The TERASPARC collaboration is one of the first experiment in the world concerning the extraction, and the measure of sub-ps THz radiation produced through a Free Electron Laser. The SPARC FEL working at LFN in Frascati provides this unique and exciting possibility.
In the first year of activity we mounted the vacuum chamber for the extraction of coherent THz radiation.
In the second year of activity we have fully characterized the spectral properties of the THz source. The main figures of merit of TERASPARC show very good performances in terms of spectral extension, stability, and power per pulse. In particular we obtained an energy per pulse in the range of 10 microJoule, a spectral interval up to 5 THz and pulse length, using the velocity bunching technique, down to 100 fs:
E. Chiadroni et al, Appl. Phys. Lett. 102, 094101 (2013);
E. Chiadroni et al., J.Phys.359, 012018 (2012);
E. Chiadroni et al., J.Phys., 357, 012034 (2012);
S Lupi et al ., J. Phys.359, 012001 (2012);
These figures of merit show that in comparison with the main competitors (a FEL at NSLS in USA and a FEL in Korea), we are in a very good position.
During the 2012 we have also characterized also exotic bunch shapes like comb (2 and 4 bunches) structures in the fs scale. Data show a strong sensitivity of THz emission and spectral dependence on the comb structure.
In 2011 and following in the 2012 we started the investigation of the THz response of detectors based on YBCO High-Tc superconductor in collaboration with the Unit of Torino and Catania.
NUCL INSTRUM METH B, 272, (2012); SUPERCOND SCI TECH, 25, 115007 (2012);
IEEE T APPL SUPERCON, 21-3, (20112))
During 2012 we have also mounted a new experimental and diagnostic station just at the end of the SPARC linac. This is the second THz station at SPARC working together the first station along the branch line.
Comparative measurements show the effect of spreading in the bunch length induced by the magnetic structure along the branch line. These measurements have shown the importance of the THz diagnostic in a IV generation machine.