Determining the polarization state of an extreme ultraviolet free-electron laser beam using atomic circular dichroism

Abstract

Ultrafast extreme ultraviolet and X-ray free-electron lasers are set to revolutionize many domains such as bio-photonics and materials science, in a manner similar to optical lasers over the past two decades. Although their number will grow steadily over the coming decade, their complete characterization remains an elusive goal. This represents a significant barrier to their wider adoption and hence to the full realization of their potential in modern photon sciences. Although a great deal of progress has been made on temporal characterization and wavefront measurements at ultrahigh extreme ultraviolet and X-ray intensities, only few, if any progress on accurately measuring other key parameters such as the state of polarization has emerged. Here we show that by combining ultra-short extreme ultraviolet free electron laser pulses from FERMI with near-infrared laser pulses, we can accurately measure the polarization state of a free electron laser beam in an elegant, non-invasive and straightforward manner using circular dichroism.

Determination of accurate electron chiral asymmetries in fenchone and camphor in the VUV range: sensitivity to isomerism and enantiomeric purity

“…In addition, in the context of a growing development of VUV/XUV CPL sources from FELs 57 , HHG 29,58,59 , plasma--based laser 60 and associated polarizing optics 61 , PECD could, like other dichroic effects 62 , be used as a "molecular polarimeter template", especially when either the β parameter is null or known, or when the linear polarization components of light (S1 and S2) are negligible, in which case accurate PECD benchmarking with the present data would allow the disentangling of the unpolarized component (S4) from the circular one (S3). This would be a complementary approach from the molecular polarimetry data deduced from molecular--frame photoelectron angular distributions (MF--PADs), recently demonstrated 63 and valid in the dissociative ionization continuum range of small molecules, i.e., above 20 eV or so.…”

Polarization Characterization of Soft X-Ray Radiation at FERMI FEL-2

“…Several established methods exist to characterize the polarization of an undulator [27,[37][38][39][40]. In our previous work [28], we extensively compared the merits of different instruments, namely, an optical, a fluorescence, and an eTOF polarimeter.…”

“…In the past years of FERMI operation, users have already exploited the circularly polarized light to study dichroic effects [3,[25][26][27]. The purity of the polarization is a key parameter for the success of users' experiments.…”

Probing the energy flow in Bessel light beams using atomic photoionization

“…Therefore, the angular distribution of the photoelectrons differ from each other if Λ X and Λ L have either equal or opposite signs. Indeed, it is the sign of Λ L Λ X that leads to the circular dichroism in the twocolor photoionization of atoms by plane-wave radiation [26,28].…”

“…Later, it was shown theoretically [26] that the two-color ATI sideband spectra are rather sensitive also with regard to the circular polarization of both, the XUV and NIR light, and an asymmetry in the photoelectron spectra was found, if the circular polarization of one of the field is changed from same to the opposite direction, a phenomenon that is termed today as circular dichroism in two-color ATI. This circular dichroism, that is associated with some flip of the spin-angular momentum (SAM) of the incident light field, has recently been utilized, e.g., for measuring the polarization state of an ultra-violet free electron laser [26][27][28]. For molecules, in addition, the question has been raised how two-color ATI spectra are affected by the molecular symmetry and the polarization of the incident radiation [29,30].…”