Photo:
Marta Berholts

Physicumi seminar

Physicumi seminar: Rydbergi lainepaketil põhinev kvantkell

Neljapäeval, 24. novembril 2022 kell 16:15 

Physicum B103 ja Zoom (Meeting ID: 991 9634 2908; Passcode: 926502)

Marta Berholts (TÜ)

In this talk, I will present the concept of the quantum watch that was developed during my postdoctoral project at Uppsala University in the HELIOS laser laboratory. The watch consists of a helium atom that is excited into a wave packet of Rydberg states using an ultrashort laser pulse with a wide energy bandwidth. Rydberg states are excited states in atoms that exhibit long lifetimes and have orbitals that extend micrometers away from the atomic core. By coherently exciting more than one Rydberg state, it is possible to perform quantum beat spectroscopy where the energy difference between the states results in constructive and destructive interference of the photoelectron yield. We found a remarkably rich beat structure in the time-resolved photoelectron yield when exciting multiple Rydberg states located close to He ionisation potential. Furthermore, we found an almost perfect agreement between simulations and the complex, almost chaotic, experimental signal. With this quantum watch, we show how to measure time in a different way, not by counting the clock's ticks as it is usually done, but by obtaining time fingerprints and therefore knowing the time very accurately on the femtosecond timescale without using a counter. The quantum watch has the potential to become a valuable tool in time-resolved spectroscopy. The study is recently published in Physical Review Research journal https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.4….

 

Image

Joonis. Simulated photoelectron yield as a function of the delay between two laser pulses. Top: wave packet consists from two Rydberg states. No time fingerprint could be obtained. Bottom: wave packet consists from 40 Rydberg states. Time fingerprint is created.

Physicumi seminarid on mõeldud füüsikute ja materjaliteadlaste, aga ka teiste loodus- ja täppisteadlaste laiale ringile (alates bakalaureuse astme üliõpilastest) ning püüavad avada seda, mis mingis valdkonnas on parasjagu oluline ja uudne või kuhu teatud uurimissuund on tänaseks välja jõudnud.

Seminar toimub inglise keeles. Kõik huvilised on teretulnud.

Neljapäeval, 10. novembril 2022 kell 16:15 

Zoom'is

Seminar on järelvaadatav [video]

Prof Saulius Juodkazis (Swinburne tehnikaülikool, Austraalia)

High average power 10W and high repetition rate ~1 MHz of ultra-short sub-1 ps lasers have become a widely available, affordable and reliable tool for material processing. We showed that average power of ultra-short lasers is increasing exponentially and follows the Moore’s law from 2000 [1]. Review of current developments in industrial applications of ultra-short lasers will be presented with focus on laser ablation, patterning, nanoscale alloying, and nano-texturing over large areas with cross sections in tens-of-centimeters.

Current strength of fs-laser processing is in the fields of micro- machining: cutting, drilling, inscribing refractive index patterns and waveguides.  Complexity of approaches where fs-laser microfabrication is combined with other material processing steps including plasma etching and sputtering, thermal post-processing further strengthens versatility of fs-laser micro-fabrication. Radiation of X-rays and THz from the light-matter interaction region during laser processing can be used for characterisation of interactions as well as utilised as a radiation source. We review recent results.

[1] M. Han, D. Smith, S.H. Ng, V. Anand, T. Katkus, S. Juodkazis, Ultra-Short-Pulse Lasers—Materials—Applications, 2021, Eng. Proc., 11, 44.

Saulius Juodkazis is Professor of nanophotonics and Director of the nanotechnology facility at Swinburne’s Centre for Micro-Photonics. His current research is focused on applying principles of light-field enhancement and its spectral control for applications in micro-optics, sensing, solid-state lighting, and solar energy conversion.

Seminar toimus inglise keeles.

Neljapäeval, 3. novembril 2022 kell 16:15

Physicum B103 ja Zoom

Seminar on järelvaadatav [video]

Dr. Sergei Vlassov ja Elyad Damerchi esitlevad seminaril hiljuti hangitud seadet, mis võimaldab skaneerivas elektronmikroskoobis asuvaid väikseid objekte kuumutada reaalajaliste mõõtmiste käigus kuni 800 kraadini. Ettekandes tutvustatakse seadme peamisi omadusi ja piiranguid ja näidatakse esimesi katsetulemusi soojendamise mõjust hõbe ja kulla nanoosakeste morfoloogiale.

Seminar toimus inglise keeles.

Neljapäeval, 20. oktoobril 2022 kell 16:15

Physicum B103 ja Zoom 

Seminar on järelvaadatav [video]

Tänavuse Nobeli füüsikapreemia pälvisid Alain Aspect, John Clauser ja Anton Zeilinger kvantpõimitud osakestega läbi viidud katsete eest. Need katsed on kvantinformatsiooni edastamise ja töötlemise tehnoloogia arengu alguspunkt.

Seminari kavas on lühikesed ettekanded TÜ füüsika instituudi ja IQM Finland OY teadlastelt:

  • Laur Järv (UT): EPR paradoksist Belli teoreemini
  • Peeter Saari (UT): Nobeli preemia toonud eksperimendid
  • Johannes Heinsoo (IQM Finland OY): põimitus rangemates testides ja kvantinfotehnoloogias

Seminar toimus eesti keeles.

Neljapäeval, 13. oktoobril 2022 kell 16:15

Physicum A106 

Artur Tamm (TÜ arvutusliku füüsika kaasprofessor)

Järelvaadatav [video]

Kõrge entroopiaga sulamid on materjalide klass, mis koosnevad mitmest põhikomponendist võrdsetes kogustes. Elementide arvukus suurendab entroopia panust vabaenergiasse ning selle läbi stabiliseerib korrastuseta oleku. Suur varieeruvus materjalis on kasulik rakendustes, kus materjal peab vastu pidama keerulistes tingimustes, nagu näiteks intensiivne kiirgus või korrosioon. Kõrge entroopiaga sulamite omadusi on võimalik kujundada elementide koostise muutmisega. 

Cantori sulam koosneb viiest metallilisest elemendist (NiCrCoFeMn) ning seda kasutatakse tüüpmaterjalina kõrge entroopiaga sulamite omaduste uurimisel. Enamlevinud eelduseks on elementide juhuslik paigutus materjalis. Hiljutusid arvutuslikud ning eksperimentaalsed uurimistööd on näidanud, et "keskmise" entroopiaga sulamites esineb lähikorrastus.

Meie arvutuslik uuring keskendub lähikorrastuse uurimisele Cantori sulamis. Lisaks analüüsime kuidas lähikorrastuse olemasolu mõjutab defektide energiaid sulamis ning vesiniku sidumisvõimet.

Seminar toimus inglise keeles.

Neljapäeval, 06. oktoobril 2022 kell 16:15

Teams: Click here to join the meeting

Martin Sláma (Product marketing manager)

TESCAN FIB/SEM system and TEM lamella preparation

Mr. Martin Sláma, Product marketing manager for FIB SEM, TESCAN will give and overview presentation about Tescan Amber FIB-SEM system and its applications.

More info about Amber FIB-SEM can ve found from the brochure: https://tescan.canto.global/b/ICHNV

Seminar toimus inglise keeles, esinejad osalesid üle Teamsi.

Neljapäeval, 22. septembril 2022 kell 16:15

Physicum A106

Akad prof Markku Kulmala (Helsingi Ülikool)

Meie ainsa planeedi hüvanguks

Seminar on järelvaadatav [video].

Understanding the details responsible for the changing climate are under constant research and new atmospheric physical and chemical mechanisms are discovered constantly. Academician professor Markku Kulmala will give an overview of the recent research highlights done in the Institute for Atmospheric and Earth System Research at University of Helsinki.

Seminar toimus inglise keeles.

Neljapäeval, 15. septembril 2022 kell 16:15

Physicum A106 ja veebis Teams

Daniel Phifer (Thermo Fisher Scientific.)

Ülevaade Helios 5 DualBeam Technology arengutest

The move to Helios 5 series DualBeam platform has introduced several features for ease of use, updates to automation and new configuration options. Chief among these are the alignment automation for the SEM (no user alignments), “Flash” one button focus-stig.-lens align, and automated on-demand FIB alignments. Additionally, AutoTEM 5 and AutoSlice and View 5 were released to increase robustness and flexibility. New options such as CleanConnect (inert transfer), rotatable cryo stage and a cryo-EasyLift manipulator also expand options.

Base models for Helios 5 include Ga+ and Xe+ or Xe/O/N/Ar FIB sources. On top of this models can be extended with fs laser for cutting deep or wide trenches. This presentation will introduce much of this technology to help you think about what could be useful for your future research needs.

Seminar toimus inglise keeles.

Neljapäeval, 8. septembril 2022 kell 16:15

Physicum A106 ja veebis Zoom 

Sven Oras (TTÜ) ja Tauno Tiirats ()

Kokkuvõte FCC nädalast

Järelvaadatav [video]

19. aprillil 2022 allkirjastas Tartu ülikool CERNiga vastastikuse mõistmuse memorandumi tuleviku ringkiirendi (FCC) ehitamiseks. FCC seisust ja võimalikest koostööpunktidest antakse ülevaade igal aastal toimuval konverentsil FCC week. Sven Oras ja Tauno Tiirats võtsid konverentsist osa ja tutvustavad erinevaid valdkondi, millega FFC arendamise puhul tegeletakse ja otsitakse kollaboratsiooni.

Seminar toimus eesti keeles, ettekannete slaidid olid koostatud ja küsimusi võis esitada ka inglise keeles.

Teisipäeval, 6. septembril 2022, kell 16:15

Physicum A106

Teoreetilise füüsika seminar/ Physicumi seminar: Raamatuesitlus

Saateks kaks ettekannet:

  • Manuel Hohmann (Tartu Ülikooli füüsika instituut), „Vaatlustest Einsteini teooriateni ja sealt edasi“
  • Laurits Leedjärv (Tartu Ülikooli Tartu observatoorium), „Müstiline geenius Arthur Eddington“

Ülekanne ka BigBlueButtoni kanalil: https://button.ut.ee/b/mar-8sl-8g6-mw7.

Pärast ettekandeid on avatud väike kohvilaud ruumis A101. Kohapeal on võimalik osta raamatuid kirjastuse hinnaga.

Üritus Facebookis.

Neljapäeval, 16. juunil 2022 kell 16:15

Physicum A106 ja veebis Zoom

Vijayakumar Anand (TÜ arvutusliku kuva kaasprofessor)

FINCHing objects with a super-resolution – Fundamentals to Applications

Fresnel Incoherent Correlation Holography (FINCH) invented by Joseph Rosen and Gary Brooker is a milestone in the history of holography. FINCH has the ability to break the Lagrange invariant conditions and exhibit a super resolution which makes it an attractive imaging tool for various applications. The versatility of FINCH enabled it as a resolution booster suitable for integration with other super resolution imaging techniques such as structured illumination. In this talk, the basic differences between coherent and incoherent imaging systems and the concept of FINCH will be introduced. Some interesting hybridization approaches with coded aperture correlation holography and structured illumination will be presented. The talk will conclude with the description of the current state of the art FINCH technology.

Seminar toimus inglise keeles.

Neljapäeval, 7. aprillil 2022 kell 16:15

Physicum A106 ja veebis Zoom 

Järelvaadatav [Video]

Seekordse Ukraina teadusteemalise seminari eesmärk on osutada tähelepanu ja rõhutada ukrainlaste panusele füüsika ajaloos ning tänapäevases füüsikas ja näidata sõja hävitavat mõju Ukraina teadusele. Seminaril esitatakse lühike ülevaade mitmetest tuntutest Ukrainaga seotud füüsikutest ja Tartu Ülikoolis tegutsevate füüsikute ning inseneride teadustööst:

  • Manuel Hohmann (TÜ füüsika instituut) - Harkivi ajalooline roll teoreetilises füüsikas ja kosmoseteaduses
  • Vitalii Checha (TÜ Tartu observatoorium) – Tähtede pulsatsioon
  • Iaroslav Iakubivskyi (TÜ Tartu observatoorium) – Sergei Korolev ja Ukraina raketiteadus
  • Indrek Jõgi (TÜ füüsika instituut) - Julius Edgar Lilienfeld ja tema panus elektroonikasse
  • Maksym Golub (TÜ füüsika instituut)– Lähenemisviisid lahuses olevate valkude SANS/SAXS-andmete modelleerimiseks
  • Volodymyr Gulik ja Oleksandr Trofymenko (TÜ füüsika instituut ja Tuumajaamade ohutusprobleemide instituut, Kyiv, Ukraine) – Tuumajaamade ohutusalased uuringud
  • Leonid Dolgov (TÜ füüsika instituut) – Raman spektroskoopia ja madalatemperatuurse luminestsents spektroskoopia koostöökogemus TÜ füüsika instituudi ja Ukraina teaduste akadeemiaga.

Seminar toimus inglise keeles.

Neljapäeval, 17. veebruaril 2022 kell 16:15
Veebis Zoom keskkonnas

Järelvaadatav Video

9. veebruaril 2022 avaldas EUROfusion konsortsium viimaste kümnendite olulisima tuumasünteesi alase uudise - Ühendkuningriigis Oxfordis asuvas maailma suurimas tuumasünteesi rajatises Joint European Torus (JET) saavutati ajalooline tuumasünteesi energiarekord. Protsessi käigus vabanes 5 sekundi jooksul 59 MJ energiat, mis ületab peaaegu kolmekordselt 1997. aastast püsinud varasemat energiarekordit. Rekordtulemus saavutati EUROfusion konsortsiumi poolt läbi viidud katseseerias, mille eesmärgiks oli testida kahe aastakümne jooksul kogunenud teadmisi tuumasünteesi vallas ja valmistuda parimal viisil rahvusvahelise ITERi projekti alguseks. Mõne aasta pärast Prantsusmaal valmiv ITER on JETi mantlipärija, mis peab näitama tuumasünteesil põhineva energia teaduslikku ja tehnoloogilist teostatavust.

Physicumi seminaril antakse lühike ülevaade JET rekordtulemustest, sellele eelnenud ajaloost ja järgnevatest plaanidest. Seejärel tutvustavad füüsika instituudi teadlased meie tegevusi tuumasünteesi uuringuid koordineerivas EUROfusion konsortsiumis.

  • Indrek Jõgi (TÜFI plasmatehnoloogia kaasprofessor) JET DTE2 katseseeriast ja selle olulisusest
  • Aleksandr Luštšik (TÜFI tahkisefüüsika professor) laia keelutsooniga materjalid tuumasünteesi reaktorite diagnostikaks vajalike akende jaoks,
  • Volodymyr Gulik (TÜFI materjaliteaduse teadur) kiirguskindlate betoonseinte disainimine tuumasünteesi elektrijaamadele.
  • Indrek Jõgi (TÜFI plasmatehnoloogia kaasprofessor) laser-indutseeritud plasma spektroskoopia (LIBS) reaktoriseinte diagnostikaks

Seminar toimus inglise keeles.

Teisipäeval, 04. jaanuaril 2022 kell 16:15
Veebis Zoom keskkonnas

Artur Tamm (TÜ arvutusliku füüsika kaasprofessor)

Mittetasakaalulised protsessid klassikalises molekulaardünaamikas

Ettekandes tutvustan värskeid arenguid mittetasakaaluliste protsesside simuleerimisel klassikalises molekulaardünaamikas, mis hõlmab elektronide ja ioonide vastastikmõju. Kõigepealt näitan, kuidas meie poolt loodud uudset mudelit saab kasutada laserite poolt ergastatud metalliliste süsteemide arengu uurimiseks. Seejärel tutvustan pooljuhtide ja väga erinevate süsteemide käsitsemise uusi arenguid.

Seminar toimus inglise keeles.

Zoomi link.

2021

Neljapäeval, 28. oktoobril 2021 kell 16:15
Physicum A106 ja veebis
 Zoom

Kalev Tarkpea

Alates aastast 2016 toimib varasema füüsika või materjaliteaduse bakalaureuseõppe asemel füüsika, keemia ja materjaliteaduse (FKM) õppekava, milles üliõpilast asutakse lõputöö kirjutamiseks ette valmistama juba 2. õppeaastal. See algab aines LTFY.01.012 Loodusteadusliku meetodi seminar (LTMS) ning jätkub 3. aasta aines LTFY.01.013 Lõputöö seminar. Tudengite-poolne juhendaja valimine toimub enam mitte 3. aasta sügisel vaid enamasti oluliselt varem. Ettekandes tuleb juttu asjaoludest, mida peaksid arvestama need akadeemilised töötajad, kes sooviksid olla FKM üliõpilastele lõputöö juhendajateks. Millised strateegiad pakutava teema atraktiivsuse suurendamisel on seni osutunud edukateks ja millised vähem edukateks? Ühtlasi saab tehtud mõningane kokkuvõte LTMS ja Lõputöö seminari õppejõudude senisest kogemusest nende ainete läbiviimisel.

Seekordne Physicumi seminar on mõeldud ennekõike Physicumi töötajatele.

Kolmapäeval, 20. oktoobril 2021 kell 16:15
Physicum A106 ja veebis Zoom

Järelvaadatav video

Tänavuse Nobeli füüsikapreemia pälvisid Syukuro Manabe, Klaus Hasselmann, kes modelleerisid Maa kliimat ja ennustasid usaldusväärselt globaalset soojenemist ning Giorgio Parisi, kes avastas peidetud mustreid isegi näiliselt korrapäratutes materjalides. Seminari kavas on lühikesed ettekanded TÜ füüsika instituudi teadlastelt:

  • Piia Post: Nobeli preemia atmosfäärifüüsikutele
  • Miks anti füüsikapreemia kliimateadlastele? Syukuro Manabe ja Klaus Hasselmann kujundasid füüsikalise arusaama Maa kliimast.
  • Velle Toll: Kliimamudeli sünnist ja ennustusvõimest
  • Milles seisneb Syukuro Manabe eelmise sajandi kuuekümnendatel loodud kliimamudeli geniaalne lihtsus? Klaus Hasselmann selgitas kliima ennustatavuse piire: kuivõrd on kliima prognoositav?
  • Jaak Kikas: Spinnklaasid ja palju muud
  • Giorgio Parisi leidis efektiivsed matemaatilised meetodid spinnklaaside (interakteeruvate magnetmomentide kollektiivid tahkistes) termodünaamika kirjeldamiseks, mis hiljem on osutunud tulusaks väga erinevate komplekssüsteemide korral.
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Pildil: Nobeli füüsikapreemia laureaadid 2021 Syukuro Manabe, Klaus Hasselmann ja Giorgio Parisi (autor Niklas Elmehed © Nobel Media)

NB! Kohalviibijatele kehtivad Tartu Ülikooli suunised viiruse leviku tõkestamiseks, st nõue esitada COVID-tõendit vaktsineerituse, läbipõdemise või varasemalt tehtud negatiivse testi tulemuste kohta.

Ülekanne veebis Zoom keskkonnas.

Teisipäeval, 31. augustil kell 16:15 TÜ Physicumi suures auditooriumis A106 (W. Ostwaldi 1, Tartu)

Raamatuesitlus

Saateks kaks ettekannet

  • Piret Kuusk (TÜFI) "Albert Einstein ja tema üldrelatiivususteooria"
  • Laur Järv (TÜFI) "Sümmeetria kui 20. saj. fundamentaalfüüsika võti"

Peale ettekandeid on avatud väike kohvilaud ruumis A101. Kohapeal on võimalik osta raamatuid kirjastuse hinnaga.

Üritusest on ülekanne ka BigBlueButtoni kanalil
https://button.ut.ee/b/mar-8sl-8g6-mw7

NB! Kohalviibijatele kehtivad Tartu Ülikooli suunised viiruse leviku tõkestamiseks, st nõue kanda maski või olla valmis näitama koroonapassi.

Esmaspäeval, 10. mail 2021 kell 16:15
Zoom ja järelvaadatav video

Adam S. Backer (Apple Inc., USA)

Pushing the Limits of Single Molecule Microscopy

In recent years, the fluorescence microscope has transformed the field of biological imaging. Using single-molecule methods and machine-learning-assisted reconstruction algorithms, it is now possible to resolve structures an order of magnitude smaller than the wavelength of light, thus achieving super-resolution. My research seeks to enhance the computational and optical tools that underpin super-resolution microscopy. By constructing non-traditional microscopes that record additional physical parameters on a molecule-by-molecule basis, we stand to gain unique insights into a variety of biological and materials systems. In my talk today, I will first present one of my Ph.D. projects developing three-dimensional super-resolution methods and describe how this work will benefit from emerging nanophotonic technologies such as optical metasurfaces. Next, I will present a recent project using fluorescence polarization and optical tweezers to reveal hidden structural features of the DNA molecule. Finally, I will discuss how this methodological toolkit could be further expanded to realize adaptive, task-aware imaging systems.

Bio
Adam’s work aims to create nanophotonic devices, optical techniques, and computational algorithms to investigate biological systems at the nanoscale. He has pursued an eclectic mix of research topics and enjoyed collaborations with industrial and academic labs around the world. Adam is currently an optical engineer at Apple, and recently completed a Harry S. Truman Fellowship at Sandia National Labs. Adam received his Ph.D. in Computational Mathematical Engineering from Stanford in 2016, where he performed his doctoral research in the lab of W. E. Moerner. He also holds an M.Phil. in Engineering from Cambridge University, and a B.S. in Engineering and Physics from Brown University.

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Neljapäeval, 21. jaanuaril 2021 kell 16:15
Zoom ja video

19. juunil peaminister allkirjastas ning 25. novembril 2020 riigikogu ratifitseeris Eesti Euroopa Tuumauuringute Keskuse CERN assotsieerunud liikmeks saamise kokkuleppe, millele mõne aasta pärast peaks järgnema täisliikme staatus. CERNi asutasid 1954. a 12 Euroopa riiki, hetkel on täisliikmeid 23 ning veel kaks riiki ootavad  assotsieerunud liikmetena täisliikmeks saamist. Alates 1996. aastast on Eesti CERNi eksperimentaalsetes ja teoreetilistes osakestefüüsika uuringutes osalenud koostöölepingu alusel.

Seminari esimene pool tutvustab põgusalt Tartu Ülikooli teadlaste CERNiga seotud tegevust:

  • Marco Kirm (TÜFI eksperimentaalfüüsika professor) Stsintillaator-detektorite arendus Crystal Clear Collaboration raames,
  • Vahur Zadin (TÜTI materjalitehnoloogia professor) Vaakumläbilöökide modelleerimine kompaktse lineaarkiirendi CLIC ehituse jaoks,
  • Stefan Groote (TÜFI teoreetilise füüsika kaasprofessor) Raskete hadronite teke sisemise šarmkvargi mehanismi kaudu COMPASSi eksperimendis.
  • Heikki Junninen (TÜFI keskkonnafüüsika professor) CLOUD eksperiment - Cosmics Leaving Outdoor Droplets.

Seminari teises pooles on juttu CERN liikmelisusega avanevatest uutest võimalustest Eesti teadlastele, õppuritele ja ettevõtetele:

  • Triin Kangro (EAS CERNi projektijuht) Eesti võimalused CERNi liikmena

Seminar toimus eesti keeles, ettekannete slaidid olid koostatud ja küsimusi võis esitada ka inglise keeles.

 Üritus Facebookis.

Zoomi link.

2020

Neljapäeval, 15. oktoobril 2020 kell 16:15
Physicum A106 ja online BBB

Tänavuse Nobeli füüsikapreemia pälvisid Roger Penrose, kes näitas, et mustade aukude teke on üldrelatiivsusteooria vahetu järeldus, ning Reinhard Genzel ja Andrea Ghez, kes avastasid, et meie galaktika keskmes on nähtamatu ja äärmiselt raske kompaktne objekt, mis mõjutab sealsete tähtede orbiite ja mille hetkel ainuke tõsiseltvõetav seletus on ülimassiivne must auk. Seminari kavas on lühikesed ettekanded TÜ füüsika instituudi ja Tartu observatooriumi teadlastelt:

  • Piret Kuusk (TÜFI) Mille eest tänavune Nobel?
  • Manuel Hohmann (TÜFI) Roger Penrose panus mustade aukude teooriasse
  • Rain Kipper (TÜTO) Ülimassiivne must auk meie galaktika südames
  • Laur Järv (TÜFI) Roger Penrose originaalsed ideed universumi, kvantfüüsika ning teadvuse kohta
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Pildil: Nobeli füüsikapreemia laureaadid 2020 Roger Penrose, Reinhard Genzel ja Andrea Ghez (autor Niklas Elmehed © Nobel Media)

Ülekanne internetis BigBlueButton keskkonnas.

Facebooki üritus.

Esmaspäeval, 2. märtsil 2020 kell 16:15 TÜ Physicumi auditooriumis B103 (W. Ostwaldi 1, Tartu)

Kristjan Kunnus (TÜFI ajalise lahutusega röntgenspektroskoopia spetsialist, Stanfordi ülikooli PULSE instituudi järeldoktor)

Femtosecond Time-Resolved X-ray Spectroscopy and Scattering with X-ray Free Electron Lasers

X-ray Free Electron Laser (XFEL) light sources deliver high brightness and femtosecond duration X-ray pulses that have revolutionized the field of ultrafast science in the past ten years. In this talk I will discuss the current capabilities of pump-probe X-ray Emission Spectroscopy (XES) and X-ray Solution Scattering (XSS) at XFELs. Specifically, I will present results from a series of experiments where we investigated photoinduced excited state electron transfer and intersystem crossing dynamics in solvated Fe photosensitizer model complexes. These experiments track simultaneously electronic state and nuclear structure of the molecules, and allowed us to observe branching of electronic relaxation pathways and coherent nuclear wavepacket dynamics. In addition, I will discuss vibronic effects that emerge in time-resolved XES experiments and are necessary to interpret the ultrafast time-dependent signals.

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Illustratsioon: Greg Stewart/SLAC National Accelerator Laboratory

Kristjan Kunnus received his B.Sc. and M.Sc. degree in Materials Science from University of Tartu, Estonia. In 2014, he received his Dr. rer. nat. degree in experimental physics from University of Potsdam in Germany for his work on soft X-ray spectroscopy of transition metal complexes in solution. His current research as a post-doctoral researcher in Stanford University and SLAC National Laboratory focuses on time-resolved X-ray experiments of photoinduced excited states dynamics in metal complexes.

Neljapäeval, 27. veebruaril 2020 kell 16:15 Physicumi auditooriumis B103 (W. Ostwaldi 1, Tartu)

Järelvaadatav video

Laur Järv, Manuel Hohmann, Margus Saal (TÜFI teoreetilise füüsika vanemteadurid)

Laiendatud geomeetrilised gravitatsioniteooriad

Ehkki avastatud esimesena on gravitatsioon jäänud neljast fundamentaaljõust kõige suuremaks mõistatuseks. Tema seos kvantteooriaga ning täppisvaatlused kosmoses on püstitanud seni lahendamata küsimusi, mis kuuluvad tänapäeva füüsika suurimate probleemide hulka. Esimesed sammud mõistatuse lahendamisel astus Newton formuleerides oma universaalse gravitatsiooniseaduse (1687), mille järgi gravitatsioon mõjub kehade vahel sõltuvalt vaid nende massist. Seda seadust üldistas geniaalselt Einstein, kes võttis kasutusele diferentsiaalgeomeetria matemaatika. Tema loodud üldrelatiivsusteoorias (1915) ilmub gravitatsioon kui aegruumi kõverus -- kuid täpsemalt tuleb öelda: kui meetrilise aegruumi Levi-Civita seostuse kõverus. Viimane osutab, et kõverus pole tegelikult aegruumi, vaid selle matemaatilise, ehk geomeetrilise kirjelduse omadus. Oma hilisemates töödes (1928) leidis Einstein kõverusele alternatiivi aegruumi geomeetria ja seega ka gravitatsiooni kirjeldamiseks kõveruseta Weitzenböcki seostuse iseloomuliku omaduse väände näol, mis on teleparalleelsete teooriate aluseks. Kolmas geomeetriliste omaduste pere liige -- mittemeetrilisus -- hakkas tähelepanu pälvima alles eelmise sajandi teisel poolel ja pakub samuti võimalust esitada üldrelatiivsusteooriale alternatiivne geomeetriline alus (1999). Kuigi üldrelatiivsusteooria tasemel on nimetatud geomeetriad füüsikaliste ennustuste poolest ekvivalentsed, ei kehti see olukord siis, kui teooriat laiendada, näiteks lisada tumeenergiat seletava täiendava välja. Seega pakuvad erinevad geomeetrilised kirjeldused erinevaid võimalusi läheneda gravitatsiooniteooriate lahendamata küsimustele. Ettekanne tutvustab nii probleemi kui võimalikke lahendusi -- geomeetriast gravitatsioonini.

Tartu Ülikooli füüsika instituudi teoreetilise füüsika vanemteadurid Laur Järv, Manuel Hohmann ja Margus Saal pälvisid oma töödega 2020. a riigi teaduse aastapreemia täppisteaduste valdkonnas.


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Neljapäeval, 20. veebruaril 2020 kell 16:15 Physicumi auditooriumis B103 (W. Ostwaldi 1, Tartu)

Mikhail G. Brik (TÜFI materjalide kompuutermodelleerimise professor)

Red for LED

White light emitting diodes (LEDs) are widely used for both indoor and outdoor lighting applications. One of the main aims of research in this area is to produce white LEDs that mimic sunlight as closely as possible. Mixing emission of different colors is the way to get white light, but the main characteristics of the resultant emission depend crucially on properties of each component. For many years, white LEDs were composed of a blue GaN LED chip with yellow phosphor Y3Al5O12:Ce3+, that partially converts blue light into yellow. However, due to the lack of red light in this device, the produced white light is perceived to be a “cold” white light. Addition of a red phosphor to such LED can improve the emitted white light characteristics enormously.

In this presentation several basic approaches to get white light will be discussed, with highlighting their pros and cons. The role of different red phosphors in the white phosphor-converted LEDs for the lighting and agricultural applications will be shown, with several examples based on the original publications, e.g. [1-6].

The final part of the talk will be devoted to a short review of the book on spectroscopy of the transition metal and rare earth ions published recently [7].

Mikhail G. Brik received his PhD from Kuban State University (Russia) in 1995 and his DSc (habilitation) from the Institute of Physics, Polish Academy of Sciences (Poland) in 2012. Since 2007 he is a professor at the Institute of Physics, University of Tartu, Estonia. Before that, he worked at Kyoto University (Japan) from 2003 to 2007, Weizmann Institute of Science (Israel) in 2002, Asmara University (Eritrea) from 2000 to 2001, and Kuban State University from 1995 to 2000. He is also a distinguished visiting professor at Chongqing University of Posts and Telecommunications (China) and Professor at Jan Długosz University (Poland). Since 2015 he serves as one of the editors of Optical Materials (Elsevier). Prof. Brik’s scientific interests cover theoretical spectroscopy of transition metal and rare earth ions in optical materials, crystal field theory, and ab initio calculations of the physical properties of pure and doped functional compounds. He is a coeditor of two books and author of 12 book chapters and about 390 papers in international journals. According to Google Scholar (November 2019), he has more than 7500 citations with h index 41. He received the Dragomir Hurmuzescu Award of Romanian Academy in 2006 and the State Prize of the Republic of Estonia in the field of exact sciences in 2013. In 2018 he received the state professor title from the President of Poland.

References:

[1] M.G. Brik, A.M. Srivastava, J. Lumin. 133 (2013) 69.
[2] M.G. Brik, S.J. Camardello, A.M. Srivastava, ECS J. Solid State Sci. & Technol. 4 (2015) R39.
[3] M.G. Brik, S.J. Camardello, A.M. Srivastava, N.M. Avram, A. Suchocki, ECS J. Solid State Sci. & Technol. 5 (2016) R3067.
[4] Q. Zhou, L. Dolgov, A.M. Srivastava, L. Zhou, Z.L. Wang, J.X. Shi, M.D. Dramićanin, M.G. Brik, M.M. Wu, J. Mater. Chem. C 6 (2018) 2652.
[5] A.M. Srivastava, M.G. Brik, H.A. Comanzo, W.W. Beers, W.E. Cohen, T. Pocock, ECS J. Solid State Sci. & Technol. 7 (2018) R3158.
[6] M.G. Brik, W.W. Beers, W. Cohen, S.A. Payne, N.J. Cherepy, M. Piasecki, A.M. Srivastava, Opt. Mater. 91 (2019) 338.
[7] M.G. Brik, C.-G. Ma, “Theoretical Spectroscopy of Transition Metal and Rare Earth Ions: From Free State to Crystal Field”, Jenny Stanford Publishing Pte. Ltd, Singapore, 2020, ISBN 978-981-4800-56-3, 460 p.

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Esmaspäeval, 17. veebruaril 2020 kell 16:15 Physicumi auditooriumis B103

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Hasan Yılmaz (Yale University, Department of Applied Physics)

Coherent control of light transport and imaging through scattering opaque media

Materials such as white paint, fog, paper or biological tissue have spatial inhomogeneities in the refractive index which cause multiple scattering of light. In such opaque materials, most of the light reflects in the backward direction, hindering the transport of optical energy and spatial information. The transmittance can be enhanced by utilizing the interference of scattered coherent waves-a striking phenomenon first theoretically predicted in the context of mesoscopic electron transport through conducting wires [1-4]. In recent years, spatial light modulators (SLMs) have been used to control the transmittance of light by finding transmission eigenchannels of the scattering system [5,6]. By coupling light into transmission eigenchannels, transmittance through the medium can be controlled between 0 (closed channels) and 1 (open channels). Furthermore, not only the transmittance but also the imaging resolution can be enhanced through opaque scattering media by exploiting angular correlations “angular memory effect” [7].

First, the recent discovery on transmission eigenchannels through a layer of white paint is presented. It was discovered that transmission eigenchannels are exponentially localized in the transverse directions, even in the diffusive regime far from Anderson localization [8]. The results show that open channels not only enhance total transmitted power, but also energy density inside and on the back surface of a scattering opaque medium, which is important for applications such as optogenetics and multiphoton imaging that aim for enhancement of light-matter interactions in complex optical systems. It is further demonstrated that selective coupling of light into a single transmission eigenchannel modifies the angular memory effect correlation range [9]. Open channels have a wider memory effect range than a plane wave or a Gaussian beam, thus will provide a wider field of view for memory-effect-based imaging through opaque media.

Next, the speckle correlation resolution enhancement (SCORE) imaging that simultaneously produces wide-field and high-resolution fluorescence images is introduced [7]. SCORE is a scanning optical microscopy method that benefits from the angular memory effect through a scattering opaque layer. The high-resolution of SCORE is due to very fine speckle grains that are generated by a solid immersion medium which is made of a gallium phosphide (GaP) substrate with an opaque layer. Using SCORE, we demonstrated a deconvolved Abbe resolution of 116 nm with a field-of-view of 10 µm × 10 µm.

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Figure 1. (a) When a beam of a flashlight shines through an opaque medium such as white paint or a fog, the light spreads in both longitudinal and lateral directions. Consequently, the transmitted beam becomes wider and the transmitted light intensity is lower. (b) By shaping its wavefront using a SLM, a laser beam propagates through the opaque medium without lateral spread. Moreover, the transmitted light intensity is enhanced. The enhancement of light transmittance and the suppression of lateral beam spreading keep the optical energy density high throughout the opaque medium.

Hasan Yılmaz received his B.Sc. degree in Physics Engineering from İstanbul Technical University in 2008. He received his M.Sc. degree in Materials Science and Engineering at Koç University in 2011, where he worked with Prof. Ali Serpengüzel at the Microphotonics Research Laboratory. In 2015, he received his Ph.D. degree from University of Twente in The Netherlands for his work on “Advanced Optical Imaging with Scattering Lenses,” with Prof. Allard Mosk. He is currently an Associate Research Scientist at Yale University, Department of Applied Physics, working on physics and applications of complex optical systems with Prof. Hui Cao.

References:

[1] O. N. Dorokhov, Solid State Commun. 51, 381–384 (1984).
[2] Y. Imry, Europhys. Lett. 1, 249 (1986).
[3] P. A. Mello, P. Pereyra, and N. Kumar, Ann. Phys. 181, 290–317 (1988).
[4] Y. V. Nazarov, Phys. Rev. Lett. 73, 134 (1994).
[5] A. P. Mosk, A. Lagendijk, G. Lerosey, and M. Fink, Nat. Photonics 6, 283–292 (2012).
[6] S. Rotter and S. Gigan, Rev. Mod. Phys. 89, 015005 (2017).
[7] H. Yılmaz, E.G. van Putten, J. Bertolotti, A. Lagendijk, W.L. Vos, A.P. Mosk Optica 2, 424-429 (2015).
[8] H. Yılmaz, C. W. Hsu, A. Yamilov, and H. Cao, Nat. Photonics 13, 352-358 (2019). [9] H. Yılmaz, et al., Phys. Rev. Lett. 123, 203901 (2019).
[9] H. Yılmaz, et al., Phys. Rev. Lett. 123, 203901 (2019).

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 Esmaspäeval, 27. jaanuaril 2020 kell 16:15 Physicumi auditooriumis B103

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Amit Kumar Mishra (University of Cape Town)

Bio-inspired Methods for Sensing & Instrumentation

Biosphere has tremendous potential to inspire engineers and scientists in exploring interesting avenues and in innovating unique solutions. In this talk, the presenter shall discuss some of his past work, all of which have the common factor of being inspired by biological systems. He shall also discuss some of his proposals for the new Computational Imaging Group.

Amit Kumar Mishra is currently a full Professor in the Department of Electrical Engineering, at the University of Cape Town (#136 as per THES 2020 Ranking). He did his PhD in the University of Edinburgh in 2006 and has worked in three continents so far. He works mainly in the domain of radar system design, applied machine learning and bio-inspired AI. He has authored/co-authored more than 40 journal papers and has invented six patents.

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Esmaspäeval, 20. jaanuaril 2020 kell 16:15 Physicumi auditooriumis B103

Manoj Kumar Sharma (Rice University, USA)

Computational Imaging: Using Computation to Overcome Fundamental Imaging Limits

The goal of computational imaging is to disentangle additional information through advanced image processing algorithms. In disparity to traditional imaging, computational imaging systems involve a close integration of the sensing hardware system and the computation to form the images of interest.

In this talk, it will be shown how computation can help in breaking some of the fundamental limits in imaging to achieve sub-diffraction limited resolution imaging performance to image optically rough objects at large distances. It is well known that the achievable resolution is directly proportional to the numerical aperture of the imaging lens, which in turn, depends on the diameter of the imaging device as well as the distance of the object from its entrance pupil. As the distance between the object and the imaging device increases, the NA decreases, and hence, the achievable resolution decreases too. In order to keep the NA fixed, the diameter of the imaging lens is increased. Lohmann’s scaling law suggests that an m-fold distance change comes with a proportionate cost as well as the weight changed by a factor of m3.

Manoj Kumar Sharma will be talking about two pieces of his recent work carried out to achieve sub-diffraction limited resolution imaging performance without increasing the weight and the cost of the imaging device, as suggested by the Lohmann’s scaling law. This is done in two ways: one via forming a synthetic aperture by means of Fourier ptychography where we sample the Fourier plane to form a stack of low-resolution images and later using computation, a high-resolution image is formed from the captured low-resolution images. Second, by using a large, inexpensive, and light-weight Fresnel lens to achieve a high-resolution performance comparable to that of a good quality lens, by correcting it for the aberrations it carries. It is possible by characterizing the lens first and then use it for imaging. In both cases, we could achieve high-resolution imaging performance without increasing the weight and cost as per Lohmann’s scaling, which shows that computation can help to overcome fundamental imaging limitations.

Manoj Kumar Sharma is a research scientist at Rice University. He received his PhD in Physics in 2014 from the Indian Institute of Technology Delhi, New Delhi, India and has done two postdoctorals at the University of Arizona and at Northwestern University. His research interests include computational imaging, compressed sensing, inverse problems, phase retrieval, super-resolution imaging etc.

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Reverse side of U.S. $2 bill [1].

[1] Science Advances, 14 Apr 2017: Vol. 3, no. 4, e1602564 DOI: 10.1126/sciadv.1602564

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Teisipäeval, 7. jaanuaril kell 14:15, TÜ Physicumi auditooriumis B103 (W. Ostwaldi 1, Tartu)

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Janek Uin (Brookhaven National Laboratory, USA)

MOSAiC, the largest Arctic expedition in history

This talk will give an overview of the Multidisciplinary drifting Observatory for the Study of Arctic Climate -- MOSAiC, the largest Arctic expedition in history. The expedition started in September 2019, when German research ship RV Polarstern left Tromsø, Norway and headed towards the North Pole to be frozen in with the ice for a year.

On board among the various groups participating in the expedition, were the scientists and technicians from the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program, managing several shipping containers full of instruments for studying the properties of the Arctic atmosphere. The presenter of this talk spent a month and a half in the Arctic, setting up atmospheric aerosol measurements as part of the ARM deployment within MOSAiC.

The talk will give a background of the expedition, explain the role of the DOE ARM program in it, and share the personal experiences of the presenter working in the challenging Arctic conditions.

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Janek Uin graduated from University of Tartu in 2011 and defended his PhD thesis on aerosol measurements. Since 2015 he works as a staff scientist at the Brookhaven National Laboratory in New York as part of the U.S. DOE ARM program. He is responsible for conducting atmospheric aerosol measurements at the ARM measurement sites situated across the world, with the 30+ field instruments under his care.

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2019

neljapäeval, 5. detsembril kell 16:15 Physicumi auditooriumis A106 (W. Ostwaldi 1, 50411 Tartu).

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Madis Kõiv (05.12.1929--24.09.2014) oli eesti füüsik, filosoof ja kirjanik, kelle mõtlemises ja loomingus mängis üht keskset rolli küsimus ajast. Madis Kõivu 90. sünniaastapäeva tähistava seminari kavas on neli ettekannet.

  • Piret Kuusk (TÜFI teoreetilise füüsika vanemteadur) "Teoreetilise füüsika aeg"
    Madis Kõiv lõpetas Tartu ülikooli 1953. aastal teoreetilise füüsika erialal. Ta töötas TPI füüsika kateedris aastail 1953-1961 (sellesse aega jääb ka kandidaaditöö "Mesonite ja hüperonide süstemaatika" kaitsmine) ning ENSV Füüsika ja Astronoomia Instituudi teoreetilise füüsika sektoris 1961-1991. Tema teadustöö põhisuund oli alusosakeste teooria matemaatiliste esituste sisu ja tähenduse selgitamine. Kolmekümne Tartu  aasta kestel oli ta kahtlemata siinsete teoreetikute vaimne juht ja suunaja.
     
  • Kaupo Palo (PerkinElmer Cellular Technologies Germany GmbH teadur) "Dünaamiline aeg"
    Füüsikalise süsteemi analüüs põhineb dünaamilistel muutujatel nagu ruumikoordinaatidel, mis kirjeldavad süsteemi osiste vastastikust paiknemist, impulssmuutujatel, mis kirjeldavad liikumist, ja energial, mis määrab süsteemi evolutsiooni või tasakaalu.  Aga kus on siin pildil aeg?  Kas tõesti on aja roll olla paradoksaalsel kombel statist, tumm tunnistaja ja kroonik, pannes sündmused lihtsalt üksteise järgi ritta? Või mängib ta mingis alternatiivses füüsikalises pildis aktiivset rolli võrdväärselt teiste dünaamiliste muutujatega?  Nii küsis Madis Kõiv.
     
  • Veiko Palge (TÜFI teoreetilise füüsika teadur) "Filosoofiline aeg"
    Aeg on Madis Kõivu kirjutistes kesksel kohal, võttes erinevaid vorme kirjanduse, füüsika ja filosoofia kontekstides. Lühiettekandes vaatame, milline on analüütilise filosoofia aeg, kuidas tekkis aja nn "ABC teooria" 20. sajandil, ja kuidas see ajalugu oleks võinud olla teistsugune.
     
  • Jaan Kangilaski (ajakirja "Akadeemia" toimetaja) "Analüütiline aeg: Kõiv ja analüütilise filosoofia seminar"
    Madis Kõivu algatusel pandi 1991. aasta mais Tartus alus Analüütilise filosoofia seminarile, mis käib koos seniajani. Kõiv ise oli seminari juht aastani 2000. Analüütiline filosoofia on oma taotlusilt täppisteadustelähedane filosoofiaharu, mis sai alguse 19. sajandi lõpul -- 20. sajandi algul Saksamaal Jenas ja Inglismaal Cambridge’is, selliste autorite töödes nagu Gottlob Frege, Bertrand Russell, George Edward Moore ja Ludwig Wittgenstein.  Ajal, mil Eesti oli taas iseseisvumas, tuli ka filosoofias iseseisvuda senisest nõukogude traditsioonist ja analüütiline filosoofia kui kõige rangem ja täpsem distsipliin paistis Madis Kõivu jaoks selleks kõige sobivamana ja kergemini omandatavana, et seejärel saaksid noored filosoofid hakata seda varsti ka ise „tegema”. Ettekandes annan lühiülevaate seminari esimestest tegevusaastatest ja Madis kõivu rollist selles.

Physicumi seminarid on mõeldud füüsikute ja materjaliteadlaste, aga ka teiste loodus- ja täppisteadlaste laiale ringile (alates bakalaureuse astme üliõpilastest) ning püüavad avada seda, mis mingis valdkonnas on parasjagu oluline ja uudne või kuhu teatud uurimissuund on tänaseks välja jõunud.

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Seminarile järgneb Madis Kõivu maalide näituse "Madis Kõivu ruum" avamine Physicumi galeriis kell 18:00. Samal õhtul kell 19:00 etendub Vanemuise väikeses majas Madis Kõivu ja Vaino Vahingu näidend "Faehlmann".

Viiteks:

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Madis Kõiv, 1982. a (Kuulo Vestre foto)

Thursday, 17 October 2019, 4:15 p.m.
Physicum auditorium B103
W. Ostwaldi 1, Tartu

This year the Nobel Prize in Physics was awarded to James Peebles as well as to Michel G. E. Mayor and Didier Queloz, whose achievements in cosmology and astrophysics have contributed the understanding of the evolution of the universe and Earth's place in the cosmos. In the seminar the researchers from UT Tartu Observatory will speak about the scientific achievements of the Nobel laureates and point out the connections with the work in the observatory. There will be four short presentations, two in Estonian and two in English.

Jukka Nevalainen: How has Peebles helped us to understand the Universe?

Jaan Einasto: Kokkupuuteid Jim Peeblesiga

Jaan Pelt: Kuidas avastatakse eksoplaneete?

Mihkel Pajusalu: Latest developments in the field of exoplanet science and the role of Tartu Observatory

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Nobeli Prize in Physics 2019 laureates James Peebles, Michel G. E. Mayor, Didier Queloz (picture by Niklas Elmehed © Nobel Media)

The Physicum seminars are meant for a broad auditorium of physicists and materials scientists, as well as for interested people from other natural and exact sciences (including bacheleor level students) and aim at introducing what is important and new in a certain field, or where a specific reasearch direction has reached today.

Everybody is welcome to attend.

The 6th Physicum seminar takes place on Friday, 17 May 2019 at 14:15 in the Physicum lecture hall B103 (W. Ostwaldi 1, Tartu). The Physicum seminars are meant for a broad auditorium of physicists and materials scientists, as well as for interested people from other natural and exact sciences (including bacheleor level students) and aim at introducing what is important and new in a certain field, or where a specific reasearch direction has reached today. The current seminar will be held in English.

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Tõnu Pullerits
Chemical Physics, Lund University, Sweden

Ultrafast Spectroscopy of Semiconductor Nanostructures

Nano-size semiconductor structures have a rich spectrum of properties related to quantum confinement which are not available in the corresponding bulk materials. Size-tuneable spectrum is, perhaps, the best known and understood such property. Here we investigate dissipation and transport dynamics of various semiconductor nanosystems and their composites which are relevant for optoelectronics applications. We have studied colloidal quantum dots, plasmonic metal nanoparticles, hybrid and all inorganic perovskite nanocrystals and Ruddlesden–Popper 2D perovskites. We apply a set of modern ultrafast techniques like photocurrent and fluorescence detected coherent 2D spectroscopy, transient terahertz and absorption spectroscopies revealing detailed information about photoexcitation dynamics.

 

Tõnu Pullerits graduated University of Tartu in solid state physics in 1986 and defended PhD in 1991 at the Institute of Physics under the supervision of Arvi Freiberg. He was a postdoctoral researcher at Free University of Amsterdam,  University of Umeå, and Lund University, where he works till today. Since 2008 Tõnu Pullerits is a professor of chemical physics at Lund University. Tõnu Pullerits has co-authored over two hundred research publications, which have acquired more than 11000 citations (Google h-index 59). He has supervised six PhD theses. Tõnu Pullerits has been an invited speaker at many international conferences and seminars, he has organized a number of scientific symposia, and is a member of several commissions of trust. As an expert of the field, he has evaluated project proposals for the European Research Council, the Estonian Research council, an for other foundations. He belongs to the editorial board of "Nature Scientific Reports", and acts as a referee for a number of leading journals. In 2016 Tõnu Pullerits became an elected member of the Swedish Royal Academy of Sciences.

 

The 5th Physicum seminar takes place on Thursday, 25 April 2019 at 16:15 in the Physicum lecture hall A106 (W. Ostwaldi 1, Tartu). The Physicum seminars are meant for a broad auditorium of physicists and materials scientists, as well as for interested people from other natural and exact sciences (including bacheleor level students) and aim at introducing what is important and new in a certain field, or where a specific reasearch direction has reached today. The current seminar will be held in English.


THE DAWN OF BLACK HOLE ASTRONOMY
how to observe something completely dark and why is it so exciting?

On 10 April 2019 the international Event Horizon Telescope collaboration revealed the first image of a black hole. The seminar aims to give a concise scientific background of this major discovery and highlight some future perspectives. There will be five short talks:

A Brief Introduction to Dark Compact Objects
how to distinguish black holes from more exotic wormholes, gravastars, boson stars, etc?
Laur Järv (University of Tartu, Institute of Physics)

The Astrophysics of Supermassive Black Holes
where to find the beasts and how they feed?
Indrek Vurm (University of Tartu, Tartu Observatory):

Observations with the Event Horizon Telescope
how an interferometer of the size of the Earth got the picture, and what was actually measured?
Antti Tamm (University of Tartu, Tartu Observatory)

The Black Hole "Shadow"
where can the light rays near a black hole go, and how does the image arise?
Christian Pfeifer (University of Tartu, Institute of Physics)

The Dawn of Black Hole Astronomy
what can be inferred from the image of M87*, what are the next tasks and targets?
Manuel Hohmann (University of Tartu, Institute of Physics)

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Hello, M87* (Pōwehi)!

["Pōwehi" is a proposed unofficial name for the supermassive black hole in the galaxy M87. It means the "embellished dark source of unending creation" in the Hawaii language and is inspired by the Kumulipo, a chant about the origins of the world from a Hawaiian perspective.]

 Neljas Physicumi seminar toimub neljapäeval, 4. aprlllil kell 16:15 Physicumi auditooriumis B103. Physicumi seminarid on mõeldud füüsikute ja materjaliteadlaste, aga ka teiste loodus- ja täppisteadlaste laiale ringile (alates bakalaureuse astme üliõpilastest) ning püüavad avada seda, mis mingis valdkonnas on parasjagu oluline ja uudne või kuhu teatud uurimissuund on tänaseks välja jõunud.

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Esineb dr. Arved Vain (TÜ füüsika instituudi biomehaanika dotsent)

PEALKIRI: Omnitoni saamise lugu ehk kuidas ennetada haigestumist

KOKKUVÕTE:

Lihashaigusi peetakse ravimatuteks. Selle on tinginud asjaolu, et lihashaigusi diagnoositakse liiga hilja – siis, kui patoloogiline protsess on tekitanud skeletilihases pöördumatuid morfoloogilisi muutusi. Järelikult on oluline vältida lihashaigusi. Paraku puuduvad laialtkasutatavad meetodid ja seadmed skeletilihaste muutuste lihtsaks ja odavaks jälgimiseks ning patoloogia varajaseks avastamiseks.

Tüüpilisteks vigadeks seni leiutatud seadmetele lihastoonust iseloomustava parameetri registreerimisel on mõõtmisprotseduuri mehaaniline järelmõju, mis muudab mõõtekorratavust halvemaks. Roomavuse ja mehaanilise pinge relaksatsiooniaja karakteristikuid mõõtvaid seadmeid pehmetele bioloogilistele kudedele ei ole teada peale müomeetri.

Bioloogiliste kudede testimise põhiprobleem on see, et need on palju muutlikumad kui elutud materjalid. Pehmete bioloogiliste kudede biomehaaniliste omaduste iseloomustamisel tekitavad kõige suuremaid raskusi koe mittelineaarsus, viskoelastsus ja anisotroopne käitumine, mis võivad aja jooksul muutuda. Keha erinevates piirkondades varieeruvad bioloogiliste kudede biomehaanilised omadused. Omnitoni uus programm ja seade võimaldavad täiendavalt:

  1. Seadistada seadet nii, et on välistatud mõõtmisel uuritava koe elastsuspiiri ületamine;
  2. Kordusmõõtmistel: järgmine päev, nädal, kuu või aasta saab alustada mõõtmisi täpselt regiooni sellest punktist, millist mõõdeti eelmine kord;
  3. Ühe impulsi rakendamisel saadakse infot pehme bioloogilise koe erinevatest kihtidest.

 

ESINEJA:

Arved Vain lõpetas Tallinna Polütehnilise Instituudi masinaehituse insenerina 1961. aastal. Aastatel 1965–1968 oli ta  Tartu Ülikoolis aspirantuuris biofüüsika erialal, sai 1970 a. kandidaadikraadi ja töökoha Tartu Ülikoolis, kus on tegutsenud kuni tänaseni. 1993. a kaitses Arved Vain Riias biomehaanika alal dr. habil. biol. kraadi teemal “Mehaanilise pinge transmissiooninähtus skeletilihases”.

Arved Vain on õpetanud erinevaid meditsiinifüüsikaga seotud aineid, praegustes õppekavadest leiab näiteks tema loengukursused "Biomehaanika alused ja biomaterjalid", "Müomeetria", "Funktsionaalse anatoomia põhimõisted". Tema juhendamisel on kaitstud 10 doktoriväitekirja, 12 magistritööd ja üle 30 bakalaureusetöö. Arved Vain on olnud külalisprofessor Sumõ Riiklikus Ülikoolis (Ukraina) ja Vanderbilti Ülikoolis (Nashville, TN, USA).

Müomeetria meetodile ja seadmele sai Arved Vain esimese autoritunnistuse 1977, esimese patendi 1996, teise 2011 ning kolmas rahvusvaheline patenditaotlus on esitatud 2019. a märtsis. Arved Vain on ülikooli spinn-off ettevõtte OÜ Müomeetria asutaja (1999), praegu kannab firma nime AS Myoton.

 

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TAUSTAKS:

3rd Physicum seminar takes place on Thursday, 21 February 2019 at 14:15 in the Physicum room B103. The Physicum seminars are meant for a broad auditorium of physicists and materials scientists (including bacheleor level students) and aim at introducing what is important and new in a certain field.

SPEAKER: Prof. Alexey E. Romanov (ITMO university, St. Petersburg, Russia)

TITLE: Disclination ensembles in graphene and pseudo-graphenes

ABSTRACT: In this talk, we consider wedge disclinations as the main structural defects in 2D graphene crystal hexagonal lattice. Disclinations are associated with improper carbon rings, i.e. rings having 4, 5, 7 or 8 members to the contrary of proper 6-member carbon rings constituting ideal 2D graphene crystal lattice. With the help of disclinations, we build the models for grain boundaries and other interfaces in graphene polycrystals as well as for pseudo-graphenes. The pseudo-graphenes are treated as graphene crystals with high density of periodically distributed disclinations with zero total charge. The geometry and energy of disclinated graphene configurations are analyzed with the help of molecular dynamics (MD) simulation technique and in the framework of the theory of defects in elastic continuum. In conclusion, it is argued that studying the properties of disclinations in graphene opens a new direction in graphene science and technology – graphene defect engineering.

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IMAGE: Examples of pseudo-graphene crystals with disclination networks (a) 5-7A pseudo-graphene – phagraphene [1]; 5-7B pseudo-graphene [2]; 5-8-5D pseudo-graphene – PO graphene [3]; 4-8 pseudo-graphene [2].  Red circles denote carbon atoms; empty and black triangles denote negative and positive disclinations, respectively.

SPEAKER: Alexey Romanov graduated St. Petersburg Polytechnic University in 1971 with a degree on the physics of metals. In 1981 Alexey defended his PhD thesis in solid state physics and in 1989 he completed a professorial thesis on screened disclinations in solids. He is an author or co-author of over 300 publications with h-index 43. The R&D he is involved in is mainly focused, but not limited to the structure and mechanical properties of solids with emphasis on defects in nanocrystals and thin films. One of his main activities was dedicated to the development of the theory of disclinations in crystals. At the moment Alexey is the Dean of the Faculty of Laser Photonics and Optoelectronics at ITMO University (St. Petersburg, Russia) and the Head of International Research Center of Functional Materials and Devices of Optoelectronics and Electronics. Incidentally, in the period of 2010-2014 Alexey Romanov held a professor position at the Institute of Physics, University of Tartu.

REFERENCES:

[1] Zh. Wang, X.-F. Zhou, X. Zhang, Q. Zhu, H. Dong, M. Zhao, A.R. Oganov, Phagraphene: A low-energy graphene allotrope composed of 5–6–7 carbon rings with distorted Dirac cones // NanoLetters 15 (2015) 6182.

[2] Ch.-P. Tang, Sh.-J. Xiong, A graphene composed of pentagons and octagons // AIP Advances 2 (2012) 042147.

[3] М.А. Rozhkov, А.L. Kolesnikova, I.S. Yasnikov, А.Е. Romanov, Disclination ensembles in graphene // Low Temperature Physics 44 (2018) 1171.

The current seminar is supported by the Graduate School of Functional materials and technologies receiving funding from the European Regional Development Fund in University of Tartu, Estonia.

The second Physicum seminar will be held on Thursday, 31st of January, at 16.15 in the Physicum auditorium B103. The Physicum seminar is a new seminar format, which is meant to be comprehensible and entertaining for listeners of all levels, and in which strictly top-level scientists are invited to hold a talk. This seminar will be held by Georg Pucker, PhD, and the seminar will be held in English.

 

TITLE: Silicon Quantum Dots

ABSTRACT: Silicon quantum dots - often also called silicon nanocrystals - are attracting a lot of interest since the early work on light emission from porous silicon by L. Canham in UK and U. Gössele in Germany back in 1990. Silicon quantum dots embedded in a dielectric matrix can be seen as a more stable form of porous silicon maintaining the strong, typical red to near-infrared photoluminescence.

While the photoluminescence efficiency of silicon quantum dots can easily achieve some percent efficiency, electroluminescence is more difficult to obtain due to different barrier heights for holes and electrons and poor electrical transport. However, careful optimisation of growth parameters allows to control the average dimension of quantum dots and their distance. A study, in which Silicon quantum dots on top of a silicon solar cell were used will be presented. Indeed, an enhancement of the UV-blue efficiency and overall cell efficiency could be obtained. Finally, use of a Si-light emitting diode as light source in a compact quantum number generator will be presented as a potential application.

Image: Silicon wafer with hundreds of silicon quantum dot based light emitting diodes (LEDs), zoom on single LED, high resolution TEM image of silicon quantum dots.

 

SHORT BIOGRAPHY: Georg Pucker obtained his master's (1993) and doctor's degree (1996) in Technical Chemistry from the Technical University Graz – Austria, for his work in the field of optical spectroscopy of rare-earth doped glasses. From 1996 to 2000 he was a Post-Doc at the Department of Physics at the University of Trento, Italy, performing research in the field of optical spectroscopy of rare-earth ions and silicon nanostructures. In 2000 he joined ITC-IRST, now Bruno Kessler Foundation (FBK) in Italy. The R&D he is involved in ranges from research on organic and inorganic solar cells, radiation hard silicon detectors for particle tracking to thermo-electric devices. Since 2011, his research has focused on integrated photonics. He is author or co-author of over 90 publications in peer-reviewed journals, author of a book chapter and inventor of 4 patents.

https://www.facebook.com/events/2288466198066882/b

The first Physicum seminar will be held on Thursday, 17th of January, at 14.15 in the Physicum auditorium A106. The Physicum seminar is a new seminar format, which is meant to be comprehensible and entertaining for listeners of all levels, and in which strictly top-level scientists are invited to hold a talk.

Järelvaadatav video

This seminar will be held by Professor Daniele Faccio, and the seminar will be held in English.

Daniele Faccio is a renowned researcher in the field of photonics. He has studied and worked in more than half a dozen of universities and research institutes in Europe, UK and USA, and contributed to the field through reviewing and editing of various scientific journals, organizing international research schools and many more. The scope of his research is very wide and his work has drawn much attention through stating very creative analogues between phenomena in optics and fundamental physics.

 

TITLE: Imaging with quantum technologies 

 

ABSTRACT: We will give an overview of recent developments of single-photon detection technologies and cameras. One of the main features we have focused on is the ability of single-photon cameras to capture images with 10-100 ps temporal resolution, thus introducing a paradigm change the field of what is often referred to as “trillion frames per second photography”. This technology allows us for example to freeze light in flight but can also be used to create 3D images of scenes that are hidden behind a corner. Other applications involve a combination with computational retrieval techniques and allow imaging through opaque materials or through optical fibres. Finally, we will briefly overview some new approaches to quantum imaging, in the sense of imaging with entangled states light where the goal is to image objects that classically would not be visible.

https://www.facebook.com/events/344018009654767/

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Doctoral defence: Maido Merisalu “Nanostructured coatings for car and aerospace industries”

8. 12 at 16.15  Maido Merisalu defends his doctoral thesis "Nanostructured Coatings for Car and Aerospace Industries".
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Physicum seminar

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Conference “Natural scientists on sustainable development: what colour is the future?”