
April 24, 2014 17:36 PSP Book - 9in x 6in 05-Rashid-A.-Ganeev-c05
144 Plasma HHG Using Femtosecond Pulses
Figure 5.1 (a) Emission times, and (b) temporal profile corresponding to
the 11th–19th harmonic orders. Reproduced from Ref. 9 with permission
from Optical Society of America.
The relative phase between neighboring harmonic orders is
accessed through two-photon XUV + IR ionization of the target gas.
When the IR beam is superimposed on the XUV beam in argon
gas, sidebands appear in the photoelectron spectrum between the
main lines. They correspond to two-photon transitions: absorption
of a harmonic photon, qω
0
, accompanied by either absorption or
stimulated ...