May 2021
Vol 7, Issue 21

About The Cover

Cover image expansion

ONLINE COVER While the field of nonlinear optics is almost as old as the laser itself and has been applied in the optical and infrared range for decades, limited peak power has prevented scientists from expanding nonlinear experiments with shorter wavelength pulses beyond the ultraviolet range. For the first time, Helk et al. demonstrate second harmonic generation (a nonlinear optical process in which two photons "combine" to generate a new photon with twice the energy while conserving the coherence of the excitation) in the extreme ultraviolet at a wavelength of 33 nanometers using a table-top source. The researchers applied this technique to study the surface of titanium. By realizing second harmonic generation on a table-top extreme ultraviolet source, the study creates opportunities for scientists to study element-specific dynamics in multi-component systems, with the possibility to access spectral regimes with higher flux than other techniques permit. [CREDIT: ELLA MARU STUDIO]