The effect of interaction time and saturation of rock on specific energy in ND:YAG laser perforating

Laser perforating in oil and gas wells is a new scientific approach to the generation of uniform holes at a selected pitch to increasing the permeability of rocks. The influence of laser irradiation time and rock saturation by water and heavy oil on the specific energy, the energy required to remove the unit weight of rock, used during Nd:YAG laser perforating. The results show that an increase in the laser irradiation time increases the depth of the rock hole as well as the specific energy used, with a nonlinear relationship. Here, the estimated equation of rate of penetration as a function of the specific energy (SE) is free from saturation effects. The type of saturation influences the specific energy; the amount of SE required for water saturated samples is more than that required for the heavy oil saturated samples, and heavy oil saturated samples needed more SE than the dry samples.     

The effects of pulsed Nd:YAG laser irradiation on surface energy of copper

The effect of laser surface treatment on the surface energy of copper plate was investigated in terms of the surface microstructure analysis and theoretical computation in this paper. The surfaces of the copper plates were treated by Nd:YAG pulsed laser with different powers. The microstructures of the treated copper plates were analyzed by optical microscopy and X-ray diffraction (XRD), and the wetting experiment was performed to evaluate the variation of surface energy. The results showed that the surface microstructure and the corresponding surface energy of copper, changed with the variation of the laser power. The experimental results further explained by XRD results and theoretical calculation, demonstrated that the surface energy changed when the crystal structure in the surface layer was re-oriented in a preferred orientation after laser irradiation.     

Subhertz-linewidth Nd:YAG laser

Light from a Nd:YAG laser at 1064 nm is independently stabilized to two Fabry-Perot etalons situated on separate vibration-isolation platforms. A heterodyne beat measurement shows their relative frequency stability to be at the part-in-10(15) level at 5 s and the relative linewidth to be less than 1 Hz.     

High energy negative feedback controlled passively mode-locked Nd: YAG laser

High energy picosecond pulse trains from a passively mode-locked Nd: YAG laser are obtained. The negative feedback controlled oscillator delivers 10–30 s trains with energies of up to 30 mJ and single pulse duration of less than 25 ps. The laser is operated with a repetition rate of 10 Hz. An active Q-control of the cavity generates a short pulse train with duration of 30–40 ns. The long pulse train energy reproducibility is better than ± 1.5%.     

脉冲激光二极管侧面抽运Nd:YAG激光器晶体时变热效应

采用数值计算的方法,对脉冲激光二极管三向侧面抽运固体激光器中,激光晶体的温度场时变分布进行了计算. 分析了三向侧面抽运情况下晶体内光强分布,在此基础上,采用有限元法,以脉冲激光二极管侧面抽运Nd:YAG激光器为例,对单脉冲过程中晶体温度分布及其影响因素进行分析. 结果表明,晶体升温过程受到抽运条件以及散热条件的影响,但是主要受到抽运条件即抽运光强度和光束半径的影响,降温过程受到晶体热物性参数和晶体半径以及散热条件的影响. 当晶体温度达到周期性分布后,由于晶体径向温度梯度的周期性变化,引起通过晶体的平面光波的中心和边缘光线相对光程差也随时间作周期性变化.     

Suppressing effect of the laser extraction on heat generation in Nd:YAG

The suppressing effect of the laser extraction on heat generation in Nd:YAG was investigated. The extraction efficiency could be deduced from the slope efficiency, and heat generation in Nd:YAG could be obtained with the heat model developed, which was verified by the previous experiment. The essential reasons were given to explain the change trend of heat generation under the condition of laser extraction.     

Dual-polarization mode-locked Nd:YAG laser

A mode-locked solid-state laser containing a birefringent element is shown to emit synchronously two frequency combs associated to the two polarization eigenstates of the cavity. An analytical model predicts the polarization evolution of the pulse train, which is determined by the adjustable intracavity birefringence. Experiments realized with a Nd:YAG laser passively mode locked by a semiconductor saturable absorber mirror are in perfect agreement with the model. Locking between the two combs arises for particular values of their frequency difference, e.g., half the repetition rate, and the pulse train polarization sequence is then governed by the relative overall phase offset of the two combs.     

Solar pumped Nd:YAG laser

We report the high efficiency of solar pumped laser. The sunlight is concentrated by the concentrator system, which is composed by the Fresnel lens and the cone-channel condenser. The power density of sunlight concentrated by the concentrator system surpasses the lasing threshold for pumping laser. In the experiment, the sunlight concentrated is coupled into the conical chamber pumping Nd:YAG laser media. Laser output of 3.5 W has been achieved; the collect efficiency is 3.5 W/m². The conversion efficiency is 1.0% from solar power into laser, and the slope efficiency is achieved 1.86%.     

Nd：YAG激光器中的自锁模

本文报道在Nd:YAG激光器中首次获得的自锁模脉冲序列.自锁模是由于Nd:YAG棒中的自相位调制引起的.在主被动对撞锁模运转情况下,自锁模对脉冲波形有较大的影响.     

高功率四波长Nd:YAG激光实验

四波长Nd：YAG激光实验是利用非线性晶体BBO，通过倍频、混频和二次倍频等激光变频技术，分别获取了4个波段相干辐射光，本文介绍了各波长相干辐射光的获取方法及其时空特性的测量。     

High energy flash-lamp pumped Nd:YAG laser emitting at 1073.8 nm

A flash-lamp pumped Nd:YAG laser emitting 1073.8 nm is demonstrated. A thin film polarizer is inserted into the cavity for generating linearly polarized lasers. With incident pump energy of 69.6 J and pulse repetition rate of 1 Hz, output pulse energy of up to 487 mJ is obtained from a 1.0 at % Nd-doped Nd:YAG rod with a size of Ø6 mm × 110 mm. And the polarization ratio is more than 1000:1 at the output pulse energy of 487 mJ. The beam quality factors in the two orthogonal directions are 24.4 ± 0.2 and 24.6 ± 0.2, respectively.     

二极管泵浦Nd:YAG薄片激光器技术研究

固体激光器向高平均功率发展的最大障碍是激光介质的热效应.采用薄片激光介质可以实现热流近一维分布,因而是解决固体激光器热效应的有效手段之一,但许多因素都会影响薄片的一维热分布.对薄片热分布的主要影响因素进行的计算分析表明,在均匀泵浦条件下,泵浦区径向温度的均匀性不仅和泵浦区面积与薄片厚度之比有关,而且和冷却区与泵浦区的相关尺寸有关.采用均匀耦合技术并合理设计薄片的散热冷却结构以实现热流近一维分布,用平均功率336 W的激光二极管阵列泵浦一块NdYAG薄片,获得了平均功率超过120 W的准连续激光输出.     

Nd:YAG薄片激光器热致波前畸变

 理论分析了激光二极管端面泵浦薄片Nd:YAG 激光器的激光介质热效应对波前相位分布的影响,给出了薄片激光器波前热畸变的计算公式。数值模拟了理想均匀泵浦及4阶超高斯泵浦下的波前分布,分析了介质厚度和泵浦均匀性与波前畸变量的关系。研究表明,介质越薄,激光泵浦光均匀性越好,泵浦功率密度越小,激光波前畸变越小;与介质厚度、泵浦功率密度相比,泵浦光光强分布对波前的影响更为显著。     

脉冲LDA侧面泵浦大能量Nd:YAG激光器时变热效应分析

建立了激光二极管阵列（LDA）侧面泵浦棒状Nd:YAG增益介质时变热效应理论计算模型。采用有限元Ansys软件模拟分析了脉冲LDA侧面泵浦大能量固体激光器的时变热效应特性。研究结果表明,所研究的脉冲LDA侧面泵浦大能量Nd:YAG激光器热效应具有时变特性,介质横截面内中心点处的稳态温度场分布随时间呈锯齿形周期变化,锯齿形变化频率为LDA泵浦频率,脉冲LDA泵浦参数对介质稳态温度场分布有较大影响。分析和计算了介质内热梯度、应力双折射以及激光晶体端面效应等导致的晶体热透镜焦距。计算表明,介质的热焦距主要来源于介质内温度梯度引起的热透镜焦距。     

Frequency-tripled Nd:YAG laser ablation in laser structuring process

With the increasing demand for finer lines/spaces on PCB boards, a new technology—laser structuring—has emerged in recent years. In this research, the frequency-tripled Nd:YAG laser is selected as the laser source in laser structuring; this laser is often used in miniaturization machining. This paper describes in detail the processing parameters’ influences, such as laser power, numbers of repetition, repetition rate and bite size, on laser structuring results. From the research results, it can be concluded that the line width and depth are increased with increases in the laser power and numbers of repetition. Repetition rate, bite size and velocity are related to one another. When the bite size is fixed, the velocity increases with the repetition rate and the depth of the line is decreased at the same time. When the repetition rate is fixed, velocity increases with the bite size.     

大功率Nd∶YAG固体激光器

介绍了一台单级输出灯泵浦大功率脉冲Nd∶YAG激光器。该激光器脉宽0.1-10ms可调,频率1-1000hz可调,总注入电功率12kw。试验得到激光器参数脉冲宽度和频率协调改变,可使激光器在整个脉宽范围内都能稳定500w输出;最大单脉冲能量56J;总体电光效率4.2%;光束质量为25mm.mrad;功率稳定性±2%。     

High-energy long-pulse Nd:YAG picosecond laser

A long train of actively mode-locked pulses is obtained from a negative feedback controlled Nd:YAG laser. The 70s pulse train contains up to 0.1 J energy and the duration of the picosecond pulses is 120 ps. The laser is operated at a repetition rate of 20 Hz. ActiveQ-control of the cavity generates a short pulse train of duration 50 to 70 ns. An excellent peak-to-background intensity ratio of the correlation function for the picosecond pulses in the train of 5×10³ is reported.     

Diode-pumped 1123-nm Nd:YAG laser

We demonstrated a diode-pumped Nd:YAG laser with a plano-concave resonator. When the pump power is 1.57 W, the output power of 1123-nm laser is 132 mW at the temperature of 20 ℃, and the power change is less than 2% in an hour. A periodically poled LiNbOa (PPLN) was used as outer cavity frequency-doubling crystal and 561-nm laser was observed.     

Stable tunable single-frequency Nd:YAG laser

Single frequency operation of a Nd:YAG laser is obtained with a temperature-compensated, sealed intracavity etalon which is optimized with respect to selectivity and loss by taking spatial hole burning of the laser medium into account. For stabilization purposes we calculate the response of the laser when (i) the etalon's thickness is modulated and when (ii) the laser cavity length is modulated. We find orders of magnitude better stability for (i) and demonstrate the feasibility of a system with 100 mW output power, a longterm frequency stability of 3×10^?9, and an intensity stability of 10^?4.     

Additive pulse mode-locked Nd: YAG laser

Additive pulse mode locking applied to lamppumped Nd: YAG lasers results in an attractive source of picosecond pulses at 1.06 m or 1.32 m with average powers at the Watt level. We provide detailed information on construction and operation and give data on performance. A modified active stabilization scheme allows not only improved stability of operation but also insight into the dynamics of pulse formation.