Negative frequencies are considered to be an exotic concept in the physics of waves. Many people still doubt their physical reality, but in this work Dr. Biancalana and his research team at IPaQS show that some part of the spectrum in the negative range of a laser can be greatly enhanced by using the right materials and wavelengths.  This work conclusively proves the reality of negative frequencies and opens up fascinating new points of view on electromagnetism.

Physical Review Letters 118, 043902