Scheme for teleportation of unknown states of trapped ion

A scheme is presented for teleporting an unknown state in a trapped ion system. The scheme only requires a single laser beam. It allows the trap to be in any state with a few phonons, e.g. a thermal motion. Furthermore, it works in the regime, where the Rabi frequency of the laser is on the order of the trap frequency. Thus, the teleportation speed is greatly increased, which is important for decreasing the decoherence effect. This idea can also be used to teleport an unknown ionic entangled state.     

Influence of a high-speed dielectric spherical particle''''s movement on its scattering characteristics

The scattered field and differential scattered section (DSS) of a moving spherical particle with a high speed are investigated numerically.The coordinate and vector transformations are used to establish a theoretical basis for studying the laser scattering of a moving particle.The DSS of a moving spherical particle is explained by the electric and magnetic field from Mie scattering theory.Assuming the laser wavelength of 1.06μm,we compute the ratio of the laser DSS of the moving dielectric spherical particle to that of the static dielectric spherical particle,which changes with radii,speeds and scattering angles of the particle.The numerical results show that the laser DSS of the moving spherical particle is tightly connected with its speed and scattering zenith angle.If a spherical particle moves with high speed,the laser DSS due to movement of the particle could not be neglected.If the speed of the dielectric spherical particle is fluctuating,the Doppler effect and the frequency spectrum expansion play important roles.     

The dependence of high-order harmonic generation on the laser frequency and inter-nuclear distance from multi-atom molecular ions

High-order harmonic generation from one-dimensional (1D) multi-atom molecular ions in an ultra-short laser field is theoretically investigated. The dynamics of the electron in a linearly polarized intense laser field is analyzed in terms of 1D Schrodinger equation with the Crank-Nicolson algorithm. The dependence of high-order harmonics on the laser frequency and the inter-nuclear distance is discussed. It is found that the optimum range of inter-nuclear distance should be changed to get extended harmonic generation for different laser frequency, and the lower frequency laser pulse is favorable to higher order harmonic generation as the inter-nuclear distance increases.     

Frequency-Shift of a Frequency Stabilized Laser Based on Zeeman Effect

We introduce a new method of frequency-shifting for a diode laser in laser cooling experiments, the method is based on the Zeeman egect of^87 Rb atoms. The laser frequency is stabilized by absorption spectrum line of atoms in magnetic field. We show that a magnetic field can be added up to 10^-2T. The corresponding frequency shift is 10^2 MHz and the response time is about 1ms. The large range of the frequency shift is suffcient for laser-cooling experiments.     

Stabilized DFB laser system with large tuning range

We propose, design, and realize a compact stabilized laser system that can be tuned within 24 GHz automatically.This laser system consists of two distributed feedback(DFB) lasers, one of which is reference and locked to the D2 line of ~(87)Rb, the other laser is a slave that is locked to the reference laser via a loop servo. We measured the frequency of the beating signal of the two lasers and generated an error signal, which controlled the frequency of the slave laser to close the loop. We compressed the fluctuation of the beating signal's frequency to less than 1 MHz.Furthermore, the system can also automatically determine and control whether the slave is red detuned or blue detuned to the reference. The dimensions of our laser system are about 15 cm × 20 cm × 10 cm. This kind of laser system can be applied in many important applications, such as atomic interferometer and cold atomic clock.     

Use of wavelet in specifying optics

Using power spectral density (PSD) function to specify large aperture optical components' quality of laser system is universal. But it cannot provide effective guidance to eliminate certain frequency segment error. In order to solve this problem, two-dimensional discrete wavelet transform (2D-DWT) is used to separate frequency segment error and detect the corresponding region of certain frequency segment error, which is used as feedback to a machining process. The experimental results show that the corresponding region of certain frequency segment can be found and machining can be guided effectively by using wavelet.     

Design of new seismometer based on laser Doppler effect

In order to improve the resolution of seismic acquisition,a new seismic acquisition system based on tangential laser Doppler effect with an optimized differential optical configuration is proposed.The relative movement of the inertia object and the immobile frame is measured by laser Doppler effect,which can avoid the electromagnetic and thermometric interference,and the adoption of frequency-modulated (FM) transmission can improve the ability of anti-jamming.The frequency bandwidth is properly determined by analyzing the frequency of the Doppler signal.The velocity, displacement,acceleration, and frequency to be measured can be real-time acquired by frequency/velocity (F/V) converting the FM Doppler signal. A 100-dB dynamic range and the linear frequency range of 1.0 to 1000 Hz are realized.     

Mitigation of laser damage growth in fused silica by using a non-evaporative technique

A non-evaporative technique is used to mitigate damage sites with lateral sizes in a range from 50 μm to 400 μm and depths smaller than 100 μm.The influence of the pulse frequency of a CO 2 laser on the mitigation effect is studied.It is found that a more symmetrical and smooth mitigation crater can be obtained by increasing the laser pulse frequency form 0.1 to 20 kHz.Furthermore,the sizes of laser-affected and distorted zones decrease with the increase of the laser pulse frequency,leading to less degradation of the wave-front quality of the conditioned sample.The energy density of the CO 2 laser beam is introduced for selecting the mitigation parameters.The damage sites can be successfully mitigated by increasing the energy density in a ramped way.Finally,the laser-induced damage threshold(LIDT) of the mitigated site is tested using 355 nm laser beam with a small spot(0.23 mm 2) and a large spot(3.14 mm 2),separately.It is shown that the non-evaporative mitigation technique is a successful method to stop damage re-initiation since the average LIDTs of mitigated sites tested with small or large laser spots are higher than that of pristine material.     

A robust method for frequency stabilization of 556-nm laser operating at the intercombination transition of ytterbium

A frequency-stabilized 556-nm laser is an essential tool for experimental studies associated with 1 S 0-3 P 1 intercombination transition of ytterbium (Yb) atoms.A 556-nm laser light using a single-pass second harmonic generation (SHG) is obtained in a periodically poled MgO:LiNbO 3 (PPLN) crystal pumped by a fiber laser at 1111.6 nm.A robust frequency stabilization method which facilitates the control of laser frequency with an accuracy better than the natural linewidth (187 kHz) of the intercombination line is developed.The short-term frequency jitter is reduced to less than 100 kHz by locking the laser to a home-made reference cavity.A slow frequency drift is sensed by the 556-nm fluorescence signal of an Yb atomic beam excited by one probe beam and is reduced to less than 50-kHz by a computer-controlled servo system.The laser can be stably locked for more than 5 h.This frequency stabilization method can be extended to other alkaline-earth-like atoms with similar weak intercombination lines.     

Precision frequency measurement of ~1S_0–~3P_1 intercombination lines of Sr isotopes

We report on frequency measurement of the intercombination(5s2)1S0–(5s5p)3P1transition of the four natural isotopes of strontium,including88Sr(82.58%),87Sr(7.0%),86Sr(9.86%),and84Sr(0.56%).A narrow-linewidth laser that is locked to an ultra-low expansion(ULE)optical cavity with a finesse of 12000 is evaluated at a linewidth of 200 Hz with a fractional frequency drift of 2.8×10-13at an integration time of 1 s.The fluorescence collector and detector are specially designed,based on a thermal atomic beam.Using a double-pass acousto-optic modulator(AOM)combined with a fiber and laser power stabilization configuration to detune the laser frequency enables high signal-to-noise ratios and precision saturated spectra to be obtained for the six transition lines,which allows us to determine the transition frequency precisely.The optical frequency is measured using an optical frequency synthesizer referenced to an H maser.Both the statistical values and the final values,including the corrections and uncertainties,are derived for a comparison with the values given in other works.     

Stabilization and Shift of Frequency in an External Cavity Diode Laser with Solenoid-Assisted Saturated Absorption

A simple method to realize both stabilization and shift of the frequency in an external cavity diode laser （ECDL） is reported. Due to the Zeeman effect, the saturated absorption spectrum of Rb atoms in a magnetic field is shifted. This shift can be used to detune the frequency of the ECDL, which is locked to the saturated absorption spectrum. The frequency shift amount can be controlled by changing the magnetic field for a specific polarization state of the laser beam. The advantages of this tunable frequency lock include low laser power requirement, without additional power loss, cheapness, and so on.     

Frequency locking of a 399-nm laser referenced to fluorescence spectrum of an ytterbium atomic beam

The laser cooling of ytterbium(Yb) atoms needs a 399-nm laser which operates on the strong1S0-1P1 transition and can be locked at the desired frequencies for different Yb isotopes.We demonstrate a frequency locking method using the fluorescence spectrum of an Yb atomic beam as a frequency reference.For unresolved fluorescence peaks,we make the spectrum of the even isotopes vanish by using the strong angular-dependence of the fluorescence radiations;the remained closely-spaced peaks are thus clearly resolved and able to serve as accurate frequency references.A computer-controlled servo system is used to lock the laser frequency to a single fluorescence peak of interest,and a frequency stability of 304 kHz is achieved.This frequency-locked laser enables us to realize stable blue magneto-optic-traps(MOT) for all abundant Yb isotopes.     

Laser frequency locking based on Rydberg electromagnetically induced transparency

We present a laser frequency locking to Rydberg transition with electromagnetically induced transparency(EIT)spectra in a room-temperature cesium vapor cell. Cesium levels 6S_(1/2), 6P_(3/2), and the n D_(5/2) state, compose a cascade three-level system, where a coupling laser drives Rydberg transition, and probe laser detects the EIT signal. The error signal, obtained by demodulating the EIT signal, is used to lock the coupling laser frequency to Rydberg transition. The laser frequency fluctuation, ~0.7 MHz, is obtained after locking on, with the minimum Allan variance to be 8.9 × 10~(-11).This kind of locking method can be used to stabilize the laser frequency to the excited transition.     

Multi-cavity-stabilized ultrastable laser

We demonstrate a proposal for making an ultrastable laser referenced to a multi-cavity, enabling a lower thermal noise limit due to the averaging effect. In comparison with a single-cavity system, relative frequency instability of the synthesized laser can be improved by a factor of the square root of the cavity number. We perform an experiment to simulate a two-cavity system with two independent ultrastable lasers. Experimental results show that the relative frequency instability(Allan deviation) of the synthesized laser is 5 × 10~(-16), improved by a factor of √2 from a single-cavity-stabilized laser.     

Theoretical study of the trapping efficiency of an optical tweezers array system

Optical tweezers have been a valuable research tool since their invention in the 1980s. One of the most important developments in optical tweezers in recent years is the creation of two-dimensional arrays of optical traps. In this paper, a method based on interference is discussed to form gradient laser fields, which may cause the spatial modulation of particle concentration. The parameters related to the optical tweezers array are discussed in detail and simulated by the Matlab software to show the influence of important parameters on the distribution of particle concentration. The spatial redistribution of particles in a laser interference field can also be predicted according to the theoretical analysis.     

Self—Trapping State and Atomic Tunnelling Current of an Atomic Bose—Einstein Condensate Interacting with a Laser Field in a Double—Well Potential

We present a theoretical treatment of dynamics of an atomic Bose-Einstein condensation interacting with a single-mode quantized travelling-wave laser field in a double-well potential.When the atom-field system is initially in a coherent state,expressions for the energy exchange between atoms and photons are derived.It is revealed that atoms in the two wells can be in a self-trapping state when the tunnelling frequency satisfies two specific conditions,in which the resonant and far off-resonant cases are included.It is found that there is an alternating current with two different sinusoidal oscillations between the two wells,but no dc characteristic of the atomic tunnelling current occurs.It should be emphasized that when without the laser field,both the population difference and the atomic tunnelling current are only a single oscillation.But they will respectively become a superposition of two oscillations with different oscillatory frequencies in the presence of the laser field.For the two oscillations of the population difference,one always has an increment in the oscillatory frequency,the other can have an increment or a decrease under different cases.These conclusions are also suitable to those of the atomic tunnelling current.As a possible application,by measurement of the atomic tunnelling current between the two wells,the number of Bose-condensed atoms can be evaluated.By poperly selecting the laser field,the expected atomic tunnelling current can be obtained too.     

A 532 nm molecular iodine optical frequency standard based on modulation transfer spectroscopy

We report construction of an iodine-stabilized laser frequency standard at 532 nm based on modulation transfer spectroscopy(MTS) technology with good reproducibility. A frequency stability of 2.5 × 10~(-14) at 1 s averaging time is achieved,and the frequency reproducibility has a relative uncertainty of 3.5×10~(-13), demonstrating the great stability of our setup.The systematic uncertainty of the iodine-stabilized laser frequency standard is evaluated, especially the contribution of the residual amplitude modulation(RAM). The contribution of the RAM in MTS cannot be evaluated directly. To solve this problem, we theoretically deduce the MTS signal with RAM under large modulation depth, and prove that the nonsymmetric shape of the MTS signal is directly related to the MTS effect. The non-symmetric shape factor r can be calibrated with a frequency comb, and in real experiments, this r value can be obtained by least-squares fitting of the MTS signal,from which we can infer the RAMinduced frequency shift. The full frequency uncertainty is evaluated to be 5.3 k Hz(corresponding to a relative frequency uncertainty of 9.4×10~(-12)). The corrected transition frequency has a difference from the BIPM-recommended value of 2 k Hz, which is within 1σ uncertainty, proving the validity of our evaluation.     

Influence of Feedback Levels on Polarized Optical Feedback Characteristics in Zeeman-Birefringence Dual Frequency Lasers

The influence of feedback levels on the intensity and polarization properties of polarized optical feedback in a Zeeman-birefringence dual frequency laser is systematically investigated. By changing the feedback power ratio, different feedback levels are obtained. Three distinct regimes of polarized optical feedback effects are found and defined as regimes Ⅰ, Ⅱ and Ⅲ The feedback level boundaries among the regimes are acquired experimentally. The theoretical analysis is presented to be in good agreement with the experimental results.     

High power red laser generation by second harmonic generation with GTR-KTP crystal

In this Letter, a gray-tracking-resistant—potassium titanyl phosphate(GTR-KTP) crystal is used for intracavity frequency doubling red laser generation for the first time. Under the 808 nm LD pump power of 180 W, as high as 12.5 W of red laser output is obtained with the optimum repetition rate of 7 k Hz. Within the red laser power variation range between the maximum to 70%, a temperature tolerance is measured to be 35°C. The results prove that GTR-KTP should be a potential nonlinear crystal for red laser generation.     

Stable single frequency Er-doped all-fiber ring laser with fiber Bragg grating Fabry-Perot filter

Using a fiber Bragg grating (FBG) and a Fabry-Perot cavity composed of two fiber Bragg gratings (FBGFP) as its frequency-selective components, a type of single frequency all-fiber ring laser permits oscillation only on one longitudinal mode of the main cavity without modehopping while the cavity length can be up to tens of meters. The salient feature is due to the single narrowband resonance of the FBGFP filter. Such a fiber ring laser is achieved experimentally, and the laser mode is limited inside the single resonance of the FBGFP.