Influence of absorption on phase-matched generation of coherent extreme ultraviolet radiation in a long interaction geometry

The pressure dependent high-order harmonic generation in a semi-infinite gas cell with two different absorbing gaseous media (argon and helium) is analyzed to reveal the influence of absorption on the radiation process in the extreme ultraviolet region. The absorption cross section of a particular wavelength in this region is measured. Moreover, in consideration of macroscopic response, the geometrical phase mismatch and the dipole phase mismatch which are independent to the pressure are clearly studied. A Young's double slit experiment is also performed to indicate a high spatial coherence of the harmonic radiation. This measurement shows that a narrow bandwidth, bright, and highly coherent high harmonic source can be generated in gas cell filled with absorbing gases which could be useful for coherent diffractive imaging.