Data di Pubblicazione:
2017
Citazione:
POSITRONIUM LASER EXCITATION IN THE AEGIS EXPERIMENT / Z. Mazzotta ; supervisore: F. Castelli ; co-supervisore: M. Giammarchi ; coordinatore: F. Ragusa. DIPARTIMENTO DI FISICA, 2017 Jan 19. 29. ciclo, Anno Accademico 2016. [10.13130/mazzotta-zeudi_phd2017-01-19].
Abstract:
The AEgIS experimental program on antimatter systems involves the formation of antihydrogen
atoms for gravitational and CPT studies. One of the key ingredients of the
AEgIS strategy for the synthesis of antihydrogen atoms is the creation and manipulation
of Positronium (Ps) atoms laser excited to Rydberg states (n > 15).
In AEgIS, Ps is produced in bunched mode and the Rydberg excitation is achieved with
a two laser pulse technique, by passing through a n = 3 intermediate level. Because
excitation on Ps n = 3 state has never been proposed before, in AEgIS a dedicated experimental
apparatus and several detection strategies have been studied in order to observe
the first measurement ever on this interesting process. In this work we present and discuss
the experimental findings about the successful Ps n = 3 excitation.
Moreover, in this thesis, a study of the impact of involved nonlinear processes on the
excitation efficiency of a Doppler broadened atomic cloud is carried out. Presented simulation
results show that, by exploiting properly nonlinear processes in the generation of
the desired wavelength, it is possible to improve the excitation efficiency of a laser pulse.
It is crucial, in AEgIS, the use of a periodically poled crystal in quasi phase matching
regime. This gives a broadband continuous output spectrum whose wings survive to the
spectral cutting of the last nonlinear crystal of the chain (which has insufficient spectral
acceptance). This means that, at high laser energies, these wings can be amplified and
the spectrum gaps can be filled in, leading to high reachable saturation efficiencies. On
the contrary, in a laser pulse with a comb-shaped spectrum with a Gaussian envelope,
both wings and gaps drop rapidly to zero, and amplification hardly occurs at usually
employed energy regimes.
The presented model is finally used to fit AEgIS Ps n = 3 excitation experimental data.
Tipologia IRIS:
Tesi di dottorato
Keywords:
spectroscopy; lasers; excitation; laser excitation; doppler; spectrum; positronium; positrons; aegis; antimatter; antihydrogen; silica converter; nanochannels; nonlinear optics; nonlinear crystals
Elenco autori:
Z. Mazzotta
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