基于半导体可饱和吸收镜实现闪光灯抽运Nd∶YAG激光器的被动调Q与锁模

基于同一块半导体可饱和吸收镜(SESAM),实现了闪光灯抽运的Nd∶YAG激光器的被动调Q与锁模。实验结果表明:腔长较小时,激光器运转在调Q状态,调Q脉冲宽度为90 ns;随着腔长的增加,调Q脉冲中出现调制,而且调制深度随着腔长的增加而加深。当腔长为140 cm,全反射凹面镜曲率半径为300 cm时,激光器运转在稳定的被动锁模状态,输出的锁模脉冲序列能量为27 mJ、脉宽为35 ps。实验比较了SESAM器件在平凹稳定腔和平凸非稳腔激光器中实现被动锁模的差异,并给出理论解释。SESAM有望取代有机染料成为闪光灯抽运的Nd∶YAG激光器理想的被动锁模器件。     

染料调Q的Nd3+:YAG激光器偏振性测试

为了确定染料调Q的Nd3+:YAG激光器发射的单次激光脉冲的偏振性,利用偏振分束立方体和双通道激光能量计,实验测量了激光脉冲经偏振分束后P偏振光和S偏振光的能量比,分析总结了激光器的偏振性.结果表明:激光器偏振性个体差异很大,不存在统一性;每一台激光器都有各自的偏振性,同一台激光器前后发射的激光脉冲的偏振性可能一致,也可能变化较小,也可能完全随机.产生偏振性的具体原因有待进一步研究.     

染料调Q的Nd3+∶YAG激光器偏振性测试

为了确定染料调Q的Nd3+:YAG激光器发射的单次激光脉冲的偏振性,利用偏振分束立方体和双通道激光能量计,实验测量了激光脉冲经偏振分束后P偏振光和S偏振光的能量比,分析总结了激光器的偏振性.结果表明:激光器偏振性个体差异很大,不存在统一性;每一台激光器都有各自的偏振性,同一台激光器前后发射的激光脉冲的偏振性可能一致,也...     

染料调Q的Nd3+∶YAG激光器偏振性测试

为了确定染料调Q的Nd3+∶YAG激光器发射的单次激光脉冲的偏振性,利用偏振分束立方体和双通道激光能量计,实验测量了激光脉冲经偏振分束后P偏振光和S偏振光的能量比,分析总结了激光器的偏振性。结果表明:激光器偏振性个体差异很大,不存在统一性;每一台激光器都有各自的偏振性,同一台激光器前后发射的激光脉冲的偏振性可能一致,也可能变化较小,也可能完全随机。产生偏振性的具体原因有待进一步研究。     

YAG电光调Q激光器发光特性的测试

电光调Q技术是利用晶体的电光效应来实现Q突变的方法。在电光调Q激光器上,就激光器静态状态下氙灯光和出射激光的波形、激光发光阈值等状态进行了测试;并就调Q状态下的激光波形的变化及脉宽、峰值功率等进行了测试与讨论,从而对电光调Q激光器的发光特性给出了较为完整的测试。结果证明该测试方法直观可靠,对了解和掌握电光调Q激光器有较大的帮助。     

基于Yb∶YAG/Cr~(4+)∶YAG/YAG键合晶体的被动调Q激光器

为了研究键合晶体在被动调Q激光器上的应用优势,采用Yb∶YAG/Cr~(4+)∶YAG/YAG键合晶体搭建了紧凑的端面泵浦被动调Q激光器,获得了高效的1 030nm和515nm脉冲激光。实验研究了泵浦功率和初始透过率T0对各项激光性能的影响,结果在T0=95%时得到了平均功率为1.97 W的1 030nm激光,对应33%的斜效率,而当T0=85%时输出的1 030nm脉冲峰值功率高达87kW,脉冲宽度低至3.14ns。另外在与LBO的倍频实验中,用T0=90%的键合晶体获得了较高的绿光输出功率634mW,对应11.2%的斜效率和15ns的脉冲宽度。最后还研究了光谱的红移和输出镜的漏光现象,找出进一步提高绿光功率的方法。     

被动锁模掺铒光纤激光器中的有理数谐波锁模现象的研究

在分析有理数谐波锁模的理论和非线性放大环镜（NALM）传输特性的基础上,对被动锁模掺铒光纤激光器进行了相关的研究。实验中除了观测到了稳定的谐波锁模脉冲外,还观察到了的有理数谐波锁模脉冲的产生现象,分析其脉冲重复频率也证实此类脉冲序列具有属于3阶、5阶和6阶有理数谐波锁模脉冲序列重复频率的一样的规律。     

四程抽运Yb:YAG薄片激光器

设计了四程抽运的Yb:YAG薄片激光器.选用掺杂原子数分数为10%,几何尺寸为Ф10 mm=300m的薄片状Yb:YAG晶体,采用铟焊工艺将其焊接到水冷系统上,用可调式恒温水箱对其进行温度控制.使用两个Ф一30 mm,R=50 mm的球面反射镜,完成了四程抽运.利用蒙特卡罗方法对抽运光斑的大小进行了计算,将反射镜轴向与光纤头轴向夹角控制在12°以内,以使抽运光斑半径与基模光斑半径比符合模式匹配原则.在LDA抽运功率为4.13 W时,获得了最高功率为670 mW的1 030 nm连续激光输出,光-光转换效率为16.2%.实验结果表明:该结构可降低激光介质的热透镜效应和应力双折射效应,获得高光束质量的激光输出,但散热系统和焊接工艺需进一步优化.     

四程抽运Yb:YAG盘式激光器

报道了激光二极管阵列(LDA)抽运Yb:YAG盘式激光器。Yb:YAG晶体掺杂浓度10-at.%,几何尺寸为Φ10mm×300μm,采用铟焊工艺将其焊接到水冷系统上,用可调式恒温水箱对其进行温度控制。利用蒙特卡罗方法对抽运光斑的大小进行了计算,将反射镜轴向与光纤头轴向夹角控制在120以内,以使抽运光斑半径与基模光斑半径比符合模式匹配原则。使用两个Φ=30mm,R=50mm的球面反射镜,完成了四程抽运。在LDA抽运功率为4.13W时,获得了最高功率为670mW的1030nm连续激光输出,光-光转换效率为16.2% 。     

半导体量子点材料在Nd:YAG激光辐照下的非线性光学效应

使用10 n,脉冲调Q Nd:YAG激光器Z-scan技术测量了化学合成的无掺杂硫化锌量子点(QDs)以及掺Mn2+硫化锌量子点(QDs)的非线性光学特性,并使用透射电镜技术(TEM)以及X射线衍射法(XRD)表征合成材料的纳米结构.在室温下,分别利用UV-VIS分光光度计和分光荧光计测量了人工合成QDs胶体溶液的线性光学吸收特性以及光致发光的发射特性.样品的吸收特性表明,由于量子限制效应的影响,样品的截止吸收低于硫化锌的截止吸收.样品的光致发光特性显示,掺Mn2+的硫化锌样品显示出明显的光致发光现象,发射峰大约在580 nm;而无掺杂的硫化锌样品在紫外区辐射,发射峰大约在365 nm.对样品的UV-VIS吸收特性分析和TEMXRD分析表明,硫化锌样品的平均粒度(半径)大约为1.2 nm.分析开放光圈(OA) Z-scan技术得到的实验数据,发现在1 064 nm处两种试验样品都会发生四光子吸收(FPA)现象.拟合实验数据得到了两种试验样品的FPA系数以及FPA横截面,结果表明,ZnS QD的FPA横截面的计算值是4.9×1-106cm8·s3·photon-3,比硫化锌的FPA横截面大了5个数量级,而且人工合成的ZnS QD也有光学限制的性质.掺Mn2+离子的样品具有大的FPA横截面和在可见光区有高的发光效率这两个特点,使得该材料适合用于多光子荧光成像.     

准基模纯风冷激光二极管泵浦Nd∶YAG激光器

介绍一种纯风冷激光二极管泵浦的脉冲Nd∶YAG激光器,单脉冲能量250mJ,重复频率25Hz,脉冲宽度7ns,光光转换效率13.6%。激光器输出为准基模,垂直和水平方向的M2值测量结果分别为2.81和4.09。同样结构下将风冷系统换成风冷水冷结合方式,激光器脉冲能量345mJ,重复频率提高到50Hz,光光转换效率上升为15.2%。两种形式的激光器连续工作时间5min,并进行了高温+55℃和低温-25℃的环境试验。     

垂直腔面发射激光端面泵浦的高能量调Q Nd:YAG激光

采用垂直腔面发射激光端面泵浦Nd∶YAG获得了高能量的1 064 nm调Q激光输出。与边发射半导体激光相比,垂直腔面发射激光具有各向发散角相同、波长随温度漂移小等优点,更适合用作泵浦源以产生高效率、结构紧凑的激光。泵浦能量为200 mJ时,产生了最高45 mJ的1 064 nm激光输出,光光转换效率达到22.5%,激光脉宽为8 ns,发散角为1.2 mrad。基于模拟计算优化了Nd3+掺杂浓度,通过采用低浓度的Nd∶YAG晶体减小泵浦端面增益,从而有效抑制了影响调Q激光能量提高的自激振荡,为获得高能量的端面泵浦调Q激光输出提供了有效的技术手段。     

Surface texturing by pulsed Nd:YAG laser

Introducing specific textures on a tribological surface can contribute to friction reduction in sliding contacts. In the present paper, a pulsed Nd:YAG laser emitting at 1064 nm, was used against 100Cr6 steel samples in order to produce well-defined surface micro-pores, which can act as lubricant reservoirs, micro-hydrodynamic bearings as well as traps for wear debris. Due to the high flexibility of the laser system, structural features such as shape, size, density and depth can be varied easily by changing the laser parameters. To optimize the parameters of the laser surface texturing process, an investigation was performed using different pulse numbers, various pulse energies and two different modes (single- and multi-mode). The microtextures were characterized with optical microscopy, scanning electron microscopy (SEM) and by topography techniques. The relationship between the laser processing parameters and qualitative and quantitative profile of the micro-pores was studied. Tribological testing of laser textured surfaces was performed in a low frequency–long displacement reciprocating sliding wear tester under boundary lubrication and results compared to un-textured case. Tribological comparison of textured, textured and lapped, and untextured surfaces shows only minimal influence of texturing for contact conditions investigated.     

The laser dressing of resin-bonded CBN wheels by a Q-switched Nd: YAG laser

Resin-bonded cubic boron nitride (CBN) grinding wheels are widely used in industry due to their good grinding ability. There is, therefore, a need to find a good method suitable for the dressing of these wheels. This paper presents a new method dressed by an acoustic-optic Q-switched Nd: YAG laser based on thermal interaction, which is unlike the conventional mechanical dressing methods based on force interaction. The mechanism of the selective removal of the bond was analysed. Experiments of a single pulse ablation on the resin bond and the CBN grains, and the laser dressing of resin-bonded CBN wheels with different dressing parameters have been carried out. The grinding force has been compared for the conventional mechanical dressed wheel and the laser dressed wheel. It is shown that the resin-bonded CBN grinding wheel is suitable for an acoustic-optic Q-switched Nd: YAG laser dressing with radial irradiation, which is better than a continuous wave (CW) laser dressing with radial irradiation and conventional mechanical dressing methods.     

Fabrication of polycrystalline diamond microtool using a Q-switched Nd:YAG laser

A Q-switched Nd:YAG laser (1,064 nm, 100 ns) was used to machine 2?×?1.5?×?0.5-mm rhombus-shaped tool inserts from a 60?×?0.5-mm circular disk of polycrystalline diamond. A systematic experimental study was undertaken to examine the effects of pulse repetition rate, feed rate, and number of laser passes on kerf, material removal rate, recast layer, surface morphology, and surface roughness. The optimal laser parameters for generating two-dimensional tool profiles were an average power of 3 W, a pulse repetition rate of 2 kHz, a feed rate of 1 mm/s, and a total of 45 laser passes. The beneficial results were a material removal rate of 0.02 mm³/min, kerf width of 27 μm, cutting edge radius of 6 μm, and surface roughness (Ra) of 0.625 μm. Recast layer formation, undulations, and striations were observed in the laser-cut regions. These features were attributed to the presence of a molten layer of cobalt binder, and amorphous carbon and graphite transitioned from diamond. An intriguing feature is the presence of fine particulate matter ranging in size from nanometers to a few micrometers in the laser-cut regions. It is believed that phase transition of diamond and cobalt during laser machining created thermal expansion mismatch stresses sufficient to fracture the solid into fine fragments.     

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.     

Development of controlled Nd:YAG laser for medical applications

Several medical fields are concerned with applications of thermal lasers such as neodymium-doped, yttrium aluminum garnet (Nd:YAG), argon, and CO2. However, quantification of the necrotic volume of Nd:YAG laser-induced damage is not possible at the time of treatment. Mathematic models and feedback control can help to optimize Nd:YAG laser treatments. We therefore formulated mathematic models for coagulation processes and developed an intelligent Nd:YAG laser system with closed-loop feedback control. Surface temperature evolution proved to be valuable data for real-time control of coagulation and ablation. Infrared thermometry provided the noncontact measurement of temperature. A computer stored the temperature data calculated by the mathematic model. Deviations of surface temperature during the treatment beyond established tolerances causes the Nd:YAG laser system to adjust the laser power automatically.     

Pulsed Nd:YAG laser treatment of monocrystalline silicon substrate

To minimize reflection and increase the opportunity for photovoltaic (PV) devices to absorb incident light, we produced rough-textured surfaces using a pulsed Nd:YAG laser. We investigated the effect of various operating parameters on surface features and optical performance. The parameters investigated were pulse repetition frequency, pulse energy, and textured surface exposure time. Following laser surface treatment, no chemical solution etching or anti-reflective coatings were necessary. Reflectance values were measured by spectrophotometer. Structural properties including surface morphology and surface roughness of the textured surfaces were analyzed by a three-dimensional confocal laser scanning microscope. The resulting surface reflection curves indicated that, of the different laser machining paths, the vertical and circular paths produced identical optical properties in the samples. Surface reflection values decrease as the pulse energy and exposure times increase. By contrast, surface roughness increases with exposure time. An increase in pulse frequency reduces surface roughness, although the extent of the reduction depends upon the pulse energy. Following surface texturing of the monocrystalline silicon samples, the total reflection was reduced from 40% to approximately 10% of incident light. Our experimental results indicate that the rougher surfaces attained by laser surface treatment provide better light-trapping properties for PV devices.