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The characterization of the transverse phase space for high charge density and high energy electron beams is demanding for the successful development of the next generation light sources and linear colliders.

Due to its non-invasive and non-intercepting features, Optical Diffraction Radiation (ODR) is considered as one of the most promising candidates to measure the transverse beam size and angular divergence.

The recent results of our experiment, based on the detection of the ODR angular distribution to measure the electron beam transverse parameters and set up at FLASH (DESY), are presented. A thin stainless steel mask has been installed at 45° with respect to the DR target and normally to the beam propagation to reduce the contribution of synchrotron radiation (SR) background. In addition, interference between the ODR emitted on the shielding mask in the forward direction and the radiation from the DR target in the backward direction is observed. This is what we call Optical Diffraction Interferometry (ODRI). The contribution of this interference effect to the ODR angular distribution pattern and, consequently, its impact on the beam transverse parameters is discussed.

In the last couple of years, free electron lasers (FELs) have been a remarkable success as fourth generation light sources all over the world. Operating in the SASE mode, they produce laser-like radiation in a broad wavelength range. Especially in the soft and hard X-ray ranges, these light sources open unique and completely new fields in physics and allow a vast range of applications in most scientific fields. This article gives an overview of the principles of FELs and the SASE process, discusses technological challenges and solutions, and presents an outlook for future developments.

Diffraction Radiation is receiving ever more consideration as a non-intercepting diagnostic tool. On the superconducting linac at FLASH diagnostic instruments based on DR are routinely used, and new developments are continuously experimented.

The analysis of the coherent part of DR spectrum allows the measurement of the longitudinal charge distribution in the bunch, while the incoherent emission at optical wavelengths can give information on the transverse beam size. In this last case the interference effects that are at the basis of the Optical Diffraction Radiation angular distribution must be properly taken into account.

The characterization of the transverse phase space for high charge density and high energy electron beams is demanding for the successful development of the next generation light sources and linear colliders.

Due to its non-invasive and non-intercepting features, Optical Diffraction Radiation (ODR) is considered as one of the most promising candidates to measure the transverse beam size and angular divergence.

The recent results of our experiment, based on the detection of the ODR angular distribution to measure the electron beam transverse parameters and set up at FLASH (DESY), are presented. A thin stainless steel mask has been installed at 45° with respect to the DR target and normally to the beam propagation to reduce the contribution of synchrotron radiation (SR) background. In addition, interference between the ODR emitted on the shielding mask in the forward direction and the radiation from the DR target in the backward direction is observed. This is what we call Optical Diffraction Interferometry (ODRI). The contribution of this interference effect to the ODR angular distribution pattern and, consequently, its impact on the beam transverse parameters is discussed.

In the last couple of years, free electron lasers (FELs) have been a remarkable success as fourth generation light sources all over the world. Operating in the SASE mode, they produce laser-like radiation in a broad wavelength range. Especially in the soft and hard X-ray ranges, these light sources open unique and completely new fields in physics and allow a vast range of applications in most scientific fields. This article gives an overview of the principles of FELs and the SASE process, discusses technological challenges and solutions, and presents an outlook for future developments.