Extreme Ultraviolet Light Source Pushes Limits Of Circular Dichroism Spectroscopy

Circular dichroism spectroscopy with light in the extreme ultraviolet region can be used to study the photoionization of chiral molecules or the magnetic properties of solids. Such experiments usually require synchrotron radiation or free-electron lasers—which generate high-intensity, broad-spectrum light—at specialized facilities. A team led by Yann Mairesse, a researcher at the Center for Intense Lasers & Applications at the University of Bordeaux, in France, has developed a tabletop extreme UV source that could bring such circular dichroism experiments into ordinary labs (Nat. Photonics 2014, DOI: 10.1038/nphoton.2014.314). The researchers focus a titanium-sapphire laser on an argon gas cell to produce various harmonic signals. By using an extreme UV polarizer, they show that the fifth harmonic generates elliptical, quasicircular, ultrashort laser pulses. By swapping argon for sulfur hexafluoride, they can extend the spectral range of the light source. They used the modified source for photoelectron circular dichroism of the enantiomers of fenchone, a well-characterized chiral cyclic ketone natural product. The ultrashort pulses make the light source suitable for time-resolved measurements.