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SwissFEL photocathode laser optimization and stabilization using data-driven optimization
To achieve continuous stability, we propose to optimize the swiss-FEL UV seed laser beam, using images of the beam from two cameras and measurements of the laser power. In this project, we will use sequential data-driven optimization to achieve efficiently the correct alignment via motorized mirrors
SwissFEL is a relatively compact X-ray Free Electron Laser (FEL) operated by Paul Scherrer Institute in Villigen AG. A bunch of electrons is generated from a photocathode by a pulsed optical laser (100 Hz) in the ultraviolet spectral range. These electrons are accelerated and produce intense femtosecond X-ray pulses, which are used for various research applications.
In this multidisciplinary project, we aim to optimize the long-term stability of the seeding UV laser beam shape and energy, as they have direct impact on the performance and stability of the FEL facility. The optimization and feedback system will be implemented and tested on a dedicated development system that will be installed by the student in our laser laboratory at the Paul Scherrer Institute, under the supervision of scientists at PSI. The generation of ultraviolet laser beams usually does not lead to a uniform Gaussian intensity distribution in the spatial beam profile. This problem is further enhanced by unavoidable UV-radiation damage of optical components, which generates more and even time-depended structure in the beam. The standard approach is to use Fourier filtering to create a uniform beam for the application.
Two mirror mounts with piezoelectric actuators are used to steer the focused beam through a small hole for filtering. Currently, the beam pointing is fixed by the evaluation of the center of a Gaussian fit to the beam images at two locations. This method has the major drawback that the fitted beam position changes as soon as the beam profile changes. This effect causes the focal point to move away from the center of the filter, therefore changing the output beam profile and decreasing the transmission and energy stability.
The data-driven optimization and feedback algorithm is expected to initially find the optimal transmission through the spatial filter and later on keep the output conditions (beam profile and energy stability) constant, by defining data-driven performance metrics of the slowly changing input beam profiles via image processing and measurements of the pulse energy, and continuously monitoring for deviations. An efficient sequential optimization procedure integrating learning of the performance-based objective and constraints will ensure that the beam stability is maintained, via automated adjustments of the angles of two beam steering mirrors before the spatial filter. The data-driven optimization will be supervised by scientists at the Automatic Control Laboratory at ETH Zurich.
SwissFEL is a relatively compact X-ray Free Electron Laser (FEL) operated by Paul Scherrer Institute in Villigen AG. A bunch of electrons is generated from a photocathode by a pulsed optical laser (100 Hz) in the ultraviolet spectral range. These electrons are accelerated and produce intense femtosecond X-ray pulses, which are used for various research applications.
In this multidisciplinary project, we aim to optimize the long-term stability of the seeding UV laser beam shape and energy, as they have direct impact on the performance and stability of the FEL facility. The optimization and feedback system will be implemented and tested on a dedicated development system that will be installed by the student in our laser laboratory at the Paul Scherrer Institute, under the supervision of scientists at PSI. The generation of ultraviolet laser beams usually does not lead to a uniform Gaussian intensity distribution in the spatial beam profile. This problem is further enhanced by unavoidable UV-radiation damage of optical components, which generates more and even time-depended structure in the beam. The standard approach is to use Fourier filtering to create a uniform beam for the application.
Two mirror mounts with piezoelectric actuators are used to steer the focused beam through a small hole for filtering. Currently, the beam pointing is fixed by the evaluation of the center of a Gaussian fit to the beam images at two locations. This method has the major drawback that the fitted beam position changes as soon as the beam profile changes. This effect causes the focal point to move away from the center of the filter, therefore changing the output beam profile and decreasing the transmission and energy stability.
The data-driven optimization and feedback algorithm is expected to initially find the optimal transmission through the spatial filter and later on keep the output conditions (beam profile and energy stability) constant, by defining data-driven performance metrics of the slowly changing input beam profiles via image processing and measurements of the pulse energy, and continuously monitoring for deviations. An efficient sequential optimization procedure integrating learning of the performance-based objective and constraints will ensure that the beam stability is maintained, via automated adjustments of the angles of two beam steering mirrors before the spatial filter. The data-driven optimization will be supervised by scientists at the Automatic Control Laboratory at ETH Zurich.
Continuous optimization of the laser beam to improve its stability, using data of the beam profile from images, and measurements of the pulse energy.
Continuous optimization of the laser beam to improve its stability, using data of the beam profile from images, and measurements of the pulse energy.
Dr. Alisa Rupenyan ralisa@control.ee.ethz.ch, Dr. Martin Huppert martin.huppert@psi.ch, Dr. Alexandre Trisorio alexandre.trisorio@psi.ch
https://www.psi.ch/en/lno/gun-laser-group ;
https://control.ee.ethz.ch/
Dr. Alisa Rupenyan ralisa@control.ee.ethz.ch, Dr. Martin Huppert martin.huppert@psi.ch, Dr. Alexandre Trisorio alexandre.trisorio@psi.ch