Rotational Population Measurement of Ultracold 85Rb^133Cs Molecules in the Lowest Vibrational Ground State

We measure the rotational populations of ultracold SS Rbla3 Cs molecules in the lowest vibrational ground state by a depletion spectroscopy and quantify the molecular production rate based on the measurement of single ion signal area. The SSRb133Cs molecules in the X1∑＋（v = 0） are formed from the short-range （2）^3П0＋（V = 10, J = 0） molecular state. A home-made external-cavity diode laser is used as the depletion laser to measure the rotational populations of the formed molecules. Based on the determination of single ion signal, the production rates of molecules in the J=0 and J = 2 rotational levels are derived to be 4800mole/s and 7200mole/s, respectively. The resolution and quantification of molecules in rotational states are facilitative for the manipulation of rotational quantum state of ultracold molecules.

Enhanced optical molasses cooling for Cs atoms with largely detuned cooling lasers

We report a detailed study of the enhanced optical molasses cooling of Cs atoms,whose large hyperfine structure allows to use the largely red-detuned cooling lasers.We find that the combination of a large frequency detuning of about-110 MHz for the cooling laser and a suitable control for the powers of the cooling and repumping lasers allows to reach a cold temperature of^5.5μK.We obtain 5.1×10^7 atoms with the number density around 1×10^12 cm^-3.Our result gains a lower temperature than that got in other experiments,in which the cold Cs atoms with the temperature of^10μK have been achieved by the optical molasses cooling.

Non-crossover sub-Doppler DAVLL in selective reflection scheme

We demonstrate a non-crossover sub-Doppler dichroic atomic vapor laser locking(DAVLL)in selective reflection scheme,which allows us to obtain a modulation-free laser locking with wide tuneable range.The dependence of peak-to-peak amplitude,tuneable range and the slope near the zero-crossing point of error signal on the frequency shift induced by the magnetic fields are studied.The adjustable error signal by the varying external magnetic field can offer the laser locking from the order of tens MHz to hundreds MHz.The ultimate dither of locked laser frequency is less than 0.5 MHz.The square root of Allan variance of the error signals reaches a minimum of 3×10^-10 for an averaging time of 130 s.

Coherent 420 nm laser beam generated by four-wave mixing in Rb vapor with a single continuous-wave laser

We demonstrate the generation of the coherent 420 nm laser via parametric four-wave mixing process in Rb vapor.A single 778 nm laser with circular polarization is directly injected into a high-density atomic vapor,which drives the atoms from the 5S1/2 state to the 5D5/2 state with monochromatic two-photon transition.The frequency up-conversion laser is generated by the parametric four-wave mixing process under the phase matching condition.This coherent laser is firstly certified by the knife-edge method and a narrow range grating spectrometer.Then the generated laser power is investigated in terms of the power and frequency of the incoming beam as well as the density of the atoms.Finally,a 420 nm coherent laser with power of 19μW and beam quality of Mx^2=1.32,My^2=1.37 is obtained with optimal experimental parameters.This novel laser shows potential prospects in the measurement of material properties,information storage,and underwater optical communication.

Signatures for Coexistence of Monoclinic and Hexagonal Phases in GaTe Nanoflakes

The burgeoning two-dimensional(2D)layered materials provide a powerful strategy to realize efficient light-emitting devices.Among them,gallium telluride(Ga Te)nanoflakes,showing strong photoluminescence(PL)emission from multilayer to bulk crystal,relax the stringent fabrication requirements of nanodevices.However,detailed knowledge on the optical properties of Ga Te varies as layer thickness is still missing.Here we perform thickness-dependent PL and Raman spectra,as well as temperature-dependent PL spectra of Ga Te nanoflakes.Spectral analysis reveals a spectroscopic signature for the coexistence of both the monoclinic and hexagonal phases in Ga Te nanoflakes.To understand the experimental results,we propose a crystal structure where the hexagonal phase is on the top and bottom of nanoflakes while the monoclinic phase is in the middle of the nanoflakes.On the basis of temperature-dependent PL spectra,the optical gap of the hexagonal phase is determined to be 1.849 eV,which can only survive under temperature higher than 200 K with the increasing phonon population.Furthermore,the strength of exciton-phonon interaction of the hexagonal phase is estimated to be 1.24 me V/K.Our results prove the coexistence of dual crystalline phases in multilayer Ga Te nanoflakes,which may provoke further exploration of phase transformation in Ga Te materials,as well as new applications in 2D light-emitting diodes and heterostructure-based optoelectronics.

Transition Dipole Moment Measurements of Ultracold Photoassociated ^(85)Rb^(133)Cs Molecules by Depletion Spectroscopy

The transition dipole moments（TDMs） of ultracold85 Rb133 Cs molecules between the lowest vibrational ground level, （X^1Σ~＋（ v= 0, J= 1）, and the two excited rovibrational levels, 2~3Π0＋（v′= 10, J′= 2） and 2~1Π1（v′= 22,J′= 2）, are measured using depletion spectroscopy. The ground-state85 Rb133 Cs molecules are formed from cold mixed component atoms via the 2~3Π0-（ v= 11, J= 0） short-range level, then detected by time-of-flight mass spectrum. A home-made external-cavity diode laser is used as the depletion laser to couple the ground level and the two excited levels. Based on the depletion spectroscopy, the corresponding TDMs are then derived to be 3.5（2）×10^（-3）eαα and 1.6（1）×10^（-2）eαα, respectively, where 0）（60 represents the atomic unit of electric dipole moment. The enhance of TDM with nearly a factor of 5 for the 21Π1（v′= 22, J′= 2） excited level means that it has stronger coupling with the ground level. It is meaningful to find more levels with much more strong coupling strength by the represented depletion spectroscopy to realize direct stimulated Raman adiabatic passage transfer from scattering atomic states to deeply molecular states.

Efficient loading of ultracold sodium atoms in an optical dipole trap from a high power fiber laser

We report on a research of the loading of ultracold sodium atoms in an optical dipole trap,generated by two beams from a high power fiber laser.The effects of optical trap light power on atomic number,temperature and phase space density are experimentally investigated.A simple theory is proposed and it is in good accordance with the experimental results of the loaded atomic numbers.In a general estimation,an optimal value for each beam with a power of 9 W from the fiber laser is achieved.Our results provide a further understanding of the loading process of optical dipole trap and laid the foundation for generation of a sodium Bose–Einstein condensation with an optical dipole trap.

Enhancement of the photoassociation of ultracold atoms via a non-resonant magnetic field

We report an effective method for enhancing the photoassociation of ultracold atoms using a non-resonant magnetic field,which enables the manipulation of the coupling between the wavefunctions of the colliding atomic pairs and the excited molecules.A series of photoassociation spectra are measured for different magnetic fields.We show that the photoassociation rate is significantly dependent on the non-resonant magnetic field.A qualitatively theoretical explanation is provided,and shows a good agreement with the experimental result.

Experimental Study on Double Resonance Optical Pumping Spectroscopy in a Ladder-Type System of ^(87)Rb Atoms

Double resonance optical pumping spectroscopy has an outstanding advantage of high signal-to-noise ratio, thus having potential applications in precision measurement. With the counter propagated 780nm and 776nm laser beams acting on a rubidium vapor cell, the high resolution spectrum of 5S1/2 - 5P3/2 - 5D5/2 ladder-type transition of ST Rb atoms is obtained by monitoring the population of the 5S1/2 ground state. The dependence of the spectroscopy lineshape on the probe and coupling fields are comprehensively studied in theory and experiment. This research is helpful for measurement of fundamental physical constants by high resolution spectroscopy.

Measurement of Zeeman Shift of Cesium Atoms Using an Optical Nanofiber

Nanofibers have many promising applications because of their advantages of high power density and ultralow saturated light intensity. We present here a Zeeman shift of the Doppler-broadened cesium D2 transition using a tapered optical nanofiber in the presence of a magnetic field. When a weak magnetic field is parallel to the propagating light in the nanofiber, the Zeeman shift rates for different circularly polarized spectra are observed.For the ＋component, the typical linear Zeeman shift rates of = 3 and = 4 ground-state cesium atoms are measured to be 3.10（±0.19） MHz/G and 3.91（±0.16） MHz/G. For the -component, the values are measured to be-2.81（±0.25） MHz/G, and-0.78（±0.28） MHz/G. The Zeeman shift using the tapered nanofiber can help to develop magnetometers to measure the magnetic field at the narrow local region and the dispersive signal to lock laser frequency.

Experimental quantum secure direct communication with single photons

Quantum secure direct communication is an important mode of quantum communication in which secret messages are securely communicated directly over a quantum channel.Quantum secure direct communication is also a basic cryptographic primitive for constructing other quantum communication tasks,such as quantum authentication and quantum dialog.Here,we report the first experimental demonstration of quantum secure direct communication based on the DL04 protocol and equipped with single-photon frequency coding that explicitly demonstrated block transmission.In our experiment,we provided 16 different frequency channels,equivalent to a nibble of four-bit binary numbers for direct information transmission.The experiment firmly demonstrated the feasibility of quantum secure direct communication in the presence of noise and loss.

Review of methodological and experimental LIBStechniques for coal analysis and their application in power plants in China

Laser-induced breakdown spectroscopy (LIBS) is an emerging analytical spectroscopy technique. This review presents the main recent developments in China regarding the implementation of LIBS for coal analysis. The paper mainly focuses on the progress of the past few years in the fundamentals, data pretreatment, calibration model, and experimental issues of LIBS and its application to coal analysis. Many important domestic studies focusing on coal quality analysis have been conducted. For example, a proposed novel hybrid quantification model can provide more reproducible quantitative analytical results; the model obtained the average absolute errors (AREs) of 0.42%, 0.05%, 0.07%, and 0.17% for carbon, hydrogen, volatiles, and ash, respectively, and a heat value of 0.07 MJ/kg. Atomic/ionic emission lines and molecular bands, such as CN and C-2, have been employed to generate more accurate analysis results, achieving an ARE of 0.26% and a 0.16% limit of detection (LOD) for the prediction of unburned carbon in fly ashes. Both laboratory and on-line LIBS apparatuses have been developed for field application in coal-fired power plants. We consider that both the accuracy and the repeatability of the elemental and proximate analysis of coal have increased significantly and further efforts will be devoted to realizing large-scale commercialization of coal quality analyzer in China.

Engineering of electrolyte ion channels in MXene/holey graphene electrodes for superior supercapacitive performances

MXene has given great promises to superca-pacitor electrode material due to its high conductivity and redox properties.However,the self-agglomeration of the MXene lamella will reduce its contact area with the elec-trolyte and generate a tortuous transportation pathway of the electrolyte ions,thereby reducing its capacitive per-formance and rate capability.In this work,we engineered the electrolyte ion channels by adjusting the MXene lamella size and inserting holey graphene(HG)nanosheets into the interlayer of the MXene flakes.The developed MXene/HG electrode can not only avoid the self-restack-ing of MXene but also provide unimpeded ion transport channels.As a result,the supercapacitive and rate perfor-mances of the small MXene lamella-based MXene/HG(S-MXene/HG)supercapacitor are prominently ameliorated.By adjusting the content of HG,the S-MXene/HG0.05 electrode exhibits excellent gravimetric capacitance of 446 F·g^(-1)and a rate capability of 77.5%.The S-MXene/HG0.05-based symmetric supercapacitor provides an impressive energy density of 14.84 Wh·kg^(-1)with excellent cyclic stability of 96%capacitance retention after 10,000 cycles.This demonstration of the engineering of the ion channels shows great potential in two-dimensional mate-rial-based supercapacitor electrodes.

Giant enhancement of photoluminescence emission in monolayer WS_(2)by femtosecond laser irradiation

Monolayer transition metal dichalcogenides have emerged as promising mat erials for opt oelectTonic and nanophotonic devices.However,the low photoluminescence(PL)quantum yield(QY)hinders their various potential applications.Here we engineer and enhance the PL intensity of monolayer WS_(2)by femtosecond laser irradiation.More than two orders of magnitude enhancement of PL intensity as compared to the as-prepared sample is determined.Furthermore,the engineering time is shortened by three orders of magnitude as compared to the improvement of PL intensity by continuous-wave laser irradiation.Based on the evolution of PL spectra,we attribute the giant PL enhancement to the conversion from trion emission to exciton,as well as the improvement of the QY when exciton and trion are localized to the new-formed defects.We have created microstructures on the monolayer WS_(2)based on the enhancement of PL intensity,where the engineered structures can be stably stored for more than three years.This flexible approach with the feature of excellent long-term storage stability is promising for applications in information storage,display technology,and opto electronic devices.

Controllable electromagnetically induced grating in a cascade-type atomic system

A controllable electromagnetically induced grating (EIG) is experimentally realized in a coherent rubidium ensemble with 5S1/2-5P3/2-5D5/2 cascade configuration.In our work,a whole picture de-scribing the relation between the first-order diffraction efficiency and the power of the coupling field is experimentally presented for the first time,which agrees well with the theoretical prediction.More important,by fine tuning the experimental parameters,the first-order diffraction efficient of as high as 25% can be achieved and a clear three-order diffraction pattern is also observed.Such a controllable periodic structure can provide a powerful tool for studying the control of light dynamics,pave the way for realizing new optical device.

Linear dipole behavior of single quantum dots encased in metal oxide semiconductor nanoparticles films

Understanding of charge/energy exchange processes and interfacial interactions that occur between quantum dots (QDs) and the metal oxides is of critical importance to these QD-based optoelectronic devices. This work reports on linear dipole behavior of single near-infrared emitting CdSeTe/ZnS core/shell QDs which are encased in indium tin oxide (ITO) semiconductor lianoparticles films. A strong polarization anisotropy in photohiminescence emission is observed by defocused wide-field imaging and polarization measuremen11echniques, and the average polarization degree is up to 0.45. A possible mechanism for the observation is presented in which the electrons, locating at single QD surface from ITO by electron transfer due to the equilibration of the Fermi levels, result in a significant Stark distortion of the QD electron/hole wavefunctions. The Stark distortion results in the linear polarization property of the single QDs. The investigation of linear dipole behavior for single QDs encased in ITO films would be helpful for further improving QD-based device performance.

Influence of surface charges on the emission polarization properties of single CdSe/CdS dot-in-rods

We report an experimental investigation of the influence of surface charges on the emission polarization properties of single CdSe/CdS dot-in-rods(DRs),which is important for their polarization-based practical applications.By covering the single DRs with N-type semiconductor indium tin oxide(ITO)nanoparticles,the surface of single DRs is charged by ITO through interracial electron transfer.This is confirmed by the experimental observations of the reduced photoluminescence intensities and lifetimes as well as the suppressing blinking.It is found that the full width at half maximum of histogram of polarization degrees of the single DRs is broadened from 0.24(on glass)to 0.41(in ITO).In order to explain the exprimental results,the band-edge exciton fine structure of single DRs is calculated by taking into account the sample parameters,the emission polarization,and the surface charges.The calculation results show that the level ordering of the emitting states determines the polarization degrees tending to increase or decrease under the influence of surface electrons.The surface electrons can induce an increase in the spacing between the emitting levels to change the populations and thus change the polarization degrees.In addition,different numbers of surface electrons may randomly distribute on the long CdSe/CdS rods,leading to the heterogeneous influences on the single DRs causing the broadening of polarization degrees also.

Light-induced frequency shifts for the lowest vibrational levels of ultracold Cs2 in the molecular pure long-range 0^-g state

The light-induced frequency shift(LIFS)of ultracold molecular ro-vibrational levels originates from the strong coupling of the atomic-scattering state and the bound-molecular state.In this paper,we present our experimental determination of the LIFSs of the lowest vibrational levels(v=0,1)in the purely long-range 0^-g state of ultracold cesium molecules.A high-resolution double photoassociation spectroscopy is developed,which serves as frequency ruler to measure the frequency shifts of the lowest molecular levels for Cs2.The experimental results are qualitatively consistent with the theoretical expectations.

Modification of single molecule fluorescence using external fields

Controlling and manipulating the fluorescence of single fluorophores is of great interest in recent years for its potential uses in improving the performance of molecular photonics and molecular electronics, such as in organic light-emitting devices, single photon sources, organic field-effect transistors, and probes or sensors based on single molecules. This review shows how the fluorescence emission of single organic molecules can be modified using local electromagnetic fields of metallic nanostructures and electric-field-induced electron transfer. Electric-field-induced fluorescence modulation, hysteresis, and the achievement of fluorescence switch are discussed in detail.

Investigation on the Cs 6S_(1/2)to 7D elec trie quadrupole tr ansition via monochromatic two-photon process at 767 nm

We experimentally demonstrate the cesium electric quadrupole t ransition from the 6S_(1/2)ground st ate to the 7D_(3/2,5/2)excited state t hrough a virtu al level by using a single laser at 767 nm.The excited state energy level population is characterized by varying the laser power,the temperature of the vapor,and the polarization combinations of the laser beams.The optimized experimentai parameters are obtained for a high resolution transition interval identification.The magnetic dipole coupling constant A and elec trie quadrupole coupling constant B for the 7D_(3/2,5/2)states are precisely determined by using the hyperfine levels intervals.The results,A=7.39(0.06)MHz,B=-0.19(0.18)MHz for the 7D_(3/2)state,and A=-1.79(0.05)MHz,B=1.05(0.29)MHz for the 7D_(5/2)state,are in good agreement with the previous reported results.This work is beneficial for the determination of atomic structure information and parity non-conser vat ion,which paves the way for the field of precision measurements and atomic physics.