In this interview, AZoM talks to Dr. Tim Day, Senior Vice President and General Manager of Daylight Solutions, about the current state of the industry and quantum cascade technology.
Can you tell our readers about how you became interested in science and technology when you were very young?
When I was seven years old, my father gave me a book. It was a translation of a US book illustrated by Walt Disney called ‘Our Friend the Atom’, which contained the history of nuclear physics, including all the greats of the past.
It was love at first sight. I don't think I showed any particular talent for science and technology, but I said, "I want to become a physicist," and I never wavered. It's extraordinarily simple, I just felt this was my calling.
How did you find your way into photonics?
Italy was great for nuclear physics and high energy physics. I studied at the University of Rome, and there was a huge influence from Enrico Fermi and his school. Three of my professors had studied and worked with Fermi. Fermi was a (friendly) giant in the field, and I fell in love. I said, "I want to become a high energy physicist." But I realized after a while that this was too daunting, and the math was probably too hard for me.
I had some great people like Giorgio Parisi around me. He was one of the world's most distinguished theoretical physicists working on spin glasses, among other things. I said, "No, I have to find another way. That's not my path."
Then I met Francesco De Martini, who became my advisor when he joined the University of Rome. He had worked with Charlie Townes at MIT for 40 years. I asked him if he would take me on as a student for my thesis, and he said yes.
I started to think about lasers in the 1970s when they were still quite new. There was a lot of exciting work in nonlinear optics at that time, so I did my doctorate in nonlinear optics. At the same time, optical fibers were starting to be developed.
In the Italian system, you first had to work for a professor for free, then, if they liked your work, they would get you a fellowship. I didn’t want to do that, so I taught for a year at a high school until I found a job working in a laboratory for the Italian telecom and post office. It was here that I first worked with fiber-optics.
This work eventually got me to Bell Labs, after I had won a Rotary Fellowship. I developed a taste for lasers and nonlinear optics early on – it was very exciting. Fiber-optics was in its infancy then, and Corning had just demonstrated its famous low loss fibers.
My friend Herb Kroemer, the Nobel Prize winner, always used say, "In choosing research you should be opportunistic, in a good sense. Choose what you are good at, where you can realistically make an impact, or where there is some low hanging fruit." I decided that if I wanted to make my name at Bell Labs I was going to have to work in an area where there were currently very few people, so I worked on avalanche photodiodes, and that was the beginning of band engineering for me.
Overall, it has been a path with many turns. I never fell in love with a particular topic, instead, I’d go with the flow. I'm still in this mode.
What are some of the biggest impacts that you have seen during your career in photonics?
I wanted to do something that would make a big impact. If I had continued on the beaten path in traditional linear optics (which was still new), semiconductor lasers (which were exploding), or even fiber-optics, it was going to be very hard to make a name for myself. That's why I decided to work on detectors, and in areas where it was not too crowded.
I worked on band engineering for the head of research first, before deciding to move into lasers. I discovered Kazarinov and Suri's paper, and that inspired me. I said, “I want to try to make a laser like this,” but it turned out that it had to be done very differently.
Again, I was sort of looking around for the path, and at that point, I realized that with molecular beam epitaxy you could create extraordinary control structures. I felt like a kid in a candy store.
I remember those magic days in 1981. I came up with the idea of superlattice avalanche photodiodes. Shortly after that, I realized that if I want these electrons to get out of the quantum well, I have to grate it. Next came the magic staircase - the energy staircase. I called it the staircase solid-state photomultiplier, which I couldn't make because I didn't have the material. This inspired me to move towards the quantum cascade laser.
The quantum cascade laser is a cascade. If you look at Jerome Faist’s book, one of the first pictures of the quantum cascade laser is sawtooth - there are no quantum wells. As I tilt with bias, it becomes a stair. That was the basis of the detector that I designed, and this was the initial inspiration for the QCL.
I realized that you could engineer new materials with man-made properties. Leo Esaki, Tsu, and others also at Bell Labs were working on this. I realized that this meant I could combine anything I wanted - any kind of shape. Based on this, I decided to make a transistor. If my work were to be characterized, I would call it materials engineering in a broad sense.
Why didn’t I choose metamaterials? There was great science there, but it kept making promises, while I wanted real devices that had an impact. Cloaking? No way. The perfect lens? No way. The perfect lens is a great theoretical construct, but that’s no way to make an actual lens. The technology was too complicated, and it was too difficult to construct these materials in three dimensions. Then it hit me; we have to approach optical materials like we would do electronics.
We started working with planar optics, but some thought it was better to call these flat optics. It was inspirational, and it’s taking off now - it has a life of its own. It’s all based on the idea that it’s easier to make these materials than traditional 3D metamaterials.
What did you think was going to be the biggest impact of the QCL?
We started to socialize with some people from the US before publication, and we realized that there was an untapped area of chemical sensing - trace-gas analytics. We realized the potential in this area during a symposium in Florence. The idea was there, but because we only had a CO2 laser and a semiconductor laser had to be kept at low temperatures, this essentially left a lot of potential untapped.
My atmospheric chemist colleagues and friends tell me that it's been game-changing using atmospheric chemistry in the area of chemical sensing. For example, there was the famous EPA mission where they used two QCLs, flying these for four years from the South pole to the North pole at different heights to spatially map greenhouse gases with a precision of parts per billion – 1 % precision over the average value - plus carbon monoxide.
A lot of people told me that this was an eyeopener for them. There was a problem with the high power, and it took us a while to realize this when we wrote the paper on QCL. We didn't realize that the power was proportional to the number of stages. It was obvious, and we eventually realized that in our second paper, when we did experiments.
It was dramatically different from semiconductors. With everything else, you gain a factor of N in actual power. You gain more because it is very hard to get a room temperature mid-IR laser from a diode laser. We advertised at the CLEO talk a year ago, but we didn't pursue it, for a variety of reasons.
The future is in using QCL in FTIRs. You do not have the tunability of bandwidth of a globe, but you gain a factor of five orders of magnitude in terms of signal to noise. We did an experiment, but we only published it when we looked at the spectrum of creatinine in water, which you simply cannot do with an FTR - you just don't have enough tunability, but you can detect things.
I'm now excited about quantum - the quantum revolution, and the fact we can use entanglement for all kinds of applications. It's a technological revolution, but I also think that scientifically this might lead us to the second quantum revolution. We need to do some key experiments that might tell us, ultimately, if there is an interpretation of quantum mechanics beyond the Copenhagen interpretation. It's fascinating.
Because this field of quantum optics, quantum science and technology tend to attract the very top people, I think we are going to be in for a great ride over the next 10 years.
Herb Kroemer in his Nobel lecture said, “The principal applications of any sufficiently new and innovative technology always have been and will continue to be applications created by that technology.” Technology is largely unpredictable because it is created by invention. It comes from an invention that is also inherently unpredictable, and these inventors will then create their applications. The laser is one example – when it was invented, nobody had thought about optical communication or fiber-optics.
The transistor seems to be an exception though because it started as a replacement. Mervyn Kelly came up with the idea then formed a group of solid-state physicists with Shockley and Bardeen. That was the beginning of the transistor as a means of getting away from using mechanical switches. In reality, the transistor was much more than a replacement for the vacuum tube, and nobody predicted how cost-effective these would become – it prompted a revolution. This all happened in my lifetime - I was born in 1949, and the transistor was invented in 1947.
I have a CD of beautiful lectures entitled, ‘The Dilemma of Science and Technology - a celebration of the legacy of John Von Neumann.’ He said that the moment you create technology, it outpaces our ability to understand its implication, largely because it is so unpredictable. This leads to ethical debates. As scientists, we create things and it is up to other people how they use them, but that feels like a cop-out to me.
Can you tell our readers about what you're working on now?
Right now we are working on molecular lasers, which are pumped by quantum cascade lasers. The molecular laser has been around since the seventies, and the idea is very simple. Molecules have vibrational transitions called rotor vibrational transitions. You can take a rotational level corresponding to one vibrational state, then by pumping it using an infrared photon, you excite this to the rotational state of a different vibrational band.
People used CO2 lasers before the QCL was available, but the system was not tunable because a CO2 laser has limited tunability and wavelengths, as well as being bulky.
I had a conversation with Henry Everett who has done some very nice work in his thesis on molecular lasers. We hit it off and thought to combine the two. So, we created a new class of molecular laser, which is competent and widely tunable. We took a Daylight Solutions laser, tuned it, and used it on laughing gas. We tuned the output from a 50-centimeter long cavity from 200 gigahertz to one terahertz.
Next, using other gases, CO and Methyl Fluoride, we hope to use a tunable QC laser to pump in the whole terahertz gap. This is really the Holy Grail because, in the terahertz gap, you lose efficiency at higher frequencies. The optical sources are either in discrete wavelengths, bulk, or cool, or they have some other disadvantage. Our approach could be the solution.
I predict that in at least five years we’ll be able to open up a lot of applications in the terahertz range. The terahertz range has been a bit like 3D metamaterials in many areas. A lot of people say, for example, “You can scan the body,” or “You can see if the terrorist has a bomb,” but where are the sources? They're not very efficient, or the QCLs are not suitable for scanners.
I think it has opened up a space for applications like optical wireless - short path communication using the peaks in the absorption of water. By using the valleys rather than the peaks, you could have short high-frequency communication that could be used for covert operations. This is not a new idea.
I got an email from Bob Wilson, who with Arno Penzias had discovered the microwave background. He said that if we can create a widely tunable source, we can use a heterodyne detector and a heterodyne receiver, and our laser could become the local oscillator. This would allow us to see many molecules with high sensitivity. Currently, you have to have multiple modules operating at different frequencies in electronic local oscillators. This is very exciting, and radio astronomy is also proving to be very exciting.
What advice would you give to new graduate students as they enter these fields?
Optics is a platform. It’s a super discipline. I don't want to be partisan about it, but if you have an education in optics, you can enter practically any field in science.
When gravitational waves were discovered, I got so excited that I stayed up one night, and instead of giving my regular class, I gave a class on this discovery. I got some slides together and I said, “Look at this huge impact in fundamental astrophysics. Look at medicine, look at biology - that's the power of optics.”
If you have a good Ph.D. with a good background, and you don't become over-specialized, you’ll have the opportunity to change from one discipline to another. That's what I did in my career. I started to work on lasers, then on fiber-optics, then on detectors and optoelectronics, then back to nonlinear optics and quantum wells, then onto real lasers and metamaterials. Optics gives you options because it's a platform.
If you go into optics and you have the passion, you can create your own successful path and not get stuck. Not getting stuck is important - you have to rejuvenate yourself. If you do your Ph.D. in one area, even if you've been successful, don't necessarily stick with it. Consider doing a postdoc in another area, and above all, keep learning.
In my group meetings, I’ll say, "Guys, wake up. I'm 40 years older than you. You have to learn because if you have the drive to learn and ask questions, even if you make mistakes, you will have an impact." Learning and impact go hand in hand. I’m very passionate about this idea.
I can give you a beautiful anecdote. My father in law was a very distinguished figure in high energy physics. He created the first synchrotron over in Frascati near Rome. His team made the first storage ring of positrons and electrons working under the leadership of a very famous Austrian physicist.
He was in love with science. He passed away at 94 years old, and for what would have been his hundredth birthday, his institute showed a short video of a talk he gave. In the talk, he said, “Look, I know I'm near the end, but what drives me is my love for the universe.” He talked about curiosity, discovering more. And as we discover more, we are always surprised at how the universe is much smarter than we are. Nature has more imagination than us. I think that as teachers and as researchers, we have a responsibility to pass on this passion to the next generation.
About Dr. Timothy Day
Dr. Timothy Day is Senior Vice President and General Manager of DRS Daylight Solutions. Daylight Solutions is an advanced manufacturer of molecular detection and imaging products, serving markets that include industrial process control, medical diagnostics, and defense and security using Mid IR lasers and sensor systems. Dr. Day has over 25 years' experience in both technical and business management in the photonics industry. He has led engineering, research, product development, manufacturing, and marketing operations.
Dr. Day began his career in 1990 as a co-founder of New Focus, where he served until the sale of the company to Bookham Technologies PLC in 2004. In 2004, Dr. Day cofounded Daylight Solutions where he developed extensive patent and product portfolios and transferred numerous products into production, both onshore and overseas.
Dr. Day actively participates on the boards for the following companies: Northern Colorado Veterans Resource Center, Cold Quanta, and IRSweep. Dr. Day holds both a BS and an MS in Physics from San Diego State University and a Ph.D. in Electrical Engineering from Stanford University.
Disclaimer: The views expressed here are those of the interviewee and do not necessarily represent the views of AZoM.com Limited (T/A) AZoNetwork, the owner and operator of this website. This disclaimer forms part of the Terms and Conditions of use of this website.