Observation of Raman forward scattering and electron accelerationin the relativistic regime

Raman forward scattering (RFS) is observed in the interaction of a high intensity (>10¹⁸ W/cm²) short pulse (<1 ps) laser with an underdense plasma (n_e~10¹⁹ cm ^-3). Electrons are trapped and accelerated up to 44 MeV by the high-amplitude plasma wave produced by RFS. The laser spectrum is strongly modulated by the interaction, showing sidebands at the plasma frequency. Furthermore, as the quiver velocity of the electrons in the high electric field of the laser beam becomes relativistic, various effects are observed which can be attributed to the variation of electron mass with laser intensity     

Gd3+/Y3+共掺对Nd:CaF2晶体光谱性能的影响

通过坩埚下降法生长了系列共掺Nd,Gd:CaF₂和Nd,Y:CaF₂晶体, 研究了Gd³⁺/Y³⁺共掺对Nd³⁺光谱性能以及Nd:CaF₂晶体晶胞参数的影响规律. 对于0.5 at.%Nd, x at.%Gd(x=2,5,8,10):CaF₂系列晶体, 当调控Gd³⁺掺杂浓度为2 at.%时, 具有最大的荧光寿命499 μs; 当Gd³⁺掺杂浓度为5 at.%时, 具有最大的吸收截面1.47×10^-20 cm², 最大的发射截面1.9×10^-20 cm²; 当Gd³⁺掺杂浓度为8 at.%时, 具有最佳的发射带宽29.03 nm. 对于0.6 at.%Nd, xat.%Y(x=2, 5, 8, 10):CaF₂系列晶体, Y³⁺掺杂浓度为5 at.%时, 有最大的吸收截面2.41×10^-20 cm², 最大的发射截面3.17×10^-20 cm²; 当Y³⁺掺杂浓度为10 at.%时, 具有最长的荧光寿命359.4 μs,并且具有最大发射带宽26 nm.     

钬铥双掺钨酸镱钾激光晶体光谱参数计算

采用顶部籽晶提拉法（TSSG）生长了钬铥双掺钨酸镱钾（KHo_0.04Tm_0.06Yb_0.9（WO₄）₂）激光晶体。测试了该晶体的吸收及荧光光谱,计算了其光谱参数。实验结果表明：该晶体在890~1 000 nm范围吸收带较宽,半峰宽为90 nm,计算了主峰1 000 nm处吸收截面为16.92×10^-20 cm²;Tm³⁺在1 690~1 812 nm范围存在较宽的吸收带,半峰宽为118 nm,易于实现Yb→Ho、Yb→Tm、Tm→Ho的能量传递。根据Judd-Ofelt理论,计算了该晶体的光谱强度参数。根据Tm³⁺、Ho³⁺、Yb³⁺离子能级图,讨论了产生1 750~2 200 nm荧光发射的3种能量传递方式。最后计算了主峰2 030 nm处受激发射截面为3.47×10^-20 cm²,表明该晶体可作为2 μm波段优异的激光增益介质。     

LiNbO3和LiTaO3晶体Er3+/Yb3+掺杂水热外延层室温吸收光谱分析

本文引入与浓度和厚度有关的k_NL待定参数, 在J-O理论基础上, 对Er³⁺/Yb³⁺掺杂的LiNbO₃和LiTaO₃单晶衬底上 的多晶水热外延样品进行了基于吸收光谱的拟合计算. LiNbO₃:Ω₂=2.34× 10^-20 cm², Ω₄=0.77× 10^-20 cm², Ω₆=0.31×10^-20 cm², k_NL=4.32× 10^-2 mol·m^-2. LiTaO₃:Ω₂=1.68×10^-20 cm², Ω₄=0.84×10^-20 cm², Ω₆=0.45×10^-20 cm², k_NL=9.17×10^-3 mol· m^-2. 该方法可尝试推广到粉体或胶体等难以直接获得浓度和厚度数据的体系. 经上转换发光测试及光谱参数计分析认为Er³⁺/Yb³⁺离子的掺杂浓度比为1:1的情况下, 样品呈现绿色上转换发光光谱; 可尝试以降低基质声子能量的方法提高⁴I_13/2能级 对²H_11/2和⁴S_3/2能级的量子剪裁效率.     

基于窄带隙聚合物的高性能可见-近红外光伏探测器

聚合物光伏探测器是一种极具应用前景的新型光电探测器件.研究了基于窄带隙聚合物的高性能可见-近红外光伏探测器,结果表明,所制备的光伏探测器在可见至近红外光谱范围内具有宽的光谱响应(380—960 nm)、出色的响应度(840 nm时达到380 mA/W)和归一化探测度;同时,器件在暗态反偏条件下的能级示意图揭示了器件内平均电场较低是较厚光敏层器件具有低噪声电流的主要原因.电容-电压与时间周期性响应曲线研究表明聚合物光伏探测器具有快速的响应能力和良好的周期重复性.     

Er3+/Yb3+共掺锗碲酸盐玻璃的光谱性质及Judd-Ofelt理论分析

用高温熔融法制备了一种Er³⁺/Yb³⁺共掺的70TeO₂-5Li₂O-10B₂O₃-15GeO₂玻璃,测试和分析了其热稳定性、吸收光谱、荧光光谱以及红外吸收谱。应用Judd-Ofelt理论计算了玻璃中Er³⁺的强度参数、自发辐射跃迁几率、辐射寿命以及荧光分支比,同时比较了OH^-的存在对玻璃发光特性的影响。结果表明:这种玻璃具有较好的热稳定性,较宽的荧光半峰全宽和较大的受激发射截面,是一种较为合适的宽带光纤放大器的基质材料,OH^-的存在使得Er³⁺离子的荧光强度降低,荧光寿命减小。     

Picosecond nonlinear optical response of Ba0.5Sr0.5TiO3 thin films fabricated by pulsed laser deposition

Well-crystallized Ba_0.5Sr_0.5TiO₃ thin films with good surface morphology were prepared on MgO(1 0 0) substrates by pulsed laser deposition technique at a deposition temperature of 800 °C under the oxygen pressure of 2 × 10⁻³ Pa. X-ray diffraction and atomic force microscopy were used to characterize the films. The full width at half maximum of the (0 0 2) Ba_0.5Sr_0.5TiO₃ rocking curve and the root-mean-square surface roughness within the 5 μm × 5 μm area were 0.542° and 0.555 nm, respectively. The nonlinear optical properties of the films were determined by a single beam Z-scan method at a wavelength of 532 nm with laser duration of 55 ps. The results show that Ba_0.5Sr_0.5TiO₃ thin films exhibit a fast third-order nonlinear optical response with the nonlinear refractive index and nonlinear absorption coefficient being n₂ = 5.04 × 10⁻⁶ cm²/kW and β = 3.59 × 10⁻⁶ (m/W), respectively.     

Carrier relaxation in InGaAs

A modelocked Nd: YAG pumped optical parametric amplifier providing 35 ps pulses in the wavelength range λ = 1.45−2.1 μm has been used to study photoexcited carrier recombination in InGaAs. At carrier densities in excess of 10¹⁸ cm^-3 Auger processes are found to dominate the carrier recombination. An Auger rate of 2.5±0.5×10^-28 cm⁶ s^-1 is determined.     

Laser ablated bismuth cuprate thin films preparation and effect of oxygen nonstoichiometry upon superconductivity

Thin films of Bi₂Sr₂CaCu₂O₈ and (Bi, Pb)₂Sr₂Ca₂Cu₃O₁₀ have been prepared on monocrystalline (100) MgO substrates, using a laser ablation method with post annealing treatment. The influence of substrate temperature and oxygen pressure during deposition were investigated. SEM observations, EDS analysis, electric and magnetic measurements have been used to characterize the films. Superconducting “2212” films, with T_c(R = 0) at 80–83 K and J_c (50 K) up to 5 × 10⁵ A/cm², have been currently achieved, while Pb-doped “2223” films exhibit T_c as high as 110 K with J_c = 5 × 10⁴ A/cm² at 77 K. The effect of annealing at low temperature (350°C) in an argon flow has been studied for the 2212 phase, it shows the influence of the oxygen non-stoichiometry, i.e. of the hole carrier density upon T_c's which can be measured up to 89 K (zero resistance).     

脉冲激光沉积法制备高温压电薄膜0.20 BiInO$lt;sub$gt;3$lt;/sub$gt;-0.80PbTiO$lt;sub$gt;3$lt;/sub$gt;$lt;strong$gt;$lt;font color="#ff0000"$gt;$lt;font color="#ff0000"$gt;（已撤稿）$lt;/font$gt;$lt;/font$gt;$lt;/strong$gt;

采用脉冲激光沉积法制备了0.20BiInO₃-0.80PbTiO₃（20BI-PT）高温压电薄膜,并与0.15BiInO₃-0.85PbTiO₃（15BI-PT）样品进行了比较研究. X射线衍射谱显示,20BI-PT样品100峰出现了明显的劈裂,显示样品具有更高的四方对称性. FESEM图显示,20BI-PT样品中出现了部分111取向的三角形晶粒. 20BI-PT样品的铁电剩余极化（P_r）为～28 μC/cm²,矫顽场（E_c）为～120 kV/cm,相较15BI-PT样品,P_r略有增加,但同时E_c也有增加. 20BI-PT样品的横向压电系数（e_31,f）约为–4.7±0.6 C/m²,和15BI-PT相比几乎一样. 介电温度谱显示,20BI-PT 样品的居里温度比15BI-PT增加了约30 ℃,达590 ℃,且介电峰没有明显的频率依赖性. Rayleigh分析显示,20BI-PT样品中内在本征因素及可翻转畴对介电非线性的贡献和15BI-PT基本相同,但是外在因素的贡献没有15BI-PT的贡献大,这可能和20BI-PT样品中晶粒111相对取向率较高有关. 关键词： 薄膜 脉冲激光沉积 铁电 压电     

超短脉冲激光烧蚀石墨产生的喷射物的时间分辨发射光谱研究

本文使用不同激光能流(18 J/cm²–115 J/cm²)和脉冲宽度(50 fs–4 ps)的超短脉冲激光在真空中(4×10^-4 Pa)烧蚀高定向热解石墨. 通过测量烧蚀喷射物的时间分辨发射光谱研究喷射物的超快时间演化. 在喷射物发射光谱中, 观察到了C₂基团的天鹅带光谱系统, 416 nm附近C₁₅基团的由电子能级¹Σ_u⁺ 和¹Σ_g⁺之间的振动跃迁产生的光谱峰以及连续谱. 50 fs, 115 J/cm²的脉冲激光烧蚀产生的喷射物的连续谱的强度衰减分为快速下降和慢速下降两个阶段(以20 ns时间延迟为分界). 这表明连续谱是由两种不同的组分贡献的. 快速下降阶段, 连续谱主要由碳等离子体通过韧致辐射产生; 慢速下降阶段, 连续谱主要由烧蚀后期产生的大颗粒碳簇的热辐射贡献. 实验结果还揭示了激光能流的提高, 会明显增加喷射物中碳等离子体和激发态C₂的含量, 但对质量稍大的C₁₅的影响较小; 此外, 50 fs脉冲激光烧蚀产生的连续谱的存在时间会随着激光能流的减小而增大, 这说明低能流更有利于在烧蚀后期产生碳簇. 脉宽主要影响喷射物连续谱的时间演化. 4 ps脉冲激光烧蚀产生的连续谱的整个时间演化过程明显慢于50 fs脉冲产生的连续谱.     

Giant nonlinear optical properties of bismuth thin films grown by pulsed laser deposition

Thin films of Bi were grown by pulsed laser deposition on glass substrates at room temperature. The thickness and roughness of the films were characterized by grazing-incidence x-ray reflectivity, and the complex refractive indices were measured in the range from 1.5 to 4 eV by spectroscopic ellipsometry. We performed Z-scan measurements to study the third-order optical nonlinearity of the films. It was found that the Bi films exhibited an unusually large nonlinear refractive coefficient, n(I)~1.24x10(-1) cm(2)/kW and nonlinear absorption coefficient, alpha(I)~-3.97 cm/W , at low laser intensity, ~60 kW/cm(2) . This anomaly is believed to have an origin related to melting of the Bi films at the focus spot by the laser beam.     

Picosecond nonlinear absorption and phase conjugation in BSO and BGO crystals

We have observed a very strong nonlinear absorption in BSO and BGO crystals when they are illuminated by picosecond laser pulses with optical intensity on the order of 10⁸ W/cm². In addition, a phase conjugate reflectivity of 2×10^-3 is obtained in a degenerate four-wave mixing (DFWM) experiment using the same optical power. We derive the nonlinear coupled-wave equations to explain the experimental results. We show that the creation of the conjugate wave can be explained by the presence of a strong nonlinear absorption.     

掺Er3+碲酸盐玻璃的光谱性质与Judd-Ofelt理论分析

用高温熔融法制备了碲酸盐玻璃(70TeO₂-9B₂O₃-6Nb₂O₅-5Na₂O-10ZnO-1%(质量分数)Er₂O₃)样品。测试了玻璃样品的吸收光谱和荧光光谱。应用Judd-Ofelt理论计算了Er³⁺离子的谱线强度、自发辐射跃迁几率、荧光分支比、辐射寿命等光谱参数,并拟合了相应的强度参数Ω_t(t=2,4,6)(Ω₂=8.01×10^-20cm²,Ω₄=2.09×10^-20cm²,Ω₆=1.15×10^-20cm²)。结果发现该碲酸盐玻璃具有较大的Ω₂值,说明Er—O键的共价性强于它在硅酸盐、锗酸盐、氟化物、铋酸盐和磷酸盐玻璃中的共价性。Er³⁺在碲酸盐玻璃中⁴I_13/2→⁴I_15/2跃迁几率约为492s^-1,表明Er³⁺可能有较强的1.5μm发射。分析了Er³⁺在碲酸盐玻璃中能级⁴I_13/2→⁴I_15/2发射的荧光半峰全宽(FWHM=73nm),并应用McCumber理论计算了Er³⁺的受激发射截面(σ_e=1.08×10^-20cm²),发现其FWHM×σ_e远大于Er³⁺在铋酸盐、磷酸盐、锗酸盐和硅酸盐玻璃中的受激发射截面,说明碲酸盐玻璃是一种制备宽带光纤放大器的优良基质材料。     

Joint transfer of time and frequency signals and multi-point synchronization via fiber network

A system of jointly transferring time signals with a rate of 1 pulse per second(PPS) and frequency signals of 10 MHz via a dense wavelength division multiplex-based(DWDM) fiber is demonstrated in this paper.The noises of the fiber links are suppressed and compensated for by a controlled fiber delay line.A method of calibrating and characterizing time is described.The 1PPS is synchronized by feed-forward calibrating the fiber delays precisely.The system is experimentally examined via a 110 km spooled fiber in laboratory.The frequency stabilities of the user end with compensation are1.8×10~(-14) at 1 s and 2.0×10~(-17) at 10~4 s average time.The calculated uncertainty of time synchronization is 13.1 ps,whereas the direct measurement of the uncertainty is 12 ps.Next,the frequency and 1PPS are transferred via a metropolitan area optical fiber network from one central site to two remote sites with distances of 14 km and 110 km.The frequency stabilities of 14 km link reach 3.0×10~(-14) averaged in 1 s and 1.4×10~(-17) in 10~4 s respectively;and the stabilities of 110 km link are 8.3×10~(-14) and 1.7×10~(-17),respectively.The accuracies of synchronization are estimated to be 12.3 ps for the14 km link and 13.1 ps for the 110 km link,respectively.     

Active species in microwave postdischarge for steel-surfacenitriding

Production of nitrogen atoms has been studied in a 2.45-GHz flowing postdischarge in N₂ and N₂-H₂ gas mixtures with Ar as a buffer gas in the high-pressure regime (5×10³ to 6.5×10⁴ Pa). N atom densities have been measured by NO titration in the 10¹⁴-10 ¹⁵ cm³ range and monitored by the first positive emission resulting from the N atom recombination. The rate coefficient of the N+N+N₂ recombination has been found to be _k=6×10^-33 cm⁶ atom^-2 s ^-1 at T₀=300 K, which agrees with previously published data. The N atom production (or degree of N/N₂ dissociation) in front of an Fe-0.1%C substrate correlates well with the thickness of a γ' Fe₄N layer produced by the postdischarge treatment. The H₂ gas was first introduced in the initial phase of treatment to remove surface oxidizing and then was cut off to keep high densities of N atoms. It is deduced that N atoms are more active nitriding species than NH-type radicals     

Nonlinear optical properties of an azobenzene polymer

The nonlinear optical properties of an azobenzene polymer azol2-MO were investigated by a Z-scan technique. The polymer was synthesized by assembling the liquid-crystalline polymer azol2 with methyl orange. The nonlinear refrac- tive index （1.39×10^-15 cm2/W） and the nonlinear absorption coefficient （0.11 cm/GW） of azol2-MO were determined with 532-nm picosecond laser pulses at the irradiance of 92.40 GW/cm2. When compared to the nonlinear properties of azol2 and methyl orange, azol2-MO possesses the advantages of its two constituents and shows larger nonlinear optical properties.     

激光加热碳、金平面靶等离子体膨胀过程

利用软X射线条纹相机与针孔成象装置相结合,测得了碳、金平面靶靶面X射线时、空分辨图象,从而推算出靶面等离子体膨胀平均速度分别为(碳):5.11×10⁷cm/s,(金):6.13×10⁷cm/s。实验用1.06μm的钕玻璃激光轰击靶面,X射线能谱范围为0.1—10keV。测量在激光功率密度≈10¹⁴W/cm²的情况下进行。 关键词：     

Atomic-layer-deposited Al_2O_3 and HfO_2 on InAlAs: A comparative study of interfacial and electrical characteristics

Al_2O_3 and HfO_2 thin films are separately deposited on n-type InAlAs epitaxial layers by using atomic layer deposition(ALD).The interfacial properties are revealed by angle-resolved x-ray photoelectron spectroscopy(AR-XPS).It is demonstrated that the Al_2O_3 layer can reduce interfacial oxidation and trap charge formation.The gate leakage current densities are 1.37×10~6 A/cm~2 and 3.22×10~6 A/cm~2 at+1V for the Al_2O_3/InAlAs and HfO_2/InAlAs MOS capacitors respectively.Compared with the HfO_2/InAlAs metal-oxide-semiconductor(MOS) capacitor,the Al_2O_3/InAlAS MOS capacitor exhibits good electrical properties in reducing gate leakage current,narrowing down the hysteresis loop,shrinking stretch-out of the C-V characteristics,and significantly reducing the oxide trapped charge(Q_(ot)) value and the interface state density(D_(it)).     

Optical nonlinearities and photo-excited carrier lifetime in CdS at 532 nm

Bound-electronic and free-carrier optical nonlinearities, and relaxation of photo-excited free carriers in CdS have been investigated by the use of a single-beam Z-scan technique at 532 nm. Under pulsed radiation of 35-ps duration with the input irradiances up to 4.8 GW/cm², the two-photon absorption coefficient, the bound-electron nonlinear refractive index, the free-carrier absorption cross-section, and the change in the refractive index per unit carrier density are determined to be 5.4±0.8 cm/GW, −(5.3±0.8)×10⁻¹³ cm²/W, (3.0±0.5)×10⁻¹⁷ cm² and −(0.8±0.1)×10⁻²¹ cm³, respectively. By using these values in the open-aperture Z-scans conducted with 7-ns laser pulses, the carrier recombination time is extracted to be 3.6±0.7 ns. The measured parameters are compared to theoretical calculations.