Ultraviolet laser transverse profile shaping for improving x-ray free electron laser performance

The photocathode rf gun is one of the most critical components in x-ray free electron lasers. The drive laser strikes the photocathode surface, which emits electrons with properties that depend on the shape of the drive laser. Most free electron lasers use photocathodes with work function in the ult...

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Bibliographic Details
Published in:Physical review. Accelerators and beams 2017-08, Vol.20 (8), p.080704, Article 080704
Main Authors: Li, S., Alverson, S., Bohler, D., Egger, A., Fry, A., Gilevich, S., Huang, Z., Miahnahri, A., Ratner, D., Robinson, J., Zhou, F.
Format: Article
Language:English
Subjects:
Coherent light
Critical components
Electron beams
Free electron lasers
Iterative algorithms
Laser outputs
Lasers
Light sources
PARTICLE ACCELERATORS
Photocathodes
Quantum efficiency
Ultraviolet lasers
Work functions
X ray lasers
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Summary:The photocathode rf gun is one of the most critical components in x-ray free electron lasers. The drive laser strikes the photocathode surface, which emits electrons with properties that depend on the shape of the drive laser. Most free electron lasers use photocathodes with work function in the ultraviolet, a wavelength where direct laser manipulation becomes challenging. In this paper, we present a novel application of a digital micromirror device (DMD) for the 253 nm drive laser at the Linear Coherent Light Source. Laser profile shaping is accomplished through an iterative algorithm that takes into account shaping error and efficiency. Next, we use laser shaping to control the X-ray laser output via an online optimizer, which shows improvement in FEL pulse energy. Lastly, as a preparation for electron beam shaping, we use the DMD to measure the photocathode quantum efficiency across cathode surface with an averaged laser rms spot size of 59μm . Our experiments demonstrate promising outlook of using DMD to shape ultraviolet lasers for photocathode rf guns with various applications.
ISSN:2469-9888
2469-9888
DOI:10.1103/PhysRevAccelBeams.20.080704