Intense laser field effects on the linear and nonlinear intersubband optical properties of a semi-parabolic quantum well

By using the compact-density matrix approach, the effect of a nonresonant intense laser field on the linear and nonlinear optical absorptions based on intersubband transitions and the refractive index changes in an asymmetric semiconductor quantum well have been presented. Our results show that the peak position of the absorption coefficient is sensitive to intense laser field, the absorption maximum shifts towards lower energies for increasing intense laser field value. Also we observe as the intense laser field strength increases, the total refractive index change has been increased in magnitude and also shifted towards lower energies. The results indicate that linear and nonlinear optical properties of the low dimensional semiconductor heterostructures can be adjusted in a desired energy range by using intense laser field.     

Phonon-assisted stimulated emission in 2H type PbI2

The stimulated emission in 2H type PbI₂ crystals has been observed under N₂ laser beam excitation at 4.2 K. The analysis of its gain spectrum shows that the emission is induced by the recombination of free exciton assisted by the emission of one longitudinal optical phonon. At a higher level of excitation, the gain spectrum peak shifts to lower energy side. Possible mechanisms of this spectral change are discussed.     

Lasing and high intensity photoluminescence in InGaAs---GaAs strained layer superlattices

A pulsed nitrogen laser was used to excite lasing and photoluminescence (PL) in InGaAs---GaAs strained-layer superlattices (SLS). At moderate excitation intensities the PL spectrum consisted of a single narrow peak. But at higher intensities a second peak, up to 16 meV lower in energy, was also seen due to optical gain induced in the waveguiding SLS structure. In a laser geometry gain could also be seen at an intermediate wavelength, about 4 meV below the spontaneous emission line center.     

使用硅橡胶涂敷的全光纤Mach-Zehnder干涉仪的压力传感研究

用硅橡胶对Mach-Zehnder干涉仪的传感臂进行涂敷,可以增加干涉仪压力传感的灵敏度.实验中分别使用宽带和窄带光源,借助光谱仪和光功率计观测干涉谱波长改变和光谱峰值功率变化,对微小压力进行了测量.当压力改变为1.03×10－4 MPa时,波长改变约0.02 nm,系统传感灵敏度为1.96×10－4 nm/Pa,是涂敷前的2.15倍.     

双光子吸收光谱

本文报道以皮秒脉冲激光抽运的光参量放大器为宽带可调谐激发光源，直接测量非线性光学材料的双光子吸收谱的方法。光参量放大器不但可调谐谱带很宽，而且可用一对尼科尔棱镜很容易地实现全波段功率足够强和相等，使此方法的测量结果准确可靠。用此方法研究了一个新有机化合物的双光子吸收谱。实验结果表明所测的新有机化合物在很宽的波长范围内呈现出很大的双光子吸收截面。     

Gain recovery in semiconductor optical amplifiers

Pump-probe measurements are presented of gain compression and recovery in a series of four semiconductor optical amplifiers of different lengths but otherwise identical structures. A continuous wave probe beam from a tunable laser is used to measure the wavelength dependence of gain compression and recovery times. A good level of agreement is obtained when these results are compared with numerical simulations using a model that includes the material gain spectrum, saturation effects and the variation of optical intensities with longitudinal position in the device. In addition the experimental results are interpreted in terms of a recent theory that offers approximate analytic expressions connecting recovery time with transmission gain. The spectral dependence of the recovery time and the gain are used to verify the correlations between these quantities and their dependence on device length. The results for recovery time show a strong dependence on probe wavelength with a pronounced minimum which is coincident with the peak of the gain spectrum for each device. A rather weak correlation of speed with length is found.     

In掺杂ZnO超晶格光学性质的研究

采用基于第一性原理的线性缀加平面波方法, 计算了超晶格ZnO掺In的光学性质. 计算结果表明, 掺入In元素后Fermi能级进入导带, 介电函数、吸收系数、折射率、反射率都在Fermi面附近产生新的跃迁峰. 随着掺杂层数的增多, 跃迁峰发生红移, 当掺杂两层In时跃迁峰峰值最大, 同时吸收系数的吸收边随掺杂层数的增多而逐渐减小. 与In掺杂ZnO超晶胞相比, ZnO超晶格在可见光范围内具有高透过率的特点.     

15波长输出的布里渊掺铒光纤激光器

多波长布里渊掺铒光纤激光器是一种新型的多波长光纤激光器,其原理是利用受激布里渊增益和掺铒光纤的线性增益,可以在常温下得到波长间隔约为0．08nm(～10GHz)的多波长输出。报道的布里渊掺铒光纤激光器,在布里渊抽运功率为1．7mW、980nm抽运功率为300mW的情况下得到稳定的15个波长(间隔～10GHz)的输出,这种激光器用作光传感器、光谱分析仪以及密集波分复用系统的光源。实验发现,输出波长的个数随着980nm抽运功率的增大而增加。另外,布里渊掺铒光纤激光器的信号功率主要来自于掺铒光纤的增益,而布里渊增益对它的影响不大。     

1410 nm波段分布式光纤拉曼增益放大器的研究

讨论了分布式光纤拉曼增益放大器的工作原理,采用1320nm固体激光器作为抽运源,获得了1410nm波段附近的光放大,在单模GI光纤长度为23km时,初步研究了拉曼放大器增益与光纤作用长度的关系,抽运脉冲峰值功率分别为50W、30W时,光纤的有效作用长度分别为15．5km和10.5km;研究了在不同的光纤有效作用长度时,拉曼放大器增益与抽运功率的关系;从光纤拉曼光谱图估算了光纤拉曼放大器的光谱宽度为50nm或250cm^-1。     

激光波长对拉曼散射水温遥感系统测温精度及探测深度的影响

机载激光拉曼散射雷达技术可以快速获取次表层海水温度的三维分布,具有重要的实用价值和经济价值.首先,从理论上分析了水的伸缩振动拉曼谱峰值位置和半高全宽与激发波长之间的对应关系,发现随着激发波长的增大,拉曼峰逐渐向长波方向移动,且拉曼光谱半高全宽显著增大.然后,实验测量了不同温度下450 nm激光和532 nm激光激发的水的拉曼光谱,对比验证了上述理论分析结果.并采用单高斯峰拟合法分析了两组拉曼光谱,拟合出高斯峰峰值位置与温度之间的关系,分析了激发波长对温度测量精度的影响.研究发现,采用较长波长的激发光可以提高拉曼光谱的测量精度,从而改善测温精度.最后,建立了拉曼散射雷达方程,分析了拉曼散射系数与激光波长之间的关系,研究了激光波长对雷达系统探测深度的影响.结果表明,激光波长对雷达系统探测深度有很大的影响,采用480 nm以下波长的激光时雷达系统探测深度较大,而采用长波段激光时雷达系统探测深度会大幅降低.实际系统设计中选取激光光源时需要综合考虑上述两方面的影响.     

正弦锥光纤光栅的数值计算分析

本文利用耦合模方程对正弦锥光纤光栅的反射谱进行了较为详细的计算和分析,发现,这种光纤光栅的反射谱与普通均匀周期光栅的反射谱有着很大的不同,通过控制光栅锥的形状,可得到类似于梳状滤波器的功能,对这种新型光栅在光纤激光器等方面的应用有指导意义。     

Widely tunable Raman ring laser using highly nonlinear fiber

An all-optical widely tunable Raman fiber laser has been realized by incorporating a highly nonlinear fiber in a ring cavity. By feedback a portion of Raman Stokes wave back into the highly nonlinear gain medium, a Raman fiber laser is generated. We found that the lasing wavelength of Raman fiber laser can be tuned from 1537 to 1568 nm with peak power fluctuation within 1 dB, giving a total wavelength tunability of 31 nm. The optical signal-to-noise ratio is found to be wavelength dependent, and the highest optical signal-to-noise ratio of about 59 dB is recorded. The lasing threshold of the Raman fiber laser with this configuration is found to be as low as 300 mW.     

毫米级高分辨率的混沌激光分布式光纤测温技术

近年来,随着分布式光纤传感技术在各大基础设施健康监测领域的广泛应用,人们对能够实现毫米量级精准定位和监测技术的需求日益增长.本文提出了一种基于宽线宽混沌激光的高分辨率分布式光纤测温技术.实验通过改变光反馈混沌源的偏振匹配态和反馈强度等外部参数,产生了–3 dB线宽约为7.5 GHz的宽线宽混沌激光,并在300 m传感光纤实现了空间分辨率为7.05 mm的分布式温度测量.同时,为了抑制光源线宽增加造成的布里渊增益谱恶化,在泵浦路中引入了时间门控技术,其中经脉冲调制后的泵浦光峰值功率提高了约9.5 dB,同时脉冲调制使混沌互相关锁定于脉冲持续时间内,从而布里渊增益谱的信号背景噪声比由约2.28 dB提升为4.55 dB,最终实现了空间分辨率为3.12 mm的分布式温度测量.     

二极管泵浦准三能级板条固体激光器的优化设计

基于最大激光增益条件，分析和优化了二极管泵浦准三能级Yb∶YAG固体板条激光器的激光增益、板条的最佳光学长度和最佳宽度参数。结果表明：在低功率侧面泵浦条件下，板条增益介质的掺杂浓度和板条宽度满足一定的关系，这为研究该类激光器提供了一条有效途径，其结果可应用于其他准三能级固体激光器设计。     

Cross-relaxation and spectral broadening of gain for Nd/Cr:YAG ceramic lasers with white-light pump source under high-temperature operation

Spectral broadening of the fluorescence of a Nd/Cr:YAG ceramic at the 1064 nm lasing wavelength was observed, and the amplification properties at a high temperature were investigated by considering cross-relaxation. These ceramics are promising for use as a solid-laser material pumped with solar or lamp light. It has been found that whenever the temperature of a laser medium is high and a spectral shift occurs, a high small-signal gain remains owing to the broad spectral band and the cross-relaxation. This optical property is remarkably different from that of a Nd:YAG laser. For a conventional Nd:YAG laser, the bandwidth at 1064 nm is 0.45 nm, and a reduction in small-signal gain occurs at a temperature of 373 K because the spectral peak shift is 0.005 nm/K. However, for the Nd/Cr:YAG ceramic, the bandwidths are 1.2 and 1.9 nm in the case of 0.1% Cr ion doping and 3% Cr ion doping, respectively, owing to the existence of excited Cr ions and the shortening of the effective Nd ion coherence time. It is prospected that the laser medium can be used at a high temperature of 600 K.     

一种新型的Tapered光纤光栅

利用耦合模方程对正弦型Ｔａｐｅｒｅｄ光纤光栅的反射谱进行了较为详细的计算和分析,并从实验上进行了验证。利用叠加均匀周期光纤光栅的模板和周期性振幅光栏一次成栅的方法,获得了具有三个反射峰、中心波长间隔为０．８ｎｍ的Ｔａｐｅｒｅｄ光纤光栅,这种光栅具有类似于梳状滤波器的功能,在多波长光纤激光器等方面有重要应用。     

Experimental observation of lasering behavior in wavelength-switchable fiber laser with arrayed waveguide grating

A simple and wavelength-switchable fiber laser consisting mainly of an Erbium-doped fiber amplifier (EDFA) which provides the optical gain and an 1 × 40 (1 input channel to 40 output channels) arrayed waveguide grating (AWG) that supports wavelength selection is reported. The lasering behavior in wavelength-switchable fiber laser is investigated experimentally. One can obtain wavelength-switchable single-longitudinal-mode (SLM) single wavelength laser with different wavelength by changing different channel of the AWG as the wavelength selection element. Lasering wavelength hopping in dual wavelength laser operation for low pump power is experimentally observed. The wavelength hopping and the output power of the laser is controlled by using a variable optical attenuator (VOA). The wavelength hopping operation is eliminated for high pump power. One can obtain switchable dual wavelength laser with different wavelength by selecting different two channels of the AWG. The output laser exhibits a good performance having a high sidemode suppression ratio (SMSR), narrow line-width and symmetrical spectrum.     

Ag-S共掺杂AlN电子结构和光学性质的第一性原理研究

用第一性原理平面波赝势方法对纯AlN和Ag-S共掺杂AlN的结合能、电子结构和光学性质进行计算分析.结果表明：施主杂质S原子的引入可以有效增加受主杂质Ag原子在AlN中的掺杂浓度,降低受主能级,对受主Ag原子起到了激活的作用,Ag-S共掺杂有助于实现高效的p型AlN.体系掺杂后的介电函数虚部和光吸收谱分别在低能区出现新的峰,其吸收边向低能方向偏移,增强了体系对低频电磁波的吸收.     

铜掺杂氧化锌纳米棒的非线性光学响应竞争特性

利用飞秒脉冲激光激发Cu掺杂ZnO纳米棒,研究其特有的非线性光学性质和激发机制。在激发波长为750 nm的荧光光谱中,二次谐波峰非常弱,几乎可以忽略,存在非常强的激子发光峰和Cu掺杂导致缺陷发光峰。激发强度的增大会导致这两个发光峰强度呈非线性增大,激子发光峰位产生明显红移,而缺陷发光峰位没有变化。进一步增大激发强度,缺陷发光峰强度会出现饱和甚至有所下降,而激子发光峰强度持续增大。当激发波长增加到760 nm时,从样品的荧光光谱可以清楚地识别到二次谐波峰和激子发光峰以及缺陷发光峰并存。随着激发波长的进一步增加,二次谐波强度不断增大,而激子发光峰和缺陷发光峰的强度却随之下降。当激发波长为790 nm和800 nm时,未发现激子发光峰和缺陷发光峰,非线性光谱以二次谐波为主导。研究结果表明,通过选择合适的激发波长和激发强度,可以实现发光颜色的转变,使得Cu掺杂ZnO纳米棒在全光显示方面具有潜在的发展前景。     

中红外可调谐大能量飞秒脉冲激光产生

可调谐中红外飞秒光纤激光器具有非常普遍的应用,从而引起了人们的广泛关注。目前,非线性光纤中的拉曼孤子自频移效应是实现大范围可调谐飞秒脉冲激光的理想方法之一。然而,非线性光纤中其他高阶非线性效应的产生通常会限制拉曼孤子脉冲的能量提升。本文提出了利用有源掺杂光纤作为非线性介质和增益介质实现可调谐大能量中红外飞秒激光脉冲的方法。在理论上研究了有源掺杂非线性光纤中高阶孤子劈裂和孤子自频移效应的产生,以及线性增益对波长移动拉曼孤子能量、脉宽、光谱的影响。结果表明,通过为波长红移的低能量拉曼孤子提供线性增益,孤子脉冲的能量得到了显著提升且保持了其单脉冲特性,脉冲宽度为45 fs,且孤子脉冲的波长可通过所提供的增益进行大范围调谐。因此,利用有源掺杂光纤作为非线性介质是实现大能量可调谐中红外飞秒脉冲激光的一种有效方法。