四波混频光谱术

本文介绍我们用四波混频研究光与物质相互作用方面取得的新进展．其中包括拉曼增强非简并四波混频，用时间延迟方法区分分子取向栅及热栅，多能级吸收带的非相干光时间延迟四波混频，激光感生螺旋结构及用时间分辨简并四波混频研究原子的碰撞线宽变窄效应．     

用非相干光激发布居光栅技术研究物质的纵向弛豫过程

详细分析了用非相干光时延四波混频研究物质纵向弛豫过程的原理和技术关键，从实验上测定了几种染料分子的纵向弛豫时间并作了讨论。     

非相干光时延四波混频的多能级理论——非均匀加宽情形

本文将我们建立的非相干光时延四波混频(TDFWM-IL)的多能级理论由均匀加宽情形发展到非均匀加宽情形,得到吸收带同时存在均匀和非均匀加宽时,TDFWM-IL多能级理论给出的信号强度随两束泵光相对延时的一般关系式,讨论非均匀加宽占绝对优势时,非相干光光子回波的多能级理论结果,及其与二能级理论结果的差异,论证等效二能级模型同样适用于近似分析存在非均匀加宽影响时,吸收带TDFWM-IL的实验结果,报道在红宝石零声子线和甲酚紫固体膜吸收边上的实验结果,并与上述理论做了比较。     

染料分子电子激发态振动失相过程的非相干光时延四波混频研究

本文对噁嗪(Oxagine)、甲酚紫(cresyl violet)染料分子的吸收带和吸收边进行了非相干光时延四波混频(TDFWM-IL)的详细研究,得到了有关失相参量的数据,并利用非相干光时延四渡混频的多能理论解释了实验结果和失相参量的物理意义。     

用非相干光激发布居光栅技术研究物质的纵向驰豫过程

详细分析了用非相干光时延四波混频研究物质纵向驰豫过程的原理和技术关键，从实验上测定了几种染料分子的纵向驰豫时间并作了讨论。     

半导体光放大器的非简并时延四波混合理论

用二能级宽带模型研究了半导体光放大器(SOA)中非简并相共轭四波混合信号强度随时间延迟的变化规律。结果表明,对这种情形的非简并四波混合共轭信号强度随时间延迟τ变化表明为载流子脉动,且脉动信号以退相速率衰减。鉴于目前用简并四波混合对半导体光放大器超快过程的测量需要大功率激光器作激发源、大光学实验平台和复杂的探测设备的情况下,提出了基于全光通信器件构成非简并四波混合观测半导体光放大器载流子脉动、退相时间新方法,这不仅便于选取抽运与探测光源波长(光通信窗口波长),而且可使测试设备微型化。     

瑞利增强非简并四波混频的时域不对称性研究

基于场关联原理,采用非相干光时延四波混频法研究了瑞利增强非简并四波混频的时域特性.利用二阶场关联函数理论揭示出混频信号在时域的细微变化,发现信号展示出时域不对称性并且在τ<0时会出现振荡结构,而这种时域不对称性反映了该三阶非线性极化过程的特点.     

非相干光时延四波混频中V型三能级原子的布居弛豫量子拍的理论研究

对简并非相干光时延四波混频中布居弛豫量子拍的物理机制及产生过程进行了理论研究,并根据真空与原子耦合观点,具体分析讨论了两种情形的三宽带光脉冲作用于V型三能级原子布居弛豫量子拍的形成过程和讯号特征.经比较发现,理论与实验结果相当吻合.     

用非相干光时间延迟四波混频测量甲酚紫皮秒布居弛豫时间

用相共轭配置的非相干光时间延迟四波混频技术测量了甲醇中甲酚紫的皮秒布居弛豫时间T_1大约为157ps.这个结果与用相干光锁模脉冲的泵浦—探测技术测得的结果符合得比较好.     

超低温下掺Er3+玻璃的相干拍频调制效应研究

采用非相干光时延四波混频(TDFWM-IL)实验装置,在7K温度下,利用波长为800 nm的飞秒脉冲激光,观测到掺Er3+玻璃的光子回波效应,发现信号随延时变化的拍频调制结构.根据TDFWM-IL多能级理论,运用其非均匀加宽占主导时的公式拟合实验结果,从最佳拟合获得的退相时间T2=300 fs,这与由相干控制实验测得的...     

激光多普勒测速仪中散射光特性的研究

后向散射光特性与多普勒信号的质量密切相关。为了设计高性能的激光多普勒测速仪,运用散斑理论详细分析了激光多普勒信号的强度与散射光斑大小的关系,结合泛函理论给出了计算多普勒电流的散斑表达式,并通过实验的方法研究了回波信号的偏振特性及其强度分布。理论分析与实验结果表明,激光多普勒信号的强度与接收器件光敏面的直径成正比,与光斑的直径成反比;选用光斑较小的圆偏振激光束,并用光敏面尺寸较小的探测器在镜面反射方向上接收信号光,可以大大提高多普勒信号的信噪比,增强系统的探测能力,为提高系统的测量精度创造有利的条件。     

Influence of laser linewidth on performance of Brillouin optical time domain reflectometry

The effects of optical sources with different laser linewidths on Brillouin optical time domain reflectometry (BOTDR) are investigated numerically and experimentally. Simulation results show that the spectral linewidth of spontaneous Brillouin scattering remains almost constant when the laser linewidth is less than 1 MHz at the same pulse width; otherwise, it increases sharply. A comparison between a fiber laser (FL) with 4-kHz linewidth at 3 dB and a distributed feedback (DFB) laser with 3-MHz linewidth is made experimentally. When a constant laser power is launched into the sensing fiber, the fitting linewidths of the beat signals (backscattered Brillouin light and local oscillator (LO)) is about 5 MHz wider for the DFB laser than for the FL and the intensity of the beat signal is about a half. Furthermore, the frequency fluctuation in the long sensing fiber is lower for the FL source, yielding about 2 MHz less than that of the DFB laser, indicating higher temperature/strain resolution. The experimental results are in good agreement with the numerical simulations.     

Numerical investigation on photonic microwave generation by a sole excited-state emitting quantum dot laser with optical injection and optical feedback

Based on three-level exciton model, the enhanced photonic microwave signal generation by using a sole excited-state(ES) emitting quantum dot(QD) laser under both optical injection and optical feedback is numerically studied. Within the range of period-one(P1) dynamics caused by the optical injection, the variations of microwave frequency and microwave intensity with the parameters of frequency detuning and injection strength are demonstrated. It is found that the microwave frequency can be continuously tuned by adjusting the injection parameters, and the microwave intensity can be enhanced by changing the injection strength. Moreover, considering that the generated microwave has a wide linewidth, an optical feedback loop is further employed to compress the linewidth, and the effect of feedback parameters on the linewidth is investigated. It is found that with the increase of feedback strength or delay time, the linewidth is evidently decreased due to the locking effect. However, for the relatively large feedback strength or delay time, the linewidth compression effect becomes worse due to the gradually destroyed P1 dynamics. Besides, through optimizing the feedback parameters, the linewidth can be reduced by up to more than one order of magnitude for different microwave frequencies.     

Photoacoustic-guided convergence of light through optically diffusive media

We demonstrate that laser beams can be converged toward a light-absorbing target through optically diffusive media by using photoacoustic-guided interferometric focusing. The convergence of light is achieved by shaping the wavefront of the incident light with a deformable mirror to maximize the photoacoustic signal, which is proportional to the scattered light intensity at the light absorber.     

Nano‐opto‐mechanical effects in plasmonic waveguides

In order to achieve interaction between light beams, a mediating material object is required. Nonlinear materials are commonly used for this purpose. Here a new approach to control light with light, based on a nano‐opto‐mechanical system integrated in a plasmonic waveguide is proposed. Optomechanics of a free‐floating resonant nanoparticle in a subwavelength plasmonic V‐groove waveguide is studied. It is shown that nanoparticle auto‐oscillations in the waveguide induced by a control light result in the periodic modulation of a transmitted plasmonic signal. The modulation depth of 10% per single nanoparticle of 25 nm diameter with the clock frequencies of tens of MHz and the record low energy‐per‐bit energies of 10⁻¹⁸ J is observed. The frequency of auto‐oscillations depends on the intensity of the continuous control light. The efficient modulation and deep‐subwavelength dimensions make this nano‐optomechanical system of significant interest for opto‐electronic and opto‐fluidic technologies.     

基于准周期光学超晶格的高效电光调制差频转换

为获得尽可能大的差频转换效率,基于准周期极化铌酸锂(QPPLN)光学超晶格,提出了级联电光和差频理论,用于高效的差频转换。其方法是沿QPPLN光学超晶格的y方向施加一个外加电场,用来控制能量在抽运光、信号光、o偏振的差频光和e偏振的差频光四个光波之间的转移。计算结果表明,在一个100℃,40mm长的QPPLN光学超晶格中,当1550nm信号光与1064nm抽运光光强比值r<0.324时,对光强超过特定值的任意抽运光都可以通过施加一个适当的外加电场将抽运光完全转化为1550nm信号光和3393.4nm差频光;当r≥0.324,只当抽运光光强落在一定范围内时,才可以通过施加外加电场使抽运光完全转化为信号光和差频光;超过该范围,外加电场不能增加差频光转换效率。计算结果还表明,电光调制差频转换效率对温度和畴构造误差都不敏感。     

Surface plasmon polariton-based optical beam profiler

We describe a surface plasmon polariton- (SPP-) based device for measuring the intensity distribution of strongly focused light beams. A gold thin film configured as a sharp step is positioned in the focal region of a light beam, converting light into SPPs. The SPPs emit directional leakage radiation into the glass substrate beneath the thin film. The intensity of the leakage radiation is proportional to the intensity of the incident local light at the position of the step, allowing us to reconstruct the optical field profile by scanning the thin film's edge through the focal region.     

基于平行偏振光注入的1550nm波段垂直腔表面发射激光器获取窄线宽光子微波的理论和实验研究

提出一种基于1550 nm垂直腔表面发射激光器(1550 nm-VCSEL)获取高质量微波信号的全光方案.在该方案中,采用波长位于VCSEL中被抑制模式的中心波长附近、振动方向与VCSEL中主导模式相同的偏振光注入(即平行注入)1550 nm-VCSEL获取高频微波,并借助双光反馈对该高频微波的线宽进行窄化.一方面,基于VCSEL的自旋反转模型,从理论上分析了采用该方案产生微波信号的可行性;另一方面,通过构建相应的实验系统,对该方案产生的微波的特性进行初步实验研究.实验结果表明:在合适的注入条件下,1550 nm-VCSEL能够产生30 GHz左右的微波信号,但该信号的线宽较宽(百兆水平);引入双光反馈后,微波线宽可被压窄两个数量级以上,得到了线宽低于1 MHz、信噪比大于40 d B的微波信号.