PhD Position Available
Non-Linear Optics of Polar Nematic Liquid Crystals
Application deadline: 5.7.2021
The technology of display devices was revolutionized by the introduction of liquid crystal displays (LCDs) based on liquid crystalline (LC) materials exhibiting a room-temperature nematic LC phase. In this phase, the constituent molecules exhibit a random head-to-tail arrangement of molecular dipoles, which prevents the establishment of long-range polar order in the medium. In addition to the standard nematic phase, about a century ago, Born and Debye envisioned the existence of a polar nematic phase that was, however, experimentally realized only very recently. Our research laboratory importantly participated in the pioneering discoveries in this field, and we are continuing with further investigation of the physical properties of these fascinating substances.
In our research, we also use methods based on optical second harmonic generation (SHG). This is a nonlinear optical process that occurs only in structures without inversion symmetry and is therefore very suitable for detecting structural polarity. Experiments with the polar LC phase allow one to study polarity, ferroelectricity, SHG, and the associated phenomena in a truly 3D liquid. A combination of those properties with a nematic-like fluidity results in electro-optical and nonlinear optical effects that have a vast potential for applications in various nonlinear optical components. A prerequisite first step towards those applications is gaining a thorough fundamental understanding of nonlinear optical properties of the polar nematic phase and finding suitable ways to control those properties via the application of small external voltages.
The new Ph.D. researcher will start with this essential first step and then continue with the design and fabrication of nonlinear optical elements. The candidate will join an active research group with more than 15 members and an internationally recognised experience in Soft Matter research.
Figure 2: Photograghy of the SHG microscopy system (left). Schematic of the structure ofrientation and a SHG snapshot of the sample (right).
Experimental techniques:
– Polarization optical (video)microscopy (POM)
– Dynamic light scattering (DLS)
– Cross-differential dynamic microscopy (cDDM)
– Dielectric spectroscopy
– Characterization of electro-optic properties
– Measurements of bulk SHG
– SHG microscopy
– SHG interferometry
Requirements:
– Master degree in physics (2nd cycle) accomplished at latest until 15.09.2021.
– An aspiration to pursue a Ph.D. program in the field of physics.
– Enthusiasm about soft matter, lasers, optics, and experimental work.
– Curiosity for unusual phenomena and willingness to solve new puzzles by systematic and determined experimental research.
– Interest for collaboration with local and foreign researchers active in the field
– Age below 29 years (as required by the ARRS call).
Contact:
Razpis za kandidata (m/ž) za mladega razizkovalca
Nelinearna optika v polarnih nematskih tekočih kristalih
Rok za prijavo: 5.7.2021
Tehnologija zaslonskih naprav se je revolucionarno spremenila z uvedbo zaslonov na tekoče kristale (LCD), ki temeljijo na tekočekristalnih materialih z nematsko fazo pri sobni temperaturi. V tej fazi imajo sestavne molekule naključno porazdelitev molekularnih dipolov, kar preprečuje vzpostavitev polarnega reda dolgega dosega. Poleg standardne nematske faze, sta Born in Debye pred približno sto leti predvidela tudi obstoj polarne nematske faze, ki pa je bila eksperimentalno dokazana šele pred kratkim. Pri pionirskih odkritjih na tem področju je pomembno prispeval naš laboratorij, kjer nadaljujemo z raziskavami fizikalnih lastnosti teh nenavadnih snovi.
Pri raziskavah med drugim uporabljamo metode, ki temeljijo na generaciji druge optičneharmonične frekvence (SHG). Gre za nelinearni optični proces, ki se pojavlja le v strukturah brez simetrije inverzije in je zato zelo primeren za odkrivanje strukturne polarnosti. Poskusi v polarni fazi tekočega kristala omogočajo preučevanje polarnosti, feroelektričnosti, SHG in drugih z njimi povezanih pojavov v 3D tekočini. Kombinacija teh in nematskih lastnosti vodi do elektrooptičnih in nelinearnih optičnih pojavov, ki imajo velik potencial za uporabo v različnih nelinearnih optičnih komponentah. Prvi korak za razvoj takšnih aplikacij je temeljno razumevanje nelinearnih optičnih lastnosti polarne nematske faze in iskanje ustreznih metod za nadzor teh lastnosti z uporabo majhnih zunanjih napetosti.
Novi doktorski raziskovalec bo začel svojo raziskovalno pot z opisanim prvim korakom in nato nadaljeval z načrtovanjem ter izdelavo nelinearnih optičnih elementov.
Slika 2: Fotografija sistema za SHG mikroskopijo (levo). Shema orientacijske strukture in posnetek vzorca (desno).
Eksperimentalne metode
– Polarizacijska optična (video)mikroskopija (POM),
– dinamično sipanje svetlobe (DLS),
– križno-diferenčna dinamična mikroskopija (cDDM),
– meritve dielektričnega odziva,
– karakterizacija elektrooptičnih lastnosti,
– meritve odziva SHG,
– mikroskopija SHG,
– interferometrija SHG.
Kandidat naj izpolnjuje naslednje pogoje:
– Magistrski študij fizike (2. stopnja), opravljen najpozneje do 15.9.2021,
– želja po nadaljevanju raziskovalne kariere v sklopu doktorskega študija na področju fizike,
– navdušenje nad mehko snovjo, laserji, optiko in eksperimentalnim delom v optičnem laboratoriju,
– radovednost za nenavadne pojave in pripravljenost za reševanje novih ugank s sistematičnim in vztrajnim eksperimentalnim raziskovanjem,
– zanimanje za sodelovanje z domačimi in tujimi raziskovalci, dejavnimi na tem področju,
– starost do 29 let.
Kontakt: