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Affordable High-Performance Fiber Laser Frequency Combs

Physics professor Chad Hoyt on his plans to build affordable fiber laser frequency combs, Bethel's Physics Department, and working with great students.

My grant is through the physics division of the National Science Foundation (NSF). It’s for developing low-cost, high-performance fiber laser frequency combs. A frequency comb is like millions of lasers, but it all comes from one laser. So let’s say what we’re normally used to is something like a laser pointer. It has one frequency to it, one wavelength. A lot of times they’re red, sometimes green, sometimes blue.

Frequency combs use a physical phenomenon to make millions of frequencies, instead of just one. The essence of how it works…instead of making a laser pointer, where the light comes out continuously, you make the laser pulsed, with regular pulses that are very short in duration. In the end, this laser light ends up being like a ruler. A normal ruler is divided up into millimeters, and ten millimeters is a centimeter, etc.

A frequency comb is a ruler in frequency, instead of space. So you can have an entire octave of very even, very stable frequency separations, from blue frequency all the way down to red frequency. The original use for it was to make absolute time and frequency measurements. You can take this frequency comb and reference it to the atomic clock. With that information you can go and make really high-precision absolute measurements.

For example, if you wanted to measure the length of my office door, you might use a ruler. But how do I know how good that ruler is? Well, I’d have to know the definition of a meter, right? Where do I get that information? Well, it turns out the meter is now defined against the speed of light. But there’s actually, sitting in Paris, a piece of metal that’s kept in very hermetic conditions that defines the meter. Or used to define the meter. So an absolute measurement of my door would once have required some reference to that meter bar in Paris. But now we can do this sort of thing with a frequency comb, referenced to the atomic clock.

Frequency combs are useful for many different kinds of science. What we’re building with the NSF grant is a laser that generates pulses of a few hundred femtoseconds. That’s 10-13seconds in duration. Very short pulses. Which is amazing in itself.

When you have a laser light that is that short, you can actually start to ask questions about nature that happen on that timescale. This is where the interdisciplinary part comes. Biologists can use this to study processes at the DNA level. Chemists can use ultra-fast optics to study what’s happening during chemical reactions.

One of the leading scientists that revolutionized measurements with frequencies is a Bethel alum. I worked with him at the National Institute of Standards and Technology in Boulder, CO. as a post doc. His name is Scott Diddams. He helped lead the way for this frequency comb business.

We’re leveraging the telecommunications industry to build a cheaper frequency comb.We can use standard telecomm parts to build the laser and we can get those very cheaply.

We think we can make an ultrafast, pulsed laser for less than $5,000. And then to stabilize it we need to build up some steps that are probably another $12,000. Commercial fiber frequency combs are maybe $200,000. So our idea, and our proposal, is to build these up, and then disseminate the recipe to other undergraduate and graduate labs around the country and around the world so they can build their own.

It makes frequency combs affordable for other schools. A lot of different experiments can be done with them. A second part of the grant is using a frequency comb for measurements with cold lithium, which is another big project we’re working on.

Students are a big part of this project. That’s a big part of everything we do around here. It’s student centered. Without student work, stuff wouldn’t get done.

There are a couple of factors that have enabled us to get three NSF grants in such close proximity. Jay Barnes has made it possible with his support. And all three of us (Keith SteinNathan Lindquist, and I) have built on the wonderful work of people that have come before us. In my case it’s physics professor Dick Peterson. Dick Peterson has been in the trenches, building our optics program, for decades. He was always very resourceful in getting funds and equipment from different sources. He created this ethos of advanced labs, and high-quality undergraduate research. All three of us had him as a teacher and as a research mentor.

Dick Peterson created the infrastructure. He’s a very skilled networker. He knows people. He put Bethel on the map. That’s a big deal. When a reviewer gets a grant proposal, and they’ve never heard of the college or university, that’s different than if they say ‘oh Bethel, I know Bethel. They do good work there. I’ve seen presentations on their advanced lab. They’ve been doing this for years.’

Professor Tom Greenlee has been the key in getting NASA funds through the University of Minnesota to pay summer research students for years and years. And without those summer research students we wouldn’t get the results we’ve had, we wouldn’t be able to point to them in our proposals. Professor Brian Beecken is great in seeing the priority of research. He does his own research, and he’s great at making things happen administratively that let us do this. There’s no question to me that what has gone before has paved the way for Jay Barnes to say ‘ok, go for it.’

And great students. We get great students.

I believe in the way Bethel does physics. Students learn skills. They learn how to make measurements with different instruments, interpret data, record data. These are marketable skills. On a resume they can say ‘I’ve done this and this and this.’ Employers really like that. We get students very close to real research situations. We bring them into our research.

Physics is always new. It’s always a new challenge. There’s always something new to think about. Recently I’ve been doing some engineering, experimental design work. It’s fun to solve these engineering problems. If you’re able to discover something new about nature, it’s pretty exciting.

Learn more about Chad's research.

More info about Chad

Program
Physics

School
College of Arts & Sciences

Hometown
San Diego, CA

Interests
Interesting books, old school hip-hop, family, physics. I want to retire in a place where I can surf and do physics every day.