Statistical properties of a free-electron laser revealed by the Hanbury Brown and Twiss interferometry

We present a comprehensive experimental analysis of statistical properties of the self-amplified spontaneous emission (SASE) free-electron laser (FEL) FLASH at DESY in Hamburg by means of Hanbury Brown and Twiss (HBT) interferometry. The experiments were performed at the FEL wavelengths of 5.5 nm, 13.4 nm, and 20.8 nm. We determined the 2-nd order intensity correlation function for all wavelengths and different operation conditions of FLASH. In all experiments a high degree of spatial coherence (above 50%) was obtained. Our analysis performed in spatial and spectral domains provided us with the independent measurements of an average pulse duration of the FEL that were below 60 fs. To explain complicated behaviour of the 2-nd order intensity correlation function we developed advanced theoretical model that includes the presence of multiple beams and external positional jitter of the FEL pulses. By this analysis we determined that in most experiments several beams were present in radiating field and in one of the experiments external positional jitter was about 25% of the beam size. We envision that methods developed in our study will be used widely for analysis and diagnostics of the FEL radiation.Comment: 29 pages, 14 figures, 3 table

Seeded x-ray free-electron laser generating radiation with laser statistical properties

The invention of optical lasers led to a revolution in the field of optics and even to the creation of completely new fields of research such as quantum optics. The reason was their unique statistical and coherence properties. The newly emerging, short-wavelength free-electron lasers (FELs) are sources of very bright coherent extreme-ultraviolet (XUV) and x-ray radiation with pulse durations on the order of femtoseconds, and are presently considered to be laser sources at these energies. Most existing FELs are highly spatially coherent but in spite of their name, they behave statistically as chaotic sources. Here, we demonstrate experimentally, by combining Hanbury Brown and Twiss (HBT) interferometry with spectral measurements that the seeded XUV FERMI FEL-2 source does indeed behave statistically as a laser. The first steps have been taken towards exploiting the first-order coherence of FELs, and the present work opens the way to quantum optics experiments that strongly rely on high-order statistical properties of the radiation.Comment: 24 pages, 10 figures, 37 reference

Spontaneous supercrystal formation during a strain-engineered metal-insulator transition

Mott metal-insulator transitions possess electronic, magnetic, and structural degrees of freedom promising next generation energy-efficient electronics. We report a previously unknown, hierarchically ordered state during a Mott transition and demonstrate correlated switching of functional electronic properties. We elucidate in-situ formation of an intrinsic supercrystal in a Ca2RuO4 thin film. Machine learning-assisted X-ray nanodiffraction together with electron microscopy reveal multi-scale periodic domain formation at and below the film transition temperature (TFilm ~ 200-250 K) and a separate anisotropic spatial structure at and above TFilm. Local resistivity measurements imply an intrinsic coupling of the supercrystal orientation to the material's anisotropic conductivity. Our findings add an additional degree of complexity to the physical understanding of Mott transitions, opening opportunities for designing materials with tunable electronic properties

Synthesis of nanocrystalline ZnO by the thermal decomposition of [Zn(H2O)(O2C5H7)(2)] in isoamyl alcohol

It was studied how the conditions of heat treatment of a [Zn(H2O)(O2C5H7)(2)] solution in isoamyl alcohol at 120-140A degrees C for 2-60 min affect the precursor decomposition mechanism and the characteristics of the obtained nanocrystalline zinc oxide. In all the cases, the product was a crystalline substance with the wurtzite structure and a size of crystallites of 14-18 nm, which was independent of the synthesis conditions. The thermal behavior and microstructure of the separated and dried nanostructured ZnO powder were investigated. It was determined how the duration and temperature of the heat treatment of the precursor solution affects the microstructure of ZnO coatings dip-coated onto glass substrates using dispersions produced at 120 and 140A degrees C. The nanosized ZnO application procedure was shown to be promising for creating a gas-sensing layer of chemical gas sensors for detecting 1% H-2 ( was 58 +/- 2 at an operating temperature of 300A degrees C) and 4 ppm NO2 ( were 15 +/- 1 and 1.9 +/- 0.1 at operating temperatures of 200 and 300A degrees C, respectively)