20.500.12556/RUL-187977 Optični mikroresonatorji kot senzorji tlaka in lomnega količnika v celici z diamantnim nakovalom Optical microresonators as a sensor of pressure and refractive index in a diamond anvil cell Raziskave snovi pri visokih tlakih danes v veliki meri potekajo v celici z diamantnim nakovalom (DAC), v kateri je vzorec stisnjen med prozornima nakovaloma in je zato dostopen optičnim meritvam. Tlak v njej izmerimo posredno, najpogosteje iz fluorescence rubina, dodanega v vzorec. Obetavna dopolnitev teh senzorjev so prozorni sferični mikroresonatorji. V njih svetloba kroži tesno pod površino v šepetajočih galerijskih načinih (angl. whispering gallery modes, WGM), katerih valovne dolžine so ostro določene in odvisne le od polmera mikroresonatorja ter od lomnih količnikov njegove snovi in okoliškega medija. Tak mikroresonator je zato po zgradbi hkrati senzor tlaka in senzor lomnega količnika. Doslej je bilo pokazano, da so taki resonatorji uporabni kot senzorji tlaka, ne pa tudi kot merilci lomnega količnika. Cilj tega magistrskega dela je bil te mikroresonatorje umeriti kot senzorje tlaka in lomnega količnika tekočega medija v DAC. Opravil sem tri eksperimente z mikroresonatorji iz barijevotitanatnega stekla, dopiranega z evropijem, ki sem jih skupaj s sferičnimi rubini suspendiral v mediju za prenos tlaka, tlak pa določal iz rubinov. Poskus v mešanici metanola in etanola 4:1 se je ponesrečil, zato sem umeritev opravil v silikonskem olju in jo nato preizkusil v destilirani vodi. Iz prilagoditve približne modalne enačbe izmerjenim spektrom dobim pri vsakem tlaku dve količini, optični polmer, to je zmnožek polmera mikroresonatorja in njegovega lomnega količnika, ter razmerje $N$ med lomnim količnikom mikroresonatorja in medija. Tlačna odvisnost lomnega količnika, ki jo dobim iz umeritve, se ujema z objavljeno vrednostjo za to steklo. Kot senzor tlaka se je optični polmer izkazal za nenatančnega, saj se stiskanje mikroresonatorja in rast njegovega lomnega količnika v njem skoraj odštejeta. Odstopanje od rubinove lestvice, to je uveljavljene zveze med tlakom in premikom fluorescenčne črte rubina, tudi v najboljšem primeru znaša okoli 1 GPa, v slepem preizkusu na meritvah v vodi pa umeritvena krivulja pri večini odčitkov sploh nima rešitve. Razmerje $N$ je precej občutljivejše, vendar zahteva znan medij in zato kot samostojen merilec tlaka ne pride v poštev. Prav ta občutljivost pa je prednost, kadar mikroresonator uporabimo kot merilec lomnega količnika medija, saj se ta skriva samo v razmerju $N$. Iz umerjenega optičnega polmera in izmerjenega razmerja $N$ sem rekonstruiral lomni količnik vode, ne da bi vanj vstopila kakršna koli predpostavka o vodi. Dobljene vrednosti se z objavljenimi ujemajo na nekaj odstotkov. Z mikroresonatorji sem izmeril tudi fazni prehod led VI${}\to{}$led VII, saj pri tlaku prehoda vsi neodvisno pokažejo skok lomnega količnika, katerega velikost je skladna s pričakovano. Uporabni so pri tem le mikroresonatorji v ozkem razponu velikosti, ki ga postavi razmerje lomnih količnikov in ne velikost sama. Pokazal sem torej, da mikroresonatorji niso posebej primerni za merjenje tlaka, so pa zelo uporabni kot merilci lomnega količnika, kar odpira nove možnosti za preprostejše meritve različnih snovi pri visokih tlakih. Research on materials at high pressure is today carried out largely in the diamond anvil cell (DAC), in which the sample is compressed between two transparent anvils and therefore remains accessible to optical measurements. The pressure inside the cell is measured indirectly, most often from the fluorescence of ruby added to the sample. A promising complement to these sensors are transparent spherical microresonators. In them light circulates just below the surface in whispering gallery modes (WGM), whose wavelengths are sharply defined and depend only on the radius of the microresonator and on the refractive indices of its material and of the surrounding medium. Such a microresonator is therefore by construction a sensor of both pressure and refractive index. It has been shown so far that such resonators are usable as pressure sensors, but not as gauges of refractive index. The aim of this thesis was to calibrate these microresonators as sensors of pressure and of the refractive index of the liquid medium in a DAC. I carried out three experiments with microresonators of europium-doped barium titanate glass, suspended together with spherical rubies in the pressure-transmitting medium, which gave the pressure. The experiment in the 4:1 methanol-ethanol mixture failed, so I carried out the calibration in silicone oil and then tested it in distilled water. Fitting an approximate modal equation to the measured spectra yields two quantities at every pressure, the optical radius, that is the product of the radius of the microresonator and its refractive index, and the ratio $N$ between the refractive index of the microresonator and that of the medium. The pressure dependence of the refractive index obtained from the calibration agrees with the published value for this glass. As a pressure sensor the optical radius proved imprecise, because the compression of the microresonator and the rise of its refractive index almost cancel in it. The deviation from the ruby scale, that is from the established relation between pressure and the shift of the ruby fluorescence line, is about 1 GPa even at best, and in a blind test on the measurements in water the calibration curve has no solution at all for most readings. The ratio $N$ is considerably more sensitive, but it requires a known medium and is therefore not an option as a stand-alone pressure gauge. This sensitivity, however, is an advantage when the microresonator is used as a gauge of the refractive index of the medium, which enters only through the ratio $N$. From the calibrated optical radius and the measured ratio $N$ I reconstructed the refractive index of water without any assumption about water entering the calculation. The values obtained agree with the published ones to within a few percent. With the microresonators I also measured the ice VI${}\to{}$ice VII phase transition, since at the transition pressure they all independently show a jump in the refractive index whose magnitude is consistent with the expected one. Only microresonators within a narrow range of sizes are usable for this, a range set by the refractive index ratio and not by size alone. I have thus shown that microresonators are not particularly suited to measuring pressure, but that they are very useful as gauges of refractive index, which opens up new possibilities for simpler measurements of various substances at high pressure. celica z diamantnim nakovalom visoki tlaki optični mikroresonator načini WGM lomni količnik rubinova tlačna lestvica barijevotitanatno steklo diamond anvil cell high pressure optical microresonator whispering gallery modes refractive index ruby pressure scale barium titanate glass true false false Slovenski jezik Angleški jezik Magistrsko delo/naloga 2026-09-17 08:15:47 2026-09-17 08:15:56 2026-09-18 04:30:30 0000-00-00 00:00:00 2026 0 0 0000-00-00 NiDoloceno NiDoloceno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 164332 291426307 24448.pdf 24448.pdf 1 D9C6242AE6357C44BDF72132E06AEB6D 6fdaed7074ed4d31432cf69014d5b43a16c6f8b4687fd18a32c8d181b01f7d44 353fee41-b25f-11f1-8bc5-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=247827 Fakulteta za matematiko in fiziko 0 0 0