Spectrometer Based on a VLS Grating for Diagnostics of a Vacuum-Ultraviolet Free Electron Laser

Journal Article · Wed May 12 00:00:00 EDT 2004 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.1757861· OSTI ID:20653011

Reininger, R ^[1]; Feldhaus, J; Ploenjes, E; Treusch, R ^[2]; Roper, M D; Quinn, F M; Bowler, M A ^[3]

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1. Scientific Answers and Solutions, 5708 Restal St., Madison, WI (United States)
2. Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85, D- 22607 Hamburg (Germany)
3. CLRC Daresbury Laboratory, Warrington, WA4 4AD (United Kingdom)

Photon beam diagnostics for vacuum-ultraviolet free electron lasers (VUV FEL) are critical to monitoring and understanding their performance characteristics. Due to the shot-to-shot fluctuations inherent in FELs based on the self amplified spontaneous emission (SASE) process, it is mandatory to use pulse-resolved diagnostics. We have designed a spectrograph based on a variable-line-spacing (VLS) plane grating and a phosphor/CCD to monitor single shot spectra of the free electron laser at DESY. The basic concept is to allow most of the beam to be reflected towards an experimental station while the first order light is dispersed and focused by the VLS grating onto the CCD. The spectrograph will cover the wavelength range 6.4-60 nm with the CCD accepting a bandwidth of {approx}10%. The grazing angle of incidence on the grating is 2 deg., the central line density is 1200 l/mm, and the distance grating-CCD is approximately 2 m. The linear variation of the grating line spacing combined with positioning the detector at the focal curve, allows zeroing the defocus in the full spectrograph wavelength range. The correction of higher order grating aberrations yields a theoretical resolving power greater than 20000 over the full length of the 20 mm CCD when the CCD is positioned tangent to the focal plane. Based on power considerations, a shallow blazed grating is the preferred profile. Efficiency calculations over the spectrograph range show that with a carbon coating the absolute efficiency for zeroth order is higher than 0.85 and the first order efficiency varies between 0.5% and 8%.

• OSTI ID: 20653011
• Journal Information: AIP Conference Proceedings, Vol. 705, Issue 1; Conference: 8. international conference on synchrotron radiation instrumentation, San Francisco, CA (United States), 25-29 Aug 2003; Other Information: DOI: 10.1063/1.1757861; (c) 2004 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
BEAM MONITORING
BEAM MONITORS
BEAM OPTICS
CHARGE-COUPLED DEVICES
CORRECTIONS
DESY
FAR ULTRAVIOLET RADIATION
FLUCTUATIONS
FREE ELECTRON LASERS
INCIDENCE ANGLE
MUTATION FREQUENCY
PERFORMANCE
PHOTON BEAMS
POSITIONING
PULSES
SPECTROMETERS
ULTRAVIOLET SPECTRA
WAVELENGTHS
X RADIATION
X-RAY SPECTROSCOPY