影响KNSBN∶Cu晶体中全息光栅读取时间长短的因素

系统分析了掺铜钾钠铌酸锶钡(KNSBN∶ Cu)晶体中全息光栅的读取过程,发现全息光栅读取时间的长短与读取光的强度以及样品的温度有关,实验表明,温度为50℃读取时间约为95℃时的2倍;读取光强为1.8 mW时的读取时间为38 mW时的6倍,而且在实验范围内,读取时间和写入时间近似为线性关系.     

光聚合物中全息光栅的温度依赖性研究

在Polyacrylic Acid(PPA)光聚合物中用双光束相干的方法成功地写入了全息光栅,用He-Ne 激光器作为探测光对光栅的写入过程进行了实时监测.分两种情况重点研究了温度对光栅成栅过程的影响,一是在不同的温度下写入光栅;二是在室温下写入光栅,待光栅强度达到最高时再改变温度来研究温度对光栅的影响.实验中温度的变化范围为25 ℃~100℃.     

光学微球腔的热光效应用于温度传感器研究

为研究光学微球腔的热光效应,采用1550nm波段可调谐激光器和宽带光源两种泵浦源,分别测量了二氧化硅、碲酸盐玻璃微球及其掺杂了稀土离子的微球在激励光功率、环境温度变化时其谐振峰波长的变化量,得到了二氧化硅微球激励功率灵敏度为32.4pm/mW,温度灵敏度为13.4pm/℃;铥离子的掺杂使激励功率灵敏度达到48.7pm/mW,温度灵敏度达到15.2pm/℃.相应的碲酸盐微球激励功率灵敏度为71.1pm/mW,温度灵敏度为0.0191nm/℃,比光纤光栅温度传感器的灵敏度10pm/℃大了将近1倍,若掺杂了稀土离子,则高1.1倍.本文研究对微腔在温度传感器方面的应用具有参考意义.     

基于聚合物分散液晶全息光栅的可调增益均衡器

从理论和实验两方面分析研究了聚合物分散液晶全息光栅在632.8 nm光波的入射下的衍射谱特性和电压可调特性，实验结果与耦合波理论的计算结果具有很好的一致性，从实验上验证了用耦合波理论来描述聚合物分散液晶全息光栅的衍射特性是恰当的.并且提出了利用聚合物分散液晶全息光栅对掺饵光纤放大器增益谱进行平坦化的方法，利用聚合物分散液晶全息光栅的电压可调特性可实现动态增益均衡.运用该方法，可使掺饵光纤放大器在C波段1530~1560 nm内，温度在0℃~65℃范围内变化，掺饵光纤放大器自发辐射谱的不平坦度从3.3 dB降到0.2 dBp－p（峰-峰值）.     

基于应力分析的电镀保护光纤布喇格光栅传感性能分析(英文)

为保护光纤光栅,提出了一种镀层和光纤光栅结合良好的无粗化过程的化学镀和电镀保护方法.基于应力分析法,得到镀镍光纤光栅的温度灵敏度公式,采用ANSYS有限元软件分析了电镀后光纤光栅应力随温度变化关系,并进行了实验证实.结果表明:光纤光栅电镀后温度灵敏度理论和实验值分别为20.6951pm/℃、22.076pm/℃.理论分析和实验、仿真结果基本一致.相比裸光纤光栅,温度灵敏度增加到原来的2.2倍.该方法不仅可以获得厚度理想的保护层,还可以提高光纤光栅的温度灵敏度.     

基于全息液晶/聚合物光栅的分布反馈式激光器的波长调谐特性研究

首先制备了不同周期的染料掺杂全息液晶/聚合物光栅并进行激光抽运实验, 得到了激光器的调谐曲线,确定了激光器在574 nm到685 nm的谱带里均可以实现激光输出, 即激光器具有110 nm左右的可调谐范围. 之后, 通过温控仪控制样品的温度, 对周期为610 nm的染料掺杂全息液晶/聚合物光栅进行激光抽运, 探测不同温度下的输出激光光谱, 观察到随着温度由20℃升高到65℃, 激光器的中心波长由627.9 nm减小到623 nm, 产生了4.9 nm的波长蓝移.     

一种测量温度和流速的光纤光栅传感器

提出一种基于铝片的测量温度和流速的光纤布喇格光栅(FBG)传感器。采用一种耐高温胶将光纤布喇格光栅封装在一小铝片上，经过高温固化处理，可保持光纤光栅传感器的稳定性。通过-20℃～100℃温度实验，得到该传感器的温度灵敏度系数为0.0392nm/℃,是封装前的3.5倍，且传感器温度响应保持了很好的线性和重复性。从水温14.5℃时的流速实验中得到水流速在0～20m/s范围变化时，FBG峰值波长漂移了0.13nm,验证了此光纤光栅传感器测量流速的可行性。试验结果表明，该传感器既可以作为温度传感器，又可以作为流量传感器，并且制作简单，成本较低。     

利用偏振全息记录可重复擦写的偶氮相位光栅

利用偏振全息技术在偶氮苯侧链聚合物薄膜上进行了记录全息相位光栅的研究.从理论和实验两方面分析了不同的偏振全息模式、偶氮高分子聚合物材料和全息曝光时间对相位光栅生成的影响.通过实验比较,确定了最佳的实验条件,在形成折射率相位光栅的同时,最大限度的避免了由于大分子运动而导致的表面起伏对相位光栅的破坏,并在此基础上,记录了可重复擦写的全息相位光栅.这种全息光栅制作比较方便,光栅系数可以方便的调整,在室温下非常稳定并且能用圆偏振光完全擦除后重复写入.     

低陡度光刻胶光栅槽形研究

为控制全息光刻胶光栅槽形,从研究显影时间、显影液温度等对光刻胶特性曲线的影响出发,采用计算机模拟和实验方法,制作出底部占宽比30%左右,陡度65°左右的低陡度光刻胶光栅掩模.研究发现：启动曝光量随显影时间的延长而减小,光刻胶特性曲线线性部分的斜率随着显影时间的增加而增加;显影液温度高的光刻胶启动曝光量大,其特性曲线线性部分的斜率也较大.这决定了制作低陡度光刻胶光栅掩模需要使用非1∶1的干涉曝光,以及必须采用较低温度的显影液进行显影处理.最终选用1∶7的干涉曝光和15℃的显影液.     

基于可调谐F-P滤波器的FBG波长解调系统的动态实时校准方法

为减小可调谐法布里-珀罗(F-P)滤波器驱动元件的温度漂移及非线性导致的光纤布拉格光栅(FBG)波长解调误差,在分析比较串联型和并联型两种校正方案基础上,提出了一种改进型串联实时校准方法。设计了具备高热稳定性且内部温度分布均匀的参考光栅模块,通过实时测量紧贴参考光栅埋入的高精度热电阻温度值及事先标定的4支参考光栅波长与热电阻温度值对应关系,获取4个精确波长参考点,在每次扫描时实时校准可调谐F-P滤波器透射波长与驱动电压函数关系。实验结果表明采用改进的动态实时校准方法解调FBG波长的最大误差为±3 pm。与通过直接读取驱动电压确定FBG中心波长的方法相比,解调精度提高了6倍;与已报道的串联校正方法相比,解调精度提高了3倍。     

入射光参量对Ce∶KNSBN晶体中光扇效应的影响

采用非同时读出条件下晶体两波耦合实验装置,研究了入射光强度及光入射角对Ce∶KNSBN晶体中光扇效应的影响.结果表明,光扇效应存在明显的入射光强度阈值特性,入射光强度阈值为38.2 mW/cm2.对应相同的入射光强度,光入射角θ为15°时稳态光扇强度Ifsat最强,如:入射光强度为38.2 mW/cm2时,Ifsat最大为0.7 mW/cm2;入射光强度为57.3 mW/cm2时,Ifsat最大为1.8 mW/cm2.     

A new method for measuring the threshold of stimulated Brillouin scattering

A new method for measuring the threshold of stimulated Brillouin scattering (SBS) based on the generation location of a Stokes beam is proposed for the first time to our knowledge. The length of the medium cell is selected to be longer than the free gain length of pump pulses in the Brillouin medium. The reflected light from a certain mirror in front of the medium cell is chosen as the reference beam, and the SBS threshold is measured by the "jump" of the delay between the Stokes beam and the reference beam. An 8-ns Q-switched single-longitudinal-mode pulse is used as the pump and the typical SBS medium FC-72 is selected as the nonlinear medium in our experiment. The SBS threshold intensity is measured to be 173-178 mW/cm 2 , which is consistent with existing results measured with the transmitted energy limiting method.     

Ce∶KNSBN晶体两波耦合中的光扇效应

采用两波耦合非同时读出实验装置 ,测量了掺铈钾钠铌酸锶钡 (Ce∶KNSBN)晶体两波耦合过程中的信号光和抽运光非同时打开条件下两波耦合增益的时间变化规律 ,讨论了光扇的入射光强阈值及光扇效应对两波耦合动态过程的影响。结果表明 :6 32 .8nmHe Ne激光在Ce∶KNSBN晶体中写入体光栅时 ,光扇效应存在明显的写入光强阈值特性 ,当入射光强大于 30mW /cm2 时 ,才存在强烈的光扇效应。利用修正耦合波方程对Ce∶KNSBN晶体中的两波耦合动态过程、增益随着信号光和抽运光打开时间间隔Δt的变化进行了模拟计算 ,理论模拟结果与实验测量结果基本一致     

超导加速器CW模式的高阶模初步分析

 超导加速器由于具有极高的Q值,因此表现出较强的腔束相互作用,尤其是在以CW模式运行下,严重时会产生束流崩溃(BBU)效应。德国TESLA式的9-cell超导串腔在束流负载为1 mA,束团重复频率为81.25 MHz情况下,对其高阶模的产生及相应的功率水平进行了分析。结果表明：对于该腔的主要高阶模,谐振偏差值在π/4以上,束流没有发生谐振,高阶模功率在mW量级。     

Wavelength dependent damage in biological multi-photon confocal microscopy: A micro-spectroscopic comparison between femtosecond Ti:sapphire and Cr:forsterite laser sources

Molecular excitation by the simultaneous absorption of two photons provides intrinsic three-dimensional resolution in laser scanning fluorescence microscopy. Thus induced two-photon absorption and the accompanied multi-photon absorption/ionization not only cause photo-bleaching but also cell damage in the vicinity of the focal point. In this paper, we study the wavelength dependent cell damage induced by high intensity femtosecond near infrared lasers. The study was performed with a Ti:sapphire laser and a Cr:forsterite laser. With a longer output wavelength from a Cr:forsterite laser, multi-photon absorption and auto-fluorescence were found to be significantly suppressed and the destructive plasma formation was found to be greatly reduced. Sustained multi-photon spectra can be observed in most plant specimens with a tightly focused Cr:forsterite laser beam under long term irradiation with more than 100 mW laser average power. In contrast, multi-photon absorption induced destructive plasma formation were frequently observed with a tightly focused Ti:sapphire laser beam within seconds with more than 10 mW laser average power.     

Erasure effect of the reading beam on the decay process of χ(2) in all-optical poling

We have studied the effect of the reading beam on the decay process of the photoinduced second-order susceptibility χ⁽²⁾ in both the guest-host system (disperse red 1-doped polymethyl methactrylate) and the side-chain system (disperse red 19-functionalized polyimide polymer). Both experimentally and theoretically, we have proved that the reading beam has the erasure effect on the decay process, that is, χ⁽²⁾ decays faster in the high intensity than in the low intensity of the reading beam. Furthermore, the relationship between the time constant τ_B of the slow component of the decay process and the intensity of the reading beam I_1.06 is derived from the theoretical equations, which is fitted well with the experimental results. Based on the fitting parameters, we also compare, quantitatively, the thermal-induced orientational diffusion of trans- and the quantum efficiency of trans-to-cis photoisomerization in the two systems. Received: 8 September 1999 / Revised version: 14 March 2000 / Published online: 16 August 2000     

Green laser photocoagulator for the treatment of diabetic retinopathy developed at Raja Ramanna Centre for Advanced Technology

An all-solid-state green laser photocoagulator at 532 nm with output power varying from 100 mW to 1 W in a step of 10 mW and exposure time varying from 50 ms to 1000 ms in a step of 10 ms is developed for the treatment of diabetic retinopathy. The output power stability is better than ±1.5% with a nearly diffraction-limited beam quality. The system includes various safety and operational features like internal power monitoring system, safety interlock, emergency switch-off, graphical LCD display with table-top touch mode portable control panel, smart delivery device selection, aiming laser beam with controllable intensity, foot switch, patient records, service mode etc. The system has successfully passed the clinical trials and is being used on patients.     

Strong beam coupling in mesogenic materials with photorefractive Bragg gratings

Strong beam coupling was observed in mesogenic materials consisting of low- and high-molar-mass liquidcrystal mixtures with high concentration ratios of the latter type of liquid crystal. The beam-coupling effects originate in orientational photorefractive Bragg gratings, and a weak signal beam with an intensity of 1 mW is amplif ied to 8 mW by energy exchange with a strong pump beam after the passage of a 50-mum-thick film under a low operating voltage of 1-4 V/ mum. There is a superior net two-beam coupling gain of more than 600 cm(-1) with the low operating voltage and high resolution.     

980 nm激光泵浦下掺Er3+碲酸盐玻璃的光子雪崩上转换

在980 nm激光二极管的抽运下,掺Er3 碲酸盐玻璃辐射出很强的绿色上转换荧光,荧光强度与抽运功率呈非线性关系,发光强度和积累时间与激光抽运功率的关系研究表明存在雪崩阈值44 mW.发现光子的积累时间(几十毫秒量级)远大于荧光的寿命,且积累时间随抽运功率的增大而减小.与早先报道的690和579 nm抽运波长相比,980 nm是更加有效的抽运波长.     

风对光束控制系统内热效应的抑制作用

 用光强沿x轴方向呈线性变化的方形环状光束模拟高功率激光，利用自编四维仿真程序对高功率激光在光束控制系统中的传输作了详细的数值计算研究。结果表明：热效应使远场光束的峰值光强和可聚焦能力下降。入射光强的非均匀分布进一步降低峰值光强和可聚焦能力，导致远场光束重心和峰值光强位置移动，并产生像散。光束的非均匀程度越高，远场光束质量越差。横向风和轴向风对热效应均有抑制作用。然而，轴向风不会引起远场光束重心偏移和像散，但是轴向风比横向风建立稳态所用时间更长。