A compact Hartmann wavefront sensor specifically optimized for the EUV spectral range was developed in a cooperation of Laser-Laboratorium Göttingen and DESY / Hamburg. Primarily designed for optics adjustment and beam characterization of the free electron laser FLASH, the self-supporting device can also be used in combination with any other EUV radiation source, as e.g. for at-wavelength fine-tuning of EUVL beam line optics. Tests performed at FLASH and LCLS indicate an average wavefront measurement repeatability of λ/116 (w_rms) at λ=13.5nm for the EUV Hartmann sensor. The device can be successfully employed for characterization of the unfocused FEL beam, as well as for fine-adjustment of EUV optics, as demonstrated for an ellipsoidal focusing mirror at beam-line BL2 of FLASH. The wavefront monitored behind this mirror provided information on typical misalignment effects such as astigmatism or coma. Improved alignment allowed for reduction of the wavefront rms (w_rms) from 3.9nm to 1.5nm. Tests performed with LPP EUV sources indicate that the new sensor can also be used for actinic optics characterization and real-time fine-tuning of EUVL optics systems.

Date Published: 1 April 2013
PDF: 9 pages
Proc. SPIE 8679, Extreme Ultraviolet (EUV) Lithography IV, 867922 (1 April 2013);

Published in SPIE Proceedings Vol. 8679:
Extreme Ultraviolet (EUV) Lithography IV
Patrick P. Naulleau, Editor(s)