Our new publication on a focal field shaping technique

Point Spread Function (PSF) design to shape the focal field distribution of an optical system is very important to many applications: optical microscopy, lithography, optical tweezers, etc.  However, often this design process includes tedious numerical calculations and complex optimisation procedures.

In this paper, we explain to the readers the benefits of the well-established Extended Nijboer-Zernike theory(a most recent updates of the ENZ theory can be found in https://www.jeos.org/index.php/jeos_rp/article/view/13044/1026 ) :

1. The 3-D focal field distribution of each Zernike mode on the exit pupil can be analytically obtained and the contribution of each mode to the total focal field are solely related by its Zernike coefficient;
2. The Zernike modes(polynomials ) form a complete and orthogonal set on a unit circle.

Based on these merits, we developed an optimisation algorithm to find a focal field with extended depth of focus. Since the focal fields of Zernike modes are analytically obtained, our optimization parameters  are reduced to the number of Zernike modes applied.

We have build up an experimental setup to demonstrate this idea: a Spatial Light Modulator(SLM) is used to shape the pupil field and a scanning stage is used to measure the 3D focal intensity distribution.

And the actual measurements validated our theoretical results:

Ref.:

A. P. Konijnenberg, L. Wei, N. Kumar, L. C. C. P. Filho, and H. P. Urbach. Demonstration of an optimised focal field with long focal depth and high transmission obtained with the extended nijboer-zernike theory. Opt. Express, 22(1):311–324, Jan 2014.

http://dx.doi.org/10.1364/OE.22.000311

不忘初心（以前写的，再同大家分享一下这些思考）

今天读了曾经台湾清大教授彭明辉的blog，他最近主动辞职了，辞职信里写到“主因是不滿於學術風氣的敗壞，而自己無力阻擋”。他的文章“學術自由的本意與淪喪”看的出来是他的严肃思考。彭先生的文章其实有shock到我，就像小和尚念经，正昏昏欲睡，不知其意之时，师傅后脑门一击，醍醐灌顶。他说的是台湾的现实，却也投射这我们同样的问题。

联想到前段时间Nature 专门做了一期特刊有关于PhD的教育的(The future of PhD)，而新科研究人员（PhD candidates）的培育只不过是当代学术或许现实问题的冰山一角罢了。 

当然我不希望如此悲观，（以至于有可能能够改变游戏规则的人（精英）失望离开。）Nature中提到当前制度的一个后果是“研究人员的过度饱和”，我在想，真的过多了吗？ 还是其实远远不够？ 想想我们这个世代所面临的能源问题、粮食问题、土壤和水资源的污染问题，穷人的医疗问题，哪一个问题缺少得了专业人士的研究、分析与解决？ 我们有做足够这方面的研究吗？也难怪整个世界都在抱怨充斥全宇宙的博士生呢...

我想先问你“为什么而研究？”

我记得印象里里小时候和科学家或科技相关联的画面总是“高精尖”、“最先进”、“突破性的”、“诺贝尔奖”等等，长大后老师说影响因子就是学术的全部，science、nature在中国的大学里会是一件很轰动的事。 我感觉很多人心目中的研究大概是“做前人之未作，或在前人的基础上做的更好”，我们称之为“追求卓越”。然而这是一种追逐的过程，向前奔跑，没有止境的路。你想在哪里停止呢？ 

学术的意义是在于追求卓越吗？我们一窝蜂地追逐最新最热的研究，这就是意义本身吗？

宗萨钦哲仁波切说过“我们的社会总是用一个人拥有什么，而不是他是什么样的人来评价一个人”，这不仅是指物质上的拥有，也包括精神上的。 比如北大的柳智宇拒绝了MIT的录取而选择出家，当然在社会上掀起轩然大波。我们会觉得柳智宇先生“理所当然”地应该接受这份顶级的offer，“理所当然”地该去做最顶尖的研究，我们的社会总是这样“理所当然”地运行着...

如果去想象一个很棒的博士选择去用技术改造一整个村庄而不是去顶级的研究所做研究发表顶级刊物，这真的很难。

然而彭明辉先生说：

“學術的本務不是研究成果的競爭，不是「學術卓越」的追求，不是新穎知識的生產，也不需要有「在五年內要成為數一數二的佼佼者」（李遠哲，2001）這樣的抱負。學術不是一種「專長」，而是一種態度：為了社會更好的未來，而嚴肅探究社會既有的價值、信念與制度，找出其中的盲點，秉著學術良知說出自己能信服的價值、信念與制度，從而使社會獲得自我校正與自我改善的力量。羅素對婚姻與宗教的態度，跟他在學術圈內普受讚譽的數理邏輯無關，但是他對婚姻、宗教與學術自由的省思，卻對社會的進步有不能抹滅的貢獻。”

他的文章有引用罗素的「大學教師理應是具有特殊知識和訓練的人，他們能夠從不尋常的角度去探索具有爭議性的問題，並很有機會因而使我們對該問題有新的瞭解。」（Russell, 1975）

盲目地追逐排名与SCI指标正在使我们的研究与我们本地的问题日渐脱离，我始终不能忘当年大连海湾石油泄漏新闻上的那一幕幕，我们的国家依靠着小小的船没有防护的渔民去清理油污，而与此同时我们的大学们个个都正在宣称自己的努力目标是世界一流的研究型大学！当然这些所谓一流的指标里面，论文分子占了不少，可是这又有什么意义？！我宁愿那个学校用科学安全的方法把那油污给清了，我们就承认那个大学是“一流”。

关键还是想想我们为什么要做研究，然后“不忘初心”

Good book by Kurt E. Oughstun

Kurt E. Oughstun() wrote really nice book on "Electromagnetic and Optical pulse propagation", very much recommended. 

First Bachelor thesis student finished

Last Friday, my first bachelor student Sander has successfully defended his bachelor thesis.
I am very happy to work with him, and together with him and other colleagues we are able to demonstrate an idea I proposed.
He is both curious and diligent, reminding me of the famous phrase of Zen: 'Never forget the beginner's mind'(in chinese: 不忘初心).

Nice book by Jean Bladel: Singular electromagnetic fields and sources

Electromagnetic theory is a quite broad research area, and forms the basis in understanding a wide branch of scientific phenomena, and consequently you can find lots of books using EM theory as their theoretical basics, and the main topics can diverges drastically.
Interestingly, this book by Jean Bladel: Singular electromagnetic fields and sources, aims to summarize a group of problems one may encounter in this area, the 'source/geometrical singularities', one common example is the Green's function which no one can escape when jumping into this area.
It is a very nice companion book as it aims, which provides with a nice read, and I would like to share with you.

Prefaces of a researcher

Knowledge is of great importance for our society, Nobody (or at least not so many) would doubt it any more. Techniques have made knowledge easily accessible to more and more people, just as some said before:"The techniques possibly make a fool of this generation more knowledgeable than genius of last generation"

 But knowledge doesn't come from nothing. Here come the researchers, often at the frontiers of knowledge, providing original new data or new perspectives of our world.

 People often forget that behind those 'cold' data/theories, there exist the researchers with beating hearts. There are not so many places where a researcher could post his/her opinion about researches themselves, or unfortunately, not every researcher is necessarily a good writer at the same time.

 Of course, time has left us with some of sparkling masterpieces, a nice written book or research paper or device. J.M. Ziman's book "Principles of the Theory of Solids" is of course of this kind. Even from its preface, you can learn so much about his opinion on writing/acquiring scientific knowledge. He was aiming to write a book full of ideas, instead of a collection of facts or complex formulas, which would distract the readers away from the science's hard core. Isn't it the very lack of many scientific publications?


 Anyway, I invite you with the preface of this true researcher, and hope it is inspiring for you as well. ---Lei, @Delft Link to the Preface of J.M. Ziman's book The link from the publisher is broken, you may search online about this book's preface, it is worth to read.

'Candle light': Manipulating light and matter at the nanoscale for high-resolution imaging and spectroscopy.