Optics Seminar
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2022-11-24 (Thursday)
room 0.06, Pasteura 5 at 10:15 
prof. Andrzej Sobolewski (IF PAN)Hund's Rule Violating Molecules as Precursors of New Optoelectronic Materials
Almost one century ago, Friedrich Hund formulated his famous multiplicity rule according to which the term with maximummultiplicity has the lowest energy for a given electron configuration [1]. This rule provides the base for the Jablonski diagram [2]which is commonly used for discussions of molecular spectroscopy and photophysics. No stable organic molecules which violateHund’s Rule for the S1 and T1 excited states were definitely known until three years ago, when the existence of such moleculeswas discovered with wavefunction-based ab initio calculations [3,4] and was confirmed experimentally[3,5]. Further theoreticalinvestigations have shown that there exists a wide class of stable organic molecules in which the lowest excited singlet state liesbelow the lowest excited triplet state [6].This observation may have important implications in the field of organic light emitting diodes (OLEDs) because according to spinstatistics, the recombination of charge carriers generated by voltage in optoelectronic materials produces (emissive) singlet and(dark) triplet excitons in the ratio 1:3, so the luminescence quantum yield of such “standard” materials cannot nominally exceed25%. The discovery of stable organic molecules with inverted singlet-triplet ordering breaks a ground for creation of a newgeneration of organic optoelectronic materials where the triplet “traps” are spontaneously drained and allows in principle toachieve 100% yield of electron to photon conversion in OLEDs [7].In this presentation, the results of extensive computational explorations of novel classes of organic molecules exhibiting singlet-triplet inversion will be presented in order to provide understanding of the fundamental mechanisms which are responsible forthe violation of Hund’s rule and to determine the electronic and geometric factors that govern the phenomenon. Provided thatsuch molecules with appreciable fluorescence rates can be synthetized, they will become the next (forth) generation of OLEDmaterials.1. F. Hund, Zeitschrift f. Physik, 40 (1927) 742.2. A. Jabłoński, Nature 131 (1933) 839.3. J. Ehrmaier,E. Rabe, S. Pristash, K. Corp, C. Schlenker, A. L. Sobolewski, W. Domcke, J. Phys. Chem. A 123 (2019) 8099.4. P. de Silva, J. Phys. Chem. Lett. 10 (2019) 5674.5. N. Aizawa1, Y J. Pu1, Y. Harabuchi, A. Nihonyanagi, R. Ibuka, H. Inuzuka, B. Dhara1, Y. Koyama, K. Nakayama, S. Maeda, Nature609 (2022) 502.6. S.Pios, X. Huang, A. L. Sobolewski, W. Domcke, PCCP 23 (2021) 12968.7. A. L. Sobolewski and W. Domcke, J. Phys. Chem. Lett., 12 (2021) 6852
2022-11-17 (Thursday)
room 0.06, Pasteura 5 at 10:15
dr Mateusz Łącki (Uniwersytet Jagielloński)Dark states and bands for ultracold atoms
A proposal [Phys. Rev. Lett. 117, 233001 (2016)] to use a three-level Lambda system to create opticalpotentials for ultracold atoms has lead to effective lattice with subwavelength potential peaks. Thispotential is for atoms that occupy the dark state manifold. The proposal was extended from atomic statesto the bands of Hofstadter-Harper model in a Lambda system configuration. This allows to create a darkstate flat band with Chern number, |C| > 1. Another possible extension of the original work was achievedby considering a four level atomic setup in the tripod configuration which gives an interesting tight-bindingmodel with long range hopping and interaction. Finally, by resonant coupling of many-level system withfields that include random speckle fields, one creates random dark state potentials, that open interestingpossibilities for Anderson localization. In the talk I will present the three above extensions of the originalLambda system.
2022-11-03 (Thursday)
room 0.06, Pasteura 5 at 10:15
prof. Ryszard Piramidowicz (Politechnika Warszawska)Photonic integrated circuits – technologies, applications, trends
The contemporary world is a universe of information technologies (ICT) - we live surrounded by information generated, aggregated, and processed using sophisticated computer systems, transmitted over high-speed teletransmission networks, and analyzed by artificial intelligence. Dynamic development of ICT is driven by the technologies of electronic integration, developed since the 70s, which marked the beginning of the microelectronic revolution, which resulted in the omnipresence of integrated electronic circuits. The beginning of the 21st century observed a rapid development of technology with a similarly revolutionary potential - integrated photonics - analogous to integrated electronics, with the only difference of using photons instead of electrons as information carriers. Indeed, photonic integrated circuits (PICs) have revolutionized the telecom and datacom market. After two decades of development with enormous dynamics, they are ready to enter entirely new application areas related to broadly defined sensor technologies (including the IoT and smart environment). In this presentation, the issues of technology and applications of integrated photonics systems will be explained, with particular emphasis on global development trends. In particular, mature technological platforms with an established market position (silicon and indium phosphide) and emerging platforms will be presented and discussed. Specific attention will be put on the MIRPIC platform, dedicated to mid-infrared integrated photonics systems, developed jointly by VIGO Photonics, Warsaw University of Technology, and Institute of Microelectronics and Photonics of Lukasiewicz Research Network. The main application areas of PIC-based systems - optical telecommunications, datacom, and sensor technology - will be analyzed and illustrated with examples of commercially offered products complemented with the original PIC designs of the IMiO PW team. The main challenges will also be discussed, which integrated photonics is currently facing.
2022-10-27 (Thursday)
room 0.06, Pasteura 5 at 10:15
mgr Arkadiusz Hudzikowski (Politechnika Wroclawska)Spectral broadening and compression of ultrashort pulses of light in systems based on noble gases filled multi-pass cells
Spectral broadening and compression of ultrashort laser pulses is recently a widely investigated field dueto the availability of high power lasers. Multipass cells filled with noble gases are ideally suited for pulsebroadening in µJ and mJ energy range.This presentation shows the results of spectral broadening in a compact, Herriott multi-pass cellfilled successively with argon, xenon and krypton, and pulse compression using a dispersive mirror array.Multi-pass cell setup filled with noble gases was experimentally characterized for different pressures andenergies of the input pulses. The results of measurements were compared with simulations made with thecustom developed software based on direct ray tracing and the split-step Fourier method implemented inPyNLO library.A 280 fs, 110 µJ pulse was compressed down to 31.2 fs in a single-stage system based on the multipass cell filled with xenon at a pressure of 3.25 bar, which led to a compression ratio of 9.
2022-10-20 (Thursday)
room 0.06, Pasteura 5 at 10:15
mgr Mateusz Król (Wydział Fizyki UW)Non-Hermitian effects in microcavities filled with liquid crystals: annihilation of exceptional point
In quantum mechanics, the assumed hermicity of the Hamiltonian ensures that the probability of finding aparticle is constant over time. The description of dissipation or gain in a system typically requiresintroduction of non-Hermitian terms. The resulting non-Hermitian Hamiltonian can exhibit propertiesunavailable for typical Hermitian systems. The most striking example of such behavior is the existence ofso-called Exceptional Points (EP), points in parameter space where both eigenvalues and eigenvectorscoalesce (are degenerate).In this work, we introduce the basics of non-Hermitian physics with special emphasis on the properties ofEPs. Specifically, we consider a planar optical microcavity filled with a birefringent liquid crystal. We showhow polarization dependent losses in such a system lead to emergence of EPs. We demonstrate, boththeoretically and experimentally, how owing to the sensibility of the liquid crystal to an external electricfield, it is possible to change the position of the EPs. In particular, we show how EPs can be removed(annihilated) from the system when two of them are brought into a single position
2022-10-13 (Thursday)
room 0.06, Pasteura 5 at 10:15
Mariusz Semczuk (IFD UW)Towards ground state molecules of KCs and CsAg
Ultracold molecules of alkali atoms have been studied quite extensively for nearly three decades, providing invaluable information on collisional properties of constituent atoms. In recent years, the main focus has been on heteronuclear species in the absolute ro-vibrational ground state, as these molecules can exhibit long-range, relatively strong dipolar interactions enabled by the presence of an electric dipole moment.In this talk I will discuss our progress on the way to form ultracold ground state molecules of KCs. In particular, I will present experimental results confirming a decade-old theoretical prediction regarding the number of vibrational levels of one of the excited molecular potentials of Cs2.In the second part of the talk I will introduce new atomic mixtures that we are planning to investigate in the years to come, Cs+Ag and K+Ag, with the goal to eventually turn them into ultracold ground state molecules with enormous electric dipole moment (~10 Debye).
2022-10-06 (Thursday)
room 0.06, Pasteura 5 at 10:15
dr Agnieszka Popiołek - Masajada (Wydz. Podstawowych Problemów Techniki Politechniki Wrocławskiej)Optical fields' phase singularities in optical measurements
Structured light with non-Gaussian intensity profiles and with spatially variant phase distributions is getting attention in many fields of optical science and technology. A special case of such beams is a vortex beam, which features a helical shaped wavefront and annular intensity distribution. An optical vortex is a singular phase structure having a point to which the equiphase lines converge (vortex point). They attract attention in modern optical metrology because they are stable structures having a characteristic point of zero intensity (at the vortex point) and can serve as precise position markers. On the other hand, they are well-defined points on the phase map and can be localized with arbitrary accuracy, at least in theory. In the talk, I will present the approaches that have been made to apply optical vortices in metrology. In particular, I will focus on the optical vortex scanning microscope. In this instrument, we propose to use the focused vortex beam to illuminate the sample. The investigated sample interacts with the illuminating beam that contains an area of low amplitude and fast-changing phase. That makes the beam sensitive to any phase or amplitude perturbations. I will present the results we obtained during our research on this instrument.