Search Results (4 total)

This paper shows how the MAX linac injector and transport system can be efficiently retuned to suit free electron laser (FEL) performance. In a collaboration between MAX-lab and BESSY, a seeded harmonic generation free electron laser is being constructed at MAX-lab. The setup uses the existing MAX-lab facility upgraded with a new low emittance photocathode gun, a Ti∶Sa 266 nm laser system used for both the gun and seeding and an FEL undulator system. To produce the high quality electron beam needed, it is shown how the magnet optics in an achromatic dogleg can be tuned to create an optimum bunch compression and how a good quality beam can be maintained through the beam transport and delivered to the FEL undulators. In extensive start-to-end simulations from the cathode of the gun to the generation of photons in the undulators, FEL performance and stability has been calculated using simulation tools like ASTRA, ELEGANT, and GENESIS. This has been done for both the third and fifth harmonic of the seed laser. The results from the calculation are 30 fs light pulses with a power of 11 MW at 88 nm and 1.4 MW at 53 nm.

A physical optics approach to wavefront tracking is presented based on the stationary phase approximation. It allows for modeling transmission of radiation through a system of optical elements including coherence properties with an acceptable numerical effort. The code PHASE incorporating these ideas assumes small angles as it is the case for most synchrotron radiation and the free electron laser beam lines.

The orientation of magnetic moments at the (100) surface of antiferromagnetic NiO single crystals is studied by x-ray linear magnetic dichroism in photoemission microscopy. T domains are observed terminating at the surface, with domain boundaries running mostly along in-plane [10] directions. From the detailed polarization dependence we find that the magnetic surface structure of a cleaved crystal is bulk terminated. This is in contrast to sputtered surfaces, where magnetic moments lie within the surface plane, forming a magnetically relaxed structure. These findings are of importance for understanding the exchange bias phenomenon.

Population distributions of vibrational levels within the first excited electronic state A ³Σ_u⁺ of N₂ molecules embedded in a Xe matrix have been derived from emission spectra resulting from selective excitation of individual levels with monochromatized synchrotron radiation. The steady-state population distributions strongly depend on the originally excited level and are incompatible with a simple stepwise nonradiative relaxation process between successive vibrational levels. The experimental distributions are attributed to relaxation by nonradiative electronic energy transfer processes between neighboring N₂ molecules via exchange interaction. The cascade in the A ³Σ_u⁺ state involves relaxation to lower energies in steps of two vibrational quanta and an up conversion of the energy in steps of three vibrational quanta. The probability of these processes follows an energy-gap law for the excess energy.