Lasers light the way to new technologies

This year, the Nobel Prize in Physics was awarded to three individuals for “groundbreaking inventions in the field of laser physics”: Arthur Ashkin with Bell Laboratories in the United States; Gerard Mourou of the École Polytechnique, Palaiseau, France, and the University of Michigan, Ann Arbor; and Donna Strickland from the University of Waterloo in Canada.

Steve Smith, who earned his Ph.D. doing research in a National Science Foundation Science and Technology Center directed by Mourou at the University of Michigan, was pleased to hear Mourow was receiving a share of the Nobel Prize.

“It’s nice he received a part of this prize. But it also gives acknowledgement to a lot of people in different areas of laser physics. That’s usually how it works—one person gets the prize but there are hundreds of people doing similar work that is very impactful, and this elevates their research as well,” said Smith, who is a professor and director of Nanoscience and Nanoengineering at the South Dakota School of Mines & Technology (SD Mines).

At Deep Talks: Nobel Day, Smith will discuss the topics relating to this year's Nobel Prize in Physics, including Mourou’s work in the field of laser physics and how it has impacted a variety of scientific and technological applications. He and students will also have some optical science demonstrations to interact with.  The event takes place Thursday, Dec. 13, beginning at 5 p.m. at the Sanford Lab Homestake Visitor Center in Lead. 

Mourou and Strickland shared ½ of the Nobel Prize for their work in the area of high-powered, ultra-fast lasers, in which they developed the “chirp pulsed amplification (CPA)” method.

“It’s really the concept of stretching laser pulses out in time, amplifying them, and then compressing them in time,” Smith said. “The technology allowed scientists to develop intense laser sources that have been used for laser eye surgery, for communication technology, for precise measurements of time, for generating coherent x-rays, and for fundamental studies of the behavior of matter under extreme conditions.”

Ashkin, on the other hand, invented optical tweezers that grab particles, atoms, viruses and other living cells using light. According to the Nobel Academy, “this new tool allowed Ashkin to realize an old dream of science fiction—using the radiation pressure of light to move physical objects.”

Ashkin’s discovery allows scientists to study the mechanical properties of single molecules, including DNA.

Smith was a Ph.D. student when he began working in the Center for Ultrafast Optical Science, directed by Mourou, and was able to be involved in some of the groundbreaking research into ultrafast laser science and technology Mourou and others were engaged in at the time.

“Mourou’s group concentrated on generating ever more intense laser pulses with higher and higher energies, approaching PetaWatts (10^15 joules per second). That has since been exceeded,” Smith said. “It was said that a PetaWatt was roughly equivalent to the peak electrical power required in the entire United States during a work day (9-5). That’s a lot of power!”

Of course, that amount of power existed for a very short amount of time—one millionth of one billionth of one second (or a femtosecond), meaning the total energy created is just one joule, which is not a lot of energy.

“A light bulb, for example, burns 100 joules every second. However, in that very short period of time, the intensity created by the laser pulses is so high it causes matter to behave in very unusual ways,” Smith said. “The electrons can be accelerated to relativistic speeds, generating x-rays as a consequence.”

Smith’s work as a Ph.D. student combined ultrafast lasers with nanophotonics. “Gerard focused on building and developing high-powered lasers; my group focused on using the lasers to do science. My pulses were much weaker than his—we were sort of like David and Goliath.”

Mourou squeezed photons in time whereas Smith’s efforts centered on squeezing photons in space as well, Smith said. “We wanted to use these photons as a kind of nanometer strobe light. We wanted to ‘see’ what electrons inside semiconductors were doing and how it affected the properties of devices like transistors as they got smaller and smaller, where quantum mechanical effects become important.”

Smith said the work is important to future technologies, which could lead to smaller, more compact and more powerful electronic devices.

New technologies include coherent x-rays, which were generated by ultrafast lasers for use in nano-scale imaging in the STROBE center, headed by Margaret Murnane at the University of Colorado, Boulder; and a high-power laser system similar to Mourou’s, built by Don Umstader at the University of Nebraska-Lincoln, to study high temperature plasmas and other so-called high-field phenomena.

Smith’s research at SD Mines focuses on optics, using photonic methods to image live cells, and to understand the light matter interaction in a nanostructure that could lead to finer scale, all-optical circuits, sensors and energy devices.

“All materials interact with light—that’s why we can see colors,” Smith said. “The interaction of light with materials helps us understand the properties of matter. That’s what my research is all about—the nature of that interaction.”

But what really gets him excited is his work with students and other faculty members.

“We are doing new and novel imaging experiments that are seeing things no one has ever seen. It’s exciting to see their accomplishments and to share a bit of what I’ve learned,” Smith said. “One of the nice things about teaching is that you get to keep being a student—you learn all the time. That’s one of the most exciting things about teaching.”