Suomen Ilmavoimien johtamisjärjestelmän evoluutio ilmasotateorian, kansallisten instituutioiden ja johtamisjärjestelmän ulkomaisen kehityksen näkökulmasta

Ilmavoimien johtamisjärjestelmä on osa Ilmavoimien järjestelmäkokonaisuutta, jonka kaksi muuta osaa ovat taistelujärjestelmä ja tukeutumisjärjestelmä. Ilmavoimien materiaalista suorituskykyä rakennetaan tämän järjestelmäajattelun pohjalta. tässä tutkimuksessa Ilmavoimien johtamisjärjestelmää tutkitaan kolmen kokonaisuuden, ilmavalvontajärjestelmän, ilmatilannekuvan muodostamisjärjestelmän ja tulenkäytön johtamisjärjestelmän, näkökulmasta. Ilmavoimien johtamisjärjestelmän laajuuden vuoksi tutkimusaluetta on jouduttu rajaamaan. Tutkimus perustuu evoluutioparadigmaan, jonka mukaisesti kaikki olevainen on evolutionaarista. Mikään tässä ajassa oleva ilmiö ei ole historiaton. Jokaisella ilmiöllä on nykyisyytensä lisäksi historia ja tulevaisuus. Evoluutioparadigman avulla laajennetaan Ilmavoimien johtamisjärjestelmän nykyisyyden ymmärtämistä kuvaamalla ja analysoimalla sen evoluutiota. Tutkimusaineistoa analysoidaan käyttäen hyväksi polkuriippuvuutta evolutionaarisena mallina. tätä mallia on käytetty uusinstitutionaalisessa ja evolutionaarisessa taloustieteessä ja taloushistoriassa tutkittaessa yritysten, toimialojen tai tuotteiden pysyvyyttä markkinoilla sekä erilaisten innovaatioiden vaikuttavuutta menestymiseen eri markkinatilanteissa. Tutkimusasetelman lähtökohtana on Ilmavoimien johtamisjärjestelmäevoluution kuvaaminen kolmen tekijän tasapainoasetelman suhteen, joita ovat instituutiot, ilmasotateoria ja kansainvälinen ilmavoimien johtamisjärjestelmän kehitys. tutkimuksen tavoitteena on löytää institutionaalinen logiikka Ilmavoimien johtamisjärjestelmän evoluutiolle sekä sen eri kehitysprosesseihin liittyvä mahdollinen polkuriippuvuuden logiikka. Tutkittavina instituutioina ovat kansallinen poliittinen päätöksenteko, joka ilmentyy erilaisina komiteamietintöjä, raportteina ja selontekoina. Sotilaallista instituutiota edustavat eri operatiiviset ohjeet, ohjesäännöt ja doktriinit, jotka ovat ohjanneet johtamisjärjestelmäkehitystä. Ilmasotateorian vaikuttavuuden analyysiä varten tutkimuskohteiksi on valittu seitsemän merkittävää ilmasotateoreetikkoa. Kenraalimajuri Giulio douhet, ilmamarsalkka Hugh Trenchard ja kenraalimajuri William Mitchell edustavat ilmasotateorian varhaista kautta. Kansallista ilmasotateorian kehitystä edustavat eversti Richard Lorentz ja kenraalimajuri Gustaf Erik Magnusson. Yhdysvaltalaiset everstit John Boyd ja John Warden III ovat uuden ajan ilmasotateoreetikkoja. Näiden henkilöiden tuottamien teorioiden avulla voidaan piirtää kuva muutoksesta, jota ilmasodankäynnin teoreetti- sessa ajattelussa on tapahtunut. Ilmavoimien johtamisjärjestelmän evoluutiolle haetaan vertailua kehityksestä, jota on tapahtunut Yhdysvalloissa, Isossa-Britanniassa ja Saksassa. Ilmavoimat on saanut vaikutteita muistakin maista, mutta näiden maiden kehityksen avulla voidaan selittää Suomessa tapahtunutta kehitystä. Tutkimuksessa osoitetaan, että kansainvälisellä johtamisjärjestelmäevoluutiolla on ollut merkittävä vaikutus suomalaiseen kehitykseen. Tämä tutkimus laajentaa prosessuaalista tutkimusteoriaa ja polkuriippuvuusmallin käyttöä sotatieteelliseen tutkimuskenttään. tutkimus yhdistää toisiinsa aivan uudella tavalla sotilasorganisaation institutionaalisia tekijöitä pitkässä evoluutioketjussa. Tutkimus luo pohjaa prosessuaaliseen, havaintoihin perustuvaan evoluutioajatteluun, jossa eri tekijöiden selitysmalleja ja kausaalisuutta eri periodien aikana voidaan kuvata. Tutkimuksen tuloksena ilmavoimien johtamisjärjestelmäevoluutiossa paljastui merkittäviä piirteitä. Teknologia on ollut voimakas katalysaattori ilmapuolustuksen evoluutiossa. Uusien teknologisten innovaatioiden ilmestyminen taistelukentälle on muuttanut oleellisesti taistelun kuvaa. Sodankäynnin revoluutiosta huolimatta sodankäynnin tai operaatiotaidon ja taktiikan perusperiaatteissa ei ole tapahtunut perustavanlaatuista muutosta. Ilmavoimien johtamisjärjestelmän kehitys on voimakkaasti linkittynyt ulkomaiseen johtamisjärjestelmäkehitykseen, jossa teknologiaimplementaatiot perustuvat usean eri ilmiön paljastumiseen ja hyväksikäyttöön. Sotilas- ja siviili-instituutiot ovat merkittävästi vaikuttaneet Ilmavoimien johtamisjärjestelmän kansalliseen kehitykseen. Ne ovat antaneet poliittisen ohjauksen, taloudellisten resurssien ja strategis-operatiivisten käskyjen ja suunnitelmien avulla perusteet, joiden pohjalta johtamisjärjestelmää on kehitetty. Tutkimus osoittaa, että Suomen taloudellisten resurssien rajallisuus on ollut merkittävin institutionaalinen rajoite Ilmavoimien johtamisjärjestelmää kehitettäessä. Useat poliittiset ohjausasiakirjat ovat korostaneet, ettei Suomella pienenä kansakuntana ole taloudellisia resursseja seurata kansainvälistä sotilasteknologiakehitystä. Lisäksi ulko- ja turvallisuuspoliittinen liikkumavapaus on vaikuttanut kehittämismahdollisuuksiin. Ilmasotateorian evoluutio on luonut johtamisjärjestelmän kehitykselle välttämättömän konseptuaalisen viitekehyksen, jotta ilmasota on voitu viedä käytännön tasolle. Teoria, doktriini ja instituutiot toimivat vuorovaikutuksessa, jossa ne interaktiivisesti vaikuttavat toinen toisiinsa. Tutkimus paljasti kuusi merkittävää sokkia, jotka saivat aikaan radikaaleja muutoksia johtamisjärjestelmän evoluutiopolulla. tutkimuksen perusteella vaikuttavimmat muutoksia aiheuttavat sokit olivat radikaalit turvallisuuspoliittiset muutokset kuten sota ja voimakkaat kansantalouden muutokset kuten lama. Sokkeja aiheuttaneet kuusi ajankohtaa olivat: 1. Puolustusvoimien rakentamisen aloittaminen vapaussodan jälkeen 1918 2. Maailmanlaajuinen lama 1929–1933 ja eurooppalainen rauhanaate 1928–1933 3. Talvi- ja jatkosota 1939–1944 4. Uusi alku Pariisin rauhansopimuksen 1947 ja YYA-sopimuksen 1948 varjossa 5. Kylmän sodan päättyminen ja Suomen lama 1990–1993 6. Maailmanlaajuinen lama 2008- Tutkimuksen perusteella voidaan todeta, että Suomen ilmavoimien johtamisjärjestelmän kehittäminen on perustunut rationaalisiin päätöksiin, jotka ovat saaneet vaikutteita ulkomaisesta ilmasotateorian ja -doktriinien kehityksestä sekä kansainvälisestä johtamisjärjestelmäkehityksestä. Johtamisjärjestelmän evoluutioon on vaikuttanut globaali konvergenssi, johon on tehty kansallisen tason ratkaisuja järjestelmien adaptaation ja implementaation yhteydessä.

Liquid transportation and distribution during (re)wetting : impact on coated papers in printing

In many industrial applications, such as the printing and coatings industry, wetting of porous materials by liquids includes not only imbibition and permeation into the bulk but also surface spreading and evaporation. By understanding these phenomena, valuable information can be obtained for improved process control, runnability and printability, in which liquid penetration and subsequent drying play important quality and economic roles. Knowledge of the position of the wetting front and the distribution/degree of pore filling within the structure is crucial in describing the transport phenomena involved. Although exemplifying paper as a porous medium in this work, the generalisation to dynamic liquid transfer onto a surface, including permeation and imbibition into porous media, is of importance to many industrial and naturally occurring environmental processes. This thesis explains the phenomena in the field of heatset web offset printing but the content and the analyses are applicable in many other printing methods and also other technologies where water/moisture monitoring is crucial in order to have a stable process and achieve high quality end products. The use of near-infrared technology to study the water and moisture response of porous pigmented structures is presented. The use of sensitive surface chemical and structural analysis, as well as the internal structure investigation of a porous structure, to inspect liquid wetting and distribution, complements the information obtained by spectroscopic techniques. Strong emphasis has been put on the scale of measurement, to filter irrelevant information and to understand the relationship between interactions involved. The near-infrared spectroscopic technique, presented here, samples directly the changes in signal absorbance and its variation in the process at multiple locations in a print production line. The in-line non-contact measurements are facilitated by using several diffuse reflectance probes, giving the absolute water/moisture content from a defined position in the dynamic process in real-time. The nearinfrared measurement data illustrate the changes in moisture content as the paper is passing through the printing nips and dryer, respectively, and the analysis of the mechanisms involved highlight the roles of the contacting surfaces and the relative liquid carrier properties of both non-image and printed image areas. The thesis includes laboratory studies on wetting of porous media in the form of coated paper and compressed pigment tablets by mono-, dual-, and multi-component liquids, and paper water/moisture content analysis in both offline and online conditions, thus also enabling direct sampling of temporal water/moisture profiles from multiple locations. One main focus in this thesis was to establish a measurement system which is able to monitor rapid changes in moisture content of paper. The study suggests that near-infrared diffuse reflectance spectroscopy can be used as a moisture sensitive system and to provide accurate online qualitative indicators, but, also, when accurately calibrated, can provide quantification of water/moisture levels, its distribution and dynamic liquid transfer. Due to the high sensitivity, samples can be measured with excellent reproducibility and good signal to noise ratio. Another focus of this thesis was on the evolution of the moisture content, i.e. changes in moisture content referred to (re)wetting, and liquid distribution during printing of coated paper. The study confirmed different wetting phases together with the factors affecting each phase both for a single droplet and a liquid film applied on a porous substrate. For a single droplet, initial capillary driven imbibition is followed by equilibrium pore filling and liquid retreat by evaporation. In the case of a liquid film applied on paper, the controlling factors defining the transportation were concluded to be the applied liquid volume in relation to surface roughness, capillarity and permeability of the coating giving the liquid uptake capacity. The printing trials confirmed moisture gradients in the printed sheet depending on process parameters such as speed, fountain solution dosage and drying conditions as well as the printed layout itself. Uneven moisture distribution in the printed sheet was identified to be one of the sources for waving appearance and the magnitude of waving was influenced by the drying conditions.

Luminescent Lanthanide Reporters: New Concepts for Use in Bioanalytical Applications

Lanthanides represent the chemical elements from lanthanum to lutetium. They intrinsically exhibit some very exciting photophysical properties, which can be further enhanced by incorporating the lanthanide ion into organic or inorganic sensitizing structures. A very popular approach is to conjugate the lanthanide ion to an organic chromophore structure forming lanthanide chelates. Another approach, which has quickly gained interest, is to incorporate the lanthanide ions into nanoparticle structures, thus attaining improved specific activity and binding capacity. The lanthanide-based reporters usually express strong luminescence emission, multiple narrow emission lines covering a wide wavelength range, and exceptionally long excited state lifetimes enabling timeresolved detection. Because of these properties, the lanthanide-based reporters have found widespread applications in various fields of life. This study focuses on the field of bioanalytical applications. The aim of the study was to demonstrate the utility of different lanthanide-based reporters in homogeneous Förster resonance energy transfer (FRET)-based bioaffinity assays. Several different model assays were constructed. One was a competitive bioaffinity assay that utilized energy transfer from lanthanide chelate donors to fluorescent protein acceptors. In addition to the conventional FRET phenomenon, a recently discovered non-overlapping FRET (nFRET) phenomenon was demonstrated for the first time for fluorescent proteins. The lack of spectral overlap in the nFRET mechanism provides sensitivity and versatility to energy transfer-based assays. The distance and temperature dependence of these phenomena were further studied in a DNA-hybridization assay. The distance dependence of nFRET deviated from that of FRET, and unlike FRET, nFRET demonstrated clear temperature dependence. Based on these results, a possible excitation mechanism operating in nFRET was proposed. In the study, two enzyme activity assays for caspase-3 were also constructed. One of these was a fluorescence quenching-based enzyme activity assay that utilized novel inorganic particulate reporters called upconverting phosphors (UCPs) as donors. The use of UCPs enabled the construction of a simple, rather inexpensive, and easily automated assay format that had a high throughput rate. The other enzyme activity assay took advantage of another novel reporter class, the lanthanidebinding peptides (LBPs). In this assay, energy was transferred from a LBP to a green fluorescent protein (GFP). Using the LBPs it was possible to avoid the rather laborious, often poorly repeatable, and randomly positioned chemical labeling. In most of the constructed assays, time-resolved detection was used to eliminate the interfering background signal caused by autofluorescence. The improved signal-to-background ratios resulted in increased assay sensitivity, often unobtainable in homogeneous assay formats using conventional organic fluorophores. The anti-Stokes luminescence of the UCPs, however, enabled the elimination of autofluorescence even without time-gating, thus simplifying the instrument setup. Together, the studied reporters and assay formats pave the way for increasingly sensitive, simple, and easily automated bioanalytical applications.

Resonant tunneling effects in semiconductor heterostructures

The thesis is devoted to a theoretical study of resonant tunneling phenomena in semiconductor heterostructures and nanostructures. It considers several problems relevant to modern solid state physics. Namely these are tunneling between 2D electron layers with spin-orbit interaction, tunnel injection into molecular solid material, resonant tunnel coupling of a bound state with continuum and resonant indirect exchange interaction mediated by a remote conducting channel. A manifestation of spin-orbit interaction in the tunneling between two 2D electron layers is considered. General expression is obtained for the tunneling current with account of Rashba and Dresselhaus types of spin-orbit interaction and elastic scattering. It is demonstrated that the tunneling conductance is very sensitive to relation between Rashba and Dresselhaus contributions and opens possibility to determine the spin-orbit interaction parameters and electron quantum lifetime in direct tunneling experiments with no external magnetic field applied. A microscopic mechanism of hole injection from metallic electrode into organic molecular solid (OMS) in high electric field is proposed for the case when the molecules ionization energy exceeds work function of the metal. It is shown that the main contribution to the injection current comes from direct isoenergetic transitions from localized states in OMS to empty states in the metal. Strong dependence of the injection current on applied voltage originates from variation of the number of empty states available in the metal rather than from distortion of the interface barrier. A theory of tunnel coupling between an impurity bound state and the 2D delocalized states in the quantum well (QW) is developed. The problem is formulated in terms of Anderson-Fano model as configuration interaction between the carrier bound state at the impurity and the continuum of delocalized states in the QW. An effect of this interaction on the interband optical transitions in the QW is analyzed. The results are discussed regarding the series of experiments on the GaAs structures with a -Mn layer. A new mechanism of ferromagnetism in diluted magnetic semiconductor heterosructures is considered, namely the resonant enhancement of indirect exchange interaction between paramagnetic centers via a spatially separated conducting channel. The underlying physical model is similar to the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction; however, an important difference relevant to the low-dimensional structures is a resonant hybridization of a bound state at the paramagnetic ion with the continuum of delocalized states in the conducting channel. An approach is developed, which unlike RKKY is not based on the perturbation theory and demonstrates that the resonant hybridization leads to a strong enhancement of the indirect exchange. This finding is discussed in the context of the known experimental data supporting the phenomenon.

Calculation of the magnetic field penetration depth for high-Tc cuprate superconductors based on the Interlayer Pair Tunneling model /

In this work, the magnetic field penetration depth for high-Tc cuprate superconductors is calculated using a recent Interlayer Pair Tunneling (ILPT) model proposed by Chakravarty, Sudb0, Anderson, and Strong [1] to explain high temperature superconductivity. This model involves a "hopping" of Cooper pairs between layers of the unit cell which acts to amplify the pairing mechanism within the planes themselves. Recent work has shown that this model can account reasonably well for the isotope effect and the dependence of Tc on nonmagnetic in-plane impurities [2] , as well as the Knight shift curves [3] and the presence of a magnetic peak in the neutron scattering intensity [4]. In the latter case, Yin et al. emphasize that the pair tunneling must be the dominant pairing mechanism in the high-Tc cuprates in order to capture the features found in experiments. The goal of this work is to determine whether or not the ILPT model can account for the experimental observations of the magnetic field penetration depth in YBa2Cu307_a7. Calculations are performed in the weak and strong coupling limits, and the efi"ects of both small and large strengths of interlayer pair tunneling are investigated. Furthermore, as a follow up to the penetration depth calculations, both the neutron scattering intensity and the Knight shift are calculated within the ILPT formalism. The aim is to determine if the ILPT model can yield results consistent with experiments performed for these properties. The results for all three thermodynamic properties considered are not consistent with the notion that the interlayer pair tunneling must be the dominate pairing mechanism in these high-Tc cuprate superconductors. Instead, it is found that reasonable agreement with experiments is obtained for small strengths of pair tunneling, and that large pair tunneling yields results which do not resemble those of the experiments.

Modeling premartensitic effects in Ni2MnGa: A mean-field and Monte Carlo simulation study

ic first-order transition line ending in a critical point. This critical point is responsible for the existence of large premartensitic fluctuations which manifest as broad peaks in the specific heat, not always associated with a true phase transition. The main conclusion is that premartensitic effects result from the interplay between the softness of the anomalous phonon driving the modulation and the magnetoelastic coupling. In particular, the premartensitic transition occurs when such coupling is strong enough to freeze the involved mode phonon. The implication of the results in relation to the available experimental data is discussed.

Multiple edges of a quantum Hall system in a strong electric

In this paper we show that if the electrons in a quantum Hall sample are subjected to a constant electric field in the plane of the material, comparable in magnitude to the background magnetic field on the system of electrons, a multiplicity of edge states localized at different regions of space is produced in the sample. The actions governing the dynamics of these edge states are obtained starting from the well-known Schrödinger field theory for a system of nonrelativistic electrons, where on top of the constant background electric and magnetic fields, the electrons are further subject to slowly varying weak electromagnetic fields. In the regions between the edges, dubbed as the "bulk," the fermions can be integrated out entirely and the dynamics expressed in terms of a local effective action involving the slowly varying electromagnetic potentials. It is further shown how the bulk action is gauge noninvariant in a particular way, and how the edge states conspire to restore the U(1) electromagnetic gauge invariance of the system. In the edge action we obtain a heretofore unnoticed gauge-invariant term that depends on the particular edge. We argue that this term may be detected experimentally as different edges respond differently to a monochromatic probe due to this term

Finite-size scaling analysis of the avalanches in the three-dimensional Gaussian random-field Ising model with metastable dynamics

A numerical study is presented of the third-dimensional Gaussian random-field Ising model at T=0 driven by an external field. Standard synchronous relaxation dynamics is employed to obtain the magnetization versus field hysteresis loops. The focus is on the analysis of the number and size distribution of the magnetization avalanches. They are classified as being nonspanning, one-dimensional-spanning, two-dimensional-spanning, or three-dimensional-spanning depending on whether or not they span the whole lattice in different space directions. Moreover, finite-size scaling analysis enables identification of two different types of nonspanning avalanches (critical and noncritical) and two different types of three-dimensional-spanning avalanches (critical and subcritical), whose numbers increase with L as a power law with different exponents. We conclude by giving a scenario for avalanche behavior in the thermodynamic limit.

Influence of the driving mechanism on the response of systems with athermal dynamics: The example of the random-field Ising model

We investigate the influence of the driving mechanism on the hysteretic response of systems with athermal dynamics. In the framework of local mean-field theory at finite temperature (but neglecting thermally activated processes), we compare the rate-independent hysteresis loops obtained in the random field Ising model when controlling either the external magnetic field H or the extensive magnetization M. Two distinct behaviors are observed, depending on disorder strength. At large disorder, the H-driven and M-driven protocols yield identical hysteresis loops in the thermodynamic limit. At low disorder, when the H-driven magnetization curve is discontinuous (due to the presence of a macroscopic avalanche), the M-driven loop is reentrant while the induced field exhibits strong intermittent fluctuations and is only weakly self-averaging. The relevance of these results to the experimental observations in ferromagnetic materials, shape memory alloys, and other disordered systems is discussed.

Studies in quantum field theory at finite temperature

The thesis deals with certain quantum field systems exhibiting spontaneous symmetry breaking and their response to temperature. These models find application in diverse branches such as particle physics, solid state physics and non~linear optics. The nature of phase transition that these systems may undergo is also investigated. The thesis contains seven chapters. The first chapter is introductory and gives a brief account of the various phenomena associated with spontaneous symmetry breaking. The chapter closes with anote on the effect of temperature on quantum field systems. In chapter 2, the spontaneous symmetry breaking phenomena are reviewed in more detail. Chapter 3, deals with the formulation of ordinary and generalised sine-Gordon field theories on a lattice and the study of the nature of phase transition occurring in these systems. In chapter 4, the effect of temperature on these models is studied, using the effective potential method. Chapter 5 is a continuation of this study for another model, viz, the m6 model. The nature of phase transition is also studied. Chapters 5 and 6 constitute a report of the investigations on the behaviour of coupling constants under thermal excitation D1 $4 theory, scalar electrodynamics, abelian and non-abelian gauge theories

Normalization factors for magnetic relaxation of small particle systems in non-zero magnetic field.

We critically discuss relaxation experiments in magnetic systems that can be characterized in terms of an energy barrier distribution, showing that proper normalization of the relaxation data is needed whenever curves corresponding to different temperatures are to be compared. We show how these normalization factors can be obtained from experimental data by using the Tln (t/t0) scaling method without making any assumptions about the nature of the energy barrier distribution. The validity of the procedure is tested using a ferrofluid of Fe3O4 particles.

Quantum suppression of shot noise in field emitters

We have analyzed the shot noise of electron emission under strong applied electric fields within the Landauer-Bttiker scheme. In contrast to the previous studies of vacuum-tube emitters, we show that in new generation electron emitters, scaled down to the nanometer dimensions, shot noise much smaller than the Schottky noise is observable. Carbon nanotube field emitters are among possible candidates to observe the effect of shot-noise suppression caused by quantum partitioning.

Effects of new nonlinear couplings in relativistic effective field theory

We extend the relativistic mean field theory model of Sugahara and Toki by adding new couplings suggested by modern effective field theories. An improved set of parameters is developed with the goal to test the ability of the models based on effective field theory to describe the properties of finite nuclei and, at the same time, to be consistent with the trends of Dirac-Brueckner-Hartree-Fock calculations at densities away from the saturation region. We compare our calculations with other relativistic nuclear force parameters for various nuclear phenomena.

" Studies on Laser induced Phatothermal Phenomena in Selected Organic Compounds and Fullerenes"

In the pre—laser era it was difficult to believe that the optical properties of a medium depend upon the intensity of the radiation incident on it. The basis for this conclusion is that the electric field strength associated with the conventional light sources used before the advent of lasers was much smaller than (103 V/cm) the field sttrengths of atomic or interatomic fields (2 107 —- 10” V/cm). The radiation with such low intensity is not able to affect atomic fields to the extent of changing optical parameters. The invention of laser in 1960 was a turning point. The high degree of coherence of the laser radiation provides high spatial concentration of optical power. With the availability of the femtosecond lasers it has become possible to get extremely high peak powers 2 1013 W/cmz). At such high fields, the relationship between electric ‘polarization P and the electric field strength E ceases to be linear and several nonlinear effects begin to occur. Nonlinear absorption, a branch of nonlinear optics, refers to the interaction between radiation and matter accompanied by absorption of more than one photon. Nonlinear absorption has acquired great importance after the invention of high power lasers. One of the objectives of the present work is to investigate the nonlinear absorption processes occurring in fullerene, selected organic solvents and laser dyes. Fullerenes and laser dyes were chosen because of their highly nonlinear behaviour. Fullerenes, the most beautiful among molecules, offer fascinating field of research owinglto their significant structural properties. As toluene, benzene and carbon disulphide are themost widely used solvents for fullerenes, it seems important to study the nonlinear properties of these liquids as well. Like fullerenes, laser dyes also possess highly delocalized 7r electrons which are responsible for their nonlinear absorption. Dye lasers were the fulfillment of an experimenter’s pipe dream - to have a laser that is easily tunable over a wide range of wavelengths. A better understandingof the photophysical properties of laser dyes can significantly enhance the development and technology of dye lasers. We studied the nonlinear absorption properties of two rhodamine dyes to have some insight into their nonlinear optical properties.

Studies on the interaction of two level atoms with quantized electromagnetic field

The present study described about the interaction of a two level atom and squeezed field with time varying frequency. By applying a sinusoidal variation in the frequency of the field, the randomness in population inversion is reduced and the collapses and periodic revivals are regained. Quantum optics is an emerging field in physics which mainly deals with the interaction of atoms with quantised electromagnetic fields. Jaynes-Cummings Model (JCM) is a key model among them, which describes the interaction between a two level atom and a single mode radiation field. Here the study begins with a brief history of light, atom and their interactions. Also discussed the interaction between atoms and electromagnetic fields. The study suggest a method to manipulate the population inversion due to interaction and control the randomness in it, by applying a time dependence on the frequency of the interacting squeezed field.The change in behaviour of the population inversion due to the presence of a phase factor in the applied frequency variation is explained here.This study also describes the interaction between two level atom and electromagnetic field in nonlinear Kerr medium. It deals with atomic and field state evolution in a coupled cavity system. Our results suggest a new method to control and manipulate the population of states in two level atom radiation interaction,which is very essential for quantum information processing.We have also studied the variation of atomic population inversion with time, when a two level atom interacts with light field, where the light field has a sinusoidal frequency variation with a constant phase. In both coherent field and squeezed field cases, the population inversion variation is completely different from the phase zero frequency modulation case. It is observed that in the presence of a non zero phase φ, the population inversion oscillates sinusoidally.Also the collapses and revivals gradually disappears when φ increases from 0 to π/2. When φ = π/2 the evolution of population inversion is identical to the case when a two level atom interacts with a Fock state. Thus, by applying a phase shifted frequency modulation one can induce sinusoidal oscillations of atomic inversion in linear medium, those normally observed in Kerr medium. We noticed that the entanglement between the atom and field can be controlled by varying the period of the field frequency fluctuations. The system has been solved numerically and the behaviour of it for different initial conditions and different susceptibility values are analysed. It is observed that, for weak cavity coupling the effect of susceptibility is minimal. In cases of strong cavity coupling, susceptibility factor modifies the nature in which the probability oscillates with time. Effect of susceptibility on probability of states is closely related to the initial state of the system.