Investigation of the nonlinear CPT spectrum of ^87Rb and its application for large dynamic magnetic measurement

The coherent population trapping（CPT） phenomenon has found widespread application in quantum precision measurements. Various designs based on the narrow resonant spectrum corresponding to the linear Zeeman effect have been demonstrated to achieve high performance. In this article, the nonlinear Zeeman split of the CPT spectrum of ^87Rb in the lin｜｜lin setup is investigated. We observe re-split phenomenon for both magnetic sensitive and magnetic insensitive CPT resonant lines at a large magnetic field. The re-split in the magnetic sensitive lines raises a practical problem to magnetometers worked in the lin｜｜lin setup while the other one shows a good potential for applications in large magnetic field. We propose a design based on the nonlinear split of the magnetic insensitive lines and test its performance. It provides a much larger measurement range compared to the linear one, offering an option for atomic magnetometers where a large dynamic range is preferred.

Light People:Prof.Eric Mazur speaks about ultrafast optics and education

Prof.Eric Mazur is a great influencer over and beyond the optics community.As a physicist,he is a pioneer of ultrafast optics and was one of the inventors of colliding-pulse mode-locked laser.As an educator,he not only gave talks to thousands,but also revolutionized teaching with his globally renowned methodology“Peer Instruction”.As a leader and entrepreneur,he co-founded several companies and was President of Optica(formerly the Optical Society)and currently is the Chair of the Optica Foundation.Here,Light:Science&Applications talked with Prof.Eric Mazur about his opinions on research,education and industry.The full interview video can be found in the Supplementary File.

Calibration of line structured light vision system based on camera’s projective center

Based on the characteristics of line structured light sensor, a speedy method for the calibration was established. With the coplanar reference target, the spacial pose between camera and optical plane can be calibrated by using of the camera’s projective center and the light’s information in the camera’s image surface. Without striction to the movement of the coplanar reference target and assistant adjustment equipment, this calibration method can be implemented. This method has been used and decreased the cost of calibration equipment, simplified the calibration procedure, improved calibration efficiency. Using experiment, the sensor can attain relative accuracy about 0.5%, which indicates the rationality and effectivity of this method.

Prediction-based Manufacturing Center Self-adaptive Demand Side Energy Optimization in Cyber Physical Systems

Cyber physical systems（CPS） recently emerge as a new technology which can provide promising approaches to demand side management（DSM）, an important capability in industrial power systems. Meanwhile, the manufacturing center is a typical industrial power subsystem with dozens of high energy consumption devices which have complex physical dynamics. DSM, integrated with CPS, is an effective methodology for solving energy optimization problems in manufacturing center. This paper presents a prediction-based manufacturing center self-adaptive energy optimization method for demand side management in cyber physical systems. To gain prior knowledge of DSM operating results, a sparse Bayesian learning based componential forecasting method is introduced to predict 24-hour electric load levels for specific industrial areas in China. From this data, a pricing strategy is designed based on short-term load forecasting results. To minimize total energy costs while guaranteeing manufacturing center service quality, an adaptive demand side energy optimization algorithm is presented. The proposed scheme is tested in a machining center energy optimization experiment. An AMI sensing system is then used to measure the demand side energy consumption of the manufacturing center. Based on the data collected from the sensing system, the load prediction-based energy optimization scheme is implemented. By employing both the PSO and the CPSO method, the problem of DSM in the manufac^ring center is solved. The results of the experiment show the self-adaptive CPSO energy optimization method enhances optimization by 5% compared with the traditional PSO optimization method.

Realtime Vision-Based Surface Defect Inspection of Steel Balls

In the proposed system for online inspection of steel balls, a diffuse illumination is developed to enhance defect appearances and produce high quality images. To fully view the entire sphere, a novel unfolding method is put forward based on geometrical analysis, which only requires one-dimensional movement of the balls and a pair of cameras to capture images from different directions. Moreover, a realtime inspection algorithm is customized to improve both accuracy and efficiency. The precision and recall of the sample set were 87.7% and 98%, respectively. The average time cost on image processing and analysis for a steel ball was 47 ms, and the total time cost was less than 200 ms plus the cost of image acquisition and balls' movement. The system can sort 18 000 balls per hour with a spatial resolution higher than 0.01 mm.

Phase transition model of water flow irradiated by high-energy laser in a chamber

In the absorption chamber of a high-energy laser energy meter, water is directly used as an absorbing medium and the interaction of the high-power laser and the water flow can produce a variety of physical phenomena such as phase transitions. The unit difference method is adopted to deduce the phase transition model for water flow irradiated by a high-energy laser. In addition, the model is simulated and verified through experiments. Among them, the experimental verification uses the photographic method, shooting the distribution and the form of the air mass of water flow in different operating conditions, which are compared with the simulation results. The research shows that it is achievable to reduce the intensity of the phase transition by increasing the water flow, reducing the power intensity of the beam, shortening the distance the beam covers, reducing the initial water temperature or adopting a shorter wavelength laser. The study＇s results will provide the reference for the design of a water-direct-absorption-type high-energy laser energy meter as well as an analysis of the interaction processes of other similar high-power lasers and water flow.

Semi-classical theory and experimental research for polarization flipping in a single frequency laser with feedback effect

In this paper, we propose a semi-classical theory to successfully explain the polarization flipping in a single frequency laser. An experimental setup is built to verify this theory. The observed experimental phenomena are consistent with the theoretical analysis. We perform phase retardation measurements of birefringent components using this experimental system. The results show that the measurement repeatability is 0.12° and the measurement accuracy is 0.22°.

Comparison between Two Kinds of Semiconductor Absorbers for Mode-Locking in Nd：YVO4 Laser

我们示威了被动在 diode-end-pumped Nd 锁模式:用区域其松驰来自在低温度(副)和 GaAs/air 接口种的 In0.25Ga0.75As 的二种半导体吸收器的 YVO4 激光分别地锁模式用 theGaAs/air 接口松驰区域的吸收器，用副 In0.25Ga0.75As 松驰区域的吸收器比那有更少的 切换Q 趋势和更高平均的产量力量的特征，但是不象后者一样稳定。

Atomic magnetometer with microfabricated vapor cells based on coherent population trapping

An atomic magnetometer based on coherent population trapping(CPT) resonances in microfabricated vapor cells is demonstrated. Fabricated by the micro-electro-mechanical-system(MEMS) technology, the cells are filled with Rb and Ne at a controlled pressure. An experimental apparatus is built for characterizing properties of microfabricated vapor cells via the CPT effects. The typical CPT linewidth is measured to be about 3 k Hz(1.46 k Hz with approximately zero laser intensity) for the rubidium D1 line at about 90℃. The effects of pressure, temperature and laser intensity on CPT linewidth are studied experimentally. A closed-loop atomic magnetometer is finally finished with a sensitivity of 210.5 p T/Hz1/2 at 1 Hz bandwidth. This work paves the way for developing an integrated chip-scale atomic magnetometer in the future.

Visible-to-near-infrared photodetector based on graphene–MoTe2–graphene heterostructure

Graphene and transition metal dichalcogenides(TMDs), two-dimensional materials, have been investigated wildely in recent years. As a member of the TMD family, MoTe2 possesses a suitable bandgap of ~1.0 eV for near infrared(NIR)photodetection. Here we stack the MoTe2 flake with two graphene flakes of high carrier mobility to form a graphene–MoTe2–graphene heterostructure. It exhibits high photo-response to a broad spectrum range from 500 nm to 1300 nm. The photoresponsivity is calculated to be 1.6 A/W for the 750-nm light under 2 V/0 V drain–source/gate bias, and 154 mA/W for the 1100-nm light under 0.5 V/60 V drain–source/gate bias. Besides, the polarity of the photocurrent under zero Vds can be efficiently tuned by the back gate voltage to satisfy different applications. Finally, we fabricate a vertical graphene–MoTe2–graphene heterostructure which shows improved photoresponsivity of 3.3 A/W to visible light.

Ionospheric vertical total electron content prediction model in low-latitude regions based on long short-term memory neural network

Ionosphere delay is one of the main sources of noise affecting global navigation satellite systems, operation of radio detection and ranging systems and very-long-baseline-interferometry. One of the most important and common methods to reduce this phase delay is to establish accurate nowcasting and forecasting ionospheric total electron content models. For forecasting models, compared to mid-to-high latitudes, at low latitudes, an active ionosphere leads to extreme differences between long-term prediction models and the actual state of the ionosphere. To solve the problem of low accuracy for long-term prediction models at low latitudes, this article provides a low-latitude, long-term ionospheric prediction model based on a multi-input-multi-output, long-short-term memory neural network. To verify the feasibility of the model, we first made predictions of the vertical total electron content data 24 and 48 hours in advance for each day of July 2020 and then compared both the predictions corresponding to a given day, for all days. Furthermore, in the model modification part, we selected historical data from June 2020 for the validation set, determined a large offset from the results that were predicted to be active, and used the ratio of the mean absolute error of the detected results to that of the predicted results as a correction coefficient to modify our multi-input-multi-output long short-term memory model. The average root mean square error of the 24-hour-advance predictions of our modified model was 4.4 TECU, which was lower and better than5.1 TECU of the multi-input-multi-output, long short-term memory model and 5.9 TECU of the IRI-2016 model.

Applying the reference-wavelength method to improve the precision of glucose measurement by near infrared spectroscopy

The reference-wavelength method is proposed to diminish the influence of noises on glucose measurement by differentially processing two signals at the reference and measuring wavelengths. At the reference wavelength, the radiation intensity is insensitive to the changes of glucose concentration. Therefore, it can be used as the internal reference to estimate the noise and then to extract the effective glucose signal at the other wavelengths. The validation experiments are constructed in the non-scattering samples with the reference wavelength of glucose at 1525 nm. The results show that the reference-wavelength-based glucose-specific signal extracting method can largely improve the glucose prediction precision from 17.56 to 8.87 mg/dL in the two-component experiment aad from 26.82 to 9.94 mg/dL in the three-component experiment.

A new method of continuous blood pressure monitoring using multichannel sensing signals on the wrist

Hypertension is a worldwide health problem and a primary risk factor for cardiovascular disease.Continuous monitoring of blood pressure has important clinical value for the early diagnosis and prevention of cardiovascular disease.However,existing technologies for wearable continuous blood pressure monitoring are usually inaccurate,rely on subject-specific calibration and have poor generalization across individuals,which limit their practical applications.Here,we report a new blood pressure measurement method and develop an associated wearable device to implement continuous blood pressure monitoring for new subjects.The wearable device detects cardiac output and pulse waveform features through dual photoplethysmography(PPG)sensors worn on the palmar and dorsal sides of the wrist,incorporating custom-made interface sensors to detect the wearing contact pressure and skin temperature.The detected multichannel signals are fused using a machine-learning algorithm to estimate continuous blood pressure in real time.This dual PPG sensing method effectively eliminates the personal differences in PPG signals caused by different people and different wearing conditions.The proposed wearable device enables continuous blood pressure monitoring with good generalizability across individuals and demonstrates promising potential in personal health care applications.

Reference point of floating-reference method for blood glucose sensing

A problem in terms of the accuracy of noninvasive measurement of blood glucose with near-infrared（NIR） spectroscopy is mainly caused by the weak glucose signal and strong background variations.We report the existence of the radial reference point in a floating-reference method,which is supposed to solve this problem.Based on the analysis of the infinite diffusion theory,the local condition of the reference point is deduced theoretically.Then the experiments using the intralipid solutions are constructed to testify the existence of the reference point.In order to further validate our results,Monte Carlo simulations are performed to calculate the diffused light distribution according to the variation of the glucose concentration in the intralipid solutions.All the reference points existing in three-layer skin model are also listed at the wavelength of 1200-1700 nm.

Propulsion Principles of Water Striders in Sculling Forward through Shadow Method

Semi-aquatic arthropods skate on water surfaces with synergetic actions of their legs. The sculling forward locomotion of water striders was observed and analyzed in situ to understand and reproduce the abovementioned feature. The bright-edged elliptical shadows of the six legs of a water strider were recorded to derive the supporting force distributions on legs. The propulsion principles of water striders were quantitatively disclosed. A typical sculling forward process was accomplished within approximately 0.15 s. Water striders lifted their heads slightly and supported their weight mainly by the two driving legs to increase the propulsion force and reduce the water resistance during the process. The normalized thrust-area ratio （defined as the ratio of the propulsion force to the projected area） was usually lower than 0.4 after sculling for approximately 0.08 s. The entire normal supporting force remained nearly constant during a stroke to reduce the mass center fluctuation in the normal direction. In addition, water striders could easily control the locomotion direction and speed through the light swinging of the two hind legs as rudders. These sculling principles might inspire sophisticated biomimetic wa- ter-walking robots with high propulsion efficiency in the future.

On-chip integrated optical stretching and electrorotation enabling single-cell biophysical analysis

Cells have different intrinsic markers such as mechanical and electrical properties,which may be used as specific characteristics.Here,we present a microfluidic chip configured with two opposing optical fibers and four 3D electrodes for multiphysical parameter measurement.The chip leverages optical fibers to capture and stretch a single cell and uses 3D electrodes to achieve rotation of the single cell.According to the stretching deformation and rotation spectrum,the mechanical and dielectric properties can be extracted.We provided proof of concept by testing five types of cells(HeLa,A549,HepaRG,MCF7 and MCF10A)and determined five biophysical parameters,namely,shear modulus,steady-state viscosity,and relaxation time from the stretching deformation and area-specific membrane capacitance and cytoplasm conductivity from the rotation spectra.We showed the potential of the chip in cancer research by observing subtle changes in the cellular properties of transforming growth factor beta 1(TGF-β1)-induced epithelial–mesenchymal transition(EMT)A549 cells.The new chip provides a microfluidic platform capable of multiparameter characterization of single cells,which can play an important role in the field of single-cell research.

Calibration error analysis of electro-optical detection systems

We present detailed analysis of calibration process error for electro-optical detection systems, which can be simplified as the plane rotation around a non-orthogonal axis. By means of octonions it firstly proves that the plane rotation around a non-orthogonal axis can be decomposed into rotations around two perpendicular axes. The rotation is further divided into three steps, and the calibration error is hence discussed and obtained. The simulation and test results indicate that there are large calibration errors in calibration process. The pointing error can be effectively improved after separating error components, which provides a more accurate set data for further comDensation.

A wide-field and high-resolution lensless compound eye microsystem for real-time target motion perception

Optical measurement systems suffer from a fundamental tradeoff between the field of view(FOV),the resolution and the update rate.A compound eye has the advantages of a wide FOV,high update rate and high sensitivity to motion,providing inspiration for breaking through the constraint and realizing high-performance optical systems.However,most existing studies on artificial compound eyes are limited by complex structure and low resolution,and they focus on imaging instead of precise measurement.Here,a high-performance lensless compound eye microsystem is developed to realize target motion perception through precise and fast orientation measurement.The microsystem splices multiple sub-FOVs formed by long-focal subeyes,images targets distributed in a panoramic range into a single multiplexing image sensor,and codes the subeye aperture array for distinguishing the targets from different sub-FOVs.A wide-field and high resolution are simultaneously realized in a simple and easy-to-manufacture microelectromechanical system(MEMS)aperture array.Moreover,based on the electronic rolling shutter technique of the image sensor,a hyperframe update rate is achieved by the precise measurement of multiple time-shifted spots of one target.The microsystem achieves an orientation measurement accuracy of 0.0023°(3σ)in the x direction and 0.0028°(3σ)in the y direction in a cone FOV of 120°with an update rate~20 times higher than the frame rate.This study provides a promising approach for achieving optical measurements with comprehensive high performance and may have great significance in various applications,such as vision-controlled directional navigation and high-dynamic target tracking,formation and obstacle avoidance of unmanned aerial vehicles.

Rapid switching and durable on-chip spark-cavitation-bubble cell sorter

Precise and high-speed sorting of individual target cells from heterogeneous populations plays an imperative role in cell research.Although the conventional fluorescence-activated cell sorter(FACs)is capable of rapid and accurate cell sorting,it occupies a large volume of the instrument and inherently brings in aerosol generation as well as crosscontamination among samples.The sorting completed in a fully enclosed and disposable microfluidic chip has the potential to eliminate the above concerns.However,current microfluidic cell sorters are hindered by the high.complexities of the fabrication procedure and the off-chip setup.In this paper,a spark-cavitation-bubble-based fluorescence-activated cell sorter is developed to perform fast and accurate sorting in a microfluidic chip.It features a simple structure and an easy operation.This microfluidic sorter comprises a positive electrode of platinum and a negative electrode of tungsten,which are placed on the side of the main channel.By applying a high-voltage discharge on the pair of electrodes,a single spark cavitation bubble is created to deflect the target particle into the downstream collection channel.The sorter has a short switching time of 150μs and a long lifespan of more than 100 million workable actions.In addition,a novel control strategy is proposed to dynamically adjust the discharge time to stabilize the size of the cavitation bubble for continuous sorting.The dynamic control of continuously triggering the sorter,the optimal delay time between fluorescence detection and cell sorting,and a theoretical model to predict the ideal sorting recovery and purity are studied to improve and evaluate the sorter performance.The experiments demonstrate that the sorting rate of target particles achieves 1200 eps,the total analysis throughput is up to 10,000 eps,the particles sorted at 4000 eps exhibit a purity greater than 80%and a recovery rate greater than 90%,and the sorting effect on the viability of HelLa cells is negligible.

Magnetically tunable zero-index metamaterials

Zero-index metamaterials(ZIMs)feature a uniform electromagnetic mode over a large area in arbitrary shapes,enabling many applications including high-transmission supercouplers with arbitrary shapes,directionindependent phase matching for nonlinear optics,and collective emission of many quantum emitters.However,most ZIMs reported to date are passive;active ZIMs that allow for dynamic modulation of their electromagnetic properties have rarely been reported.Here,we design and fabricate a magnetically tunable ZIM consisting of yttrium iron garnet(YIG)pillars sandwiched between two copper clad laminates in the microwave regime.By harnessing the Cotton–Mouton effect of YIG,the metamaterial was successfully toggled between gapless and bandgap states,leading to a“phase transition”between a zero-index phase and a single negative phase of the metamaterial.Using an S-shaped ZIM supercoupler,we experimentally demonstrated a tunable supercoupling state with a low intrinsic loss of 0.95 d B and a high extinction ratio of up to 30.63 d B at 9 GHz.We have also engineered a transition between the supercoupling state and the topological one-way transmission state at10.6 GHz.Our work enables dynamic modulation of the electromagnetic characteristics of ZIMs,enabling various applications in tunable linear,nonlinear,quantum,and nonreciprocal electromagnetic devices.