Polarization Gratings at the Nanoscale: A New Tool to Study Dichroic Samples

Recent years saw the development of EUV transient gratings that were applied to study thermoelastic and magnetic dynamics at the nanoscale [1], [2]. The EUV TG technique so far, makes use of two equally polarized pulses that interfere at the sample position to generate a nanoscale grating of light intensity. Such grating periodically deposits heat on the sample, which in turns gives rise to thermal re-equilibration between excited and non-excited fringes, acoustic waves and, in magnetic samples, demagnetization dynamics. However, the intensity grating is not the only possible grating. The FERMI FEL is well known for its “exotic” pulse's configurations, which were often exploited to develop new techniques [3]. In this work, we show how the synergy between the machine, which was able to generate two spatially separated and orthogonally polarized pulses, and the EUV TG beamline allowed us to develop a new class of transient grating experiments, i.e. nanoscale polarization gratings. Contrary to the intensity grating, the polarization one exhibits a constant spatial profile of light intensity, but a periodic variation of the polarization. The possibility to exploit polarization gratings with dichroic samples such as magnetic ones and biological molecule [4] will be presented and briefly discussed. Combined with the background free characteristic of the transient grating scheme, this may lead to a spectroscopic tool able to detect weak chiral centers, pure spin dynamics and achiral-to-chiral transformation in the excited states.