Guided-Mode Resonance Biochemical Sensor Technology

So far, the optical trapping potential is controlled by tuning the physical conditions of the system. Herein, for the first time, an approach, in which the induced optical force or optical potential is controlled, by an external chemical stimulus, is reported. The key to realize this is to design an optical trapping condition in conjunction with resonant excitation, the so‐called optical resonance effect (ORE). For this purpose, phenalenone, a well‐known triplet photosensitizer, is embedded inside polystyrene particles. The optical resonance effect is achieved through a two‐laser system: a 405 nm widefield laser to excite the phenalenone molecules to T1 state and a 488 nm trapping laser to induce the T1–Tn–T1 resonance cycle. Thus, the triplet state is mainly responsible for the optical force enhancement. Since oxygen is an excellent triplet quencher, the triplet populations, and hence, the optical force is controlled by changing the dissolved oxygen concentration. The results presented here pave the way to chemically control the optical force through ORE with promising applications in several research fields ranging from physics to biology.

A spherical particle can be used as a lens for focusing laser radiation. It has potential applications in high-density data storage and high-resolution optical lithography for nano-device fabrication.

A theoretical demonstration of optical bistability in periodic layered media, particularly in long-period GaAs/AlAs superlattices is presented. The proposed structure consists of a periodic multilayer system, as opposed to previously demonstrated nonlinear bistable devices which employed Fabry-Perot etalons. The optical resonance effect which is essential for bistable devices is, in this case, induced by a refractive index modulation. The nonlinear active medium is distributed in the whole structure rather than placed between the two mirrors of a Fabry-Perot cavity. It is shown by a complete calculation of wave propagation in the periodic nonlinear medium that a multiple valued feature appears in the structure's nonlinear reflectivity spectrum. The input/output characteristics of the structure exhibit bistable hysteresis similar to that of a nonlinear Fabry-Perot etalon.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Intermolecular charge transfer (CT) states at the interface between electron-donating and electron-accepting (A) materials in organic thin films are characterized by absorption and emission bands within the optical gap of the interfacing materials. In this contribution, we will discuss the fundamental properties of CT states and link them to organic solar cell and light emitting diode performance. Furthermore, we introduce a new device concept, using an optical cavity resonance effect to boost CT absorption at photon energies below the optical gap of both donor and acceptor, enabling sensitive narrow-band, near infrared photo-detection.

Polymer blends: Processing, morphology and properties: E. Martuscelli. Plenum Publishing Corp., New York (1981), 510 pp. Price: $59.50

The elementary solutions of the wave equation in a periodic waveguide (Fig. 1) are waves of the Floquet-Bloch type.1,2 They are formed by the superposition of a set of plane waves, called space harmonics (SHs). An equivalent description is possible3 by the coupled mode formalism, considering plane waves (the SHs) as the elementary excitations which are coupled by the structure of the guide. For a discussion of wave propagation over extended areas of periodic guides we adopt here the Bloch viewpoint. Below, we summarize briefly the properties of optical Bloch waves of general direction s → of propagation. We show their direct excitation by a prism coupler, permitting a measurement of the complete dispersion characteristic ω β → of the guide. We then discuss transitions between periodic and nonperiodic guides, showing the unusual optical effect of negative refraction.

Recent advances in nanophotonics have demonstrated that various optical resonances in nanostructures can achieve strong field confinement with substantially suppressed scattering. This study investigates the optical Kerr effect (OKE) enhancement in high-refractive-index metasurfaces featuring non-BIC trapped-mode resonances, using gallium phosphide (GaP) as a model material. Three-dimensional finite-difference time-domain simulations reveal a significant enhancement of the effective second-order refractive index, reaching values up to 700 times greater than bulk GaP. The numerical results show strong electromagnetic field localization at the trapped-mode resonance, characterized by a wide transmittance dip (low Q-factor) and near-unity reflectance. Remarkable stability is observed, with the OKE enhancement maintaining less than 5% variation for moderate polarization angles and tolerating random nanohole rotations that model fabrication imperfections. Compared to bound states in the continuum (BIC), the non-BIC trapped mode demonstrates superior robustness to structural disorder while achieving comparable nonlinear enhancement. These findings suggest promising applications in reflective nonlinear optics, particularly for high harmonic generation and polarization-insensitive photonic devices.

In this paper, we develop dielectric micro-optical sensors based on whispering gallery mode phenomenon (WGM) for monitoring and treating of drinking water environments through two phases. Some sort of chemical impurities could be toxic and carcinogenic to humans and animals. The biogeochemical reactions are governing the chance and the movement of these impurities in the drinking water environment. Based on that, the first phase in this paper will focus to measure and quantify the concentration of these impurities in the water medium. While the second phase will exploit the use of the light based on the same phenomena (WGM) to create water treatment and purification using a nano charged dielectric polymeric beads. In the current paper, a high-resolution micro-optical sensor concept is used to detect these chemical impurities. The sensing element is a silica microsphere acts as an optical resonator. The proposed technique aims to provide preliminary results demonstrating the practical success of these sensors for effective monitoring of chemical impurities concentrations and contaminants which can cause serious kidney damage and possibly death. The second phase is basically depend on the optogenetic approach which is a biological technique that involves the use of light to control cells in living tissue, typically neurons that have been genetically modified to express light-sensitive ion channels. In this approach, the beads will be coated with a photosensitive protein called channelrhodopsin. This protein is a subfamily of retinylidene proteins (rhodopsins) that function as light-gated ion channels. They serve as sensory photoreceptors in unicellular green algae, controlling phototoxic: movement in response to light. The nano coated beads then poled for +4hrs under 1MV/m. When these nano charged beads mixed with water that have high turbidity, the beads starts to attract the colloids in that water. Since, the beads are coated with a photosensitive protein so by using a specific wavelength of the light we can control the motion of the spheres inside the water. Using a pulse width modulation (PWM) algorithm to control the speed of switching on/off the light; so it becomes easy to control the nano beads. The higher duty cycles for the PWM the charged beads makes the colloids aggregate and come together in a very short time (< 5 min) compared to the typical flocculation approaches that needs (~55min). This approach is called an optical flocculation technique and it shows one order of magnitude enhancement in the flocculation time. Results indicate that the WGM based-sensors are sensitive enough to refractive index changes in the case of liquid media (water). Experiments were carried out to validate the analysis and to provide an assessment of this sensor concept. Also, Preliminary experiments were carried out to provide an assessment of this concept using more than one duty cycle to control the speed of the beads. Results shows that we can purify the drinking water in time less than 3 minutes under 80% duty cycle using this approach.

We report fabrication of THz fiber Bragg gratings (TFBG) using CO(2) laser inscription on subwavelength step-index polymer fibers. A fiber Bragg grating with 48 periods features a ~4 GHz-wide stop band and ~15 dB transmission loss in the middle of a stop band. The potential of such gratings in the design of resonant sensors for the monitoring of paper quality is demonstrated. Experimental spectral sensitivity of the TFBG-based paper thickness sensor was found to be ~-0.67 GHz/10 μm. A 3D electromagnetic model of a Bragg grating was used to explain experimental findings.

Application of FBG sensors for geotechnical health monitoring, a review of sensor design, implementation methods and packaging techniques

Laser directly writing of nanostructures on metal film surfaces with optical near field effects has been investigated. Spherical silica particles (500-1000 nm) were placed on metal films. After laser illumination with a pulsed ultraviolet laser, naoholes were obtained at the original position of the particles. The mechanism of the formation of nanostructure pattern was investigated and found to be the near-field optical resonance effect induced by particles on the surface. The size of the nanohole has been studied as a function of laser fluence and silica particle size. A comparison with relative theoretical calculations of near-field light intensity distribution showed good agreement with the experiment results. The method of particle enhanced laser irradiation allows the study of field enhancement effects as well as its potential applications for nanolithography.

Index-matching fluid immersion as means for reducing optical resonance effects in rotary compensators

Principles and applications are described for a form of Doppler-free optical double resonance spectroscopy which uses amplitude modulation sidebands (v L ±v) imposed on a single laser frequency (v L ). The sidebands are generated by passing the carrier radiationv L through an electro-optic modulator, driven at a radiofrequency ν, which enables the intensity and polarization characteristics of the emerging radiation to be varied for enhancement of selected double-resonance processes. The technique has been applied to infrared-infrared double-resonance studies of the Stark effects of a variety of molecules—13CH3F,12CH3F, PH3,15NH3, GeH4, SiH4, and CH3D—for which physical results are presented and discussed. These results include determination of extremely small electric dipole moments (10−3–10−5 debye) for GeH4 and CH3D and, for the dipole moment of PH3, a vibrational state dependence which is extremely small (Δμ=0.0028(5) debye for ∣Δv 2∣=1) and a rotational state dependence which is of an unexpected sign. The spectra recorded in some cases display unusual polarization and optical saturation effects which deviate markedly from the predictions of a simple three-wave polarization theory.

In this paper a rigorous quantum mechanical multi-valley model is developed to assess the optical equivalent of the electrical Gunn effect: a laser beam pumps free electrons from the central conduction band valley of n-doped bulk GaAs towards its satellite values. The computational complexities involve a central fully nonparabolic degenerated (Gamma) - valley, an anisotropic L-valley of arbitrary degeneracy, impurity assisted, thermal and hot polar optical phonon assisted intravalley absorption mechanisms, and intervalley phonon assisted equivalent and nonequivalent intervalley absorption mechanisms. The influences of the doping concentrations, electron temperature, optical power density and the equivalent LL-intervalley deformation potential (IDP) on the magnitude and relaxation time of the optical Gunn effect are discussed and compared with experimental results. We found that the optically induced nonlinear absorption and intervalley transfer strongly depend on the equivalent LL-IDP. The large scattering on the available data for LL-IDP leads to large variations in the theoretical estimations. Under optical plasma resonance conditions we find an energy relaxation time in the L-valley of about 0.3 to 2.2 ps, a nonlinear refractive index n<SUB>2</SUB> of about 2.7 to 3.75 X 10<SUP>-81</SUP> cm<SUP>2</SUP>/W and e.g. a 10 percent electron transfer of about 1.8 to 3.2 MWcm<SUP>-2</SUP>.

III-V compound semiconductor nanowires (NWs) are being developed for the next generation of optoelectronic devices such as photodetectors, photovoltaics, betavoltaics and thermoelectrics. The self-assisted vapor-liquid-solid method is now a well-established technique for the growth of III-V NWs on silicon substrates. In this method, an array of holes in a SiO2 film is used for metal droplet formation, which seeds the growth of vertically oriented NWs within a periodic array. The free lateral surfaces of NWs allow elastic relaxation of lattice misfit strain without the generation of dislocations, permitting unique heterostructures and the direct integration of III-V materials on silicon substrates. Furthermore, NWs permit high optical absorption due to an optical antenna effect. The optical absorption in NW arrays can exceed that due to a thin film of equivalent thickness, enabling high efficiency NW-based photonic devices. Furthermore, optical resonances that depend on the NW diameter allow multispectral absorption. Some of the challenges associated with NW materials and devices, including quantum dot formation, will be illustrated.