Monday, December 25, 2006

computing the extraction efficiency of slab

弄了好久,一直没有好的结果,sigh.

> In the post "How to calculate the extraction efficiency of spontaneous
> emission from slabs using C++ interface?" by Jun She, he constructed a
> geometry without slab and defined the flux through the top surface as total
> emitted flux, and then put a slab in the geometry and re-compute the flux
> through the top surface, and the extraction efficiency is the ratio of the
> later flux to the former flux. The computation looks like that for
> transmission spectrum. However, you have ever said that "...the same current
> source puts on a different amount of power depending on its surroundings..."
Exactly, but this difference is a real physical effect and directly influences the extraction efficiency. The reason is that the total power emitted by a dipole source at a point in a given structure is proportional to the local density of states at that point, and the local density of states in turn is proportional to the rate of spontaneous emission (by Fermi's Golden Rule). So, the ratio of the emitted flux spectra from a point current source between two structures (e.g. slab vs. no slab) is proportional to the ratio of the spontaneous emission extraction efficiency of those two structures as a function of frequency.
> In my intuitionistic opinion, the total flux and the flux through top
> surface should be computed in the same run and in the same geometry.
It all depends upon what you want to compute. If you want to compute the fraction of the power that goes upwards vs. in all directions, then yes you want to have a single structure and compute both the total flux and the upwards flux spectra and take the ratio. If you want to know how much a particular structure enhances spontaneous emission relative to another structure, including the effect of changes in the local density of states, then you want to take the ratio of the upwards ("extracted") flux spectra in the two different structures. And there might be other questions that you would answer in different ways. The point is, you should always keep in mind what reference you want to compare to when looking at flux spectra. Steven

Friday, December 22, 2006

Ubuntu中Adobe Reader的中文支持

一般从Ubuntu源中安装的Adobe Reader不能正常显示没有内嵌中文字体的PDF。除了直接从Adobe下载安装脚本直接重新安装外,还可以在http://www.adobe.com/products/acrobat/acrrasianfontpack.html下载中文支持。运行脚本安装即可。

注:安装时会提示输入安装路径,一般从Synaptic里安装的Adobe Reader会在/usr/lib/Adobe/Acrobat7.0

Monday, December 18, 2006

免电灯,另一种投机取巧

在88上看了一条新闻,全文转载如下,

上海一些灯具交易市场和网上商城最近热销一种号称免电的台灯.售价几元、几十元
的“免电灯”不用自家电,因而购者踊跃.
  “免电灯”实际不免电.上海市通信管理局副局长李振坤说,这种灯用的是电话线
的馈电.“免电灯”虽然没有电源线,却有一根连着插头的电话线,接上就有了“电源
”,灯就亮了.附图

  据有关专家介绍,“免电灯”实际用的是电信部门的电,可达到15瓦白炽灯的亮度
.这种灯通过采用超高亮度LED发光管和内设变阻器,利用电话线路就能发出高亮光.目
前电话线的电压在36伏上下,LED发光管刚好能在此范围内工作.

  李振坤指出,“免电灯”侵害了电信部门的合法权益,也侵犯了用户正常使用通信
业务的权益.上海市通信管理局和上海市电信公司表示将着手调查此事,对电信设备的
影响、线路损耗要作出评估,然后提出相关管理措施.

  “免电灯”偷了电信部门的电,将产生不良后果.首先“免电灯”的使用会影响电
话的通话质量,如果电阻过大,还容易造成电话短路,严重时会影响电话终端设备,加重
电信公司设备负荷,造成系统损害;其次,使用人甚至会因为不付电费而开长明灯,造成
电力浪费.

  法律专家认为,按照有关法律的规定,销售和使用这种“免电灯”属违法行为.

看完了这条新闻,不知道说什么好了,商人的头脑是很精明的,可是,用的地方,似乎不对了。
在淘宝上搜了一下,还真是不少。

Tuesday, December 05, 2006

说说LED照明(2)

说到LED照明,首先让人想到的就是由GaN为基础的蓝(白)光LED。与此同时,一定会让人联想到一个日本的科学家,中村修二(Shuji Nakamura)先生。这里我全文转载一下Wikipedia上关于中村先生的介绍(检索词条,比Wikipedia方便的比较少了。可惜原因种种,在中国大陆,想查Wikipedia 还是有点小麻烦的):

Shuji Nakamura (中村 修二 Nakamura Shūji, born in May 22, 1954, Seto, Ehime, Japan) is a professor at the University of California, Santa Barbara (UCSB).
Nakamura graduated from the University of Tokushima in 1977 with a degree in electronic engineering, and obtained a master's degree in the same subject two years later, after which he joined the Nichia Corporation, also based in Tokushima. It was while working for Nichia that Nakamura invented the first high brightness GaN LED which has the distinctive advantage of producing blue light, and which went into production in 1993. He was awarded a Doctor of Engineering degree from the University of Tokushima in 1994. He left Nichia Corporation in 1999 and took a position as a professor of engineering at the University of California, Santa Barbara.
In 2001, Nakamura sued his former employer Nichia over his bonus for the discovery, which was originally 20,000 Yen (~US$180). Although Nakamura originally won an appeal for 20 billion Yen (~US$180 million), Nichia appealed the award and the parties settled in 2005 for 840 million Yen (~US$7 million), at the time the largest bonus ever paid by a Japanese company.
Nakamura has also worked on green and white LEDs, and blue laser diodes, which will be used in Blu-ray Discs and HD DVDs.
In 2006, Nakamura was awarded the second Finland's Millennium Technology Prize for his continuing efforts to make cheaper and more efficient light sources.

05年秋天的APOC,我有幸能参加中村先生做的全场报告。当然我只能远远的瞻仰这位在LED照明领域做出了不可磨灭的贡献的科学家。让我印象最深的就是他不停的说I don't know。

1990年,中村先生开始在日亚(Nichia)研究GaN器件。那一年,36年中村先生只是一位普通的工程师,没有博士学位,没有一篇论文,在整个学术界,他是默默无闻的。不到十年的时间,也就是在上个世纪90年代晚期,因其在氮化物半导体结晶膜的成长,P型氮化镓的制造和氮化镓系化合物结晶成长等方面的杰出贡献,中村修二成为了加州大学圣巴巴拉分校 (UCSB) 的教授,并于06年,获得了千禧技术奖。中村已经成为了LED照明领域举足轻重的学者。因为和日亚的巨额专利费的官司,中村也进入了普通人的视野。真的希望有一天,中国也能出现这样的人物 (袁隆平?)。但从现在的情况来看,似乎很难。

顺便说个八卦故事,当年斯坦福,HP都想请中村修二,可是中村选择了圣巴巴拉。圣巴巴拉给中村修二的年薪是20万美金,中村不需要钱,他看中的是圣巴巴拉的技术和人材的支撑,所以每到年底就把钱捐给学校。因为他的到来,UCSB得到了数千万美元的捐赠,所以,圣巴巴拉的校长把中村看成是摇钱树了。

中村修二在圣巴巴拉的小组的主页:
http://ssldc.ucsb.edu/



Sunday, December 03, 2006

说说LED照明(1)

说说LED照明(1)--写在前面的话

近两年,固体照明(Solid State lighting)的市场发展的非常快,仅仅在江浙一带,就有大量的厂商在开发一些下游的产品。国家也投入了大量的人力物力,研发新型的固体照明材料。感谢ZJU/TUe/Philips Research的合作,我有幸能从事高发光效率的GaN芯片的研发工作。我也是外行,只能把自己所见的写下来,还希望大家来指正其中的错误。

一个偶然的机会,我在浙大的图书馆借阅了Schubert教授所写的Light-emitting Diodes。
翻了翻,我想试图把这本书的内容简单的翻译一下,借用了老先生的图片,还希望他能谅解。
也不知道有没有人会看,也不知道我能不能坚持写下去。不管怎么样,开个好头总是需要的。
(再次感谢浙大图书馆的工作人员,热心而且耐心)




由上图,我们可以看到,实现固体(白光)照明,主要有两种方式:
1. 全部由半导体材料构成的发光器件;
主要是由(红、绿、蓝)三种半导体材料构成。大功率LED照明器件似乎主要是通过这种方式来实现的。印象中,浙江省科技厅十一五规化里就列了这种器件的研发工作。这里,问题还是有很多的,一个是发热,发热会导致色温的漂移等很多问题。另外,想做好高效率的绿光的LED也是比较困维的。

2. 由半导体材料和荧光粉共同构成的器件。
主要通过蓝光LED+荧光粉,UV+荧光粉等方式来实现。现在通常在市场上见到的白光LED都是通过这种实现的。

固体照明主要的应用:
1. 通用的照明
这个现在应用的还比较少。较为常见的产品只是一些简单的LED灯具。浙赣线上的2185/2186的卧铺车厢的床头灯都是LED的。
2. 车灯
车灯的指示灯用得比较多了,好像广本的前车灯车也采用LED了,看到过广告, 我是穷人,买不起车,也没关心过车。
3. 液晶的背光源
手机里用的很多了,索尼的笔记本也采用了。不过我觉得OLED更适合做显示。液晶显示的原理就决定了它的效率是不高的。当然,现在OLED的技术还远不如液晶成熟。
4. 投影
还没见过。看到过说三星有做的。



附:
1. 一个很好的网站 http://lighting.sandia.gov/。美国能源部(DOE)似乎安排了不少项目在这里。

2. LED的上游产业主要是指LED发光材料外延制造和芯片制造。
中游产业是指LED器件封装产业。下游产业是指应用LED显示或照明器件后形成的产业。