Effects of the Various Cooling Conditions on 1,064-nm nd:Yag Laser Treatment for Selective Photothermolysis

The purpose of this study was to find optimum treatment conditions for selective photothermolysis by evaluating internal–external heat distributions according to different cooling methods. The 1,064-nm Nd:YAG laser was transmitted into a skin-mimicking phantom with different cooling conditions, and its minimum temperatures and sub-zero times were measured. The cooling methods were classified into a total of eight conditions composed of five cryogen spray cooling conditions and three air cooling conditions. Based on the experimental results, condition 2 was selected as the optimum cooling condition for selective photothermolysis obtained from the cryogen spray cooling method.     

Cooperative Processes in Nd3☎/Yb3☎ Co-Doped Yag Nanocrystallites

The cooperative processes in doubly doped Nd/Yb:YAG nanocrystallites were investigated. An extremely strong Yb^3? ion concentration influence on absorption intensities was noticed. An efficient Nd^3? → Yb^3? energy transfer in YAG nanocrystallites was found. However no back transfer was observed. The mechanisms of cooperative interactions between Nd^3? and Yb^3? ions in YAG nanocrystallites responsible for the observed concentration effects are discussed.     

Electron Spin Resonance Study of Yttrium Aluminum Garnet Films Doped with Nd and Yb Ions

Yttrium aluminum garnet (YAG) thin films doped with optical active rare earth ions grown on YAG substrate can be used as wave-guide laser. Measured layers YAG:Yb, Nd (grown by the isothermal liquid phase epitaxy (LPE)) was additionally doped with Ga and Lu ions in order to increase film refractive index and decrease strains in layers, respectively. Electron spin resonance measurements have been performed on a number of YAG:Yb, Nd thin films with Yb concentrations ranging from 0at.% to 15at.% and Nd concentration equals to 1 at.% and 3 at.%. It was found that the measured angular dependence of the Yb^3? ion linewidth is typical for a mosaic structure. Moreover, it was shown that internal strains in the layers depend on the kind of dopant as well as on their concentration.     

Characterization of spectral hole depth in Tm^3＋ ：YAG within the cryogenic temperature range

In this paper, spectral hole depth dependence on temperature below 10 K in Tm^3＋ ：YAG crystal is investigated in detail. A novel model is proposed to analyze the temperature dependence on the spectral hole. By using the proposed model, we theoretically deduce the temperature dependence of spectral hole depth. The results are compared with experimental results and they are in good agreement. According to the theoretic results, the optimum temperature in experiment can be found.     

Spectral Characterization of Nitrogen in Farmland Soil by Laser-Induced Breakdown Spectroscopy

Nitrogen is one of the most important elements in farmland soil, and nitrogen content is one of the evaluation indicators of fertilizers. It is difficult to measure the nitrogen content in farmland soil because the chemical and physical properties of farmland soil are complex. Through the adoption of buffer gases to remove the influence of the nitrogen in air, this paper studied the laser-induced breakdown spectroscopy (LIBS) characteristics of nitrogen in soil to establish a foundation for in situ measurement of nitrogen in farmland soil. Three characteristic spectral lines have been found. Based on the precise controlling of laser power and triggering of delay time between laser generation and spectra collection, we have studied the effects of laser energy on LIBS spectral characteristics and the time evolution characteristics to supply the basis of parameter optimization for the measurement. In addition, we have studied the relationship between nitrogen concentration and LIBS spectral intensity. The results demonstrated that LIBS was an effective measurement method of nitrogen content in farmland soil with simple hardware structure, fast detection, and high precision.     

Morphological and structural characterizations of different oxides formed on the stainless steel by Nd:YAG pulsed laser irradiation

The effects of laser surface irradiation on microstructure of AISI 304 stainless steel were investigated. The stainless steel surface was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). XRD patterns indicated that different oxides, such as chromium oxides and manganese oxides were fabricated successfully on the surface of the stainless steel by Nd:YAG pulsed laser irradiation. The effects of the growth conditions such as the laser power density on the morphologies of the different oxides have been investigated. From the FESEM, EDS (energy-dispersive spectrum) and TEM observations, the oxides with triangle-like, quadrangular and hexagonal morphologies have been fabricated successfully. The XPS was used to verify the formed oxides which had been detected by the XRD patterns. It was considered that laser power density had a critical role in the formation of different oxides.     

Formation of nano-crystalline and amorphous phases on the surface of stainless steel by Nd:YAG pulsed laser irradiation

Thin surface layers consisting of nano-crystalline and amorphous phases on the surface of stainless steel have been attained under the Nd:YAG pulsed laser irradiation. The phases and microstructures were investigated by X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM). The phase compositions of the surface determined by XRD were α-Fe (ferrite) and γ-Fe (austenite) or only γ-Fe in the near surface region on the bases of the different laser power densities. The nano-crystalline grains with sizes of 4-100 nm could result from high cooling rate and crystallization in amorphous region by homogeneous and heterogeneous nucleation. The formation of the amorphous phase was attributed to the higher cooling rates.     

Y_3Al_5O_(12)∶Ce~(3 )的合成及真空紫外发光性质

采用高温固相反应及共沉淀法合成Y3-xAl5O12∶Ce3x (x=0.01,0.03,0.05,0.07,0.09)黄色系列粉末状发光材料。经X射线衍射分析产物为单相,属立方晶系,其结果与JCPDS标准卡(88-2047)相符。分析了两种方法合成的粉末样品的SEM照片,发现共沉淀法不仅能降低合成温度,对细化粉体晶粒粒度也有较大作用。检测了材料的真空紫外激发光谱和发射光谱。发现,Y3Al5O12∶Ce3 的真空紫外激发光谱,在100~300nm范围内呈三个带状峰,峰值分别在126,177,230nm附近。随着Ce3 含量x由0.01增加到0.05,YAG∶Ce3 发射强度逐渐增加到最大值,之后随着x继续增加其发射强度逐渐下降,呈现明显的浓度猝灭现象。     

1 319和1 338 nm双波长Nd:YAG脉冲激光输出实验研究

 根据计算得到的双波长激光振荡的阈值条件,激光实验中对全反镜镀制1 319和1 338 nm的全反膜（其反射率大于99.73%,而对1 064 nm激光的反射率约为7%）;输出镜采用对1 064 nm强谱线95%的高透过率,而对1 319和1 338 nm谱线的透过率分别为34.7%,32.5%,有效抑制了强线1 064 nm振荡,成功实现了1 319和1 338 nm Nd:YAG同时双波长激光脉冲输出。当输入能量为125 J时,1 319和1 338 nm脉冲双波长激光的单脉冲总输出能量为0.89 J,电-光转换效率为0.71%,斜率效率为0.89%。输出的双波长激光的中心波长分别在1 318.8和1 338.2 nm处,谱线宽度（FWHM）分别为0.35和0.48 nm,强度之比为36:44。     

LD泵浦Cr4+∶YAG被动调Q锁模Nd∶Gd0.42Y0.58VO4激光器

理论和实验研究了LD泵浦Nd∶Gd0.42Y0.58VO4/Cr4+∶YAG被动调Q锁模激光器.在分析Cr4+∶YAG晶体能级结构和调Q锁模物理过程的基础上,通过数值模拟给出了Cr4+∶YAG调Q锁模的参量要求,然后进行了实验验证.实验中Cr4+∶YAG的初始透过率T0分别为86.3%、95%,输出镜的透过率T分别为10%、20%,在其他条件不变的情况下构成四种不同的组合,均实现了激光器的调Q锁模运转.实验结果表明,降低Cr4+∶YAG的初始透过率T0或提高输出镜透过率T有利于获得较好的锁模效果,与理论分析一致.