Measurement of the 5S1/2 to 5D5/2 two-photon clock transition frequency of rubidium-85 in high vacuum.

We present a scheme to precisely resolve the unperturbed line shape of an optical rubidium clock transition in a high vacuum, by which we avoided the systematic errors of "collision shift" and "modulation shift." The spectral resolution resolved by this scheme is significantly improved such that we can use "Zeeman broadening" to inspect the stray magnetic field, through which we were able to compensate the magnetic field inside the Rb cells to be below 10-3 Gauss. We thus update the absolute frequency of the clock transition and propose a standard operation procedure (SOP) for the clock self-calibration.

Absolute frequency of cesium 6S1/2-6D3/2 hyperfine transition with a precision to nuclear magnetic octupole interaction.

We have determined the fundamental frequency of the cesium atom 6S1/2-6D3/2 two-photon transition, for the first time, to our knowledge. Moreover, our high-resolution scheme made it possible to address the influence of the nuclear magnetic octupole on the hyperfine structure. We found that the octupole-interaction hyperfine constant deduced from the cesium 6D-level has a value nearly eight times larger than what has been deduced from the 6P-level.

Time-Resolved Luminescence Nanothermometry with Nitrogen-Vacancy Centers in Nanodiamonds.

Measuring temperature in nanoscale spatial resolution either at or far from equilibrium is of importance in many scientific and technological applications. Although negatively charged nitrogen-vacancy (NV(-)) centers in diamond have recently emerged as a promising nanometric temperature sensor, the technique has been applied only under steady state conditions so far. Here, we present a three-point sampling method that allows real-time monitoring of the temperature changes over ±100 K and a pump-probe-type experiment that enables the study of nanoscale heat transfer with a temporal resolution of better than 10 µs. The utility of the time-resolved luminescence nanothermometry was demonstrated with 100 nm fluorescent nanodiamonds spin-coated on a glass substrate and submerged in gold nanorod solution heated by a near-infrared laser, and the validity of the measurements was verified with finite-element numerical simulations. The combined theoretical and experimental approaches will be useful to implement time-resolved temperature sensing in laser processing of materials and even for devices in operation at the nanometer scale.

Multilevel Optical Labeling by Spectral Luminescence Control in Nanodiamond Color Centers.

Distinguishing a multitude of optical labels is crucial to improving the spatial and temporal resolution of bioimaging. However, current multicolor imaging approaches are limited by the spectral overlap of employed fluorophores. We here discern different instances of a single optical label type through their emission intensity. Such multilevel optical labels are enabled by an optical writing process that permanently modifies their spectral response in a predictable manner and by a separate spectral feature that serves as normalization in the presence of sample variability. The proposed approach was realized by independently controlling the emission properties of highly functionalized fluorescent nanodiamond. Upon laser irradiation, the contribution of the spectral region associated with the N3 color center decreases in a predictable and permanent fashion, while the nitrogen vacancy (NV) emission remains stable. This selective photobleaching of N3 centers was found to originate from a two-photon-assisted dissociation process that results in a 105 higher mobility of photoexcited carriers in N3 centers compared to NV. The resulting write once read many (WORM) memory exhibits multiple distinct memory levels that can be stored and read out with high robustness and reproducibility. The potential of our approach was demonstrated by characterizing markers in HeLa cells with high fidelity, despite the complex emission background. Finally, direct manipulation of label information inside of cells was demonstrated, opening up new routes in advanced bioimaging.

Intraocular pressure assessment in both eyes of the same patient after laser in situ keratomileusis.

PURPOSE: To measure intraocular pressure (IOP) after laser in situ keratomileusis (LASIK) in both eyes of the same patient and analyze the correlation between IOP measurement and keratometric (K) power, central corneal thickness (CCT), and laser ablation depth. SETTING: Private practice, Kaohsiung, Taiwan. METHODS: This prospective cohort study enrolled patients with myopia or myopic astigmatism. In all patients, the targeted post-LASIK spherical equivalent was within +/-0.25 diopter. The IOP was measured using noncontact tonometry; K power, by autokeratorefractometry; and CCT, by ultrasound pachymetry. Laser ablation depth was determined using the excimer laser's software, and the ratio of laser ablation depth to decreased IOP was calculated. Correlations were determined by stepwise multiple regression analysis and the Mann-Whitney U test. RESULTS: High preoperative IOP was significantly associated with high postoperative IOP (P<.001) and with a large decrease in IOP (P<.001). Thus, 62.7% and 37.5% of postoperative IOP and decreased IOP measurements, respectively, were explainable by the preoperative IOP. Postoperative IOP (P = .904), decreased IOP after LASIK (P = .479), and the ratio of laser ablation depth to decreased IOP (P = .971) did not significantly differ and were positively correlated (P<.001) between eyes of the same patient. CONCLUSIONS: The IOP measurement reduction after LASIK was greater in cases of higher preoperative IOP and smaller in cases of lower preoperative IOP. The IOP measurements after LASIK were not significantly associated with laser ablation depth, and the measurements were similar and proportional in eyes of the same patient.

Enhanced spectral profile in the study of Doppler-broadened Rydberg ensembles.

Combination of the electromagnetically-induced-transparency (EIT) effect and Rydberg-state atoms has attracted great attention recently due to its potential application in the photon-photon interaction or qubit operation. In this work, we studied the Rydberg-EIT spectra with room-temperature 87Rb atoms. Spectroscopic data under various experimental parameters all showed that the contrast of EIT transparency as a function of the probe field intensity is initially enhanced, reaches a maximum value and then decays gradually. The contrast of spectral profile at the optimum probe field intensity is enhanced by 2-4 times as compared with that at weakest intensity. Moreover, the signal-to-noise ratio of the spectrum can potentially be improved by 1 to 2 orders of magnitude. We provided a theoretical model to explain this behavior and clarified its underlying mechanism. Our work overcomes the obstacle of weak signal in the Rydberg-EIT spectrum caused by an apparent relaxation rate of the Rydberg polariton and weak coupling transition strength, and provides the useful knowledge for the Rydberg-EIT study.

Radiation pressure on a biconcave human Red Blood Cell and the resulting deformation in a pair of parallel optical traps.

We calculated the three-dimensional optical stress distribution and the resulting deformation on a biconcave human red blood cell (RBC) in a pair of parallel optical trap. We assumed a Gaussian intensity distribution with a spherical wavefront for each trapping beam and calculated the optical stress from the momentum transfer associated with the reflection and refraction of the incident photons at each interface. The RBC was modelled as a biconcave thin elastic membrane with uniform elasticity and a uniform thickness of 0.25 µm. The resulting cell deformation was determined from the optical stress distribution by finite element software, Comsol Structure Mechanics Module, with Young's modulus (E) as a fitting parameter in order to fit the theoretical results for cell elongation to our experimental data.

Retinal nerve fibre layer thickness and optic nerve head size measured in high myopes by optical coherence tomography.

BACKGROUND: The retinal nerve fibre layer (RNFL) thickness is reportedly decreased in myopia; however, magnification adjustment is an important consideration when using optical coherence tomography (OCT) to evaluate myopic eyes. In this study, RNFL thickness and optic nerve head (ONH) size were measured in highly myopic eyes with and without magnification adjustments. The measurements were compared with magnification-adjusted OCT measurements of emmetropic control eyes. METHODS: In this cross-sectional study, RNFL thickness (global circle and quadrants) and ONH size (disc and rim areas) were measured in one eye of each of 70 participants with high myopia. Magnification-adjusted measurements taken in the high myopes were then compared with magnification-adjusted measurements taken in 70 emmetropic controls. RESULTS: Comparisons of magnification-adjusted measurements between highly myopic and emmetropic control eyes showed that the highly myopic eyes had significantly thicker global and temporal RNFLs (p < 0.05), significantly thinner nasal RNFL (p < 0.05), and significantly larger disc and rim areas (p < 0.05). Superior and inferior RNFL thickness measurements did not differ significantly between the two groups (p > 0.05). CONCLUSION: The OCT measurements obtained with magnification adjustment show global and temporal RNFL thicknesses and ONH size increase in highly myopic eyes.

Effects of age and disc area on optical coherence tomography measurements and analysis of correlations between optic nerve head and retinal nerve fibre layer.

BACKGROUND: The aim here was to investigate whether optic nerve head (ONH) parameters or retinal nerve fibre layer (RNFL) thickness correlate with age or disc area and whether the neuroretinal rim correlates with RNFL thickness. METHODS: This cross-sectional study enrolled 133 healthy subjects and analysed one randomly selected eye of each subject. All measurements of ONH parameters (including neuroretinal rim, disc and cup areas and cup-to-disc ratios) and RNFL thickness (global and quadrants) were taken by a single experienced operator using optical coherence tomography (OCT). RESULTS: Of the rim parameters analysed, average nerve width (the height of the nerve fibre bundle) was independent of age or disc area (p > 0.05). Disc area correlated positively with cup area (p < 0.05) but not with cup-to-disc ratios (p > 0.05). Of the RNFL thickness measurements analysed, temporal RNFL was independent of both age and disc area (p > 0.05). According to the analysis of the correlation between RNFL thickness and neuroretinal rim, global or non-temporal RNFL correlated positively with horizontal integrated rim width (p < 0.05, F > 4.000) and temporal RNFL was independent of all rim parameters (p > 0.05, F < 4.000). CONCLUSION: Aging effect on neuroretinal rim loss or RNFL thickness change is non-uniform, and age is not a constant confounder when using OCT. The temporal RNFL is independent of age, disc area and neuroretinal rim.

Forces for morphogenesis investigated with laser microsurgery and quantitative modeling.

We investigated the forces that connect the genetic program of development to morphogenesis in Drosophila. We focused on dorsal closure, a powerful model system for development and wound healing. We found that the bulk of progress toward closure is driven by contractility in supracellular "purse strings" and in the amnioserosa, whereas adhesion-mediated zipping coordinates the forces produced by the purse strings and is essential only for the end stages. We applied quantitative modeling to show that these forces, generated in distinct cells, are coordinated in space and synchronized in time. Modeling of wild-type and mutant phenotypes is predictive; although closure in myospheroid mutants ultimately fails when the cell sheets rip themselves apart, our analysis indicates that beta(PS) integrin has an earlier, important role in zipping.