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和電線介質
具有負折射率的材料？通常被稱為電漿子的材料，因為沿著金屬表面舞動的耦合激
發光子-電子對被稱為表面電漿子。在1997年，甚至電漿這領域爆紅之前，就已經可能有
數以千計的電漿材料的論文。表面電漿子這領域（在當時）許多所知甚少和有爭議的光學
現象曾被認為是令人興奮的關鍵機制，，如表面增強Raman散射（SERS）。有關電漿子的
理論可以隨處可見，但果斷地和定量地將理論連接實驗數據是極為困難的。電漿子是一種
光學，奈米尺度的東西 - 你不能在你的手上就握著電漿子並且看著它。你必須根據許多
不同顯微鏡和一些光散射技術來推論大量的信息。
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.
雖然都是關於光的工作，我在做博士後是微波散射的這跟當初在當研究生時候已經
大不相同。相較之下，微波很容易！任何類型的結構都可以模擬，不管模仿甚至是測量幾
乎是正確的。很少涉及到猜測。你也可以做出樣品並做測量，真的，真的很快。部分原因
是我們使用的微波是電磁波，具有許多英吋的波長，不像光波只有幾百奈米的大小。如果
你想做個東西來反射或散射微波，它非常大！ - 通常大約是你的手大小或更大的尺寸。
微波結構材料的交互作用方式你真的可以得到很直觀的感受，並可以快速地作大量的實驗
測試。
在當時我完成畢業作品的時候，我可以設計一個光子晶體並在一天內完成所有測量，
模擬其性能，製造該結構。這是太棒了。但是對於光學電漿子我們肯定不能這樣做。
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.
我開始迷戀是否有可能發明是一種方式來類比微波與金屬奈米粒子。創新微波
“電漿”材料最大的問題是:是否有在微波頻率的介電常數ε是負的未知材料。負介電常數
ε在以前被認為只發生在導體在波長在接近可見光和紫外光的光學現象。在微波頻率金屬
表現很好，但只是金屬：他們排除電磁場。如果該電磁場不能進入金屬，它們就不能與金
屬進行任何有趣的交互作用。金屬在微波頻率下不能支撐表面電漿子，則肯定不能被視為
是“電漿的”。但是，也許有一種可能性。在瀏覽數好幾千篇的電漿子的論文，我看到一
篇1996年John Pendry和他的同事發表在物理評論通訊(PRL)的論文，他們建議一種電線組
成的人工材料- 它可以在任何頻率表現地完全像電漿材料的。包括微波頻率。這正是我一
直在尋找的論文！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論文要求真的真的非常細金屬線的結構。遠遠超過任何一般市面上可買到的
細金屬線。如果能得到這些金屬線，你必須非常小心安排他們和他們在一起 - 它幾乎像
一個外螺紋所編織的金屬線。至少在沒有極大的努力之前這不是我們當時所能做到的。是
否還有其他方法？
Pendry的金屬導線結構是實驗簡單的，但理論是相當複雜的。我把Pendry的論文到處
與加州大學聖地亞哥分校各地的好幾個理論同事討論，當時沒有一個人能理解它，至少沒
有人願意花更多的時間這論文上面。此外，Pendry的理論漸漸引起極大的爭議，有很多其
他科學家和理論物理學家反對Pendry二個解決方法和結果。根據Pendry的評論，電漿子在
微波頻率？沒有機會!。
所以，沒有一種方法使細線結構成真; 並且周圍的沒人看得懂論文; 並且論文陷入
爭議，我真的不能夠再對這個題目做更進一步的鑽研。
去法國旅行！
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.
以前我一直想參觀法國。這是一個終身追求的目標。我已經去過很多不同國家參加各
種不同的會議，但從來沒有被邀請到法國。然而，在1998年，一封電子郵件邀請我到一個
叫PIERS會議 - 在電磁研究進展研討會。在這次之前我從沒有聽說過這個研討會，我真的
不知道這到底是討論有關什麼的，但它是在法國Nantes，我看到了機會。我跟Shelly討論
過了，他贊同這是一個很好的事，所以我設定我只是需要一個主題。我趕快地把與Olivier
Martin一起工作的一些想法組合在一起，並買了機票。
且這就是生命的隨機性真正開始發揮作用。該會議被證明是真正地偶然和關鍵的。
在會議上，我發現原來有很多人在談論負的介電常數ε，甚至Pendry的金屬線介質。有二
個團隊實際上做了詳細的數值模擬，並已成功地驗證Pendry的預測。目前還沒有實驗，但
是至少有越來越多的證據證實該理論是正確的。不過這需要非常非常的細的導線。
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