Sintetička Lorentzova sila za neutralne hladne atome

Presented in this thesis are results of research on two topics in the field of cold atoms. These topics are connected by the fact they both employ laser induced forces caused by momentum transfer from photons to atoms. In both cases the laser induced forces change the velocity distribution of the atomic ensemble. In the first part of the thesis a new way to implement a synthetic Lorentz force into a cold atomic gas is presented. The synthetic Lorentz force (SLF) is based on radiation pressure and the Doppler effect, making it straightforward to implement in a large volume, for a broad range of velocities, and can be extended to different geometries. The force is perpendicular to the velocity of an atom, and zero for an atom at rest. This SFL is experimentally demonstrated in a system of cold rubidium atoms in two scenarios: first, by observing the center-of-mass motion of a cold atomic cloud and second, by observing the angular deflection of a rotationally asymmetrical cloud when released from a magneto-optical trap. The introduction of synthetic magnetism into the system of cold thermal atoms makes it an excellent candidate to emulate numerous complex classical systems, for example a tokamak fusion reactor or a star. In the second part of the thesis, the possibility of laser cooling with a frequency comb (FC) is explored. For this purpose a scheme for full stabilization of a fiber based FC that does not require traditional self-referencing is developed and implemented; the repetition frequency is locked to a stable microwave reference while the offset frequency is indirectly stabilized by referencing the frequency comb to a continuous wave laser that is stabilized by polarization spectroscopy in rubidium vapor. The FC stabilized in this way is used to cool rubidium atoms on a dipole-allowed transition at 780 nm to sub-Doppler temperatures. Temperatures as low as 55 μK were measured in a one-dimensional FC cooling geometry using the time-of-flight method. Laser cooling with FCs could enable achieving sub-Doppler temperatures for atoms with dipoleallowed transitions in the vacuum ultraviolet. This can significantly improve the precision of optical frequency standards, enable measurements of fundamental constants with unprecedented accuracy, and open up the possibility to reach quantum degeneracy with atoms that have optical transitions unreachable by continuous wave lasers such as hydrogen, deuterium and antihydrogen.U ovom doktorskom radu predstavljeni su rezultati istraživanja dvije različite tematike u području hladnih atoma. Ove dvije tematike su povezane činjenicom da se u obje koriste laserski inducirane sile uzrokovane prijenosom impulsa s fotona na atome. U oba slučaja laserski inducirane sile mijenjaju brzinsku raspodjelu atomskog ansambla. Rezultati predstavljeni u ovom radu su dobiveni radom u Laboratoriju za hladne atome na Institutu za fiziku u Zagrebu pod mentorstvom Ticijane Ban. Prve dvije i pol godine mojeg poslijediplomskoga studija istraživanja na kojima sam radio su bila dio projekta Pseudo-magnetic forces and fields for atoms and photons čiji voditelj je bio prof. Hrvoje Buljan s Fizičkog odsjeka Prirodoslovno-matematičkog fakulteta u Zagrebu. Preostalo vrijeme sam radio na projektu Frequency-Comb-induced OptoMechanics koji je u tijeku u trenutku pisanja ove radnje i čiji je voditelj Ticijana Ban sa Instituta za fiziku u Zagrebu. Spomenute dvije tematike istraživanja su se vezale na ova dva projekta. Ovaj rad je organiziran na sljedeći način. U uvodu, poglavlje 1, dan je kratki povijesni pregled istraživanja hladnih atoma i posljednjih dostignuća u području. U poglavlju 2 se nalazi teorijski pregled interakcije lasera i atoma što je temelj za obje prethodno spomenute tematike. Sličan pregled se može naći u literaturi [1], u ovom radu je uključen zbog cjelovitosti rada. Dva različita eksperimentalna postava, magneto-optičke stupice, su izrađena tokom izrade ovog rada. U poglavlju 3 je izložen njihov dizajn te su objašnjene specifičnosti oba postava. U poglavlju 4 predstavljen je novi način implementacije sintetičke Lorentzove sile za hladni atomski plin. Ova sintetička Lorentzova sila se temelji na tlaku zračenja i Dopplerovom efektu, što ju čini jednostavnom za implementaciju u velikom volumenu, za veliki raspon brzina te se može primijeniti na različite geometrije. Sila je okomita na brzinu atoma te iznosi nula za atome koji miruju. Sintetičku Lorentzovu silu demonstriramo na dva načina: prvo, promatramo gibanje centra mase oblaka hladnih atoma i drugo, promatramo za koliki kut se rotacijski nesimetričan oblak otklonio od početnog položaja pri ispuštanju iz magneto-optičke stupice. Uvođenjem sintetičkoga magnetizma u sistem hladnih termalnih atoma ovaj sistem postaje odličan kandidat za emulaciju brojnih kompleksnih klasičnih sistema, na primjer tokamak fuzijskog reaktora ili zvijezda. U poglavlju 5 istraživana je mogućnost laserskog hlađenja frekventnim češljem. U tu svrhu bilo je potrebno osmisliti i implementirati tehniku za potpunu stabilizaciju frekventnog češlja koji se temeljeni na optičkim vlaknima, i to na način koji ne koristi uobičajeno samo-referenciranje; frekvencija repeticije je stabilizirana pomoću vrlo stabilne mikrovalne reference, dok je frekvencija odmaka indirektno stabilizirana referenciranjem frekventnog češlja pomoću kontinuiranog lasera koji je pak stabiliziran pomoću polarizacijske spektroskopije u rubidijevim parama. Frekventni češalj stabiliziran na ovaj način je korišten za hlađenje atoma rubidija na dipol dozvoljenom prijelazu na 780 nm do sub-Dopplerovskih temperatura. Izmjerene su temperature do 55 μK prilikom hlađenja u jednoj dimenziji pomoću tehnike vremena proleta. Ovime je pokazano da bi se lasersko hlađenje frekventnim češljem može koristiti za postizanje sub-Dopplerovskih temperatura s atomima koji imaju dipol dozvoljene prijelaze u vakuum ultraljubičastom području. Ovo bi značajno unaprijedilo preciznost optičkih frekventnih standarda, omogućilo bi mjerenje fundamentalnih konstanti s do sad ne postignutom preciznošću te bi se omogućilo dobivanje kvantno degeneriranih uzoraka atoma koji imaju optičke prijelaze u spektralnim područjima koja nisu pokrivena s kontinuiranim laserima, kao što su na primjer vodik, deuterij i antivodik

Sintetička Lorentzova sila za neutralne hladne atome

Presented in this thesis are results of research on two topics in the field of cold atoms. These topics are connected by the fact they both employ laser induced forces caused by momentum transfer from photons to atoms. In both cases the laser induced forces change the velocity distribution of the atomic ensemble. In the first part of the thesis a new way to implement a synthetic Lorentz force into a cold atomic gas is presented. The synthetic Lorentz force (SLF) is based on radiation pressure and the Doppler effect, making it straightforward to implement in a large volume, for a broad range of velocities, and can be extended to different geometries. The force is perpendicular to the velocity of an atom, and zero for an atom at rest. This SFL is experimentally demonstrated in a system of cold rubidium atoms in two scenarios: first, by observing the center-of-mass motion of a cold atomic cloud and second, by observing the angular deflection of a rotationally asymmetrical cloud when released from a magneto-optical trap. The introduction of synthetic magnetism into the system of cold thermal atoms makes it an excellent candidate to emulate numerous complex classical systems, for example a tokamak fusion reactor or a star. In the second part of the thesis, the possibility of laser cooling with a frequency comb (FC) is explored. For this purpose a scheme for full stabilization of a fiber based FC that does not require traditional self-referencing is developed and implemented; the repetition frequency is locked to a stable microwave reference while the offset frequency is indirectly stabilized by referencing the frequency comb to a continuous wave laser that is stabilized by polarization spectroscopy in rubidium vapor. The FC stabilized in this way is used to cool rubidium atoms on a dipole-allowed transition at 780 nm to sub-Doppler temperatures. Temperatures as low as 55 μK were measured in a one-dimensional FC cooling geometry using the time-of-flight method. Laser cooling with FCs could enable achieving sub-Doppler temperatures for atoms with dipoleallowed transitions in the vacuum ultraviolet. This can significantly improve the precision of optical frequency standards, enable measurements of fundamental constants with unprecedented accuracy, and open up the possibility to reach quantum degeneracy with atoms that have optical transitions unreachable by continuous wave lasers such as hydrogen, deuterium and antihydrogen.U ovom doktorskom radu predstavljeni su rezultati istraživanja dvije različite tematike u području hladnih atoma. Ove dvije tematike su povezane činjenicom da se u obje koriste laserski inducirane sile uzrokovane prijenosom impulsa s fotona na atome. U oba slučaja laserski inducirane sile mijenjaju brzinsku raspodjelu atomskog ansambla. Rezultati predstavljeni u ovom radu su dobiveni radom u Laboratoriju za hladne atome na Institutu za fiziku u Zagrebu pod mentorstvom Ticijane Ban. Prve dvije i pol godine mojeg poslijediplomskoga studija istraživanja na kojima sam radio su bila dio projekta Pseudo-magnetic forces and fields for atoms and photons čiji voditelj je bio prof. Hrvoje Buljan s Fizičkog odsjeka Prirodoslovno-matematičkog fakulteta u Zagrebu. Preostalo vrijeme sam radio na projektu Frequency-Comb-induced OptoMechanics koji je u tijeku u trenutku pisanja ove radnje i čiji je voditelj Ticijana Ban sa Instituta za fiziku u Zagrebu. Spomenute dvije tematike istraživanja su se vezale na ova dva projekta. Ovaj rad je organiziran na sljedeći način. U uvodu, poglavlje 1, dan je kratki povijesni pregled istraživanja hladnih atoma i posljednjih dostignuća u području. U poglavlju 2 se nalazi teorijski pregled interakcije lasera i atoma što je temelj za obje prethodno spomenute tematike. Sličan pregled se može naći u literaturi [1], u ovom radu je uključen zbog cjelovitosti rada. Dva različita eksperimentalna postava, magneto-optičke stupice, su izrađena tokom izrade ovog rada. U poglavlju 3 je izložen njihov dizajn te su objašnjene specifičnosti oba postava. U poglavlju 4 predstavljen je novi način implementacije sintetičke Lorentzove sile za hladni atomski plin. Ova sintetička Lorentzova sila se temelji na tlaku zračenja i Dopplerovom efektu, što ju čini jednostavnom za implementaciju u velikom volumenu, za veliki raspon brzina te se može primijeniti na različite geometrije. Sila je okomita na brzinu atoma te iznosi nula za atome koji miruju. Sintetičku Lorentzovu silu demonstriramo na dva načina: prvo, promatramo gibanje centra mase oblaka hladnih atoma i drugo, promatramo za koliki kut se rotacijski nesimetričan oblak otklonio od početnog položaja pri ispuštanju iz magneto-optičke stupice. Uvođenjem sintetičkoga magnetizma u sistem hladnih termalnih atoma ovaj sistem postaje odličan kandidat za emulaciju brojnih kompleksnih klasičnih sistema, na primjer tokamak fuzijskog reaktora ili zvijezda. U poglavlju 5 istraživana je mogućnost laserskog hlađenja frekventnim češljem. U tu svrhu bilo je potrebno osmisliti i implementirati tehniku za potpunu stabilizaciju frekventnog češlja koji se temeljeni na optičkim vlaknima, i to na način koji ne koristi uobičajeno samo-referenciranje; frekvencija repeticije je stabilizirana pomoću vrlo stabilne mikrovalne reference, dok je frekvencija odmaka indirektno stabilizirana referenciranjem frekventnog češlja pomoću kontinuiranog lasera koji je pak stabiliziran pomoću polarizacijske spektroskopije u rubidijevim parama. Frekventni češalj stabiliziran na ovaj način je korišten za hlađenje atoma rubidija na dipol dozvoljenom prijelazu na 780 nm do sub-Dopplerovskih temperatura. Izmjerene su temperature do 55 μK prilikom hlađenja u jednoj dimenziji pomoću tehnike vremena proleta. Ovime je pokazano da bi se lasersko hlađenje frekventnim češljem može koristiti za postizanje sub-Dopplerovskih temperatura s atomima koji imaju dipol dozvoljene prijelaze u vakuum ultraljubičastom području. Ovo bi značajno unaprijedilo preciznost optičkih frekventnih standarda, omogućilo bi mjerenje fundamentalnih konstanti s do sad ne postignutom preciznošću te bi se omogućilo dobivanje kvantno degeneriranih uzoraka atoma koji imaju optičke prijelaze u spektralnim područjima koja nisu pokrivena s kontinuiranim laserima, kao što su na primjer vodik, deuterij i antivodik

Sintetička Lorentzova sila za neutralne hladne atome

Presented in this thesis are results of research on two topics in the field of cold atoms. These topics are connected by the fact they both employ laser induced forces caused by momentum transfer from photons to atoms. In both cases the laser induced forces change the velocity distribution of the atomic ensemble. In the first part of the thesis a new way to implement a synthetic Lorentz force into a cold atomic gas is presented. The synthetic Lorentz force (SLF) is based on radiation pressure and the Doppler effect, making it straightforward to implement in a large volume, for a broad range of velocities, and can be extended to different geometries. The force is perpendicular to the velocity of an atom, and zero for an atom at rest. This SFL is experimentally demonstrated in a system of cold rubidium atoms in two scenarios: first, by observing the center-of-mass motion of a cold atomic cloud and second, by observing the angular deflection of a rotationally asymmetrical cloud when released from a magneto-optical trap. The introduction of synthetic magnetism into the system of cold thermal atoms makes it an excellent candidate to emulate numerous complex classical systems, for example a tokamak fusion reactor or a star. In the second part of the thesis, the possibility of laser cooling with a frequency comb (FC) is explored. For this purpose a scheme for full stabilization of a fiber based FC that does not require traditional self-referencing is developed and implemented; the repetition frequency is locked to a stable microwave reference while the offset frequency is indirectly stabilized by referencing the frequency comb to a continuous wave laser that is stabilized by polarization spectroscopy in rubidium vapor. The FC stabilized in this way is used to cool rubidium atoms on a dipole-allowed transition at 780 nm to sub-Doppler temperatures. Temperatures as low as 55 μK were measured in a one-dimensional FC cooling geometry using the time-of-flight method. Laser cooling with FCs could enable achieving sub-Doppler temperatures for atoms with dipoleallowed transitions in the vacuum ultraviolet. This can significantly improve the precision of optical frequency standards, enable measurements of fundamental constants with unprecedented accuracy, and open up the possibility to reach quantum degeneracy with atoms that have optical transitions unreachable by continuous wave lasers such as hydrogen, deuterium and antihydrogen.U ovom doktorskom radu predstavljeni su rezultati istraživanja dvije različite tematike u području hladnih atoma. Ove dvije tematike su povezane činjenicom da se u obje koriste laserski inducirane sile uzrokovane prijenosom impulsa s fotona na atome. U oba slučaja laserski inducirane sile mijenjaju brzinsku raspodjelu atomskog ansambla. Rezultati predstavljeni u ovom radu su dobiveni radom u Laboratoriju za hladne atome na Institutu za fiziku u Zagrebu pod mentorstvom Ticijane Ban. Prve dvije i pol godine mojeg poslijediplomskoga studija istraživanja na kojima sam radio su bila dio projekta Pseudo-magnetic forces and fields for atoms and photons čiji voditelj je bio prof. Hrvoje Buljan s Fizičkog odsjeka Prirodoslovno-matematičkog fakulteta u Zagrebu. Preostalo vrijeme sam radio na projektu Frequency-Comb-induced OptoMechanics koji je u tijeku u trenutku pisanja ove radnje i čiji je voditelj Ticijana Ban sa Instituta za fiziku u Zagrebu. Spomenute dvije tematike istraživanja su se vezale na ova dva projekta. Ovaj rad je organiziran na sljedeći način. U uvodu, poglavlje 1, dan je kratki povijesni pregled istraživanja hladnih atoma i posljednjih dostignuća u području. U poglavlju 2 se nalazi teorijski pregled interakcije lasera i atoma što je temelj za obje prethodno spomenute tematike. Sličan pregled se može naći u literaturi [1], u ovom radu je uključen zbog cjelovitosti rada. Dva različita eksperimentalna postava, magneto-optičke stupice, su izrađena tokom izrade ovog rada. U poglavlju 3 je izložen njihov dizajn te su objašnjene specifičnosti oba postava. U poglavlju 4 predstavljen je novi način implementacije sintetičke Lorentzove sile za hladni atomski plin. Ova sintetička Lorentzova sila se temelji na tlaku zračenja i Dopplerovom efektu, što ju čini jednostavnom za implementaciju u velikom volumenu, za veliki raspon brzina te se može primijeniti na različite geometrije. Sila je okomita na brzinu atoma te iznosi nula za atome koji miruju. Sintetičku Lorentzovu silu demonstriramo na dva načina: prvo, promatramo gibanje centra mase oblaka hladnih atoma i drugo, promatramo za koliki kut se rotacijski nesimetričan oblak otklonio od početnog položaja pri ispuštanju iz magneto-optičke stupice. Uvođenjem sintetičkoga magnetizma u sistem hladnih termalnih atoma ovaj sistem postaje odličan kandidat za emulaciju brojnih kompleksnih klasičnih sistema, na primjer tokamak fuzijskog reaktora ili zvijezda. U poglavlju 5 istraživana je mogućnost laserskog hlađenja frekventnim češljem. U tu svrhu bilo je potrebno osmisliti i implementirati tehniku za potpunu stabilizaciju frekventnog češlja koji se temeljeni na optičkim vlaknima, i to na način koji ne koristi uobičajeno samo-referenciranje; frekvencija repeticije je stabilizirana pomoću vrlo stabilne mikrovalne reference, dok je frekvencija odmaka indirektno stabilizirana referenciranjem frekventnog češlja pomoću kontinuiranog lasera koji je pak stabiliziran pomoću polarizacijske spektroskopije u rubidijevim parama. Frekventni češalj stabiliziran na ovaj način je korišten za hlađenje atoma rubidija na dipol dozvoljenom prijelazu na 780 nm do sub-Dopplerovskih temperatura. Izmjerene su temperature do 55 μK prilikom hlađenja u jednoj dimenziji pomoću tehnike vremena proleta. Ovime je pokazano da bi se lasersko hlađenje frekventnim češljem može koristiti za postizanje sub-Dopplerovskih temperatura s atomima koji imaju dipol dozvoljene prijelaze u vakuum ultraljubičastom području. Ovo bi značajno unaprijedilo preciznost optičkih frekventnih standarda, omogućilo bi mjerenje fundamentalnih konstanti s do sad ne postignutom preciznošću te bi se omogućilo dobivanje kvantno degeneriranih uzoraka atoma koji imaju optičke prijelaze u spektralnim područjima koja nisu pokrivena s kontinuiranim laserima, kao što su na primjer vodik, deuterij i antivodik

Molecular and Atomic Confinement in Large Core Photonic Microcells for Slow Light and Laser Metrology Applications

This thesis describes developments in the fabrication and applications of photonic microcells (PMCs). A PMC is a length of gas-filled hollow core-photonic crystal fibre (HC-PCF) that is hermetically sealed by splicing both ends to standard single mode fibre. A PMC enables integration of gas-filled HC-PCF into all-fibre systems with low insertion loss. PMCs have applications in coherent optics and metrology, where specific HC-PCF designs are advantageous. Two types of state-of-the-art HC-PCF, double bandgap HCPCF and large-pitch Kagome fibre, are fabricated. The double bandgap HC-PCF extends the usable bandwidth of the fibre by providing low loss guidance across two transmission bands. The large-pitch Kagome HC-PCF has a record low attenuation of 0.3 dB/m at 800 nm, while maintaining broadband guidance, which is partially attributed to the core shape. Three distinct developments in the field of PMCs are described. Firstly, a record length 20 metre acetylene-filled PMC is fabricated which is the key component in the first demonstration of an all-fibre slow and fast light system based on electromagnetically induced transparency. Secondly, a technique based on fibre tapering is presented which enables low loss integration of large core Kagome HC-PCFs into PMC form. Thirdly, micromirrors are developed and integrated with HC-PCF to confine light in the longitudinal dimension, providing a means to fabricate multi-pass PMCs. Two uncoated micromirrors are used to form a low finesse microcavity in Kagome HC-PCF, with record high fringe visibility using reflections from a silica/air junction. In collaboration with Kansas State University, an acetylene optical reference with sub-10 KHz accuracy and the first acetylene laser based on population inversion are demonstrated using Kagome HC-PCF.Finally, this thesis reports on rubidium vapour loading in HC-PCF with the ultimate aim being the production of a rubidium-filled PMC for applications in metrology. Preliminary results highlight the limited loading distance of the current technique and modified loading schemes are outlined accordingly.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Generalized averaged Gaussian quadrature and applications

A simple numerical method for constructing the optimal generalized averaged Gaussian quadrature formulas will be presented. These formulas exist in many cases in which real positive GaussKronrod formulas do not exist, and can be used as an adequate alternative in order to estimate the error of a Gaussian rule. We also investigate the conditions under which the optimal averaged Gaussian quadrature formulas and their truncated variants are internal

MS FT-2-2 7 Orthogonal polynomials and quadrature: Theory, computation, and applications

Quadrature rules find many applications in science and engineering. Their analysis is a classical area of applied mathematics and continues to attract considerable attention. This seminar brings together speakers with expertise in a large variety of quadrature rules. It is the aim of the seminar to provide an overview of recent developments in the analysis of quadrature rules. The computation of error estimates and novel applications also are described

Laser spectroscopic studies of plasma

This thesis describes the application of sensitive optical absorption techniques in order to probe inductively coupled plasmas of oxygen and nitrogen. Radio frequency plasmas formed from these simple molecular species have found an increasingly important role in many industrial applications and high resolution spectroscopy provides a means to probe their chemistry with unrivalled specificity and sensitivity. In particular, this work applies the technique of cavity ringdown spectroscopy (CRDS) to detect atomic, ionic and electronically excited molecular species as a function of plasma operating conditions. The plasma probed in this work is created in a low pressure (10 − 100 mTorr) inductively coupled plasma chamber by application of up to 500 W of 13.56 MHz radio frequency power via a 1.5 turn double spiral antenna in a stove top arrangement. The optical cavity utilised in the measurements probes the plasma 120 mm below to top window (which separates the driven coil from the plasma) and 50 mm above the lower, ground electrode. CRDS results are supplemented with observations of plasma emission spectra and comprehensively interpreted by kinetic modelling. The work is divided into two sections according to the plasma being probed. The first section concerns oxygen plasma with CRDS measurements of O(3P) and O2(a1∆g) utilising forbidden transitions. These measurements reveal dissociation fractions as high as ≈ 15%, metastable molecule fractions of ≈ 5% and translation temperatures up to ≈ 450 K. The target species, by virtue of their different threshold energies for electron impact production, provide insight into different regions of the electron energy distribution function (EEDF). As a result, measurements of O(3P) and O2(a1∆g) in combination with a volume averaged kinetic plasma model allow changes in the EEDF to be investigated as the plasma transitions from the E to the H-mode of operation. In addition, aspects of the spectroscopy of O2(a1∆g) are clarified with respect to the appropriate sum rule for Honl-London factors, necessary in order to properly deduce absolute concentrations. The volume averaged modelling, although quantitatively useful, does not account for spatial inhomogeneity within the plasma. This inhomogeneity is investigated using measurements of O2(X3Σ−g) in the v = 0 and v = 1 vibrational states. These observations also elucidate the degree of vibrational excitation within the plasma and reveal a vibrational temperature (amongst the low v states) of ≈ 750 ± 150 K at 100 mTorr and 300 W. A 1D model utilising physically reasonable line of sight variation in plasma temperature and composition corroborates the CRDS measurements. The second section of this thesis concerns nitrogen plasma and focuses on CRD measurements of the molecular cation, N+2(X2Σ+g ), and the electronically excited N2(A3Σ+u) state. These species can be probed using allowed transitions, but due to their low density, the sensitivity enhancement afforded by CRDS is still advantageous. Notably, the use of large intracavity radiation intensities to probe allowed transitions results in optical saturation, the effects of which must be carefully accounted for when determining species temperatures and densities. With adjustments made for the effects of optical saturation the CRD measurements show ion (and therefore electron) densities of the order of 109−1010 cm−3 in the plasma bulk (depending on operating conditions) and metastable densities an order of magnitude higher. Interestingly the two species show rather different translational temperatures with the ions typically ≈ 1000 K and the metastables ≈ 600 K. Once again the absolute density measurements are interpreted in terms of a volume averaged kinetic model. The model reveals a limitation in the understanding of nitrogen discharges that has arisen consistently in the literature, namely, the inability to account quantitatively for the density of Nu(A3Σ+u the literature rate coefficients for the processes typically deemed most important in its production and loss. The possible reasons for the discrepancy are explored in depth. In addition, spatially resolved measurements of the same nitrogen species are presented, with particular reference to how ion densities change as the edge of the chamber is approached (in regions known as the plasma pre-sheath and sheath). Measurements with a spatial resolution of ≈ 100 µm show that the ion density is reduced by almost an order of magnitude close to the chamber’s lower electrode. Finally, the effects of saturation on the CRD spectra are explored and the possible contributions to the Lamb dip width are discussed in the context of spectral broadening mechanisms. The laser linewidth is measured by a self-heterodyne beat note experiment to be < 100 kHz indicating that it contributes little to the observed Lamb dip widths (> 100 MHz) and that other processes are dominant. It is concluded that, whilst power broadening plays a significant role in explaining the width of the Lamb dips, the dominant cause of the broadening is unresolved hyperfine structure arising due to the non-zero nuclear spin of 14N

Nanoscale Electric Phenomena at Oxide Surfaces and Interfaces by Scanning Probe Microscopy

Scanning Probe Microscopy is used to study and quantify the nanoscale electric phenomena in the two classes of oxide systems, namely transport at electroactive grain boundaries and surface behavior of ferroelectric materials. Scanning Impedance Microscopy is developed to study the capacitance and local C-V characteristic of the interfaces combining the spatial resolution of traditional SPMs with the precision of conventional electrical measurements. SPM of SrTiO3 grain boundaries in conjunction with variable temperature impedance spectroscopy and I-V measurements allowed to find and theoretically justify the effect of field suppression of dielectric constant in the vicinity of the electroactive interfaces in strontium titanate. Similar approaches were used to study ferroelectric properties and ac and dc transport behavior in a number of polycrystalline oxides. In the second part, the effects of local charge density on the chemistry and physics of ferroelectric surfaces are studied. The kinetics and thermodynamics parameters of adsorption are assessed by variable temperature SPM. Piezoresponse force microscopy is used to engineer domain patterns on ferroelectric surfaces. Localized photochemical activity of ferroelectric surfaces is explored as a new tool for metallic nanostructures fabrication.Comment: Ph.D. Thesis, September 2002, 304 pages, 108 figures, 2.4 MB PDF file, Higher quality version available at sergei2.kalininweb.co