When the researchers first started to work with ultrafast, mid-infrared lasers just a few years ago, they actually made a step backwards and generated bright extreme-ultraviolet light of longer wavelengths than they used to achieve in the lab.
"However, we discovered a new regime that helped us to realize, just on paper, that we could make this giant step forward towards much shorter electromagnetic wavelengths and generate bright, laser-like, soft and hard X-rays," adds Popmintchev. "What the experiments were suggesting back then looked too good to be true! It seemed that Mother Nature has combined together, in the most simple and beautiful way, all the microscopic and macroscopic physics. Now, we are already at X-ray wavelengths as short as roughly 7.7 angstroms, and we do not know the limit."
To truly control the beam of photons, the researchers needed to understand the HHG process at the atomic level and how X-rays emitted from individual atoms combine to form a coherent beam of light.
That understanding combines microscopic and macroscopic models of the HHG process with the fact that those interactions occur at very high intensity in a dynamically changing medium. The development of such a conceptual understanding took the last decade to develop.
The result was the realization that there is no fundamental limit to the energy of the photons that can be generated using the HHG process. To obtain higher-energy photons, the system paradoxically begins with laser light using lower energy photons--specifically, mid-infrared lasers.
The JILA researchers demonstrated the validity of that principle in their labs in Colorado, but to achieve their breakthrough, the researchers traveled to Vienna with their beam-generating setup. There, they used a laser developed by co-author Andrius Baltuka and colleagu
|Contact: Josh Chamot|
National Science Foundation