29 research outputs found
KMC/EDAM : A new approach for the visualization of K-Means Clustering results
In this work we introduce a method for classification and visualization. In contrast to simultaneous methods like e.g. Kohonen SOM this new approach, called KMC/EDAM, runs through two stages. In the first stage the data is clustered by classical methods like K-means clustering. In the second stage the centroids of the obtained clusters are visualized in a fixed target space which is directly comparable to that of SOM. --
Fundamental Carrier-Envelope Phase Noise Limitations during Pulse Formation and Detection
The difference between the positions of the maximum peak of the carrier wave of a laser pulse and the maximum
of its intensity envelope is termed carrier-envelope phase (CEP). In the last decades, the control and stabilization
of this parameter has greatly improved, which enables many applications in research fields that rely on
CEP-stable pulses such as attosecond science and optical frequency metrology. Further progress in these fields depends
strongly on minimizing the CEP noise that restricts stabilization performance. While the CEP of most high
repetition-rate low-energy laser oscillators has been stabilized to a remarkable precision, some types of oscillators
show extensive noise that inhibits precise stabilization. The CEP stabilization performance of low repetition-rate
high peak-power amplified laser systems also remains limited by noise, which is believed to stem mainly from the
CEP detection process.
In this thesis, the origins of the CEP noise within four oscillators as well as the noise induced by the measurement
of the CEP of amplified pulses are investigated. In the first part, the properties of the CEP noise of one
Ti:sapphire oscillator and three different fiber oscillators are extracted by analyzing the unstabilized CEP traces by
means of time-resolved correlation analysis of carrier-envelope amplitude and phase noise as well as by methods
that reveal the underlying statistical noise properties. In the second part, investigations into the origin of CEP noise
induced by the measurement of the CEP of amplified pulses are conducted by comparing several different CEP
detection designs that are based on f -2 f interferometry. These detection setups differ in the employed sources of
spectral broadening as well as frequency doubling media, both necessary steps to measure the CEP. The results
in both parts of this thesis show that white quantum noise dominates most CEP measurements. In one particular
fiber oscillator, the strong white noise is found to be a result of a correlating mechanism within the employed
SESAM. During amplifier CEP detection, the CEP noise is found to be originating only to a marginal degree from
the number of photons that are detected during the measurement, which excludes shot noise as a limiting source.
Instead, the analysis reveals that the origin of the observed strong white noise can be interpreted as a loss of coherence
during detection. This type of coherence is termed here intra-pulse coherence and describes the phase
transfer within f -2 f interferometry. Its degradation is a result of amplitude-to-phase coupling during the spectral
broadening process that leads to pulse-to-pulse fluctuations of the phases at the edges of the extended spectrum.
Numerical simulations support the concept of intra-pulse coherence degradation and show that the degradation is
substantially stronger during plasma-driven spectral broadening as compared to self-phase modulation-dominated
spectral broadening. This difference in degradation also explains the much stronger CEP noise typically observed
in amplified systems as compared to oscillators, as the former typically rely on filamentation-based and hence
plasma-dominated spectral broadening for CEP detection. The concept of intra-pulse coherence constitutes a
novel measure to assess the suitability of a spectral broadening mechanism for application in active as well as in
passive CEP stabilization schemes and provides new strategies to reduce the impact of the CEP detection on the
overall stabilization performance of most lasers.Diese Arbeit beschäftigt sich mit der Identifizierung und Minimierung fundamentaler Rauschquellen, die zu einer
Limitierung des erreichbaren Carrier-Envelope Phasen (CEP) Jitters fĂźhren. Die Carrier-Envelope Phase beschreibt
die Differenz zwischen dem Maximum der Trägerwelle und dem Scheitelpunkt der Intensitätseinhßllenden. In den
letzten Jahrzehnten hat sich die Kontrolle und Stabilisierung der CEP deutlich verbessert, was zu einem schnellen
Fortschritt in Forschungsfeldern gefĂźhrt hat, bei denen CEP-stabile Pulse notwendig sind. Diese Forschungsfelder
umfassen die Attosekundenforschung und optische Frequenzmetrologie. Weitere Entwicklungen in diesen Feldern
hängt stark von der Minimierung von CEP Rauschen ab, welches die CEP Stabilisierung stark beeinträchtigt.
Obwohl die CEP der Pulse der meisten Laseroszillatoren mit hohen Repetitionsraten äuĂerst genau stabilisiert
werden kann, existieren einige Laseroszillatoren bei denen starke Rauschquellen eine Stabilisierung verhindern
oder stark einschränken. Des Weiteren zeigen vor Allem verstärkte System mit niedrigen Repetitionsraten und
hohen Spitzenleistungen eine Beschränkung der CEP Stabilisierung aufgrund von Rauschen, dass vermutlich zum
groĂen Teil durch den Detektionsprozess entsteht. In dieser Arbeit ist der Ursprung von CEP Rauschen in vier unterschiedlichen
Laseroszillatoren sowie während der Detektion der CEP von verstärkten Systemen untersucht worden.
Im ersten Teil wurden die Eigenschaften des CEP Rauschens eines Ti:Saphir-basierten Oszillators und drei
verschiedener Faserlaser analysiert. Hierzu wurde das Rauschen unter anderem mittels zeitaufgelĂśster Korrelationsanalyse
von Carrier-Envelope Amplituden- und Phasenrauschen sowie mittels Methoden, die die statistischen
Eigenschaften des Rauschens offenlegen, analysiert. Im zweiten Teil der Arbeit wurde das Rauschen untersucht,
welches durch den Messprozess der CEP von verstärkten Pulsen mittels f -2 f Interferometrie entsteht. Experimentell
wurden hierzu vier unterschiedliche Detektionsanordnungen verwendet, die sich durch die Nutzung unterschiedlicher
nichtlinearer Prozesse zum Erzeugen der spektralen Verbreiterung sowie zur Erzeugung der zweiten
Harmonischen unterscheiden. Die Ergebnisse in beiden Teilen der Arbeit zeigen dominierendes weiĂes Quantenrauschen
in den meisten CEP Messungen. In einem bestimmten Faserlaser, in dem besonders starkes weiĂes
Rauschen vorlag, konnte der Ursprung einerWechselwirkung innerhalb des verwendeten halbleiterbasierten sättigbaren
Absorbers zugeordnet werden. Bei der Detektion der CEP bei verstärkten Systemen wurde hingegen gezeigt,
dass niedrige Photonenzahlen und damit Schrotrauschen nur zum kleinen Teil fĂźr die starken weiĂen Rauschanteile
verantwortlich gemacht werden kann. Stattdessen kann die Ursache des starken Rauschens einem Verlust von Kohärenz
zugeordnet werden. Diese Art von Kohärenz ist hier mit intra-Puls Kohärenz bezeichnet und beschreibt
den Phasentransfer innerhalb der Detektion mittels f -2 f Interferometrie. Der Verlust von intra-Puls Kohärenz ist
eine Folge von Amplituden-zu-Phasen Koppelung während der spektralen Verbreiterung. Von Puls zu Puls fßhrt
dies zu Fluktuationen der Phase an beiden Rändern der erzeugten spektralen Verbreiterung. Numerische Simulationen
unterstßtzen das Konzept der intra-Puls Kohärenz und zeigen auf, dass die Degradation bedeutend stärker
bei plasmadominierten Prozessen ausfällt als im Vergleich zu spektraler Verbreiterung mittels Selbstphasenmodulation.
Dieser unterschiedlich starke Verlust der intra-Puls Kohärenz erklärt das deutlich hÜhere Rauschniveau in
verstärkten Systemen im Vergleich zu Oszillatoren, da verstärkte Systeme plasmadominierte Prozesse zur spektralen
Verbreiterung nutzen. Das Konzept der intra-Puls Kohärenz stellt ein neues Maà zur Einschätzung einer
Methode zur spektralen Verbreiterung fĂźr eine bestimmte Anwendung dar, die sowohl in aktiven sowie passiven
CEP Stabilisierungen von Lasern eine Rolle spielt. Es ermĂśglicht somit neue Strategien, um den Einfluss der
Detektion auf die CEP Stabilisierung der meisten Laser zu senken
Prediction of spiralling in BTA deep-hole drilling: estimating the system's eigenfrequencies
One serious problem in deep-hole drilling is the formation of a dynamic disturbance called spiralling which causes holes with several lobes. Since such lobes are a severe impairment of the bore hole quality the formation of spiralling has to be prevented. Gessesse et al. [2] explain spiralling by the coincidence of bending modes and multiples of the rotation frequency. They derive this from an elaborate finite elements model of the process. In online measurements we detected slowly changing frequency patterns similar to those calculated by Gessesse et al. We therefore propose a method to estimate the parameters determining the change of frequencies over time from spectrogram data. This significantly simplifies the explanation of spiralling for practical applications compared to finite elements models which have to be correctly modified for each machine and tool assembly. It turns out that this simpler model achieves to explain the observed frequency patterns quite well. We use this for estimating the variation of the frequencies as good as possible. This opens up the opportunity to prevent spiralling by e.g. changing the rotary frequency. --
Identifying different areas of inhomogeneous mineral subsoil
We use a recently proposed
fluctuation-type procedure for detecting breaks in
spatial regions to distinguish between hard and soft areas of inhomogeneous mineral subsoil like additives, air pockets and adhesion. For a proper application,
some refinements of the procedure are necessary. Both simulation evidence of the
refinement and the application on the subsoil yield favorable results
Deriving a statistical model for the prediction of spiralling in BTA deep hole drilling from a physical model
One serious problem in deep-hole drilling is the occurrence of a dynamic disturbances called spiralling. A common explanation for the occurrence of spiralling is the coincidence of time varying bending eigenfrequencies of the tool with multiples of the spindle rotation frequency. We propose a statistical model for the estimation of the eigenfrequencies derived from a physical model. the major advantage of the statistical model is that it allows to estimate the parameters of the physical model directly from data measured during the process. This represents an efficient way of detecting situations in which spiralling is likelyy and of deriving countermeasures
KMC/EDAM: A new approach for the visualization of K-Means Clustering results
In this work we introduce a method for classification and visualization. In contrast to simultaneous methods like e.g. Kohonen SOM this new approach, called KMC/EDAM, runs through two stages. In the first stage the data is clustered by classical methods like K-means clustering. In the second stage the centroids of the obtained clusters are visualized in a fixed target space which is directly comparable to that of SOM
Local Models in Register Classification by Timbre
Investigating a data set containing different sounds of several instruments suggests that local modelling may be a promising approach to take into account different timbre characteristics of different instruments. For this reason, some basic ideas towards a local modelling are realized in this report yielding a framework for further studies. --
Modelling and Understanding of Chatter
Recent analysis in chatter modelling of BTA deep-hole drilling consisted in phenomenological modelisation of relationships between the observed time series and appearance of chatter during the process. Using the newly developed MEWMA control chart [4, 5], it has even been possible to predict the occurence of chatter about 30 to 50 mm in advance (i.e. up to one minute before the chatter starts). Unfortunately, no relationships between the machine and model parameters have been detected. Therefore, in this paper a physical model of the boring bar is taken into account. Simulation studies of the regenerative process are performed. These simulated time series show the same characteristics as the data recorded during the drilling process and thus support the validity of our model. By running such simulations, we intend to find strategies for chatter prevention in future work. --
Statistical process modelling for machining of inhomogeneous mineral subsoil
Because in the machining process of concrete tool wear and production
time are very cost sensitive factors the adaption of the tools to the particular machining
processes is of major interest.
We show how statistical methods can be used to model the influences of the process
parameters to the forces affecting the workpiece as well as the chip removal rate and
the wear rate of the used diamond. Based on these models a geometrical simulation
model can be derived which will help to predetermine optimal parameter settings
for specific situations.
As the machined materials are in general abrasive, usual discretized simulation
methods like Finite Elements Models can not be applied. Hence our approach is
another type of discretization namely subdividing both material and diamond grain
into their Delaunay tessellations and interpreting the resulting micropart connections
as predetermined breaking points. Then the process is iteratively simulated
and in each iteration the interesting entities are computed