstrate the effects of different cutting parameters such as laser power, cutting speed, different gas types and pressures, and focus position on the cutting quality characteristics of attached dross, kerf width and cut surface roughness. Using a six axes robot, cutting speed was limited to 6 m/min because of the noticeable vibration at higher speeds. Results showed that the cutting surfaces achieved were very sharp and smooth. In cutting, Nd:YAG required less power and attained higher speeds than the published results of a CO₂ laser, which makes Nd:YAG an economical alternative to cut zinc and metal-coated materials. In addition, laser cutting using robots provided efficient and consistent cutting quality, especially in the case of 3D and countered cutting. Apart from using low speed, robots proved to be more economical than costly, specially designed CNC tables.     

Influence of shielding gas mixtures on bead profile and microstructural characteristics of super austenitic stainless steel weldments by laser welding

A planned and orderly analysis of the microstructures and bead profiles of AISI 904 L super austenitic stainless steel bead-on-plate welds was accomplished by coupling up diffusion cooled slab 3.5?kW CO₂ laser with two dissimilar shielding gaseous mixture namely 100% nitrogen (N) and 50% argon?+?50% nitrogen (A?+?N). AISI 904 L Super Austenitic Stainless Steel (SASS) incorporates higher levels of Mo, Cr, Ni, N, and Mn under normal conditions. In heating applications, it offers a superior corrosion resistance at moderate and higher temperatures. The microstructure of SASS is exhaustively austenitic in nature, when subjected to a solution-quenched state. The objective of this study is to determine the phenomenon that follows the action of two shielding gas mixtures on microstructural and bead profiles of laser-welded 904 L SASS. The weld bead profile of laser welding depends on various parameters such as beam power; travel speed, and focal position of the laser spot, and these factors have to be chosen in an appropriate manner to obtain the desired output. The cross-sectioned area of the bead profiles like bead width and depth of penetration is measured using an optical microscope. Two different shielding gas mixtures were used to examine the microstructural changes in the weld region. Besides, the variation in the hardness of the weld region was analyzed through the Vickers hardness tester.