Fast waveform metrology : generation, measurement and application of sub-picosecond electrical pulses

This thesis describes work performed at the National Physical Laboratory to improve the electrical risetime calibration of instruments such as fast sampling oscilloscopes. The majority of the work can be divided into four sections: development of an ultrafast optoelectronic pulse generator; measurement of fast electrical pulses with an electrooptic sampling system; de-embedding of transmission line and transition effects as measured at different calibration reference planes; and calibration of an oscilloscope. The pulse generator is a photoconductive switch based on low-temperature Gallium Arsenide, which has a very fast carrier recombination time. Sub-picosecond electrical pulses are produced by illuminated a planar switch with 200 fs optical pulses from a Ti: sapphire laser system. The pulses are measured using a sampling system with an external electro-optic probe in close proximity to the switch. The electro-optic sampling system, with a temporal resolution better than 500 fs, is used to measure the electrical pulses shape at various positions along the planar transmission line. The results are compared to a pulse propagation model for the line. The effects of different switch geometries are examined. Although the pulse generator produces sub-picosecond pulses near to the point of generation, the pulse is shown to broaden to 7 ps after passing along a length of transmission line and a coplanar-coaxial transition. For a sampling oscilloscope with a coaxial input connector, this effect is significant. Frequency-domain measurements with a network analyser, further electro-optic sampling measurements, and the transmission line model are combined to find the network transfer function of the transition. Using the pulse generator, the electro-optic sampling system and the transition knowledge, a 50 GHz sampling oscilloscope is calibrated. The determination of the instrument step response(nominal risetime 7 ps) is improved from an earlier value of 8.5 -3.5 / +2.9 ps to a new value of 7.4 -2.1 / +1.7 ps with the calibration techniques described

A cryogenic electrostatic ion trap and first experiments on delayed emission of aluminium anion clusters and self-bunching

The Cryogenic electrostatic Trap for Fast ion beams (CTF) has been successfully built, fulfilling the Cryogenic Storage Ring (CSR) project goals of developing and testing the technologies and concepts to build this instrumentally challenging device, and demonstrating rest-gas-densities on the order of 2000 particles/cm^3 (or a room-temperature equivalent pressure of 8x10^{-14} mbar) with mean storage lifetimes of over 5 min for 7.1 keV N_2^+ ions. Since this is the first cryogenic electrostatic ion beam trap (EIBT), the resulting environment of greatly reduced blackbody radiation was exploited by investigating the time dependence of delayed electron emission from aluminum cluster anions at different temperatures. Dramatic deviations from the commonly observed 1/t decay of hot clusters were observed, demonstrating this decay's dependence on the temperature of the storage environment. Delayed emission following the excitation of the aluminum clusters with a pulsed laser was also observed. The results indicate a considerable reduction in the cluster temperature than seen so far and raises questions about the validity of the present model. The very low rest gas densities achieved also enabled the exploration of many properties of self-bunching and RF bunching with unprecedented sensitivity. An in-situ mass-selection technique exploiting the resonant transverse excitation of the stored ions was also demonstrated inside an EIBT for the first time

X-RAY INDUCED EFFECT ON CHARGE CARRIER TRAPPING LIFETIME OF a-Se PHOTOCONDUCTORS AND THE RECOVERY PROCESS

Amorphous selenium (a-Se) alloy x-ray detectors are currently used in commercial mammographic detectors for breast cancer detection and diagnosis. They have been only recently commercialized and there are now at least five companies manufacturing these detectors. This work focuses on the study of the X-ray induce effects on the carrier trapping lifetime in a-Se, and the recovery process of the X-ray induced damage in the bulk of a-Se samples. The x-ray dose effect on the carrier trapping lifetime was studied alongside the temperature effect on the induced x-ray damage and recovery process. The carrier trapping lifetime reduces as the accumulated dose deposited in the a-Se samples increases. Upon the cessation of x-ray exposure, carrier lifetime recovered slowly (over many hours) back to its original state. The damage was not permanent. Several a-Se detectors samples have been exposed to high doses of x-ray and the recovery process has been observed under different temperature, 23.5 oC and 35.5 oC. The time of flight (TOF) measurement technique was employed to measure the carrier drift mobility and the interrupted filed time of flight (IFTOF) technique was used to measure the carrier trapping lifetime . All samples used in this project are pure a-Se for hole transport measurements, a-Se: 0.3%: 2.5ppm Cl and a-Se: 0.5%: 10ppm Cl for electron transport measurements. Sample thickness ranges from 50 μm to 200 μm with a variance of ±5 μm at different positions on the sample. The applied dose rate during the x-ray irradiation ranges from 1.9 Gy/s to 2.5 Gy/s. The difference in dose rate does not affect the change in the hole trapping lifetime but has a non-significant effect on the electron trapping lifetime. The rate of decrease in the hole normalized lifetime is more rapid at 35.5oC than at room temperature (23.5oC). The recovery processes were also observed to be more rapid at the higher temperature

A cryogenic electrostatic ion trap and first experiments on delayed emission of aluminum anion clusters and self-bunching

The Cryogenic electrostatic Trap for Fast ion beams (CTF) has been successfully built, fulfilling the Cryogenic Storage Ring (CSR) project goals of developing and testing the technologies and concepts to build this instrumentally challenging device, and demonstrating rest-gas-densities on the order of 2000 particles/cm^3 (or a room-temperature equivalent pressure of 8x10^{-14} mbar) with mean storage lifetimes of over 5 min for 7.1 keV N_2^+ ions. Since this is the first cryogenic electrostatic ion beam trap (EIBT), the resulting environment of greatly reduced blackbody radiation was exploited by investigating the time dependence of delayed electron emission from aluminum cluster anions at different temperatures. Dramatic deviations from the commonly observed 1/t decay of hot clusters were observed, demonstrating this decay's dependence on the temperature of the storage environment. Delayed emission following the excitation of the aluminum clusters with a pulsed laser was also observed. The results indicate a considerable reduction in the cluster temperature than seen so far and raises questions about the validity of the present model. The very low rest gas densities achieved also enabled the exploration of many properties of self-bunching and RF bunching with unprecedented sensitivity. An in-situ mass-selection technique exploiting the resonant transverse excitation of the stored ions was also demonstrated inside an EIBT for the first time

Scintillation Light Detection and Application of Silicon Photomultipliers in Imaging Calorimetry and Positron Emission Tomography

Diese Arbeit befasst sich mit den schwachen Lichtsignalen von organischen und anorganischen Szintillatoren und deren Nachweis mit Silizium Photomultipliern (SiPM). In diesem Zusammenhang werden zwei Anwendungsgebiete untersucht: Hadronkalorimeter und das bildgebende Verfahren der Positronen-Emissions-Tomographie. Das Ergebnis einer Messung des Birksschen Koeffizienten kB wird vorgestellt für die Plastikszintillatorkacheln des analogen hadronischen Kalorimeterprototyps der CALICE Kollaboration. Der ermittelte kB-Wert ist signifikant größer als der bisher in Geant4-Simulationsstudien benutzte Wert. Eine neue Simulationsmethode wurde entwickelt, mit deren Hilfe eine verbesserte Beschreibung des Ionisations-Quenching-Effekts möglich ist. Der Einfluss auf das simulierte Kalorimetersignal wird anhand einer Teilchenschauer-Simulationsstudie verdeutlicht. Eine Testumgebung wurde entwickelt um eine vollständige SiPM Charakterisierung zu ermöglichen und verschiedene SiPM Bauarten zu vergleichen. Das Messspektrum umfasst die Bestimmung der Photon-Detektions-Effizienz unter Berücksichtigung der Beiträge des optischen Übersprechens und der auftretenden Nachpulse. Zusätzlich wurde das räumliche Ansprechverhalten einzelner Pixel gemessen. Die gewonnenen Erkenntnisse zu den unterschiedlichen Sensortypen und die daraus abgeleitete Qualifikation für verschiedene Anwendungsgebiete werden diskutiert. Um die Eignung von SiPMs für die Positronen-Emissions-Tomographie zu untersuchen, wurde ein Detektorprototyp im kleinen Maßstab entwickelt. Erste Charakterisierungsstudien des Systems werden vorgestellt

Advanced Photonic Sciences

The new emerging field of photonics has significantly attracted the interest of many societies, professionals and researchers around the world. The great importance of this field is due to its applicability and possible utilization in almost all scientific and industrial areas. This book presents some advanced research topics in photonics. It consists of 16 chapters organized into three sections: Integrated Photonics, Photonic Materials and Photonic Applications. It can be said that this book is a good contribution for paving the way for further innovations in photonic technology. The chapters have been written and reviewed by well-experienced researchers in their fields. In their contributions they demonstrated the most profound knowledge and expertise for interested individuals in this expanding field. The book will be a good reference for experienced professionals, academics and researchers as well as young researchers only starting their carrier in this field

Novel Approaches for Nondestructive Testing and Evaluation

Nondestructive testing and evaluation (NDT&E) is one of the most important techniques for determining the quality and safety of materials, components, devices, and structures. NDT&E technologies include ultrasonic testing (UT), magnetic particle testing (MT), magnetic flux leakage testing (MFLT), eddy current testing (ECT), radiation testing (RT), penetrant testing (PT), and visual testing (VT), and these are widely used throughout the modern industry. However, some NDT processes, such as those for cleaning specimens and removing paint, cause environmental pollution and must only be considered in limited environments (time, space, and sensor selection). Thus, NDT&E is classified as a typical 3D (dirty, dangerous, and difficult) job. In addition, NDT operators judge the presence of damage based on experience and subjective judgment, so in some cases, a flaw may not be detected during the test. Therefore, to obtain clearer test results, a means for the operator to determine flaws more easily should be provided. In addition, the test results should be organized systemically in order to identify the cause of the abnormality in the test specimen and to identify the progress of the damage quantitatively

Attosecond multidimensional interferometry of single and two correlated electrons in atoms

Within this work, electron dynamics in atoms are experimentally and numerically investigated on their natural attosecond time scales. To access these dynamics, ultrashort and moderately-intense few-cycle laser pulses are superposed with attosecond pulsed radiation in the extreme-ultraviolet spectral region. Both these sources are combined in a new experimental vacuum setup which was designed and built up from scratch, also in order to generate the attosecond pulses. Novel experimental schemes are developed which involve the temporal and spectral interferometric utilization of both ultrashort light sources and include the multidimensional spectroscopy employing different dynamical parameters. These are the intensity and the carrier-envelope phase of the laser pulses, as well as their temporal delay with respect to the attosecond pulses. Scientifically, the observation and control of the quantum-motion of bound electrons, as well as the laser-driven quasi-classical motion of free electrons was a key goal of this work. In particular, a bound two-electron wave packet in helium on attosecond time scales was experimentally observed for the first time. This was realized by combining unprecedented high temporal and spectral resolution. In addition, a new coupling mechanism of several doubly-excited states to an effective single-electron continuum is identified and analyzed. Both these two-electron states as well as single-electron states are interferometrically investigated with access to the phase of their quantum-mechanical wave function. This allows the observation and control of the quantum dynamics of two correlated electrons in atoms on the attosecond time scale which was demonstrated within the scope of this work

Environmental Physics Laboratory Practice

A jegyzetben 17 laboratóriumi mérés leírását foglaltuk össze, melyek a környezetfizika témakörébe tartoznak. Ezek a mérések a környezeti sugárzások vezérfonalára vannak felfűzve, kezdve az akusztikus hullámoktól a háztartásokban is észlelhető elektromágneses hullámokon, látható fény energiáján, a polarizált fényen keresztül a radioaktív sugárzások témaköréig. Ebben a témában a röntgensugárzás, gamma-sugárzás, annihilációs sugárzás, Cserenkov- sugárzás és az alfa- és beta- sugárzások témaköreit tárgyalják az egyes mérések. A leírt módszerek az Eötvös Loránd Tudományegyetem Környezettudományi Centrumának műszeres lehetőségeire épülnek, és a kiválasztott témák sokszínűségét ezek határozták meg, amiket az ettől jóval szélesebb általános környezetfizika témájából választottunk