University of Michigan
Mar 6, 2019
Q1: What was your path into the field of physics?
A1: Alec Thomas received his PhD in Physics at the Imperial College London. He originally became interested in physics, specifically fusion, with the desire to help mankind through clean sources of energy, and transitioned into the study of radiation sources driven by lasers. Thomas appreciated the challenging problems of physics and was interested in the workings of nature at a fundamental level.
Q2: Were you thinking about the model of an atom during your early days in physics?
A2: Alec Thomas is interested in the complexity of nuclear engineering due to the considerations of quantum mechanics and having to make sense of the bizarre behavior of matter at the fundamental level. Modeling an atom is a complex process. There are known equations describing the quarks and gluons which stick together to form a nucleus, but the equations are very challenging to solve. Thomas’ PhD thesis focused on laser plasma accelerators. A plasma is a state of matter resulting from ionizing material sufficiently that the electrons become separated from the ions. The behavior of the matter is dominated by electric effects. Plasma temperature is measured in eV, electronvolts. Lasers have a field strength strong enough to accelerate the particles, which then reach equilibrium and have a thermodynamic temperature. A strong enough laser field will rip the electrons from their atoms, move them around, resulting in matter with extremely high temperatures. The electrons don’t escape completely, but are flying around the ions.
Q3: Why do we care about plasma?
A3: Alec Thomas cares about plasma due to the oscillations of plasma, which can be harnessed into energy. One of the most fundamental behaviors of plasma is wave oscillations. When electrons are pulled away from ions, a force will pull electrons back to the ions, but overshoot the target and end up oscillating. The laser creates a perturbation which causes a strong electric field and creates an oscillation that travels behind the laser, similar to a wake. Charged particles “surf” on this electric wave and obtain very high energy. Plasma accelerators can be smaller in size than high energy physics accelerators, allowing the technology to be more commercially viable. One possible use for this technology could be identifying and diagnosing porosity and cracking in 3D printed material in situ.
Q4: How was titanium doped sapphire discovered?
A4: Alec Thomas appreciates the scientific process because things can be discovered that are not necessarily practical, such as the titanium doped sapphire. In the early days of laser technology, lots of discoveries were made by trial and error. Titanium doped sapphire gives a very short laser, but the field strength comings from having a lot of photons. In 1985, Gerard Mourou and Donna Strickland came up with a technique to split all the colors in the pulse up using an arrangement of gratings so the colors go different paths and stretch out in time. The pulse can be sent through crystals, amplify it to very high powers, and use an arrangement of gratings that reverses the process to combine all the colors again in a very short pulse. Mourou and Strickland received the Nobel Prize for this invention. Mourou then set up the Center for Ultrafast Optical Science at the University of Michigan, where Alec Thomas now works. These lasers can accelerate ions, which could be used for types of medical therapy, or to produce neutrons through fusion. Since the lasers are very small and the timescales are so short, temporal and spatial scales that can be resolved with this technology that can’t be achieved with conventional processes.
Q5: What do you see as the biggest impact for this technology in the next 10-20 years?
A5: In the future, Alec Thomas predicts laser plasma technology could have the most impact in the x-ray field. The laser technology needs to progress more before this is achieved, due to the complexity of the lasers. Alec Thomas envisions portable x-ray sources for high resolution imaging and 3D reconstruction of objects available at one thousandth of the cost of a synchrotron facility in the next 20 years.
Top 8 Bullets
- Alec Thomas’ path to plasma physics at the University of Michigan - Challenges of modeling an atom - How laser plasma accelerators create energy - The interactions between charged particles and plasma wave oscillations - Benefits of plasma accelerators compared to high energy physics accelerators - Use of titanium doped sapphire crystals in lasers - Plasma technology for medical applications - Economic advantages of laser plasma accelerators.