气溶胶粒子散射和吸收特性对复折射率依赖性的数值研究

利用米散射理论数值计算分析了尺度参数为0.1~100时球形典型气溶胶粒子的散射和吸收特性对复折射率的依赖性关系。气溶胶粒子复折射率的实部和虚部是一个有机的整体,粒子复折射率的实部和虚部可以分别影响其散射和吸收特性。若实际大气气溶胶粒子大多是成核模态和积聚模态的小粒子,基于气溶胶的散射和吸收特性可以获得其复折射率的唯一解。但是,如果大气中存在大量的粗模态粒子时,气溶胶散射和吸收特性对其复折射率的依赖性较为复杂,只有选择有限的合适复折射率库区间,才有可能获得更合适的有效复折射率。     

CO2激光脉冲边缘写入的长周期光栅折射率特性研究

报道了一种用高频CO2激光脉冲在普通通信光纤包层边缘单侧写入的新型长周期光纤光栅。研究发现,这种长周期光纤光栅的折射率变化主要发生在光纤包层区域,而纤芯的折射率变化较小;同时该光栅的附加损耗低于0.5 dB。进一步折射率特性实验研究表明,由于其特殊的折变结构,这种光栅具有较高的外界环境灵敏度,当外界折射率在1.41~1.45范围内变化时,其谐振波长漂移量高达15.52 nm,比实验测得的用传统方法写入的长周期光纤光栅谐振波长漂移量高出近3倍,这种光栅结构在光纤传感中将具有重要的应用。     

关于折射率对散射光场分布影响的研究

根据Mie散射理论,采用理论计算和实验相结合的手法,研究了光散射现象以及散射介质的折射率对散射光场分布的影响.通过对空气中不同折射率的散射介质形成的散射光场光强的实验比较,论证了散射介质折射率的实部变化对散射光强的影响不大,其主要影响是通过对相位的变化来实现的,也即散射介质折射率的虚部变化对光强的影响很大,在实际应用中不可忽略.这一结论对以散射光场的分布为基础的各种研究具有一定的指导意义.     

Enhanced Coupling of Light from Organic Electroluminescent Device Using Diffusive Particle Dispersed High Refractive Index Resin Substrate

To improve light extraction from organic electroluminescent (EL) devices, we introduced a diffusive substrate with 25 μm thickness consisting of high refractive index resin and scattering particles. It is expected that the diffusive substrate with high refractive index matrix converts the waveguided emission into external emission from both glass substrate and indium-tin-oxide/organic layer. We used the ray tracing method to optimize the scattering effect and to verify the coupling out effect of the diffusive high refractive index substrate. With the use of the ray tracing calculation, an increase in the external emission up to a factor of 2.7 was expected compared to use of a common glass substrate. Experimentally, the coupling out effect of the diffusive high refractive index substrate strongly depended on the thickness of electron transporting layer (ETL) due to the well-known interference effect. The current efficiency increased by a factor of 1.3 for an organic EL device with a 60-nm-thick ETL and by a factor of 6.8 for one with a 120-nm-thick ETL.     

利用劈尖的等厚干涉测量液体的折射率

利用劈尖的等厚干涉测量了不同液体的折射率。在不改变劈尖夹角前提下,通过读数显微镜,分别得到劈尖在空气和液体中的干涉条纹间距ΔX_空、ΔX_液,从而运用n=ΔX_空/ΔX_液得到各液体的折射率。通过本实验,丰富了折射率测量的方式。     

双散射角光学粒子计数器测量气溶胶折射率的新方法研究

根据米氏(Mie)散射理论,通过数值模拟分析了气溶胶折射率虚部n_i在不同散射角度上对双散射角激光光学粒子计数器(L-OPC)响应曲线的影响,定义了敏感函数。根据分析,散射角应该在小于20°和40°～60°之间选取。以散射角系统ψ=9°,β=5°,λ=0．65μm和ψ=50°,β=20°,λ=0．65μm为例,其中一个散射角受折射率虚部n_i的影响较小,另一个较大。在测量粒子谱分布的同时,利用n_i对不同散射角度响应曲线的影响差异,来确定n_i值,并提出确定n_i的方法。还给出了双散射角激光光学粒子计数器的模拟测量结果。     

光纤中慢光群折射率限定特性研究

粒子在基态和亚稳态之间的振荡会导致探测光吸收的降低,而探测光束在很窄的频率范围内吸收的降低,会使介质的感生折射率在同样范围内迅速变化,从而改变群折射率ng=n(ω)+ωdn/dω。本文利用光纤慢光理论,对不同条件下的群折射率限定和群速度的变化特性展开讨论。群折射率随光纤长度的增加而降低,不同离子浓度的掺铒光纤中慢光的感生群折射率均随调制频率的增加而降低,同时在不同的调制频率条件下,群折射率随入射信号光强度的增大均有一个饱和的过程。     

用光速测定仪探究水的折射率

用光速测定仪探究折射率是测量介质折射率的一种方法。本实验特别适合液体折射率的研究,我们以水为参考尝试测量它的折射率。     

体全息光栅线性记录折射率分布的修正

在讨论非线性记录体全息光栅的光谱特性时,发现一些文献在线性记录时折射率分布的表达式有些不妥.重新讨论了线性记录情况下折射率分布的表达式,引入了光束比和总光强折射率调制系数,用耦合波理论计算讨论了不同光束比和总光强折射率调制系数对光栅衍射光谱特性的影响.计算结果表明,光栅衍射光谱主峰峰值随总光强调制系数的减小而略有降低,主峰峰值随光束比减小下降得不大,带宽随总光强调制系数和光束比的减小而明显变窄,次峰峰值随总光强调制系数和光束比的减小而明显减小.     

Estimation of the Refractive Index Change in Glass Induced by Femtosecond Laser Pulses

It is known that local refractive index change occurs when femtosecond laser pulses with extremely high peak power are launched into glass. We focused 130-femtosecond laser pulses of 800 nm into the bulk of glass and examined the shape of the induced refractive index change. We found that the length of the spot of the refractive index change along the optical axis reached about 30 μm despite the diameter being about 2 μm. To estimate the distribution of induced refractive index change, we fabricated Bragg grating by scanning the focused spot and calculated the amount of the change by applying Kogelnik’s coupled mode theory to the measured diffraction efficiencies of the higher order diffracted beams.     

双凹厚透镜曲率半径和折射率的测定

观察双凹厚透镜的球面反射成像,利用这一实验现象结合物像公式测定双凹厚透镜前后表面的曲率半径和折射率。利用两次球面反射成像可求出双凹厚透镜的曲率半径,两种方法可比较。对于薄透镜,这种方法可以修正在实际测量中忽略透镜厚度所产生的误差。     

Study on the Vertical Profile of Refractive Index in the Troposphere

The vertical profiles of atmospheric pressure and optical refractive index have been theoretically analyzed. The refractive index can be determined at any altitude above the sea level in the troposphere. The ranging error has been analyzed and ranging accuracy could be improved when the average refractive index along the ray path is used.     

用光拍法研究葡萄糖溶液密度和折射率的关系

实验根据葡萄糖溶液浓度不同对折射率的影响,采用光拍法测定液体的折射率,计算出液体的密度,并采用最小二乘法进行线性拟合,最后发现葡萄糖溶液的密度和折射率几乎呈线性关系.     

C＋＋语言在最小偏向角法测折射率实验中的应用

介绍了用C＋＋语言编程来处理最小偏向角法测量固体折射率的实验数据，为处理实验数据提供了简捷、准确、快速的方法，避免了传统实验数据处理的繁琐及大误差，为使用者提供了方便。     

红外光学材料折射率温度系数测量装置

本文介绍一台红外光学材料折射率温度系数测量装置。该装置是由温控系统、精密测角系统、光学系统和电器控制系统等组成的一台高精度全自动化测量系统，采用改进的自准直法测量折射率温度系数值。该装置达到的主要技术指标：工作波长为2～12μm，温度范围为-50～150℃，测量不确定度为3%，可满足各种红外光学材料折射率温度系数测量的要求。利用该装置对红外材料锗折射率温度系数值进行了测量，并对测量数据进行了报道。     

米氏理论的近似及在粒度测量中的应用

将夫琅禾费衍射理论与几何散射 (包括折射和反射 )相结合 ,给出平行光入射下圆形颗粒在前向大角度范围内的散射光强分布近似算法。由于考虑了衍射、折射和反射相互间的干涉效应和颗粒对光的吸收性 ,对于正常或非正常衍射状态下无因次参量α≥ 40的耗散颗粒 ,在前向 0°～ 60°散射之内 ,该方法对散射光强计算结果与米氏理论结果是吻合的。由于计算速度比米氏理论快 ,有效角度范围比夫琅禾费衍射理论宽 ,因而适合于大颗粒的前向光强计算。将这一计算方法应用到大角度采光时的激光粒度测量实验中 ,收到了良好的效果     

低功率近红外光的偏振方向对光致折射率变化影响的实验研究

研究了利用低功率近红外光辐照In:Fe:LiNbO3晶体时写入光束的偏振方向对光致折射率变化(Δn)的影响.分别采用正常偏振(o光)和非常偏振(e光)的近红外细激光束,在In:Fe:LiNbO3晶体中进行了光折变实验.研究表明,两种偏振方向引起晶体的Δn实测曲线相似,但变化规律恰好相反,o光引起的折射率变化量约是e光的3倍左右.近红外光写入下两种偏振光束引起晶体的Δn分布规律都不同于可见光,尤其是e光辐照区域中心晶体的折射率升高.因此,通过选择不同偏振方向的近红外光可以在光折变晶体中制作不同折射率分布的非线性光学器件.     

镀有SiO_2-WO_3薄膜LPFG折射率传感特性研究

采用四层阶跃折射率几何模型,研究了镀有SiO2-WO3薄膜LPFG在溶液折射率测量方面的特性,并与未镀膜情况进行了比较。当LPFG包层外镀膜后,测量纯水、CaCl2溶液(浓度为450gL-1,折射率为1.4056)时波长漂移量分别是未镀膜时的1.67和2.55倍;谐振峰的损耗变化分别是未镀膜时的4.44和2.82倍;在1.36-1.38折射率范围内,传感器的灵敏度和分辨率分别是216.58nm和0.82×10-5,是镀膜前的3.27和0.30倍,说明镀膜后LPFG对溶液折射率测量的灵敏度和分辨率得到了很大的提高。     

Implementation of the Laser Diffraction Technique for Acoustic Cavitation Bubble Investigations

Knowledge of the acoustic cavitation cloud would be useful for improving ultrasound reactor design. Among the characterisation techniques, few are adapted to bubble investigations in an intense ultrasound field. Some problems raised by these measurements result from interactions between the acoustic pressure wave and the measuring light wave. This paper reports the implementation of the laser diffraction technique to determine the size and volume concentration of bubbles generated by a dipping horn operating at 20 kHz. Measurements were performed with a Malvern 2600 instrument. The size distribution, deduced from the diffraction pattern scattered by the bubble cloud crossed by a laser beam, is disturbed by the acoustic pressure wave involving deviation of a light beam at low diffusion angles (acousto‐optic effect). A bubble size correction procedure based on the subtraction of the light energy due to the ultrasound wave is described. The size measurements, and thus the correction procedure, were validated by a second laser technique based on a different measuring principle: phase Doppler interferometry. The measurement reliability was further confirmed by an original application of laser diffraction based on measurements performed just after sonication. These three methods lead to a mean bubble size (Sauter mean diameter) of about 10 μm at a high ultrasound power input. Concerning the void fraction, only measurements achieved after sonication and by laser diffraction predict a correct estimation of this parameter.