In recent research, profound effects have been observed when clusters are blasted with ultra-bright reddish-color lasers. While recent research has uncovered these new phenomena, controversy still exists where the connection between theory and experimental results has broken down Dr. Edward Ackad wants to settle the decade-long controversy and determine if an existing microscopic model of laser-cluster interactions is valid.
For Ackad, the world of atomic ions is a playground where X-ray lasers can reveal new information about how elements interact with each other and how they can be stabilized or destabilized to create new states of matter. Ackad, an assistant professor of physics, is an atomic physicist with an infectious eagerness for projects that involve nanoscopic particles and powerful lasers.
He is particularly interested in how X-ray lasers apply energy to and interact with ambiguous atom “clusters,” elements that seem to hover between a solid and gaseous state. Funded through a United States Air Force Young Investigator Program (YIP) grant, Ackad’s research explores whether X-ray laser blasts can offer new information about how atomic clusters behave when energized.
Ackad explains, “How many atoms does it take to make a solid? It certainly is more than one, but what about 100? If 100 atoms ‘stick’ together, does that make it a solid? That small number of atoms stuck together can still float in the air, and each cluster can be quite far away from another cluster. So should we say they are a gas or still a solid? Well, both are correct. A cluster is a phase of matter in between solid and gas with very unique properties—especially when blasted with a high-powered laser!”
Compared with a gas, a solid is very dense, making it especially receptive to energy. It is also large enough to dissipate any energy it receives across many atoms. A gas, however, is made of single atoms or molecules. It is difficult to give gas energy due to its low density, but once energy is applied, dissipation of that energy slows and the gas experiences significant effects.
Clusters, being an intermediate state of matter, have the best of both worlds. They are dense like solids, but the small number of atoms means the energy will have a significant effect.
According to Ackad, clusters make great targets for laser beams, as they are easy to hit and energy is not easily dissipated. In recent research, profound effects have been observed when clusters are blasted with ultra-bright reddish-color lasers. Charged atoms accelerate to near the speed of light; high energy neutrons similar to an A-bomb are produced; intense bursts of X-rays are generated; and even antimatter is created.
However, while recent research has uncovered these new phenomena, controversy still exists where the connection between theory and experimental results has broken down. Theoretical advances and some experimentation have enhanced our understanding about the effects of lasers on clusters and these newly observed phenomena, but reproduction of successful experimental models remains problematic.
Furthermore, current experimental models cannot tell us if the new phenomena are fundamental to the nature of clusters, or if they are an emergent product of laser-cluster interactions. Ackad wants to settle the decade-long controversy and determine if an existing microscopic model of laser-cluster interactions is valid.
Specifically, Ackad is trying to understand what happens to clusters when they are blasted with an X-ray laser. An X-ray laser detects a cluster differently from a reddishlaser. The reddish-laser sees the cluster as a solid blurry ball, but the X-ray laser sees each atom separately. Ackad’s team hopes to determine whether everything that happens when a cluster is blasted with an ultra-bright X-ray laser is predicted by current understanding of atomic physics, or are new physics phenomena created?
Thanks to the YIP grant funding, Ackad is able to recruit SIUE students in Air Force-related fields to participate in the research. For example, Zachary Harwick, a recent physics department graduate, worked with Ackad to explore how charge is transferred from one element to another element in a cluster that is layered with xenon atoms in the middle and a shell of argon atoms around them.
Though the X-ray laser is at just the right setting to target the xenon atoms and thus highly charge them with energy, in the experiments, it was the argon atoms showing the highest charge after the laser blast. Harwick used high-performance computing to peer into the cluster as it was hit by the laser to determine how the charge was transferred from xenon to argon atoms.
Kasey Barrington, a senior majoring in physics, is looking at how the symmetry of the cluster changes the way it disintegrates. Spherical clusters disintegrate spherically, but how do elliptical clusters disintegrate? Barrington also uses high-performance computing to examine the cluster from start to finish to see how the shape changes and how the charges are distributed. This fits into the wider scientific context of free-electron lasers since many proteins which will be studied are not spherical, and other research groups may use X-ray lasers to determine the 3D structure of those proteins. Knowing how a protein will disintegrate will help optimize the 3D image process in order to better see virus details. This may be crucial in understanding how viruses work and in developing drugs to stop them.
Ackad and his team are attempting to validate (or invalidate) an atomistic model of laser-cluster interactions to determine if there is any evidence for new, fundamental phenomena that are not emergent properties of the laser-cluster system. According to Ackad, the tools and models his team proposes to develop may make them one of the first U.S. groups capable of detailed microscopic descriptions of these atomic interactions.