LiF晶体M带色心的超发光

在碱卤晶体中F_2色心的发光过程可用四能级系统来描述,且发射截面大,因而有可能成为激光激活中心。在国内外的文献中已报道了室温下LiF晶体F_2色心的可调谐激光作用,激光中心波长约为700nm。本文报道了室温下我们对LiFM带色心超发光的观察。我们用氮分子激光泵浦香豆素染料,输出为中心波长440nm的宽带激光,且与通常色心激光器的纵向泵浦方式不同,我们采用横向泵浦方式,即用一柱透镜将染料激光聚焦在着色LiF     

国外简讯

西伯利亚分院热物理所研制成调Q和锁模YAG:Nd激光器二次谐波泵浦流动染料激光器。调Q用放在谐振腔内成布儒斯特角的F_2~-色心线性吸收晶体实现。晶体的初始吸收为7％。激光输出脉宽为300毫微秒,重复频率25千赫。锁模用声光调制器。用90°切割LiNbO_3晶体倍频,在基波功率为3瓦时,获得输出平均功率300毫瓦。在泵浦平均功率140毫瓦时,染料激光器输出30毫瓦,波长590毫微米,在泵浦平均功率175毫瓦时,染料激光器输出36毫瓦。采用滤光片在560～630毫微米范围内获得可调谐振荡波长。     

调Q开关紫翠宝石激光治疗雀斑64例

目的观察调Q开关紫翠宝石激光治疗雀斑的临床疗效.方法选用调Q开关紫翠宝石755nm波长激光治疗雀斑64例.结果64例全部治愈,其中经1次治愈58例,经2次治愈6例,总有效率为100%,未发生瘢痕,随访3～24个月,无一例复发.结论调Q开关紫翠宝石激光是治疗雀斑的一种新的方法.激光治疗雀斑疗效高、操作简单、安全、无副作用,是目前理想的治疗方法.     

高功率、高效率调Q绿光抽运的钛宝石宽调谐纳秒脉冲激光

自行研制出钛宝石晶体抽运的波长为532 nm的全固态高功率激光器,实现了高功率、高转换效率的可调谐钛宝石激光输出。使用3列重复频率为1 kHz的激光二极管阵列对称式抽运Nd:YAG晶体,通过调Q及腔内倍频,获得功率为37.8 W、波长为532 nm的抽运光,每个激光二极管的抽运脉冲包络内包含5个调Q脉冲,单脉冲宽度为90 ns,重复频率为5 kHz。采用该绿光抽运钛宝石晶体,获得733.5～871.1 nm波长范围内的连续调谐激光,在771 nm处获得的输出功率最大,为8.26 W,光-光转换效率高达42%,脉冲宽度为14 ns,30 min内输出功率稳定性优于±4.4%。     

喇曼频移准分子激光泵浦掺钛宝石获得高效率可调谐输出

波长可调谐的掺钛宝石(Ti:Al_2O_3)激光是近年来发展起来的一种性能优良的固体可调谐激光器。掺钛宝石具有较宽的吸收带,吸收峰在500nm附近,以往采用的泵浦源为氩离子激光及倍频YAG激光,其波长对上述最强吸收峰都有一定偏离。     

LiF色心(F_2~ )频率可调谐脉冲激光输出

我系在纯LiF晶体中实现中心波长在0.69微米的F_2心宽带色心激光振荡,并在数百埃范围内进行了频率调谐后,又观察到该晶体在近红外波段的F_2~ 心宽带色心激光振荡。进一步研究表明,LiF色心(F_2~ )宽带色心激光振荡的带宽达10~3埃,约0.89～1.00微米,在谐振腔内引入色散元件后,实现了F_2~ 心频率调谐的激光输出。     

红外可调谐NaCl(OH~-)∶(F_2~+)_H色心激光

采用我们研制的优质Nacl(OH~-)∶(F_2~+)_H色心晶体作激光介质,在X型激光腔中,实现了中心波长为1.57μm,可调谐波段为1.40～1.75μm的低温红外连续可调谐色心激光运转。探讨了(F_2~+)_H心的几个吸收带,激光输出与工作介质和辅助光的关系等问题。     

新型激光泵浦源—可调谐紫翠宝石激光器

本文讨论了可调谐紫翠宝石激光器作为激光泵浦源的特点,并报导了泵浦Nd∶YAG,Nd∶LMA及NaF∶F~+_2激光晶体的实验结果。     

窄脉冲宽调谐调Q Cr:LiSAF激光器及其应用研究

研究了窄脉冲宽调谐调 QCr:Li SAF激光器的输出特性 ,在峰值波长 850 nm附近获得了单脉冲能量为 2 1 4 m J,脉宽为 2 0 ns的稳定调 Q输出 ,线宽小于 0 .2 nm。分析了 Cr:Li SAF激光器中影响调 Q的因素和晶体损伤问题 ,研究了基于 Cr:Li SAF的双波长可调谐激光器在差分吸收激光雷达中的应用     

单光束双脉冲、双波长巨脉冲Cr:LiSAF激光器

为实现单光束、双波长、双脉冲Cr:LiSAF调Q激光输出,实验中创造性地采用高压方波驱动电光Q开关实现了双波长、双脉冲的Cr:LiSAF可调谐激光输出。获得了波长分别为890nm与900nm,脉冲能量分别为31mj与38mj,脉冲宽度分别为30ns和27ns,脉冲间隔82μs的单光束、双波长、双脉冲Cr:LiSAF调Q激光输出,双脉冲的不同轴度不大于0.15mrad。为差分吸收激光雷达系统所需单光束、双波长、双脉冲激光器的进一步研制奠定了良好的理论与实验基础。     

碱卤色心晶体激光研究的新进展

本文提出了碱卤色心晶体激光综合研究的结果，比较详细地介绍了碱卤色心晶体生长研究、几种类型色心的特性，色心激光输出性能以及色心热光稳定性研究的新进展。     

色心激光材料——掺杂KCl单晶的研制

用引上法生长了掺锂KCl色心激光晶体,获得尺寸为φ25×100毫米的单晶,晶体中锂原子的含量可控制在10~(-3)～10~(-2)％(重量比)之间。测定了三种掺杂KCl单晶X-射线辐照后的吸收光谱。     

KCl:Na晶体中的激光工作色心F_B(Ⅱ)

采用附加着色法,在KCl:Na晶体中获得密度为10~(16)～10~(18)厘米~(-3)的F心。利用F带光进行转型,得到了FB(Ⅱ)激光工作色心,其77K荧光发射带在2.1～2.8微米,峰值位置为2.5微米。     

Edge-based color constancy.

Color constancy is the ability to measure colors of objects independent of the color of the light source. A well-known color constancy method is based on the gray-world assumption which assumes that the average reflectance of surfaces in the world is achromatic. In this paper, we propose a new hypothesis for color constancy namely the gray-edge hypothesis, which assumes that the average edge difference in a scene is achromatic. Based on this hypothesis, we propose an algorithm for color constancy. Contrary to existing color constancy algorithms, which are computed from the zero-order structure of images, our method is based on the derivative structure of images. Furthermore, we propose a framework which unifies a variety of known (gray-world, max-RGB, Minkowski norm) and the newly proposed gray-edge and higher order gray-edge algorithms. The quality of the various instantiations of the framework is tested and compared to the state-of-the-art color constancy methods on two large data sets of images recording objects under a large number of different light sources. The experiments show that the proposed color constancy algorithms obtain comparable results as the state-of-the-art color constancy methods with the merit of being computationally more efficient.     

Example-based color transformation of image and video using basic color categories.

Color transformation is the most effective method to improve the mood of an image, because color has a large influence in forming the mood. However, conventional color transformation tools have a tradeoff between the quality of the resultant image and the amount of manual operation. To achieve a more detailed and natural result with less labor, we previously suggested a method that performs an example-based color stylization of images using perceptual color categories. In this paper, we extend this method to make the algorithm more robust and to stylize the colors of video frame sequences. We present a variety of results, arguing that these images and videos convey a different, but coherent mood.     

Reversible integer color transform.

In this correspondence, we introduce a systematic algorithm that can convert any 3 x 3 color transform into a reversible integer-to-integer transform. We also discuss the ways to improve accuracy and reduce implementation complexity. We derive the integer RGB-to-KLA, IV1 V2, YCbCr, DCT, YUV, and YIQ transforms that are optimal in accuracy.     

Hypercomplex Fourier transforms of color images.

Fourier transforms are a fundamental tool in signal and image processing, yet, until recently, there was no definition of a Fourier transform applicable to color images in a holistic manner. In this paper, hypercomplex numbers, specifically quaternions, are used to define a Fourier transform applicable to color images. The properties of the transform are developed, and it is shown that the transform may be computed using two standard complex fast Fourier transforms. The resulting spectrum is explained in terms of familiar phase and modulus concepts, and a new concept of hypercomplex axis. A method for visualizing the spectrum using color graphics is also presented. Finally, a convolution operational formula in the spectral domain is discussed.     

Lossless compression of color mosaic images.

Lossless compression of color mosaic images poses a unique and interesting problem of spectral decorrelation of spatially interleaved R, G, B samples. We investigate reversible lossless spectral-spatial transforms that can remove statistical redundancies in both spectral and spatial domains and discover that a particular wavelet decomposition scheme, called Mallat wavelet packet transform, is ideally suited to the task of decorrelating color mosaic data. We also propose a low-complexity adaptive context-based Golomb-Rice coding technique to compress the coefficients of Mallat wavelet packet transform. The lossless compression performance of the proposed method on color mosaic images is apparently the best so far among the existing lossless image codecs.     

四方相KTN晶体的拉曼光谱

本文报道四方相KTN晶体的拉曼振动谱,并比较不同掺杂和在不同温度下的振动谱图,讨论了其中的差异及其产生的原因。     

Color demosaicing using variance of color differences.

This paper presents an adaptive demosaicing algorithm. Missing green samples are first estimated based on the variances of the color differences along different edge directions. The missing red and blue components are then estimated based on the interpolated green plane. This algorithm can effectively preserve the details in texture regions and, at the same time, it can significantly reduce the color artifacts. As compared with the latest demosaicing algorithms, the proposed algorithm produces the best average demosaicing performance both objectively and subjectively.