Optimization of extreme ultraviolet vortex beam based on high harmonic generation

In high harmonic generation(HHG),Laguerre–Gaussian(LG) beams are used to generate extreme ultraviolet(XUV)vortices with well-defined orbital angular momentum(OAM),which have potential applications in fields such as microscopy and spectroscopy.An experimental study on the HHG driven by vortex and Gaussian beams is conducted in this work.It is found that the intensity of vortex harmonics is positively correlated with the laser energy and gas pressure.The structure and intensity distribution of the vortex harmonics exhibit significant dependence on the relative position between the gas jet and the laser focus.The ring-like structures observed in the vortex harmonics,and the interference of quantum paths provide an explanation for the distinct structural characteristics.Moreover,by adjusting the relative position between the jet and laser focus,it is possible to discern the contributions from different quantum paths.The optimization of the HH vortex field is applicable to the XUV,which opens up a new way for exploiting the potential in optical spin or manipulating electrons by using the photon with tunable orbital angular momentum.

Elliptically polarized high-order harmonic generation of Ar atom in an intense laser field

High-order harmonic generation(HHG) of Ar atom in an elliptically polarized intense laser field is experimentally investigated in this work.Interestingly,the anomalous ellipticity dependence on the laser ellipticity(ε) in the lower-order harmonics is observed,specifically in the 13rd-order,which displays a maximal harmonic intensity at ε ≈ 0.1,rather than at ε = 0 as expected.This contradicts the general trend of harmonic yield,which typically decreases with the increase of laser ellipticity.In this study,we attribute this phenomenon to the disruption of the symmetry of the wave function by the Coulomb effect,leading to the generation of a harmonic with high ellipticity.This finding provides valuable insights into the behavior of elliptically polarized harmonics and opens up a potential way for exploring new applications in ultrafast spectroscopy and light–matter interactions.

P60树脂直接充填与椅旁树脂嵌体修复Ⅱ类洞微渗漏的比较研究

目的:观察P60树脂直接充填与椅旁树脂嵌体修复Ⅱ类洞时产生的微渗漏,比较两种修复方法的边缘封闭性。方法:采集80颗新鲜拔除的上颌前磨牙,随机分为直接充填组和嵌体组,每组各40颗,直接充填组按照标准Ⅱ类洞制备洞型,进行直接树脂充填,嵌体组则按嵌体修复预备洞型,制作椅旁树脂嵌体并粘结。将修复后的离体牙经冷热水浴循环处理后,平行于牙体长轴从近远中向将修复体连同牙体平均切开成3份在体视显微镜下观察。对所获取的数据进行统计学分析。结果:直接充填组龈壁和轴壁的微渗漏程度均显著高于嵌体组,差异具有统计学意义(P<0.01)。结论:椅旁树脂嵌体修复后牙Ⅱ类洞修复体的边缘封闭性明显优于树脂直接充填。

飞秒强激光场下分子的场致电离和库仑爆炸

利用飞行时间质谱仪和飞秒激光放大系统 ,对分子在飞秒强激光脉冲作用下的场致电离和库仑爆炸过程进行了研究。在飞行时间质谱中 ,原子离子的谱峰分裂标志着这些原子离子来源于高价母体离子的库仑爆炸。通过对不同结构的分子在飞秒强激光下的库仑爆炸研究 ,发现这些分子离子的爆炸是一个协同过程。母体离子的角分布呈现了高度的各向同性 ,而原子离子则呈现了高度的各向异性分布。这说明分子在飞秒激光场中发生了空间准直和重新定位。

观察口腔治疗操作时间长短对老年患者血压的影响

目的：探讨老年患者合适的口腔治疗操作时间，确保患者就医安全。方法选择2013年9月-2014年9月在我院口腔门诊拟行疏通根管、拔髓、根管封药、根管预备及根管窝洞充填的老年患者89例，根据是否合并高血压分为两组，动态观察术前10 min、术中15 min、30 min、45 min、60 min、75 min血压变化。结果两组老年患者操作前SBP、DBP比较，差异无统计学意义（P＞0.05），操作15 min、30 min、45 min两组患者SBP、DBP持续升高，尚在140/90 mmHg以下，60 min时高血压组患者SBP、DBP均超过140/90 mmHg，两组患者60 min收缩压（SBP）和舒张压（DBP）均明显高于操作前，差异有统计学意义（P＜0.05）。治疗48 h后两组患者SBP、DBP明显下降，且略低于治疗前。高血压组操作30 min、45 min、60 min血压≥140/90 mmHg患者构成比例分别为2.35%、57.14%、95.24%，非高血压组分别为0%、36.17%、65.96%，两组45 min、60 min血压≥140/90 mmHg患者构成比较差异有统计学意义（P＜0.05）。结论长时间的口腔操作会导致老年患者血压升高，血压升高幅度与操作时间呈正相关，无论是否合并高血压，老年患者行口腔操作时均应控制在45min内，避免血压升高引起心脑血管并发症。

钙处理泥浆在内蒙古芒来煤矿钻探生产中的应用

内蒙古锡林郭勒盟芒来煤矿区在钻进过程中由于泥岩、碳质泥岩中粉土膨胀,水化分散,易发生提下钻困难、泥浆粘度增大、成孔后测井困难等原因。下钻扫孔还极易造成钻孔偏离原孔位,使得钻孔报废,从而使钻进效率低下,影响施工进度。应用钙处理泥浆取得了明显的效果。

基于高次谐波产生的极紫外偏振涡旋光

突破传统涡旋光场束缚,发展短波极紫外涡旋光场是实现阿秒脉冲偏振控制的有效途径.本研究利用自制的平场光栅光谱仪和超快时间保持的单色仪,以800 nm,35 fs高斯或具有偏振奇点的涡旋光脉冲驱动诱导氩原子产生高次谐波,分别获得相应的高次谐波光谱以及谐波谱单阶光源的分布.实验结果表明,基于高次谐波产生实现近红外波段的涡旋光束特性转移到极紫外波段,优化后的极紫外涡旋可以实现每秒108光子数输出.同时发现极紫外波段的涡旋场和高斯场高次谐波产生具有相似相位匹配机制.基于高次谐波产生的极紫外波段的偏振涡旋光为探究和操控原子分子量子态的含时演化动力学以及形成阿秒矢量光束提供了重要的方法和技术手段.

椭圆偏振强激光场中准直的乙炔分子的高次谐波发射（英文）

本文利用自制的高次谐波光谱仪，实验研究了35-fs800-nm强激光场诱导的准直的乙炔分子的高次谐波发射（HHG）．实验观测到分子HHG几率随着激光椭偏率的增加而降低，这与隧穿后重散射的理论框架的预言是一致的．通过引入一束弱飞秒激光作用对分子非绝热准直，研究了线偏振和椭圆偏振光场下分子结构效应对HHG的影响．结果表明，分子轴垂直于激光电场方向时谐波产率最大．分析表明，最高占据分子轨道（HOMO）以及内层轨道（HOMO-1）对乙炔分子的强场HHG部有贡献．本文将有助于深入理解分子与超快强激光场的相互作用．

HPLC法测定川芎七味散中甘草酸的含量

目的：建立HPLC法测定川芎七味散中的有效成分甘草酸含量测定的方法。方法：采用色谱柱为C18柱，流动相：甲醇-0.2mol/L醋酸铵溶液-冰醋酸（67∶33∶1），检测波长为250nm。结果：甘草酸在0.0861-0.8610μg范围内与峰面积呈线性关系，散剂中甘草酸的平均回收率为99.59%，RSD=1.42%。结论：方法简便、稳定，能有效地控制该制剂的质量。

7Li20,±1分子体系基态振-转能级的全电子计算

采用单参考与多参考耦合簇理论结合相关一致高斯基组计算研究了77Li2(0,±1)分子体系的电子基态的势能曲线,计算考虑了体系所有电子的关联效应与相对论效应,拟合得到了体系的光谱常数,并获得了电子基态的振动-转动能级信息.计算得到的中性与阳离子体系的光谱常数与实验值符合得很好;对于阴离子体系,平衡核间距的计算仍需进一步改进,其他光谱常数符合较好.计算结果表明,中性和阳离子体系基态波函数具有明显的单参考组态特点,而阴离子分子基态应采用多参考组态波函数描述.对于基态的振动-转动能级,与现有实验值符合得很好;尽管各种计算方法对阴离子基态的平衡核间距计算结果仍有差异,但振动能级间隔的结果相互符合得很好.本文的研究可为Li2分子体系基态,尤其是光谱学信息很少的阴离子体系的电子结构与光谱的精确研究提供了有用的光谱信息.

沉管灌注桩质量缺陷处理实践

天津某小区沉管灌注工程桩经检测发现部分桩存在缺陷和承载力不足问题,采用高压旋喷注浆技术对缺陷桩进行修补,对承载力不足桩进行补强,处理后经检测合格达到设计要求。介绍了处理方案及施工技术措施。

Ellipticity-dependent ionization/dissociation of carbon dioxide in strong laser fields

Ionization and dissociation of linear triatomic molecules, carbon dioxide, are studied in 50-fs 800-nm strong laser fields using time-of-flight mass spectrometer. The yields of double charged ions CO2^2＋ and various fragment ions（CO^＋,O^n＋, and C^n＋（n = 1, 2）） are measured as a function of ellipticity of laser polarization in the intensity range from 5.0 ×10^13W/cm2 to 6.0 × 10^14W/cm^2. The results demonstrate that non-sequential double ionization, which is induced by laser-driven electron recollision, dominates double ionization of CO2 in the strong IR laser field with intensity lower than2.0 × 10^14W/cm^2. The electron recollision could also have contribution in strong-field multiple ionization and formation of fragments of CO2 molecules. The present study indicates that the intensity and ellipticity dependence of ions yields can be used to probe the complex dynamics of strong-field ionization/dissociation of polyatomic molecules.

Accurate all-electron calculation on the vibrational and rotational spectra of ground states for O2 and its ions

The potential energy curves, spectroscopic constants, and low-lying vibration–rotation levels of ground-state O2 and its cation O2+ and anion O2- were calculated with the explicitly correlated multireference configuration interaction method.The zeroth-order reference wavefunction was treated with the complete active space multiconfigurational self-consistent field method, in which the active space was carefully selected, and an additional molecular orbital πu was added into the full valence active space.The electron correlation of the 1s core in the oxygen atom was considered in the computations.The Davidson correction on molecular energy was considered to account for higher electron excitation.The relativistic effects, including the scalar relativistic effect and spin–orbit coupling, were considered in the computation of potential energy curves.These physical effects on the spectroscopic constants were examined.The low-lying levels of vibration–rotation spectra of O2 and its ions were determined based on the computed potential energy curves.Comparisons with available experiments were made and excellent agreement was obtained for the vibrational and rotational parameters.The spectroscopic constants and vibration–rotation spectrum of O2-, which is sparse in experiments, were provided.Our study will shed some light on further theoretical and experimental studies on these simple but important molecular systems.

Resolving multi-orbital effects on high harmonic generation from aligned N2 molecules in linearly and elliptically polarized intense laser fields

We perform an experimental study of the multi-orbital effect on the high-order harmonic generation(HHG) from aligned N_2 molecules in both linearly and elliptically polarized intense laser fields.Measured by a home-built extreme ultraviolet(XUV) flat grating spectrometer with the pump-probe method, the angular distributions of different orders of HHG are obtained, which show distinctive behaviors for harmonics in the plateau and the cut-off regions.The ellipticity dependence of HHG is investigated by aligning the molecular axis parallel or perpendicular to the laser polarization.Our results indicate that both the highest occupied molecular orbital(HOMO) as well as the lower one(HOMO-1) contribute to the HHG of N2 molecules, in either linearly or elliptically polarized intense laser field.The study paves the way for understanding the ultrafast electron dynamics of molecules exposed to an intense laser field.

Quantum interference of multi-orbital effects in high-harmonic spectra from aligned carbon dioxide and nitrous oxide

We investigate experimentally multi-orbital effects in high-order harmonic generation(HHG) from aligned CO2 and N2O molecules by intense femtosecond laser fields with linear and elliptical polarizations.For either of the aligned molecules, a minimum in the harmonic spectrum is observed, the position of which shifts to lower-order harmonics when decreasing the intensity or increasing the ellipticity of the driving laser.This indicates that the minimum originates from the dynamic interference of different channels, of which the tunneling ionization and recombination are contributed via different molecular orbitals.The results show that both the highest occupied molecular orbital(HOMO) and low-lying HOMO-2 in CO2(or HOMO-1 in N2O) contribute to the molecular HHG in both linearly and elliptically polarized strong laser fields.Our study would pave a way for understanding multi-electron dynamics from polyatomic molecules irradiated by strong laser fields.

A tunable XUV monochromatic light source based on the time preserving grating selection of high-order harmonic generation

We accomplish a laboratory facility for producing a femtosecond XUV coherent monochromatic radiation with a broad tunable spectral range of 20 eV-75 eV. It is based on spectral selected single-order harmonics from intense laser driven high harmonic generation in gas phase. The time preserving for the selected harmonic radiation is achieved by a Czerny-Turner type monochromator designed with a conical diffraction grating mount for minimizing the time broadening caused by grating diffraction and keeping a relatively high diffraction efficiency. Our measurement shows that the photon flux of the 23-order harmonic（H23） centered at 35.7 eV is 1×10~9 photons/s approximately with a resolving power E/？E ≈ 36.This source provides an ultrashort tunable monochromatic XUV beam for ultrafast studies of electronic and structural dynamics in a large variety of matters.

Minimum structure of high-harmonic spectra from aligned O_(2) and N_(2) molecules

We experimentally investigated the high-order harmonic generation(HHG)from aligned O_(2) and N_(2) molecules in a linearly polarized laser field,and presented the dependence of the harmonic spectrum on the driving laser intensity and molecular alignment angle.The minimum position of HHG of O_(2) varies with changing the laser intensity,which is caused by multi-orbital interference.However,the location of the observed minimum structure in N_(2) harmonic spectrum remained unchanged upon changing the laser intensity.The mechanism of the spectral minimum for N_(2) case is regarded as a Cooperlike minimum in HHG associated with the molecular electronic structure.This work indicates that harmonic spectroscopy can effectively uncover information about molecular structure and electron dynamics.