铋纳米薄膜相干光学声子研究

利用共轴双色飞秒激光泵浦-探测技术测量了铋(Bi)纳米薄膜的相干光学声子。采用自相关技术测量得到探测光的脉宽约为45 fs,用探测光和泵浦光的互相关信号得到泵浦光经过脉冲整形以后的脉宽约为250 fs,进而测量得到Bi纳米薄膜的对称振动模频率为2.86 THz,与自发Raman光谱的结果吻合。采用指数衰减函数与互相关信号的卷积拟合延迟时间在10 ps以内的差分反射信号,确定了相干光学声子振幅衰减的特征时间约为2.6 ps,与电子衰减特征时间相近,却远小于晶格加热的特征时间,从而为进一步揭示材料内部载流子与声子的相互作用提供了依据。     

被动锁模Yb3+光纤环形腔激光器的研究

 采用974 nm半导体激光器作为泵浦源，超高掺杂Yb³⁺光纤作为增益介质，利用光纤的非线性偏振旋转效应，得到稳定的ps量级锁模光脉冲。泵浦功率220 mW时，激光器锁模阈值功率150 mW，输出功率26 mW，锁模光脉冲中心波长1 046 nm，3 dB带宽6.01 nm，20 dB带宽16 nm，脉宽22 ps，重复频率20 MHz。与同类光纤激光器相比，该激光器输出功率高，具有更好的稳定性。     

半导体光放大器中光波传输特性研究

根据半导体光放大器(SOA)载流子速率方程和光波在SOA内的传输方程,采用分段的方法计算出光波功率和相位与载流子浓度的关系公式。在泵浦光输入功率分别为5mW和15mW情况下通过仿真得到泵浦光输出波形和归一化转换光波形,其中归一化转换光的波形变化可间接体现不同泵浦光输入功率对SOA内载流子浓度的影响。分析了泵浦光波长和SOA注入电流对探测光的归一化输出、相位和频率啁啾产生的影响。结果表明,随着泵浦光波长的增加,探测光的三种光波特性曲线逐渐趋于平缓。注入电流将会直接影响到SOA的载流子浓度,以此对探测光的输出产生影响,注入电流越大,探测光的频率漂移越远。     

抽运-探测反射技术研究本征CdTe的载流子动力学

采用抽运-探测反射技术,研究了室温下本征CdTe晶体的光致非平衡载流子布局与光子能量和抽运光强的关系.根据实验结果,发现随着抽运光光子能量的提高,快过程在载流子弛豫过程中所占的比例增大;随着抽运光功率的提高,反射率随之增大,快过程时间常数也随之增大.通过建立简单的本征半导体受激载流子弛豫过程模型,讨论了载流子散射、载流子-声子相互作用和载流子复合等的贡献.在抽运光光子能量为1.49 eV(比CdTe的禁带宽度约高20 meV)时,通过双指数函数拟合,得到了本征CdTe中载流子弛豫过程的快、慢时间常数,分别为2.8 ps和158.3 ps.     

基于XGM的SOA波长变换器噪音特性分析及优化设计

利用动态载流子恢复时间可以精确模拟基于交叉增益调制的SOA全光波长变换器的饱和增益效应,本文将SOA分段ASE噪音功率和分段动态模型结合,得到沿长度分布的ASE噪音功率,并讨论了偏置电流、泵浦光和探测光的波长、功率、SOA长度对消光比和信噪比的影响理论计算结果表明,大的偏置电流有利于提高消光比和信噪比;对于一定的输入波长,相对较大的泵浦光和相对较小的探测光变换效果好;SOA的长度存在最佳值.     

基于MoO_3可饱和吸收体的掺镱被动锁模光纤激光器

报道了一种基于MoO_3可饱和吸收体的连续锁模、调Q锁模掺镱光纤激光器.采用环形腔结构,在泵浦功率为95mW时,获得了稳定的重复频率为17MHz的连续锁模脉冲输出,单脉冲宽度为130ps,光谱中心波长为1 067.06nm,谱线3dB带宽为0.27nm.在泵浦功率为280mW时,产生稳定的调Q锁模脉冲输出.当泵浦功率从280mW变化到400mW的过程中,调Q锁模包络重复频率从26.51kHz变化到48.7kHz,包络半高宽度从14.6μs变化到4.1μs,子脉冲的宽度和光谱中心波长基本保持不变,谱线3dB带宽变为0.62nm.     

GaAs在光通讯波段的超快非线性光学研究

采用Z-扫描和泵浦-探测技术,在光通讯波段对砷化镓(GaAs)单晶进行了非线性动力学以及非线性光学的实验研究.飞秒泵浦-探测实验结果表明,三阶非线性光学效应源于砷化镓单晶对飞秒激光的瞬态双光子吸收,而五阶非线性光学效应源于砷化镓单晶双光子吸收诱导的自由载流子吸收效应.通过Z扫描实验,得到了关于GaAs单晶所有的非线性光学参数,包括双光子吸收系数、三阶非线性折射系数、双光子吸收诱导的自由载流子吸收截面以及双光子吸收诱导的自由载流子折射截面.结果表明,砷化镓单晶在制造光限幅器件和光电探测器方面具有良好的发展前景.     

CdSe/CdS/ZnS 量子点体系中的超快载流子动力学

利用飞秒泵浦探测技术对CdSe/CdS/ZnS量子点体系中的超快载流子动力学过程进行了研究. 通过选择不同波长的泵浦光分别激发样品壳层和核层,研究了载流子在壳层和核层中的超快动力学过程. 实验结果表明,载流子在CdS壳层导带中弛豫过程非常迅速(约130 fs),时间明显短于载流子在CdSe核层导带中的弛豫时间(约400 fs). 实验中也发现在CdS壳层和CdSe核层的分界面存在一定量的缺陷态.     

制备工艺对掺杂NaYF4:Er3+,Yb3+发光纳米晶的聚合物光波导放大器性能的影响

制备了NaYF₄：Er³⁺,Yb³⁺纳米晶,表征了纳米晶的形貌,通过物理掺杂的方式将纳米粒子掺杂到SU-8中作为光波导放大器的芯层材料,优化了波导放大器的尺寸,利用旋涂、刻蚀等工艺,在二氧化硅衬底上制备了光波导放大器。实验中用光漂白法和湿法刻蚀两种方法制备光波导放大器,分别给出了两种方法制备的器件的结构、工艺流程、光场模拟结果,并对两种方法制备的器件的放大特性进行了测试。测试结果表明,当980 nm波长的泵浦光功率为241 mW且1 550 nm波长的信号光功率为0.1 mW时,使用湿法刻蚀法制备的放大器得到2.7 dB的相对增益。当980 nm波长的泵浦光功率为235 mW且1 550 nm波长的信号光功率为0.1 mW时,使用光漂白法制备的放大器得到4.5 dB的相对增益。根据以上测试结果,分析了两种工艺对器件性能的影响。     

基于啁啾光纤布拉格光栅的掺镱保偏锁模光纤激光研究

利用啁啾光纤布拉格光栅作为光谱滤波器和色散控制元件来控制掺镱保偏锁模光纤激光的光谱形状和腔内色散.实验装置采用线性腔设计,利用半导体饱和吸收镜作为锁模器件,实现掺镱保偏光纤激光器的被动锁模激光输出.当泵浦功率为52 mW时,获得了脉冲宽度为4.26ps,重复频率为15.7 MHz,平均功率为9.8mW的稳定锁模脉冲激光输出.输出激光中心波长为1 030nm,3dB谱宽为7.2nm,对应理想傅里叶变换极限脉宽约为150fs.     

Observation of coherent phonon states in porous silicon films

The dynamics of differential transmission and reflectance spectra of porous silicon films was studied using the femtosecond excitation technique (τ≈50 fs, ?ω_pump=2.34 eV) with supercontinuum probing (?ω_probe=1.6–3.2 eV) and controlled time delay with a step of Δt=7 fs between the pump and probe pulses. A short-lived region of photoinduced bleaching was observed in the differential transmission spectra at wavelengths shorter than the pump wavelength. The excitation of coherent phonon states with a spectrum corresponding to nanocrystalline silicon with an admixture of a disordered phase was observed. The relaxation of electronic excitation was found to slow down in the spectral region where the amplitude of excited coherent vibrations was maximal.     

LP—MOCVD研制InGaAs/InP应变量子阱LD

本文指出在LP-MOCVD生长过程中,采用量子阱有源区和上限制层不同的生长温度以及生长非掺杂过渡层等技术能有效地控制InGaAs/InP量子阱激光器的p-n结结位,给出了采用DEZn和H₂S做掺杂源在InP材料中p型和n型杂质溶度和p-n结控制的条件,并研制出有源区阱层InGaAs与InP存在0.5%压缩应变量子阱激光器,这一结构LD实现室温脉冲激射,得到峰值功率为106mW以上,阈值电流密度为2.6kA/cm².     

基于类噪声脉冲抽运的平坦超连续谱光源

设计了一种由类噪声脉冲抽运的全光纤结构平坦超连续谱光源。在色散管理掺铒光纤激光器中通过调节腔内偏振态,在泵浦功率为450 mW时,实现了稳定的类噪声脉冲锁模,锁模脉冲的中心波长为1 600 nm,脉冲宽度为303 fs。在最大泵浦功率为1 W时,谐振腔直接输出功率为8.6 mW。较低的功率无法有效拓展超连续谱宽度,为此设计一种掺铒光纤放大器进行功率放大,放大器最大输出功率为338 mW,将功率放大后的类噪声脉冲耦合进高非线性光纤以产生超连续谱,超连续谱的20 dB光谱范围为1 530 nm～2 300 nm,在1 736 nm～2 134 nm范围内,光谱的平坦度优于0.5 dB。     

Picosecond ultrasonics time resolved spectroscopy using a photonic crystal fiber

We present a broadband picosecond ultrasonics time resolved spectroscopy. Detection of picosecond coherent acoustic phonons using a wavelength continuum generation in a photonic crystal fiber (PCF) with femtosecond laser pulses is developed. Measurements are performed for selected wavelengths of a broad wavelength probe pulse within a bandwidth of 250 nm with an 825 nm center wavelength on two samples made of tungsten and of gallium arsenide.     

Diode-pumped sub-100 fs Kerr-lens mode-locked Yb3+:Sc2O3 ceramic laser

Diode-pumped Kerr-lens mode-locked laser operations of Yb3+:Sc2O3 ceramics have been achieved. 92 fs pulses with the average power of 850 mW under 3.89 W incident pump power were obtained at a center wavelength of 1042 nm. The optical-to-optical efficiency was 21.9%. 90 fs pulses with the average power of 160 mW were also obtained at a center wavelength of 1092 nm. To our knowledge, this is the first demonstration of a Kerr-lens mode-locked Yb3+:Sc2O3 laser.     

Photo-induced absorption in the pump probe spectroscopy of single-walled carbon nanotubes

Femtosecond pump probe spectroscopy is employed to study the photo-induced absorption feature in the single-walled carbon nanotube transient spectrum. The two advantages of the experiment, a chirality enriched sample and tuning the pump wavelength to the resonance of a specific nanotube species, greatly facilitate the identification of the photo-induced absorption signal of one tube species. It is found that a photo-induced absorption feature is located at one radial breathing mode to the blue side of the E11 state. This finding prompts a new explanation for the origin of the photo-induced absorption: the transition from the ground state to a phonon coupled state near the E ii state. The explanation suggests a superposition mechanism of the photo-bleach and photo-induced absorption signals, which may serve as a key to the interpretation of the complex pump probe transient spectrum of carbon nanotubes. The finding sheds some light on the understanding of the complex non-radiative relaxation process and the electronic structure of single-walled carbon nanotubes.     

位于第三近红外窗口的平坦光纤超连续谱产生

报道了一种基于非线性偏振旋转效应的被动锁模光纤激光器。采用980 nm分布式反馈激光器作为泵浦源,0.5 m长的高掺杂掺铒光纤作为增益介质。实现了脉冲宽度为822 fs的传统孤子锁模脉冲,输出脉冲的平均功率为2.8 mW,信噪比为55.8 dB。通过微调腔内的偏振控制器,实现了传统孤子脉冲和孤子分子脉冲间的切换,孤子分子的脉冲宽度为312 fs,信噪比为53.86 dB。孤子分子脉冲经掺铒光纤放大器放大后泵浦一段57 m长的高非线性光纤,产生了位于第三近红外窗口（1600 nm～1870 nm）的超连续谱,其20 dB谱宽为355.8 nm。     

Terahertz tomography of a photo-induced carrier based on pump-probe spectroscopy using counterpropagation geometry

A novel technique for the terahertz (THz) tomography of a photo-induced carrier that is based on optical-pump THz-probe time-resolved reflection spectroscopy using counterpropagation geometry of the pump and probe pulses has been proposed. Transient reflection due to the photo-induced carrier provides information about the physical properties and spatial distribution separately. We have experimentally demonstrated this method using a silicon wafer. The obtained complex reflection can be reproduced by the exact solution of Maxwell's equations, assuming an exponential distribution of the photo-induced carrier density.     

Electrophysical characteristics of accidental-doping defects in epitaxial n-type gallium arsenide

The Hall effect and electrical conductivity in the temperature range 10–900?K were used to investigate the electrophysical parameters of accidental defects in epitaxial n-type gallium arsenide. The experimentally determined parameters of the shallow donor impurity found in n-type gallium arsenide are similar to those of silicon. The anomalous behavior of the Hall constant at T>500?K can be accounted for by the hypothesis of thermal conversion of oxygen-containing defects (complexes of intrinsic and extrinsic defects) from a neutral state to an electrically active state. The kinetic parameters of this process are evaluated. The deviation of the experimental behavior of the electron mobility at temperature above 500?K can be attributed largely to the nonuniformity of the electrophysical parameters over the thickness of the gallium arsenide films and to the presence of accidental oxygen-containing defects in the investigated material.     

Stable mode-locked fiber laser using 49 cm long bismuth oxide based erbium doped fiber and slow saturable absorber

A stable mode-locked fiber laser employing a 49 cm long bismuth oxide based erbium doped fiber (Bi-EDF) by using a slow saturable absorber is demonstrated. Near transform limited short pulses with a repetition rate of 8.27 MHz are obtained at a wavelength of 1560 nm with a maximum spectral width of 15 nm. Results indicate that pulse characteristics are strongly dependent on pump power rather than spectral width. Moreover the Time-Bandwidth products (TBWP), pulse duration, the energy fluctuation and timing jitter decrease with increasing pump power. The pulse width is continuously varied from 1.2 ps to less than 300 fs. It produces stable mode locking with a maximum spectral width of 15 nm, minimum timing jitter of 4 ps and energy fluctuations of 2.5%. The pulse train was amplified using a two-stage amplifier up to 447 mW average power corresponding to peak powers of 177.3 kW.