基于横向热流抑制的半导体激光芯片封装实验研究

为降低半导体激光芯片的慢轴远场发散角,提高其慢轴方向的光束质量,设计了横向热流抑制的封装结构。利用热沉间的物理隔离,削弱了半导体激光芯片慢轴方向上的温度梯度,有效降低了半导体激光芯片慢轴方向的发散角。采用热分析模拟了不同封装结构下芯片发光区的温度分布,并对波长915 nm的窄条宽半导体激光芯片进行封装。实验结果表明,在工作电流15 A,封装在隔离槽长4 mm,脊宽120 μm刻槽热沉上的芯片,其慢轴远场发散角由12.25°降低至10.49°,相应的光参量积（BPP）由5.344 mm·mrad 降低至4.5763 mm·mrad,慢轴方向亮度提升了约5.5%。实验结果表明,横向热流抑制的封装结构可以有效地削弱半导体激光芯片慢轴方向上由热透镜效应引起的高阶模激射,从而降低其慢轴远场发散角。     

大长宽比、变发散角光束二维变焦整形研究

为实现激光束形状的二维整形,同时灵活适应入射光束发散角、尺寸等参数的变化,提高光束质量,提出了一种适用于大长宽比、变发散角的激光束二维变焦整形方法。该方法利用光线变换矩阵方法分析光路,采用柱透镜、球透镜对光束进行二维变焦整形,通过镜片位置和间距的动态调节,实现对光束在x,y两个维度上的尺寸、发散角共四个参数各自独立的调整,实时校正激光束的低阶像差,使出射光束始终保持为预定状态。试验研究表明,该方法具有光路结构简单、综合像差小、调节范围大等优点,能够显著改善高功率激光器的光束质量,尤其适用于具有大长宽比增益区的板条激光器和化学激光器的输出光束整形。     

980 nm半导体激光器n型波导结构优化

为了提高980 nm半导体激光器的输出功率并获得较小的远场发散角,在非对称波导结构的基础上设计了n型波导结构,即在n型波导中引入高折射率的内波导层。采用理论计算和SimLastip软件模拟对常规非对称波导结构和内波导结构进行了研究。利用分子束外延系统生长980 nm内波导结构的外延材料, 并制作了激光器。对于条宽为100 m、腔长为1000 m的器件,阈值电流为97 mA,斜率效率为1.01 W/A;当注入电流为500 mA时,远场发散角为29(垂直向) 8(水平向),与模拟结果相符。理论计算和实验结果表明：较之于常规非对称波导结构,内波导结构可有效降低光场限制因子,提高输出功率,减小远场发散角。     

A modified EM algorithm for mixture models based on Bregman divergence

The EM algorithm is a sophisticated method for estimating statistical models with hidden variables based on the Kullback–Leibler divergence. A natural extension of the Kullback–Leibler divergence is given by a class of Bregman divergences, which in general enjoy robustness to contamination data in statistical inference. In this paper, a modification of the EM algorithm based on the Bregman divergence is proposed for estimating finite mixture models. The proposed algorithm is geometrically interpreted as a sequence of projections induced from the Bregman divergence. Since a rigorous algorithm includes a nonlinear optimization procedure, two simplification methods for reducing computational difficulty are also discussed from a geometrical viewpoint. Numerical experiments on a toy problem are carried out to confirm appropriateness of the simplifications.     

圈图函数中的红外发散

介绍一种判断和计算圈图函数红外发散的有效方法.利用该方法研究了C函数(即三点圈图函数)和D函数(即四点圈图函数)的红外发散性质,并且给出常见的C函数的红外发散形式.     

A novel distribution classifier

We present a novel classifier for a collection of nonnegative L¹ functions. Given two sets of data, one set coming from “similar” distributions labeled as normal, and the other unspecified labeled as abnormal. To understand the structure of normality, and further to classify new data with minimal errors, we propose to find the smallest CKL spheres (based on Csiszar divergences) including as many normal data as possible and excluding as many abnormal data as possible. We prove the existence and uniqueness of such a classifier.     

回流式水冷超薄多层镜的研究

从理论和实验上讨论了水冷铜镜变形的规律, 从而设计出多种多层镜, 其中回流式多层镜在0.13MPa通水压力下净吸收86.9W激光功率时, 总变形仅 0.10μm,约为同等条件下普通水冷铜镜变形量的1/40。     

“多靶串接”饱和增益软X光激光实验研究

采用“多靶串接”设计,利用强度为0.8×10~(13)～1.0×10~(13)W/cm~2,波长为1.05μm,脉宽约1ns的两路钕玻璃激光线聚焦辐照四块串接的平面厚锗靶,观察到波长为23.2和23.6nm的接近饱和的类Ne锗软X光激光输出。当总靶长为5.6cm时,这两种波长的软X光激光输出的GL值都达到16左右,沿靶法线和靶平面方向的发散角都只有3～4mrad。     

An information-theoretic framework for robustness

This is a paper about the foundation of robust inference. As a specific example, we consider semiparametric location models that involve a shape parameter. We argue that robust methods result via the selection of a representative shape from a set of allowable shapes. To perform this selection, we need a measure of disparity between the true shape and the shape to be used in the inference. Given such a disparity, we propose to solve a certain minimax problem. The paper discusses in detail the use of the Kullback-Leibler divergence for the selection of shapes. The resulting estimators are shown to have redescending influence functions when the set of allowable shapes contains heavy-tailed members. The paper closes with a brief discussion of the next logical step, namely the representation of a set of shapes by a pair of selected shapes.     

Beam divergence effects on high power optical parametric oscillation

The beam divergence effects of the input pump laser on a high power nanosecond optical parametric oscillator （OPO） have been numerically simulated. The OPO conversion efficiency is affected due to the angular deviation of real laser beams from ideal phase matching conditions. Our theoretical model is based on the decomposition of the Gaussian beam and assumes each component has a single deviation angle and thus a particular wave vector mismatch. We take into account the variable intensity profile in the spatial and temporal domains of the Gaussian beam, the pump depletion effects for large-signal processes as well as the oscillatory effects of the three waves. Two nonlinear crystals β-BaB2O4 （BBO） and LiB305 （LBO） have been investigated in detail. The results indicate that the degree of beam divergence strongly influences the maximum pump intensity, optimum crystal length and OPO conversion efficiency. The impact of beam divergence is much more severe in the case of critical phase-matching for BBO than in the case of non-critical phase-matching for LBO. The results provide a way to choose the optimum parameters for a high power ns OPO such as the nonlinear material, the crystal length and the pump intensity, etc. Good agreement is obtained with our experimental results.