Fluctuations In Emission Intensity Research Articles

Blinking characteristics of organic fluorophores for blink-based multiplexing

Single-molecule fluorescence experiments have transformed our understanding of complex materials and biological systems. Whether single molecules are used to report on their nano-environment or provide for localization, understanding their blinking dynamics (i.e., stochastic fluctuations in emission intensity under continuous illumination) is paramount. We recently demonstrated another use for blinking dynamics called blink-based multiplexing (BBM), where individual emitters are classified using a single excitation laser based on blinking dynamics, rather than color. This study elucidates the structure-activity relationships governing BBM performance in a series of model rhodamine, BODIPY, and anthraquinone fluorophores that undergo different photo-physical and-chemical processes during blinking. Change point detection and multinomial logistic regression analyses show that BBM can leverage spectral fluctuations, electron and proton transfer kinetics, as well as photostability for molecular classification—even within the context of a shared blinking mechanism. In doing so, we demonstrate two- and three-color BBM with ≥ 93% accuracy using spectrally-overlapped fluorophores.

A Proposal to Evaluate Electron Temperature and Electron Density Fluctuations Using Dual Wavelength Emission Intensity Tomography in a Linear Plasma

A procedure to calculate normalized electron temperature and electron density fluctuations using dual wavelength emission intensity tomography in a linear magnetized plasma is proposed. Expression of emission intensity is modeled as \(\epsilon_{k} \propto T_{\text{e}}^{\alpha_{k}}n_{\text{e}}^{2}\) where \(\epsilon_{k}\) is emission intensity, Te is electron temperature, ne is electron density, k = 1 for ArI, and k = 2 for ArII. Using the model, normalized Te and ne fluctuations can be expressed as linear function of both the normalized emission intensity fluctuations. To calculate αk, we perform least squares method between real \(\epsilon_{k}\) measured with a tomography system and artificial \(\epsilon_{k}\) reconstructed using Te and ne measured with a Langmuir probe located downstream of the tomography system. The results show that α1 = 2.2 and α2 = 2.6, and normalized Te and ne fluctuations are preliminarily evaluated from emission intensity tomography data.

Nonlinear dynamics of attenuation behavior in combustion oscillations in a swirl-stabilized combustor

We experimentally examine the attenuation behavior in combustion oscillations from the perspective of symbolic dynamics, dynamical systems theory, complex networks, and machine learning. The periodicity of combustion oscillations gradually decreases with increasing amount of air steadily injected into flame base, maintaining a nearly in-phase synchronized state between pressure and OH* chemiluminescence emission intensity fluctuations. Both the dynamic behaviors of pressure and OH* chemiluminescence emission intensity fluctuations in the attenuation regime close to well-suppressed combustion oscillations exhibit pseudo-periodic oscillations with deterministically nonperiodic intercycle dynamics. They lead to noisy chaotic oscillations and exhibit a desynchronized state during well-suppressed combustion oscillations.

Laser-based generation of random numbers

Optoelectronics The security of our digital networks is underpinned by the ability to generate streams of random numbers or bits. As networks expand in an ever-connected way, the challenge is to increase the generation rate of the random numbers to keep pace with demand. Kim et al. designed a chip-scale laser diode that generates random bits at an ultrahigh rate (see the Perspective by Fischer and Gauthier). By tailoring the geometry of the cavity, they were able to exploit the spatiotemporal interference of many lasing modes to generate picosecond-scale emission intensity fluctuations in space and time, producing ultrafast random bit streams in parallel. Such a device will find a wide range of applications requiring an ultrafast, compact, robust, and energy-efficient random bit generator. Science , this issue p. [948][1]; see also p. [889][2] [1]: /lookup/doi/10.1126/science.abc2666 [2]: /lookup/doi/10.1126/science.abg5445

Massively parallel ultrafast random bit generation with a chip-scale laser.

Random numbers are widely used for information security, cryptography, stochastic modeling, and quantum simulations. Key technical challenges for physical random number generation are speed and scalability. We demonstrate a method for ultrafast generation of hundreds of random bit streams in parallel with a single laser diode. Spatiotemporal interference of many lasing modes in a specially designed cavity is introduced as a scheme for greatly accelerated random bit generation. Spontaneous emission, caused by quantum fluctuations, produces stochastic noise that makes the bit streams unpredictable. We achieve a total bit rate of 250 terabits per second with off-line postprocessing, which is more than two orders of magnitude higher than the current postprocessing record. Our approach is robust, compact, and energy-efficient, with potential applications in secure communication and high-performance computation.

Random laser spectroscopy and replica symmetry breaking phase transitions in a solvent-rich polymer thin film waveguide

We present the statistical analysis of random lasing intensity fluctuations in a 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminos-styryl)-4H-pyran (DCM) doped polyvinyl alcohol (PVA) thin film waveguide subjected to a constant heat treatment. The microscopic changes occurring in the density of the polymer thin film during the various stages of solvent evaporation are probed using the changes in the statistics of random laser (RL) emission intensities. In the solvent rich wet film, stronger RL emission intensity fluctuations are observed compared to the dried film, leading to a relatively slower decay of the survival function distribution of the emission intensities for a mode at the gain maxima of the averaged spectrum. The mode interactions in the wet and dried films, studied using covariance between lasing mode intensities, are found to be different. Further, replica symmetry breaking studies indicate the changes in the mode interactions with the microscopic modifications in the system during solvent evaporation at a constant pump energy above the lasing threshold. The statistical analyses of the RL emission intensity fluctuations are proposed as a spectroscopic tool to probe material properties.

The influence various sources of fluctuation on the statistical parameters of the vertical cavity surface emitting lasers output radiation

Based on statistical modeling, a numerical analysis of the effects exerted by different factors (fluctuations of the spontaneous emission intensity, nonequilibrium carrier concentration, injection current density) on the statistical characteristics of radiation at the output of surface emitting semiconductor lasers in the region of polarization instability has been performed. In this region the effect of fluctuations is maximal, offering the possibility for substantiated conclusions about relative effects of the parameters. In a theory of semiconductor lasers it is thought that the intensity fluctuations of spontaneous emission represent the dominant source of fluctuations, whereas all other sources may be neglected. As demonstra ted by the results of conducted statistical modeling, this statement is too rigorous; moreover, such a source is not dominant. Taking into consideration fluctuations of the carrier concentration, which result in fluctuations of the amplification factor, we can derive a complete set of the relationships observed experimentally. This result cannot be associated with features our model because in our theory spontaneous emission is a significant factor. If the influence of spontaneous emission would be the dominant factor, it would affect the simulation results. The obtained data make it possible to doubt the key role of the spontaneous emission intensity fluctuations in the process of statistical characteristics formation for the output radiation and to take into account fluctuations of the nonequilibrium carrier concentration.

Fluorescence Blinking Beyond Nanoconfinement: Spatially Synchronous Intermittency of Entire Perovskite Microcrystals.

Abrupt fluorescence intermittency or blinking is long recognized to be characteristic of single nano-emitters. Extended quantum-confined nanostructures also undergo spatially heterogeneous blinking; however, there is no such precedent in dimensionally unconfined (bulk) materials. Herein, we report multi-level blinking of entire individual organo-lead bromide perovskite microcrystals (volume=0.1-3 μm3 ) under ambient conditions. Extremely high spatiotemporal correlation (>0.9) in intracrystal emission intensity fluctuations signifies effective communication amongst photogenerated carriers at distal locations (up to ca. 4 μm) within each crystal. Fused polycrystalline grains also exhibit this intriguing phenomenon, which is rationalized by correlated and efficient migration of carriers to a few transient nonradiative traps, the nature and population of which determine blinking propensity. Observation of spatiotemporally correlated emission intermittency in bulk semiconductor crystals opens the possibility of designing novel devices involving long-range (mesoscopic) electronic communication.

Fluorescence Blinking Beyond Nanoconfinement: Spatially Synchronous Intermittency of Entire Perovskite Microcrystals

AbstractAbrupt fluorescence intermittency or blinking is long recognized to be characteristic of single nano‐emitters. Extended quantum‐confined nanostructures also undergo spatially heterogeneous blinking; however, there is no such precedent in dimensionally unconfined (bulk) materials. Herein, we report multi‐level blinking of entire individual organo–lead bromide perovskite microcrystals (volume=0.1–3 μm3) under ambient conditions. Extremely high spatiotemporal correlation (>0.9) in intracrystal emission intensity fluctuations signifies effective communication amongst photogenerated carriers at distal locations (up to ca. 4 μm) within each crystal. Fused polycrystalline grains also exhibit this intriguing phenomenon, which is rationalized by correlated and efficient migration of carriers to a few transient nonradiative traps, the nature and population of which determine blinking propensity. Observation of spatiotemporally correlated emission intermittency in bulk semiconductor crystals opens the possibility of designing novel devices involving long‐range (mesoscopic) electronic communication.

Single Molecule Fluroescence Approaches to Plasma Membrane Biophysics

The plasma membrane is the fundamental component of a cell. Not only is the plasma membrane the outer barrier of the cell, it also regulates many cellular functions including endocytosis, exocytosis, receptor signalling and cell migration. As essential as the plasma membrane is, methods to capture the structure of and the proteins within the membrane on biologically-relevant length scales remain lacking. A particularly vexing issue is whether membrane rafts - regions of locally-ordered lipids and associated proteins observed in model membrane systems - are present in intact cells. Much of the previous evidence for these rafts relies on invasive biochemical techniques and the little imaging evidence available shows that these regions are small (< 100 nanometres) and short-lived (< 100 milliseconds).While still limited by the diffraction limit of visible light, single-molecule fluorescence imaging allows such small and transient features to be detected. We will present three new approaches to investigating these structures in intact membranes. The first is a spectral fluorescence correlation spectroscopy approach demonstrating the presence of regions of local membrane order and disorder within live cell membranes. These regions have lifetimes of 5 to 25 ms and through simulations we can show that both probe diffusion and domain diffusion give rise to the observed fluctuations in emission intensity. The second technique is a self-calibrating image analysis method that is capable of capturing the coordination of local differences in membrane order with membrane protein distribution within intact cells. This approach demonstrates the presence of protein sorting within intact cells as well as the effect of expression level on effective protein sorting. The final technique is a 3D super-resolution method to map the nanometer-scale topography of the plasma membrane. We will show initial results demonstrating our ability to map these topographical features and their correlation with protein sorting.

Synthetic polymers for solar harvesting

Synthetic polymers incorporating appropriate chromophores can act as light harvesting antennae for artificial photosynthetic systems. The photophysical processes occurring in a polymer based on phenylene vinylene have been investigated at the single chain level and in bulk solution to study energy transfer processes. Most single chains of an alternating copolymer of 2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene and 1,4-phenylene vinylene (alt-co-MEH-PPV) dispersed in a transparent polymer matrix act as single chromophore emitters demonstrating that energy transfer is an efficient process in these polymers. However for individual polymer chains there are fluctuations in emission intensity ('blinking') and shifts in emission spectra, decay lifetimes and emission dipole orientation occurring on a time-scale of tens of seconds. Fluorescence blinking also occurs on a sub-millisecond time-scale and follows exponential kinetics, whereas the longer blinking is better described by a power law. These observations can be interpreted as arising from environmental relaxation processes and/or changes in the emitter and demonstrate the wide distribution of photophysical behaviours that can be observed among the individual molecules of a polymer sample. The relevance of these studies to the application of polymer materials for solar harvesting is highlighted.

Conformation-dependent Room-temperature Emission Spectra of Single MEH-PPV Chains in Different Polymer Matrices

Abstract Emission spectra of single molecules of the conjugated polymer MEH-PPV in host matrices of ZEONEX® and polystyrene are reported. Depending on the matrix, the polymer chains attain different conformations, from compact defect cylinders to extended defect coils. The conformations are correlated with photophysical properties, such as emission intensity fluctuations, and with shapes and peaks of emission spectra. The observed bimodal distribution of the spectral peaks is related to distribution in conjugated segment lengths.

Hysteresis of giant intensity fluctuations of emission for two-dimensional electrons in the conditions for the integer quantum Hall effect

On observation of giant intensity fluctuations for the emission of two-dimensional electrons in two-layer electronic systems in the conditions for the integer quantum Hall effect, a hysteresis is detected in the magnetic-field dependences of the amplitude in these fluctuations. It is shown that the hysteresis is observable only at a certain thickness for the barrier separating the electronic layers, and the thickness is such that the inter-layer spacing is comparable with the spacing between electrons in the two-dimensional plane. It is established that the amplitude for the hysteresis in a magnetic field depends on the temperature and on the difference between the concentrations of electrons in the layers. The observed phenomenon can suggest that, in coupled two-layer electronic systems in the conditions for the quantum Hall effect, a new coherent ordered state characterized by two critical temperatures is formed.

Translational and Rotational Dynamics of Individual Single-Walled Carbon Nanotubes in Aqueous Suspension

Near-infrared fluorescence videomicroscopy has been used to study simultaneously the translational and rotational diffusion of individual semiconducting single-walled carbon nanotubes (SWCNTs) in aqueous suspension. Analysis of translational trajectories revealed diffusion coefficient values from approximately 0.3 to 6 microm(2)/s. The nanotube lengths deduced from these values ranged between approximately 130 nm and 6 microm. From the minor bending motions observed in individual nanotubes several micrometers in length, we confirmed that the shorter SWCNTs of primary interest here can be considered to be rigid rods under normal conditions. Because the nanotubes act as highly rigid, photostable, steady, and anisotropic fluorophores, it was possible to monitor their rotational reorientations through fluctuations in emission intensity under linearly polarized excitation. The magnitudes of observed orientational fluctuations varied substantially among individual nanotubes. These magnitudes correlated strongly with translational diffusion coefficient, reflecting the length dependence of both types of motions. Combined translational and rotational measurements also revealed the influence of local environment on nanotube mobility.

Two-Dimensional Spectroscopic Analysis of a Flame Using Highly Preheated Combustion Air

The effect of highly preheated combustion air on the combustion characteristics of propane flames is presented. Data have been obtained on the spatial distribution of emission intensity from selected radicals, fluctuations of emission intensity, and flame temperature using several diagnostic techniques. Several propane and high-temperature air flames, produced with the crossflow diffusion of gas into highly preheated combustion air (obtained by a regenerative combustion facility) having normal oxygen content and reduced oxygen content (<21% by volume) have been examined. The diagnostics used include a UV-charge coupled device (CCD) camera integrated with an interference filter, a high-speed video camera, array of thermocouples, and gas analyzers for NO x and O 2 . The UV-CCD camera fitted with the desired optical interference filter provided the spontaneous emission signature of the flames produced. Fast Fourier transform applied to the video camera recorded image provided information on the two-dimensional distribution of emission intensity fluctuation. The emission results show that the intensity level of OH and C 2 radicals in the flame with highly preheated and lower oxygen concentration air is much lower than the corresponding normal air flames. The fluctuations of emission intensity with highly preheated combustion air are significantly lower in the high-temperature combustion region of the flame. The temperature measured from the ratio of the emission intensities had much higher spatial resolution than those obtained with the conventional thermocouple array. The results indicate that preheated air drastically reduces both the temperature gradient and temperature fluctuations in the flames. NO x measurements were made in the exhaust gas using a chemiluminescence analyzer. The results showed that reducing the oxygen concentration in the high temperature combustion air reduces NO x emission levels in the exhaust gas.

In vivo fluorescence correlation microscopy (FCM) reveals accumulation and immobilization of Nod factors in root hair cell walls.

Fluorescence correlation microscopy (FCM) is a new single-molecule detection technique based on the confocal principle to quantify molecular diffusion and concentration of fluorescent molecules (particles) with sub-micron resolution. In this study, FCM is applied to examine the diffusional behaviour of fluorescent Nod factor analogues on living Vicia sativa root hairs. Three recently described Nod factors with a fluorescent acyl chain (Goedhart et al. Biochemistry 1999, 38, 10898-10907) were used. Plasmolysis of fluorescently labelled root hairs showed that the Nod factors are predominantly located in the cell wall, as hardly any fluorescence could be detected in the plasma membrane. After Nod factor-induced root hair deformation, the new outgrowth was not labelled, indicating a lack of migration of Nod factors to the newly synthesized cell wall. In agreement, FCM showed a > 1,000-fold reduction of molecular mobility of the fluorescence Nod factors upon binding to the cell wall. In addition, FCM demonstrated that Nod factors, when exogenously applied in aqueous solution at 10 nM, markedly concentrate in the cell wall of root hairs (up to 50-fold). The feasibility of applying FCM for the study of living plant cells as well as the implications of our results for the perception of Nod factors are discussed.

Incompletely desolvated droplets in argon inductively coupled plasmas: their number, original size and effect on emission intensities

The presence of incompletely desolvated droplets in the Ar ICP results in changes in Ca I emission intensity as large as a factor of 20 and variations in the Ca II emission intensity as great as a factor of 2.5. Most of the signal fluctuations are due to the effect of vaporizing droplets or their vaporization products on analyte atoms and ions produced from previously vaporized and atomized droplets. Above the normal analytical zone some peaks in the time-resolved analyte emission intensity result from vaporizing, desolvated particles. The number of incompletely desolvated droplets in the plasma varies from more than 15000 per second low (5 mm above the load coil) in the plasma to less than 100 per second high (above the normal analytical zone) in the plasma. The number of incompletely desolvated droplets in the plasma is a strong function of the center (nebulizer) gas flow rate as well as the applied power. Emission intensities from locations within about 1.4 mm of a vaporizing droplet are dramatically affected. Ca I emission intensities are enhanced near vaporizing droplets while Ca II emission intensities are depressed. The size of droplets at the exit of the spray chamber that produce detectable laser light scattering signals and emission intensity fluctuations are greater than about 12 μm in diameter. The size of droplets that are incompletely desolvated in the plasma depends on the applied power and center (nebulizer) gas flow rate. The results have far reaching implications on fundamental understanding of processes controlling emission intensities in Ar ICPs. Potential biases introduced into time-integrated measurements due to the presence of incompletely vaporized droplets must be considered.

Signal fluctuations due to individual droplets in inductively coupled plasma atomic emission spectrometry.

Large emission intensity fluctuations are observed from analyte species in inductively coupled plasmas. Relative standard deviations are as large as 71% when emission is viewed with time resolution of 10 microseconds. Low in the plasma, peaks in atom emission intensity are accompanied by depressions in ion emission. This behavior appears to be due to local cooling by aerosol droplets. High in the plasma, peaks in atom emission are followed by peaks in ion emission. These emission spikes result from atomization and ionization of analyte from vaporizing particles. Laser light scattering experiments show that droplets or particles exist in a conventional 1.0-kW plasma up to 20 mm above the load coil. Emission signals detected high in the plasma correlate with laser light scattering signals below.

Effect of emission intensity fluctuations on the accuracy of temperature measurements on a plasma stream by means of absolute line intensities

Effect of emission intensity fluctuations on the accuracy of temperature measurements on a plasma stream by means of absolute line intensities

Night airglow zenith intensity variations at El Leoncito Observatory, Argentina

Seasonal and diurnal variations for [O I] λ5577 A, [O I] λ6300 A, and NaI λλ5890–5896 A emissions during 1967 are reported. The southern hemisphere station results for λ5577 and λ6300 emissions are similar to results reported from a northern hemisphere tropical station. The λ6300 emission variation is in phase for both hemispheres. The λλ5890–5896 emission variation is seasonal, the primary maximum being in the fall and the secondary maximum being in the spring, i.e., 6 months out of phase for both hemispheres. The suggested connection between the λ6300 emission intensity fluctuations and electric fields in the F layer is strengthened.