Happy fourth of Advent!

We are lighting our fourth candle on our scientific Advent wreath.

Let’s light the final candle on our scientific Advent wreath. Each week of the Advent season, our associated DOLPHIN group of Andreas Döpp has been lighting a special candle to showcase their experimental techniques normally used in high-power laser experiments at CALA.

For the last candle flame, the researchers wanted to showcase the method of interferometry: a technique that leverages the physical phenomenon of interference to extract valuable information.

Take a closer look at the image below, where you'll see the interference pattern of a candle flame, first stationary and then with a gentle air flow. By analyzing this pattern, one can, in principle, determine how the refractive index varies across the flame.

When the candle flame was gently perturbed by the light airflow, the interference patterns changed and became wavier. These changes indicate local variations in the flame’s refractive index, which correspond to differences in density within the flame. 

This is where interferometry truly shines – it allows us to observe subtle variations in the structure of the flame that are invisible to the naked eye. Even small movements of hot gas and density differences become detectable, highlighting the technique's capability for detailed plasma diagnostics. 

With this, we close the final chapter of our scientific Advent wreath. We hope you've enjoyed this journey and wish you a wonderful holiday season! 

Pictures: Advent candles: AI-generated / Nina Beier
Measurements: Matilde Nunes, Johannes Altmann and Marguerite Dion