Two-bunch operation with ns temporal separation at the FERMI FEL facility

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Nanoscale transient polarization gratings

We present the generation of transient polarization gratings at the nanoscale, achieved using a tailored accelerator configuration of the FERMI free electron laser. We demonstrate the capabilities of such a transient polarization grating by comparing its induced dynamics with the ones triggered by a more conventional intensity grating on a thin film ferrimagnetic alloy. While the signal of the intensity grating is dominated by the thermoelastic response of the system, such a contribution is suppressed in the case of the polarization grating. This exposes helicity-dependent magnetization dynamics that have so-far remained hidden under the large thermally driven response. We anticipate nanoscale transient polarization gratings to become useful for the study of any physical, chemical and biological systems possessing chiral symmetry

A new method for measuring angle-resolved phases in photoemission

Quantum mechanically, photoionization can be fully described by the complex photoionization amplitudes that describe the transition between the ground state and the continuum state. Knowledge of the value of the phase of these amplitudes has been a central interest in photoionization studies and newly developing attosecond science, since the phase can reveal important information about phenomena such as electron correlation. We present a new attosecond-precision interferometric method of angle-resolved measurement for the phase of the photoionization amplitudes, using two phase-locked Extreme Ultraviolet pulses of frequency $\omega$ and $2\omega$, from a Free-Electron Laser. Phase differences $\Delta \tilde \eta$ between one- and two-photon ionization channels, averaged over multiple wave packets, are extracted for neon $2p$ electrons as a function of emission angle at photoelectron energies 7.9, 10.2, and 16.6 eV. $\Delta \tilde \eta$ is nearly constant for emission parallel to the electric vector but increases at 10.2 eV for emission perpendicular to the electric vector. We model our observations with both perturbation and \textit{ab initio} theory, and find excellent agreement. In the existing method for attosecond measurement, Reconstruction of Attosecond Beating By Interference of Two-photon Transitions (RABBITT), a phase difference between two-photon pathways involving absorption and emission of an infrared photon is extracted. Our method can be used for extraction of a phase difference between single-photon and two-photon pathways and provides a new tool for attosecond science, which is complementary to RABBITT

COMMISIONING OF THE FERMI@ELETTRA LASER HEATER*

Abstract The linac of the FERMI seeded free electron laser includes a laser heater to control the longitudinal microbunching instability, which otherwise is expected to degrade the quality of high brightness electron beam sufficiently to reduce the FEL power. The laser heater consists of a short undulator located in a small magnetic chicane through which an external laser pulse enters to modulate the electron beam energy both temporally and spatially. This modulation, which varies on the scale of the laser wavelength, together with the effective R52 transport term of the chicane increases the incoherent energy spread (i.e., e-beam heating). We present the first commissioning results of this system, and its impact both upon the electron beam phase space, and upon the FEL output intensity and quality

Hypofractionated simultaneous integrated boost (IMRT-SIB) with pelvic nodal irradiation and concurrent androgen deprivation therapy for high-risk prostate cancer: results of a prospective phase II trial

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A detailed investigation of single-photon laser enabled Auger decay in neon

Single-photon laser enabled Auger decay (spLEAD) is an electronic de-excitation process which was recently predicted and observed in Ne. We have investigated it using bichromatic phase-locked free electron laser radiation and extensive angle-resolved photoelectron measurements, supported by a detailed theoretical model. We first used separately the fundamental wavelength resonant with the Ne+ 2s?2p transition, 46.17 nm, and its second harmonic, 23.08 nm, then their phase-locked bichromatic combination. In the latter case the phase difference between the two wavelengths was scanned, and interference effects were observed, confirming that the spLEAD process was occurring. The detailed theoretical model we developed qualitatively predicts all observations: branching ratios between the final Auger states, their amplitudes of oscillation as a function of phase, the phase lag between the oscillations of different final states, and partial cancellation of the oscillations under certain conditions

Real-world data to build explainable trustworthy artificial intelligence models for prediction of immunotherapy efficacy in NSCLC patients

IntroductionArtificial Intelligence (AI) methods are being increasingly investigated as a means to generate predictive models applicable in the clinical practice. In this study, we developed a model to predict the efficacy of immunotherapy (IO) in patients with advanced non-small cell lung cancer (NSCLC) using eXplainable AI (XAI) Machine Learning (ML) methods.MethodsWe prospectively collected real-world data from patients with an advanced NSCLC condition receiving immune-checkpoint inhibitors (ICIs) either as a single agent or in combination with chemotherapy. With regards to six different outcomes - Disease Control Rate (DCR), Objective Response Rate (ORR), 6 and 24-month Overall Survival (OS6 and OS24), 3-months Progression-Free Survival (PFS3) and Time to Treatment Failure (TTF3) - we evaluated five different classification ML models: CatBoost (CB), Logistic Regression (LR), Neural Network (NN), Random Forest (RF) and Support Vector Machine (SVM). We used the Shapley Additive Explanation (SHAP) values to explain model predictions.ResultsOf 480 patients included in the study 407 received immunotherapy and 73 chemo- and immunotherapy. From all the ML models, CB performed the best for OS6 and TTF3, (accuracy 0.83 and 0.81, respectively). CB and LR reached accuracy of 0.75 and 0.73 for the outcome DCR. SHAP for CB demonstrated that the feature that strongly influences models’ prediction for all three outcomes was Neutrophil to Lymphocyte Ratio (NLR). Performance Status (ECOG-PS) was an important feature for the outcomes OS6 and TTF3, while PD-L1, Line of IO and chemo-immunotherapy appeared to be more important in predicting DCR.ConclusionsIn this study we developed a ML algorithm based on real-world data, explained by SHAP techniques, and able to accurately predict the efficacy of immunotherapy in sets of NSCLC patients

Two-Bunch Operation at the FERMI FEL Facility

International audienceFERMI is a linac-driven free electron laser (FEL) based upon the High Gain Harmonic Generation (HGHG) scheme. In standard conditions a bunch of 700 pC of charge with sub mm-mrad emittances is accelerated to 1.2-1.5GeV in a normal conducting S-band linac and drives FEL-1 or FEL-2 undula-tor line, which lase respectively in the range 100-20nm or 20-4nm. A number of two-color schemes have been implemented at FERMI for pump/probe experiments, all consisting in making two portions of the same electron bunch lase at two different wavelengths, with a time-separation from 0 to few hundreds of fs. In order to increase the time separation to ns and tens of ns we have explored the acceleration of two inde-pendent electron bunches separated by multiple of the linac main radio-frequency period, i.e. 333ps. Measure-ments and characterization of this two-bunch mode oper-ation are presented, including trajectory control, impact of longitudinal and transverse wakefields on the trailing bunch and manipulation of the longitudinal phase space

Non-Standard Use of Laser Heater for FEL Control and THz Generation

International audienceThe laser heater system is currently used at various FEL facilities for an accurate control of the electron beam energy spread in order to suppress the micro-bunching instabilities that can develop in high brightness electron beams. More recently, studies and experiments have shown that laser-electron interaction developing in the laser heater can open new possibilities for tailoring the electron beam properties to meet special requirements. A suitable time-shaping of the laser heater pulse opened the door to the generation of (tens of) femtosecond-long FEL pulses. Using standard laser techniques it is also possible to imprint onto the electron bunch, energy and density modulations in the THz frequency range that, properly sustained through the accelerator, can be exploited for generation of coherent THz radiation at GeV beam energies. Such recent results at the FERMI FEL are here reported, together with near future plans