Favorable Wavelength Research Articles

An optical atomic clock using 4DJ states of rubidium

Abstract We analyze an optical atomic clock using two-photon 5 S 1 / 2 → 4 D J transitions in rubidium. Four one- and two-color excitation schemes to probe the 4 D 3 / 2 and 4 D 5 / 2 fine-structure states are considered in detail. We compare key characteristics of Rb 4 D J and 5 D 5 / 2 two-photon clocks. The 4 D J clock features a high signal-to-noise ratio due to two-photon decay at favorable wavelengths, low dc electric and magnetic susceptibilities, and minimal black-body shifts. Ac Stark shifts from the clock interrogation lasers are compensated by two-color Rabi-frequency matching. We identify a ‘magic’ wavelength near 1060 nm, which allows for in-trap, Doppler-free clock-transition interrogation with lattice-trapped cold atoms. From our analysis of clock statistics and systematics, we project a quantum-noise-limited relative clock stability at the 10 − 13 / τ ( s ) -level, with integration time τ in seconds, and a relative accuracy of ∼ 10 − 13 . We describe a potential architecture for implementing the proposed clock using a single telecom clock laser at 1550 nm, which is conducive to optical communication and long-distance clock comparisons. Our work could be of interest in efforts to realize small and portable Rb clocks and in high-precision measurements of atomic properties of Rb 4 D J -states.

Heteroleptic Complexes of Ruthenium Nitrosyl with Pyridine and Bypiridine-Synthesis and Photoisomerization.

The reaction of [RuNO(Py)2Cl2OH] with bipyridine in water-ethanol media results in trans-(NO, OH)-[RuNO(Py)(Bpy)ClOH]+ with an acceptable yield (60-70%) as hexafluorophosphate salt. Further treatment of the hydroxy-complex with concentrated HF quantitatively leads to trans-(NO, F)-[RuNO(Py)(Bpy)ClF]+. Despite the chirality of both coordination spheres, the hexafluorophosphate salts crystallized as racemates. A NO-linkage isomerism study of the obtained complexes was performed at 80 K with different excitation wavelengths (405, 450, 488 nm). The most favorable wavelengths for the MS1 isomer (Ru-ON) formation were 405 and 450 nm, where the linkage isomer populations were 17% and 1% for [RuNO(Py)(Bpy)ClOH]PF6 and [RuNO(Py)(Bpy)ClF]PF6. The shift of the excitation wavelength to the green (488 nm) sharply decreased the MS1 population. The IR-spectral signatures of MS1 were registered. Reverse-transformation Ru-ON (MS1)-Ru-NO (GS) was investigated for [RuNO(Py)(Bpy)ClOH]PF6 using IR and DSC techniques that made it possible to determine the kinetic parameters (Ea and k0) and decay temperature.

Long-term ultraviolet B irradiation at 297 nm with light-emitting diode improves bone health via vitamin D regulation.

Ultraviolet radiation is the primary determinant for vitamin D synthesis. Sunlight is inefficient and poses a risk, particularly for long-term exposure. In this study, we screened the most favorable wavelength for vitamin D synthesis among four types of narrowband light-emitting diodes (LEDs) and then irradiated osteoporosis rats with the optimal wavelength for 3-12 months. The 297 nm narrowband LED was the most efficient. Long-term radiation increased vitamin D levels in all osteoporotic rats and improved bone health. No skin damage was observed during irradiation. Our findings provide an efficient and safe method of vitamin D supplementation.

Thermal stability improvement of azobenzene for the integration of photochemical and solar thermochemical energy conversion

Azobenzene is a typical photoisomerization material that is widely used in photochemical energy conversion. However, it's generally operated below 200 °C to avoid thermal decomposition. To improve the thermal stability of azobenzene for higher temperature applications, this paper discussed an option that grafting azobenzene onto graphite-like carbon nitride sheets. The synthesis was evaluated based on the performance of micro morphology and structure, thermal stability, and photochemical energy conversion. Furthermore, the photochemical conversion performance was analyzed with diverse irradiation intensities. The results demonstrate that the synthesis has a strong thermal stability below 530 °C. In this study, the most favorable excitation wavelength for photochemical conversion was 445 nm with an irradiation intensity of 40 mW/cm2.

High Fidelity State Preparation and Measurement of Ion Hyperfine Qubits with I>1/2.

We present a method for achieving high fidelity state preparation and measurement (SPAM) using trapped ion hyperfine qubits with nuclear spins higher than I=1/2. The ground states of these higher nuclear spin isotopes do not afford a simple frequency-selective state preparation scheme. We circumvent this limitation by stroboscopically driving strong and weak transitions, blending fast optical pumping using dipole transitions, and narrow microwave or optical quadrupole transitions. We demonstrate this method with the I=3/2 isotope ^{137}Ba^{+} to achieve a SPAM infidelity of (9.0±1.3)×10^{-5} (-40.5±0.6 dB), facilitating the use of a wider range of ion isotopes with favorable wavelengths and masses for quantum computation.

Synthesis and application of concanavalin A-conjugated green luminescent gold nanoparticle/fluorescent polydopamine nanoparticles for specific differentiation of cancer cells from normal cells using glycan bioreceptors

Glycan receptor is a cell-surface bioreceptor which has been expressed on the membrane of several cancer cells. This bioreceptor was employed for different medicinal disciplines such as drug-delivery, sensing, etc. In this work, concanavalin A (Con A)-conjugated green luminescent gold nanoparticle/fluorescent polydopamine nanoparticles (FPNPs) were synthesized and utilized for bioimaging of the glycan bioreceptor-positive breast cancer cells. The produced AuNPs/Cysteine/FPNPs/Con A NPs showed a specific manner towards biorecognition of glycan receptor-overexpressed MCF 7 cancer cells through Con A and glycan receptor interactions. Fluorescence microscope and flow cytometry techniques were employed to evaluate the accuracy of the bioimaging process. Furthermore, the specific attachment of AuNPs/Cysteine/FPNPs/Con A NPs to the MCF 7 cancer cells was tested using HEK 293 normal cells as a negative control. Viability results proposed that the AuNPs/Cysteine/FPNPs/Con A NPs are biocompatible at levels up to 100 μg/mL. This nanoparticle showed some advantageous features such as high stability, favorable emission wavelength, and low toxicity, enabling for application of in vivo bioimaging of MCF 7 tumoral cells.

Chandra Observations of Spikey: A Possible Self-lensing Supermassive Black Hole Binary System

Abstract This work examines the recent X-ray observations of the active galactic nucleus KIC 11606854 (nicknamed “Spikey”) by the Chandra space telescope. Based on previous observations of a symmetric flare in the system’s light curve by the Kepler space telescope, Spikey has been proposed to be a self-lensing supermassive black hole binary system in which the more massive black hole gravitationally lenses the accretion flow of its smaller companion. The recent Chandra observations (2020 March–May) correspond to the time when the next pulse was expected to occur and were separated in enough time to observe the apparent relativistic Doppler boosting effect from the high orbital velocities of the black holes. We model the expected self-lensing plus Doppler boosting light curve using our wavelength-dependent extended source self-lensing model combined with our relativistic orbital motion code. This orbital motion code is capable of modeling the expected apsidal precession for Spikey, which can be used to predict future pulses. We show that the expected signal was undetectable in the Chandra data as the intrinsic X-ray variability associated with the system was large relative to the changes expected by self-lensing and Doppler boosting. Expected flux increases in more favorable wavelengths were also calculated using our wavelength-dependent self-lensing model, revealing a relationship between the observing wavelength and measured orbital inclination.

Stretching Hookean ribbons part II: from buckling instability to far-from-threshold wrinkle pattern.

We address the fully developed wrinkle pattern formed upon stretching a Hookean, rectangular-shaped sheet, when the longitudinal tensile load induces transverse compression that far exceeds the stability threshold of a purely planar deformation. At this "far-from-threshold" parameter regime, which has been the subject of the celebrated Cerda-Mahadevan model (Cerda and Mahadevan in Phys Rev Lett 90:074302, 2003), the wrinkle pattern expands throughout the length of the sheet and the characteristic wavelength of undulations is much smaller than its width. Employing Surface Evolver simulations over a range of sheet thicknesses and tensile loads, we elucidate the theoretical underpinnings of the far-from-threshold framework in this setup. We show that the evolution of wrinkles comes in tandem with collapse of transverse compressive stress, rather than vanishing transverse strain (which was hypothesized by Cerda and Mahadevan in Phys Rev Lett 90:074302, 2003), such that the stress field approaches asymptotically a compression-free limit, describable by tension field theory. We compute the compression-free stress field by simulating a Hookean sheet that has finite stretching modulus but no bending rigidity, and show that this singular limit encapsulates the geometrical nonlinearity underlying the amplitude-wavelength ratio of wrinkle patterns in physical, highly bendable sheets, even though the actual strains may be so small that the local mechanics is perfectly Hookean. Finally, we revisit the balance of bending and stretching energies that gives rise to a favorable wrinkle wavelength, and study the consequent dependence of the wavelength on the tensile load as well as the thickness and length of the sheet.

Liposomes Loaded with Activatable Disulfide Bridged Photosensitizer: Towards Targeted and Effective Photodynamic Therapy on Breast Cancer Cells

The motivation of the current study is to develop a strategy providing targeted and effective photodynamic therapy (PDT) on breast cancer cells by eliminating the limitations of PDT. For this purpose, a disulfide bridged phthalocyanine with favorable wavelength absorbance that is activatable in cancer cells was synthesized and encapsulated in liposome nanoparticles. The synthesized molecule was characterized using Fourier transform-infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, Matrix-Assisted Laser Desorption/Ionization Time of Flight (MALDI-TOF) Mass Spectrometry, Ultraviolet-visible (UV-Vis) spectrophotometry, and particle size analyzer; and the nano-formulation was tested on MCF-7 breast cancer cell line using MTT assay, fluorescence microscopy, and flow cytometry. The results have illustrated that the synthesized disulfide bridged phthalocyanine has a therapeutically active wavelength absorbance value (685 nm), the liposome nanoparticles with the favorable characteristics (average size of 167.6 nm and polydispersity index (PDI) of 0.108) containing the synthesized disulfide bridged phthalocyanine have low dark toxicity, and significant light toxicity (P < 0.001 vs. dark toxicity) characterized with significant apoptosis (p < 0.05 vs. control group). Thus, for further investigations, these results suggest the great potential of the nano-formulation towards targeted and effective PDT on breast cancer cells.

Infrared neural stimulation at different wavelengths and pulse shapes

Neural stimulation with infrared radiation has been explored for brain tissue, peripheral nerves, and cranial nerves including the auditory nerve. Initial experiments were conducted at wavelengths between λ = 1850 and λ = 2140 nm and the radiant energy was delivered with square pulses. Water absorption of the infrared radiation at λ = 1860 nm is similar to absorption at wavelengths between λ = 1310 and λ = 1600 nm, which are in the radiation wavelength range used for the communication industry. Technology for those wavelengths has already been developed and miniaturized and is readily available. The possibility of the infrared light to evoke compound action potentials (CAP) in the cochlea at λ = 1,375, λ = 1,460, and λ = 1550 nm was explored and compared to that of λ = 1860 nm in guinea pigs. Furthermore, rise and fall times of the 100 μs long pulses were changed and four basic pulse shapes (square, triangular, ramp-up, and ramp-down) were explored in their ability to evoke a CAP. In animals with pure tone threshold averages (PTAs) above 70 dB SPL, the results show that the favorable wavelength is λ = 1460 nm to reach threshold for stimulation and λ = 1375 nm or λ = 1460 nm for obtaining maximum amplitude. The most favorable pulse shape is either ramp-up or triangular.

Isolator-free unidirectional dual-wavelength thulium-doped fiber laser assisted by a two-mode fiber filter

A switchable, thulium-doped, isolator-free fiber laser is proposed and demonstrated. The isolator-free configuration, wavelength selective element and stabilization mechanism were achieved by using a theta cavity design, a two-mode fiber filter and nonlinear polarization rotation, respectively. By properly adjusting the polarization controllers to induce polarization-dependent loss, single- and dual-wavelength outputs can be obtained, and the stability of single- and dual-wavelength operations was measured for 30 min in each case. The single wavelength can be switched from 1959.17 to 1994.86 nm in a lasing range of ~35.7 nm with an optical signal-to-noise ratio (OSNR) of up to ~60 dB. When lasing dual-wavelength, the wavelength interval can be changed from ~4 to 27.36 nm with an OSNR higher than 42 dB, and the maximal lasing range of the dual-wavelength is 23.38 nm. In addition, the wavelength drift and power fluctuation of the proposed fiber laser are less than 0.14 nm and 1.976 dB, respectively, at room temperature, which demonstrates that the thulium-doped fiber laser has favorable wavelength and power stability.

Electronic transport properties of hydrogenated and fluorinated graphene: a computational study

Hydrogenation and fluorination have been presented as two possible methods to open a bandgap in graphene, required for field-effect transistor applications. In this work, we present a detailed study of the phonon-limited mobility of electrons and holes in hydrogenated graphene (graphane) and fluorinated graphene (graphene fluoride). We pay special attention to the out-of-plane acoustic (ZA) phonons, responsible for the highest scattering rates in graphane and graphene fluoride. Considering the most adverse cut-off for long-wavelength ZA phonons, we have obtained electron (hole) mobilities of 28 (41) cm2 V−1 s−1 for graphane and 96 (30) cm2 V−1 s−1 for graphene fluoride. Nonetheless, for a more favorable cut-off wavelength of ∼2.6 nm, significantly higher electron (hole) mobilities of 233 (389) cm2 V−1 s−1 for graphane and 460 (105) cm2 V−1 s−1 for graphene fluoride are achieved. Moreover, while complete suppression of ZA phonons can increase the electron (hole) mobility in graphane up to 278 (391) cm2 V−1 s−1, it does not affect the carrier mobilities in graphene fluoride. Velocity–field characteristics reveal that the electron velocity in graphane saturates at an electric field of ∼4 × 105 V cm−1. Comparing the mobilities with other two-dimensional (2D) semiconductors, we find that hydrogenation and fluorination are two promising avenues to realize a 2D semiconductor while providing good carrier mobilities.

How Reliable Are Enantiomeric Excess Measurements Obtained By Chiral HPLC?

AbstractUncertainties and errors in enantiomeric excess determinations obtained by high performance liquid chromatography (HPLC) with a chiral column are evaluated with different peak resolutions and elution orders using (R)‐ and (S)‐ibuprofen standards. Five injections of each sample were made to reduce the variability in the data and each chromatogram was monitored at multiple wavelengths to facilitate the detection of chemical impurities. Using appropriate sample concentrations, the most favorable detection wavelengths, and default instrument parameters led to large errors (>10 %) whereas properly set integration values gave impressive reproducibilities (±0.5 % or better) and accuracies (<1 %) in the most favorable situations. Uncertainties and errors of up to±2.0 % and 5.2 % ee, respectively were also observed under separation conditions routinely reported in chemistry journals. This study aims to provide a practical guide to the accuracy and precision that can be achieved with HPLC, and suggestions for obtaining reliable results.

Wavelength scaling laws for high-order harmonic yield from atoms driven by mid- and long-wave infrared laser fields

High-order harmonic generation (HHG) in gases is known to benefit from using mid-infrared driving laser fields, since, due to a favorable wavelength scaling of the electron ponderomotive energy, higher-energy photon production becomes feasible with longer-wavelength drivers. On the other hand, recent studies have revealed a number of physical effects whose importance for HHG increases with increasing laser wavelength. These effects, as a rule, result not only in a general decrease of the harmonic yield but also in a reshaping of the emission spectrum. Therefore, detailed study of the dependence of HHG yield on the laser wavelength has become an important issue for producing intense extremely short extreme ultraviolet (XUV) and x-ray pulses using HHG driven by long-wavelength laser fields. Here we address this issue by calculating the HHG spectra for laser wavelengths ranging from 2 to 20 µm. This study has been carried out in a frame of strong-field approximation modified properly to take into account the effect of the magnetic field of a laser pulse on the dynamics of the field-ionized electron and the atomic bound-state depletion. We show that different regions of the HHG spectrum behave differently with the laser wavelength and discuss the origins of this behavior. In particular, we show that in a weak ionization regime, the dipole-approximation scaling law for the harmonic yield, which is calculated as the integral over the spectral interval of fixed width and relative position with respect to the cutoff energy, obeys the power law, where the absolute value of the exponent is an integer equal to $\mu = {7}$μ=7 for the cutoff and $\mu = {8}$μ=8 for the plateau harmonics. Above a certain critical wavelength, due to the nondipole effects, the efficiency of HHG decreases more strongly than according to a power law, and this decrease is different for different regions of the spectrum. The analytical formulas are derived that match well the calculated wavelength scalings.

Glucose sensing in the anterior chamber of the human eye model using supercontinuum source based dual wavelength low coherence interferometry

Supercontinuum source based dual wavelength low coherence interferometry (DWLCI) technique is proposed to measure glucose in the aqueous humor of the eye. Studies were conducted in the second overtone region, first overtone region and combination band to determine the favourable wavelength region for glucose measurement. Bandpass filters at centre wavelengths 1300 nm, 1580 nm, 2100 nm and 2250 nm were used to filter out appropriate bands of interest for the study from the broad wavelength range of 900–2800 nm. In the studies, human eye model was used to simulate the anterior chamber of the eye containing artificial aqueous humor with varying physiological concentrations of glucose ranging from 0 to 250 mg/dl. Studies based on spectral shift measurements and relative reflectivity were conducted. Enhancement in the resolution of glucose was obtained in the combination band at 2100 nm compared to the first overtone region at 1580 nm, due to the increase in the absorption of glucose in the combination band. Glucose resolution of ≈10.3 mg/dl was estimated in the first overtone region. Whereas, an enhancement in the resolution of glucose of ≈2.4 mg/dl was attained in the combination band.

Tunable dual-wavelength ytterbium-doped fiber ring laser based on a Sagnac interferometer

A tunable dual-wavelength ytterbium-doped fiber ring laser based on Sagnac interferometer is proposed and experimentally demonstrated. Due to a broad gain bandwidth of ytterbium-doped fiber, a tuning range of 17.9 nm for single-wavelength lasing output and 8.4 nm for dual-wavelength lasing have been achieved with side-mode suppression ratio higher than 38 dB. In addition, experimental results indicate that the lasing output has favorable wavelength and power stability with the maximum wavelength shift and the peak power fluctuation less than 0.06 nm and 0.94 dB, respectively. Such a wide tunable ytterbium-doped fiber ring laser around the wavelength of 1 µm with simple structure has potential applications in metrology, medical treatments or laser cooling, where the laser wavelength need adjusted accurately.

Spontaneous capillary breakup of suspended gradient polymer stripes into spatially ordered dot arrays

We describe the experimental study on the spontaneous capillary instability of gradient poly(methyl methacrylate) (PMMA) stripes beneath the continuous polystyrene (PS) film. Upon vapor annealing using a selective solvent only for PMMA, the PMMA stripes were transformed into well-ordered dot-arrays beneath the continuous PS film via capillary force driven rupture. Dimensional features of the PMMA dots strongly did not depend upon the initial width and height of the PMMA microscopic stripes. Repeatedly, such this gradient stripe geometry triggered a competition between the phase correlation of neighboring stripes and the kinetically favorable wavelength, thus leading to the formation of an intriguing, recursive surface sub-patterns.

Recent progress on new infrared nonlinear optical materials with application prospect

Nonlinear optical (NLO) crystals can convert the frequencies of existing lasers to other favorable wavelength ranges, and are hence important material basis of photoelectron technology. Currently, there is an urgent need to investigate new NLO materials in the deep UV and IR range. In this review, we focus on the recent progress on new IR NLO materials with application prospect. The main challenge of discovering new practically usable IR NLO crystals is to synthesize new materials that can achieve the coexistence of various desirable properties including sufficient SHG coefficients, wide mid-far IR transparency range, high laser damage threshold, moderate birefringence, favorable single-crystal growth habit, and stable physicochemical properties. Here, we highlight that the research strategy combining “structural design” with “exploratory synthesis” can greatly increase the efficiency of identifying new practical IR NLO materials in metal chalcogenides. Several classes of IR NLO materials with excellent overall performance have been found, such as BaGa4Se7 and BaGa2GeSe6. Moreover, the research on these materials has gone beyond crystal structure and preliminary characterization. Great efforts have been carried out in the bulk crystal growth, in the thorough measurement of their physical properties using bulk crystals, in the evaluation of their IR laser output performance, and eventually in the fabrication of laser device. In the frequency down-conversion OPOs pumped by the conventional 1 µm laser, BaGa4Se7 has realized the stable output of mid-far IR laser output with the highest power and widest wavelength range so far. In this review, instead of covering all compounds with IR NLO properties, our discussion will only focus on those showing good overall IR NLO performance and application prospect, especially on those of which large size single crystals have been already obtained. This review then concludes with an outlook on what efforts could be made in the future.

Multi-color luminescence in Eu3+/Tb3+ co-doped ZnAl amorphous materials and their annealed samples

Multi-color luminescence basing on amorphous Eu3+/Tb3+ co-doped Zn-Al hydroxides and their annealed samples were studied in detail. Results suggest that excellent red emissions due to Eu3+ and green emissions attributed to Tb3+ appear under the excitation of favorable wavelength for all the as-prepared amorphous samples. Moreover, the emission intensity depends on the Eu3+/Tb3+ molar ratio. The samples annealed at 300, 500, and 700 °C still exhibit amorphous state, and multi-color luminescence kept in the samples annealed at 300 °C, while luminescence quenched for the samples annealed at 500 and 700 °C. However, a broad emission ranging from 450 to 650 nm occurs in some samples annealed at 900 °C. Further, the fluorescence decay and lifetimes for the as-prepared samples and the samples annealed at 300 °C were investigated. It is found that all the decay curves of emissions due to Tb3+ and Eu3+ present characteristic double exponential function despite their different lifetimes. The present work may be a good example for developing new multi-color even white light emitting materials.

Atomic-like high-harmonic generation from two-dimensional materials.

The generation of high-order harmonics from atomic and molecular gases enables the production of high-energy photons and ultrashort isolated pulses. Obtaining efficiently similar photon energy from solid-state systems could lead, for instance, to more compact extreme ultraviolet and soft x-ray sources. We demonstrate from ab initio simulations that it is possible to generate high-order harmonics from free-standing monolayer materials, with an energy cutoff similar to that of atomic and molecular gases. In the limit in which electrons are driven by the pump laser perpendicularly to the monolayer, they behave qualitatively the same as the electrons responsible for high-harmonic generation (HHG) in atoms, where their trajectories are described by the widely used semiclassical model, and exhibit real-space trajectories similar to those of the atomic case. Despite the similarities, the first and last steps of the well-established three-step model for atomic HHG are remarkably different in the two-dimensional materials from gases. Moreover, we show that the electron-electron interaction plays an important role in harmonic generation from monolayer materials because of strong local-field effects, which modify how the material is ionized. The recombination of the accelerated electron wave packet is also found to be modified because of the infinite extension of the material in the monolayer plane, thus leading to a more favorable wavelength scaling of the harmonic yield than in atomic HHG. Our results establish a novel and efficient way of generating high-order harmonics based on a solid-state device, with an energy cutoff and a more favorable wavelength scaling of the harmonic yield similar to those of atomic and molecular gases. Two-dimensional materials offer a unique platform where both bulk and atomic HHG can be investigated, depending on the angle of incidence. Devices based on two-dimensional materials can extend the limit of existing sources.