Publications with Fulltext
Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open Access Direct conversion of cytochrome c spectral shifts to fluorescence using photochromic FRET(Royal Society of Chemistry (RSC), 2014) Department of Physics; Department of Chemistry; Department of Chemical and Biological Engineering; Manioğlu, Selen; Atış, Müge; Aas, Mehdi; Kiraz, Alper; Bayraktar, Halil; PhD Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Department of Chemical and Biological Engineering; College of Sciences; N/A; N/A; N/A; 22542; N/APhotochromic fluorescence resonance energy transfer (pcFRET) was used to monitor the redox activity of non-fluorescent heme protein. Venus fluorescent protein was used as a donor where its emission intensity was reversibly modulated by the absorption change of Cytochrome c.Publication Open Access Droplet resonator based optofluidic microlasers(Society of Photo-optical Instrumentation Engineers (SPIE), 2014) Brzobohaty, Oto; Jezek, Jan; Pilat, Zdenek; Zemanek, Pavel; Anand, Suman; McGloin, David; Department of Physics; Kiraz, Alper; Aas, Mehdi; Karadağ, Yasin; Jonas, Alexandr; Faculty Member; PhD Student; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; 22542; N/A; N/A; N/AAn SU-8 polymer microdisk resonator coated with a palladium (Pd) layer and coupled to a single-mode optical waveguide is used to as a hydrogen (H-2) gas sensor. In the presence of H2 a red shift is observed in the spectral positions of the microdisk whispering gallery modes (WGMs) due to the expansion in the Pd lattice. H-2 concentrations below the flammable limit (4%) down to 0.3% could be detected in nitrogen atmosphere at room temperature. For H-2 concentrations between 0.3 1%, WGM spectral positions shifted linearly with H-2 concentration at a rate of 32 pm/%H-2. Average response time of the devices was measured to be 50 s for 1% H-2. The proposed device concept can also be used to detect different chemical gases by using appropriate sensing layers.Publication Open Access Dye lasing in optically manipulated liquid aerosols(Optical Society of America (OSA), 2013) Anand, S.; McGloin, D.; Department of Physics; Karadağ, Yasin; Aas, Mehdi; Jonas, Alexandr; Kiraz, Alper; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 22542We report lasing in airborne, rhodamine B-doped glycerol-water droplets with diameters ranging between 7.7 and 11.0 mu m, which were localized using optical tweezers. While being trapped near the focal point of an infrared laser, the droplets were pumped with a Q-switched green laser. Our experiments revealed nonlinear dependence of the intensity of the droplet whispering gallery modes (WGMs) on the pump laser fluence, indicating dye lasing. The average wavelength of the lasing WGMs could be tuned between 600 and 630 nm by changing the droplet size. These results may lead to new ways of probing airborne particles, exploiting the high sensitivity of stimulated emission to small perturbations in the droplet laser cavity and the gain medium.Publication Open Access Dye lasing in optically manipulated liquid aerosols(Society of Photo-optical Instrumentation Engineers (SPIE), 2013) McGloin, David; Anand, Suman; Department of Physics; Department of Electrical and Electronics Engineering; Karadağ, Yasin; Aas, Mehdi; Jonas, Alexandr; Kiraz, Alper; PhD Student; Faculty Member; Department of Physics; Department of Electrical and Electronics Engineering; College of Sciences; N/A; N/A; N/A; 22542We present dye lasing from optically manipulated glycerol-water aerosols with diameters ranging between 7.7 and 11.0 mu m confined in optical tweezers. While being optically trapped near the focal point of an infrared laser, the droplets stained with Rhodamine B were pumped with a Q-switched green laser and their fluorescence emission spectra featuring whispering gallery modes (WGMs) were recorded with a spectrograph. Nonlinear dependence of the intensity of the droplet WGMs on the pump laser fluence indicates dye lasing. The average wavelength of the lasing WGMs could be tuned between 600 and 630 nm by adjusting the droplet size. These results may lead to new ways of probing airborne particles, exploiting the high sensitivity of stimulated emission to small perturbations in the droplet laser cavity and the gain medium.Publication Open Access Effect of spatial coherence of LED sources on image resolution in holographic displays(Society of Photo-optical Instrumentation Engineers (SPIE), 2017) Department of Electrical and Electronics Engineering; Ghoushchi, Vahid Pourreza; Aas, Mehdi; Ulusoy, Erdem; Ürey, Hakan; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; N/A; N/A; 111927; 8579Holographic Displays (HDs) provide 3D images with all natural depth cues via computer generated holograms (CGHs) implemented on spatial light modulators (SLMs). HDs are coherent light processing systems based on interference and diffraction, thus they generally use laser light. However, laser sources are relatively expensive, available only at some particular wavelengths and difficult to miniaturize. In addition, highly coherent nature of laser light makes some undesired visual effects quite evident, such as speckle noise, interference due to stray light or defects of optical components. On the other hand, LED sources are available in variety of wavelengths, has small die size, and no speckle artifact. However, their finite spatial size introduce some degree of spatial incoherence in an HD system and degrade image resolution, which is the subject of the study in this paper. Our theoretical analysis indicates that the amount of resolution loss depends on the distance between hologram and SLM image planes. For some special configurations, the source size has no effect at all. We also performed experiments with different configurations using lasers and LEDs with different emission areas that vary from 50 mu m to 200 ae m, and determined Contrast Transfer Function (CTF) curves which agree well with our theoretical model. The results show that it is possible to find configurations where LEDs combined with pinholes almost preserve natural resolution limit of human eye while keeping the loss in light efficiency within tolerable limits.Publication Open Access In vitro and in vivo biolasing of fluorescent proteins suspended in liquid microdroplet cavities(Royal Society of Chemistry (RSC), 2014) Jonas, Alexandr; Anand, Suman; McGloin, David; Department of Physics; Department of Chemistry; Bayraktar, Halil; Kiraz, Alper; Aas, Mehdi; Karadağ, Yasin; Manioğlu, Selen; Faculty Member; Faculty Member; PhD Student; Department of Physics; Department of Chemistry; College of Sciences; N/A; 22542; N/A; N/A; N/AFluorescent proteins are indispensable for selective, quantitative visualization of localization, dynamics, and interactions of key molecular constituents of live cells. Incorporation of fluorescent proteins into an optical cavity can lead to a significant increase in fluorescence signal levels due to stimulated emission and light amplification in the cavity, forming a laser with biological gain medium. Utilization of lasing emission from fluorescent biological molecules can then greatly enhance the performance of fluorescence-based biosensors benefiting from the high sensitivity of non-linear lasing processes to small perturbations in the cavity and the gain medium. Here we study optofluidic biolasers that exploit active liquid optical resonators formed by surface-supported aqueous microdroplets containing purified yellow fluorescent protein or a suspension of live E. coli bacterial cells expressing the fluorescent protein. We first demonstrate lasing in fluorescent protein solutions at concentrations as tow as 49 mu M. Subsequently, we show that a single fluorescent bacterial cell of micrometre size confined in a droplet-based cavity can serve as a laser gain medium. Aqueous droplet microcavities allow the maintenance of the bacterial cells under conditions compatible with unimpeded growth. Therefore, our results also suggest a direct route to microscopic sources of laser light with self-regenerating gain media.Publication Open Access Optically trapped droplets of liquid crystals as flexible, tunable optofluidic microcavities(Optical Society of America (OSA), 2017) Jonáš, A.; Pilát, Z.; Ježek, J.; Bernatová, S.; Zemánek, P.; Department of Physics; Aas, Mehdi; Kiraz, Alper; Faculty Member; Department of Physics; College of Sciences; N/A; 22542We demonstrate reversible spectral tuning of optofluidic microcavities formed by optically trapped, dye-doped emulsion droplets of liquid crystals by changing ambient temperature or exposing the droplets to AC electric field of varying magnitude.Publication Open Access Quantum dot optofluidic lasers and their prospects for biochemical sensing(Society of Photo-optical Instrumentation Engineers (SPIE), 2016) Jonas, Alexandr; Chen, Qiushu; Fan, Xudong; Department of Physics; Kiraz, Alper; Aas, Mehdi; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; 22542; N/AWe achieved four types of laser emissions with quantum dots (QDs) using the same high-Q-factor optofluidic ring resonator (OFRR) platform. In the first type, 2 mu M QDs dissolved in toluene that filled the entire OFRR cavity volume were employed as the gain medium. The lasing threshold was 15-22 mu J/mm(2). In the second type, mu M aqueous QDs were in bulk buffer solution that filled the entire OFRR cavity volume. The lasing threshold was 0.1 mu J/mm(2), over 3 orders of magnitude lower than the state-of-the-art. In the third type, the aqueous QDs were immobilized as a single layer on the interface between the OFRR inner wall and buffer solution with a surface density as low as 3 x 10(9) - 10(1)0cm(-2). The lasing threshold of 60 mu J/mm(2) was achieved. In the fourth type, we achieved optofluidic FRET lasing using aqueous QDs as FRET donors and Cy5 dye molecules as acceptors. We observed lasing from Cy5 emission band in QD-Cy5 pair when excited at QD absorption band, far away from Cy5 absorption maximum. We also report a comprehensive theoretical analysis of optofluidic FRET lasers that was performed based on a Fabry-Perot microcavity using a rate equation model. By comparing FRET lasing based sensors with conventional sensors using FRET signals obtained by spontaneous fluorescence emission, we show that for optimal pump fluence and FRET pair concentration, FRET lasing can lead to more than 20-fold enhancement in detection sensitivities of conformation changes for linker lengths in the Forster radius range.Publication Open Access Spectral tuning of lasing emission from optofluidic droplet microlasers using optical stretching(The Optical Society (OSA) Publishing, 2013) Brzobohaty, Oto; Jezek, Jan; Pilat, Zdenek; Zemanek, Pavel; Department of Physics; Aas, Mehdi; Jonas, Alexandr; Kiraz, Alper; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 22542We introduce tunable optofluidic microlasers based on active optical resonant cavities formed by optically stretched, dye-doped emulsion droplets confined in a dual-beam optical trap. To achieve tunable dye lasing, optically pumped droplets of oil dispersed in water are stretched by light in the dual-beam trap. Subsequently, resonant path lengths of whispering gallery modes (WGMs) propagating in the droplet are modified, leading to shifts in the microlaser emission wavelengths. Using this technique, we present all-optical, almost reversible spectral tuning of the lasing WGMs and show that the direction of tuning depends on the position of the pump beam focus on the droplet. In addition, we study the effects of temperature changes on the spectral position of lasing WGMs and demonstrate that droplet heating leads to red-tuning of the droplet lasing wavelength.Publication Open Access Tunable optofluidic microlasers based on optically stretched emulsion droplets(Society of Photo-optical Instrumentation Engineers (SPIE), 2013) Brzobohaty, Oto; Jezek, Jan; Pilat, Zdenek; Zemanek, Pavel; Department of Physics; Department of Electrical and Electronics Engineering; Aas, Mehdi; Jonas, Alexandr; Kiraz, Alper; Faculty Member; Department of Physics; Department of Electrical and Electronics Engineering; College of Sciences; N/A; N/A; 22542We introduce tunable optofluidic microlasers based on optically stretched, dye-doped emulsion droplets confined in a dual-beam optical trap. Optically trapped microdroplets of oil emulsified in water and stained with fluorescent dye act as active ultrahigh-Q optical resonant cavities hosting whispering gallery modes (WGMs) which enable dye lasing with low threshold pump powers. In order to achieve tunable dye lasing, the droplets are pumped with a pulsed green laser beam and simultaneously stretched by light in the dual-beam trap. For a given stretching power, the magnitude of the droplet deformation is dictated by the interfacial tension between the droplet and the host liquid which is adjustable by adding surfactants. Increase of power of the dual-beam trap causes a directly proportional change of the droplet stretching deformation. Subsequently, resonant path lengths of different WGMs propagating in the droplet are modified, leading to shifts in the corresponding microlaser emission wavelenghts. Using this technique, we present all-optical, almost reversible spectral tuning of the lasing WGMs and show that the direction of wavelength tuning depends on the position of the pump beam focus on the droplet, consistent with the deformation of originally spherical droplet towards a prolate spheroid. In addition, we study the effects of changes of the droplet and immersion medium temperature on the spectral position of lasing WGMs and demonstrate that droplet heating leads to red-tuning of the droplet lasing wavelength.Publication Open Access Tunable WGM resonators from optically trapped dye doped liquid crystal emulsion droplets(Society of Photo-optical Instrumentation Engineers (SPIE), 2014) Sery, Mojmir; Pilat, Zdenek; Jezek, Jan; Zemanek, Pavel; Department of Physics; Department of Electrical and Electronics Engineering; Aas, Mehdi; Kiraz, Alper; Faculty Member; Department of Physics; Department of Electrical and Electronics Engineering; College of Sciences; N/A; 22542We have built a complex apparatus for optical trapping, stretching, heating and concurrent whispering gallery mode (WGM) lasing excitation of liquid crystal (LC) emulsion micro-droplets doped with various fluorescent dyes. We have explored the changes of WGM lasing wavelength when the LC droplets were optically stretched or electrically heated beyond the transition to the isotropic phase. We have found that the range of lasing wavelengths was in some cases considerably higher than when we optically stretched ordinary fluorescent oil droplets in our previous experiments.