Echelon grating refractive index sensor.

There are few reports on optical refractive index sensors that have both high resonant-wavelength resolution (RWR) and high refractive index sensitivity (RIS). Herein, based on an echelon grating, we design a refractive index sensor that combines the two advantages together. The principal fringe of echelon grating has a small full width at half maximum and a good signal-to-noise ratio, leading to a high RWR. The wavefront splitting interference makes the sensor have high RIS. The large free spectral range (FSR) of the principal fringes expands the dynamic range of the sensor. The experimentally realized RWR, RIS, and FSR are 2 × 10-2 nm, 1.14 × 104 nm/RIU (RIU: refractive index unit), and 130 nm, respectively. The detection limit of refractive index is 1.59 × 10-6 RIU. The dynamic range of the sensor is 1.14 × 10-2 RIU. In addition, there are schemes to improve RWR and RIS, which can further reduce the detection limit of refractive index. The echelon grating refractive index sensor features low detection limit, low cost, high stability, and good robustness.

Hyperspectral measurement of dispersion in aqueous solution and its effect on ultra-sensitive interferometer.

Since the reported Sellmeier equation of water is fitted with sparse sampling points in the near-infrared region, the simulated refractive index sensitivity of dispersion enhanced interferometers deviates from the true value. Here, we measure the refractive index of aqueous sample based on hyperspectra, and research the effect of dispersion on ultra-sensitive interferometer. A piece of quartz plate is used to generate hyperspectra in the near-infrared region by building a wavefront splitting fiber Mach-Zehnder interferometer (WFSF-MZIs). The refractive index of saline water is tested after measuring the thickness of the quartz plate. By taking the wavelength of 1450 nm as break-point, the empirical dispersion equations of saline water are piecewise fitted. When the normal and abnormal dispersion are taken into account, the theoretical sensitivity of phase compensated WFSF-MZI is in good agreement with the experimental results. Our methodology provides a good reference in designing dispersion sensitized optical refractive index sensor for detecting aqueous samples.

Temperature-related single-photon transport in a waveguide QED.

We propose a scheme to realize a novel, to the best of our knowledge, scenario that the single-photon transport in a one-dimensional waveguide can be affected by the temperature. The scheme is composed by a waveguide-atom interacting structure linked to a thermal bath. The single-photon reflection (or transmission) coefficient can be controlled by adjusting the temperature of the thermal bath. This provides a thermal control of the single-photon transport. Moreover, the scheme provides an approach for implementing the optical thermometer, in which the temperature of the thermal bath is estimated by measuring the photonic transport. The thermometer can accurately measure the temperature in the low-temperature region.

All-optical control of thermal conduction in waveguide quantum electrodynamics.

We investigate the heat conduction between two one-dimensional waveguides intermediated by a laser-driving atom. The laser provides the optical control of the heat conduction. The tunable asymmetric conduction of the heat against the temperature gradient is realized. Assisted by the modulated laser, the heat conduction from either waveguide to the other waveguide can be suppressed. The heat currents can be significantly amplified by the energy flow of the laser.

Steady-State Thermodynamics of a Cascaded Collision Model.

We study the steady-state thermodynamics of a cascaded collision model where two subsystems S1 and S2 collide successively with an environment R in the cascaded fashion. We first formulate general expressions of thermodynamics quantities and identify the nonlocal forms of work and heat that result from cascaded interactions of the system with the common environment. Focusing on a concrete system of two qubits, we then show that, to be able to unidirectionally influence the thermodynamics of S2, the former interaction of S1-R should not be energy conserving. We finally demonstrate that the steady-state coherence generated in the cascaded model is a kind of useful resource in extracting work, quantified by ergotropy, from the system. Our results provide a comprehensive understanding on the thermodynamics of the cascaded model and a possible way to achieve the unidirectional control on the thermodynamics process in the steady-state regime.

Alkali etched fiber Mach-Zehnder interferometer with compact sensor head.

We demonstrate a scheme for fabricating compact fiber Mach-Zehnder interferometer (MZI). A section of Ge-doped fiber (GDF) is sandwiched between two single-mode fibers. The sandwich structure is side polished to make the core of GDF exposed to the surroundings. Alkali solution is utilized to etch the core of GDF. A compact fiber MZI is achieved when about half of the core is etched. Compared with the traditional ones, our scheme for fabricating fiber MZI has the characteristics of low cost, environmentally friendly, and regular transmission spectrum. This fiber MZI not only reduces the consumption of the sample, but also brings forth a good potential for micro-scale detection of refractive index.

Refractive index modulation in magnetophoresis of bioreaction induced self-assembled magnetic fluid.

We explore the refractive index (RI) modulation of bioreaction induced self-assembled magnetic fluid (SAMF) so as to facilitate the design of sensitive biosensors. Bovine serum albumin (BSA) is taken as a model protein to induce self-assembly of carboxylated magnetic nanoparticles (MNPs). A bidirectional magnetophoresis (BDMP) system is designed to generate uniform and large RI modulation to SAMF. A robust Mach-Zehnder interferometer compatible to the BDMP system is used for the RI detection. It is found that BDMP has greater ability in modulating the RI of magnetic fluid than the alignment of MNPs in a uniform magnetic field. The modulation depth of the RI increases with the increase of BSA concentration when applying a certain external magnetic field for a period of time. A larger magnetic field has greater ability to modulate the RI of SAMF. However, it may generate an over-modulation.

Color night vision ghost imaging based on a wavelet transform.

Night vision imaging is a technology that converts objects not visible to the human eye into visible images for night scenes and other low-light environments. However, conventional night vision imaging can directly produce only grayscale images. Here, we report a novel, to the best of our knowledge, color night vision imaging method based on a ghost imaging framework and optimized coincidence measurement based on wavelet transformation. An interesting phenomenon is that color night vision image can be directly produced by this new method. To our knowledge, this is the first direct color night vision imaging method without any conventional pseudocolor image fusion techniques. The experimental results show that this method can restore color very well for some objects. Moreover, the color of the night vision image is more natural and friendly to the human eye than that of conventional color night vision images. Due to the advantages of wavelet transforms, this method has high reconstruction ability for distorted signals.

Effects of chemical compositions in fine particles and their identified sources on hygroscopic growth factor during dry season in urban Guangzhou of South China.

Knowledge of aerosol hygroscopicity is essential to assess visibility improvement and aerosol radiative forcing. Aerosol hygroscopicity is highly dependent on emission sources, while the hygroscopicity of different sources remains largely unexplored. In the current study, the hygroscopic growth factor (i.e., f(RH)) and relevant chemical compositions (e.g., water-soluble inorganic ions, carbonaceous fractions and elements) in fine particles were synchronously measured for nearly 3 months within 2019-2020 in an urban site of Guangzhou. The mean value (± standard deviation) of f(RH) at 70% RH was 1.50 (± 0.11). The diurnal cycle in aerosol hygroscopic growth strongly depended on the mass fraction of hydrophilic chemical compositions (e.g., SO42-, NO3- and NH4+) in fine particles and variation in contributions of aerosol sources. A Positive Matrix Factorization model was applied to distinguish the different hygroscopicity of specific source factors in a mixed aerosol. Secondary nitrate and secondary sulfate were more hydrophilic, whereas emissions from primary combustion processes (i.e., ship emission, coal combustion and road traffic) were less hygroscopic. Soil dust was almost insoluble. The hygroscopic growth of each source was parameterized that quantified the emission sources and f(RH) relationship for use of air quality and radiative transfer models either as input or as validation.

Flexibly modulated Poincaré sphere vector optical field in input and focal planes.

We theoretically design and experimentally generate the flexibly modulated Poincaré sphere vector optical field (PS-VOF), which can be constructed by flattening the Poincaré sphere surface. This new kind of PS-VOF provides additional degrees of freedom to modulate the spatial structure of polarization based on Poincaré sphere. The focal property of the PS-VOF is further studied, and we focus on studying the polarization coverage of the Poincaré sphere in the focal plane. In focusing process, the conversion and annihilation of spin angular momentum are presented. In addition, when the proportion of right-handed polarizations from the northern hemisphere of the Poincaré sphere satisfies Golden ratio (0.618) in the input plane, a full PS-VOF with high quality can be achieved in the focal plane. We hope this study of PS-VOF in both input and focal planes can enrich the family of VOFs, provide a new avenue in studying VOFs based on the Poincaré sphere, and can be potentially applied in the regions with sensitivity to polarizations.

Pseudo color night vision correlated imaging without an infrared focal plane array.

Night vision is the ability to see in low-light conditions. However, conventional night vision imaging technology is limited by the requisite high-performance infrared focal plane array. In this article, we propose a novel scheme of color night vision imaging without the use of an infrared focal plane array. In the experimental device, the two-wavelength infrared laser beam reflected by the target is modulated by a spatial light modulator, and the output light is detected by a photomultiplier tube. Two infrared night vision images are reconstructed by measuring the second-order intensity correlation function between two light fields. Thus, the processing mode of optical electric detection in conventional night vision imaging is transformed into the processing mode of light field control. Furthermore, two gray images with different spectra are processed to form a color night vision image. We show that a high-quality color night vision image can be obtained by this method.

Spectral absorption properties of organic carbon aerosol during a polluted winter in Beijing, China.

A fraction of organic carbon (OC) is found to exhibit the capability to absorb solar radiation. However, the absorption properties of OC remain poorly characterized partly due to uncertainties in determination methods. In this study, the absorption coefficient (bap) of OC (bap,OC) in Beijing during a polluted winter was estimated on the basis of the combined measurements of black carbon (BC) size distribution and total aerosol bap (bap,meas). The bare BC bap (bap,bareBC) calculated using Mie theory on the basis of measured size distribution exhibited weak wavelength dependence, with a mean absorption Ångström exponent (AAE) of 0.56 ± 0.04 within the 470-660 nm wavelength range, which was lower than the value of 1 commonly used for freshly emitted BC. The calculated bap,bareBC was compared with bap,meas at 950 nm to derive the coating thickness of BC, from which the calculation of coated BC bap (bap,coatBC) within 370-660 nm was based using the core-shell Mie model. Given the thick coatings, the AAE of coated BC, with a mean of 0.53 ± 0.12, was slightly lower than that of bare BC. Subsequently, bap,OC was obtained by subtracting bap,coatBC from bap,meas, accounting for 59.57 ± 4.82% of bap,meas at 370 nm on average. The average mass absorption efficiency of OC was estimated to be 1.48 ± 0.36 m2 g-1 at 370 nm. bap,OC significantly decreased as wavelength increased, deriving an AAE of OC with a mean of 2.72 ± 0.32 within the 370-660 nm range. The level of bap,OC estimated on the basis of a widely used attribution method assuming a constant BC AAE of 1 was ~60% lower than the currently presented value, probably underestimating OC radiative effect by a factor of >3. More accurate estimations of bap,OC based on more advanced measurements and suitable theory calculations are recommended to provide more reliable assessments of OC radiative effects.

Effect of source variation on the size and mixing state of black carbon aerosol in urban Beijing from 2013 to 2019: Implication on light absorption.

Black carbon (BC) is the most important aerosol light-absorbing component, and its effect on radiation forcing is determined by its microphysical properties. In this study, two microphysical parameters of refractory BC (rBC), namely, size distribution and mixing state, in urban Beijing from 2013 to 2019 were investigated to understand the effects of source changes over the past years. The mass equivalent diameter of rBC (Dc) exhibited bimodal lognormal distributions in all seasons, with the major modes accounting for most (>85%) of the rBC masses. The mass median diameter (MMD) was obviously larger in winter (209 nm) than in summer (167 nm) likely due to the contribution of more rBC with larger Dc from solid fuel combustion and enhanced coagulation of rBC in polluted winter. More rBC particles were thickly coated in winter, with the number fraction of thickly coated rBC (fcoatBC) ranging within 29%-48% compared with that of 12%-14% in summer. However, no evidential increase in BC light-absorption capability was observed in winter. This finding was likely related to the lower absorption efficiency of larger rBC in winter, which partly offset the coating-induced light enhancement. Two stage of decreases in MMD and fcoatBC were observed, accompanied with a persistent decrease in rBC loading, thereby reflecting the discrepant effects of source control measures on rBC loading and physical properties. The control measures in the earlier stage before 2016 was more efficient to reduce the rBC loading but slightly influenced the microphysical properties of rBC. As of 2016, the reduction in rBC concentration slowed down because of its low atmospheric loading. However, rBC showed a more obvious decrease in its core size and became less coated. The decrease in fcoatBC may have weakened the BC absorption and accelerated the decrease in light absorption resulting from the reduction in rBC loading.

Variation in black carbon concentration and aerosol optical properties in Beijing: Role of emission control and meteorological transport variability.

Black carbon (BC), which is a by-product with incomplete combustion of carbonaceous materials, can be used as an indicator of combustion emissions and is an important climate forcer. In this study, a spatial-temporal synthesis of BC aerosols and the affecting factors was conducted in urban Beijing. As observed, BC showed a spatial pattern with high concentration in south and low in north. BC concentration evidently decreased by approximately 61% between 2005 and 2017. From 2015 to 2017, the mass ratio of BC/PM2.5 dropped by 28%, which suggested a more efficient effect of control measures to BC than PM2.5. The BC/CO ratio dropped by 22%, which indicated the decreasing emission from fossil fuel sources. With regard to BC loading, the spectral dependence of absorption aerosol exhibited significant seasonal variations. High absorption Ångström exponent (α) was observed during heating season, which reflected the increasing contribution of brown carbon (BrC) to light absorption. Backward trajectory analysis showed that the levels of BC and PM2.5 were high in Cluster-South and Cluster-West. BrC absorption was high in Cluster-West, Cluster-Northwest and Cluster-Northeast, due to the biomass and coal burning for domestic heating and aging processes on a regional scale. The effects of emission control and transport variability on pollutant variation were estimated on the basis of the cluster analysis. Results indicated that the effect of emission reduction was the major reason for the decrease of BC from 2015 to 2017, which resulted in a 34% reduction of BC concentration. Meanwhile, transport variability caused a 15% reduction.

Performance and toxicity of different absorption enhancers used in the preparation of Poloxamer thermosensitive in situ gels for ketamine nasal administration.

The purpose of this study was to investigate the nasal absorption rate and nasal mucosal toxicity of thermosensitive ketamine in situ gels containing various absorption enhancers. The optimal composition ratio for the gel matrix was determined to be 17.2% Poloxamer 407 and 2% Poloxamer 188, as this combination resulted in solutions with a gelation point within the range found in the nasal cavity. Ketamine gels containing the tested enhancers, namely, ethylenediaminetetraacetic acid disodium salt, hydroxypropyl-ß-cyclodextrin, propylene glycol, or Tween-80, were compared with enhancer-free counterparts to determine the absorption of the drug, in vivo by measuring its plasma levels in rats and in vitro using a Franz diffusion cell. Moreover, the toxicity of each gel type was assessed by microscopic observation of the morphology of rat nasal mucosa as well as by determining the mobility of the mucosal cilia using an established toad model. The results showed that gels containing hydroxypropyl-ß-cyclodextrin could promote the absorption of ketamine without added toxicity compared to enhancer-free gels. Thus, we consider hydroxypropyl-ß-cyclodextrin as the most promising absorption enhancer for the nasal administration of ketamine using in situ gels.

Non-degenerate wavelength computational ghost imaging with thermal light.

Non-degenerate wavelength computational ghost imaging with thermal light source is studied theoretically and experimentally. The acquired computational ghost images are of high quality when the wavelength of computed light is different from the light detected by bucket detector. Compared to the necessary light of short wavelength in previous ghost imaging, the use of longer wavelength light is demonstrated to bring about ghost images with higher spatial resolution, in strong atmospheric turbulence.

Theoretical and experimental study of the color of ghost imaging.

In this article, the color of ghost imaging (GI) was studied theoretically and experimentally. The theoretical analysis and experimental data show that the color of GI with rotating ground glass plate and computational GI are the same as the light source. If multiwavelength source is used in these schemes, a full color image without distortion can be obtained. In contrast, the color of GI with spatial light modulator as well as that in a quantum system is a superimposed one, depending on the idle and object light beams, and following the principle of light color superposition. Correspondingly, a full color image can also be obtained under the condition of multiwavelength source, but with color distortion existing.

Entanglement of photons in their dual wave-particle nature.

Wave-particle duality is the most fundamental description of the nature of a quantum object, which behaves like a classical particle or wave depending on the measurement apparatus. On the other hand, entanglement represents nonclassical correlations of composite quantum systems, being also a key resource in quantum information. Despite the very recent observations of wave-particle superposition and entanglement, whether these two fundamental traits of quantum mechanics can emerge simultaneously remains an open issue. Here we introduce and experimentally realize a scheme that deterministically generates entanglement between the wave and particle states of two photons. The elementary tool allowing this achievement is a scalable single-photon setup which can be in principle extended to generate multiphoton wave-particle entanglement. Our study reveals that photons can be entangled in their dual wave-particle behavior and opens the way to potential applications in quantum information protocols exploiting the wave-particle degrees of freedom to encode qubits.Here the authors experimentally realize a scheme that deterministically generates entanglement between the wave and particle states of two photons using a scalable all-optical scheme. They achieve this result by first showing generation of controllable single-photon wave-particle superposition states.

Roles of regional transport and heterogeneous reactions in the PM2.5 increase during winter haze episodes in Beijing.

Regional transport and chemical conversions are two major processes that lead to the severe haze pollution in China. Our observations during five haze episodes in Beijing between February 19 and March 12 of 2014 show that the two processes played different roles as PM2.5 increased from the clean (<75µgm-3) to the light-medium pollution level (75-150µg m-3) and to levels of heavy (150-250µgm-3) and severe (>250µgm-3) pollution. In the initial twelve hours of each episode, the PM2.5 reached the light-medium level with an increase of approximately 120µgm-3. At the same time, the particle (~10-700nm) number concentration also showed a distinct increase accompanied by a rapid increase in the mean diameter. A light-medium PM2.5 occurred in the south areas prior to the haze occurrence in Beijing and the southerly winds were predominant, indicating the rapid increase of PM2.5 in the initial stage was caused by the regional transport from the south. Subsequently, PM2.5 elevated to the heavy and severe levels when the wind was weak, relative humidity was high and ozone concentration was low. The increase of PM2.5 in the elevated stages was characterized by a high percentage (45% for the heavy level and 55% for the severe level) of secondary inorganic components, indicating the substantial contribution of the formation of secondary aerosols. In addition, the increases of the mean diameter (from 108nm to 120nm) and the total volume concentration (by 67%) are regarded as a consequence of heterogeneous reactions on the surfaces of aerosol particles because the particle number concentration remained nearly constant in these two stages. Our results indicate that, during the five winter haze episodes, the regional transport from the south was the major reason for the initial-stage PM2.5 increase, while heterogeneous reactions dominated the later elevation.

Simultaneous observation of particle and wave behaviors of entangled photons.

We theoretically study wave-particle duality of two entangled photons in the spirit of quantum version of delayed-choice experiments using Hadamard gate controlled by the quantum state of an ancilla and show that the two photons may globally exhibit particle-like, wave-like or simultaneously both particle-like and wave-like behavior. We prove that the obtained results cannot be satisfactorily explained by any hidden-variable theory. We also propose an efficient and experimentally feasible scheme without using any ancilla and controlled-gates to directly (i.e., without postselection) observe the two-photon wave-particle superposed state as well as the continuous transition of their behavior between wave-like one and particle-like one.