Development of a 756 nm, 3 W injection-locked cw Ti:sapphire laser

We have developed a 756 nm, 3 W single-frequency cw Ti:sapphire laser by using the technique of injection locking. A cw Ti:sapphire laser in a ring-type configuration was forced to lase unidirectionally by use of an optical diode to prevent a high-power backward laser from disturbing the injection laser. A master laser was amplified by a broad-area laser diode and coupled into a single-mode fiber to generate a 50 mW injection laser with a Gaussian beam profile, which was enough to lock the Ti:sapphire laser at full power of 3 W. Such a high-power single-frequency Ti:sapphire laser enables a watt-level blue or near-ultraviolet single-frequency laser to be generated by frequency doubling.     

Dependence of the laser two-photon ionization process in solution on the laser pulse width

The laser two-photon ionization process has been investigated using simultaneous irradiation of an UV beam and an IR beam. When the laser pulse width was 300 ps, it proceeded through a geminate pair state (a stepwise process), as indicated by the signal enhancement with simultaneous irradiation of the two laser beams. Although no signal enhancement was observed when the laser pulse width was 100 fs, and because molecules with no absorption at the laser wavelength showed an intense signal, the two-photon ionization excited by a femtosecond laser should proceed through a simultaneous two-photon process. The detection limit was quite susceptible to the laser fluctuations.     

光纤饱和吸收体稳频窄线宽光纤激光器

结合光纤饱和吸收体与光纤光栅法布里-珀罗标准具,研制出了全光纤结构1550nm单频窄线宽掺铒光纤环形激光器.采用两个976nm激光二极管双向抽运作为抽运源,高掺杂浓度铒光纤作为增益介质,以行波腔消除空间烧孔效应,利用光纤光栅法布里-珀罗标准具窄带选模特性,以10m长低掺铒光纤饱和吸收体稳频,得到了十分稳定的窄线宽激光输出.激光器抽运阈值功率21mW,在抽运光功率为145mW时输出光功率39mW,斜率效率30%,信噪比大于50dB.采用延迟自外差方法精确测量光纤激光器线宽小于10kHz.     

Imprinting on empty hard gelatin capsule shells containing titanium dioxide by application of the UV laser printing technique

The purpose of this study was to examine the application of ultraviolet (UV) laser irradiation to printing hard gelatin capsule shells containing titanium dioxide (TiO₂) and to clarify how the color strength of the printing by the laser could be controlled by the power of the irradiated laser. Hard gelatin capsule shells containing 3.5% TiO₂ were used in this study. The capsules were irradiated with pulsed UV laser at a wavelength of 355?nm. The color strength of the printed capsule was determined by a spectrophotometer as total color difference (dE). The capsules could be printed gray by the UV laser. The formation of many black particles which were agglomerates of oxygen-defected TiO₂ was associated with the printing. In the relationship between laser peak power of a pulse and dE, there were two inflection points. The lower point was the minimal laser peak power to form the black particles and was constant regardless of the dosage forms, for example film-coated tablets, soft gelatin capsules and hard gelatin capsules. The upper point was the minimal laser peak power to form micro-bubbles in the shells and was variable with the formulation. From the lower point to the upper point, the capsules were printed gray and the dE of the printing increased linearly with the laser peak power. Hard gelatin capsule shells containing TiO₂ could be printed gray using the UV laser printing technique. The color strength of the printing could be controlled by regulating the laser energy between the two inflection points.     

Production of Raman laser beams using injection-locking technique

We produced two Raman-laser beams with a frequency offset of 9.2 GHz by injection-locking of a master diode-laser to a slave diode-laser. The master laser was phase-modulated at 9.2 GHz while the laser beam passed through an electrooptic modulator. The phase-modulated beam was injected into the slave laser that was oscillating around one of the side-bands of the master laser. The relative linewidth of the two lasers was less than 10 Hz. Using these laser beams, coherent population trapping resonance of cesium atoms was observed for the purpose of testing the phase-coherence of the laser beams.     

Nanomechanical properties of silicon surfaces nanostructured by excimer laser

Excimer laser irradiation at ambient temperature has been employed to produce nanostructured silicon surfaces. Nanoindentation was used to investigate the nanomechanical properties of the deformed surfaces as a function of laser parameters, such as the angle of incidence and number of laser pulses at a fixed laser fluence of 5 J cm⁻². A single-crystal silicon [311] surface was severely damaged by laser irradiation and became nanocrystalline with an enhanced porosity. The resulting laser-treated surface consisted of nanometer-sized particles. The pore size was controlled by adjusting the angle of incidence and the number of laser pulses, and varied from nanometers to microns. The extent of nanocrystallinity was large for the surfaces irradiated at a small angle of incidence and by a high number of pulses, as confirmed by x-ray diffraction and Raman spectroscopy. The angle of incidence had a stronger effect on the structure and nanomechanical properties than the number of laser pulses.     

磷酸盐激光玻璃中杂质离子铁和铜对激光效率的影响

实验研究了Fe和Cu离子对N31型激光玻璃在激光波段1053 nm激光斜率效率的影响。研究发现, 随着Fe离子含量的增加, 激光斜率效率呈e指数快速下降, 激光阈值呈二次方程形式快速增加, 并得出Fe离子含量与斜率效率和激光阈值之间的经验关系式。同时发现, 在相同掺杂浓度条件下, Cu离子比Fe离子更加严重地降低钕玻璃的激光性能。研究结果对如何提高激光玻璃的增益性能和定量控制原材料的杂质含量具有一定指导意义。     

Performance improvement in a directly 879 nm dual-end-π-polarized-pumped CW and pulsed GdVO₄/Nd:GdVO₄ laser

A continuous-wave and Q-switched 10 kHz GdVO?/Nd:GdVO? laser by 879 nm laser-diode pumping was demonstrated. We combined dual-end-π-polarized-pumping, half-wave plate (HWP) insertion, composite laser crystals, and dual Q-switching techniques to obtain a 1.06 μm nanosecond laser with high temporal and spatial quality. A polarization beam splitter was used to divide the unpolarized pump beam into two linearly polarized beams to increase the absorption efficiency. The output performance was improved obviously by inserting a HWP into the cavity. The pulse duration was compressed and the peak power was increased for a doubly Q-switched laser, in contrast to a single acousto-optical Q-switched laser under the same conditions.     

6063铝合金单模光纤激光焊接工艺研究

目的 针对采用脉冲激光点焊的6063铝合金焊点拉力较低,无法满足实际需求的问题,研究6063铝合金激光焊接的最优工艺方案,以提升焊点拉力.方法 采用单模光纤激光对6063铝合金进行焊接,通过极细的线宽组成螺旋点,代替单个脉冲激光点焊.对激光功率、焊接速度及离焦量等工艺参数进行正交实验,得到最佳工艺参数,并通过分析焊缝外...     

Nanomechanical properties of silicon surfaces nanostructured by excimer laser

Abstract

Excimer laser irradiation at ambient temperature has been employed to produce nanostructured silicon surfaces. Nanoindentation was used to investigate the nanomechanical properties of the deformed surfaces as a function of laser parameters, such as the angle of incidence and number of laser pulses at a fixed laser fluence of 5 J cm^?2. A single-crystal silicon [311] surface was severely damaged by laser irradiation and became nanocrystalline with an enhanced porosity. The resulting laser-treated surface consisted of nanometer-sized particles. The pore size was controlled by adjusting the angle of incidence and the number of laser pulses, and varied from nanometers to microns. The extent of nanocrystallinity was large for the surfaces irradiated at a small angle of incidence and by a high number of pulses, as confirmed by x-ray diffraction and Raman spectroscopy. The angle of incidence had a stronger effect on the structure and nanomechanical properties than the number of laser pulses.     

Trapping and manipulating gas bubbles in water with ultrashort laser pulses at a high repetition rate

We have experimentally observed the trapping of a gas bubble in water by focused laser radiation. The optical trap was provided by 200-fs pulses of a Ti-sapphire laser operating at a repetition rate of 100 kHz. The laser radiation was focused in water by an objective with a numerical aperture of 0.5. The trapping force in water is estimated as ∼200 pN at an average laser power of 20 mW, which is by two orders of magnitude greater than the efficiency of a traditional laser tweezers. The trapping force arises upon local heating of gas inside a bubble due to nonlinear absorption in the focal region.     

Morphological and animal study of titanium dental implant surface induced by blasting and high intensity pulsed Nd-glass laser

Machined dental implants of titanium were blasted with Al₂O₃ powder of 250 μm particle size. The surface was irradiated in vacuum with a Nd-glass pulsed laser at 1–3 J pulse energies. The morphology of these surfaces was investigated by optical and scanning electron microscopy. The low intensity laser treatment resulted in some new irregularities but we can observe the blasted elements and caves from the original blasted surface too. The blasted elements were washed out and a new surface morphology was induced by the high intensity laser treatment.The osseointegration was determined by measuring the removal torque in the rabbit experiments. The results were referred to the as machined surface. The blasting slightly increased the removal torque. The laser irradiation increased the removal torque significantly, more by a factor of 1.5 compared to the reference at high laser intensity. This shows the influence of the surface morphology on the osseointegration.The combination of the blasting with the laser irradiation is considered a method to determine the morphology optimal for the osseointegration because the pulsed laser irradiation caused modifications of the micrometer sized surface elements and decreases possible surface contamination.     

Fabrication of a distributed-feedback dye laser with a grating structure in its plastic waveguide

Two approaches of fabricating grating structures for waveguided plastic dye lasers are described and compared for lasing performance. Rhodamine6G-doped poly(methyl methacrylate) (PMMA) film on a PMMA substrate was used for the waveguide, and a distributed-feedback (DFB) laser operation with a single-propagation mode was demonstrated. The performances of both types of permanent grating structured DFB dye laser were better than those of a DFB dye laser on a plain waveguide with a dynamic grating formed by the interference of two pump beams. Wide tuning range is expected by use of a multistripe DFB laser with different grating pitches.     

Effect of nanosecond laser pre-irradiation on the femtosecond laser-induced damage of Ta2O5/SiO2 high reflector

The effect of nanosecond laser pre-irradiation on the femtosecond laser-induced damage behaviors of 800 nm 0° AOI Ta(2)O(5)/SiO(2) high reflectors fabricated by e-beam evaporation was explored. Laser pre-irradiation was carried out by Raster-scanning with scanning mode of 1-on-1 and scanning velocities timed such that there was a beam overlap at 70% of the peak fluence, utilizing 5 Hz 1064 nm 12 ns Nd:YAG fundamental lasers. Femtosecond laser damage was investigated by 1 kHz 800 nm 135 fs Ti: sapphire laser system with 1-on-1 mode test. The results indicated that nanosecond laser pre-irradiation did not promote the femtosecond laser-induced damage threshold of reflectors. Instead, the thresholds of all the samples with various fluence steps for pre-irradiation were reduced by about 20%. Furthermore, the damage morphologies were analyzed by optical microscope, SEM and AFM, which displayed deterministic field induced breakdown characteristics. To explain these phenomena, a theoretical model including photoionization, avalanche ionization, and decays of electrons was built to simulate the evolution of electron density in the conduction band. Field ionization mechanism was considered to dominate the femtosecond laser damage process, while the electronic defects induced by nanosecond laser pre-irradiation accelerated the femtosecond laser damage evolution.     

紫外激光对触摸屏产品中不可视区域刻蚀实验研究

采用紫外激光对触摸屏产品中不可视区域进行刻蚀分析,探究了紫外激光刻蚀原理,讨论了银浆薄膜激光刻蚀与传统印刷工艺异同点,并在此基础上完成一套紫外激光刻蚀系统方案的设计和建造。实验结果表明,选用波长为355nm的紫外激光器,当激光器功率为10W,重复频率100kHz,刻蚀速度为1500mm/s,刻蚀次数1次时,薄膜被完全刻蚀,最终获得功能良好的银浆线路。经测试后发现,所刻蚀后银浆线条平直而光滑,边缘热影响区域较小,最小刻蚀线宽可以达到10μm,基板未受到损伤;与传统印刷工艺相比较,简化了工艺步骤,产品良品率得到提升,是一种无排放的绿色环保先进的刻蚀工艺。     

7050铝合金激光冲击强化形貌光学表征与表面残余应力分布的研究

本研究涉及7050铝合金激光冲击强化形貌的定量光学表征和表面残余应力分布的测定。研究表明，随着激光脉冲能量的增加，冲击凹陷深度与冲击区表面粗糙度均有所增加；冲击区径向残余应力的分布与横截面凹陷深度的分布相似。冲击区径向残余应力分布与激光冲击产生的弹一塑性波分布有关；弹一塑性波产生的塑性变形越大，残余应力也越大。较大的激光脉冲能量可产生中心对称的塑性变形和相应的残余应力分布。     

Development of a Tunable, Narrow-Linewidth, CW 2.066-mum Ho:YLF Laser for Remote Sensing of Atmospheric CO(2) and H(2)O

A smoothly tunable, narrow-linewidth, cw, 32-mW, 2.066-mum Ho:YLF laser was constructed and used for the first time in preliminary spectroscopic measurements of atmospheric CO(2) and H(2)O. The laser was constructed with a 4.5-mm-long, TE-cooled, codoped 5% Tm and 0.5% Ho yttrium lithium fluoride crystal (cut at Brewster's angle) pumped by an Ar(+)-pumped 500-mW Ti:sapphire laser operating at 792 nm. Intracavity etalons were used to reduce the laser linewidth to approximately 0.025 cm(-1) (0.75 GHz), and the laser wavelength was continuously and smoothly tunable over approximately 6 cm(-1) (180 GHz). The Ho:YLF laser was used to perform spectroscopic measurements on molecular CO(2) in a laboratory absorption cell and to measure the concentration of CO(2) and water vapor in the atmosphere with an initial accuracy of approximately 5-10%. The measurement uncertainty was found to be due to several noise sources, including the effect of asymmetric intensity of the laser modes within the laser linewidth, fluctuations caused by atmospheric turbulence and laser beam/target movement, and background spectral shifts.     

163 fs被动锁模掺Er~(3+)光纤激光器

研制了一种采用非线性偏振旋转锁模效应的被动锁模掺Er3+飞秒激光器。利用性能稳定的980 nm激光二极管(LD)作为抽运光源,以高掺杂Er3+光纤为增益介质,在抽运功率为650 m W时,激光器锁模输出重复频率为31.25 MHz、平均输出功率为70 m W、中心波长为1565 nm、光脉冲宽度为163 fs的稳定飞秒脉冲激光。该激光器易于操作和调节,并且锁模状态稳定可以长时间的运行,其光纤结构更有利于小型化和便携化。     

Laser Glazing of Plasma Sprayed Ni-Cr-Al-Y Alloy

Laser surface melting provides a unique opportunity to increase the density of the relatively porous microstructure found in plasma sprayed (PS) coatings. In the current investigation a plasma sprayed Ni-Cr-Al-Y alloy was surface melted using a CO₂ laser. Melted track width was found to be strongly influenced by laser power and weakly influenced by traverse speed over the range investigated. The microstructure of the laser glazed area was examined by various techniques including optical microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and energy dispersive x-ray analysis (EDAX). Refined microstructure was observed in the laser glazed region, and under high laser power (800 W) mixing of the coating with the substrate created metallurgical bonding.     

激光参数对碳纤维复合材料质量烧蚀率的影响

为了研究激光参数对碳纤维增强有机硅改性环氧树脂复合材料质量烧蚀率的影响规律, 选用不同激光参数、采用高强度CO₂激光器对该复合材料进行了激光辐照试验。分别分析了入射激光的辐照时间、强度和光斑直径对碳纤维增强有机硅改性环氧树脂复合材料质量烧蚀率的影响规律。研究结果表明: 激光辐照时间对该复合材料的质量烧蚀率的影响不大, 而该复合材料的质量烧蚀率随入射激光强度和光斑直径的增大而增大。