CUOS: Pushing the limits of optical science

The Center for Ultrafast Optical Science (CUOS), established at Michigan Engineering in 1990 as a Science and Technology Center, confirmed Michigan’s rightful place as a leader in ultrafast optical science. It also would serve as a catalyst for the thriving optics community that now exists in Southeastern Michigan, with Ann Arbor as its hub.

Ultrafast optical science is based on the generation and application of extremely short pulses of light. How fast is ultrafast? Scientists at CUOS work in femtoseconds (10-15 seconds), and even attoseconds (10-18 seconds).

Lasers that can produce such ultrashort pulses of light produce the shortest controlled bursts of energy and the highest peak intensity ever produced by mankind. CUOS researchers not only pioneered the development of high-peak-power and high-repetition-rate ultrafast lasers but they also led to the development of numerous applications across many fields of science and technology.

Comprised of electrical engineers, physicists, astrophysicists, materials scientists, biomedical engineers, doctors, and other scientists, CUOS researchers have explored ultrafast laser applications across the entire range of pulse energy.

Comprised of electrical engineers, physicists, astrophysicists, materials scientists, biomedical engineers, doctors, and other scientists, CUOS researchers have explored ultrafast laser applications across the entire range of pulse energy. This includes low-energy laser applications such as biomedicine, femtosecond eye surgery and spectroscopy; medium-energy applications such as terahertz generation and ultra-precise micromachining; and high-energy applications that promise new treatments for cancer, improved medical imaging, breakthroughs in lithography, and new insights into fundamental science.

Mourou Comes to Michigan
CUOS was founded by Gérard Mourou, who is recognized as one of the world’s leaders in the development of ultrafast lasers. In 1985 Mourou achieved breakthrough research with Donna Strickland at the University of Rochester in chirped pulse amplification (CPA) for lasers.

The impact of CPA? The previous attainable power of laboratory-sized lasers peaked at about 1 gigawatt, and required equipment that could fill a small building. With CPA, terawatt peak powers (1,000 times more powerful) were achieved on a femtosecond laser that could fit on a table-top. It is a technique used in thousands of lasers today by researchers from many different fields of study.

When Mourou arrived at Michigan in 1988, ultrafast lasers was an area that was ripe for development, and most other schools with strong optics programs had not yet branched out into that specialty.
The early days of CUOS were driven by the development of ultrafast titanium-sapphire (Ti:sapphire) amplifiers, a new class of ultrafast laser combining high peak power with short pulses.

Ted Norris, Gérard A. Mourou Professor of EECS and a former student of Mourou, invented both the ultrafast high-repetition-rate Ti:sapphire amplifier and the 250-kHz Ti:sapphire regenerative amplifier in the early 1990s. Both lasers are still state-of-the-art and found in more than a thousand academic, government, and industrial laboratories throughout the world.

1990s CUOS researchers also were pioneering ultra-precise femtosecond laser micro-machining. In 1994, Mourou and his team discovered that as the laser pulses decrease below 10 picoseconds, the damage to the surrounding area does not follow typical scaling, which allows for highly precise micro-machining with surprisingly little collateral damage.

Tresa Pollack, professor of materials science and engineering, for example, used short pulse lasers both at Michigan and at national laboratories to attempt to detect the microscopic origins of cracks in materials that can lead to failures, without damaging the material in the process. Applications include nondestructive testing of airplane turbine blades.

“Ultrafast science is a tool that can be applied to further the understanding of almost every conceivable scientific discipline.” – Gérard Mourou in 1992

Alan Hunt, professor of biomedical engineering, and his group applied femtosecond lasers to address a variety of biological questions and to develop tools to further biomedical research. Hunt later achieved nanoscale machined holes that produced zero residual debris, and his group was able to break the diffraction limit and machine to tenths of nanometers in scale. This work has applications in subcellular surgery, as well as micro-electromechanical system fabrication and nanofluidics microelectronics.

And Steven Yalisove, professor of materials science and engineering, leads a project that uses femtosecond Laser Induced Breakdown Spectroscopy to break down extremely small amounts of material (nanograms), which can then be studied optically. His group also has discovered a novel approach to nano and micro fluidic channel manufacturing using ultrafast lasers.

But by far the most celebrated and well-known application for femtosecond lasers came from their application to eye surgery. Ronald Kurtz, then a second-year resident at Kellogg Eye Center, was amazed when treating a student with accidental burns in his eye from a femtosecond laser. It turned out that the burns caused by the laser did not affect his vision because they were very precise – more like cuts than burns.

Kurtz’s discovery ultimately led to a CUOS-based spinoff company, Intralase, founded in 1997 by Kurtz and Tibor Juhasz, a physicist working in the Center. Thanks to ultrafast femtosecond lasers, IntraLase enabled precision eye surgery that left surrounding tissue pristine, which led to the popular LASIK surgery.

HERCULES

In 1999, Mourou invited Victor Yanovsky, an expert in the development of high-power femtosecond lasers based on CPA, to join CUOS. Yanovsky led development of a 300 TW femtosecond (10-15 seconds) laser known as HERCULES (High-Energy Repetitive CUos LasEr System). In 2003, HERCULES set the world record for on-target laser intensity. At 2×1022 W/cm2, HERCULES still held the record in 2016. The ultra-fast laser pulse generated by HERCULES is 50 times more powerful than all the world’s power plants combined.

In addition to practical applications that include medical imaging, cancer treatment (targeting cancer cells while leaving healthy cells intact), and homeland security (detecting explosives and nuclear materials), HERCULES provides a bridge between optics and nuclear physics, and even enables the study of new physics.

Karl Krushelnick, CUOS Director and professor of Nuclear Engineering, is utilizing the unique properties of HERCULES to perform plasma physics experiments at unprecedented laser intensity, and to develop powerful new laser accelerators. He also is developing the generation of ultrafast coherent x-rays, a long-standing goal of the field, which will enable such new fields as dynamical structure studies of biologically important proteins.

In 2013, Krushelnick and a team of researchers developed a technique to probe the interior of highly dense plasma, for the first time, thanks to HERCULES. This research has important implications for nuclear energy research. Learning more about plasmas, which comprised 99% of the universe, could easily lead to other important practical applications in the future.

Fiber Laser Power

Almantas Galvanauskas, professor of electrical engineering and compute science, has been pushing the frontier of high average power with fiber lasers. While most high-power ultrafast lasers rely on “open-cavity” design, Galvanauskas has been defying conventional wisdom by pursuing high-power ultrafast laser pulse generation in optical fibers. Galvanauskas has invented a new class of fiber called chirally coupled core (CCC) fiber that enables ultra-short-pulse lasers. This technology, which set several records in fiber laser power and energy, is critically important for future high power fiber lasers.

Always multifaceted, ultrafast optics research even brings together the worlds of art and science. Terahertz (THz) beams, which fall between the capabilities of electronic devices and lasers, can be used to safely reveal artwork that exists beneath layers of paint or even plaster. CUOS scientists, in collaboration with the Louvre Museum and the CUOS spinoff Picometrix, used pulsed THz beams to detect an image of a butterfly beneath 4mm of plaster. Terahertz imaging is capable of revealing a level of depth and detail that other techniques cannot achieve.

Terahertz beams are also being used to study processes that are relevant to high speed optoelectronic devices, including light-emitting diodes (LEDs), lasers, solar cells, image sensors, and integrated optical circuits.

“CUOS was really an experiment on how to do interdisciplinary research at a university, and it was a tremendous success.” – Ted Norris

Technology Transfer

Nine startup companies have thus far been founded by CUOS scientists, including Intralase, the company that led to Lasik surgery. Seven of these companies remain in Southeast Michigan. When Steve Williamson, President and CTO of Picometrix, and Janus Valmanis left CUOS to form their company, Mourou supported their efforts by offering them a lab to develop their first product.  “This product is still the world’s fastest photo detector,” said Williamson about 20 years later.

The presence of CUOS and its facilities and personnel attracted several optics companies to Michigan, including IMRA-America, which has become a leading company in ultrafast fiber lasers. More recently, Thorlabs opened a business unit in Ann Arbor that is focused on high-speed optoelectronic products. Janis Valdmanis, general manager and former CUOS scientist, credited the move in part to the proximity to CUOS, the University of Michigan, and other optics companies such as IMRA-America.

Michigan is also home to Mi-Light, a Michigan photonics cluster established in 2013 to serve as a focal point for the photonics industry in Michigan. Mi-Light includes some of the industry’s biggest names, including TRUMPF Inc., IPG Photonics Corp., Fraunhofer USA, and defense giant L-3 Communications/EOTech.

These companies have created numerous high-level jobs and developed an ultrafast-optics-based industry with Ann Arbor at the center. This industry attracts outstanding scientists to Ann Arbor while benefiting from the continuous stream of excellent new engineers and scientists trained at CUOS.

An Ultrafast Future

The future of CUOS and ultrafast science is bright. Key applications that CUOS researchers expect to impact include fiber-optic biosensing to perform real-time monitoring of drug delivery in vivo; bladeless surgery; lensless and improved biological imaging; the generation of compact and economical novel radiation sources; and the study of fundamental physics. Researchers also are exploring ultrafast nanoelectronics to determine both fundamental limits and potential applications, including chemical and biological sensors as well as a wide array of electronics.

Ultrafast lasers are used to study how fast electronic processes work in graphene, the electronic material for high speed optoelectronic devices of the future. Norris’ work with Zhaohui Zhong has resulted in the world’s first room temperature infrared photodetector, and he is working with doctors in the Michigan Nanotechnology Institute for Medicine and Biological Sciences to use ultrafast optics for biomedical sensors, both inside and outside the body. This last line of research has led to the 2009 startup company, PhotonAffinity, co-founded by Norris, James R. Baker, M.D., and former CUOS research scientist Jing Yong Ye.

Galvanauskas is part of a multi-institution collaboration to develop laser technology that is expected to enable new low-cost, compact, accelerator-based light sources for a wide variety of biological, chemical, materials science, and security applications. The technology may also lead to compact, portable TeV (tera electron volt) linear colliders, and enable the same kind of research now being conducted in conventional accelerators, such as the 17 mile Large Hadron Collider, on a table top.

“Our goals in the future are to drive this technology forward, and always be at the cutting edge of laser intensity in order to study the science at the frontier of physics,” says current director, Karl Krushelnick. “We also want to continue to be leaders in the technology and applications, and show how these very unique lasers can be useful for society.”