Abstract
The coherence of free-electron laser (FEL) radiation has so far been accessed mainly through first and second order correlation functions. Instead, we propose to reconstruct the energy state occupation number distribution of FEL radiation, avoiding the photo-counting drawbacks with high intensities, by means of maximum likelihood techniques based on the statistics of no-click events. Though the ultimate goal regards the FEL radiation statistical features, the interest of the proposal also resides in its applicability to any process of harmonic generation from a coherent light pulse, ushering in the study of the preservation of quantum features in general non-linear optical processes.
Highlights
Recent years have seen an increasing interest in the generation of ultra-bright and ultrashort electromagnetic pulses by means of radiation sources, widely known as Free-Electron Lasers (FELs), through self-amplification of spontaneous emission (SASE) from a relativistic electron bunch wiggling between a series of magnetic poles known as undulators [1]
Underlying this work there is the conjecture that the coherent features of the "seeding" laser pulse are transferred to the electrons in the bunch that in turn convey them, at least in part, to the FEL radiation, first in the modulation phase and in the radiation phase, producing amplified high harmonic radiation extending up to the X-ray domain and showing a coherent, that is a lasing state, of the electromagnetic field
To apply the technique successfully to FEL light, we show by simulated experiments that it can be extended to reconstruct the statistics of hundreds of photons
Summary
Recent years have seen an increasing interest in the generation of ultra-bright and ultrashort electromagnetic pulses by means of radiation sources, widely known as Free-Electron Lasers (FELs), through self-amplification of spontaneous emission (SASE) from a relativistic electron bunch wiggling between a series of magnetic poles known as undulators [1]. Underlying this work there is the conjecture that the coherent features of the "seeding" laser pulse are transferred to the electrons in the bunch that in turn convey them, at least in part, to the FEL radiation, first in the modulation phase and in the radiation phase, producing amplified high harmonic radiation extending up to the X-ray domain and showing a coherent, that is a lasing state, of the electromagnetic field Such a conjecture is made more realistic by a recent work [10] showing that, in the case of the light-matter interaction for a single electron, its wavefunction becomes sensitive to the photon statistics. We instead propose to shift the focus from Glauber correlation functions to reconstructing the statistical properties of the FEL radiation related to the photon occupation numbers
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