- Good afternoon, everyone.
I'm really impressed at the sell-out.
I don't think we changed
the menu from last time
so it can't be just the food here.
Hi, my name's Shankar Sastry.
I'm the Dean of the
College of Engineering,
at least for now.
You know, I'm stepping down July 1, but
so I must say it's really
a great, great pleasure
to welcome you to now, the
7th Annual Ernest S. Kuh
Distinguished Lecture Series.
And so wonderful to say 7th year
because I really remember when
Bettine and Ernie first came
and started talking
about this lecture series
and how Ernie had--
And the two Ernie and Bettine
had endowed a similar series
at the University of Michigan.
And, you know, I really
remember that conversation.
He said he wanted this to
be a place where you had
leaders in academia, leaders in industry,
and leaders with a international bent
so to come and speak to
the college community.
So and ever since that
time, the Kuh Lecture
brings an outstanding leader
in technology and engineering
to the campus.
And the very first one, of course,
was the Intel co-founder, Andy Grove.
And it has been followed, I must say,
by a very wonderful list of
leaders, eminent leaders.
So we continue that
tradition of excellence today
with the 2018 Kuh Lecturer, Xiang Zhang,
who's out here you'll see in a second.
Xiang, it should be noted,
already has this title
of Ernest S. Kuh because he holds
the Ernest S. Kuh Endowed
Chair in Engineering.
So we are particularly
proud to have him here.
The Ernest S. Kuh professor delivering
the Ernest S. Kuh
Distinguished Lecture so.
The lecture series, of course,
was endowed through the
generosity of Ernie and Bettine
who have truly been exceptional citizens
of our College of Engineering.
Ernie was a professor of
EECS and a trailblazer
in the design of integrated
circuits and systems.
Beyond his research, he was
also the Dean of our college
and a national leader in
engineering education.
It has been a big loss, and
even that seems really recent,
when we lost Ernie in 2015.
But, you know, I'm very pleased
now that we have Bettine
in the audience.
Let me single her out.
There's Bettine.
And that Ted Kuh is the older son.
Anthony, of course, is
doing national service
at the National Science Foundation.
And Ted told me he was running a panel,
otherwise he'd be here.
But his wife is here and
Bettine's sister, Susan,
is here as well.
The other members of the family--
Sorry, I won't introduce every one of you.
But, you know, Bettine, this
wonderful annual lecture
is really a lasting addition
to Ernie's outstanding legacy at Berkeley.
(applause)
Now I'd like to invite Ted Kuh.
And let me say a little
bit about Ted also.
You know Ted, of course, is
a Cal Alum and also graduate
of the Haas School of Business.
And most recently, he's been very active
between the two colleges,
the Haas School of Business
and the College of Engineering
in launching a new sort of
Dual Major Program called MET,
Management, Entrepreneurship,
and Technology.
It's sort of two degrees in four years
for those who are not faint of heart.
And he's been a Trustee
and one of the founders
of this program.
But I'd like him to invite to the stage
to deliver some remarks
on behalf of the family.
Ted.
(applause)
- Thank you, Shankar.
Good afternoon and welcome to all.
I will start by saying
that I was not smart enough
to get into the College of Engineering
so I had to go to the Haas School,
which was
(laughter)
still a fine school.
We are extraordinarily
honored to have professor
Xiang Zhang as our 7th
Distinguished Lecturer.
He is incredibly accomplished
in research, in teaching,
and soon to be in administration.
And my brother, who is never
really profuse with accolades,
said to me, "He's a real
rock star in his field."
So I think we're truly
grateful that you are here.
I just wanted to say a few
words about my late father
and why he and my mother did establish
this Distinguished Lecture Series.
For my father, Cal was
really his second home.
For almost 60 years, he was a professor
and professor-emeritus
in Electrical Engineering
and Computer Science.
And he really enjoyed every aspect
of his life here at Cal.
Certainly collaborating
with wonderful colleagues,
doing his research in integrated circuits
and computer aided design, and then also
serving in the administration.
But I think what he really enjoyed most
was teaching and mentoring students.
And during his career, he
had the privilege of teaching
4,000 undergraduate students
and 40 Ph.D. students.
So in 2011, my parents
decided to establish
the Distinguished Lecture
Series because they wanted
to give back to the Cal community
for all that they had received
during their lifetime.
And it was appreciation
that they wanted to show
and provide for the Cal community to learn
from true leaders in both
industry and academia.
So my brother, who unfortunately
could not be here today,
and I do want to acknowledge my mother,
who has been a pillar
throughout our entire life.
And ...
(applause)
Jonas's representative.
And then we also wanted
to thank and acknowledge
Dean Sastry, who all of you
probably know is stepping down
after 10 years as a dean.
Certainly his contribution and leadership
at the College of
Engineering has been immense.
So thank you Shankar.
(applause)
So with that, I think Shankar's gonna
formerly introduce professor.
- Thank you, Ted.
We're delighted to welcome
members of our Dean's Society
and to also acknowledge
the fact that your support
for the college and the
students, all of whom you see,
the enthusiastic, bright,
shining faces in this audience,
has really been critical.
You know, all of the
10 years I've been Dean
have been times of budgetary duress.
And it's your support that
really has helped the college
weather this and, in
fact, thrive in the midst
of these challenging budgetary times.
So thank you very much.
Thank you to all of you
Dean's Society members.
(applause)
And this year's Kuh Lecture is co-hosted
by the Berkeley student chapter of ASME,
the American Society of
Mechanical Engineers.
And our thanks go to ASME for their help
in the preparations for this lecture.
Thank you student chapter of ASME.
Where are you?
The guys in the shirt.
(applause)
They have Berkeley Engineering polo shirts
to show for their precious
possessions not sold.
So, let me tell you a
little bit about Xiang.
So much research that comes out
of university labs influences our society,
but it's particularly
exciting when the work
also manages to capture
the public's imagination.
This is the case with
the research done by our
rock star, I'm told, Xiang Zhang.
Professor Zhang is one of the
world's preeminent scientists
working with meta-materials.
These are a class of materials
that possess characteristics
not found in nature.
They are rule-breakers.
So Xiang and his lab have shown
that they can overcome
barriers and limitations
previously set forth in
physics and that had threatened
to limit the continuation of Moore's Law.
Professor Zhang's research
has opened the doors
to imaging resolution
and optics that had been
previously considered unattainable,
including the invisibility
cloaks that bend light backwards
and that you undoubtedly seen
in the Harry Potter films.
(laughter)
But he'll tell you how
they really work today.
His work on cloaking
meta-materials has been featured
by many prominent media outlets.
And the research has been
selected by Time Magazine
as one of the "Top Ten
Discoveries of the Year,"
"50 Best Inventions of
the Year," as well as
Discover Magazine's "Top
100 Science Stories."
Of course, Zhang has
also been well-recognized
by his academic peers.
He has published hundreds of papers
in peer-reviewed journals:
"Science," "Nature,"
and of course, the usual set of journals.
It's unusual to have as many publications
in "Science" and "Nature"
in a College of Engineering.
He's been elected to the
U.S. National Academy
of Engineering, Academia Sinica,
the National Academy of
the Republic of China.
He's a fellow of five
scientific societies,
including American Association
for Advancement of Science
and ASME, of course.
Professor Zhang first came to Berkeley
as a graduate student, earning his Ph.D.
with Professor (mumbles),
I think, in 1996.
He held faculty positions
at Penn State and UCLA
before returning to Berkeley Engineering
as a faculty member in 2004.
He has served with
distinction at Berkeley.
I should say he's serving
with distinction at Berkeley.
It's not a past tense here.
He is the director of
the NSF Nanoscale Science
and Engineering Center and formerly,
up on the hill, he was the director
of the Materials Science Division at LBL.
It comes as little
surprise that his talents
and leadership are
recognized around the world.
This past December, the
University of Hong Kong
named Professor Zhang as its
16th Vice Chancellor and President.
The University of Hong
Kong is among the oldest
and most prestigious universities in Asia.
So this is clearly a true honor.
We are extremely proud of Professor Zhang
and very grateful that
in this last semester,
but at least last semester
for now, at Berkeley,
we are really proud of
everything you are doing
and continue to do.
So without further ado,
please welcome Xiang.
(applause)
- Thank you, Shankar.
It's my great honor to be here today.
Berkeley has been my home for many years,
especially, I think--
You know, today I feel I'm double honored.
I mean, Ernest Kuh Endowed Chair,
holding for last maybe 10 years.
And also today, I have the other honor
to give such a lecture in his name.
And I like to take this opportunity
to thank the College of Engineering,
Dean Shankar Sastry, Department
of Mechanical Engineering,
and the campus has been
really wonderful support
for my work, for my life, and my lab here.
So all the work I present here,
essentially without those
support, it's impossible.
And also I'd like to thank the people,
especially the student
post docs and my staff
work with me over years here.
And without their work essentially
this is also impossible.
Let me begin my talk,
I'm sorry, with a picture
of Ernie and Bettine.
Where Ernie, to me, actually
there already our Dean
speak highly about Ernie's
scholarship achievement.
But to me, actually, he's a great mentor.
When I joined Berkeley 14 years ago,
and when I was given this Chair,
I'd had the chance to meet with Ernie
and also we had in his office,
he was retired at the time, already.
And we talk about
research, life, and so on.
He give me so many great advices
and also sometimes with the jokes as well.
Also I being really benefit
from his great wisdom.
So today I like to share with you
some of the work we have
been working at Berkeley,
especially so called creating materials
that do not exist in nature.
Of course, we do not create
the materials from air.
We use nature materials,
but we build something totally different.
So three examples I'm going to talk about:
negative refraction,
superlens, and cloaking.
So I will give a very brief introduction
what is meta-material,
then I will talk about
some very unique physics associated with
this artificial composite materials.
That is optical magnetism
and that leads to
negative refraction and
one of the or two of the
major examples of such a unique material
is one of them is that you can use that
be the lens that can
see things much smaller
and below so-called diffraction limit.
On the other hand, since
you can see, for example,
you can use this material to hide it,
so-called invisibility cloak.
So I will talk these
two extreme of examples
and hopefully that give
you a sense of what
the possibilities these
materials can offer.
So what is meta-material?
We all know that, and I was told
this is a more general
audience, a public lecture,
so I will try to make
as general as possible.
We all know that materials are
made by atoms and molecules.
And specifically, if we
take a piece of silicon
or cardimarcinide, these
are the basic material
we use for making computer chips.
We know that any of the nature materials,
they have few very intrinsic,
you know, attributes.
First off, all those atoms.
We only have actually
hundred plus type of atoms
in Periodic Table.
That's what nature offers us.
And Berkeley, I think
we own about 13, right?
13 elements.
Is that, 13 or 12.
And discoveries here
so we are really proud
of almost 10 percent.
(laughter)
But, however, is there's a
philosopher sits in the audience
and he or she will wonder
well why we are limited
by 100 plus type of elements in nature.
Why can we create something
200 times, a thousand times?
Okay, yes, that's limited by the nature.
But we think about if
we enlarge these atoms
in bigger scale, okay.
And making these atoms, each
individual atoms much bigger.
Let's say become nanoparticles,
which contains millions
or billions of real atoms.
But we call it artificial
atoms, or meta-atoms.
Meta, in Greek, means go beyond ordinary,
so this name actually was
create by a DARPA manager,
not by academics.
So-called meta-materials.
Means materials go beyond ordinary.
So these are the atoms can
be as small as, you know,
a few nanometers or as big as centimeters
or in seismatic waves,
they can be a building.
This building can be considered
as a single atom, 'kay.
But anyhow, so these essentially
are composite materials
where it can interact with certain waves,
such as optic wave, acoustic
wave, or elastic waves.
One of the thing is by building
these artificial atoms,
we can assign specific properties
to each of these elements.
Therefore, we can engineer
the physical property
of wide go beyond so-called 100 elements
in the Periodic Table.
Of course, this is only
limited by your imagination
because this is where the, you know,
the entities you can engineer--
For example, you can find a
way to circulating a current
on top of that, then you
have magnetic moment, right.
And you can create magnetic
artificial magnetism,
which I will talk about
in next few slides.
So and the other thing is
you can put this into a
elastic medium like rubbers.
You can stretch them 100% of the
that is constant's change.
While in the real crystal, real crystal,
you can take any silicon or something,
if you try to press it, few
percent is already very large.
So by tuning that actually
the large distance
of the atoms, you can tune
the property very, very,
in very dramatic way.
Also you can make a compound
like sodium chloride as well.
One other thing actually is
also not only we are bounded by
a number of atoms we have a
choice in the Periodic Table,
but also if they form a solids or crystal,
they are also have a
given set of symmetries
you can play with.
For example, this only have
a certain translational
or rotational symmetry you can play with.
By doing artificial composite,
you can do much more symmetries you want.
So what's wrong with our nature?
Well, if we look at
electromagnetic property,
which means that materials respond
to electromagnetic excitations are
microwaves or optical waves.
I won't go through a details
of this Maxwell's equation,
but this is quadrant I want to show you.
This actually has a four quadrant
horizontal axis epsilon
represent electrical response
of the material.
So the external field excitation.
Y axis is the magnetic response, okay.
So for external excitation,
electrical magnetic,
they respond differently.
Now in this quadrant,
epsilon mu are both large,
or positive, which is
most of glass, water.
Those are so-called
dielectrics sits here, 'kay.
Then over here, you have
epsilon or electric response
is negative but mu is positive.
That is metals, ionic
crystals, for example.
And over here, it is actually
epsilon larger than zero
and mu less than zero,
which exists of certain
low-frequency magnetic materials.
The nature, however, is gives us imbalance
where this quadrant is missing,
especially at high frequency,
at optical frequency,
where the materials simultaneous
has epsilon or mu negative
are not exist, not exist.
So nature give us three
quadrants, but missing one.
So Mr. Veslago, a Russian
theoretician physicist in 1968
speculating what if we have
this both simultaneously
the epsilon mu electrical
magnetic property
goes to negative.
Well, he say if you look at
the high school Snell's law,
which dictates how the light
bends in from one media
to the other.
Let's say this is air.
This is glass.
We know that when the light
travels from air to the glass,
it will bend it at an angle, right.
So we know that the energy flows this way,
momentum flows this way.
But he actually speculating
what if actually
one of the indexes whether air or glass
become negative.
Now, by the way, all the nature materials
in that optical index are
positive and larger than one.
He said well what if we
have negative barriers.
Then he find out actually the energy flows
in the opposite angle
instead of on the other side,
on the same side of instant angle,
but momentum flow backwards.
And this is very interesting
because momentum flow backwards
means that actually
there's a conservation
to be conserved in the
along the tangential direction.
But there is a physics reason why
they have to move backwards.
And we will show that in experiment.
So this is actually a very interesting,
but at the time of 1968 there
isn't any continuing work
because nobody knows how to
construct such a materials.
And it is not exist in nature.
And in 2008, one of the
first optical meta-materials
shows negative index and the
both property here at Berkeley.
We actually did experiment.
Actually very hard.
And science reporter actually draw this.
This is not exactly right, by the way.
But capture general idea.
If you have a straw in the
water, it looks broken,
but it's not broken.
It should be continuous straw.
The reason you look at
it's broken is because of
there's a optical phenomena
called refraction.
The light bends from one
media to the other media,
from air to water.
'Kay, that's why it looks.
But he articulating that
if this is water contains
negative optic index, the
straw will bend this way.
It's not exactly right,
but generally capture
sort of the contrast of the ideas, 'kay.
But more accurately, my
student, Jason Valentine,
he's now professor at Vanderbilt.
He actually produced this cartoon.
That means actually in
a pond, we know that
if you have a fish, and a person
observed fish in the water,
right, and now if we changed pond water
into negative index media or
refract index is negative,
what this person will
see is a fish floating
above the water and upside down.
The thing actually is
down now instead of up.
So that is the truly, this is correct.
I verify.
(laughter)
Everything theory, okay.
Everything theory.
I couldn't create the
water in negative way.
But the whole field actually
start from a brilliant proposal
by a British scientist, Sir
John Pendry, in 2000 PRL paper.
He proposed that, by the
way, we all know that
nature materials has magnetic materials
which magnets we use that
for information storage
for your hard disk and so on.
But he said, well what
if materials of property
doesn't have a magnetic response.
The parent material, let's
say take a piece of aluminum
or gold, but use structure
in such a way, you know,
certain geometry, that gives it
collectively magnetic activity.
And that is very striking.
It's like a parents
doesn't have this skill,
but son is actually expert on that.
So this is actually through
a geometric structure
you end up with this very
interesting artificial
or collective magnetic response.
And this was actually very,
very interesting development.
And combining now, if you
try the magnetic response
at, you know, from the
low magnetic materials,
then combining the epsilon,
which is the electric response
with this we know very well.
You chop the metal become
porous, you can shift their
pulse frequency from UV
to visible to microwave.
And if you combine mu magnetic
property epsilon property
both simultaneously act you end up
with piece of composite like this.
You can make a lens out of it.
And furthermore, Mr. Pendry pointed out
this lens is very special.
It can imaging things at very small scale
and below so-called diffraction limit.
In fact, this is a cartoon I draw
when I at the UCLA and
I was a young professor
and I saw this paper I say
well gee, this is opportunity.
We do some experiment.
So we wrote the proposal in 2000.
Only few months after this published
and we try to bid so-called MURI Program.
It's involved the Department of Defense
Basic Research Program.
And we got it and we start,
you know, last 15 years
or 18 years of research on this topic.
So if this is true, can
be realized optic index
can be negative.
And there's many things could be possible.
For example, you can imaging things
way below diffraction limit
and that is at the nano-scale.
So that is very important for biology.
And also you can use the same way
to develop nano-lithography.
You can print the circuits
at very small scale.
And there's group actually
in London are actively pursue
a high frequency MRI.
In fact, actually using
these very high frequency
magnetic field, you can
do a lot of imaging stuff
over there for medical imaging.
And also, of course, for photonic circuits
you can scale down much smaller scale
and bio-sensing.
So first, actually, a
meta-material with selective index
are produced at UC San Diego
in the microwave range.
So these atoms based in
rings are much bigger.
It's about centimeter size,
one half centimeter size.
One half centimeter in size.
So these are big atoms, big atoms.
But for microwave, these are
much smaller than microwave.
I believe, in this case,
the microwave wavelength
is about maybe 10 centimeter.
So for the wave propagating
through this media
is effective media approximately.
So they produce actually both
epsilon mu smaller than zero.
But then soon people, this is
very big milestone experiment.
But people still arguing
that this, in this frequency
microwave, you do have nature materials.
Both epsilon mu are negative,
so you don't need this.
But never-the-less I think this is a
great, great achievement.
The question is in higher
frequency, optic frequency,
can we have that?
The problem with optic
frequencies in square
the index of refraction is
equal to epsilon permittivity
times permeability electromagnetic.
Right, this we all know
in the classical textbook.
But if you move up optic frequency,
where all the nature
materials do not exist,
do not display the magnetism,
magnetic response, okay,
especially after few hundred gigaHertz.
Therefore, we always take mu equal to one.
And optical engineers
always with one handle,
which is epsilon, the electrical property,
because there's no magnetic
property in optical frequency.
The reason is that optical
magnetic actually activity
or response of the materials are rised up
from the magnetic dipoles.
In contrast with the electric response,
are from the electrons,
largely, it's a monopole.
And I always use this example.
Dipoles, they cannot sustain themself.
They have to form a domain or group
and it's like a division of soldiers
and they are lined up in the field.
You ask this division of
soldiers, few thousand people,
move back and forth, back and
forth, at very high speed.
That's very hard.
Now, if you have a grid
loss like electrons
are individual monopoles, they can move
back and forth very fast.
That's why metal are shiny, right.
So the magnetic actually
activity at very high frequency
do not exist after a few,
above a few hundred gigaHertz.
That is the reason, because
they have to move together
as thousands of dipoles,
millions of dipoles,
so-called domain, magnetic domains,
fully back and forth.
That's hard.
So usually nature materials
magnetic activities fade away
above few hundred gigaHertz.
What Sir John Pendry actually proposed is
well let's take some
long magnetic materials
such as aluminum or gold.
We structure them into a
so-called split ring structure
where they have two concentric
rings, this is top view,
where they have two split.
180 degree.
That's for phase actually coupling.
Where these two concentric rings where you
excite with the external magnetic field.
You would generate a loop current.
This is induction current in the metal.
And they are capacitively coupled.
So this two split gives you
that 180 degree difference.
Therefore, they can be
capacitively coupled.
Therefore, while you have a
inductance, a capacitance,
you know what happened many
electric engineer here, right.
You have RC circuit, that gives up,
give rise of the resonancy if you drive
to the right frequency for the geometry.
And that's exactly happened here.
So if you drive that
to a certain frequency
in microwave or even higher,
and the magnetic response
indeed actually shows up, indeed shows up.
So this is very interesting.
John Pendry show that in this paper
where the microwave version
of that can be realized.
The questions we ask ourself at the time
whether we can push up
to optical frequency.
In this case, it's the
far infrared or teraHertz
where the magnetic activity
for all nature materials disappear.
So we indeed actually using
this split ring structure
and this is sort of microfabrication.
Each of the atoms is
about 26 micron in size.
It's still very big.
It's not small.
And but for teraHertz wave of 100 micron,
this is continual medium
or effective medium.
You can treat it.
Therefore we observe very
strong magnetic response
of this single layer of
atoms, of artificial atoms
at operate at teraHertz, at teraHertz.
So as you can see, you can tune this
by tuning the geometry as well.
And this is in collaboration
with Basov and Smith
and UCSD and Pendry, Imperial College.
So the question is next can we move up
to truly optical frequency.
And yep, it is not the
single layer of atoms,
rather, because we know that, you know,
we have a crystal that
is three-dimensional.
So we want to create a bulk
negative index materials.
And the way we did is actually is, again,
we take nature materials, we
build it into a composite.
The way we do that, we
do at first the stripes.
These stripes are made
by dielectrics, metals,
dielectric metals.
There's two colors represent
two different materials.
We stack them up in stripes.
Then optic wave coming from the bottom
and with the magnetic field
actually parallel to the stripe,
that will excite a magnetic resonance.
Look at here.
There's a cross-section of this stripe
where you have inductance in metal,
a capacitance across the dielectric.
And so you have this
little LC circuit operate
at very high frequency,
hopefully at optical frequency.
That give rise of really
interesting magnetic dispersion.
And this bottom curve shows the frequency
and the phase advance or k.
This the dispersion
where two magnetic mode
are show up here.
In between, there's a magnetic
band gap, these materials.
It means that any electromagnetic
wave or optic wave
if their frequency fall
into this shaded area,
cannot travel, which in other words,
their mu is negative.
The magnetic permeability
is negative over here.
Okay, they decay in this frequency.
So we take the other stripe,
which is 90 degree perpendicular,
a little bit different, similar structure.
And for the same optic beam
coming from the bottom,
now this response for
the electrical field,
which is parallel to this,
and this is actually
effectively is a diluting metal
because each of the layer's
thickness is much smaller
than wavelengths of concern.
So for optic wave, you view
this as effective media.
And for diluted metal, you
can shift the plasma frequency
to a longer or shorter,
a smaller frequency
that match with the magnetic band here.
Therefore, below this plasma frequency,
epsilon, the electrical
permeability is elected.
So we have these two
shaded area, epsilon mu,
respectively are elected.
Now, what we are looking for
is they are simultaneously
elected in this overlap
of frequency of the range.
When you have both of
these going to negative,
and this optic index of
refraction should go to negative.
So, this is exactly happened
when we combined these two
structure together, we have
so-called fishnet structure.
It's like fishnet, right.
And indeed, actually you
see though individually
these two structure prevent optic wave
are propagating through this structure.
But if you combine them
together, they allowed
actually wave propagate.
So there's a mode actually
exist in such optical band.
But not only exist, but also
if you look at their slope,
it's negative slope.
It means that energy travels this way.
Momentum travels the other way.
They are opposite in 180 degree.
Opposite direction.
So that is where the negative refraction
because the negative
index refraction is about
the phase index.
So we decide to make this structure.
This was made in the microlab here,
used to be in the, I
think, 2008 we moved here.
I think so, right.
So but anyway, either
in Corey Hall or here
that we deposit multilayer of
silver and magnesium fluoride.
Each layer is about 30, 50 nanometers.
And then after many layers application,
this is standard
semi-conductor fabrication,
then we use a cutting tool.
There's a special cutting tool
so-called focused ion beam.
It's like mechanical cutting
where this beam can be focused
to five nanometers.
And you come in and cut the square hole
like as the design.
So this is a design.
This is a fabricated structure.
And this square hole, if
you look at more carefully,
each of the layers of metal, dielectric,
metal, dielectric alternating,
as you can see here.
Now, if everything's
right, designed by theory,
this should give us a
negative index of refraction.
If we shoot beam from the bottom,
they will refract in negative angle.
So we want to do a high
school type of experiment
to shape this into a wedge.
This is a slab of material.
We believe this should
have a negative index.
We shape it into--
We use the same actually
cutting tool to shape it
into a small angle.
And by the way, we are so grateful
for the microfabrication
facility here that
which is wonderful facility and I believe
this also really was
the Kuh's former student
actually made contributions
to this building.
So we are very grateful.
This enabled us to measure the--
We're the first to actually
match index materials
in the both media where we make a prism.
The index of refraction
along the vertical direction
should be negative.
So we shoot beam from the bottom.
Now, then we watch it with a camera here.
If they are refract on this
side of the lamina line,
perpendicular to this,
if this wave come out
from this side, will be positive.
If wave come out from the
other side, will be negative.
So we basically record where the spot is
and determine that is basically
all the high school kids
probably do the same thing for
refractive index measurement.
So we measure how this spot
moved as a control experiment.
We just have a window
here without the prism.
As you can see, when we
changed the wavelengths,
the spot doesn't change.
It's just vertical passing through.
But with this prism,
which we believe contains
negative index of
refraction, this spot moves.
And we plot all the
positions and convert that
into a refraction index.
And this is the plot where
this is a index of refraction.
This is the wavelengths.
Now this materials has a dispersion.
Therefore, show the
different index of refraction
at different frequency of
our wavelengths or colors.
As you can see, actually at 1.7 micron,
this index can be indeed
minus one, minus one
where what does that mean.
It means actually that
energy travels this way.
Momentum travels backward.
But interesting, not only we
realize the negative index,
but also at 1.5 micron of the wavelengths
which is a telecommunication wavelengths,
by the way that's how our
internet are operated.
And this index is a zero.
What does a zero mean?
It means that the optic wave happen
through a finite distance
doesn't need actually
a time in terms of
phase, in terms of phase.
Now the phase speed in this case,
in this wavelength is infinite.
Might be some students
that say well wait a minute
Einstein say the phase, that
light speed is the limit.
But this is the phase speed,
it's not energy travels speed.
So there's a difference, okay.
The phase speed is essentially
when you throw a stone in the pond,
the ripples propagate out.
And that's the front, a phase front.
That is equivalent to that.
And in addition, there's
interesting phenomena
we observed here where the
index actually is not one.
All the nature materials
should be above one
because air and the
vacuum are defined by one.
Nothing below that.
But we observed that something .5 or .7,
that's even, you know, faster
than what travels in vacuum.
So that is also very interesting.
But anyhow, I want to show this video
and how that works.
So wave coming from the
bottom of the plane wave
and travels through this prism.
And when they actually at 1.2
microns is a positive index,
but less than one, by the way.
So wave front actually is in the left side
of the white line, which is
lamina of the exit plane.
And if you look at the electric field
and the magnetic field, they
travel indeed from bottom up.
You look at the wave front is going up.
And therefore, the energy
and momentum does travel
in the same direction
from bottom to the top.
Now if we switch to longer wavelengths,
where index of refraction
of this media are negative,
then what we see here,
the wave fronts skew much
toward the other side and we indeed
have the wave front become negative.
And if you look at the wave front travels
in the magnified structures here.
And we see the wave front of the phase
actually travels backwards.
While energy travel from bottom to up,
the phase travels backward.
Indeed, this verify they travels,
energy momentum travels
opposite direction.
So, you may say well
what is this used for?
Well, I'm going to show you
quickly the two examples.
One is actually this indeed
can beat the diffraction limit,
if everything works right.
And so this is the cartoon I already show.
And we haven't reached the DNA level yet.
It takes much longer
time, but we have actually
a very long project actually here,
next four or five years,
funded by Moore Foundation,
to pursue this so-called supermicroscope.
So what's a problem of diffraction limit?
Well, the resolution of optical
lenses, include our eye,
has a certain limit.
So Mr. Ernst Abbe in 18th century,
he pointed out when he use
a lens to image object,
you know, here, whether your
eye or your camera here,
when you image two dots together,
you bring these two dots
closer and closer.
At certain point, their
image merge together.
You cannot resolve them successfully.
And that is inherent limitation,
so-called diffraction limit.
And typically, this distance
between the two dots
are about, you know,
half of the wavelengths.
Now, if some of us biologists
here say, wait a minute,
we can resolve 30 nanometer today.
And we can turn molecular,
two moleculars next to each other,
one green and one red at a different time.
But physics here says at the
same time, simultaneously.
You have to resolve them simultaneously.
Of course, if you resolve
them at different times,
that's possible.
So, what's wrong with a positive index
of the nature material
made with glass or eyeball,
which largely is water in the eye, right.
So I want to go to mathematics.
Basically, if the index is positive,
epsilon mu are positive,
where you have--
When you do imaging, essentially it's
for a transfer process while I look at you
because the light's,
you know, shining on you
and scatter off from your face
and my eyes is like
lens capture your image
on the back side of the eye.
Then I say oh I see you.
So there things actually two
type of information I can see.
One is so-called propagating wave
where the k factor are small.
It means that respond
something pretty big on your
face, your eyeball, your
nose, and which I can see.
Now, there's some biologic
cells, which if I use microscope,
I can see.
But, however, the things inside of cell,
let's say proteins, anatomy
here are even smaller,
I cannot see because those are responding
very small features I
correspond very high k factor.
Now for us the kz, because
this our conservation of k
compared with omega over c.
So kz become immeasure,
if this kx, ky is too big.
That is, if you plug
in this mathematically
into the propagating wave,
this two imagery part
become negative sign.
It means this wave is decaying in space.
And typically, these are
so-called evanescent wave,
you do not collect them.
So imaging with a positive
lens is always imperfect.
You only collect maybe 98%, 99%,
but there's 1% of details
you don't capture.
That is beyond diffraction limit.
And that is why there's actually a minimum
we can resolve that is
fraction of wavelengths.
But, Mr. Pendry actually
in this theory paper
pointed out that if you
have piece of media,
at that time we don't
have that yet in 2000,
and if index is negative, you
can excite this decaying wave,
or lost treasure of
information, very fine details,
you can excite it actually
surface resonance.
In that condition, you
may actually reconstruct
the amplitude of such a wave.
And of course, this
enhancement or amplification
will decay again in the positive
space in vacuum or in air.
And but before that decay too
much, you can collect them
in the image plane.
So you can actually recover or
capture those lost treasures.
But this doesn't violate
energy or conservation.
I will probably, if I have time,
I can answer some questions.
But anyway, that through
some mathematical operations,
he show that this indeed possible.
And soon actually, my student, Nick Fang,
used a simulation indeed
to show you can resolve
two nanowires space at 60 or 80 nanometers
and you can have their image capture.
Theoretically, this was calculation.
And experiment took us
quite a bit of time.
This was maybe one of the
first paper I published
after move to Berkeley.
And essentially we have
a nanoscopic object,
which are nanowires.
Or you can use a FIB, focused
ion beam, to write a nano,
which is a width of 40,
50 nanometers width.
And through a superslab,
their epsilon can be negative
at UV frequency.
Therefore, this is a poor man's superlens
because in 2003, 2004 we don't
have negative index materials
until later on.
So we use actually, but
the physics shows the same,
if they are at electrostatic limit.
Therefore, we used this
photoresist to record image
on the other side.
So think about this blue
silver slab as a lens,
so-called poor man's superlens.
It's not negative index,
but show the same effect
because epsilom is
negative, except mu is not.
If you operate at near field
or at electrostatic limit,
that the physics is the same.
So we capture, indeed, we resolved
the 68 nanometer nanowires.
And Nick's group, Nick is
now full professor at MIT
and his group actually further pushed on
to 30 nanometer wires, as you can see.
This is image at his group.
And later on, we project this
image even to the far field,
which I'm not going to go
detail with you to time.
But anyway, idea is can you
make a scope, microscope,
now we can call nanoscope,
indeed go beyond
much smaller than diffraction limit.
So this is a project we
are ongoing right now
and actually we are in Phase Two,
funded by the Moore Foundation.
And this, we just begin the
Phase Two here at Berkeley.
And let me show you the other
interesting application,
(laughter)
which is everybody knows
that Harry Potter's story.
But, I have to say it
still takes a long time
to make a practical devices,
but we're getting, you know, step by step.
So I borrow a few slides from
my collaborator, John Pendry,
from Imperial College, where
this is very interesting
for Peter Pan.
He likes Peter Pan.
Now Peter Pan is here and you
can make Peter Pan disappear,
just paint it black.
But black is not invisible,
because you see the shadows.
Right?
So that's not good.
What really he views
that if you can make 75%,
25% of image lost, and
50%, and totally lost.
So you see his body is transparent.
That would be cool.
If he can, you know, wear something.
A cloak.
So, what this require in physics.
It requires actually a
blue color cloak here
that has a very special property.
Let's say the light travels
from left to the right.
And like water, you know,
passing through a rock here.
We want to put things, want
to hide in the orange area.
So this is the area to hide your object
and this is a cloak.
And this travels in the air.
Now the light travels around it,
usually will bring the different phases.
Therefore, by looking
at the phase difference,
you will see the fringes
and you say, oh I see you.
Or I see the ripples of
the water after rock.
I see there's something,
you know, disruptive there.
But the idea is to make this
flow of light, or water,
seamlessly where when they come out,
they are the same phase as
travel outside in the air.
So then, for the downstream
observer, if you look at
that water or light view,
nothing happened, okay.
It's like stream of the light.
So you have to make light
travels here faster,
because it travels
larger distance compared
with straight line, right.
How you make it faster, remember,
when the index is less is
less than one, less than air,
you make it faster.
So that's why you need
meta-material to do these tricks.
And this is a simulation to show
after the plane width comes
in, plane width come out
and everything reconstructed.
For the downstream
observer, nothing happened.
They see oh there's nothing there.
So in this theoretical
paper, this even earlier,
that Pendry and his student proposed that,
I won't go to theory where how
you construct such a cloak,
so he give a theoretical
blueprint for how you construct
such a cloak.
Essentially, you have to
relaminize the uniform space
in air or in water that you can the space
make the light, make it curve trajectory.
Due to the time, I will go faster.
So, again, it's very hard
to make such a cloak.
The first cloak, was made
by Dave Smith in Duke,
where they make a microwave cloak.
Because microwaves is bigger, as I say,
well all the atoms are centimeter in size,
so you can trick things,
even two machines actually.
So the idea is to make the mu
along the tangential
direction is constant,
but along the radial direction
is almost linear dependence,
less than one.
So that's the idea, okay.
So as you can see, they
indeed make a cloak
and experiment shows
that it's pretty good,
but there's a little shadows cast still.
This is, you know,
experiment imperfection.
We think about how we
make optic ray invisible.
So one of the skin we
use is the carbon cloak.
Imagine this is a carpet.
Somehow, hid in store, there
is a bump in the carpet.
So we can see the bump is pretty big.
You can see it.
The question is, can we hide it?
Well you can construct something
above that and hide it.
So, the idea is to
transform mathematically
a physical space into a virtual space,
which to the observer is a flat.
You don't see the carpet bump.
So mathematically, we can
describe a cloak design
in such a way their permittivity, epsilon,
can be varied in the space.
Therefore, when the light comes in,
they will route it around
this hided area, this bumps,
and come out and see if they
reflective from a flat mirror,
flat mirror or flat surface.
So you make bump disappear.
And this is indeed possible.
So we start experiment testing this idea.
We use optic wave guide.
This is quite common so-called
SOI wafer, silicon insulator,
where it's a guided
wave and we drill holes,
drill nanoscopic holes, many holes,
but we vary the hole distance
by this mathematical design.
Therefore, this rectangular is the cloak,
this green area is the
things you want to hide,
put it here, 'kay.
Now the whole thing is quite small.
It's a few microns.
Well this area is about 5
microns, but this area probably
is about 1500 microns.
So this is a cloak we fabricate, again,
in the microfabrication facility here.
And this is more zoom
in where the cloak shows
this is where area you
want to hide things,
very small at the time.
We can only hide
biological cells probably.
But this is demonstration of idea.
And we drill holes, therefore,
we vary effective index,
effective epsilon in the media.
So the light comes in the
wave guide, come in here,
everything travel in the
plane, in the two-dimensional,
and bounce off from here
and we observe here.
Now if there's bump, this
bump is a few microns
so if there's bump you
will see the scattering.
There's something there.
That's how we see each other.
But if we can hide it
with this successfully,
with this cloak, then
you will see reflected
from a flat mirror.
So this experiment, indeed.
So this is the mirror.
We shine in light here, bounce off,
you will see an nice caution
beam, nothing happened.
Now, if there is a bump here,
which are larger than
wavelengths, of course,
you will see the scattering.
That's why we experimentally can see,
okay, there's something there.
But we put the cloak on this bump, 'kay,
and when light hits
here, the cloak actually
make the function, make
the light route it around.
I'll see if that reflected
light coming from a flat mirror.
Nothing there.
Well, of course, this not only has to work
at 45 degree, at any angles
because if I cannot see it
from any angles, that's a cloak.
So, this video shows how cloak works.
I have time to basically.
So when the light comes
in, there's no cloak,
you see the scattering of the light.
There's a shadow cast.
Observer will see oh there's something.
But when I turn on the cloak,
when I turn on the cloak,
everything emerged as a single beam,
as if nothing happened.
But maybe I move onto next
one is more interesting.
Now that cloak is very
small we made in Berkeley,
but it's the first optical cloak.
Five or six years later,
a group in Singapore
make much bigger.
And in this case, actually
they try to cloak a fish.
This is the, well, let me show you here.
This is tank of water.
Inside there's a hexagonal cloak here.
And there's a hole.
The fish can get into the hole of the--
you can view this as a cloak
and the fish get into the hole.
Now there's grass around behind it
and then observer in front of it.
Now, if nothing happened,
you will see nothing
and you see the background.
If fish get in there, it
can make the fish disappear.
So let me show you the video,
which is published 2003.
So there's a fish there already.
You see the tails?
Here.
But is hiding that hole right now.
They try to get the fish out.
Now the head is out.
And they try to, I think,
hole is not too big
so they're somewhat stuck there
(laughter)
and they try to
think they try to shake the water
to get it out.
Think finally will be out.
So now they flow outside, right.
So there is a possibility.
But now if you look at this cloak,
my son told me that daddy, this no fun.
If I want to hide myself,
and he joked that he want
rob the bank, you know,
he has to have a big cloak carry
and somebody can touch it.
Of course, it's a big object.
So idea was can you make
cloak as a skin cloak,
as like mask, really
very thin on your cover.
And indeed, a few year
later, a student post doc
made this actually so-called
skin cloak, very thin.
It's about 80 nanometers, essentially
and cover three-dimensional object.
And essentially this
is a conformal as well.
Now, you may say well,
besides this demonstration,
what is useful?
Well if you think about we
can make something disappear,
we can make something appear as well,
if you do reverse thing.
So actually we're actively working on,
for example, how we use this technology
for so-called augmented reality.
Most of you young student
knows that the virtual reality
is most for games, but augmented reality
there's a lot of positive.
For example, trained doctors
with augmented reality
where you can see through
CT, stored images.
You can touch the surface
and you see through
a three-dimensional images automatically.
So you can project a
three-dimensional image as well
and use cloaking to
mask whatever over there
and you project a new
image on top of that.
With that, last slide, I
want to specifically thank
Endowment of Ernest Kuh Chair
that because I wasn't funded
by any other funding agency at the time.
And we, my student and post doc,
we study some very fundamental issues
of how we can break the time
transformation symmetry.
So in this paper, published
in 2012, independently
MIT group Frank Wilczek also published.
We published back-to-back independently,
proposed to call time crystal,
where you can break the time symmetry,
make a time condensate.
We know that history is the river of time
and usually even quantum mechanics,
we don't condensate time.
It's E I omega T.
T's always continuous.
But in real crystal, as we know,
the atom sits in periodically.
Now we can make it time
sits periodically as well.
And this theory was actually realized
by experiment by Maryland
group five year later.
And I like to acknowledge
all the students,
this is older slides, but
some of them already left,
but these are former student contribute
over the last 10 or 15
years work here at Berkeley.
And many of them are on faculty
at various of university.
Thank you.
(applause)
Yes.
- Okay, we'd like to
invite a few questions
from the audience and give
first preference to students.
There's some microphones there.
- How do you
- Please name, major.
(talking in background)
- How do you see these
meta-materials becoming,
like do you think we'll
be able to scale them
and mass produce them and
maybe everyone can have
invisibility cloaks in the future?
Or do you think it'll be
really difficult to make
a lot of these in the future?
- That's great question.
We haven't done that here at Berkeley,
but one of my former post doc
now in University of Colorado,
he's a professor there, they are doing
a row-to-row actually.
He showed one of the, I saw
the news that 10 feet actually
of those materials.
That is for different
application actually.
Meta-materials now, he's
using to start a company
for radiative cooling,
basically air-conditioning
without electricity.
I don't know the efficiency of
that, but sounds pretty cool.
In principle, the
meta-material actually can do,
so he show experiment and
manufacturing of that.
And his lab is five ton
of machine that row-to-row
to make those sheets of plastics
with some particles inside
where they can do 10 degree of
cooling without electricity.
- Professor Jone from Science Department.
So the question about evanescent waves.
So you said that you put
a superlens over there
and that you invented
some way you're gonna
increase in magnitude.
So where does the energy come from?
- Right, that's a great question.
I tried, I don't have time to
cover it, but great question.
Evanescence wave compare
with the propagating wave.
Propagating wave does carry
the energy forward, okay,
or backward if you, depend on direction.
Evanescence with you actually
plug in that 2 I cancel out.
So they do not actually, you know,
if you look at, it's
oscillating field in same place.
They don't even have a phase difference.
So the field is oscillating field,
doesn't propagate the energy,
that's why you essentially
use these two resonance on the surface,
redistribute the field in the space.
So therefore, you do
not actually gain energy
or lost energy, rather
it's like a, you know,
you make everybody's head raise the same.
Essentially it's a redistribution
of the energy essentially.
Because evanescent it doesn't
carry the energy forward.
- Hi, Professor Zhang.
I'm from Gru Rall Press Group.
So and I have a question
that from your presentation.
It looks like the way you
pursue the meta-materials
like the way you chase, you
increasing the frequency.
And it looks like you
started from long wavelengths
into the optical wavelengths and
also you actually managed to
fabricate the meta-material
in the optical frequency.
Then the question comes
then can you point out
or one of your colleagues
may be working on
that what would be the next
thing for meta-materials?
'Cause the wavelengths-wise,
optic wavelengths
is already that highest event.
Maybe either from other
field that we can explore?
That's my question.
- Yes, I think of course
a lot of people now
make living this field.
So they have to find something.
So one I
(laughter)
want to say that there's
many applications right now.
Even the scientific part
hasn't really explore yet.
For example, symmetry
is a one big deal here.
We already showed there is
a certain symmetries even.
Professor Flemming here
is here that, you know,
the chemistry try to make a
molecule different symmetry.
Mobile symmetry is very
hard to make in molecules,
but here actually we can use this to show
really the symmetry breaking
and very sort of interesting
material properties that do not exist in
or very hard to achieve
in nature materials.
So but then applications, of
course, there are various of.
For example, their group across
Baylaw in the other college,
you know Crosby and
they're look at, you know,
scanners for the lidar, for example.
We are also actively looking that.
So there are various of augmented reality
is a big thing actually now.
This gives you a possibility to, you know,
look at can you project your, you know,
watch into a three-dimensional pictures.
Things like that.
(speaks too softly for mic)
- That's what my former post-doc.
You know, he's making
actually this meters long
plastic has specific particles there.
They measured about 10
degree cooling down actually.
Without electricity.
- So Xiang, this has been a
fascinating afternoon here.
And a, you know, I wanted to say,
you know some other friends of the college
have endowed a, Cher-wong and Wen-She,
who endowed a sort of wives
center for augmented reality.
- Okay.
- Actually in Corey Hall.
So when you've had enough of Hong Kong.
- Right (laughs).
- We could use you to do
some augmented reality.
- I also be the augmented
reality over there too.
(laughter)
- Anyhow, this is really
fascinating, you know,
scope of your creativity here.
So on behalf of the college,
actually the students
will present you with a small remembrance
of today's event.
We recognize our deep
appreciation for your commitment
to engineering innovation.
Thank you very much.
And go ahead and pose.
(applause)
- Thank you.
Thank you.
Thank you.
- Thank you also.
We can also give you a polo shirt.
(laughter)
Thank you also to our co-host,
the American Society of
Mechanical Engineering
and especially to Bettine and Ernie Kuh
for making this
outstanding forum possible.
Thank you all for being with us today
and go Bears!
(applause)
- Thank you.
Thank you very much.
