The contribution of geographical knowledge to the project activities of the Ecoschool

Diplomsko delo se ukvarja s predstavitvijo Ekošole kot mednarodnega programa za izobraževanje in ozaveščanje o trajnostnem razvoju ter okoljski vzgoji. Z izpostavitvijo učnih ciljev slovenskih učnih načrtov pri predmetih, ki se povezujejo z okoljsko vzgojo (spoznavanje okolja, naravoslovje in tehnika, družba, gospodinjstvo, naravoslovje, biologija, geografija), smo ugotovili, da je možnih preko 160 povezav z Ekošolo že preko obstoječih učnih načrtov. Na koncu smo podali predloge za vključitev nekaterih okoljskih tem v že obstoječe učne načrte v luči aktualizacije le-teh. Mednje smo na podlagi ovrednotenja obstoječega učnega načrta za geografijo v osnovni šoli z vidika vključenosti okoljskih tem v povezavi z Ekošolo uvrstili podnebne spremembe z globalnim segrevanjem, celostno obravnavo energije, krožno gospodarstvo in trajnostno mobilnost. Z anketo, izvedeno med učitelji geografije na osnovnih šolah, ki so vključene v Ekošolo, smo prišli do treh dodatkih predlogov (pomen krasa za občutljivost Slovenije na onesnaževanje, trajnostno ekološko kmetovanje v lokalnem okolju in okoljski vplivi (masovnega) turizma), poleg teh pa smo med predloge uvrstili še problematiko čebel in drugih opraševalcev.The thesis deals with the presentation of Eco-Schools as an international program that aims to educate about and make students aware of the meaning of sustainable development and environmental education. By observing the educational goals in Slovene curricula for subjects that are closely connected with environmental education (nature study, science and technology, social studies, HE, science, biology, geography) we have found out that there are more than 160 correlations with Eco-School. In the end some new suggestions were made for including several environmental topics into the existing curricula in order to make them more topical. After assessing and scanning the existing curriculum for geography in the primary school for environmental topics in connection with Eco-School, we have suggested the following topics: climate changes and global warming, the holistic approach to energy, circular economy and sustainable mobility. A survey was conducted among primary school geography teachers who work in schools that are included in the Eco-School network and three additional suggestions were made on its basis (the significance of karst for Slovenia’s sensitivity to pollution, sustainable ecological agriculture in the local environment and the impact of (mass) tourism on the environment), in addition we have suggested the problem of bees and other pollinators

Spektralne lastnosti superfluorescence v daljnem ultravijoličnem in rentgenskem področju

Superfluorescence is a nonlinear process in light-matter interaction that leads to amplification of spontaneously emitted radiation from a target with inverted population of atomic or ionic excited states. While this process has been extensively studied in the optical domain, experimental observation in the extreme ultraviolet and X-ray spectral regions has only recently become possible with the development of free-electron lasers. However, despite successful measurements of the characteristic superfluorescence yield at short wavelengths, agreement between experimental results and theoretical predictions has thus far only been qualitative.\ The main goal of this work is to address some of the open problems in theoretical modeling of superfluorescence. To this end, we first develop a model of light-matter interaction in a three-level system, which is based on a solution of combined propagation equations for quantum correlation functions and semiclassical Maxwell-Bloch equations. This model is employed to study X-ray superfluorescence in K$alpha$ emission from a zinc target. After verifying the validity of the model and comparing it to the existing frameworks for describing superfluorescence, we investigate the spectral properties of emitted radiation for the case of pumping with sub-femtosecond free-electron laser pulses, which have been only recently produced at X-ray wavelengths.\ The improved model with quantum correlation functions still cannot provide quantitative predictions for realistic experimental setups, so in the second part of the thesis we present a formalism that describes the four-dimensional spatio-temporal evolution of a multi-level atomic system pumped by coherent light and subject to incoherent processes. The model is based on Maxwell-Bloch equations with added stochastic noise terms to simulate random fluctuations of spontaneous emission. After describing the general formalism and its numerical implementation, the model is used to simulate X-ray superfluorescence in K$alpha_1$ emission from a copper nitrate solution, and XUV superfluorescence from resonantly excited helium gas. In both examples, the range of considered parameters matches current experimental capabilities of free-electron lasers.Superfluorescenca je nelinearen kolektiven sevalni pojav, za katerega je značilno ojačanje svetlobe, ki jo spontano izseva tarča z invertirano zasedenostjo. Čeprav je ta proces v vidnem območju podrobno raziskan, lahko superfluorescenco v daljnem ultravijoličnem in rentgenskem spektralnem področju opazujemo šele od nedavne iznajdbe laserjev na proste elektrone. Kljub uspešnim meritvam značilne odvisnosti fotonskega pridelka od jakosti vzbujanja tarče, pa smo lahko z dosedanjimi teoretičnimi modeli poustvarili le kvalitativne značilnosti tega procesa. \ Glavni cilj pričujočega dela je nasloviti nekatera izmed odprtih vprašanj pri teoretičnem opisu superfluorescence. Tako v prvem delu disertacije razvijemo model interakcije svetlobe s snovjo, ki temelji na reševanju kombinacije enačb za propagacijo kvantnih korelacijskih funkcij in semiklasičnih Maxwell-Blochovih enačb. Model uporabimo za obravnavo superfluorescence pri valovni dolžini K$alpha$ v cinku, pri čemer smo v skladu z najnovejšimi eksperimentalnimi zmožnostmi trajanje črpalnih sunkov močne svetlobe omejili na nekaj sto atosekund.\ Kljub nekaterim izboljšavam glede na prejšnje teoretične opise superfluorescence, model s kvantnimi korelacijskimi funkcijami še ne more zagotoviti kvantitativnih napovedi za realistične eksperimentalne postavitve. V drugem delu disertacije zato predstavimo večji teoretični okvir, ki opiše štiridimenzionalni prostorsko-časovni razvoj večnivojskega atomskega sistema, ki ga vzbuja koherentna svetloba in je podvržen nekoherentnim procesom. Razširjeni model temelji na reševanju Maxwell-Blochovih enačb z dodanimi stohastičnimi členi, ki ustvarijo naključne fluktuacije polarizacije atomov in simulirajo vpliv spontane emisije. Najprej opišemo splošne značilnosti formalizma in njegovo numerično implementacijo, nato pa model uporabimo za obravnavo superfluorescence pri valovni dolžini K$alpha_1$ v raztopini bakrovega nitrata ter za opis ojačanja ultravijolične fluorescence v resonantno vzbujenem heliju. V obeh primerih obseg parametrov, ki jih obravnavamo, sovpada z aktualnimi tehničnimi zmožnostmi laserjev na proste elektrone

Helium ultraviolet laser

Delo obravnava samoojačanje ultravijolične svetlobe v plinastem mediju. Proces proži kratek in kolimiran sunek svetlobe laserja na proste elektrone, ki v helijevi tarči prenese del populacije iz osnovnega v izbrano dvojno vzbujeno stanje pod drugim pragom za ionizacijo. Taka atomska stanja pretežno razpadajo z avtoionizacijo, z majhno verjetnostjo pa tudi sevalno v enojno vzbujena stanja, pri čemer se izseva svetloba z valovno dolžino $sim!30,$nm v daljnem ultravijoličnem območju. Pri velikem tlaku plina v tarči in intenziteti vpadne svetlobe je intenziteta spontanega sevanja v smeri potovanja črpalnega sunka svetlobe tako velika, da pride do stimulirane emisije, zaradi katere se intenziteta izsevane svetlobe eksponentno ojača. Nastali sunek svetlobe je koherenten in usmerjen vzdolž smeri črpalnega sunka svetlobe. Pojav obravnavamo z Maxwell-Blochovimi enačbami, ki opisujejo širjenje polj v tarči ter prostorski in časovni razvoj zasedenosti atomskih stanj in koherenc med njimi. Spontano emisijo v okviru klasičnih Maxwellovih enačb simuliramo s stohastičnim členom, ki ustvari naključne fluktuacije polarizacije atomov. Dodatno ionizacijo stanj z vpadnim in izsevanim poljem obravnavamo z zasedbenimi enačbami. Predstavljeni so rezultati za široko območje intenzitet vpadne svetlobe in tlaka v tarči, tako da lahko spremljamo razvoj črpalnega in izsevanega polja v režimu spontane emisije, eksponentnega ojačanja in nasičenja. Obravnava vključuje črpanje s koherentnimi sunki svetlobe, ki jih proizvajajo semenski laserji na proste elektrone, ter črpanje z delno koherentnimi sunki laserja na proste elektrone s spontanim proženjem. V pričujočem delu prvič prikažemo numerične rešitve polnega sistema Maxwell-Blochovih enačb za trinivojski sistem z dvema sevalnima poljema, kjer je dominantni razpadni kanal zgornjega stanja avtoionizacija. Vzorčni primer takih stanj v atomski fiziki so nekatera dvojno vzbujena stanja v heliju. Za obravnavo smo izbrali stanje $3a,^1!P,^o$ z vzbuditveno energijo $63,6,$eV, katerega življenjski čas je primerljiv s trajanjem svetlobnega sunka laserjev na proste elektrone v daljnem ultravijoličnem območju.In this work a theoretical treatment of self-amplification of extreme ultraviolet light in a gas medium is presented. The process is initiated by focusing short light pulses produced by a free-electron laser onto a helium gas target, to transfer a part of the population from the ground state of the atom to the selected doubly excited state below the second ionization threshold. The main decay channel of the upper state is autoionization, but it can also decay via fluorescence to singly excited states by emitting $sim!30,$nm light belonging to the extreme ultraviolet region of the spectrum. If the target pressure and pump pulse intensity are high, the intensity of spontaneously emitted light in the direction of the pump pulse propagation increases enough to cause stimulated emission. This leads to an exponential amplification of the light intensity of the emitted pulse, which is directional and coherent. The treatment of the problem with Maxwell-Bloch equations is presented, which describe the propagation of electromagnetic fields in the target together with the temporal and spatial evolution of the state populations and coherences between them. Spontaneous emission is modeled by a source term, which injects energy into the system and produces random fluctuations of the atomic polarization. In addition to the basic three-level scheme, further ionization with the pump and emitted field is considered by means of the rate equations. Results for a wide range of pump intensities and target pressures are presented, showing clearly the regions of spontaneous emission, exponential amplification, and saturation of the emitted light. The treatment includes both the coherent pump pulses, produced by a seeded free-electron laser, as well as partially coherent pump pulses, generated by amplification of light emitted randomly by the free-electron laser. To our knowledge, this is the first time the full set of Maxwell-Bloch equations for a three-level system, where one of the states decays by autoionization, is solved, including the spontaneous decay of the autoionizing state. In our case, the upper state is chosen to be the $3a,^1!P,^o$ doubly excited state in helium, a prototype of strongly autoionizing resonances in atomic physics, featuring a lifetime similar to the pulse length of the free-electron laser light in the extreme ultraviolet region

Stochastic modeling of x-ray superfluorescence

An approach to modeling the dynamics of x-ray amplified spontaneous emission and superfluorescence -- the phenomenon of collective x-ray emission initiated by intense pulses of X-ray Free Electron Lasers -- is developed based on stochastic partial differential equations. The equations are derived from first principles, and the relevant approximations, derivation steps, and extensions specific to stimulated x-ray emission are presented. The resulting equations have a form of three-dimensional generalized Maxwell-Bloch equations augmented with noise terms for both field and atomic variables. The derived noise terms possess specific correlation properties that enable the correct reconstruction of spontaneous emission. As a result, the developed formalism is universally suitable for the description of all stages of stimulated x-ray emission: spontaneous emission, amplified spontaneous emission, and superfluorescence. Numerical examples illustrating multiple properties of the emitted field -- e.g., spatio-temporal coherence -- are presented. We expect that the developed formalism will form a solid base for interpreting stimulated x-ray emission spectroscopy measurements, modeling x-ray laser oscillators, and describing other experiments that employ x-ray superfluorescence

Modeling of 3D paraxial x-ray superfluorescence based on stochastic differential equations

Intense focused XFEL pulses can produce atoms in the core-hole state thus leading to collective x-ray emission (superfluorescence). We will present a 3 D description of paraxial x-ray superfluorescence based on rigorously derived stochastic differential equations

XUV superfluorescence from helium gas in the paraxial three-dimensional approximation

We present the results of a theoretical study of XUV superfluorescence from doubly excited states of helium resonantly pumped by free-electron laser (FEL) pulses. Our model allows us to predict both the spectrum and angular distribution of emitted XUV radiation in a wide range of experimentally accessible parameters. This is achieved by going beyond two key deficiencies of most previous models: The one-dimensional treatment in space is upgraded to three dimensions with electromagnetic fields treated in the paraxial approximation and spontaneous emission is modeled by a recently developed approach that avoids the unrealistic delayed response but preserves the expected characteristics of the emitted field in the spontaneous emission limit. The case study of 3a$^1$P$^o$ resonance in helium with 63.66 eV excitation energy is presented for realistic parameters of seeded light pulses from the FERMI FEL facility and a recently developed high-pressure gas cell. Results of numerical simulations show that both the spectral width and angular divergence of emitted radiation vary with gas pressure and pump pulse intensity in a complex way

Light-Induced Magnetization at the Nanoscale

Triggering and switching magnetic moments is of key importance for applications ranging from spintronics to quantum information. A noninvasive ultrafast control at the nanoscale is, however, an open challenge. Here, we propose a novel laser-based scheme for generating atomic-scale charge current loops within femtoseconds. The associated orbital magnetic moments remain ferromagnetically aligned after the laser pulses have ceased and are localized within an area that is tunable via laser parameters and can be chosen to be well below the diffraction limit of the driving laser field. The scheme relies on tuning the phase, polarization, and intensities of two copropagating Gaussian and vortex laser pulses, allowing us to control the spatial extent, direction, and strength of the atomic-scale charge current loops induced in the irradiated sample upon photon absorption. In the experiment we used He atoms driven by an ultraviolet and infrared vortex-beam laser pulses to generate current-carrying Rydberg states and test for the generated magnetic moments via dichroic effects in photoemission. Ab initio quantum dynamic simulations and analysis confirm the proposed scenario and provide a quantitative estimate of the generated local moments

Light-Induced Magnetization at the Nanoscale

Triggering and switching magnetic moments is of key importance for applications ranging from spintronics to quantum information. A noninvasive ultrafast control at the nanoscale is, however, an open challenge. Here, we propose a novel laser-based scheme for generating atomic-scale charge current loops within femtoseconds. The associated orbital magnetic moments remain ferromagnetically aligned after the laser pulses have ceased and are localized within an area that is tunable via laser parameters and can be chosen to be well below the diffraction limit of the driving laser field. The scheme relies on tuning the phase, polarization, and intensities of two copropagating Gaussian and vortex laser pulses, allowing us to control the spatial extent, direction, and strength of the atomic-scale charge current loops induced in the irradiated sample upon photon absorption. In the experiment we used He atoms driven by an ultraviolet and infrared vortex-beam laser pulses to generate current-carrying Rydberg states and test for the generated magnetic moments via dichroic effects in photoemission. Ab initio quantum dynamic simulations and analysis confirm the proposed scenario and provide a quantitative estimate of the generated local moments

Photoelectric effect with a twist

Photons have fixed spin and unbounded orbital angular momentum (OAM). While the former is manifested in the polarization of light, the latter corresponds to the spatial phase distribution of its wavefront1. The distinctive way in which the photon spin dictates the electron motion upon light– matter interaction is the basis for numerous well-established spectroscopies. By contrast, imprinting OAM on a mat- ter wave, specifically on a propagating electron, is gener- ally considered very challenging and the anticipated effect undetectable2. In refs. 3,4, the authors provided evidence of OAM-dependent absorption of light by a bound electron. Here, we seek to observe an OAM-dependent dichroic photo- electric effect, using a sample of He atoms. Surprisingly, we find that the OAM of an optical field can be imprinted coher- ently onto a propagating electron wave. Our results reveal new aspects of light–matter interaction and point to a new kind of single-photon electron spectroscopy