Studies

Physics (N002) themes 2022

 

No.

Field

Supervisor

Theme LT

Theme EN

N 002 Physics

1.

N 002

Dr. Ramūnas Adomavičius 

Dujinės būsenos medžiagų spektroskopija ir taikymai terachercinių bangų diapazone

Spectroscopy and applications of gasoeus materials in the terahertz range

During doctoral studies, a terahertz time-domain spectroscopy (THz-TDS) system will be used to investigate gas-phase materials. One of the tasks of the doctoral program is the acquisition and improvement of measuring equipment. Comparative studies are also planned, during which gas samples will be measured using the time-domain and the traditional Fourier spectrometer. The aim of these studies is to reveal the advantages and disadvantages of both methodologies. The result of the research should be the development of a common methodology using both continuous and pulsed terahertz radiation for complex research. In the following studies, the above methodology will be applied in gas refractive index measurements, analysis of human exhaled air, gas flow motion and other studies. THz-TDS spectroscopy is rarely used for gas studies while the real-time measurement methodology developed in the UOL laboratory has never been used in gas studies at all. The aim of the dissertation is the development of new measurement methods and their application in physics, chemistry and medicine.

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2.

 

N 002

 

Dr. Egidijus Auksorius 

 

Našios optinės koherentinės tomografijos vystymas ir taikymas akies tinklainės vaizdinimui

 

Development of light-efficient optical coherence tomography for the human retina imaging

Full-field optical coherence tomography (FF-OCT) is one of the fastest retinal imaging techniques. However, it relies on averaging multiple 3-D data sets for increasing signal-to-noise ratio (SNR), which might blur the images in in vivo imaging situations. The project idea concerns increasing SNR in FF-OCT systems by using novel interferometer designs that allows capturing more photons. Specifically, a High-Throughput interferometer configuration [7] and a Light-Efficient beamsplitter [5] will be implemented in the most advanced FD-FF-OCT system [1] that can increase SNR by up to 4 times. Both implementations rely on the pupil plane splitting and use of highly asymmetric beamsplitters. Such implementation will be most useful in human eye in vivo retinal imaging, where it is also crucial to record every single photon that is reflected from the retina since light can be phototoxic to the eye. Increase in the SNR will allow to visualize hard-to-image choroidal layers, such as choriocapillaris, with better contrast than otherwise possible. Alternatively, SNR increase could also be traded-off for imaging speed when speed is more important than attainable imaging depth. Such systems could increase diagnostic accuracy for various eye disease.

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3.

 

N 002

 

Dr. Steigvilė Byčenkienė 

 

Juodosios anglies ir smulkių aerozolio dalelių asmeninės ekspozicijos lygio tyrimai miesto aplinkoje

 

Assesment of personal exposure to black carbon and ultrafine particle levels in urban environment

SAir pollution is currently regarded as top environmental threat for our health and top priority at the EU policy agenda. Worldwide, more than 80% of people living in urban areas are still exposed to air quality levels exceeding WHO guideline values. Numerous epidemiological and toxicological studies worldwide have shown that aerosol particles in the air can have adverse effects on human health. Although most studies focus on the mass concentration of aerosol particles, it has been shown that number concentration and size distribution and chemical composition of the aerosol particles have a decisive effect.

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4.

 

N 002

 

Dr. Marius Franckevicius 

 

Elektroninių vyksmų dinamika perovskitiniuose optoelektronikos prietaisuose

 

Dynamics of electronic processes in perovskite optoelectronic devices

Description in English is not available.

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5.

 

N 002

 

Habil. Dr. Vidmantas Gulbinas 

 

Tarpusavyje susijusi elektronų ir jonų dinamika perovskitinėse medžiagose ir prietaisuose

 

Interrelated electron and ion dynamics in perovskite materials and devices

Description in English is not available.

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6.

 

N 002

 

Dr. Irmantas Kašalynas 

 

Dvimačių elektronų ir plazmonų sąveikų išoriniame elektriniame lauke poliarizacinė THz spektroskopija

 

Polarization THz spectroscopy of two-dimensional electron and plasmon interactions under external electric field

Description in English is not available.

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7.

 

N 002

 

Dr. Rokas Kondrotas 

 

Chalkogenidų sintezė, struktūrinių ir optinių savybių tyrimas

 

Synthesis, structural and optical characterization of chalcogenides

One of the main tasks of European Commission to achieve carbon neutrality in European Union by 2050, is the development of clean energy conversion technologies. Current renewable energy technologies including solar are not sustainable: fabrication processes are not environmentally friendly, employ toxic and/or expensive materials or has low efficiency. Therefore, new materials and technologies with better characteristics are constantly explored and studied to replace olds ones. Chalcogenides are inorganic chemical compounds, which have been used in various energy conversion technologies. Recently, some of chalcogenides have drawn a considerable attention in application for sustainable solar energy. Among them, antimony selenide, bismuth sulphide, barium zirconium sulphide are intensively studied as potential low-cost and non-toxic absorbers for solar cells. However, because these are emerging technologies little is known about their optical properties which are very important for maximizing chalcogenide based optoelectronic devices. In this dissertation work, selected chalcogenides will be synthesized and their optical and optoelectronic properties will be investigated.

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8.

 

N 002

 

Dr. Linas Minkevičius 

 

Terahercinė vaizdinimo sistema, pagrįsta spinduliuotės pluoštelio formavimo metodais

 

THz imaging systems based on advanced optical beam forming methods

Description in English is not available.

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9.

 

N 002

 

Dr. Ignas Nevinskas 

 

Terahercinė emisija iš paviršiniais plazmonais žadinamų puslaidininkių

 

Terahertz emission from semiconductors excited with surface plasmons

Surface plasmons have a unique property to compress light beyond the diffraction limit. The concentrated high-intensity light can be used to create a new generation of small, high-performance, low-noise optical and optoelectronic devices. The surface plasmon-enhanced solar cells, high numerical aperture flat (2D) lenses, detectors, and other devices are found in the literature. The proposed doctoral topic is dedicated to the development of a terahertz (THz) emission device. The latter device is a semiconductor crystal excited by femtosecond laser pulses. On top of this crystal a fabricated gold nanostructure interacting with a laser pulse would induce the surface plasmons. The plasmons would be absorbed by the semiconductor in a significantly smaller volume than that dictated by the absorption depth. The generated gradient of photoexcited charge carriers would induce ultrafast photocurrents, which in turn would emit a THz pulse.

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10.

 

N 002

 

Dr. Vaidas Pačebutas 

 

Nanometrinių bismuto sluoksnių (bismuteno) technologija ir tyrimai

 

Investigation and technology of nanometer bismuth (bismuthene) layers

Thin (<30 nm thick) layers of bismuth are interesting because they exhibit many unique physical phenomena. In volume Bi is a semimetal, thin becomes a semiconductor. When it thins to 55 nm, the rhombohedral crystal Bi becomes hexagonal bismuthene, which are a typical 2D crystal and even a topological insulator. Its new applications also range from IR photodetectors and thermoelectric to photochemical water decomposition and quantum computers.

The proposed topic is dedicated to the technology of ultra-thin Bi layers and the study of their properties. The layers would be grown by molecular beam epitaxy (MBE) and studied using various methods of structural analysis, optical and THz range spectroscopy. The search of new applications of those layers in infrared and THz range photodetectors and emitters are planned. After optimization the layer growth technology and studying the most important physical parameters, it is planned to focus on the research of bismuthene as a topological insulator. 

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11.

 

N 002

 

Dr. Vaidas Pačebutas 

 

Šviesos šaltinių optiniam ryšiui ir optiniams jutikliams su sudėtinėmis bismidų kvantinėmis duobėmis kūrimas

 

Development of light sources for optical communication and optical sensors with composite bismide quantum wells

Mid-infrared (MIR) wavelength range contains vibrational spectra of many important environmental and industrial gases, thus there is a large need of MIR semiconductor lasers and light emitting diodes. Semiconductor light sources operating in the 2 μm to 10 μm spectral range are being developed for a broad scope of applications in compact gas sensors for detection of environment pollutants and hazardous chemical substances as well as for industrial process monitoring. However, the development of MIR light sources still meets serious limitations. Recently, in search of new narrow-bandgap AIIIBV materials, the dilute bismides emerged in a focus of wide-scale investigations. Laser diodes based on GaAs1-xBix QWs with emission wavelengths in the 1.06–1.41 μm range were fabricated on GaAs substrates. The GaInAsBi QWs manifest a pronounced photo- and electroluminescence at sufficiently low QW widths. The luminescence of up to ≈ 2.5 μm wavelength was observed for ⩽10 nm GaInAsBi QWs with AlInAs barriers. Theoretically, the energy bandgap of the lattice-matched with InP substrate GaInAsBi compound could be as low as 0.21 eV, which corresponds to the emission wavelength of 6 μm. The proposed topic is dedicated to the technology of bismide sources and the study of their properties. The layers and structures would be grown by molecular beam epitaxy (MBE) and studied using various methods of structural analysis, optical and THz range spectroscopy. The methods for wavelength tuning including composite quantum wells but not limited will be used. After optimization the light sources growth technology and studying the most important physical parameters, it is planned to search of new applications of those sources.

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12.

 

N 002

 

Prof. dr. Artūras Plukis 

 

Elektronų greitinimas dielektrinėse struktūrose intensyvia optine spinduliuote

 

Acceleration of electrons in dielectric structures by intense optical radiation

The acceleration of charged particles in microstructures is usually attractive alternative to large conventional accelerators. Taking into account strong electric fields produced during intensive fs laser irradiation of materials, both nonrelativistic and relativistic electrons could be accelerated. The is planned to design accelerating stage from transparent dielectric material. Numerical modelling of electric and magnetic fields of laser beam will be used for particle trajectory optimization and energy gain evaluation. The structures will be manufactured by lithography, and experimentally applied for electron acceleration in the vacuum chamber. The analysis of energetic pmticle beam properties is planned with applications in areas of material modification and biomedicine.

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13.

 

N 002

 

Dr. Rita Plukienė 

 

Nuklidinio vektoriaus optimizacija in-situ nedestrukciniu gama spektrometriniu metodu

 

Nuclide vector optimization applying non-destructive in-situ gamma spectrometric method

One of important tasks for smooth and successful NPP decommissioning process is optimization of nuclear facility solid radioactive waste (SRW) management by applying grouping and separation of SRW. The materials used in the construction of the reactor become radioactive during neutron activation, and also can be contaminated with radioactive elements during radiation leakage during normal reactor operation or incident events. For the efficient management of radioactive waste, it is proposed to determine surface contamination and volume activation terms in SRW of nuclear power plants, and to optimize the current nuclide vector increasing accuracy of numerical model and analysis of conservative criteria. During doctoral studies it is planned: • To create numerical 3D model and complete modelling (SCALE 6.2 and MCNP6) of material activation in neutron flux. Analysis of nuclide activity taking into account neutron flux intensity and possible heterogeneous trace element distribution. Assessment of surface contamination term by modelling of SNF source term (using 3D SCALE6 model) and experimental measurement results. • To develop a non-destructive γ spectrometric method for estimation of surface contamination and volume activity of different geometry radioactive waste, which will serve for efficient characterization of SRW. Modelling, inter-comparison of γ-spectra and analysis of the nuclide’s peaks and Compton scattering edges in the metallic samples will provide information on easy to measure nuclides 60Co and 137Cs and will allow to assesses the scale of surface contamination. Surface contaminated waste can be decontaminated and optimally managed according to the national regulations. • To optimize the nuclide vector by sorting and combining radioactive waste with similar properties and decrease the conservative approach. To study the temporal evolution of nuclide vector taking into account decay of key nuclides, to propose the alternative nuclide vectors and novel techniques of activity determination in the sites of temporal storage and final disposal.

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14.

 

N 002

 

Dr. Gediminas Račiukaitis 

 

Elektringų dalelių greitinimas lazerinėje plazmoje silpnai difraguojančiais susieto erdvinio-laikinio skirstinio ultratrumpais lazerio impulsais

 

Laser wakefield acceleration of charged particles with spatially-temporal coupled quasi-non-diffracting ultra-short laser pulses

Description in English is not available.

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15.

 

N 002

 

Prof. Dr. Voitech Stankevič 

 

Elektromagnetinių procesų tyrimas metalų formavimo bei suvirinimo magnetiniais impulsais

 

Investigation of electromagnetic processes during magnetic pulse forming and welding

Description in English is not available.

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16.

 

N 002

 

Dr. Rima Stonkutė 

 

Trikampio galaktikos žvaigždžių spiečių sistemos struktūra

 

Structure of star cluster system of the Triangulum galaxy

Description in English is not available.

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17.

 

N 002

 

Dr. Saulius Tumėnas 

 

Optinė bismidų anizotropija, sąlygota CuPt-tipo atominio susitvarkymo

 

Optical anisotropy of CuPt-ordered bismides

Description in English is not available.

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18.

 

N 002

 

Prof. dr. Vladas Vansevičius 

 

Žvaigždžių spiečiai dangaus apžvalgose

 

Star clusters in sky surveys

Description in English is not available.

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19.

 

N 002

 

Prof. dr. Nerija Žurauskienė 

 

Feromagnetiniai nanodariniai biojutiklių taikymams

 

Ferromagnetic nanostructures for biosensing applications

The growing interest in magnetic field sensors based on so-called magnetoresistive xMR (anisotropic AMR, giant GMR tunnelling TMR and colossal CMR) effects suggests a possibility to employ these effects in ferromagnetic nanostructures of novel materials for various applications. It has to be pointed out that magnetic sensors are becoming one of the mostly important components for the growing automotive and Internet of Things (IoT) industries as well as for specific application areas of biosensing. Each application has specific requirements for the sensor fabrication technology, device specifications, magnetic field and temperature ranges of operation, and sensor’s accuracy. In this study the ferromagnetic nanostructures exhibiting GMR and TMR effects will be grown and investigated for biosensing applications using ferromagnetic nanoparticles.

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20.

 

N 002

 

Dr. Agnė Mašalaitė-Nalivaikė 

 

Aerozolio dalelių izotopiniai santykiai oro taršos stebėjimui ir jų, kaip šaltinių rodiklių, įvertinimas

 

Isotopic ratios of aerosols for air pollution observation and its assessment as source indicators

Atmospheric aerosol particles play an important role in many environmental processes, influencing climate change processes and human health. However, the real impact of atmospheric aerosols on climate change and health is called into question by a lack of knowledge about their sources, composition, properties, and mechanisms of formation. Therefore, it is important to develop new research and methods as well as tools that would serve to confirm or refute scientific hypotheses about the nature of atmospheric phenomena and to create models that describe the processes taking place in the atmosphere, assessing global and local changes in the environment around us.

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