Graded-index Multimode Fiber (MMF) Optimisation and Transmitter/Receiver Coupling for Optical Muli-Input/Output Transmission System
Multi-mode fibers provide interesting features for long distance transmissions theoretically because of the high tolerance for the non-linear effects, its relative ease for installation and high coupling efficiency due to the large core diameter. But there are problems that limit the use of multi-mode fiber: as the name indicates itself, multi-mode fibers induce more than one mode unlike single mode fibers. This modes carrying the information propagate in the fiber with different propagation property and they will arrive at the receiver end at different time, the delay between the modes, DMD, is not zero. This will cause the broadening of the signal and inter symbol interference. And as the length of the fiber increases, the broadening also increases. As a result, the application of MMF’s has been limited to short range communication. The other problem is chromatic dispersion or group velocity dispersion which caused due to the non-monochromatic nature of the light coupled to the MMF. The different frequency components of the modes will propagate at different speed which also contributes to the degradation of the signal. The third and important effect is the mode coupling due to micro and macro bending along the fiber.
In this thesis, graded index optical fibers are studied as a way to minimize DMD. The refractive index profile of GI NMF can have different structure; among the many the power-law profile function structure is studied. The propagating modes are approached both analytically and numerically to have consistent analytical equation for the modes of different profile structures. The profile of the fiber is optimized by finding a profile which gives minimum DMD. The effect of the profile optimization on the GVD is simulated as well. Mode coupling effect is not included here.
Finally MIMO system is discussed briefly. First the channel matrix is calculated with DMD and GVD, then the effect on the pulse is simulated from MIMO perspective. Then the effect of the profile optimization on the length of the fiber is simulated and discussed along with the signal processing capacity of the MIMO system.
AFM Nanolithography for the Electrical Growth of Silver (Ag)
Human mind is always thinking forward and discovering new ideas, which keep developing during the course of their life. As a result, innovative technologies and intelligent inventions keep on emerging some of them are abased on new research while other are result of utilizing the old one. Nanotechnology is one such technology that is going to be a big step forward in transforming the world.
This thesis talks about the growth of silver nanoparticles through local chemical reduction method in AFM. Different parameters deeply studied and explained in theis thesis which cause problem for the creation of silver nanoparticles e.g. tip/sample contact time, tip/sample voltage difference, humidity factor and sample preparation. Matlab coding is also used to generate graphs for Absorption, Scattering and Extinction spectrum of silver nanoparticles for different diameters.
Cylindrically Polarized Light in Nanobore PCF
Conclusions: During this work, some properties of a special kind of a solid core PCF was studied. In this kind, there is a coaxial nanobore at the centre of core which causes an increase in the birefringence between cylindrical modes. Due to this special design, it is called nanobore PCF. Doing some experiments on a sample of this kind of fiber, the results are depicted through the chapter 3.
This involves excitation of cylindrical modes, attenuation coefficient measurement, and coupling between cylindrical modes. In exciting using SLM, the cylindrical modes’ profile, azimuthal or radial, were generated beforehand and coupled to the fiber, causing to excite the same mode inside the fiber. The quality of the beam in this method of excitation were acceptable, but not perfect. Using a SLM device sometimes is handy, because makes it easy to excite higher order modes, even the results are not pure.
This devices can be engineered to excite more higher order modes, which may be of interest for some people. However, it is comparably an expensive method. Following, the loss of fiber for different modes measured. This is an important property, which determines the length that light could transfer in the fiber, while some effects like absorption and scattering try to destroy it. Roughly speaking, a mode with a higher refractive index has lower attenuation. This is because it has less interaction at the boundaries.
The measurements done in this work comply with this principle. Fundamental mode has the lowest attenuation coefficient, whereas azimuthal mode has a larger coefficient, and radial mode has a coefficient which is largest amongst. This is a sign of correct measurement, and a new measurement in its kind which was not done before. Generally, when a mode is propagating inside the fiber, it keeps all its energy for itself and doesn’t share it with other modes. This is the principle of orthogonally of modes.
However, when there is some sources of stress like bending or imperfections in the fiber structure, the mode starts to share the energy with other modes. In a simple language, the orthogonally rule is broken due to stress. In some fibers, cylindrical modes, and also HE21, are very degenerate, causing coupling of those modes to each other very easily, which is not desired in some applications.
As discussed in introduction of the thesis, enclosing a nanobore in the solid core PCF will increase the birefringence between cylindrical modes. This practically increase the beat length of fiber, and consequently those modes can propagate a longer distance without being coupled one to another.
Now there is a look from the other side; how the coupling between modes could be controlled? How to engineer sources of stress to govern the coupling between modes? This question was realized in this work using a mechanical grating, which performed very well. Starting from azimuthal mode, and pressing the grating on a stripped fiber, there was a smooth transition to radial mode, and to prove its correctness, some discussion were made.
In the last part of experiments, Sec. 3.4, azimuthally polarized light excited using gold filled nanobore PCF. That is a novel way to produce azimuthal mode, while other modes attenuated, and a clean azimuthal mode gained, which was not mixed up. The images taken in different angles of the polarizer, shows the symmetry, purity and quality of the mode. This is the one of the best generation methods if someone is looking for a real azimuthal mode. Compared to the method of exciting by SLM, it also has a simpler setup. But the only a weakness of this method is the lower output power, while most of the energy is attenuated in the gold filled part.
Characterization of the Large Fresnel Lens Used in Solar Hidden Photon Search (SHIPS)
Abstract: Solar Hidden Photon Search (SHIPS) is an experimental astroparticle project in which the existence of the postulated elementarily particles, calles hidden photons, is under investigation. Forming an image of one the sources emits such strange particles, i.e. sun, is the final goal of the SHIPS project which can prove the entity of hidden photons. This thesis will discuss the behaviour of the optics used in the SHIPS project for solar imaging. The influence of different lens structures under two distinct illuminations are observed. Images of a shiny fiber end-face are captured after a large polymer Fresnel lens via chanigng the position of the detector. To estimate the sharpness of the solar image in the SHIPS project, the dependency of the focal length on the wavelength for such lenses is examined by modifying the light source. Analyzing the results, helps to find the affiliated parameters like the size of the image, the mean intensity and the signal to noise ratio for each image. Substituting the Fresnel lens with a typical convex lens and repeating the whole process, produces images that can be considered as a reference for the images taken by the Fresnel lens. Comparing the images of both lenses, characterizes the performance of the Fresnel lens used in the SHIPS project.
Development of Biopolymer-Ceramic Composite Coatings by Electrophoretic deposition for Orthopedic Applications
The aim of this thesis is to develop biomaterials mainly biopolymer ceramic composite for orthopaedic application using Electrophoretic deposition method. First by producing PEEK coating using optimal parameters (2wt% PEEK suspension concentration, 20 V applied electric field, 1 cm electrode distance and 2 min as deposition time) on metallic substrate like stainless steel, it was proved that PEEK has a good adherent on stainless steel and can be sued as a material for long-term medical application which is using until now in spinal fusion, joint replacement, trauma applications, dental implants.
Offering several benefits such as mechanical strength, biocompatibility, imagine or sterilization properties and chemical resistance make this polymer attractive for other field of applications like aerospace, automotive and industry. This concluded also via various characterization methods like adhesion test and CO2 laser sintering as heat treatment method with the best parameters of 5% laser power, scan speed 1500 mm/s, hatch distance 0.10 mm.
Another part of this work based on production of PEEK/Bioglass composition coating by adding Biogas 45S5 with different concentration 10Vol%, 18Vol% and 30Vol% to PEEK. SEM micrographs shows the composite coating containing 18VOL% Biogas has much more homogenous, sense surface structure compared to other samples. The Taguchi design of experiment confirmed the results as well.
Further the bioactivity test was carried out to check if the PEEK/Biogas composite is able to deposit hydroxycarbonated apatite crystals on its surface. Increasing the immersion days in SBF, increased the formation of HCA layer containing calcium phosphate particles on the surface of PEEK, which was indicated with SEM images. PEEK/Bioglass coatings developed in this work should protect the stainless steel substrate from corrosion in SBF solution and also generally every coating containing Bioglass is bioactive and should improve the bonding of bone or soft tissue to the implant to change the healing process in a better way.
Rayleigh and Brillion Scattering for the Measurement of Thermal Diffusivity and Sound Speed in Multicomponent Mixtures
Introduction: According to the regulation (EC) No. 2037/2000 of the European Parliament, which controls the use of hydrochlorofuorocarbons, the refrigerant R22 is prohibited due to environmental hazards. Appropriate replacements for this widely used industrial refrigerant are thus necessary. The new refrigerant mixtures R22 M and R22 L currently constitute a direct drop-in solution for existing refrigeration systems. To optimize the performance of existing systems, the thermophysical properties for these ternary mixtures must be determined. Up to now, no experimental data have been available. Since the calculation of the transport properties for multicomponent mixtures based on the properties of the pure components still has an uncertainty range of 10%, measurements for the thermal diffusivity and sound speed, performed in this thesis via Dynamic Light Scattering (DLS), are of technical and scientific interest.
DLS is a thoroughly proven technique and known as a very accurate and absolute method to determine thermophysical properties. For example the thermal diffusivity a, the speed of sound cs, sound attenuation Ds, and the mutual diffusion coefficient D12 of fluids can be investigated in macroscopic gradient, which influences and distorts the results. DLS techniques analyze the decay of microscopic gradients present in thermodynamic equilibrium, resulting from Brownian molecular motion.
Currently available algorithms and methods for the DLS data evaluation are quite elaborate and thus not effective for technical and industrial standard. For evaluating the thermal diffusivity based on a recorded auto correlation function (ACF), the measure data have to be fitted to an ideal mathematical function, a fit model. Current methods can only handle ACFs free of any disturbing signals. Consequently, developing a new data analysis routine is necessary and the main goal of this thesis. The new method must be capable of handling erroneous ACFs in order to achieve the highest possible precision in the final result for the corresponding property.
At first in this thesis, an introduction to the basic principles of DLS will be presented, followed by a description of the experimental setup measuring in the time domain. The latter section also includes a detailed discussion about disturbing signals which have to be considered during the experiment and regarding the data evaluation procedure. Then the development of a user-firendly software, which also considers disturbing signals, with the derivation of an algorithm dealing with non-ideal ACFs, is desribed in detail. Several evaluation technique, models, and procedures are tested and discussed with helpf of experimental data as well as synthetic dta sets. This discussion leads to one evaluation procedure, which provides the bet reuslts regarding the resulting error. In the next section, the results obtained by the DLS experiment are used to finally discuss and compare the different evaluation procedures. For comparison, the transport properties of the samples are also predicted based on the properties of the pure mixture components, using of the software „RefProp“ provided by the national Institute of Standard and Technology (NiST). Furthermore, simple prediction methods are compared with the DLS results.
Surface Plasmon-Polariton and Sub-wavelength imaging
For understanding the role of plasma playing in metals, plasma itself was described. Plasma was defined using notions like quasineutrality. Debye shielding, Debye length and collision length. Collective oscallation, the condition, such as a perturbation, was explored. Building on these ideas plasma frequency was dervied using fundamental laws such as conservation of charge and Gauss’s law. Dispersion equation for plasma was described by concluding infinite phase velocity and no group velocity. Due to having group velocity equal to zero it was stated that collective oscillation was not a propagating wave. After which the quantization of plasma, the plasmon was described and shown over Stern and Ferfell’s results.
After establishing plasma and its quantized form plasmon, the conditions for achieving a surface wave was explored. It was shown that to achieve field decaying away from the surface a purely imaginary kzwas plotted for normal imgaing kz < ko and for subwavelength imaging kx > ko using the dispersion equation for light. Applying the boundary conditions for the tangential fields the disperson equations were dervied and plotted. The dispersion equation had a stop band like structure for the lossless case between plasma frequency ωp and ωs. It was shown for a lossy case this stop band disappeared. The phase velocity and group velocity were discussed and the two different regimes of the dispersion equation was stated. Due to having fields completly bound to the surface it was stated that imaging would not work for a single interface case. From the frequency dependant nature of the fields propagation depth was discussed and it was found that metals have lower penetration depth.
The focusing effect of flat slab was described for TE and TM mode. It was made clear that a metal slab was sufficient to achieve negative refraction for TM mode. Hence, the system would be polarization dependant. A simple relation was given between the permittivity and the width of the mediums.
The notion of space-frequency of an image was established using Fourier equations. The effect of artificially hiding some parts of the freqency domain was tested on a square image. The osberved effect was a blurred square with decaying artefacts. This idea of preserving wavenumbers (Fourier components) was applied to transfer functions dervied for symmetric slab. The transfer function was similarly derived, by applying the boundary conditions to the tangential fields. The effects of slab thickness and losses a medium had was shown on the tranfer function. Similarly, asymmetric transfer funciton was found and plotted using Matlab.
Finally, the transfer equation for 4 medium was dervied by using 3 boundary conditions. Applying these boundary conditions to the tangential field six equations were formed. After a cumbersome algebra normalized fields were found. However due to the quirky result, these results were not shown.
Suerlens as Pendry stated can form images using subwave components kx > ko, however it will be far from perfect.
Evaluation der detektierbaren Sensorsignale zur Regelung des Laserschweißprozesses
Im Rahmen dieser Arbeit wurden die Einsatzmöglichkeiten eines kamerabasierten Sensors zur Durchschweißkontrolle (SeamLine Pro) untersucht. Das erste Ergebnis dieser ARbeit ist, dass das Sensordetektionsvermögen mit der Vorschubgeschwindigkeit, leistung und Defokkusierung zunimmt. Es wird festgestelle, dass der Sensor bei Blindnaht mit einer Vorschubgeschwindigkeit höher als 4 m/min, einer Leistung 10% höher als die Durchweißgrenzleistung und einer Defokussierung von mindestens 2 mm im Blech gut funktionieren kann. Es wird auch festgestellt, dass der Seinso für Überlapp-Stoß nicht einsetzbar ist, weil er nicht in der Lage ist, eine Einschweißung von einer Durchschweiß8ng zu unterscheiden. Es wird auch festgestellt, dass der Sensor bei langsamer Vorschubgeschwindigkeit nicht funktioniert, weil der Auswertungsalgorythmus zum Beginn er Arbeit nicht geeignet ist.
Im Rahmen dieser Arbeit wurd eine neuer Auswertungsalgorythmus entwickelt, der im Vergleich mit dem SeamLinPro-Algorythums zu einem höheren Signalpegel (für Einschweißung sowie für Durchschweißung) führt. Er basiert auf der Tatsache, dass, wenn eine dunkle Schattierung auf dem Bild zu sehen ist, sich ein Tiefpunkt im Bildprofil abbildet. Die Existenz von Schattierungen („Pseude-Durchschweißlöcher“) bei Einschweißung und ihr Enstehungsmechanismus wird diskutiert.
Die Effekte der Prozessparametervariation auf das Schattierungsereignis wurden untersucht. Die Prozentzahl an Schattierungn, die innerhalb einer Sequenz detektieren wird müssen, um eine sichere Aussage über den Erfolg der Durchweißung machen zu können, wurden für jedes Prozessparameterset evaluiert. Es wird festgestellt, dass diese Prozentzahl an Schattierungen bei 10% Leistungsüberschuss zwischen 30 und 70%, in Abhängikgeit von den Prozessparameters, variiert. Die Entscheidungsschwellen (Erfolg der Durchschweißung ja/nein) müssen in Abhängigkeit von den Prozessparametern neu definiert werden.
Der Einfluss der Prozessparameter auf die Schattierungsgeometrie wurde auch untersucht, um die Einschweißung von der Durchschweißung besser unterscheiden zu können. Weitere Kriterien (Schattierungsquerschnitt, Helligkeitsstufenunterschied) wurden gefunden, die zusammen mit dem entwickelten neuen Auswertungsalgorythmus zur besseren Unterscheidung von Ein- und Durchschweißung führen können.
Im zzweiten Schritt dieser Arbeit wurden die Ergebnisse der gleichzeitigen Prozessbeobachtung von oben mit dem Sensor SeamLine Pro und von unten mit einer Hochgeschwindigkeitskamera dargestellt. Dabei wird festgestellt, dass die Anzahl der detktierten Löcher über die gesamte Schweißung der dunklen Schattierungen auf den Bildern der oberen Kamera nicht entsprechen. Es wird auch bewiesen, dass sie Materialstärke und der Materialtpy die Anzahl der dektierten Kapillaröffnungsereignisse von oben bzw. unten beeinflussen. Auch bei kräftiger Durchschwißung bleibt die Kapillare nicht ständig geöffnet, unbabhängig davon, ob man von oben oder von unten beobachtet.
Die Machbarkeit eines oben platzierten Durchschweißkontrollsenosrs bei hoher Vorschubgeschwindigkeit und hoher Kapillarneigung wird auch untersucht. Es wird festgestellt, dass bei konstanter Streckenenergie der Kapillarneigungswinkel unabhängig von der Vorschubgeschwindigkeit ist. Durch ein einfaches Modell wird auch bewiesen, dass die Kapillarneigung den Blick in die Kapillare verhindern kann. Eine Formel zur Abschätzung eines theoretischen Kapillarneigungsgrenzwinkles, der die Durchschweißkontrolle mit einer oben positionierten Kamera noch erlaubt, wird etabliert.
Ein weiteres Ergebnis dieser Untersuchung ist, dass es keine Periodizität in Kapillaröffnung sowie in Kapillaröffnungsdauer gibt. Mit welcher Frequenz die Kapillare sich öffnet, und wie lange sie geöffnet bleibt, lässt sich nicht vorhersagen. Aus diesem Grund konnte keine optimale Frquenz für die Untertastung mit Seamline Pro gefunden werden. Aber die Kapillaröffnungsdauer, die am häufigsten auftritt, ist gleich der Beobachtungsperiode 20 Mikrosekunden.
Implementation of an Interferometric System for Generation of Cylindrical Vector-beams Using a Parallel-Aligned Spatial Light Modulator
We document the implementation and improvement of an interferometric system for generation of cylindrical vector beams. The system uses a phase-only spatial light modulator (SLM) which is able to perform multiphase modulation of the beam wavefront by displaying customized forms. A number of separate steps were performed in order to assembly the system and test the method.
This document intends to be a reference detailing the process of implementation of the system from scratch, including convenient modifications to it, which was the core of the work. Furthermore, the feasibility to operate with this kind of setup has been examined and the most critical issues have been addressed. The method has proven to be very flexible by allowing easy switching between vector beams without further changes of the hardware. The generation of higher order modes on demand, which stands as one of the most attractive features of this method, is also realized.
By reviewing recent literature on several aspects of beam structuring, particularly polarization tailored light generation, as well as perspectives for optimization of the chosen method, we have attempted to put the technical dimension of the contribution presented here in context. Investigation and characterization of the SLM employed have been given special relevance. Additionally, interesting applications of the system have been considered.
We show in particular that the high resolution of the SLM employed, its phase-only modulation ability and the particularities of the design of the interferometric setup implemented, allow for the generation of slightly divergent cylindrical vector beams of any order with high diffraction efficiency without performing aberration corrections of the system.
Furthermore, we discuss in detail how the quality of the results can be immediately improved by correcting aberrations that are caused by the back-panel of the SLM. A precise correction can be performed by the SLM itself using a method that involves a phase retrieval algorithm. A first implementation in this direction has been conducted here. The quality of the correction process is particularly relevant for enhancing the accuracy in the generation of a collimated version of the cylindrical vector beams of higher orders, a demand that in turn is set by the final application in which the beams are employed.
Further aspects concerning the features of the cylindrical vector beams generated are examined in detail.
Performance Estimation of PolMux-QPSK Modulated Signals by Modeling Phase Variations
In this thesis the behaviour of phase variances in a polarization multiplexed 45.8 Gb/s QPSK system was analysed. The influence of the number of spans, the fibre type, the launch power, the span length, the dispersion compensation scheme and the number of channels were investigated. Tools were developed to extract the phase information from the optical and the electrical signal and to analyse the influence of the different link parameters.
The results show that the optical phase jitter increases continuously with growing numbers of spans. fibres with low dispersion like TWC and LEAF exhibit much stronger phase jitter compared to SSMF fibres. I-line dispersion compensation generally results in higher phase jitter. Especially the combination of a nine channel WDM-system with DCM management leads to strong phase jitter, because the optical bit patterns from neighbour channels cannot walk-off from each other. The distribution of the bits in the optical constellation diagram is not always Gaussian, this is due to an interaction between nonlinear effects and dispersion.
Analysis of the receiver characteristics showed that the electrical phase jitter is in general lower than the optical phase jitter, because of signal processing in the receiver. For large optical phase jitters the receiver is not able to recover the bits correctly, which leads to an increased bit-error ratio. The receiver has an intrusive noise level due to signal processing.
The simulation results were used to derive simple rules that can be used to predict the system performance based on the link parameters and amplified spontaneous emission. The predictions give good results in reasonable power regions. The agreement of the results with recent paper publications was demonstrated. If the power is too high the estimation deviates more from simulation results, because not all fiber parameters were included in the estimation.
Future works might overcome these limitations. The effect of the number of channels, the dispersion and the interactions between dispersion and nonlinear effects has to be studied in more detail. The performance prediction in this thesis is only based on the estimation of the phase jitter. Next steps have to incorporate the Kerr-induced amplitude jitter to achieve higher accuracy.
A Study on Micture Formation in Propane Spray by Laer Induced Grating Technique
Since the question in mixture formation is how spray is developing and because a spray is including the fuel in gas as well as liquid droplets, laser induced grating technique which is performable in gas phase is supposed to be carried out. The aim was to investigate the evaporated fuel concentration in a spray during injection process. Such two phase systems are difficult to investigate by commonly used optical diagnostic techniques. Therefore, in this work, the Mie scateering and the LIG techniqes have been applied together to a sirect injection process. The fuel was considered to be propane. The Mie technique hleped to figure out the evaporatoin process of propane during a direct injection proces, as well as the characteristics of the spray. After the charactrization of the bhaviour of the propane spray, based on the maximum spray length and the time duration for total evaporation, a set of LiG measurements were performed. The LIG measurements were carried out at different positons from the nozzle along spray axis where the spray is dense. By applying the LIG technique, a concentration measurement of propane in gas phase during mixutre formation could be done. The results verified that a combination of both techniques, Mie and LiG, is suitable to invetigate liquid propane spray of direct infjeciton processes in liquid and gas phase.
The following improvements could be considered to be done for next measurements. Concerning injection process it is concluded that
- The duration of the propane injection pulses should be shorter than 5 ms for a more intense air entraiument of rapid evaporation.
- In order to be sure that no gasou propane from the past measurement will exist at the next measurement the injection repetition rate should be reduced or the gas flow should be increased.
Bases in the discussed parameters before, LIG measurement should be performed
- At different positions in respect to the nozzle front vertically and horizontally at the boundary of liquid phase sprach, which was detected by Mie scattering, in order to determine the air/fuel ratio of the spray at boundarie radially as well as axially which enable us to understand the mixture formation of a spray.
- The measurements could be done at two or three different delay times after start of injection (SOI). By this way, the development of mixing the fuel in air can be suceeded.
Testing of Dynamic Light Scattering for Characterization of Hyaluronan and Human Liquid Vitreous
The current work was mainly dedicated to the practical realization of an idea applying DLS optical method for the characterization of thin layers of hyaluronan and tear film fluids. Being non-invasive, rapid and precise DLS techniques can be eomplyed for the investigation of not only non-organic materials, but also for the analysis of biological tissues in vivo. That has been confirmed during numerous clinical studies worldwide.
The aim of this work was to revise the exiting knowledge about the hyalurononic acid and tear film fluid applying DLS optical method, in order to make the preliminary preparations for the further opthalmologica research on this topic. The next steps are going to be in vivo tests of the endothelials cells of th post corneal eye region for the detection and study molecules of hyaluronan at the eye segment. Broadening knowledge on this issue might contribute to the invention of a new methodology for prevention and treating glaucoma diesease. That was the main motivation of the studies.
During this project a special set up was assembled and tested. our main goal was to construct the experimental system to perform DLS test in the homodyne reigme. In order to diminish the amount of optical components employed in the experiment mono-mode fibers were used. Having specific characteristics and features, optical fiber components require non-trivial solutions for integration them into the DLS experiments. Using optical wave-guides to supply the existing frequency of the laser light to the measuring cell and to collect the scattered signal afterward dictates a particular scattering geometry. There are limitation of adding a local oscillator field to the main laser beam at the detection stage to realize the heterodyne regime conditions. Thus only homodyne regime conditions could be fulfilled nowadays. But nevertheless, applying optical fibers in DLS experiment do already offer unchallenged advantages and have big potential to be extensively used in future.
During this project biological samples of hyaluronan and tear film fluid were tested, as well as the solutions of monodispers silica particles with know parameters-particle size. Studying the reference silica particles samples the theoretical values for the viscosity of the solutions with correction for the exact temperature measurements were confirmed. Correlation functions of the scattered light registerd and processed later on. Analysis of the autocorrlation funciton in terms of the particle size distribution was done by numerically fitting the data with calculations based on assumed distributions. IN case of truly monodisperse particle samples single exponential decay diagrams were registered to which fitting a calculated particle size distribution was relatively straightforward.