FU Berlin Digitale Dissertation
Wiebke Zimmer : Nonlinear optical effects by the interaction of femtosecond laser pulses with microdroplets Nichtlineare optische Effekte bei der Wechselwirkung von Femtosekundenlaserpulsen mit Mikrotropfen
|Abstract| |Table of Contents| |More Information|

Abstract The subject of this thesis is the study of nonlinear optical effects which are produced by femtosecond laser pulses in microdroplets. An experimental setup is described which is able to detect with high precision the angular dependence of the light emitted by the microdroplets. The measurements lead to a better understanding of the processes occurring in the droplets and are discussed with regard to an implementation of a femtosecond lidar system. Third Harmonic Generation was observed and shows an enhanced forward scattering with a pronounced pattern depending on the size parameter. For smaller droplets the measurements are in good agreement with the theoretical studies of D. Carroll and X.H. Zheng. At this time for larger size parameters their theory is not yet applicable. Therefore a simple model is described based on a combination of Mie theory and geometrical optics, by which the results can be interpreted. Additionally, for the first time Fifth Harmonic Generation was observed in microdroplets and its angular dependence was measured. High intensity laser interaction with transparent microdroplets induces an explosive vaporization of the droplets. We took photographical sequences, which show the - in respect to the center of the droplet - asymmetrical vaporization and the approximate timescale of this process. The emission of the plasma continuum in the visible spectral range shows a forward and backward emission, with an enhanced forward scattering. Due to the high laser intensity the emitting region inside the droplet is located on the side toward the laser. The observed angular distribution can be interpreted by the inverse ray-tracing method. In addition to the plasma continuum the emission of the sodium atoms exited by the plasma was characterized with spectral and angular dependent resolution using droplets containing a 5-M NaCl solution. An enhanced backward emission for the plasma fluorescence was observed.

Table of Contents Download the whole PhDthesis as a zip-tar file or as zip-File For download in PDF format click the chapter title   Titel Inhaltsverzeichnis 1 Einleitung 2 Troposphärisches Aerosol      2.1 Entstehung atmosphärischer Aerosole      2.2 Umwandlungsprozesse des troposphärischen Aerosols      2.3 Chemische Zusammensetzung      2.4 Auswirkung auf atmosphärische Prozesse      2.5 Meßverfahren 3 Theoretische Grundlagen      3.1 Nichtlineare optische Prozesse      3.2 Die klassische Mie-Theorie      3.3 Nichtlineare optische Effekte in Mikrotropfen      3.4 Laserinduzierter Durchbruch 4 Experimenteller Aufbau      4.1 Das Lasersystem      3.2 Tropfengeneration      3.3 Experimentsteuuerung und Meßverfahren 5 Resultate      5.1 Frequenzvervielfachung      5.2 Laserinduzierter Durchbruch      5.3 Plasmalumineszenz 6 Zusammenfassung 7 Literaturverzeichnis - - 1 5 5 9 11 12 16 21 22 27 37 46 53 53 64 65 69 70 94 96 107 111

More Information:
Online available:	http://www.diss.fu-berlin.de/2001/30/indexe.html
Language of PhDThesis:	german
Keywords:	microdroplets, nonlinear optics, THG, plasma spectroscopy
DNB-Sachgruppe:	29 Physik, Astronomie
Classification PACS:	42.65.-k, 42.68.Ge
Date of disputation:	12-Feb-2001
PhDThesis from:	Fachbereich Physik, Freie Universität Berlin
First Referee:	Prof. Dr. Ludger Wöste
Second Referee:	Prof. Dr. Helmut Baumgärtel
Contact (Author):	wiebke.zimmer@physik.fu-berlin.de
Contact (Advisor):	woeste@physik.fu-berlin.de
Date created:	26-Feb-2001
Date available:	28-Feb-2001

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