This year’s NobelPrize laureate in physics Anne L’Huillier discovered that many different overtones of light arose when she transmitted infrared laser light through a noble gas.
Each overtone is a light wave with a given number of cycles for each cycle in the laser light. They are caused by the laser light interacting with atoms in the gas; it gives some electrons extra energy that is then emitted as light. L’Huillier has continued to explore this phenomenon, laying the ground for subsequent breakthroughs.