Awardee Interviews | Howard A. Padmore - 2013 Albert Nerken Award - Interview

Howard A. Padmore

2013 Albert Nerken Award Winner

October 30, 2013
 
HOLLOWAY:  Good afternoon.  My name is Paul Holloway.  I’m a member of the American Vacuum Society History Committee.  Today is Wednesday, October 30, 2013, and we’re at the 60th annual International Symposium of the AVS in Long Beach, California.  Today I have the pleasure of interviewing Howard A. Padmore from Lawrence Berkeley Laboratory, who is the 2013 Albert Nerken Award winner.  His citation reads: “For sustained contributions to the design, development, and application of novel synchrotron x-ray instrumentation used to study a range of scientific problems from biology to materials and solid state science.”  So congratulations, Howard, on the award.
 
PADMORE:  Thank you.
 
HOLLOWAY:  Could we start by you giving me your date and place of birth?
 
PADMORE:  Okay.  I was born July 31, 1956 in the United Kingdom in a place on the coast called Blackpool.
 
HOLLOWAY:  Blackpool, U.K.?
 
PADMORE:  Blackpool, U.K. in the north of England.
 
HOLLOWAY:  In the north of England.  Not the south of England.  [Laughs]  Your accent says north England, doesn't it?
 
PADMORE:  Yes. It’s near Manchester and Liverpool, which are the closest big cities that people would recognize.
 
HOLLOWAY:  I see.  Good.  Could we continue by you telling us a little bit about your educational background starting as early as you would like.
 
PADMORE:  .  It depends how far you want to go back, but in terms of important landmarks, I went to a classics grammer school.  I guess this was what people here call middle school to high school.  So the center of the school was teaching Greek and Latin and classics.  If you didn’t particularly like doing these things, you could do science, and if you didn’t like doing science, you could always do engineering.  As the years went by, I graduated towards sciences and math, which I was good at, and then ultimately engineering.  So I left that school at age 16 and then went to what in England is called a technical college to do engineering with the intent of doing engineering at university.  After two years of a very interesting life doing engineering where I found a real vocation, I think, and introduced me to making instruments, I went to university to do physics, but physics with a very large component of experimental work in it.  I stayed at the same university to do then my Ph.D., and also my first post-doc was done at the same institution as well.
 
HOLLOWAY:  What institution was that?
 
PADMORE:  That was Leicester University in the midlands of England.
 
HOLLOWAY:  What year did you receive your degrees?
 
PADMORE:  ’77 for my bachelor’s degree and ’83 for my Ph.D..
 
HOLLOWAY:  Okay.  Good.  So you stayed as a post-doc in that same university.
 
PADMORE:  Yes. 
 
HOLLOWAY:  For one year or for…
 
PADMORE:  It was actually two years, but none of the work as a post-doc was actually at the University because I by then had been introduced to the wonders of synchrotron radiation.  In the University, I’d been doing x-ray experiments, and then I’d realized that these things called synchrotrons were a million times more powerful than what you could do in your own laboratory.  So I joined a group which was one of the pioneering groups in synchrotron radiation and then was sent to a synchrotron in the North of England called Daresbury where I spent the first 11 years of my professional career.
 
HOLLOWAY:  What did you study for your Ph.D. dissertation?
 
PADMORE:  So my Ph.D. dissertation was on something which has become quite trendy now which was  very new then which was doing x-ray emission spectroscopy.  This involved  hitting a target with electrons and then looking at the energy of the soft x-ray photons coming out of the material.  In my case, the materials were the heavy rare earths—so ytterbium, erbium, and thulium, fairly exotic rare earth elements and their oxides and other compounds.
 
HOLLOWAY:  Did you have a mentor that you worked with during this?
 
PADMORE:  I had a wonderful mentor.  There have been a few people in my career that I can point to as being very influential.  My mentor was a guy called Ted Wilson, who has now been dead many years.  He wasn’t a particularly successful scientist in terms of publication output, but he was one of the most creative experimental scientists that I’ve ever known.  He had the advantage of never having too much money to do his experiments, and so we had to build everything ourselves.  In England, we have these wonderful things called Army Navy surplus stores, and any power supply, electronics, whatever we needed, I would go to the Army Navy store, get a close approximation to what I needed, bring it back to the lab, and then build it into the new system.  It was a wonderful way to work.  You don’t accept the instrumentation which is given to you.  You build all of the instrumentation.  It  was painfully slow, but it was just a wonderful learning experience.  I was learning at the feet of a real master who really understood everything in how do do difficult measurements.
 
HOLLOWAY:  That’s wonderful.  So you did the heavy metals x-ray spectroscopy for your dissertation.
 
PADMORE:  Yes.
 
HOLLOWAY:  Then did you continue that work at Daresbury?
 
PADMORE:  No.  I joined  an adjacent group in the department. I was doing x-ray work, and I would go to seminars to learn about other research…  A group in the same physics department was one of the pioneering groups in using synchrotron radiation to study the electronic structure of materials—using photoelectron spectroscopy.  This was the group of Colin Norris, and he had a very good reputation as a very imaginative experimenter.  It was really the pioneering days of synchrotron radiation.  So I got a post-doc position with him to do photoelectron spectroscopy on the synchrotron, and the subject area was looking at the electronic structure of two-dimensional magnetic systems—things like manganese, cobalt, iron as a single monolayer deposited on some unreactive surface like silver.
 
HOLLOWAY:  So you had to work in ultra-high vacuum to accomplish that.
 
PADMORE:  Yes.  That was a shock and a change.  [Laughs]  I was introduced to the joys of baking chambers during that post-doc and all of the problems of ultra-high vacuum technology, but it was a real learning experience.  One of the important things in this part of my career was that when I went to the Daresbury synchrotron, I was shown to the beamline which transports the x-rays to your experiment, and there was no beamline.  It was in a box.  Again, to do experiments I ended up having to build everything.  In  a sense it was a wasteful enterprise in that I should have been doing surface science, but I ended up doing a lot of x-ray optics and a lot of instrumentation which really stood me in good stead for everything I did later.
 
HOLLOWAY:  So how long did it take you to build this system up?
 
PADMORE:  Something like two years, two to three years to get real results.  It was a labor of love.
 
HOLLOWAY:  It had to be a labor of love and frustrating at times for you.
 
PADMORE:  It was frustrating, but it was a very exciting environment.  The synchrotron was late by a couple of years so that we only missed of the order of a year.
 
HOLLOWAY:  So your schedules worked together then>
 
PADMORE:  It worked reasonably well.  But it was a wonderful time because no one in that era really truly knew that much about what they were doing.  It was a pioneering time in the sense there were no books written on the subject, and you really had to experiment and find out the best ways to do things.  That to me is the essence of science.  It’s doing things which are completely unknown.  You can’t go to a book.  This is, for me, the real enjoyment; trying to make things up, making mistakes, going back, and eventually getting to the right solution.  It’s the journey, not the destination.
 
HOLLOWAY:  Yeah.  What was the maximum energy and the brightness of the Daresbury accelerator?
 
PADMORE:  So the brightness was about seven orders of magnitude lower than the sources that we have today.
 
HOLLOWAY:  Is that right?
 
PADMORE:  Yes.  For example, the size of the source of light in the synchrotron in the early days of Daresbury was over a centimeter by 5 millimeters, and in the Advanced Light Source where I work today, the vertical beam size is about 10 microns, and it’s about 50 microns wide.  So it’s less than the size of a human hair vertically and about the size of a human hair horizontally.  I find it amazing that accelerator physics, physicists, and engineers have made such enormous progress over the years.  But on my side of the house, that’s given us also enormous challenges to build instrumentation, particularly optics, x-ray optics, to preserve the brightness and to use all of the brightness to do really challenging experiments.
 
HOLLOWAY:  So what does the size of the beam allow you to do now that the large beam prevented you from doing before?
 
PADMORE:  Well, essentially in that era which is called the second generation era of synchrotron radiation, all of the experiments were macroscopic.  Those were measurements which were done on samples which at least had a square millimeter area.
 
HOLLOWAY:  I see.
 
PADMORE:  Things which we did painfully on square millimeter areas taking weeks of time we can now do in minutes on areas which might be 10 nanometers.  So what  brightness gives you in an x-ray beam is the ability to do experiments on a much, much smaller size scale.
 
HOLLOWAY:  Now these beams are usually polarized as well.  Is that true?
 
PADMORE:  Yes.
 
HOLLOWAY:  And bunched in time.
 
PADMORE:  They’re polarized.  In fact, now, unlike the early days, we have complete control of tunability, complete control of energy, complete control of everything to do with a beam.  Very different to the original pioneering days of synchrotron radiation where you accepted what came out of the pipe.
 
HOLLOWAY:  So you stayed at Daresbury for 11 years, I believe you said.
 
PADMORE:  I stayed at Daresbury for 11 years, and it was clear at that point that other more advanced machines were really going to put places like Daresbury out of business, and there was no plan at that stage to replace Daresbury with a better machine.  The U.K. did not want to make that investment at that time.  Later on they did, and they now have a wonderful storage ring called Diamond in Oxford.  But at the time, after 11 years it was clear that across the Atlantic would be much more exciting.  I got offered a position in Berkeley to lead the experimental group at the Advanced Light Source.
 
HOLLOWAY:  Let me take you back just a minute and ask the question.  You know, you were there for 11 years.  For two years, you were building the system.  What did you do after you got the system?  You applied it to a number of different materials problems, for example?
 
PADMORE:  Well, the systems which I worked on originally were all magnetic—I continued this theme of research with the Norris group, which was looking at in general low-dimensional systems, meaning systems in which atoms could arrange themselves into a single monolayer, and the electronic structure of that monolayer was very different from the structure of a bulk material.  So in our case, we were looking at nominally magnetic materials like iron or manganese which in low dimensions, in two dimensions, became nonmagnetic.  So all of that early work was photoemission. Then I was asked to start a group in soft x-ray spectroscopy.  Again, in that group, we focused on looking at magnetic materials initially.  You can use x-ray spectroscopy for a huge variety of different measurements, so it’s hard to pin one down.  So we looked at the chemical structure of polymers, the chemical structure of rocks, the chemical structure of many, many different types of materials, and also the magnetic structure of more complex materials.
 
HOLLOWAY:  So you had people coming in from Europe and from— 
 
PADMORE:  Yes.  These synchrotron facilities are essentially photon factories.  Our job is to primarily provide tunable x-ray photons, and our users come from all around the world.  So my job was to run a group to make sure that the users had successful experiments, and really my internal research in those years was focused on improving the instrumentation—so initially making better electron spectrometers.  We made one of the first multi-channel electron detectors for angle-resolved photoemission.  I spent a lot of time theoretically and experimentally making new designs of x-ray and soft x-ray monochromators and in general improving the instrumentation infrastructure so that we could do more advanced experiments.
 
HOLLOWAY:  Now you had to have a cathode that generated the electrons to inject into the storage ring and start the cycle?
 
PADMORE:  So in storage rings there’s not really a cathode problem.  The cathodes in most storage rings are simply a filament like in a light bulb.
 
HOLLOWAY:  I see.
 
PADMORE:  That is a bright enough source when you’ve compressed it.  With various electron optics, it’s a bright enough source for the storage ring.  Where there are problems with photocathodes in light source design is in free-electron lasers because you have to pack a very, large number of electrons into a very small space, lateral space and space in time.
 
HOLLOWAY:  Okay.  So you left in 1993 for the Advanced Light Source in Berkeley.
 
PADMORE:  Yes.
 
HOLLOWAY:  And you’ve been there ever since.
 
PADMORE:  I’ve been happily there ever since, 20 years.

HOLLOWAY:  You were in charge of construction of a light source or…?
 
PADMORE:  When I went to Berkeley in ’93, I arrived in April and the storage ring itself started to work shortly afterwards.  But this facility, which in those days cost $100 million, actually had only one beamline on the first day of operation.  So my job for a large number of years was simply to build up the instrumentation: build up all the beamlines, build end stations so that we had a reasonable number of working beamlines and we could accommodate a reasonable number of users.  We built up from one beamline in ’93.  Now we have 45 beamlines which are all infinitely more complex than the original beamline.
 
HOLLOWAY:  Now I understand that there are plans for a generation two light source.
 
PADMORE:  Yes.  There are two basic types of light source both in synchrotrons and in laser science.  We have CW sources and we have ultrafast pulsed sources.  So the ultrafast pulsed sources in the x-ray domain are free-electron lasers, and the CW sources or quasi-CW sources are the synchrotrons.  It was recently discovered by pioneering work in Sweden, which has now been followed by many other countries, that in the existing third generation synchrotrons, their brightness can be improved again by anywhere between a factor of 100 and 10,000 with new designed for the magnet lattice.  At  the Advanced Light Source, what this will mean if we are funded for this upgrade will mean that the x-ray source will be completely coherent.  It has complete transverse coherence up to the energy of several kilo electron volts, and that will be essentially the ultimate CW x-ray source.  Whereas the free-electron lasers are going to be the ultimate pulse sources, this further evolution of the third generation synchrotrons really will be a fantastic step forward for CW experiments
 
HOLLOWAY:  Now talking about steps forward, there have been advances in x-ray optics in multi-layer mirrors, the refractive or diffractive lenses.  Can you say something about that?
 
PADMORE:  I can.  I can with some surety because I was recently asked by the Department of Energy with a colleague in Argonne National Laboratory, Denny Mills, to chair a national workshop in x-ray optics basically looking at x-ray optics for light sources for the next ten years.  As of last week, we finally finished our hundred-page report.  Indeed, every year we can do more difficult experiments because the optics are getting more perfect.  In terms of their deviation from the correct optical surface, angular errors are a fraction of a microradian, and in terms of the absolute height errors, we can now have mirrors with height errors of something like a nanometer.  You’re talking of these errors on mirrors which might be a meter long.
 
HOLLOWAY:  Is that right?
 
PADMORE:  And with, in some cases, rather steep curvature.  And yet we can make them, or manufacturers can make them now fairly reliably to a precision of a nanometer, which I find quite incredible.
 
HOLLOWAY:  That is incredible.
 
PADMORE:  Other optics are constantly being developed—zone plate optics, which allows to microfocus or nanofocus down into the nanometer regime.  Again, when the first zone plates were made, they had resolutions of several thousand angstroms, but the state-of-the-art now is less than 100 angstroms, and that trend is going to continue.  Refractive lenses were invented probably about 25 years ago and again have advanced out of all recognition. Its very exciting that many of the techniques which have been used  in industry in disparate areas we can now use in x-ray optics.  We can make better zone plates, as a matter of fact, simply because microelectronics has advanced so much in the last 20 years.  So as microelectronics circuit designs through, say, EUV lithography are now going to sub 10 nanometer feature sizes , we can now make x-ray optics which have the same sorts of precision.  So the future is very, very bright indeed.  No pun intended.
 
HOLLOWAY:  You should intend to have a pun there.  That was a good pun.  What about diffractive optics, photon sieves?  Are they commonly used?
 
PADMORE:  By diffractive, what you mean, things like gratings.  Zone  plates are of course diffractive.
 
HOLLOWAY:  Well, zone plates you can have the…What am I trying to think of here?
 
PADMORE:  A zone plate is just another type of diffraction grating.  For monochromatization we use large area gratings.  Then you have other types of focusing optics based on refraction.
 
HOLLOWAY:  But you can have a photon sieve where you just have arrays of holes.
 
PADMORE:  The photon sieve was a nice idea, and it was published in Nature.  It was the work of aGerman group.  It doesn't seem to have gone anywhere, and one reason is that it’s less efficient than a regular zone plate.
 
HOLLOWAY:  Right.
 
PADMORE:  It got over a few of the technical problems that zone plates had at the time.  The paper was by Kipp, I think.  But now the manufacture of zone plates has overcome all of those problems, and we don’t need to do these exotic things like make photon sieves.  A photon sieve is basically a zone plate which has pieces missing.
 
HOLLOWAY:  Right.
 
PADMORE:  And we don’t need to have the pieces missing anymore.  We can make very highly accurate, efficient, complete zone plates.
 
HOLLOWAY:  I see.  So your emphasis is on the generation of the beam and the maintenance of the beam and the equipment necessary to do that.
 
PADMORE:  That’s true, although a thing I’ve learned in instrumentation is that you have to do science as well as the instrumentation.  You have to dip your toe in science so that you understand the trends which are important.  If you’re only an instrumentation person, I think that you tend to end up doing instrumentation on things which may not be particularly important.  So I to a certain extent try to combine science and instrumentation, but certainly focusing on the instrumentation.
 
HOLLOWAY:  So what sort of science are you emphasizing right now?  What do you see it being important towards?
 
PADMORE:  Well, of course there is science in instrumentation by itself.  I want to emphasize that.
 
HOLLOWAY:  I see.  Yes.
 
PADMORE:  One of the subjects which I work on is ultra-high-resolution gratings, and the end goal of this is basically to do the x-ray version of Raman scattering.  This will require us to develop the resolution of gratings from what it is now, a resolving power of 104 to a resolving power of, say, 106.  There’s a lot of surface science in this work as an example, in how to create these near atomically perfect gratings.  There’s a lot of science in how some liquids anisotropically etch silicon, to create the facets of the grating.  There’s a lot of deposition science in all of the steps that we need to create these 3d optics.  So I’m always amazed that although we’re working on pure instrumentation projects, these always lead into really, really interesting scientific questions.
 
HOLLOWAY:  Now most of it you do, you apply your machine to inorganic compound materials or…?
 
PADMORE:  No.  Across the board.
 
HOLLOWAY:  Organic and inorganic.

PADMORE:  Everything.  One of the major activities, or a third of the activity at the Advanced Light  Source is looking at the atomic structure of proteins—so very organic.  The other end is doing things like EUV lithography for making next generation micro chips or is looking at the electronic structure of topological insulators or the electronic structure of high temperature superconductors, looking at dust which came back from a comet on the Stardust mission.  One of the wonderful things about synchrotron science is that we’re constantly introduced to a very, very wide range of science.
 
HOLLOWAY:  What about microscopy?  You can use it for microscopy.
 
PADMORE:  Well, one of the benefits of having high brightness is that you can take the x-ray flux and you can focus it down to very small size, so doing microscopy goes hand-in-hand with high brightness sources.
 
HOLLOWAY:  So if you focus it down, do you scan the beam across or you move the sample or what— 
 
PADMORE:  We can do either, and we can also now do a technique which was pioneered in England by a John Rodenburg which is called ptychography, in which you create a relatively small spot of light using optics, and then you simply record the diffraction pattern.  From the diffraction pattern, you can reconstruct the real space image at very high resolution.  Zone plates are limited to a resolution given by the outer zone width, which is limited by lithographic precision.  However, ptychography is not limited to anything like this.  It’s only limited by the wavelength of light and the numerical aperture.  So in recent work, we’ve demonstrated—this is my colleague David Shapiro who has led this—have demonstrated 3 nanometer resolution in x-ray microscopy, far beyond what you can do using simple lenses. .  If we can make this work routinely, it will openup a real new insight into the nano world.
 
HOLLOWAY:  Is this a result of working in near-field rather than far-field optics?
 
PADMORE:  This is actually far-field optics.  It’s not near-field.  Near-field is always very problematic experimentally, Inthis case it’s simply that you’re recording information not from the direct transmission of light through an object but from how the object diffracts.  Always in physics it’s been thought that if you only record the diffraction pattern, it’s impossible to get back to real space because you’ve lost phase information.  It was realized in 2000—there was a famous publication in Nature by Janos Kirtz  and colleagues that if he knew something about the object, like roughly the area in which it existed and outside that area you knew that it didn’t exist, with that prior knowledge, you could iteratively reconstruct phase, and therefore you could iteratively get back to real space.  So these are called lensless microscopies.  Ptychography is a form of robust lensless microscopy.
 
HOLLOWAY:  Now the other thing if you have a bright enough source you can do is time-resolved measurements, right?
 
PADMORE:  Yes.
 
HOLLOWAY:  What does that give you the ability to characterize?
 
PADMORE:  Some of my colleagues won’t like me for these comments, but time-resolved means different things to different people.  As a materials scientist, it means a completely different time domain to a chemist.  Time-resolved to a chemist means the time required for an electron to hop from a molecule to a molecule, which might be of the order of femtoseconds or hundreds of femtoseconds, or for slow reactions picoseconds.  But to a materials scientist, time-resolved might mean anything from hours down to milliseconds.  In biology, one of the frontiers is understanding how proteins assemble.  How proteins assemble is a diffusive process which happens very slowly on the time scale of milliseconds.  So we already do a huge amount of time-resolved work, but it’s not what I think a laser person would recognize as time-resolved work.  But I would claim that there is at least as much interest in slow dynamics today as there is in ultrafast dynamics.  Slow dynamics is important in life, in how nature works, in general.
 
HOLLOWAY:  Tell me about streak cameras.  I don't understand streak cameras.
 
PADMORE:  Streak cameras.
 
HOLLOWAY:  Could you give me an education in that area?
 
PADMORE:  Yes, I worked on streak cameras quite a bit with a wonderful experimentalist  at ALS called Jun Feng.  Essentially with a streak camera, what you do is first of all convert x-rays into electrons with a photocathode, one of my favorite subjects.  Once you have electrons of course, you can then manipulate them with electron optics so you can focus them, and you can also deflect them.  So in a simple streak camera, you focus the electron beam and then you have a pair of deflector plates essentially identical to the deflector plates in an old-style TV tube on which you put a very fast-changing voltage.  Typically  in our streak cameras, we sweep over, say, 100 volts in a few picoseconds.  That moves the beam on a detector, and so we are converting the intensity of x-rays in time into the intensity of light on a photodetector in space, by sweeping the electron beam in position.  So instead of having a  time axis, we have a position axis.  In principle, streak cameras are very simple things.  But because you’re trying to have a temporal resolution of picoseconds, there are complications.  For instance, making the electrical switch which allows you to ramp at a rate of many volts per picosecond is a non-trivial thing.
 
HOLLOWAY:  I think it would be non-trivial for sure.  What about photocathodes?  You said that’s one of your favorite subjects.  Tell me a little bit about photocathodes.
 
PADMORE:  Well, photocathodes are a core component in free-electron lasers.  They’re also a core component in doing ultrafast electron diffraction.  So if you want to do electron diffraction at sub-picosecond time scales, again the photocathode is one of the most important components.  When I started working on photocathodes about five or six years ago, photocathode physics was really a bit of a black art.  Not too much was really understood from a solid state physics point of view about what would make an ideal cathode.  So we started a program to look at the electronic structure of materials which would make good cathodes—so cathodes which would have very low energy spread and cathodes which would have high efficiency.  We have continued that work to today.  We’ve worked on metals, semiconductors and plasmonic cathodes.
 
HOLLOWAY:  What’s a plasmonic cathode?
 
PADMORE:  A plasmonic cathode—The metal cathode is very widely used today in many accelerators.  It’s today’s cathode.  Semiconductor cathodes have become practical now in real accelerators because the photoguns of real accelerators can now achieve really good ultrahigh vacuum.  The ultrahigh vacuum in our photogun as an example is better than the vacuum that one has in surface science systems in general.  We have partial pressures which are at 10-11 torr or lower.  So this means that you can use very delicate surface sensitive photocathodes.  So the photocathodes of today and tomorrow really are semiconductor photocathodes.  My blue sky sort of cathode is the plasmonic photocathode because if you introduce plasmonic interactions into a metal photocathode, it allows you to do new things which are not possible with regular cathodes.  One is to enhance the field of the optical light from the laser which is causing photoemission.  You can also use plasmonic elements to focus the electrons which come from a metal surface.  So much in the same way that radio frequency radiation is used to accelerate electrons in storage rings today or in a microwave tube in your microwave oven, tomorrow I believe that electron acceleration and electron manipulation will be done by optical fields on the nanoscale.  Again, it’s another handle that you can apply to this area which hasn’t existed up to this point.
 
HOLLOWAY:  Tell me a little bit about colleagues and mentors that you have at the Advanced Light Source and other synchrotron sources.
 
PADMORE:  Well, I told you about Ted Wilson, who was one of the most important mentors during my Ph.D.  Before that, my most important mentor by example, not through direct teaching, was my father.  My father was a teacher who in his spare time liked to dabble in electronics.  He was a self-taught electronics expert, and just through watching him I learned a lot.  He was also a chemical maniac in that he liked to experiment with all sorts of chemicals.  He was an alchemist!.  He liked to experiment with making materials and then demonstrate how they would react, make nasty smells or explode in various forms.  So he was a person that by observing  I could really get a flavor for what perhaps an experimental scientist might do in his lab at night!.  So those are very important people.  My colleagues in Berkeley; I work with some very wonderful people.  Do you want me to talk about specific individuals?
 
HOLLOWAY:  If you would like, please feel free to do so.
 
PADMORE:  Perhaps I’ll talk first about a guy called Jim Patel who died a few years ago.  He was an expert in the fracture of materials and in how defects propagate in semiconductors.  He was at Bell Labs for a long time.  He then retired and then came to my lab as my oldest post-doc.  When he came to my lab, he was about 72.  He was still doing the occasional night shift when we held a Festschrift for him on his 80th birthday.
 
HOLLOWAY:  Wow!
 
PADMORE:  He was a real inspiration.  Apart from being a very good scientist with a very good nose for interesting problems, he was a real inspiration in the way that he thought about science and in the way that he could inspire others.  At age 80, he was endlessly asking the question, “Why?”  “Why does this work like it does?  How can I do this?  How can I find this effect better?  How can I come to a theoretical understanding?”  Just constantly asking questions.  I found that a wonderful inspiration.
 
HOLLOWAY:  I often tell my students one of the most important characteristics you can demonstrate is curiosity.
 
PADMORE:  Its curiosity, absolutely.  Absolutely.  Jim died when he was about 83, and he was working until shortly before  he died writing papers
 
HOLLOWAY:  Is that right?
 
PADMORE:  Yes.  It was wonderful.  Other colleagues—I had a colleague, Malcolm Howells, in Berkeley who is now retired.  He’s an emeritus member of the Lab.  He was a person who through his papers taught me about optics.  He wrote some of the clearest and most direct and beautiful papers on x-ray optics which I’ve ever read, and it’s through those papers that I learned the subject.  He was one of the people in my group when I came to Berkeley and actually one of the motivations for me coming to the States.  Then I have really wonderful colleagues today.  Tony Warwick who is my deputy in the group is a very wonderful experimenter, very creative.  Alastair MacDowell, who I worked with in the U.K. at Daresbury via Bell Labs is also now in my group and is an unbelievably creative experimentalist.  So I’m surrounded by very, very good people.  We’re also embedded in the environment of Berkeley.  We’re 200 meters from the University, and so the only problem we really have is overstimulation.  [Laughter]  Every day in multiple places we have fantastic seminars to go to, and we’re stimulated by a wonderful array of colleagues.
 
HOLLOWAY:  That’s a nice situation to be in.
 
PADMORE:  It really is.
 
HOLLOWAY:  There are a number of synchrotrons around the world.  How does the Advanced Light Source compare to all those?  It obviously is much better.
 
PADMORE:  It’s obviously much better.  Apart from anything else, as in the talk which I gave today, I always demonstrate in the introduction to a talk that we have undoubtedly the brightest synchrotron in the world in soft x-rays, but we also have the synchrotron with the best view.  Directly out of the Advanced Light Source we can see the Golden Gate Bridge and the skyline of San Francisco.
 
HOLLOWAY:  Beautiful!
 
PADMORE:  In terms of its brightness, it’s competitive with the best that there is today.  With upgrades which we’re applying to the DOE to fund, this will drive our brightness up by another factor of up to1000 and make us the ultimate CW source of x-rays and this will see us good for another 20 or 30 years.  Having said all of this about the machine, the science that you can do is only partially related to the machine, the brightness of the machine.  It’s really the quality and type of science that is done, which is directly  related to the quality and type of colleagues which you’re working with.  As I said, in Berkeley I feel especially blessed that we have such an amazing array of people both at Light Source and in campus.
 
HOLLOWAY:  So how do you relate to people that are not on campus?  They propose to you, request time on the Advanced Light Source?
 
PADMORE:  It goes both ways.  Very often it happens that faculty on campus come to us and want to do a particular experiment.  We advise them on how to do it, and then we collaborate with them in doing experiments.  You know, campus is a big place, and other times faculty don’t know of the capabilities of the Light Source or think that experiments may be impossible.  So one of the roles we have is really to be the messiahs of synchrotron radiation! I spend a lot of time mingling with campus faculty  trying to find really interesting problems that we can study, things which will be really unique.
 
HOLLOWAY:  Let’s talk a little bit about professional societies and your interactions in that.  Is there a particular society that you like to interact with.?
 
PADMORE:  I am a fellow of the APS and a fellow of the Optical Society of America.  The society which I’ve interacted mostly with over the years has been SPIE (Society of Photo-Optical Instrumentation Engineering).  They hold their annual conferences in San Diego, and they’re a really wonderful resource for our optics community.  It’s important for the synchrotron community to contact the large optics community out there, which is very advanced in the United States, so that we can learn all the latest tricks.  So I’ve been a conference chair in many conferences and program organizer mostly for SPIE.
 
HOLLOWAY:  What about editorial boards and journals?
 
PADMORE:  Journals;  a long time ago I was on the editorial board of a journal which was then called Journal of Physics E: Instrumentation, which is a United Kingdom Institute of Physics journal.  That became, when I joined, Measurement Science and Technology.  I think it still is called Journal of Physics E.  That was fun.Then I joined the editorial board of the Journal of Synchrotron Radiation, which is obviously dedicated to our specific area of research and really publishes mainly in the area of techniques in instrumentation.
 
HOLLOWAY:  Good.  Well, what advice would you have for young people?
 
PADMORE:  Keep on asking that question of why.  Obviously find something that you’re really, really interested in doing andnot to go down the beaten track I think is good advice. As an instrumentation person, never to trust the instrumentation which is given to you.  What I see many young people doing—you know young people that we interview for jobs for example—is doing measurements and not really understanding how the measurements are done.  So a person who is doing surface science who doesn't understand how the photoelectron spectrometer works or how light-electron-matter interactions happen very often will come to the wrong conclusions about what’s really happening in their experiment.  So I think always to be supercritical of the measurements which you do you, asking the question, “Is this really the right answer?  What possibly could have gone wrong?” and in topics, to choose topics which other people haven’t trodden to death too much.  I see a lot of people going into things which are very trendy topics today, and it’s very difficult to make your mark.  I would advise people to think about new areas which might be a little bit off the beaten track which have the potential to go somewhere interesting and new.
 
HOLLOWAY:  Good.  That covers the topics I had planned to cover.  Do you have any that you would like to cover?
 
PADMORE:  I think the only other thing I would like to say is thank you very much to the American Vacuum Society for bestowing the great honor of the Nerken Award on me.  Being an instrumentation person I can say that of course instrumentation is not a lonely solo activity.  It’s almost always the activity of a group.  So this Nerken Award in particular I think is given to me and the colleagues,especially at the Advanced Light Source, that I’ve worked with for the last 20 years.
 
HOLLOWAY:  Good.  Well, congratulations on a well-deserved award.
 
PADMORE:  Thank you. 



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