Interferometric control of the ellipticity of a femtosecond extreme ultraviolet source

Abstract

A method for ultrafast ellipticity modulation of femtosecond intense lasers is introduced and demonstrated. The method is based on the coherent superimposition of two linearly polarized visible/infrared (Vis-IR) laser beams with orthogonal polarizations. Tuning their delay by a quarter of the wavelength, i.e., a few hundred nanometers, achieves the same function as the rotation of a quarter-wave plate by 45°, switching the polarization from linear to circular. We demonstrate the portability of this method to high-intensity processes by upconverting a femtosecond Vis-IR laser beam to the extreme ultraviolet (EUV) spectral range through high-harmonic generation. These results open the way to lock-in detection of small absorption chiroptical signals in the EUV spectral range, including pump probe signals.