Dr. rer. nat. Karsten Holldack
The physicist at BESSY works with THz radiation developing new concepts and applications
After studying physics from 1980-1985 at Humboldt-Universität zu Berlin Karsten Holldack finished his PhD on ion implantation in semiconductors in 1987. Gaining experience for one year in semiconductor industry he returned to Humboldt-University as a scientific assistant. Already in 1990 he became a Synchrotron Radiation user at BESSY I in Wilmersdorf.
Even changing to a postdoc-position at the University of Heidelberg he continued working with Synchrotron Radiation investigating structural and magnetic domains on surfaces with imaging photoelectron microscopy. When BESSY II was approval in 1993 he followed a call to join the team for the construction and commissioning of the new light source. The diagnostic components developed by Karsten during this time have become a standard for almost all new 3rd generation storage rings worldwide.
Once the commissioning of BESSY II was accomplished in 1999 he has gradually changed his scientific interest into the development of novel methods, instrumentation, diagnostics and applications of Synchrotron Radiation. Particularly fascinated by the fact that short relativistic electron bunches may emit Coherent Synchrotron Radiation (CSR) pulses (in the THz range) when compressed to length scales shorter than the wavelength, Dr. Holldack was engaged together with accelerator physicists from BESSY in the development of the “low alpha mode”, which has become a standard mode in the BESSY II operation schedule for THz and Picosecond X-ray experiments.
In 2002 Karsten Holldack and colleagues were awarded the Synchrotron Innovation Award for "Development of a powerful broad band source of Terahertz radiation on the basis of an electron storage ring". He continued working with THz radiation developing new concepts and applications.
Based on ideas from users (FU-Berlin and former HMI) Dr. Holldack recently established a novel technique only available in Adlershof: High Field THz-EPR with Coherent Synchrotron Radiation (funded by the BMBF project EPR-SOLAR). Excited by the interesting scientific opportunities of ultrashort electron bunches he joined the „Femtosclicing“ comissioning team in 2003. Here, circularly polarized soft X-rays are generated by laser-energy modulation of the electron bunches in the storage ring.
The detection and analysis of THz pulses has again turned out to be a key issue for the success of this project, since the pulse acts as an indicator if the ultrashort laser pulse from a few 10 m distance really hits the tiny electron bunch: a prerequisite to generate fs-X-rays.
The intriguing fact that THz pulses are emitted by a „dip“ in the electron bunch (see figure) can be employed to measure the arrival time of the electrons with 5 fs precision to perform Laser-pump THz-probe experiments on ultrashort time scales.
K. Holldack, S. Khan, R. Mitzner, T. Quast, “Femtosecond THz pulses from Femtoslicing at BESSY” Phys. Rev. Lett. 96, 054601 (2006), Phys. Rev. Lett. 96, 054601 (2006).
Contact: Dr. Karsten Holldack, e-mail: Karsten.Holldack(at)Helmholtz-Berlin.de, tel. +49 30 / 6392-3170