John Pendry and the Wire Medium
\A material with a negative ? is often called a plasmonic material, since the
coupled light-electron excitations that dance along a metal surface are
called surface plasmons. In 1997, even before the field of plasmonics
exploded, there were probably thousands of papers on plasmonic materials.
Surface plasmons were believed to be the key mechanism in lots of exciting
but (at the time) poorly understood and controversial optical phenomena, such
as surface enhanced Raman scattering (SERS). Theories about the role of
plasmons could be found everywhere, but it was incredibly difficult to
decisively and quantitatively connect the theory to measured data. A plasmon
is an optical, nanoscale thing - you can't hold a plasmon in your hand and
look at it. You have to infer a lot of information, based on lots of
different microscopy and light scattering techniques.
John Pendry和电线介质
具有负折射率的材料？通常被称为电浆子的材料，因为沿着金属表面舞动的耦合激
发光子-电子对被称为表面电浆子。在1997年，甚至电浆这领域爆红之前，就已经可能有
数以千计的电浆材料的论文。表面电浆子这领域（在当时）许多所知甚少和有争议的光学
现象曾被认为是令人兴奋的关键机制，，如表面增强Raman散射（SERS）。有关电浆子的
理论可以随处可见，但果断地和定量地将理论连接实验数据是极为困难的。电浆子是一种
光学，奈米尺度的东西 - 你不能在你的手上就握著电浆子并且看着它。你必须根据许多
不同显微镜和一些光散射技术来推论大量的信息。
The optical work I was doing as a postdoc was vastly different from the
microwave scattering work I'd done as a graduate student. By comparison,
microwaves were easy! You could model just about any kind of structure, and
whatever you modeled you could measure almost exactly. Very little guesswork
involved. You could also make samples and do measurements really, really
fast. Part of the reason is that the microwaves we were using were
electromagnetic waves, with wavelengths of many inches, unlike light waves
which are just a few hundred nanometers in size. If you want to make
something that reflects or scatters microwaves, it's big! - usually about the
size of your hand or larger. You can really get an intuitive feel for how
microwaves interact with structured materials, and can try lots of
experiments quickly. By the time I had finished my graduate work, I could
design a photonic crystal, simulate its properties, fabricate the structure
and make the measurements all in one day. That was awesome. We definitely
could not do that with optical plasmons.
虽然都是关于光的工作，我在做博士后是微波散射的这跟当初在当研究生时候已经
大不相同。相较之下，微波很容易！任何类型的结构都可以模拟，不管模仿甚至是测量几
乎是正确的。很少涉及到猜测。你也可以做出样品并做测量，真的，真的很快。部分原因
是我们使用的微波是电磁波，具有许多英吋的波长，不像光波只有几百奈米的大小。如果
你想做个东西来反射或散射微波，它非常大！ - 通常大约是你的手大小或更大的尺寸。
微波结构材料的交互作用方式你真的可以得到很直观的感受，并可以快速地作大量的实验
测试。
在当时我完成毕业作品的时候，我可以设计一个光子晶体并在一天内完成所有测量，
模拟其性能，制造该结构。这是太棒了。但是对于光学电浆子我们肯定不能这样做。
I began to obsess about whether there could be a way to create a microwave
analog to the metal nanoparticle.
The big problem with creating a microwave "plasmonic" material was that there
were no known materials that had a negative ε at microwave frequencies.
Negative ε was considered an optical phenomenon that occurred only in
conductors at near-visible and ultraviolet wavelengths. At microwave
frequencies metals are well, just metals: They exclude electromagnetic
fields. If the fields can't even get into the metal, they can't interact with
the metal in any interesting way. Metals at microwave frequencies don’t
support surface plasmons, and definitely cannot be considered "plasmonic."
But, maybe there was a possibility. While browsing through the thousands of
papers on plasmons, I ran across a paper by John Pendry and colleagues,
published in Physical Review Letters in 1996, in which they suggested an
artificial material one composed of wires - could behave exactly like a
plasmonic material, but at any frequency. Including microwave frequencies. It
was exactly what I was looking for!
Almost.
我开始迷恋是否有可能发明是一种方式来类比微波与金属奈米粒子。创新微波
“电浆”材料最大的问题是:是否有在微波频率的介电常数ε是负的未知材料。负介电常数
ε在以前被认为只发生在导体在波长在接近可见光和紫外光的光学现象。在微波频率金属
表现很好，但只是金属：他们排除电磁场。如果该电磁场不能进入金属，它们就不能与金
属进行任何有趣的交互作用。金属在微波频率下不能支撑表面电浆子，则肯定不能被视为
是“电浆的”。但是，也许有一种可能性。在浏览数好几千篇的电浆子的论文，我看到一
篇1996年John Pendry和他的同事发表在物理评论通讯(PRL)的论文，他们建议一种电线组
成的人工材料- 它可以在任何频率表现地完全像电浆材料的。包括微波频率。这正是我一
直在寻找的论文！差不多。
Pendry's structure required really, really thin wires. Much thinner than any
typical commercially available wire. If you could get those wires, you'd have
to be really careful in how you arranged them and held them together - it
would almost be like weaving a material out of thread. It wasn't anything we
could build, at least not without a lot of effort. Could there be another
approach?
As simple a structure as Pendry's wire structure was, the theory was fairly
complicated. I took Pendry’s paper around to several of our theoretical
colleagues at UCSD, and none of them could understand it, at least without
having much more time to spend on it. Moreover, Pendry's theory was becoming
wildly controversial, with lots of other scientists and theorists objecting
to both Pendry’s approach and the results. Plasmons at microwave
frequencies? Not a chance, according to Pendry's critics.
So, without a way to make the thin wire structure; with no one around who
understood the paper; and with the paper mired in controversy, I really
couldn't
justify delving much further into the subject.
Pendry论文要求真的真的非常细金属线的结构。远远超过任何一般市面上可买到的
细金属线。如果能得到这些金属线，你必须非常小心安排他们和他们在一起 - 它几乎像
一个外螺纹所编织的金属线。至少在没有极大的努力之前这不是我们当时所能做到的。是
否还有其他方法？
Pendry的金属导线结构是实验简单的，但理论是相当复杂的。我把Pendry的论文到处
与加州大学圣地亚哥分校各地的好几个理论同事讨论，当时没有一个人能理解它，至少没
有人愿意花更多的时间这论文上面。此外，Pendry的理论渐渐引起极大的争议，有很多其
他科学家和理论物理学家反对Pendry二个解决方法和结果。根据Pendry的评论，电浆子在
微波频率？没有机会!。
所以，没有一种方法使细线结构成真; 并且周围的没人看得懂论文; 并且论文陷入
争议，我真的不能够再对这个题目做更进一步的钻研。
去法国旅行！
I had always wanted to visit France. It was a lifelong goal. I’d been to a
lot of different countries for various conferences, but never had been
invited to one in France.
In 1998, however, an email showed up, inviting me to a conference called
PIERS - Progress in Electromagnetic Research Symposium. I hadn't heard of the
conference before, and I didn't know quite what it was about, but it was in
Nantes, France, and I saw my opportunity. I talked it over with Shelly, and
he agreed it was a good thing to do, so I was set. I just needed a topic. I
quickly put together some ideas based on the work I was doing with Olivier
Martin, and bought my tickets.
And here is where the randomness of life really comes into play. That
conference turned out to be truly fortuitous and pivotal. In the session that
I was in, it turned out there were lots of people talking about negative ε
and even Pendry's wire medium. A couple of groups were actually doing
detailed numerical simulations, and had succeeded in verifying Pendry's
prediction. There were no experiments, but at least there was growing
evidence that the theory was right. Still, it required really, really thin
wires.
以前我一直想参观法国。这是一个终身追求的目标。我已经去过很多不同国家参加各
种不同的会议，但从来没有被邀请到法国。然而，在1998年，一封电子邮件邀请我到一个
叫PIERS会议 - 在电磁研究进展研讨会。在这次之前我从没有听说过这个研讨会，我真的
不知道这到底是讨论有关什么的，但它是在法国Nantes，我看到了机会。我跟Shelly讨论
过了，他赞同这是一个很好的事，所以我设定我只是需要一个主题。我赶快地把与Olivier
Martin一起工作的一些想法组合在一起，并买了机票。
且这就是生命的随机性真正开始发挥作用。该会议被证明是真正地偶然和关键的。
在会议上，我发现原来有很多人在谈论负的介电常数ε，甚至Pendry的金属线介质。有二
个团队实际上做了详细的数值模拟，并已成功地验证Pendry的预测。目前还没有实验，但
是至少有越来越多的证据证实该理论是正确的。不过这需要非常非常的细的导线。
It also turned out that Eli Yablonovitch, who along with Sajeev John was one
of the founders of the field of photonic crystals - was attending the
conference and that session. Both Shelly and I had known Eli for many years,
and so when I saw him we started comparing notes on the session. At the time,
he was very interested in wire structures as well, and was also interested in
the possibility of microwave plasmons. So, we had common interests.
"You know," Eli told me, "I've organized a meeting on photonic crystals in a
few months in Laguna Beach this year. Why don't you come and talk about
microwave plasmons?"
Laguna Beach. It sounded great. I was in. But I didn’t know anything about
microwave plasmons, other than that I was hoping someone would propose a
structure that we could make.
"Sure," I responded, "but I don't know anything about microwave plasmons."
Eli, being one of the giants in the field, could be very persuasive. He
replied "that's ok, you've got a few months. Just get some ideas together and
come and talk about them."
I was still a little worried. I doubted there would be much I could do in
just a few months.
"Ok," I said, "but if I can't come up with anything, can I switch my topic to
photonic crystal accelerator cavities?" Photonic crystal accelerator cavities
were what I had studied as a graduate student. I had lots to say on that
topic. It was a good failsafe topic.
"Of course," Eli assured me. And that was that.
I spent two weeks traveling around France, and it was spectacular! Thoughts
of wire structures and plasmons left my mind. There was no rush and no
impending deadline