Characterization of low-order harmonics generated with the interferometric polarization gating technique
Χαρακτηρισμός αρμονικών χαμηλής τάξης παραγόμενες με την τεχνική πύλης-πόλωσης.
Light pulses have provided the means for observing fast-evolving processes since the invention
of photography. The evolution of ultrafast processes in the molecular and even atomic level can
be tracked by means of ultrashort laser pulses with the widely used pump-probe technique. A
pump laser pulse initiates the dynamics to be observed followed by a delayed probe pulse that
probes the evolution of the process as a function of the delay introduced between the pump and
the probe pulse. The time resolution that can be achieved with this technique is determined by
the laser pulse duration.
During the last decades, continuous efforts in laser-pulse engineering reached femtosecond and
lately attosecond pulse durations allowing with the tracking of ultrafast molecular and atomic
dynamics. High-power ultrafast laser systems are today based on Ti:Sapphire crystals emitting
pulses with a central wavelength of 800 nanometers and pulse durations in the femtosecond
regime. Low odd-order harmonics of these systems are routinely generated through the interaction
with a gas phase medium and can be utilized for time-resolved studies of photochemical
reactions as many organic molecules absorb in this wavelength range. The low-order harmonic
pulse duration is proportional to the generating fundamental pulse duration and determines the
temporal resolution that can be achieved in this kind of experiments.
The scope of the present thesis is the utilization of the previously developed Interferometric
Polarization Gating technique for generation of ultrashort low-order harmonic pulses. Taking
advantage of the harmonic generation dependence on the generating pulse polarization properties,
a temporal gate can be formed in which low-order harmonic emission takes place. In this
case the temporal gate width defines the low-order harmonic pulse duration instead of the longer
generating infrared pulse duration and as a result shorter harmonic pulses can be generated.
The present thesis deals with the generation and characterization of a third-harmonic pulse using
the Interferometric Polarization Gating technique. In the first part the parameters for the
application of the Interferometric Polarization Gating technique for low-order harmonic pulse
generation are investigated. The second part of this thesis deals with the experimental implementation
of this approach for the generation of an intense ultrashort third-harmonic pulse of a Ti:Sapphire laser system.