The storage ring of the ALS generates incredibly bright beams of x-rays. But they are only useful to users if we can steer and focus them onto the sample. Ian Lacey, working in the metrology lab of the ALS, helps measure and tune the optical elements needed for that steering.
What do you do at the ALS?
I measure the tools that do the measurements. In the non-contact optical metrology lab, we check that optical surfaces will work to either focus or collimate the light for the beamlines. These are individual optical elements that the x-rays will hit on their way from the source to the endstation. That includes a first mirror—or M1—to get light out of the storage ring, some apertures, another mirror to focus down to the sample, and sometimes other spectrometer mirrors. Basically, we do the steering for the x-rays.
We support new beamlines, as well as existing beamlines as they are upgraded, or to get better performance out of existing optics. Over the past two shutdowns, we’ve been working with Beamline 8.3.1. Over the winter shutdown last year, we looked at their M1 parabola mirror, which takes a point source and collimates it to go through the monochromator. This is a large, bent piece of silicon that we tuned to the ideal parabola specifications.
During the summer shutdown, we worked with the second mirror—or M2—which takes that collimated light from the monochromator and then focuses it down to the sample. Last month, James Holton, the beamline scientist at 8.3.1, sent some pictures from his detector, and he’s got the smallest spot size he’s ever had. Great! And that’s just using the existing mirrors, not even doing upgrades. We were able to get it in the right shape and tune it.
We have this great machine that’s a billion times brighter than the sun, and it’s fantastic, but it’s only useful if we can deliver those photons to the end user.
How or why did you get into metrology?
I’ve always been curious about zero, or what’s outside the universe. I’ve been curious about what is at the smallest level. Metrology is the science of measurements: we try to put bounds on what is knowable. Just because you click a button on a fancy tool doesn’t mean that it gives you a picture that’s accurate or real. Almost everything you see is systematic error, and the information within all that error is what we’re trying to tease out. It’s an incredibly challenging puzzle. As far as determining what is a real artifact of the world we’re in, of the optics we’re looking at, and what is just a systematic error of our tool (like reading glasses of the wrong prescription), or how we’re looking at it—that is very much in line with my personality.
My academic background is in the pursuit of fundamental physics; using precision atomic spectroscopy to test gravity—ha! That’s how I cut my teeth in the field of precision measurement. Then for a spell, I was working in industry, at a test prep company, doing the devil’s work of designing SAT. questions. My professor reached out and said, “Hey, there’s this job opening up on the hill.”
My professor worked at UC Berkeley with Valeriy Yashchuk, who then moved up here to head the metrology lab. Valeriy was looking for someone to work in his lab, and my professor recommended that I apply. I started off as a fellow for a few years, and then was hired as a full-time staff member.
What would you like people who use the metrology lab to know?
In the metrology lab, we have two working principles. The first is: trust no one, especially not yourself. And the only secret is: there are no secrets, so ask questions, take pictures, wonder what’s going on, double-check things.
We want to help. We have users, postdocs, and visiting scholars; all working on different projects. We can teach you how to use some tools for some basic alignments, for some pre-configuring: If you need microns, that’s easy, that’s fast. If you need nanometers, that is a more challenging conversation, and we can arrange things.
Is there anything else you would like to share with the ALS community?
In the decade plus I’ve been here, I’ve been really impressed with the level of curiosity, interest, and care that people have here. Their ability to help, their ability to dive in, and how they’re going about trying to solve problems. And I really appreciate the collaborative efforts that we can have here. In big science, we have subject matter experts, and no one person knows the full story. So, we communicate to work together more effectively.