Free radicals and high-power lasers

At the interface between physics and chemistry, Tim Vogler's goal is to visualize the fate of highly reactive, and therefore short-lived, particles in liquids.

Tim Vogler in the lab. Without a highly complex laser system, Tim's research would be impossible. © Volker Lannert

Lasers fascinate most of us, without knowing exactly what a laser actually does.
Tim Vogler has, of course, long been beyond this point. The physicist already dealt with lasers in his master's thesis. His PhD thesis at the Institute of Physical and Theoretical Chemistry enables him to pursue this fascination even further. Not only is he able to use a super-strong high-power laser, he also works on the border between physics and chemistry. Physical tools form the basis for Tim to visualize ultrafast chemical processes. The objects of investigation come from chemistry. For Tim, these are liquids like water and ammonia.

Tim studies the behavior of highly reactive particles, including free radicals. They are known for their harmful effects, such as in skin cancer. Chemical processes always have to do with the redistribution of charges and the reorganization of nuclei. This is where the laser comes into play. In extreme cases, light can even separate electrons from molecules and thus generate free radicals. The very potent ultraviolet portion is particularly interesting for Tim.

The most important tool for Tim's research is the high-power laser in the basement of the institute. It provides an impressive six watts of optical power. For comparison, in Germany a laser pointer may not exceed the output power of one milliwatt. The laser also delivers extremely short flashes of light – only a few femtoseconds in duration. Note, in one second, light can cover the distance from here to the moon. In a femtosecond, light only just manages to cross a bacterium.

For his experiment, Tim throttles the performance of the laser. He then manipulates the laser beam in a way that enables him to irradiate his sample with UV light. The liquid embeds the electron after its detachment from the molecule. This is how Tim generates solvated electrons. With a second ray, he can investigate the fate of the electrons in the liquid – spatially, as well as temporally.

Tim's work is still basic research, but the possible fields of application are extremely diverse. Medicine could benefit from new insights into free radicals, as they not only play a major role in the development of cancer but are also linked to Alzheimer's disease, for example. The same applies to nutrition sciences. Antioxidants, substances that we absorb with food, protect our body against free radicals. Nutrition tips could be put to the test. However, even though free radicals have a bad reputation, they can also be of great value. Chemists and pharmacists, for example, can take advantage of the free-radicals’ reactivity in developing new versatile materials and more effective drugs.

All this is still up in the air. For Tim, his doctoral thesis is in the foreground. Unfortunately even with a high-power laser, it does not write itself.

1/9 Photo / Volker Lannert. The high-pressure cell is a centerpiece of Tim's research. The stainless-steel body is equipped inside with two sapphire windows and withstands pressures of more than a thousand bars. With such forces, visual inspection for possible damage is essential, after all, the liquids to be examined should also remain inside. © Volker Lannert / Uni Bonn

2/9 Photo / Volker Lannert: All chemical reactions that Tim investigates take place in liquids. But under normal conditions, not all chemicals are liquid… © Volker Lannert / Uni Bonn

3/9 Photo / Volker Lannert: ...some are gaseous, such as ammonia. Prior to the experiment, Tim sets the chemical under high pressure to liquefy it and transfers it into the high-pressure cell. © Volker Lannert / Uni Bonn

4/9 Photo /Volker Lannert: Another way to liquefy gases is making them cold. Here, part of the apparatus was cooled with liquid nitrogen. Its boiling point is about minus 200 degrees Celsius - so cold that in a short time, beautiful ice crystals are formed. © Volker Lannert / Uni Bonn

5/9 Photo / Volker Lannert. In the first step of the experiment, the laser beam is split. In order to elicit information from the ultrafast reactions, Tim needs two laser beams. One generates the solvated electrons, the other serves their pursuit. © Volker Lannert / Uni Bonn

6/9 Photo / Volker Lannert. With the laser, Tim can produce all colors of the visible spectrum as well as ultraviolet and infrared rays, which are outside of the visible light spectrum. © Volker Lannert / Uni Bonn

7/9 Photo / Volker Lannert. And that's exactly what is important. Tim needs UV radiation to generate the solvated electrons and the infrared radiation to track the fate of highly reactive particles. © Volker Lannert / Uni Bonn

8/9 Photo / Volker Lannert. In the high-pressure cell, the rays hit the sample. Physics meets chemistry. © Volker Lannert / Uni Bonn

9/9 Photo / Volker Lannert. Models and simulations help Tim evaluate the measurement data. Tim discusses the results of the experiment with his supervisor, Professor Peter Vöhringer. © Volker Lannert / Uni Bonn

Free radicals and high-power lasers

Read more ...

Research

Chemistry with physical methods