Uni HH, Hamburg, Germany
DESY, Hamburg, Germany
This paper describes the experimental activity on the generation of very short FEL pulses in the soft x-ray range in the SASE-mode at the high-gain free-electron laser FLASH [1, 2]. The key element, a photo-injector laser which is able to generate laser pulses of about 2 ps FWHM has been optimized and commissioned. It allows the generation of shorter bunches with low bunch charge (of up to 200 pC) directly at the photo-cathode. Initially shorter injector laser pulses and thus shorter bunches eases the required bunch compression factor for short pulses below 10 fs duration which makes operation of the electron beam formation system to be more robust with respect to jitters and collective effects. As a result, overall stability of SASE FEL performance is improved. In the optimal case single-spike operation can be achieved. In this paper the experimental results on production of short electron bunches and the SASE performance using the new injector laser will be shown and the measured electron bunch and FEL radiation properties are discussed. In addition, optimizations of bunch diagnostics for low charge and short bunches are discussed.
University of Hamburg, Hamburg, Germany
CFEL, Hamburg, Germany
Uni HH, Hamburg, Germany
DESY, Hamburg, Germany
This paper discusses the generation of single spike SASE pulses at soft x-ray wavelength at the free-electron laser FLASH by using very short electron bunches of only a few micrometer bunch length. In order to achieve these extremely short bunch lengths, very low bunch charges (in the order of 20 pC) and short electron bunches exiting the photo-injector are required. For this, a new short-pulse injector laser with adjustable rms pulse duration in the range of 0.7 ps to 1.6 ps and bunch charges up to 200 pC was installed, extending the electron beam parameter range before bunch compression in magnetic chicanes. Beam dynamic studies have been performed to optimize the injection and compression of low-charge electron bunches by controlling the effect of coherent synchrotron radiation and space-charge induced bunch lengthening and emittance growth. Optimization includes the pulse parameters of the injector laser. The simulation codes ASTRA, CSRtrack and Genesis 1.3 were employed.