Optical power limiting and stabilization based on a novel polymercompound

Optical power limiting and stabilization based on the two-photon absorption (TPA) mechanism is performed in a polymer solution excited by ~810 nm and ~7-ns laser pulses. The solute is a novel polymer, a poly(2,5-dialkoxy-p-phenylene ethynylene) derivative (EBO-OPPE). Using 1-cm path-length EHO-OPPE solution in chloroform of d₀=0.03 mol of repeat unit/liter as the nonlinear absorptive medium, the dynamic transmission changes from T=0.92 to 0.28 when the input intensity of the ~810-nm laser beam is increased from I₀=15 to 600 MW/cm² . The measured nonlinear absorption coefficient is 14.5 cm/GW. Optical power stabilization is demonstrated at an average input intensity level of I₀≈400 MW/cm² with a Δ≈±25% peak-power fluctuation of the laser pulse. After passing through the nonlinear medium, the output peak-power fluctuation is reduced to Δ≈±8%. The spectral-width effect of the input laser beam on the nonlinear absorption of the EHO-OPPE solution is investigated. For three different spectral structures of the input laser beam (single narrow spectral line, multiple spectral lines, and broad spectral band), measured values of TPA cross section for EHO-OPPE are σ₂=66, 80, and 101×10^-20 cm⁴/GW, respectively. This means that EHO-OPPE is one of the best known nonlinear absorptive materials for power limiting purposes     

Power scaling in quantum-well laser amplifiers

The effects of increasing excitation on the performance of quantum-well semiconductor laser amplifiers were investigated. Amplified spontaneous emission (ASE) and gain roll over at high injected carrier densities are two limitations to the power scaling of these devices. A Rigrod analysis was used to study the effects of these limitations on the gain, ratio of signal to ASE power, and efficiency for different values of injection current, facet reflectivity, and input laser intensity. Comparisons are made with an equivalent amplifier operating with a bulk semiconductor gain medium. This analysis suggests that quantum-well semiconductor amplifier performance improves with a double-pass configuration     

共振激活介质的反射特性

基于二能级原子系统的极化率理论,对共振激活介质界面的反常反射特性作了理论分析。以Nd:YAG激光介质为例,计算了界面的反射率R与入射激光波长(相对于原子线,中心的失谐量6)与场强AA的关·系曲线。在较低强度(AA～10~(-4))时,R与AA依然有关。     

无序介质的非相干背散射

讨论两种散射,导出相应的分布函数,运用蒙特卡罗法模拟光子在无序介质中的随机行走过程,得到非相干背散射空间分布及反射率。计算结果表明：1、散射不同,非相干背散射空间分布和反射率不同,非相干背散射反射率随光入射角增大而增大;2、非相干背散射反射率随无序介质吸收系数增大而减小,通过测量非相干背散射反射率可得吸收系数,进一步可得每次散射光子被微粒吸收的概率;3、非相干背散射反射率随光子平均自由程增大而减小,通过测量非相干背散射反射率可得平均自由程,这比检测相干背散射来得到平均自由程要容易。最后,讨论了背散射对无序激光器的影响。     

Excited singlet-state absorption in dyes and their effect on dye lasers

The performance of dye lasers with excited singlet-state absorption (ESA) at the pump and the lasing wavelengths is analyzed for short pulse pumped systems in the medium range of pumping intensities. Analytical and numerical solutions are presented for a wide range of the variable parameters such as ESA cross sections, the cavity reflectivity, and the pumping intensity. An experiment is described for measuring ESA cross sections in the pumping as well as the lasing regions, and the results for rhodamine 6G and rhodamine B are given, showing that due to ESA, the effective gain of the laser will be much lower than that expected from previously published data on the stimulated emission cross sections.     

Determination of the absorption and scattering coefficients of highly scattering media from the experimentally established temporal distributions of laser pulse intensities

The passage of laser radiation through a scattering medium is studied experimentally. A method of determining the optical characteristics of a scattering media is proposed. The method is based on the measurements of time distributions of the intensity of ultrashort laser pulses for two layer thicknesses of the medium to be studied. The measurements are carried out with the use of a single-photon counting system. The proposed method is used to determine the absorption and scattering coefficients of a model medium from the experimental data.     

强度防护型激光防护机制

论述了非线性吸收、非线性折射、非线性散射等基于非线性效应以及基于相变效应的激光防护机制,分析了每种防护机制的优势和局限,指出了强度防护型激光防护技术的发展趋势。     

内腔连续波光学参量振荡器:高斯光束理论

建立了描述内腔连续波单共振光学参量振荡器(ICCWSRO)的功率特性的高斯光束理论。     

混浊介质中光子的迁移程长研究

从时间分辨漫射方程出发推导了混浊介质中光子的程长概率分布函数，研究了平均程长、最可几程长与组织光学特性参数以及光源检测器之间的距离的关系。结果显示，约化散射系数对程长分布的影响要大于吸收系数的影响；平均程长在整个范同内与光源检测器之间的距离呈现良好的线性关系；而最可几程长在光源检测器之间的距离较大时与其呈线性关系。蒙特卡罗模拟结果显示与理论计算结果吻合。     

光存储用偶氮镍螯合物染料的光学与热学性质研究

分别对三种以4-甲基噻唑、苯并噻唑和6-甲基苯并噻唑作为重氮组份,以3-二乙氨基苯酚作为偶合组份的偶氮染料的镍螯合物的光谱、热学性质和薄膜的光学常数(复折射率N=n ik)及光存储性能进行了研究.结果表明,以4-甲基噻唑作为重氮组份的偶氮镍螯合物在激光工作波长650 nm处具有较高的折射率指数(n=2.46)和较小的消光系数(k=0.18),在330℃左右分解,而且分解曲线陡峭.光盘静态测试仪的测试结果表明该染料薄膜在较低的写入功率和较窄的脉冲下,可以获得大的反射率对比度.该染料有望作为高密度可录光盘(DVD-R)的记录介质.     

LD泵浦固体激光器的输出损耗电光调Q技术

叙述了半导体泵浦Ｎｄ：ＹＶＯ４微片Ｆ－Ｐ电光调Ｑ激光器的原理．利用ＬｉＴａＯ３电光调制的ＦＰ标准具取代输出耦合腔镜作为调Ｑ器件．详细讨论了调Ｑ标准具的反射率特性、工作物质的温度特性对Ｆ－Ｐ调Ｑ器件的影响．同时讨论了Ｆ－Ｐ标准具的合适的膜系反射率以及标准具作为调Ｑ耦合镜时具有的模式选择特性。为半导体泵浦的微型调Ｑ器件的实现提供理论依据和技术保证．     

基于腔反射光控制的腔衰荡光谱测量实验研究

腔衰荡光谱(CRDS)技术是一种高灵敏的激光吸收光谱技术,它实现的关键技术是在腔内激光强度达到一定值时,迅速将激光关断来探测光强的衰减信号.在激光与腔共振时,腔的反射信号迅速减小可以产生低电平来触发由TTL信号控制的声光调制器(AOM)关断激光,从而实现CRDS.在关断激光后用快速响应探测器对腔的衰荡信号进行探测,用L...     

偶氮染料掺杂薄膜光记录性能研究

利用旋涂法 (Spin Coating)制备了新的含氮原子的杂环偶氮染料掺杂高分子聚甲基丙烯酸甲酯 (PMMA)薄膜。室温下测试了该偶氮染料在溶液和薄膜态的吸收光谱和薄膜态的反射光谱。研究了薄膜的光谱性质和短波长光记录性能。该薄膜在 4 0 0～ 550nm波长范围内具有强的吸收和反射光谱。短波长光盘静态测试结果表明 ,用低功率Ar 激光 (514 5nm)写入时 ,薄膜在写入前后的反射率变化较大。     

基于光场分布特性分析的高功率激光吸收体设计方法研究

高功率激光装置需要利用激光吸收体实现对杂散光的有效管控。然而吸收体受光面交界处极易发生激光损伤，可能导致激光装置内部的洁净环境受到污染。为了解决这一问题，基于有限元分析方法，模拟了高功率激光吸收体受光面交界处在包括无过渡、圆弧过渡和平面过渡等不同过渡条件下介质内部的光场分布，分析了吸收玻璃界面对光场的影响，得到了介质内部光场峰值强度及峰值位置的变化规律。结果显示:吸收体的损伤可能是由于过渡面为曲面导致的。研究工作为吸收玻璃的激光损伤研究和吸收体设计提供参考。     

飞秒激光致双液滴光学击穿和等离子体分布研究

为了研究超短激光脉冲与双液滴相互作用过程中的光学击穿和等离子体分布,基于麦克斯韦方程组和电离速率方程,构建了飞秒激光与双液滴的瞬态耦合模型,使用有限元分析方法,对飞秒激光辐照微米量级双液滴的自由电子密度和光场分布进行了计算,得到了双液滴结构对液滴光学击穿和等离子体变化的影响。结果表明,第2个液滴的击穿阈值约为同等条件下单液滴击穿阈值的35%;等离子体的形态和击穿点的位置随双液滴间距发生变化,且在聚焦区域产生纳米等离子体射流;第2个液滴对激光能量的吸收随着双液滴间距的增加而减少;当分别使用满足击穿阈值的光强入射,双液滴吸收的能量约为单液滴的3%;第2个液滴对激光能量的吸收随光强增大而增大,能量吸收比例最终趋于0.01,仅为单液滴的1.5%。该研究为激光诱导水击穿和激光在大气中的传输提供了一定的参考。     

琼脂糖凝胶的光学特性

为了研究应用于生物细胞打印的琼脂糖凝胶的光学特性,将不同比例的琼脂糖粉末与蒸馏水混合后加热,溶解冷却形成不同浓度的琼脂糖凝胶。测量琼脂糖热溶液冷却过程中55℃时的琼脂糖溶液的折射率及琼脂糖凝胶的折射率。通过对比细胞培养液的折射率,获得作为生物打印基质材料和生物支架的琼脂糖凝胶最佳浓度为0.786%。测量琼脂糖凝胶的可见、近红外透射光谱及衰减全反射红外吸收光谱,结果显示琼脂糖凝胶在400～1100 nm波段没有特征吸收峰,而且最大吸收只有0.171Abs;在红外波段琼脂糖凝胶的吸收特性与细胞培养液基本相同,细胞培养液在2966 cm-1处的特征吸收峰是培养液独有的。对琼脂糖凝胶表面的激光散射特性进行研究,结果表明,440 nm激光的散射最强,532 nm激光散射最弱;琼脂糖凝胶浓度越小,散射越强。     

多束强激光在大气传输中的热晕与湍流效应

强激光在非均匀光程中传输时,大气路径中分子的吸收系数不再是常数,利用内插法得出了中纬度夏季模式的分子吸收系数随海拔高度的变化规律。强激光传输会同时受到大气湍流效应和热晕效应的共同影响,这严重影响了强激光传输的效能,而采用多束强激光传输方法可以减小这些效应的影响。根据波动光学理论,建立了三束脉冲激光在湍流和热晕相互作用下的数学模型。数值结果表明:该方法对光强起伏、光斑分裂和光束扩展等现象有较好的校正效果。     

Two- and three-photon absorption based optical limiting and stabilization using a liquid dye

It is experimentally shown that both two- and three-photon absorption in a high-molar-concentration chromophore system can be more efficiently utilized to accomplish optical power limiting and stabilization at laser wavelengths of 1.064 and /spl sim/1.3 /spl mu/m, respectively. The nonlinear absorbing medium is a novel liquid dye system, trans-4-[4-(dihexylamino)styryl]-N-(2-{2-[2-(2-hydroxy-ethoxy) -ethoxy]-ethoxy}ethyl)-pyridini um p-tosylate (abbreviated as ASEPT), consisting of chromophore molecules capable of multiphoton absorption in the near IR range. The nonlinear transmission property and output/input characteristics have been studied based on this liquid dye system, using nanoseconds 1.064-/spl mu/m laser pulses for two-photon excitation and /spl sim/1.3-/spl mu/m subpicoseconds laser pulses for three-photon excitation. A fairly good optical stabilization capability of this new material has been demonstrated at both laser wavelengths. The relative intensity fluctuation of the laser pulses can be remarkably reduced by simply passing through this multiphoton absorbing medium.