Hajdu's first employment (1973) was with the Institute of Enzymology of the Hungarian Academy of Sciences (head:
Brunó Ferenc Straub). In his early work, Hajdu exploited chemistry to determine the symmetry of multi-subunit protein complexes, and characterised structural transitions in these systems. Following an invitation by
Louise Johnson Hajdu joined Johnson's crystallography team in Oxford in 1981, and spent 16 years in the Laboratory of Molecular Biophysics in Oxford (1981-1996), He was first a postdoctoral research fellow and later the head of an MRC laboratory at the Laboratory of Molecular Biophysics. in 1988, he was elected a lecturer of Christ Church, Oxford, teaching biochemistry and biophysics. In 1981, the first dedicated Synchrotron Radiation Source came to life in Daresbury, and Hajdu and his colleagues were among the first users of the facility. The new synchrotron gave them the means to pursue a new direction in structural biology which was to not only determine the structure of proteins, but to observe them functioning. The very first time-resolved X-ray diffraction experiments produced 3D movies of catalysis in crystalline enzymes and revealed structural transitions in viruses. delivering femtosecond X-ray pulses with a peak brightness exceeding synchrotrons by a factor of ten billion. Funding for building such X-ray free-electron lasers faced hurdles. The turning point occurred in 1996, when Hajdu took up a chair at Uppsala University and set up a European research network to explore the physical limits of imaging. The project engaged an interdisciplinary approach, drawing upon structural sciences, plasma physics, optics and mathematics. Hajdu presented their findings to the US Department of Energy in 2000 as part of the scientific justification for building the first hard X-ray free-electron laser, the Linac Coherent Light Source (LCLS), at Stanford. The proof of principle experiment was performed In 2006 with a soft X-ray free-electron laser in Hamburg where Hajdu with
Henry N. Chapman and colleagues demonstrated experimentally that outrunning radiation damage is possible with a femtosecond X-ray pulse. launching the methods of serial nano-crystallography, flash radiography, spectroscopy, and applications in fusion energy research == Achievements ==