Study on the relationships between Raman shifts and temperature range for α-plane GaN using temperature-dependent Raman scattering

In this paper,Raman shifts of a-plane GaN layers grown on r-plane sapphire substrates by low-pressure metal-organic chemical vapor deposition（LPMOCVD） are investigated.We compare the crystal qualities and study the relationships between Raman shift and temperature for conventional a-plane GaN epilayer and insertion AlN/AlGaN superlattice layers for a-plane GaN epilayer using temperature-dependent Raman scattering in a temperature range from 83 K to 503 K.The temperature-dependences of GaN phonon modes（A1（TO）,E2（high）,and E1（TO）） and the linewidths of E2（high） phonon peak are studied.The results indicate that there exist two mechanisms between phonon peaks in the whole temperature range,and the relationship can be fitted to the pseudo-Voigt function.From analytic results we find a critical temperature existing in the relationship,which can characterize the anharmonic effects of a-plane GaN in different temperature ranges.In the range of higher temperature,the relationship exhibits an approximately linear behavior,which is consistent with the analyzed results theoretically.

Quantification of radiation damage in natural and synthetic zircon by Raman spectroscopy:application to low-temperature thermochronology

Due to its ubiquitous occurrence in igneous,metamorphic,and sedimentary rocks and its wide application in geochronology and geochemistry,zircon has become the most widely used accessory mineral in the geological community.Nevertheless,the decay of U and Th causes radiation damage to the zircon structure,resulting in various degrees of metamictization,which can affect the accuracy of U–Pb dates and Hf and O isotope results.If the degree of zircon radiation damage can be quantified,the influence on geochemical analyses can be evaluated,and the results can be corrected more precisely.In this paper,synthetic and natural zircon crystals with different crystallization ages were selected for Raman spectroscopy analysis,cathodoluminescence imaging,and determination of the U and Th concentrations.The results show that Raman FWHM(full width at half bandmaximum)and Raman shift correlate with alpha dose(Da)ofzirconsfollowingtheseequations,FWHM=44.36(±2.32)×[1-exp(-2.74×Da)]-+1.7(±0.19),Raman Shift=-6.53×Da+1007.69.Analysis of synthetic zircon crystals shows that doped REEs(rare earth elements and P)can also lead to an increase in the FWHM.However,this effect can be ignored for natural zircon samples with REE contents at a normal level of hundreds to a few thousand ppm.The FWHM and Raman shift can be used as proxies to measure the degree of zircon radiation damage.Using the updated equations to calculate the latest age when zircon began to accumulate radiation damage,a more accurate and more meaningful“radiation damage age”can be obtained.

Broadband tunable Raman soliton self-frequency shift to mid-infrared band in a highly birefringent microstructure fiber

Raman soliton self-frequency shifted to mid-infrared band（λ 〉 2 μm） has been achieved in an air-silica microstructure fiber（MF）. The MF used in our experiment has an elliptical core with diameters of 1.08 and 2.48 μm for fast and slow axis. Numerical simulation shows that each fundamental orthogonal polarization mode has two wide-spaced λZDW and theλZDW pairs located at 701/2110 nm and 755/2498 nm along the fast and slow axis, respectively. Using 810-nm Ti：sapphire femtosecond laser as pump, when the output power varies from 0.3 to 0.5 W, the furthest red-shift Raman solitons in both fast and slow axis shift from near-infrared band to mid-infrared band, reaching as far as 2030 and 2261 nm. Also, midinfrared Raman solitons can always be generated for pump wavelength longer than 790 nm if output pump power reaches0.5 W. Specifically, with pump power at 0.5 W, the mid-infrared soliton in slow axis shifts from 2001 to 2261 nm when the pump changes from 790 nm to 810 nm. This means only a 20 nm change of pump results in 260 nm tunability of a mid-infrared soliton.

Raman Spectroscopy of Nitrogen Clathrate Hydrates

Nitrogen hydrate samples were synthesized using liquid nitrogen and powder ice at 16 MPa and 253 K. Confocal laser Raman spectroscopy was used to investigate the characteristics of nitrogen clathrate hydrates. The results show that the Raman peaks of N-N and O-H stretching vibration in nitrogen hydrates are observed at 2322.4 and 3092.1 cm^-1, respectively, which are very similar to those in natural air clathrate hydrates. For comparison, we measured the Raman peaks of N-N stretching vibration both in liquid nitrogen and nitrogen molecules saturated water, which appear at 2326.6 and 2325.0 cm^-1, respectively. The Raman spectroscopic observations on the dissociation process suggest that nitrogen molecules occupy both the large and small cages in nitrogen clathrate hydrates. However, only one Raman peak is observed for N N stretching vibration because the difference of the environment of nitrogen molecules between large and small cages is too small to be differentiated by Raman spectroscopy.

纳秒可见光全固态拉曼激光器的研究进展

纳秒脉冲可见波段激光在遥感、相干雷达系统、精密加工、激光清洗、液态染料激光器泵浦等领域广泛应用,全固态激光器以其结构紧凑、占用空间小、成本低、寿命长等特点备受青睐。近年来,纳秒可见光全固态激光器发展迅速,本文简述了传统激光二极管泵浦掺Nd ^(3+)、Yb ^(3+)等稀土离子晶体输出近红外光的二阶非线性频率变换产生纳秒脉冲可见光固体激光器的技术水平。从非线性频率变换角度介绍了几种出光波段丰富的纳秒脉冲可见光全固态拉曼激光器的技术特点,重点介绍了拉曼频移、拉曼混频和金刚石拉曼,对其性能特点和技术瓶颈进行了综述,并在最后做了总结和展望。

激光加热效应在硅显微Raman光谱测量中的影响

本文从理论和实验两方面研究了显微Raman光谱测量中,激光功率对单晶硅样品测量的影响。由于显微Raman光谱仪对激光的聚焦作用,使得激光对不同厚度的样品具有微区加热作用,被测样品产生不同程度的温升,从而对显微Raman光谱仪在硅材料应力和温度的测量中产生影响。实验结果证明,对无限厚硅样品,20mW的激光使Raman频移达到0.15cm-1;而对2μm厚的热薄硅样品,26mW的激光使Raman频移达到4.47cm-1。

色散管理孤子中 Raman效应引起的时移及定时抖动(英文)

给出了色散管理孤子中 Raman效应所引起的脉冲中心位置时移的解析表达式并讨论了孤子脉宽的波动所引起的 Raman定时抖动 .结果表明 :时移的演化和不同的色散配置有关 ,并且色散管理孤子 Raman时移和常规孤子一样与传输距离及平均色散的平方成正比 。

Third-order nonlinear wavelength conversion in chalcogenide glass waveguides towards mid-infrared photonics

The increasing demand in spectroscopy and sensing calls for infrared(mid-IR)light sources.Here,we theoretically investigate nonlinear wavelength conversion of Ge_(28)Sb_(12)Se_(60)chalcogenide glass waveguide in the mid-IR spectral regime.With waveguide dispersion engineering,we predict generation of over an octave wavelength(2.8μm-5.9μm)tuning range Raman soliton self-frequency shift,over 2.5 octaves wavelength cover range supercontinuum(1.2μm-8.0μm),as well as single soliton Kerr comb generated in suspended Ge_(28)Sb_(12)Se_(60)waveguide.Our findings evidenced that Ge_(28)Sb_(12)Se_(60)chalcogenide glass waveguides can simultaneously satisfy the generation of Raman soliton self-frequency shift,supercontinuum spectrum,and Kerr frequency comb generation through dispersion engineering towards mid-IR on chip.

基于光谱信息的拉曼成像技术助力生物质材料结构设计研究进展

近年来研究人员对生物质材料进行了诸多结构设计,以提升其性能并获得高性能生物质材料。其中,拉曼光谱技术因其高分辨率、无损检测等特点,被广泛应用于生物质材料的多尺度结构表征。介绍了拉曼成像技术,并详细总结了课题组基于拉曼峰位、拉曼峰偏移、拉曼峰强度及偏振拉曼等光谱信息对生物质材料进行拉曼成像,以辅助验证材料结构的研究进展。此研究进展为拉曼成像技术在其他材料上的扩展应用提供了参考。

多孔硅薄膜纵向分辨Raman谱研究

采用高灵敏度的micro Raman系统研究了多孔硅(PS)在纵向的Raman效应,并研究了多孔硅尺寸对Raman谱的影响.实验中采用脉冲电化学腐蚀和直流电化学腐蚀两种方法制备PS样品,纵向Raman光谱的结果表明,在纵向不同深度,用脉冲电化学腐蚀方法制备的PS,Raman光谱不存在频移,而用直流电化学腐蚀方法制备的PS在多孔层深度为70～90μm处的Raman光谱有向低波数方向约40cm-1的移动,它是由于常规电化学腐蚀方法制备的PS不同深度的尺寸分布对量子效率的影响引起的.

Raman Spectroscopy of Garnet-group Minerals

The Raman spectra of the natural end members of the garnet-group minerals, which include pyrope, almandine and spessarite of Fe-Al garnet series and grossularite, andradite and uvarovite of Ca-Fe garnet series, have been studied. Measured Raman spectra of these minerals are reasonably and qualitatively assigned to the intemal modes, translational and rotatory modes of SiO4 tetrahedra,as well as the translational motion of bivalent cations in the X site. The stretch and rotatory Alg modes for the Fe-Al garnet series show obvious Raman shifts as compared with those for the Ca-Fe garnet series, owing to the cations residing in the X site connected with SiO4 tetrahedra by sharing the two edges. The Raman shifts of all members within either of the series are attributed mainly to the properties of cations in the X site for the Fe-Al garnet series and in the Y site for the Ca-Fe gamet series.

Bismuth-content-dependent polarized Raman spectrum of InPBi alloy

We systematically investigate the optical properties of the InP1-xBix ternary alloys with 0≤x≤2.46%,by using high resolution polarized Raman scattering measurement.Both InP-like and InBi-like optical vibration modes（LO） are identified in all the samples,suggesting that most of the Bi-atoms are incorporated into the lattice sites to substitute Patoms.And the intensity of the InBi-like Raman mode is positively proportional to the Bi-content.Linear red-shift of the InP-like longitudinal optical vibration mode is observed to be 1.1 cm-1/Bi%,while that of the InP-like optical vibration overtone（2LO） is nearly doubled.In addition,through comparing the（XX） and Z（XY） Raman spectra,longitudinaloptical-plasmon-coupled（LOPC） modes are identified in all the samples,and their intensities are found to be proportional to the electron concentrations.

Magnetic field measurement based on a stimulated two-photon Raman transition

The magnetic field in the microwave interaction zone of the fountain atomic clock was measured by stimulated Raman transitions. By measuring the two-photon transition frequency between the Zeeman levels of the two ground states, we achieved a magnetic field measurement accuracy of the order of 0.28 nT, This method is immune to the Doppler shift and the AC Stark shift. The second order Zeeman shift of the fountain clock is 170.7 × 10^-15, with the uncertainty of 7,2 × 10^-16.

Fluctuations of optical phase of diffracted light for Raman–Nath diffraction in acousto–optic effect

The Raman–Nath diffraction in acousto–optic effect was studied theoretically and experimentally in the paper. Up to now, each order of diffracted light in Raman–Nath diffraction was still considered simply to be just frequency-shifted and to be a plane wave. However, we find that the phase and frequency shifts occur simultaneously and individually in Raman–Nath diffraction. The findings demonstrate that, in addition to the frequency shift, the optical phase of each order of diffracted light is also shifted by the sound wave and fluctuates with the sound wave and is related to the location in the acoustic field from which the diffracted light originates. As a result, the wavefront of each order of diffracted light is modulated to fluctuate spatially and temporally with the sound wave. Obviously, these findings are significant for applications of Raman–Nath diffraction in acousto–optic effect because the optical phase plays an important role in optical coherence technology.

FT-IR, Raman and NMR Spectra, Molecular Geometry, Vibrational Assignments, ab initio and Density Functional Theory Calculations for Diethyl Phthalate

Phthalate acid esters （PAEs） possess endocrine disruptive effects and can produce reproductive and developmental toxicities. In this paper, both experimental and theoretical studies on FT-IR, Raman and 1H NMR spectra of diethyl phthalate （DEP） have been carried out. The geometrical structure of DEP was optimized at the HF/6-31G＊, HF/6-311G＊＊, B3LYP/6-31G＊, and B3LYP/6-31 IG＊＊ levels, respectively. The harmonic vibrational frequencies, IR intensity, Raman activity and 1H NMR chemical shifts have been computed at the B3LYP/6-31G＊ and B3LYP/6-311G＊＊ levels. Anharmonic corrections to frequencies were obtained by means of second-order perturbation theory （PT2） at the B3LYP/6-31G＊ level. Based on potential energy distribution （PED）, the vibrational assignments have also been performed. The theoretical calculation values were compared with the experimental observations and the results indicate they are in excellent agreement.

色散缓变光纤中Raman孤子自频移效应的研究

利用绝热扰动法研究了色散缓变光纤中Ｒａｍａｎ孤子自频移效应，得到了色散缓变光纤中Ｒａｍａｎ孤子自频移的表达式。结果表明：光纤色散变化率存在一个可以有效抑制孤子自频移的阈值，当光纤色散变化率大于这个阈值时，色散缓变光纤可以抑制孤子自频移，而当光纤色散变化率小于这个阈值时，色散缓变光纤不仅不能抑制孤子自频移，反而加剧孤子自频移。

锥形微纳光纤激发相干反斯托克斯拉曼散射光谱研究

从数值仿真和实验测量方面验证了使用锥形微纳光纤代替聚焦物镜产生相干拉曼散射信号的可行性。通过数值计算以及实验测量分析了超短脉冲在锥形微纳光纤中的传输特性,证明锥区长度为5cm的锥形微纳光纤可以有效保证超短脉冲在其中传输时的时域和谱域特性,并且功率衰减较小,850~1100nm波长范围内的实测插入损耗最大值不超过1.05dB,平均值0.84dB。然后,使用锥形微纳光纤成功探测到环己烷在2853cm^(-1)位置处的拉曼共振峰,证明了使用锥形微纳光纤激发相干拉曼光谱的可行性。使用锥形微纳光纤激发相干拉曼光谱具有信号激发灵活方便,摆脱了传统空间光学的约束,为相干反斯托克斯拉曼散射(coherent anti-Stokes Raman scattering,CARS)系统在内窥成像领域和微创检测领域的发展提供了一种新的途径。

色散缓变光纤能有效抑制超短光脉冲的Raman孤子自频移吗?(英文)

研究了色散缓变光纤中超短光脉冲的Raman孤子自频移现象。利用绝热扰动方法得到了一个关于Raman孤子自频移的普遍表达式。结果表明：光纤色散缓变率存在一个能抑制超短光脉冲的Raman孤子自频移的阈值，只有当色散缓变率小于这个阈值时，色散缓变光纤才能有效抑制超短光脉冲的Raman孤子自频移。

拉曼光谱在精细农业土壤成分快速检测中的研究进展

拉曼光谱分析技术利用分子运动对入射光产生非弹性散射的原理对分子成分进行检测,具有受水分干扰小、样本预处理小、与红外光谱信息互补等特点,在土壤成分快速分析方面展现了很大的优势。但是拉曼光谱信号弱,受荧光干扰强,为土壤拉曼信号的有效获取带来困难。为了分析拉曼光谱在土壤成分检测中的应用潜力,该研究综述了移频激发差分拉曼光谱技术、共焦显微拉曼技术以及表面增强技术等基于拉曼光谱的土壤成分检测技术,分析了土壤成分拉曼光谱检测的研究进展,并提出进一步研究建议。结果表明:1)脂肪族化合物以及芳香族化合物都具有拉曼活性,为基于拉曼光谱的土壤有机质含量的定性、定量分析提供了理论依据。为了弥补拉曼光谱对有机质整体定量预测精度的不足,采用红外-拉曼光谱融合方式补偿单独拉曼光谱数据中缺失的土壤有机质信息,可显著改善预测精度。2)利用表面增强技术可以增强土壤溶液中可溶性氮与土壤有效氮拉曼特征波峰的强度,获得了良好的定量预测效果,回归模型决定系数R^(2)达到0.91~0.99。3)土壤中很多含磷的化合物都具有拉曼活性,拉曼光谱是识别土壤中不同磷酸盐形态的极其有效的工具,在土壤磷素含量的分析中,应用小波包分解的拉曼光谱对滤除有机质的磷酸盐参杂土壤中磷素浓度进行预测,回归模型精度R^(2)达到0.94。拉曼光谱检测的样本范围取决于激发光照射在样本上的光点尺寸,而土壤样本的空间变异性为聚焦目标物质带来困难。因此,实现现场高分辨率检测的关键是获取有效拉曼信号、同时降低背景信号的干扰。移频激发技术与显微拉曼技术为农田土壤养分的原位测量提供了技术保障。建议:1)采用光谱融合方法提升回归模型的预测精度。2)降低冗余变量,提升模型的可解读性与重现性。3)充分考虑土壤对拉曼光谱的影响,为开发农田现场土壤成分快速检测技术提供参考。

基于消荧光差分拉曼光谱技术预测食用油复热时长

为实现食用油复热时长的快速测量,选取4种常用的植物油(大豆油、花生油、玉米油、葵花籽油)进行不同时长的加热,基于自主研制的消荧光差分拉曼光谱仪完成样品的原始拉曼光谱及差分拉曼光谱测试。首先,分析植物油的拉曼光谱特征峰归属及复热时长对拉曼光谱的影响,并对原始拉曼光谱及差分拉曼光谱进行主成分对比分析。其次,基于差分拉曼光谱及经小波变换去除荧光干扰的原始拉曼光谱,分别建立食用油复热时长定量模型,并对比分析试验结果。结果表明,与经小波变换去除荧光干扰的原始拉曼光谱相比,基于差分拉曼光谱的食用油复热时长定量模型,玉米油、花生油、葵花籽油、大豆油的验证集R^(2)分别从0.976 9、0.973 1、0.980 9、0.984 2升至0.996 4、0.996 4、0.994 6、0.991 2;验证集均方根误差从1.248 9、1.348 0、1.134 0、1.031 1降至0.494 6、0.491 0、0.606 1、0.768 5。由此表明,利用差分拉曼光谱技术提高了食用油复热时长定量模型的稳定性和精确度。本研究结果为植物油复热时长定量快速检测提供了一种可行的方法。