NIR-VIS reflectivity spectra of some transition metal thiophosphates

Summary Room temperature optical-reflectivity measurements on some transition metal thiophosphates were carried out in the near infrared and visible regions. The resulting spectra, interpreted on the basis of the ?transition metal weakly interacting? model, agree well with earlier optical transmission measurements. Below the fundamental absorption edge, the observed features have been assigned to 3d–3d transitions occurring on the transition metal ion, while those observed at photon energies greater than the absorption threshold have been attributed to transitions from the valence bands to discrete 3d orbital levels or to the conduction bands. A more detailed information on the metal ion 3d levels energy distribution with respect to the valence band states belonging to the (P₂S₆)^4- cluster and a more precise determination of the MPS₃ absorption edge energy position have been obtained.     

激光辐照金属板材的温升和升温率

从光子与声子相互作用机制出发,导出金属材料的能量吸收速度;解热传导方程,求出激光辐照下金属板材料的温度分布;讨论了激光辐照时间、材料性质等对金属板材温升和升温率的影响。     

Demonstration of highly efficient photon echoes

Highly efficient two-pulse and stimulated photon echoes are experimentally demonstrated in an absorbing medium. Recall efficiencies of 235% and 150% with excellent signal contrast are measured for two-pulse and stimulated photon echoes, respectively, in a Tm:YAG crystal with an absorption length of 3.8. The reported efficiencies do not include any correction for decay or beam profile. We believe that this is the first demonstration of an uncorrected echo efficiency greater than 100% with good signal fidelity in an optically thick medium.     

Optical properties of transition metal atom adsorbed graphene: A density functional theoretical calculation

Electronic and optical properties of 3d-transition metal adsorbed graphene system, theoretically studied in the framework of density functional theory, reveals significant modification compared to the pristine system. Due to adsorption of transition metal, the emergence of closely separated electronic bands leads to substantial amount of low energy optical absorption below 2.0 eV photon energy. Very significant enhancement of static dielectric constant and large value of reflectivity in the low optical energy regime has been identified for different adsorbed systems. In the different 3d-transition metal adsorbed systems, particularly up to the half filled d-shell transition metal atom, pronounced emergence of optical absorption line in the deep ultraviolet regime beyond 30.0 eV photon energy is observed.     

Yb~(3+)/Tm~(3+)共掺的硅酸盐玻璃上转换发光性能

采用高温熔融法制备了掺杂不同比例Yb~(3+)和Tm~(3+)的硅酸盐玻璃。吸收光谱表明,Yb~(3+)和Tm~(3+)在300~1 100 nm的吸收过程彼此不干扰。研究了玻璃样品在980 nm LD泵浦下的上转换发光行为,结果表明:Yb~(3+)/Tm~(3+)在477 nm(1G4→3H6)发射强烈的上转换蓝光,在654 nm(1G4→3F4)发射较弱的红光,在795 nm(3H4→3H6)发射微弱的红外光。提高Yb~(3+)的比例均能够提高477 nm蓝光、654 nm红光和795 nm红外光的发射强度。研究分析了上转换发光强度与激光器泵浦功率之间的关系,结果表明上转换蓝光和红光发射均为三个光子过程,红外光发射为两个光子过程。分析了Yb~(3+)、Tm~(3+)在硅酸盐玻璃中上转换发光的机制。     

Bremsstrahlung spectrum of nonrelativistic electrons scattered in metallic target: Theory and experiment

This work is devoted to theoretical and experimental investigation of the bremsstrahlung (BrS) spectrum of electrons with an energy of 10–30 eV scattered in a copper plate. Modeling of the photon yield from a target has been carried out taking into account the polarization BrS channel, elastic and inelastic electron scattering by medium atoms, photon absorption in the target material, and coherent effects when electrons interact with a polycrystalline structure of metal. An FEI Quanta 200 scanning electron microscope with a supplement for X-ray microanalysis was used. Good agreement between experimental and theoretical results has been obtained.     

Tm:YAG晶体光谱的温度特性及荧光的温度淬灭

通过测量不同温度下Ｔｍ：ＹＡＧ晶体的吸收光谱、荧光光谱和荧光寿命发现,温度是影响Ｔｍ：ＹＡＧ晶体光谱特性的重要因素。温度升高不仅引起Ｔ：ＹＡＧ晶体吸收光谱、荧光光谱的加宽和新光谱线的产生,而且引起荧光淬灭现象的发生。     

Photon statistics measurement for coherent fields

An efficient scheme for photon statistics measurement is presented based on the Hanbury-Brown-Twiss configuration. We set the sampling time Ts to satisfy the relationship of Ts 〈 Td 〈 Tm, where Td is the dead time of each detector and Tm is the laser pulse repetition period. And each single photon detector cannot detect more than one photon in each pulse. The approach can sufficiently eliminate the influences of the detector＇s dead time on photon statistics. At last, the photon statistics of coherent field is experimentally determined.     

水热法合成稀土氟化物材料YLiF4:Er,Tm,Yb的上转换发光特性

利用水热法合成了不同掺杂浓度Er^3 ,Tm^3 和Yb^3 的YLiF4材料,研究了Er^3 ,Tm^3 和Yb^3 在材料中的光吸收,以及在980nm红外光激发下样品的上转换发光特性。实验发现,在980nm激光激发下,光功率为数10mW,材料可以发出很强的白光。测量发现,蓝光来源于Tm^3 绿光来源于Er^3 ,而红光来源于Tm^3 和Er^3 的共同作用。通过分析输出光强与泵浦功率的双对数曲线,发现484nm蓝光发射,524和552nm绿光发射以及665nm红光发射均属于双光子过程,450nm蓝光和359nm紫外光属于三光子过程。分析发光机理属于协作敏化和声子辅助共振能量传递过程的结合。     

NaYF4∶Eu3+, Tm3+, Yb3+材料中Stokes和反Stokes发光研究

合成了Eu3+,Tm3+和Yb3+掺杂的NaYF₄材料。360 nm光激发呈蓝色发光,峰值位于452 nm,对应Tm3+的1D₂→3F₄跃迁;395 nm光激发呈橙色发光,峰值位于591 nm,对应Eu3+的5D₀→7F₁跃迁;409 nm光激发呈红色发光,峰值位于613 nm,对应Eu3+的5D₀→7F₂跃迁;980 nm光激发呈蓝色和红色发光,发光峰位于474和646 nm。蓝光来源Tm3+的1G₄ →3H₆跃迁,红光来源Tm3+的1G₄→3F₄跃迁。在双对数曲线中,蓝光474 nm和红光646 nm的斜率分别为2.1和2.4,在980 nm光激发下,蓝光和红光发射都是双光子过程。还研究了材料的吸收光谱,并利用X射线衍射,扫描电镜测试了材料的物相结构和微观形貌。结果表明：NaYF₄∶Eu3+, Tm3+, Yb3+材料具有较规则的六方相结构,结晶良好。     

硅的间接跃迁双光子吸收系数谱

利用皮秒Nd:YAG脉冲激光器作为激发光源,测量出光子能量介于1.36 μm (0.912 eV)—1.80 μm (0.689 eV)之间的硅间接跃迁双光子吸收系数谱.尽管此波段范围内的激光光子能量小于硅间接带隙,但当激光辐照在硅基光电二极管受光面时,在二极管两电极端仍然探测到了显著的脉冲光伏信号.光伏信号峰值强度与入射光强呈二次幂函数关系,表明其是双光子吸收过程.采用pn结等效结电容充放电模型,将光伏响应信号峰值与入射光强相关联,从中提取出硅的间接跃迁双光子吸收系数,改变入射波长得到系数谱.研究表明:     

Excimer laser photolysis of molybdenum hexacarbonyl with buffer gas

We have studied the photolysis of molybdenum hexacarbonyl by focused excimer laser radiation. It was found that electronically excited Mo atoms detected in the focus region of a KrF laser are due to a direct two photon absorption transition. The upper limit of the energy for complete dissociation of Mo(CO)₆ has been derived from these results. Two photon dissociation in the gas phase should be the dominant process at metal film deposition on substrates positioned perpendicularly and near to the focus. Adding buffer gases to the organometallic vapor particle formation was observed in the whole irradiated gas volume. The analysis of scattered He-Ne laser light yields information about the density and size of these particles. Some conclusions are drawn with respect to structured metal film deposition with high spatial selectivity.Dedicated to Prof. Dr. Herbert Welling on the occasion of his 60th birthday     

Cr,Tm:YAG晶体中的能量转移

通过对Cr:YAG、Tm:YAG和Cr,Tm:YAG晶体吸收光谱和发射光谱的比较,研究了Cr,Tm:YAG晶体中的能量转移过程.指出Cr3+→Tm3+能量转移过程中,无辐射能量转移占绝对优势.     

The Spectroscopic Properties of Tm and Ho Co-doped YVO_4 Crystal

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Two photon absorption spectrum ofp-dichlorobenzene

Two photon absorption spectrum ofp-dichlorobenzene has been studied in the spectral region 497–552 nm (one photon wavelength). Bands involving several frequencies of the excited electronic state not detected in the one photon absorption are seen. The observed two photon spectrum indicates that the electronic transition retains, to a large extent, the salient features of the two photon absorption spectrum of benzene and thus confirms chlorine as weak perturber (in the sense of Goodman and Rava [1]).     

The Spectroscopic Properties of Tm and Ho Co-doped YVO4 Crystal

In this paper, the measured results of spectroscopic properties for Tm, Ho co-doped YVO4 crystals are reported. The absorption spectra, fluorescence spectra and calculated spectroscopic parameters are given. The processes of sensitized luminescence of Ho3+ by Tm3+ with 805 nm LD pumping were investigated. It was found that Tm3+ ion in YVO4 has a larger uniform absorption width (～26 nm) and a larger peak and integreted cross-section of absorption at 800nm (～1.4×10-20 cm2 and 246×10-20 cm) than that in YAG and YLF. The high energy transfer efficiency from Tm3+ to Ho3+ (up to 87%) and low pumping threshold (15 mW) show that Tm3+ can efficiently sensitize Ho3+ in YVO4 crystal. The dependence of ～2 μm emission for Ho3+ on the Tm, Ho doping concentrations was preliminarily analyzed and discussed.     

Electronic relaxation observed in Mössbauer hyperfine spectra of Tm metal

Hyperfine seectra observed with the Mössbauer effect in Tm metal can be explained by an electronic relaxation mechanism. In contrast to an earlier analysis which assumed the fast relaxation limit, the present interpretation is based on a simpler picture and accounts for the spectra well throughout the entire temperature range from helium temperatures to room temperature.     

Tm：YAG晶体的光谱及激光特性研究

测试了Ｔｍ：ＹＡＧ晶体的室温吸收光谱和荧光光谱，计算了各吸收谱线的振子强度，并根据Ｊｕｄｄ－Ｏｆｅｌｔ理论了Ｔｍ：ＹＡＧ晶体的荧光跃迁截面和荧光寿命，用红宝石激光泵浦时，获得了波长２．０１μｍ能量４０ｍＪ的激光脉冲。     

Defect annealing in the hexagonal close packed heavy rare earth metals Gd,Tb, Dy,Ho, Er,Tm and Lu after electron irradiation at low temperatures

The recovery spectra of the heavy rare earths Gd, Tb, Dy, Ho, Er and Tm were determined after irradiation with electrons at low temperatures. In the cases of Er and Tm, strong thermal cycling phenomena were observed and attributed to hydrogen atoms changing configurations and interacting with the magnetic structure of the metal. After elimination of these effects in Er and Tm, all the spectra—together with those of the earlier treated Lu—had rather similar form: several close-pair peaks followed by a broad complex substage resembling the stage I _D in f.c.c metals and attributed to long-range interstitial migration. A correlation is found between the temperature of the maximum of this substage (normalized to the melting temperature) and the c/a-ratio of the metals.