Far-Field Subwavelength Straight-Line Projection/Imaging by Means of a Novel Double-Near-Zero Index-Based Two-Layer Metamaterial.

In this paper, for the first time, tuned near-zero-index materials are used in a structure for the long-distance projection of very closely spaced objects with subwavelength separation. Near-zero-index materials have never been used for subwavelength projection/imaging. The proposed novel structure is composed of a two-layer slab that can project two slits with a subwavelength separation distance to a long distance without diverged/converged interference of the two imaged waves. The two-layer slab consists of a thin double-near-zero (DNZ) slab with an obtained tuned index of 0.05 and thickness of 0.04λ0 coupled with a high-index dielectric slab with specific thicknesses. Through a parametric study, the non-zero index of the DNZ layer is tuned to create a clear image when it is coupled with the high-index dielectric layer. The minimum size for the aperture of the proposed two-layer slab is 2λ0 to provide a clear projection of the two slits. The space between the slits is λ0/8, which is five times beyond the diffraction limit. It is shown that, through the conventional methods (e.g., only with high-index dielectric slabs, uncoupled with a DNZ layer), it is impossible to clearly project slits at a large distance (~λ0) due to the diffraction limit. An analytical analysis, as well as numerical results in a finite-element-based simulator, confirm the function of the proposed structure.

Accurate spectroscopy with sCMOS cameras at ultra-low intensities of light.

Modern image detectors with exceptionally low readout noise of about one electron (e-) per pixel allow for applications with ultra-low levels of light intensity. In this Letter, we report a property of scientific CMOS detectors that makes accurate spectroscopy at ultra-low levels of illumination depending on a thorough calibration procedure. Our results reveal that pixel sensitivity to light may have significant nonlinearity at accumulation levels smaller than 50e- per pixel. The sensitivity decreases by a factor of ∼0.7 at an accumulation level of ∼1e- per pixel and photon detection rate of about 170 Hz. We demonstrate that the nature of this nonlinearity might be quite complicated: the photoelectric response of a pixel depends on both the number of accumulated electrons and the detection count rate (at rates larger than 250 Hz).

In situ measurements of intracellular thermal conductivity using heater-thermometer hybrid diamond nanosensors.

Understanding heat dissipation processes at nanoscale during cellular thermogenesis is essential to clarify the relationships between the heat and biological processes in cells and organisms. A key parameter determining the heat flux inside a cell is the local thermal conductivity, a factor poorly investigated both experimentally and theoretically. Here, using a nanoheater/nanothermometer hybrid made of a polydopamine encapsulating a fluorescent nanodiamond, we measured the intracellular thermal conductivities of HeLa and MCF-7 cells with a spatial resolution of about 200 nm. The mean values determined in these two cell lines are both 0.11 ± 0.04 W m-1 K-1, which is significantly smaller than that of water. Bayesian analysis of the data suggests there is a variation of the thermal conductivity within a cell. These results make the biological impact of transient temperature spikes in a cell much more feasible, and suggest that cells may use heat flux for short-distance thermal signaling.

The challenge of intracellular temperature.

This short review begins with a brief introductory summary of luminescence nanothermometry. Current applications of luminescence nanothermometry are introduced in biological contexts. Then, theoretical bases of the "temperature" that luminescence nanothermometry determines are discussed. This argument is followed by the 105 gap issue between simple calculation and the measurements reported in literatures. The gap issue is challenged by recent literatures reporting single-cell thermometry using non-luminescent probes, as well as a report that determines the thermal conductivity of a single lipid bilayer using luminescence nanothermometry. In the end, we argue if we can be optimistic about the solution of the 105 gap issue.

Formation of interstitial silicon defects in Si- and Si,P-doped nanodiamonds and thermal susceptibilities of SiV- photoluminescence band.

We have produced two types of synthetic nanodiamonds Si- and Si,P-doped and have characterized the thermal susceptibilities of the spectral band of silicon-vacancy (SiV-) centers at approximately 740 nm in each case. The covered temperature range from 295 to 350 K is of interest for thermometry in biological systems. Comparison of the relative brightness of the Si- and Si,P-doped crystals shows that phosphorous significantly increases average concentration and homogeneity of distribution of SiV- centers in nanodiamonds. Moreover, linear dependence on temperature of the zero-phonon line width in Si-doped crystals is 0.061(2) nm K-1 but is 0.047(3) nm K-1, about 35% smaller in Si,P-doped nanodiamonds. This proves control of SiV- properties with additional chemical doping and close proximity of Si and P atoms.

All-optical single-nanoparticle ratiometric thermometry with a noise floor of 0.3 K Hz(-1/2).

We demonstrate a temperature noise floor of 0.3 K Hz(-1/2) and a long-term stability better than 0.6 K (peak-to-peak value) using a single crystal of diamond smaller than 50 nm across and containing about 100 nitrogen-vacancy centres as a temperature sensor. We compare the achieved characteristics to other single-particle sensors and show that it is one of the best ratiometric all-optical nano-probes of temperature to date.

All-optical thermometry and thermal properties of the optically detected spin resonances of the NV(-) center in nanodiamond.

The negatively charged nitrogen-vacancy (NV(-)) center in diamond is at the frontier of quantum nanometrology and biosensing. Recent attention has focused on the application of high-sensitivity thermometry using the spin resonances of NV(-) centers in nanodiamond to subcellular biological and biomedical research. Here, we report a comprehensive investigation of the thermal properties of the center's spin resonances and demonstrate an alternate all-optical NV(-) thermometry technique that exploits the temperature dependence of the center's optical Debye-Waller factor.

Accurate measurements of the Raman scattering coefficient and the depolarization ratio in liquid water.

Despite a long history, the Raman scattering coefficient of water has so far only been measured with 10% uncertainty using a 95% confidence interval. In this paper, we present an experiment where we have achieved 1.5% uncertainty by using a low concentration of Rhodamine 6G in ethanol as a reference along with accurate consideration of polarization-related effects and the geometry of the experimental setup. We have found that the photon-to-photon Raman scattering coefficient of the OH stretching band of liquid water is (1.84±0.03)×10(-4) m(-1) when integrated over the spectral frequency range from 620 to 700 nm while the exciting laser operates at 532 nm. We have also accurately measured the depolarization ratio across this band.

Spontaneous Spectral Diffusion in CdSe Quantum Dots.

Spectral diffusion of the emission line of single colloidal nanocrystals is generally regarded as a random process. Here, we show that each new spectral position has a finite memory of previous spectral positions, as evidenced by persistent anticorrelations in time series of spectral jumps. The anticorrelation indicates that there is an enhanced probability of the charge distribution around the nanocrystal returning to a previous configuration. We show both statistically and directly that this memory manifests as an observable spontaneous "relaxation" in the absence of a pump laser, so that spectral diffusion progresses in a manner of "two steps forward and one step back".

Luminescence of nitrogen-vacancy centers in nanodiamonds at temperatures between 300 and 700 K: perspectives on nanothermometry.

It is shown that the intensity of photoluminescence of nitrogen-vacancy (NV) centers in nanodiamond decreases 4-fold (with a wide spread among nanocrystals) when the surrounding temperature rises from 300 to 670 K. The effect is accompanied by a 2.7-fold decrease in the luminescence lifetime but negligible changes in the shape of the emission spectra. The heating-cooling circle is reversible. The effect is suggested to be practically useful for thermometry with nanometre spatial resolution but also stimulates deeper insight into the photophysics and photochemistry of NV-centers.

Numerical modeling of light propagation in a hexagonal array of dielectric cylinders.

To model the light-guiding properties of a hexagonal array of dielectric cylinders, we have numerically solved Maxwell's equations with the finite-difference time-domain technique. The sizes and refractive indices of the cylinders are representative of those of the outer segments of the cone photoreceptors in the human central retina. In the array, light propagates predominantly as a "slow" mode, with a noticeable contribution of a "fast" mode, with the optical field localized in the intra- and inter-cylinder spaces, respectively. Interference between these modes leads to substantial (up to approximately 60%) axial oscillations in optical power within the cylinders. Our numerical model offered approximate dependence of the optical intensity distribution within the cylinders on their radii and separations.

Anomalous power laws of spectral diffusion in quantum dots: a connection to luminescence intermittency.

We show that the wandering of transition frequencies in colloidal quantum dots does not follow the statistics expected for ordinary diffusive processes. The trajectory of this anomalous spectral diffusion is characterized by a sqrt[t] dependence of the squared deviation. The behavior is reproduced when the electronic states of quantum dots are assumed to interact with environments such as, for example, an ensemble of two-level systems, where the correlation times are distributed according to a power law similar to the one generally attributed to the dot's luminescence intermittency.

Single-molecule dynamic triangulation.

A proposal for using single molecules as nanoprobes capable of detecting the trajectory of an elementary charge is discussed in detail. Presented numerical simulations prove that this single-molecule technique allows determination of a three-dimensional single-electron displacement within a few seconds with an accuracy better than 0.006 nm. Surprisingly, this significantly exceeds the accuracy with which the probe molecule itself can be localized (given the same measuring time) by means of single-molecule microscopy. It is also shown that the optimal concentration of probe molecules in the vicinity of the electron (i.e. the concentration which provides the best accuracy of the inferred electron displacement) is of the order of 10(-5) m.

Synthesis and spectroscopic observation of dendrimer-encapsulated gold nanoclusters.

We report on the observation of the excitation/emission spectrum of a dendrimer-encapsulated gold nanocluster; the synthesis of Au-PAMAM was based on reduction of HAuCl4 x 3 H2O co-dissolved in methanol together with fourth-generation OH-terminated PAMAM.

Imaging and sizing of diamond nanoparticles.

Typical disturbances of biological environment such as background scatter and refractive index variations have little effect on the size-dependent scattering property of highly refractive nanocrystals, which are potentially attractive optical labels. We report on what is to our knowledge the first investigation of these scattering optical labels, and their sizing, in particular, by imaging at subvideo frame rates and analyzing samples of diamond nanocrystals deposited on a glass substrate in air and in a matrix of weakly scattering polymer. The brightness of a diffraction-limited spot appears to serve as a reliable measure of the particle size in the Rayleigh scattering limit.

Simple microcavity for single-photon generation.

A new design of an optical resonator for generation of single-photon pulses is proposed. The resonator is made of a cylindrical or spherical piece of a polymer squeezed between two flat dielectric mirrors. The mode characteristics of this resonator are calculated numerically. The numerical analysis is backed by a physical explanation. The decay time and the mode volume of the fundamental mode are sufficient for achieving more than 96% probability of generating a single-photon in a single-mode. The corresponding requirement for the reflectivity of the mirrors (~99.9%) and the losses in the polymer (100 dB/m) are quite modest. The resonator is suitable for single-photon generation based on optical pumping of a single quantum system such as an organic molecule, a diamond nanocrystal, or a semiconductor quantum dot if they are imbedded in the polymer.