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Abstract

In this work, a deeper insight into nonlinear optics will be presented. Both regimes,
the perturbative as well as nonperturbative one, were analyzed separately. It was confirmed
that for lower intensities of the perturbative regime, the intensity of the process
is dependent on the square of the intensity of the fundamental frequency, the thickness
of the used medium (Barium borate (BBO) crystal) and the phase-matching condition.
The highest measured efficiency with a 250 fs pulse duration was 36%, whereas for a
40 fs pulse duration is was only 20.8%. However, as the SHG process is saturated at
higher intensities and the intensity of the second harmonic (SH) becomes proportional to
the intensity of the fundamental frequency, this is not an efficient point. These results
are discussed in detail. The nonperturbative regime was analyzed using the process of
"high-order harmonic generation" in argon. These harmonics are measured indirectly by
detecting photoelectrons created from the XUV (of HH) radiation interacting with different
noble gases. A reaction microscope measured the photoelectrons and corresponding ions of
different target gases: helium, neon, argon, krypton, and xenon. Taking into account the
photoionization cross-section, the transmission of the installed aluminum-filter, as well as
the ionization threshold, it was possible to observe different harmonics. An interesting fact
is the unexpected low value for the intensity of the 19th harmonic.