Experimentální biofotonika
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- ItemShifty invisibility cloaks(Optica Publishing Group, 2024-01-01) Courtial, Johannes; Bělín, Jakub; Soboňa, Matúš; Locher, Maik; Tyc, TomášWe recently presented what we believe are new cloaking strategies [Belin et al., Opt. Express 27, 37327 (2019)], abstracted from the properties of an ideal-lens cloak that exists in theory only. Key to the cloaking strategies is that objects on the cloak's inside are imaged to its outside. In the simplest case, interior objects appear simply shifted, forming a "shifty cloak". Here we connect our work to several previous investigations of shifty cloaks and other shifty devices, designed using standard transformation optics, thereby bringing our cloaking strategies closer to experimental realization. We investigate to the best of our knowledge novel combinations of shifty cloaks, specifically Janus devices and optical wormholes. Finally, we demonstrate an experimental realization of a paraxial shifty cloak.
- ItemNear-field digital holography: a tool for plasmon phase imaging(Royal Society of Chemistry, 2018-12-07) Dvořák, Petr; Kvapil, Michal; Bouchal, Petr; Édes, Zoltán; Šamořil, Tomáš; Hrtoň, Martin; Ligmajer, Filip; Křápek, Vlastimil; Šikola, TomášThe knowledge of the phase distribution of near electromagnetic field has become very important for many applications. However, its experimental observation is still technologically very demanding task. In this work, we propose a novel method for the measurement of the phase distribution of near electric field based on the principles of phase-shifting digital holography. In contrast with previous methods the holographic interference occurs already in the near field and the phase distribution can be determined purely from the scanning near-field optical microscopy measurements without need of additional far-field interferometric methods. This opens a way towards onchip phase imaging. We demonstrate the capabilities of the proposed method by reconstruction of the phase difference between interfering surface plasmon waves and by imaging the phase of single surface plasmon wave. We also demonstrate a selectivity of the method towards individual components of the field.
- ItemDesign of a broadband polarization controller based on silicon nitride-loaded thin-film lithium niobate(Optica Publishing Group, 2023-10-23) Čtyroký, Jiří; Petráček, Jiří; Richter, Ivan; Kuzmiak, VladimírA novel design of a polarization controller based on "etch-less" Si3N4-loaded thin film LiNbO3 is described. Broadband operation in the spectral range between 1.45 and 1.65 mu m is achieved by using a mode evolution TM/TE splitter/converter, two mode evolution 3-dB couplers, and two electro-optic phase shifters. Numerical simulations show that the on-chip insertion loss should not exceed 1 dB. A single TE-mode output can be adjusted by applying control voltages lower than 10 V for an arbitrary input polarization state.
- ItemSingle-Shot Aspect Ratio and Orientation Imaging of Nanoparticles(American Chemical Society, 2023-08-17) Bouchal, Petr; Dvořák, Petr; Hrtoň, Martin; Rovenská, Katarína; Chmelík, Radim; Šikola, Tomáš; Bouchal, ZdeněkPlasmonic nanoparticleswith surface plasmon resonance (SPR) andscattering response dependent on their geometry and surrounding environmentare predestinated to be used as optical probes for sensing and imaging.Optical microscopy is capable of observing nanoparticles in variousmedia, but their geometry remains hidden below the diffraction limit.Here, a wide-field optical imaging technique is demonstrated, restoringthe aspect ratio and orientation of individual nanoparticles via thepolarization anisotropy (PA) measurement of the scattered light. ThePA is mapped into a single nanoparticle image, formed by decomposingthe scattered light into longitudinal and transverse SPR modes andmanipulating their angular momentum. The wide-field images providethe aspect ratio and orientation of many deposited nanoparticles allowingtheir assessment in heterogeneous suspensions or time-resolved measurements.In calibration experiments, orientation measurement accuracy and excellentsensitivity to nanoparticles with specific aspect ratios are demonstrated.Subsequently, the method is deployed in the automatic shape-dependentcategorization of hundreds of nanoparticles in a heterogeneous mixture.The single-shot capability is demonstrated in the time-resolved imagingof the electrophoretic deposition process.
- ItemBound modes in the continuum in integrated photonic LiNbO3 waveguides: are they always beneficial?(Optica Publishing Group, 2023-01-02) Čtyroký, Jiří; Petráček, Jiří; Kuzmiak, Vladimír; Richter, IvanWe discuss several types of integrated photonic LiNbO3 waveguides supporting propagation of modes which can be classified as bound states in the continuum (BICs). The key properties leading to the existence of BICs (or quasi-BICs) considered here are the material anisotropy, the waveguide birefringence, or the combination of both. Typical examples are titanium diffused and proton exchanged waveguides in bulk LiNbO3 crystals and recently proposed dielectric-loaded waveguides on LiNbO3 thin films. Proton exchanged waveguides in thin film LiNbO3 are considered, too. These waveguide structures are discussed from the point of view of their benefit for applications, especially in electro-optic devices.